waste management for the food industries || waste management in food packaging industries

Waste Management inFood PackagingIndustriesIoannis S. Arvanitoyannis

15

Introduction

Food packaging material is expected to provide optimum protective properties so thatthe product it encloses remains in satisfactory condition for its anticipated shelf-life.The packaging technique, in conjunction with the choice of a packaging materialendowed with appropriate gas and water barrier properties, aims to prevent destructionof food by microbial or insect attack. Packaging, and food packaging in particular, hasbeen very eloquently described as ‘a complex, dynamic, scientific, artistic and contro-versial segment of business’ (Paine and Paine, 1992). The veracity of this definition canbe easily certified since packaging is an exceptionally complicated process in whichmany company departments interact; it is ‘dynamic’ because of its continuously chang-ing character and ‘scientific’ since further improvement of packaging is heavily depend-ent on scientific advances and innovations; of course, the scientific contribution is morethan necessary for making the product more ‘appealing’ to the consumer (Robertson,1993). The increased consumer demand for high quality, long-shelf-life, ready-to-eatfoods has initiated the development of mildly preserved products that keep their naturaland fresh appearance as long as possible (Baldwin et al., 1995; Guilbert et al., 1996).Edible and biodegradable polymer films offer alternative packaging options with advan-tages over the synthetic ‘recalcitrant’ packaging polymers because they do not con-tribute to environmental pollution (Arvanitoyannis et al., 1996; Krochta et al., 1997).

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941Glass.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950Aluminum.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958Paper/carton. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980

Waste Management for the Food IndustriesISBN: 9780123736543

Copyright © 2008 Elsevier IncAll rights of reproduction in any form reserved

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Although edible films are not meant to replace synthetic packaging films entirely, theydo have the potential to reduce substantially the environmental burden due to food pack-aging and to limit moisture, aroma and lipid migration between food components(Krochta et al., 1994, 1997). The potential of polysaccharides and proteins as ediblefilms has long been recognized (Guilbert et al., 1989, 1995; Genadios et al., 1990, 1993;El Ghaouth et al., 1991; Wong et al., 1992; Lourdin et al., 1995) but, apart from somevery special applications (Kinsella, 1984; Park et al., 1993, 1994), polysaccharide-and/or protein-based edible films have not yet found extensive applications in the foodindustry (Kester and Fennema, 1986).

One of the major targets of society is to satisfy its population’s demands for goodsof every kind. However, this would be impossible without suitable packaging, partic-ularly since 50% of all packaging is employed for foods and another 20% for the restof household daily requirements (Eschke, 1990). Solid waste arises from processoperations, used or scrap packaging materials and even the saleable products them-selves when they are finally discarded. Under the European Union FrameworkDirective on waste (91/156/EEC), waste is defined as any substance or object whichthe holder discards or intends to discard, thus waste, in other words, means: ‘Any sub-stance or object which falls into one of sixteen categories in Annex 1 of the directive,which the holder must discard, intends to discard or requires to discard, which is an allencompassing definition’. However, according to the Environmental Protection Act,‘Waste is any substance which constitutes scrap material or an effluent or otherunwanted surplus substance or article which requires to be disposed of as being bro-ken, worn out, contaminated or otherwise spoiled’ (Clarke et al., 1999; Read, 1999).The role of packaging is to protect food from its environment. Currently, almost allpurchased products are in packaged form. The materials and designs employed foreach packaging operation depend on the product itself reflecting the role that it wasdesigned to perform. Packaging is used for meeting the following requirements(Waite, 1995; Krochta et al., 1997):

1 Protection of product from mechanical damage, contamination and deterioration2 Promotion and advertisement of the product3 Information disclosure to the consumer regarding the content, composition and

instructions for safe use4 Improvement of distribution and reduction of storage and transportation costs5 Convenience6 Safety function and prevention of inappropriate use.

Packaging, despite the convenience it provides to the consumer, is subject to manydebates concerning environmental issues. It has been considered a constant source ofenvironmental waste due to its volume, since it occupies close to two-thirds of trashcan volume (Waite, 1995; Plinke and Kaempf, 1995; Krochta et al., 1997). Further-more, the constant increase in the use of plastics makes their disposal a major envi-ronmental issue. Packaging represents approximately 30% weight of municipal solid waste (MSW), but appears much more significant because it occupies close to

942 Waste Management for the Food Industries

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65% of waste volume due to its bulkiness (Krochta et al., 1997). Sustainable develop-ment is the driving force for acting more responsibly to protect our world for futuregenerations. It encompasses a combination of environmental, social and economicaspects (http://www.apme.org/environment/htm/sustainable.future.pdf). Most con-sumers would like to have plastic packaging replaced with some other form of recy-clable packaging, such as glass or paper, if possible. However, were plastic packagingto be replaced, a scrupulous data analysis revealed that there would be a: 100%increase in energy consumption; 400% increase in raw material consumption; 150%increase in waste volume; 100% increase in packaging cost. The results of a 1992study performed by Gesellschaft für Verpackungsmarktforschung (GVM) inGermany revealed that if plastic were to be replaced by other packaging materials,packaging tonnage would rise by around 4 million tons, from 1427 to 5577 milliontons. Consequently, the volume of waste collected in trash barrels would increasefrom 50.4 billion to 130 billion liters and the energy demand would reach higher thandouble figures (Campbell, 1994). It is frequently stated that plastic waste is the majorcontributor to domestic waste. Plastic packaging, however, is 13% of the 30% weightpackaging share of MSW, thus representing only around 4–5% weight of MSW(Pearson, 1996; Krochta et al., 1997). It has been estimated that 9.4 million tons ofplastics are used in Europe for packaging purposes, representing 39% of the totalplastic utilized (Castle, 1994). Plastic packaging has several advantages to offer toconsumers; it is safe, strong, lightweight, easily processed and stored and economical.Therefore, numerous studies were conducted on safe plastic waste management inorder to minimize the undesirable environmental impacts of the utilized plastic pack-aging material (Krochta et al., 1997). The predominant method of waste disposal inmost countries all over the world (except for the Netherlands) has been and remainslandfill. The main approaches to waste management are, by priority, as follows:

1 Prevention and reduction at source, re-use2 Degradable packaging3 Recycling (mechanical, chemical, feedstock)4 Combustion for energy recovery5 Combustion for volume reduction6 Landfill (Thurgood, 1995; Mertzani, 1997; Read et al., 1997; Krishna et al., 1998;

Read, 1999b).

Although prevention and source reduction is considered to be the best waste managementoption, this approach is anticipated only partially to solve the problem (Tsimilis andHadjimanolis, 1995). Current demand for energy and virgin resources, many of whichare non-renewable, cannot continue without fostering ever geater environmental and eco-nomic degradation. Law makers and producers must, instead, recognize the necessity of anew policy for the new century – a policy based on environmentally and economicallysustainable use of materials, or ‘materials efficiency’. Recycle and re-use, which usuallyuse materials, energy and water more efficiently than virgin material industries and pro-duce less pollution, are essential elements of such a material efficient policy (http://www.grn.org; http://apme.org/environment/htm/0.4.htm, Karakasidis, 1997).

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A new market-incentive (MI) system was launched to recycle waste packaging containers in Taiwan. Since most used packaging containers have no or insufficientmarket value, the government imposes a combined product charge and subsidy policyto provide enough economic incentive for recycling various kinds of packaging con-tainers, such as iron, aluminum, paper, glass and plastic. Empirical results show thatthe new MI approach has stimulated and established the recycling market for wastepackaging containers. The new recycling system has provided 18 356 employmentopportunities and generated NT$ 6.97 billion in real-production value and NT$ 3.18billion in real GDP during the 1998 survey year. Cost-effectiveness analysis constitutesthe theoretical foundation of the new scheme, whereas data used to compute the empir-ical product charge are from two sources: marketing surveys of internal conventionalcosts of solid-waste collection, disposal and recycling in Taiwan and benefit transfer ofexternal environmental costs in the USA. The new recycling policy designed by Bor andhis coworkers (2004) provided a reasonable solution for solid-waste management in acountry with limited land resources such as Taiwan.

A proper analysis (an evaluation) of the environmental load of consumption is impor-tant in the context of sustainable development. Nowadays, different methods are used tocalculate the environmental load of household consumption, mainly in energy and orgreenhouse gas emission terms. These methods are all based on input-output energyanalysis, but use different data sources and produce different results. Three methodsused to calculate the total energy requirements of households have been discerned anddescribed and the main result produced with these methods discussed. All three meth-ods were applied to the Netherlands in order to compare differences and similarities inthe results. It was found that the total energy requirement calculated with all three meth-ods was almost the same, with differences less than 4%, however, each method providesresults at a different level. Basic energy input-output analysis generates total require-ments and requirements per consumption category and is therefore suitable for describ-ing and explaining the effect of household consumption. The hybrid method, combiningenergy input-output analysis with process analysis, generates requirements per con-sumption item and therefore offers opportunities to search for options of change ofhousehold consumption patterns to more sustainable consumption. Reviewing themethods applied to calculate household energy requirements three different types ofmethods were distinguished:

1 input-output energy analysis, based on national accounts (IO-EA-basic)2 input-output energy analysis combined with household expenditure data (IO-EA-

expenditure)3 hybrid energy analysis, input-output analysis combined with process analysis (IO-

EA-process) and data and operations needed for these three methods are shown inFigure 15.1.

The life cycle of a product as used in the IO-EA-process method is given in Figure 15.2(Kok et al., 2006). The major difference between the IO-EA-expenditure method andthe other two methods is found for agriculture, where the energy requirement with the


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Energy content ofmaterials, transport

and waste

Processanalysis

EAP: LCA of goodsand services

Energy intensitiesof sectors

Input-outputenergy analysis

Energy intensities ofgoods and services

Energy requirementsof households

Economicinput-output

data

Energydata

Finaldemand

Prices

Expendituresurvey

IO-EA-process IO-EA-expenditure IO-EA-basic

Figure 15.1 Data and operations needed for the three different energy analysis methods (adapted from Kok et al., 2006)

IO-EA-expenditure method is considerably higher due to the high average energyintensity for horticulture.

Diaz and Warith (2006) developed a Waste Analysis Software Tool for Environ-mental Decisions (WASTED) model. This model provides a comprehensive view ofthe environmental impacts of municipal solid waste management systems. The modelconsists of a number of separate submodels that describe a typical waste managementprocess: waste collection, material recovery, composting, energy recovery from wasteand landfilling. These submodels are combined to represent a complete waste man-agement system. Aluminum and steel are the only metal components in MSW consid-ered to be fit for recycling in the WASTED model. Most of the aluminum in the wastestream comes from beverage cans. Aluminum is one of the most attractive materialsfor recovery from the waste stream. This is because aluminum recycling consumes farless energy (11.7 GJ/ton) than the smelting of aluminum ore (140 GJ/ton). The recy-cling data for metals are given in Table 15.1.

The glass that is recovered is found in food and beverage containers. This fractionincludes both colored and clear glass bottles. However, this is an energy intensiveprocess that takes place at 1800 K (Wang and Pereira, 1980), so the energy required torecycle glass is 9.23 GJ/ton compared to 14.1 GJ/ton for virgin raw materials (Haight,

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Manufacturing

Trade

Residualgoods

Capitalgoods

Consumption

WasteRecycling

Basicgoods

Transport

Transport

Transport

Transport

Transport

Figure 15.2 Life cycle of a product as used in the IO-EA-process method (adapted from Kok et al., 2006)

2004). Glass can also be recycled in a closed loop. The recycling data for glass aregiven in Table 15.2.

Newspaper is typically the largest fraction of paper recycled (EPA, 2002). Finepaper comprised paper used for printing and photocopying. Cardboard is the typicalmaterial used for packaging. It includes both the smooth and corrugated fractions ofthis material. Mixed paper describes unsorted paper wastes. The recycling data forpaper products are summarized in Table 15.3.

Although the technology to recycle most plastics exists, the sorting and prepara-tion processes are complex. Therefore, most localities do not recycle all plastics.Currently, plastic is classified into seven categories, categorized by name and number:

1 polyethylene terephthalate (PET or PETE)2 high-density polyethylene (HDPE)3 polyvinyl chloride (PVC)4 low-density polyethylene (LDPE)

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Table 15.1 Recycling data for metals (kg/ton)

Parameter Aluminum Ferrous metal

Virgin Recycled Virgin Recycled

Energy (GJ) 140.00 11.70 25.20 9.43

Air emissionsCO2 2900.00 4.36 1820.00 595.00PFC (CO2 eq.) 2226.00 0.00 0.00 0.00CH4 6.53 2.71 0.0097 1.29NOx 17.30 0.62 2.76 1.77VOCs 24.50 0.30 0.23 0.02SOx 47.60 2.88 5.11 2.98PM 10.00 0.00 1.31 7.22Pb 1.93 � 10�3 0.38 7.60 � 10�4 6.59 � 10�4

Hg n/a n/a n/a n/aCd n/a 4.37 � 10�5 n/a n/aHCl 0.81 5.81 � 10�2 8.57 � 10�2 0.10

Water emissionsPb water 1.47 � 10�7 0.00 2.92 � 10�2 2.90 � 10�2

Hg water 0.00 0.00 n/a n/aCd water 0.24 0.06 9.75 � 10�5 9.38 � 10�5

TCDD Eq W 1.20 � 10�6 4.42 � 10�8 n/a n/a

Adapted from Haight, 2004

Table 15.2 Recycling data for glass (kg/ton)

Parameter Glass

Virgin Recycled

Energy (GJ) 14.10 9.23Air emissionsCO2 632.00 278.00PFC (CO2 eq.) 0.00 0.00CH4 1.11 0.83NOx 2.73 1.69VOCs 0.24 0.17SOx 4.37 3.11PM 0.89 0.43Pb 5.01 � 10�6 1.15 � 10�6

Hg 1.30 � 10�6 3.00 � 10�7

Cd 1.35 � 10�5 2.95 � 10�6

HCl 5.96 � 10�2 0.98Water emissionsPb water 3.60 � 10�8 1.90 � 10�8

Hg water 2.55 � 10�8 1.95 � 10�8

Cd water 2.20 � 10�4 2.55 � 10�4

TCDD Eq. W n/a n/aBOD 6.9 � 10�3 5.1 � 10�3

Adapted from Haight, 2004

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948W

aste Managem

ent for the Food Industries

Table 15.3 Recycling data for paper products (kg/ton)

Parameter Newspaper Fine paper Corrugated board Mixed paper

Virgin Recycled Virgin Recycled Virgin Recycled Virgin Recycled

Energy (GJ) 46.43 25.57 43.05 23.40 29.23 13.64 36.85 26.21Air emissionsCO2 2400.00 1385.00 1100.00 1507.00 896.00 1019.00 1304.00 1752.00PFC (CO2 eq.) 0.00 �3060.00 0.00 �4580.00 0.00 �4580.00 0.00 �4580.00CH4 0.03 0.02 0.02 0.02 0.01 0.01 0.02 0.01NOx 10.40 5.26 8.74 5.38 6.25 5.56 7.94 5.44VOCs 11.20 7.19 8.27 18.47 3.87 35.40 6.86 23.89SOx 16.30 9.40 12.88 9.80 7.74 10.40 11.23 9.99PM 4.63 2.80 4.81 3.10 5.07 3.56 4.89 3.25Pb 4.52 � 10�4 2.63 � 10�4 3.52 � 10�4 2.67 � 10�4 2.03 � 10�4 2.73 � 10�4 3.05 � 10�4 2.69 � 10�6

Hg n/a n/a n/a n/a n/a n/a n/a n/aCd n/a n/a n/a n/a n/a n/a n/a n/aHCl n/a 3.87 � 10�6 3.57 � 10�6 4.51 � 10�6 8.93 � 10�6 5.46 � 10�6 5.29 � 10�6 4.81 � 10�6

Water emissionsPb water 1.63 � 10�7 6.35 � 10�8 1.46 � 10�7 6.59 � 10�8 1.20 � 10�7 6.95 � 10�8 1.38 � 10�7 6.71 � 10�8

Hg water 3.82 � 10�8 2.33 � 10�8 2.69 � 10�8 1.40 � 10�8 9.92 � 10�9 0.00 2.15 � 10�8 9.51 � 10�9

Cd water 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00BOD 3.51 3.09 2.71 3.29 1.52 3.58 2.33 3.38

Adapted from EPA, 2002; Haight, 2004

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Table 15.4 Recycling parameters for plastics (kg/ton)

Parameter PET PE PP PS PVC

Virgin Recycled Virgin Recycled Virgin Recycled Virgin Recycled Virgin Recycled

Energy (GJ) 107.15 46.07 79.76 19.94 76.42 19.87 84.8 11.63 59.8 9.13Air emissionsCO2 2363 163 2400 163 2100 942 2200 942 2000 942PFC (CO2 eq.) 25 0.016 28 0.016 28 0.016 24 0.016 22 0.016CH4 9.5 0.081 6.5 0.081 6.4 0.081 6.9 0.081 6.3 0.081NOx 7.2 6.95 7.8 6.95 7.7 6.95 5.9 6.95 5.8 6.95VOCs 14 n/a 4.9 n/a 5.4 n/a 5.2 n/a 5.3 n/aSOx 4.6 n/a 1.5 n/a 1.7 n/a 2.4 n/a 1.4 n/aPM n/a n/a n/a n/a n/a n/a n/a n/a n/a n/aPb n/a n/a n/a n/a n/a n/a n/a n/a n/a n/aHg n/a n/a n/a n/a n/a n/a n/a n/a n/a n/aCd 0.058 n/a 0.011 n/a 0.014 n/a 0.014 n/a 0.016 n/aHCl n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a

Adapted from Molgaard, 1995; Eulalio et al., 2000; EPA, 2002; Haight, 2004

5 polypropylene (PP)6 polystyrene (PS)7 other plastics (Other).

Recycling parameters for plastics are given in Table 15.4.Composting has several environmental advantages over landfilling. In the first

place, when done properly composting generates no methane (CH4). This gas is pro-duced by anaerobic degradation of wastes (for example, in a landfill) and has 21 timesthe greenhouse potential of CO2 (IPPC, 1996). Additionally, mature compost can beused as a soil conditioner and does not generate long-term environmental concerns.Finally, the aerobic degradation of organic compounds results in the ‘storage’ of asmall amount of carbon that is not degraded to CO2, but is transformed into slowlydecomposable components (EPA, 2002). Modern landfills are engineered facilitiesthat are designed to stabilize the solid wastes and minimize hazards to the public.Although the ideal case is that 100% of every good produced is reintroduced to theproduction cycle, this is thermodynamically impossible. Therefore, landfills are nec-essary even when waste diversion rates are high. WASTED allows the users to selectfrom four different kinds of landfills:

1 sanitary landfill2 bioreactor landfill3 unlined landfill with leachate collection4 unlined landfill with no leachate collection.

The results for this model are comparable to other publicly available models, such asWARM or IWM. These differences are due to the different system boundaries in the

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models and in the different parameters used to describe the waste management oper-ations. Since WASTED allows the users to fine-tune the input parameters, it can beadjusted better to reflect the specific conditions in a case study.

Glass

Introduction

The discovery of glass dates back to the Phoenicians more than 5000 years ago,although it is believed that glass bottles were invented by the Egyptians with themethod of hand blowing 1000 years later. However, during the last hundred years,mechanized glass blowing techniques have revolutionized the production of glasscontainers, allowing bottles to be produced quickly and cheaply (Waite, 1995; Vogas,1995; Pearson, 1996; Read, 1999b). Glass is a melt that has been solidified withoutbeing subject to crystallization and reacts only with fluoride and hydrofluoric acid.Practically, there are no limits in glass quantity that can be produced, since 80% of theearth’s surface consists of sand, soda and limestone, the basic glass constituents.Small quantities of other substances are added to impart the desirable properties to thefinal product.

New glass is traditionally produced by melting sand, soda and limestone at temper-atures of between 1200 and 1500°C. Then the temperature decreases and through ametering unit the melted glass is removed from the furnace and is driven to the shap-ing/forming machine to receive the appropriate form and shape. Glass can be moldedin different types, shapes and colors. The common colorings are usually brown, greenand clear. Clear glass comprises over 50% of the international market while coloredglass the other 50%, thus satisfying traditional consumer demands. For example,brown glass is used to offer satisfactory protection from light and is employed forproducts like fruit juices, medicines and alcoholic drinks. Small fragments of brokencolored and clear glass can be added in the production of new colored glass contain-ers, while in the case of clear glass production only clear glass cullet can be used(White et al., 1995; Dascalopoulos et al., 1998).

Glass packaging, though fragile and heavy compared to other packaging materials, isendowed with properties that make its total replacement by lighter materials a very dif-ficult task. Glass is also an environmentally friendly material, since it is inactive andtotally degradable. When it is exposed to the environment it breaks into small fragmentsof silicon and sand, two of the most common materials in our planet. Even though glassis a degradable material, its re-use and recycling improve considerably its environmen-tal performance. Usage of recycled glass as cullet for the production of new glass con-tainers saves energy, raw material and reduces glass manufacturing costs. Containerglass is the only glass item being recycled in large quantities at the present time.Window panes, light bulbs, mirrors, ceramic dishes and pots, glassware, crystal, oven-ware and fiberglass are some representative glass items that cannot be recycled withcontainer glass and are considered contaminants in container glass recycling (Mondorfand Jensen, 1995; Nijkerk, 1995; Gilmore and Hayes, 1996; Hynes and Jonson, 1997).


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Energy is conserved because cullet melts down at a lower temperature than that requiredfor processing the raw materials for glass production. This practice does not only reduceenergy cost, but extends furnace life as well. Depending on the amount of cullet used, fur-nace life can be extended by 15–20%. The conservation of energy, in turn, contributes tonatural resources preservation. Generally, by employing recycled glass, 25% less energy isrequired and a reduction of 80% and 50% in raw materials and water quantity required is achieved, respectively (Nguyen et al., 1995; http://www.raymond.com/rates97htm,http://www.epa.gov/epaoswer/non-hw/muncpl/factbook/internet/mswf; Cook, 1995).

International situation

In 1996, glass fragments accounted for 56% of the total material in the glass industry and71% for green glass. The constantly increasing usage of glass waste in the glass manu-facturing industry over recent years resulted in decreases in soda consumption andenergy of 67% and 35%, respectively. Glass is the second most important in weight pack-aging material, since it represents 8% by weight of the municipal solid waste (MSW) and2% by volume. Therefore, reduction in glass at waste streams could be of a substantial aidin achieving targets that are typically measured as percentages of total waste weight. In waste streams, glass packaging represents around 98% of total glass waste, while the other 2% consists of light bulbs and window panes. Although industry mainly recy-cles glass packaging, other glass waste is also recycled at a smaller percentage (4%) andused primarily for the production of construction materials (http://www.britglass.co.uk/recycling/glassrec.html, http://www.britglass.co.uk/recycling/stats97.html; Barlow,1994). The three most important practices employed by European and other nationsare presented in Table 15.5. Germany, Switzerland and Holland are the leading coun-tries in glass recycling worldwide with recycling rates of 81–89%. Satisfactory recy-cling rates in other European countries (around 50%), such as France, Italy, Austria,Belgium, Norway and Denmark have also been achieved. In general, in 1996 Europerecycled around 50% of the produced glass, Australia 44%, the USA 32% and Japan60%. According to EPA (United States Environmental Protection Agency), glassrecycling rates in the USA are expected to reach 36% by the end of the year 2000(Table 15.6).

Although Holland has a very high recycling rate for glass, in 1996, there was a sur-plus of mixed glass which was not separated into the three known qualities: clear,green, brown. The problem that arose could be solved with the introduction of com-partmentalized bottle banks for color sorted glass collection, like in Germany, but thehigh expenditure of three colored sorted banks prevented their use. Therefore, inHolland, the first complete glass separation factory started operating, handling about150 000 ton/year, by making use of a laser separation system. In Germany, the recy-cling system requires that consumers use six different waste bins at their houses thatlead to the collection of undesirable materials as well. In Greece, 125 000 tonnes areproduced out of which only 25 000 are recycled, while ambitious targets have been setto reach 50 000 tonnes, aiming at a reduction of municipal solid wastes volume by100 000 m3.


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Table 15.5 Treatment routes employed by European and other nations (%MSW)

Nation Recycled and Incineration Landfillcomposted

Switzerland 29 59 12Denmark 23 48 29Sweden 19 47 34France 13 42 45The Netherlands 19 35 45Germany 18 36 46Austria 24 11 65Norway 11 22 67Finland 15 2 83Belgium 3 54 43Italy 10 16 74Spain 30 6 65Ireland 3 0 97Luxembourg 3 75 22Portugal 15 0 85UK 2 10 88Canada 12 8 80USA 17 16 67Greece 0 0 100

Adapted from Onusselt, 1997

Table 15.6 Glass recycling rates around the world (%)

Country 1991 1993 1994 1995 1996 1997

Germany 55 71 75 82 85 89France 46 48 50 50Italy 52 54 53UK 21 29 28 27 26 26Spain 29 31 35Holland 73 77 80 81Belgium 55 67 67Austria 68 76Denmark 64 67Sweden 54 56 72Portugal 29 32Greece 27 29 29Norway 72 75Finland 50Ireland 29 31Switzerland 78 84 89Australia 89USA 25 33Japan 60

Adapted from Arvanitoyannis and Bosnea, 2001

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Glass recycling process

As soon as the glass waste is delivered to glass recycling plants, its separation accordingto color starts while metal rings and bottle tops are being removed. The glass waste iscrushed into small particles and the mixture is called ‘cullet’. The recycling process ofglass depends entirely on the type of glass that will be produced (Stotzel, 1997). There aresome basic rules to be followed during glass recycling, so glass should be free from metaltops, ceramics and stones and be sorted according to color. There should be a thoroughremoval of foreign materials, otherwise the produced glass might be defective. The quan-tity of ceramics left on the cullet should not be more than 25 g per tonne, while the metalparticles should be less than 5 g per tonne. Therefore, the basic container glass recyclingprocess steps are:

1 initial rinsing, cap and lid removal2 color separation3 volume reduction by breaking or crushing4 packaging and shipping5 final treatment.

In many recycling programs, consumers sort glass containers according to color andremove labels, metal rings and bottle tops before delivery at waste disposal sites(Germany). In other cases, sorting according to color occurs in the glass recycling indus-try. Since colored glass wastes cannot be used in some applications (e.g. production ofnew clear glass), color sorting is important. Until recently, color separation was carriedout manually, but nowadays specially designed laser equipment can sort out glass, rapidlyand accurately. Color sorting based on transparency, employs light from different kindsof lamps and lasers. In laser applications, partition of light to the sensing device is guidedvery elegantly by a rotating mirror and optical fiber devices (Figure 15.3). As regardsmetal detection, theoretically, all non-ferrous and ferrous metals can be detected with ametal detection device and subsequently removed through a reject mechanism. The sys-tem sensitivity to non-ferrous metals depends on the conductivity, the shape and the sizeof individual metal particles. The design and construction of an effective and economi-cally viable metal detector for a glass recycling industry is more difficult than it seems(Dalmijn et al., 1995). However, prior to recycling the colored glass, stones and ceramicparticles must be meticulously removed. The detection of ceramic materials in glass cul-let usually makes use of the properties of transmission or reflection of light since a lasergenerated beam of light falls on to a sensing device. For every opaque particle this beamwill be broken and a signal will be transmitted to the sensing device. This informationwill be further processed with an electronic device and one or more blasting valves willbe activated to refuse the undesired particle. This type of sorting device is considered to be very rapid and reliable. The final product quality is usually determined by newmicrowave-based techniques (Dannheim and Hadrich, 1998).

Glass breaking is not desirable if it occurs before color separation. In certain mixedwaste stream processing systems, the glass fraction of the waste stream simplybecomes part of git residue, which is either land filled or just becomes a component


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of a composted waste product. In compost, glass particles usually prove to be benefi-cial because they have similar properties to sand. Where glass containers are to berecovered for usage in the glass manufacturing industry, color sorting has to occurbefore breakage, while metal neck rings, paper labels and food residues may beremoved after initial breakage. After breakage, glass is packaged, stored or shipped tothe market (Choudhary and Huff, 1997). The storage is an essential part of glass recy-cling, since only collection of a considerable amount of glass will ensure the eco-nomic viability of the recycling process and marketing. Broken glass storage shouldprovide the conservation of glass in good condition until packaging occurs. Glass cul-let of high quality is usually packaged in paperboard and employed for special appli-cations. Occasionally, broken glass is shipped unpacked in containers (Anon, 1995a).As soon as the glass cullet is delivered to industry, a second sorting takes place, inorder to assure the desired quality of the final product. Then glass cullet is mixed withraw materials used in glass production. After mixing, the batch is melted in a furnace


Light distributor

Color separation filter

Light mixer

Laser

Light converter

Processor(100x)

Figure 15.3 Glass laser sorting system (adapted from Arvanitoyannis and Bosnea, 2001)

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at 1425–1535°C, depending on the percentage of cullet contained in the batch. Themore cullet used the less heating is required for melting. The melted glass is pumpedinto a forming (blowing) machine where it assumes its final shape (Stotzel, 1997).

Glass recycling and the environment

The usage of recycled glass has the advantage of reducing furnace temperaturesrequired for raw materials melting. The amount of saved energy can theoretically becalculated with the following formula:

Saved energy � 0.25 � % recycled glass cullet used

Although, data related to glass manufacture from raw material are not available, theconsequences and energy consumption can theoretically be calculated, while severalmodels have been suggested for that purpose. The proper energy usage within theindustry is one of the major goals of industrial management and government, since itrepresents 10% of total operating costs. By employing advanced and sophisticatedtechnologies, energy costs can be significantly reduced as shown in Table 15.7.Several organizations and agencies were founded in order to offer advice to recyclingimplicated members regarding the improvement of the recycling system and recyclingrates (Kannah, 1995; Hamann et al., 1995; Krauss et al., 1995; Schaeffer, 1996). Aproblem that glass manufacturers need to face is the exploitation of the glass industrywaste. For several years, filters, pipes and discarded furnaces have caused significant


Table 15.7 Energy and emissions from recycled and virgin glass production

Source Recycled Virgin Savings/tonne Savings/tonne glass (100%)/ glass/tonne recycled glass recovered glass usedtonne produced producedproduced

Energy consumption (GJ) 5.8 9.6 3.8 3.7Air emissions (g) 428 17780 17352 16831particlesCO 57 105 48 47NOx 1586 2270 684 663N2O 12 106 94 91SOx 2652 3927 975 946HCl 6 75 69 67HF 2.4 1 �23 �22Ammonia 2 4 2 1.9Lead 16 0 �16 �15.5Water emissions (g)BOD 1 1 0 0COD 2 4 2 1.9Total organic compounds 20 26 6 5.8Solid waste (kg) 29.3 4.0 �25.3 �24.5

Adapted from Arvanitoyannis and Bosnea, 2001

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problems related to the release of hazardous substances. Part of those residues is recy-cled or undergoes appropriate treatment. Another problem that has to be urgently con-fronted resides in the lead containing crystal items that can cause health problems toconsumers. As a result, international organizations have set limits regarding the useand presence of lead in packaging materials, such as glass, crystal and ceramics(Wachter and Seiler, 1995; Anon, 1995a; Nag and Jarausch, 1995; Gutmann, 1996).The glass recycling process is given in Figure 15.4.

Roundput is one of the most important principles of the development of both natu-ral and industrial ecosystems and is especially important for the analysis of an ecosys-tem’s dynamics and overall functioning, as it is related to an extent to which energyand matter are recycled and used in a cascade-type operation. Two modeling casestudies from the UK and Switzerland were studied where increasing recycling ratesfor plastic and glass would improve the energy budget of the waste management pro-gram and, therefore, benefit the corresponding industrial ecosystems. In the first casestudy, it was shown that the major source of energy savings from glass recycling isthrough increased use of cullet in glass manufacture (5.4% reduction in total energyconsumption with 100% glass recycling when compared to the present-day situation).In terms of energy consumption, recycling is the preferred waste management option,even if a large proportion of the recycled glass is diverted for use as aggregates.Further energy savings could be achieved by the introduction of a city-wide kerbsidecollection scheme, which would result in an estimated maximum reduction (100%recycling rate) of 7.6% in energy consumption for processing of the Southamptonhousehold glass wastes. In the second case study, the situation in which all wastes areburned at an MSWI plant is compared with two scenarios assuming that 8.1% of theplastic is diverted into a cement kiln (mixed plastics; scenario 1) or a mechanical recy-cling plant (polyethylene, polypropylene, polystyrene; scenario 2). The resulting netprimary energy consumption values for both scenario 1 (5.85E8 MJ or 60% relative tothe reference scenario) and 2 (7.46E8 MJ or 76.6% relative to the reference scenario)use less primary energy than the reference scenario (9.74E8 MJ). This means that,from the point of view of resource consumption, the diversion of plastics waste awayfrom the MSWI plant has a beneficial effect. Therefore, the increased recycling ofglass and plastic would benefit the industrial ecosystems in terms of energy savings.This is similar to the patterns observed in most natural ecosystems and a careful con-sideration of this similarity within a framework of industrial ecology should help toreduce the conflict between the two systems (Krivtsov et al., 2004).

A fundamental challenge of sustainable development is to deliver massive improve-ments in resource efficiency if projected economic gowth rates are not to cause unacceptable levels of environmental degradation. An important element in the UKgovernment’s strategy to deliver on this compensation for growth agenda has been thepolicy commitments to increase levels of material recycling. Unfortunately, a numberof technical, political and attitudinal obstacles stand in the way of achieving the tar-geted improvements in material recycling. For example, in the case of waste glass (orcullet), the imbalance between the color mix and arising household and commercialglass container waste in the UK and demand from UK glass container manufacturers,presents a significant barrier to closing the loop on this material flow. Efforts to


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Waste M

anagement in Food Packaging Industries

957

Removal of wrong colors and

other impurities

Wasteglass

Color-sorted collection Pre-sorting CrushingMetal and paper

removal

Magnetextractors

Paper extractors

Glassfragments

SievingMeltingMolding/shaping

Glassbottles

Jars, jugsetc.

Figure 15.4 Glass recycling process (adapted from Arvanitoyannis and Bosnea, 2001)

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resolve this imbalance focused on alternative potential end uses for cullet and the res-olution of related technical barriers, particularly in the use of cullet as secondary feed-stock for aggregate and cement production. Butler and Hooper (2005) presented anevaluation of the environmental outcomes of various options for the use of cullet withthe aim of optimizing the environmental benefits resulting from the recycling activity.Taking energy use as a key environmental indicator, a study carried out for EMERGERecycling in Manchester has shown that, while there are environmental gains to bemade from substituting glass container feedstock for virgin raw material in the pro-duction of base aggregates, these gains are significantly less than those accruing fromthe substitution of cullet for virgin raw materials in the production of glass containers.Consequently, the paper argues that transporting household and commercial arisingsof cullet for use in glass container manufacturing in EU countries, where cullet sup-ply and demand does not suffer from the UK imbalance, provides a significantly morebeneficial environmental outcome than its use as secondary feedstock for base aggre-gate and other building materials within the UK.

Limits on current efforts to reduce the environmental impact of packaging are cir-cumscribed by a retail distribution system designed for the efficient management ofglobalized distribution of continually increasing quantities of consumer goods, in turndependent on low cost transport and packaging able to protect products from physicaldeterioration and damage in transit. Thus, an EU Commission Communication on theprevention and recycling of waste, nowhere questions the need for behavioral changeincorporating reduced consumption. Instead, it espouses the position that ‘strong eco-nomic performance must go hand in hand with sustainable use of natural resources and levels of waste’ and focuses on measures designed to reduce the impact of waste. Itis difficult to reconcile the concept of sustainability, however defined, with this idea of ‘sustainable levels of waste’ resulting from strong economic growth. The sameCommunication makes the point that ‘as all materials used in an economy sooner orlater become waste, major changes in waste generation require changes in productionand consumption patterns’. However, no policies for changes in consumption patternsare proposed. To date, all efforts at reducing the impact of packaging waste in the UKhave focused on its production, particularly light-weighting. As demonstrated in thecase of glass containers, this approach, while making a significant contribution to reduc-ing its environmental impact per unit of production, has not prevented the total quantityof glass container waste continuing to rise. This is symptomatic of current efforts toreduce the environmental impact of consumption, largely based on technical improve-ments in production and product use efficiencies. At some point, the validity of eco-nomic policies based on continually increasing consumption has to be brought into therealm of practical policy making. Without this happening, the ability of the ecosystemto carry the burdens of economic activity will be broken sooner rather than later.

Aluminum

A methodology for planning of integrated recycling concepts taking into account thepeculiarities of process engineering in the process industries was suggested by


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Schultmann et al. (2004). Process models for certain unit operations simulated with aflow-sheet program allow calculation of mass and energy balances considering the tech-nical characteristics and performance of a single process or a combined process chain.Based on principles of thermodynamics, this approach allows an assessment of inte-gated recycling strategies considering techno-economic as well as ecological criteria.The approach is illustrated with an example from the iron and steel making industrywhere the injection of plastic waste into a blast furnace is investigated. The iron and steelmaking industry not only delivers large amounts of products for different sectors (auto-motive, construction, packaging), but also uses significant quantities of residues from itsown processes (by-products like dust and sludges) and from other industrial fields (usedproducts like scrap cars) as input materials. Not only these recycling loops, such asinternal re-use of materials or the integation of (external) residues into the productionprocesses, but mainly the characteristics of thermodynamics require non-linear mathe-matical depiction (Spengler et al., 1998). Application of the hybrid approach to the steelindustry showed that the implementation of process-integated pollution control measuresdo not necessarily cause a rise in the specific production costs. With suitable technicalmeasures, the iron content of the by-products or residues can be regained in a recyclingproduct like sponge iron and can be recycled within the process chain and reduce theconsumption of other iron-bearing input materials. With regard to multinational deci-sion-making, this approach may prove to be a suitable method for defining best availabletechniques (BAT) as requested in the IPPC-Directive of the European Union, whereclusters of technical options for various industrial branches are classified (Rentz et al.,1999, 2001; IPPC, 2000; Schultmann et al., 2004).

In contrast to many other materials, in the recycling of metal there are no qualitylosses. Compared to primary metal extraction, a 95% savings in energy can be achievedwith recycling. The economic value of aluminum has always been the main reason forbringing the material into the loop of metal extraction, processing, use and recovery.Aluminum has been recycled since the days it was first commercially produced and todayrecycled aluminum accounts for one-third of global aluminum consumption worldwide.In Europe, aluminum enjoys high recycling rates, ranking from 41% in beverage cans to85% in building and construction and 95% in transportation. With the introduction of theDuales Systems Deutschland in the packaging field, an exhaustive system for acquisition,sorting and re-use of aluminum packaging has been set up. The website of the DualesSystem Deutschland, however, shows a recycling rate of more than 97% for aluminumpackaging in 2002 (Duales System Deutschland, 2004). Cans or tins made of tin plateconsist of 99.8% steel with a wafer-thin layer of tin. The recycling of used tin platecans is possible with easy processes resulting from the unique magnetic properties ofsteel (Onusseit, 2006). The flow diagram for metal recycling is shown in Figure 15.5.

According to WasteOnline, 3.2 m tonnes of the 26 m tonnes of household waste pro-duced annually come from packaging. Meanwhile, 150 m tonnes of packaging wastecome from industry and commerce each year. In the UK, 11% of household wastes isplastic, 40% of which comes from the 15 m plastic bottles used every day. Only less than3% of these plastic bottles are recycled. Less than 1% of the billion plastic bags usedannually are recycled and the majority are used only once (http://www.thesite.org.uk).In 2002, steel packaging recycling in the EU 15 reached an average rate of 60%. In


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Aluminumcan

ShreddingPaint

removal

LabelsDelaquering oven

Residualmoisture

Screening

Dirt

Contami-nants

Rotary furnace

Can melting

Blending with molten

metal

Figure 15.5 Flow diagram for metal recycling (adapted from Onusseit, 2006)

accordance with the 1994 EU Packaging Directive, new EU Member States are activelypromoting the collection and recycling of used steel packaging. In terms of meeting thelegal requirements, steel contributes significantly to reaching the EU recycling target formetal packaging (steel and aluminum), which the Packaging Directive has set at 50% bythe year 2008. In 2002, steel packaging was the most recycled packaging material inEurope, followed by glass at 57%. Across the western half of the continent, recycledquantities have tripled within the space of a decade. A recent study conducted by

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Landell Mills for APEAL in Poland, Hungary, the Czech Republic and Slovakia showsthat, in 2001, the consumption in food cans reached 1.8 billion units and is projected togrow at the rate of 3.5% per annum. Steel represents 60% of all food packaging inCentral Europe (http://www.packwire.com/news/printNewsBis.asp?id=51810).

Aluminum in packaging preserves food quality and avoids waste and its low weightreduces fuel consumption and emissions during transportation and means it is suitable forpackaging applications where weight is important. Around the world, most high voltageoverhead transmission and distribution lines over long distances are made of aluminum.Aluminum is used extensively for the protection, storage and preparation of food andbeverages. Aluminum can be rolled into ultra-thin foils which are light, strong and haveunique barrier and insulation qualities to preserve food, cosmetics and pharmaceuticalproducts and protect from ultraviolet light, odors and bacteria. Aluminum packages aresecure, tamper-proof, hygienic, easy to open and recyclable. Aluminum withstands bothheat and cold. It is easy to sterilize for food and medical applications. It is an excellentbarrier against liquids, vapors and light. It transmits conducted heat and reflects radiantheat. That is why you can oven-bake a potato in foil or insulate your home with it. Lessthan an ounce of aluminum sprayed on a polymer forms a thin insulating sheet that cankeep a newborn baby warm or save the life of someone on an exposed mountain top(http://www.world-aluminium.org/applications/index.html). Aluminum conducts heatextremely well, making it very energy efficient for preparing and serving both hot andcold food. It is non-toxic and imparts no taste or odor. Aluminum beverage cans and foodcans have a protective polymer coating applied on the inside to prolong storage life(http://www.world-aluminium.org/applications/packaging/index.html). The Swedeshave an impressive over 80% aluminum can recycling rate, which makes efforts in theUSA look comparatively weak, at a rate of under 50% that has been backsliding from ahigh of almost 60% in 1992 (Figure 15.6).

Formability is an important consideration in selecting a suitable uni-alloy for thealuminum beverage can: this includes the quality of the material recycled from usedcans. The alloy 5017, in chemical composition ranking between the currently usedcan-stock alloys, is a promising option. The formability data obtained are quite


100

90

80

70

60

50

40

301984 1986 1988 1990 1992 1994

Year

Per

cent

age

(%)

1996 1998 2000 2002 2004

Figure 15.6 Recycling rate for aluminum cans in Sweden and the USA (1984–2004) (� Sweden and �the USA) (adapted from http://container-recycling.org/alumrate/gaphs.htm)

Ch15-P373654.qxd 10/18/07 6:35 PM Page 961

comparable to those for 3004-O (Sillekens et al., 1997). The experiments reveal thatthe formability data for the 5017-based model alloys change with an increase in Fecontent, the extent to which this affects the actual behavior depending on the formingprocess employed. The overall performance, however, does not decline significantlyfor the range investigated, which includes an increase in Fe content of up to twice thestandard amount.

The new direct conversion technique introduced by Samuel (2003) is characterizedby low energy consumption, large metal savings and very low air pollution emissionas compared with conventional methods. Figure 15.7 shows a flow chart for the con-ventional and the new techniques for direct scrap conversion into extruded products.It can be seen that the new technique is characterized by fewer steps, a higher effi-ciency of recovery and low generation of new scrap. Moreover, the new techniqueprovides the following advantages over the conventional methods:

1 powder suitable for the production of green compacts can be processed from aluminumscrap

2 the chemical cleaning operation introduced in this technique removes the oxidefilm from the aluminum surface, which results in high green density (about 80%before sintering)

3 the cost of the product is about 59% of the conventional aluminum powder cost.

Usually the energy consumed for the conventional recycling of aluminum is16–19 GJ/t, whereas in the direct conversion of aluminum chips into compact materialonly 5–6 GJ of energy per ton is needed. By reducing the number of operations, thedirect conversion method allows labor to be reduced to 2.5–6.5 man-hours per ton ofthe product, while for conventional recycling, this figure is much higher, ranging from11 to 15 man-hours per ton, including 3 man-hours per ton for the production ofingots, 5 man-hours per ton needed to produce billets and 3–5 man-hours per ton for the production of sections. The benefits of the direct conversion of aluminum andaluminum-alloy chips into compact metal include also a possible reduction in thefunds spent on environmental protection as a result of the reduced consumption ofores and energy carriers and less degradation of the natural environment because ofreduced air-pollution emission. To sum up, it should be emphasized that the environ-mentally clean direct conversion of aluminum scrap into compact metal results in savings of 40% in material, 26–31% in energy and 16–60% in labor (Gonostajski et al., 2000).

The most usual process to recycle aluminum employs a rotary furnace which isheated by the burning of fossil fuel. In order to enhance the aluminum yield, a lowmelting point mixture of salts is charged before the aluminum scrap or the aluminumdross. The salt fluxes universally used are based on equimolar mixtures of sodium andpotassium chlorides; this composition corresponds to the minimum temperature ofthe isomorphous binary system. Fluorides are also frequently added to the chloridemixture; the most common fluorides added are CaF2 and Na3AlF6. The use of saltsgenerates a by-product known as ‘salt cake’ that is considered a hazardous waste.Microstructure analysis was the main tool to analyze the morphologies of aluminum


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Recycling ofaluminum

Extrudedproduct

Totalnew

scrap

Extrudedproduct

Scrap Scrap

Comminution

Fe particleseparation

Cleaning

Annealing

Blending

Cold pre-compacting

Sintering

Precompacting

Metal lossesby burning

Conventional method Direct convention method

Dross

Casting scrap

Scrap andtrimmings

Extrusionbutts

Scrap andtrimmings

Remelting

Liquidaluminum

Casting

Homogenizing

Sawing

Delivery toextrusion plant

Preheating

Hot extrusion

Cutting tofinal size

Figure 15.7 Flow charts of recycling aluminum scrap by conventional and direct convention method (adapted from Lazzaro andAtzori, 1992; Gonostajski et al., 2000; Samuel, 2003)

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dross and its interactions with liquid salt flux; consequently the study was carried outthrough the scanning electron microscope coupled with an energy dispersive X-rayspectrometry detector. Drosses collected from aluminum can recycling industrieswere used. Tests were carried out using equimolar mixtures of sodium and potassiumchlorides. The results revealed that drosses are heterogeneous systems composedessentially of oxides and aluminum. The aluminum oxides develop a chain micro-structure, with a high specific surface area, that traps aluminum. The molten salt cor-rodes this structure and breaks the oxide links, consequently liberating the retainedaluminum (Tenorio and Espinosa, 2002).

The RECAL Program was implemented in Poland in the form of a marketing campaign for the collection of aluminum cans and in conjunction with an educationalprogram (training sessions, courses and seminars in the field of recycling methods)offered to a large sector of society (school children, their teachers and parents). Thesuccess of RECAL has resulted in raising public awareness and increasing aluminumtonnage for recycling purposes. Teachers involved in RECAL activities underlined theeducational role of the program, both in the aspect of ecological awareness of the stu-dents as well as organizational abilities, group work and creativity. RECAL assistancein the action was highly regarded by all groups of program participants. In their opin-ion, the RECAL staff was professionally trained and lectures, seminars and materialswere well prepared. Teachers and students underlined that a future RECAL activityshould be expanded to a greater number of respondents mainly in kindergarten chil-dren, students of higher grades (high schools, gymnasium) and adults. In accordancewith the constant rise of beverages packaged in aluminum cans in Poland (expected1 400 000 000 in the year 2000), an increase in environmental public awareness isrequired. RECAL activity should be viewed as a case study of the best practice forother educational programs that face similar difficulties in raising awareness(Godzinska-Jurczak and Bartosiewicz, 2001a).

Aluminum and aluminum-alloy chips can be recycled by the direct conversionmethod, which is characterized by low-energy consumption and large material sav-ings. The most suitable way of recycling the chips is by processing through hot extru-sion. This method is relatively simple and it limits itself to cold press molding and hotextrusion. The main conclusions are summarized as follows:

1 bearing composites from aluminum and aluminum bronze chips can be manufac-tured without metallurgical process

2 the method involves granulation and cleaning of chips, cold compaction, hot extru-sion and heat treatment during which the reciprocal diffusion of copper and alu-minum takes place and leads to good tribological properties of composites

3 composites with a 15–22% reinforcing phase content and with larger size particles(2–4 mm) have the best tribological properties

4 to obtain the good diffusion bonding of particles separated by a layer of oxide, threeconditions must be fulfilled: high temperature, large shear plastic deformation andthin aluminum oxide layer

5 there is no significant difference of the effect of various reinforcing phases on thefrictional properties of composites (Gonostajski et al., 2002).


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The potential of nitriding combustion was investigated in terms of an energy-saving and environment-friendly process to produce high performance nitride cera-mics or recycle wastes to usable ceramics. It is possible to convert the reclaimed sili-con produced in zinc smelting to Si3N4 ceramics, both the silicon sludge dischargedin silicon wafers production and the aluminum dross discharged in aluminum foundryto sialon based ceramics. The monolithic Si2N2O ceramics can be synthesized fromthe mixture of desert sand and reclaimed silicon as well. It would be useful to find appli-cations for these recycled products in powder, porous and dense forms (Miyamoto,2003).

In order to maximize the efficiency of ever increasing aluminum recycling, differ-ent mutually related aspects need to be optimized. Economic efficiency of aluminumrecycling is greatly dependent on the costs arising at different stages of the recyclingprocess. Among these, transportation costs represent a very important part of overallcost balance. A general model, based on the principles of reverse logistics, was devel-oped and applied with the aim of reducing the extent of internal aluminum scraptransportation required between certain production units of an aluminum manufactur-ing plant. A linear optimization model was applied for calculating minimum annualtransport costs and the optimal way of in-plant transport for two transport models inorder to determine the most efficient option. In case of in-plant aluminum recyclingonly collected aluminum materials were transported which means that the mostimportant factors in this case were fixed transport costs and variable transport costs,the latter depending on distance, transported quantity, energy used for transport andother operating costs. In the first transport model, the direct transport of collected alu-minum scrap from each individual source to in-plant processing units was assumed.In the second transport model, one collection site was assumed where scrap is col-lected and then transported to in-plant processing units. The optimization model wasalso applied for determining a dependence of optimal transport model on annualquantities transported internally and on the distances between sources and processingunits. It was found out that the annual transported quantities and distances betweensources and in-plant processing units have a significant impact on the optimal trans-port model. The developed optimization model showed that environmental and eco-nomic objectives were not always in conflict. The aspects affecting the reverselogistics model for in-plant recycling were made clear and discussed (Logozar et al.,2006). This model implies that each of five sources, which are located adjacent to eachunit operation of foil production (Figure 15.8), represents its own collection site.

The ever increasing amount of electronic scrap and the steadily decreasing contentsof the precious metals used in electronics, as well as the ever-growing environmentalawareness, challenge such conventional precious-metal-oriented recycling techniquesas pyrometallurgy. Separation and beneficiation of various materials encountered inelectronic scrap might provide a correct solution ahead. In this context, a mechanicalseparation-oriented characterization of electronic scrap was conducted in an attemptto evaluate the amenability of mechanical separation processes. Liberation degrees of various metals from the non-metals, which are critical for mechanical separation,were analyzed by means of a gain counting approach. It was found that metallic particles below 2 mm achieve almost complete liberation. Particle shapes were also


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Coils,ingots

Packing

Interphase cuttingand dueling

Final cutting,trimming

and separation

Finalannealing

Cold rolling 2

Final cuttingand trimming

Cold rolling 1

Single foilproduction

Double rolledfoil production

Figure 15.8 Scheme of aluminum foil production unit (adapted from Logozar et al., 2006)

Ch15-P373654.qxd 10/18/07 6:35 PM Page 966

quantified through an image processing system. The results obtained revealed that theshapes of the particles, as a result of shredding, were heterogeneous, thereby compli-cating mechanical separation processes. In addition, separability of various materialswas ascertained with a sink–float analysis. It was shown that density-based separationtechniques will be viable in separating metals from plastics, light plastics (ABS, PSand PVC, etc.) from glass fiber reinforced resins and aluminum from heavy metals.Specifically, a high quality copper concentrate can be expected with density-basedseparation techniques. Moreover, FT-IR spectra of plastics pieces from the light frac-tions after the sink–float testing showed that PC scrap primarily contained ABS, PSand PVC plastics with the density range of �1.0–1.5 g/cm3, whereas PCB scrapmainly contained glass fiber reinforced epoxy resins plastics with the density range of�1.5–2.0 g/cm3 (Zhang and Forssberg, 1997). The metal assay approach for float andsink products is given in Figure 15.9.


Dissolve

Heat up

Filter

Dilute

AASanalysis

HCI:HNO3 � 3:1;6.67%

concentration

Deionizedwater

80°C

Perkin-ElmerAAS

Wash residue

Figure 15.9 Metal assay approach for float and sink products (adapted from Zhang and Forssberg, 1997)

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Disposal of highly saline industrial by-products in landfills is not permitted inmember states of the European Union, such as Germany. Large amounts of such by-products thus have to be disposed of in alternative ways. In many countries, barepotash mining residue mounds, consisting almost entirely of rock salt (NaCl), poseenvironmental problems. Covering such mounds with soil or soil-like material couldhelp to reduce the yearly amount of briny runoff. A fine-granular saline aluminumrecycling by-product (ALRP) has been proposed as a soil substitute to cover rock saltresidue mounds. Use of this by-product as a combined soil substitute and surface bar-rier is not considered to be a landfill disposal, but as a beneficial by-product re-use. Tojudge the feasibility of ALRP for this purpose, its properties must be known. A studywas initiated to determine the physical characteristics of an industrially producedALRP mixed with the flue gas desulfurization by-product (FGDP) of a coal combus-tion power plant. It was found that the texture of both ALRP and ALRP–FGDP mixwas silt loam. Bulk densities of ALRP and ALRP–FGDP were 0.93 and 0.88 Mg/m3

and the corresponding salt contents were 50.0 and 35.5%, respectively. The erodibil-ity factor, K, of pure ALRP was estimated as 0.65 Mgh/ha/N. Because of the stabiliz-ing effect of FGDP, this factor was reduced considerably in ALRP–FGDP. Thewater-holding capacity of unwashed ALRP was 44.5% and of washed ALRP–FGDP61.8%. In view of its physical properties, ALRP–FGDP seems to be suitable as anevaporation enhancing, runoff reducing cover material for potash mine residuemounds, even on steep slopes. Use of ALRP, mixed with FGDP, as a soil substitute ina surface barrier, thus seems to be environmentally meaningful. However, the highsalt content initially prevents plant growth. With time, after the salt has been leached,the material seems able to support plant growth, which would further reduce runoff.The physical and hydraulic parameters determined in this study may serve futureusers of similar by-products (Hermsmeyer et al., 2002).

A more general model of the ‘recycling problem’ was used to re-examine the Alcoaantitrust case of 1945. There are three primary empirical results:

1 in the Alcoa scenario, the recycling problem had been in a steady state since theearly 1920s

2 the primary source of Alcoa’s market power, in contrast to previous work, was thatmost of the aluminum sold by Alcoa was used in goods that were not economical torecycle

3 the existing, competitive secondary market was welfare-reducing, relative to amonopoly in all aluminum production (Gant, 1999).

According to Yerushalmi (1992), to prevent the undesirable reactions due to alu-minum dross recovery, the pH in the digester must be maintained below 8 and prefer-ably above 5 through magnesium chloride addition. This salt suppresses the reactionsthat increase the leaching liquid pH since it reacts with the hydroxyl ions in alkalisolutions to form non-dissociated Mg(OH)2 and HCl. In addition to the recovery ofmetallic aluminum, salt flux and magnesium chloride, the process generates a waste,known as non-metallic (NMP), which is usually disposed of in landfills. Many sec-ondary recycling industries in Brazil recover metallic aluminum using a simple


Ch15-P373654.qxd 10/18/07 6:35 PM Page 968

process of crushing and melting of white dross in the presence of a salt flux(NaCl/KCl). Therefore, new dross is generated (black dross and salt cake), which arereused as raw material by tertiary aluminum industries (Figure 15.10). Many tertiaryaluminum-recycling companies in the Sao Paulo metropolitan area operate using asimple method for treating black dross. In this process, the dross is crushed using avertical hammer mill to release the metallic portion. The remaining material is waterleached in a rotary drum. The recovered material is sorted by size using a 20-meshsieve. Particles larger than 20 meshes (containing about 60% (wt) to 80% (wt) of Al)are sent to secondary industries for remelting. Particles smaller than 20 mesh, whichrepresent 25% (wt) of Al can be sold to steel manufacturers as an exothermic product.


RecycledAI°

Wastebasin

Bauxite

NMP

AI°

White dross

Dross/recycledAI°

Black dross/salt cake

Leachingprocess

AI°

Landfill

Alumina

Hall-Heroultprocess

Bayer process

Red mud

Salt flux smelterfurnace

Figure 15.10 Aluminum schematic recycling process in Brazil (adapted from Shinzato and Hypolito, 2005)

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During the dross leaching process a semi-liquid waste, rich in soluble salts, is produced,which is disposed of in tanks for decanting the solid fraction. The measured pH of theleaching solution in those tanks is about 9 (Shinzato and Hypolito, 2005). However, apositive consideration based on this study refers to the other tests (dimensional, humid-ity and adsorption) and the acceleration of working time. This decrease in the workingtime will certainly result in an increase in the production of the concrete blocks, sincethey will be available for sale faster than the ones currently produced. Another impor-tant use of NMP would be as a synthetic aluminous aggregate for refractory concrete, aswell as cements of high alumina content specifically designed for high-temperatureapplications. The commercial use of NMP can significantly reduce the quantity of wastedisposed of and also contribute to preservation of the environment. Moreover, using alu-minum waste in preparing aluminum products, such as aluminum hydroxide, will cer-tainly be more economically feasible than the use of bauxite.

Gonostajski and coworkers (2001b) suggested a new method of recycling aluminum-alloy chips. This method consists of composites of the conversion of the chips directlyinto a finished product. The method was applied to the production of composites char-acterized by good strength properties at elevated temperatures. As a reinforcing phasethe FeCr powder with particle size below 75 µm was used, the amount of that phase waschanged from 6 to 14 wt%. The process was performed in the following steps: granula-tion of chips, mixture of granulated chips with FeCr powder and zinc stearate as lubri-cant, cold compaction of the mixture into the billets, presintering and hot extrusion. Themain conclusions of this method can be summarized as follows:

1 the effect of ferro-chromium content on the flow stress is dependent on the appliedtemperature and at higher temperatures the best results were obtained for 6% of rein-forcing phase

2 the better mechanical properties were obtained for composites made from smallerfraction of granulated chips (below 0.5 mm) than bigger (0.5–1.0 m)

3 the process was performed in the following steps: granulation of chips, mixing ofgranulated chips with FeCr powder and zinc stearate as lubricant agent, cold com-paction of the mixture into the billets, presintering and hot extrusion

4 the method can be used to manufacture the products in the form of bars, sectionsand pipes, which can be formed in further operations

5 good bonding of particles separated by a layer of oxide needs large plastic deformation.

The waste composition analysis results of Cathay Pacific flights indicate that there aremany items in the current in-flight services waste streams that can be minimized andrecycled (Li et al., 2003). In the waste composition analysis, clean paper (mainlynewspapers) was the largest component, ranging from 32 to 71% of the total weightof the in-flight waste. The next major component was plastic material, particularlytransparent PS items (drinking cups and food covers), which accounted for up to 13%of the total weight of the in-flight waste streams. Aluminum cans accounted for up to4% of the total waste on some flights. Food waste in the food carts was another impor-tant waste component resulting from the in-flight services. Based on the compositionanalysis and current recycling opportunities, clean paper items, transparent PS items


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and aluminum cans were identified as the most promising recyclable materials. Thesematerials can be separately collected on board for the recycling program. The recycla-ble items can account for up to 45–58% of the total galley and cabin waste from in-flight services. The waste reduction and recycling program has the potential tocontribute greatly to local and global environmental protection and to save substantialoperation costs for the airline industry.

A new method for recycling aluminum alloy chips by cold and hot pressing fol-lowed by hot extrusion was studied as well as the possibility of using this method torecycle aluminum matrix composite chips. It was found that hot extrusion of cold orhot pressed samples could satisfactorily promote the consolidation of the chips. Hotextrusion of hot pressed samples proved to be the best route from the point of view ofmechanical properties but, on the other hand, hot extrusion of cold pressed samplesroute has higher cost profit. Aluminium AA6061 matrix composite reinforced withAl2O3 recycled by cold pressing and hot extrusion was compared with the primarymaterial produced by conventional casting process from which the chips wereobtained. Due to the refinement of the microstructure and the dispersion of the alu-minum oxide caused by the extrusion process, the ultimate tensile strength (UTS) andthe hardness were higher for the recycled material than for the former composite(Fagagnolo et al., 2003).

The feasibility of recycling red mud and fly ash in the aluminum industries by pro-ducing glasses and glass-ceramics techniques was highlighted by Yang et al. (2006).The red mud is a CaO-rich slag from the sintering process of Al2O3 production. The flyash, a convenient SiO2-rich and Al2O3-rich solid waste directly collected from electro-static precipitator in the coal-combustion power plant, is another main raw material.The glass-ceramic of CaO-SiO2-Al2O3 system mostly made from the red mud and flyash was developed successfully. The results show that the total amount of both theindustrial solid wastes of the red mud and fly ash is up to 85 wt%, which promises lessraw materials cost, prominent economic benefits and environmental benefits.

In a typical secondary aluminum process, the scrap feed is charged into a rotary fur-nace, melting and mixing under a salt layer in the furnace. The complexity in such apyrometallurgical process is due not only to the high temperature effect and the complexchemical reactions, but also to the highly complex scrap feed with a distributed natureof aluminum types, compositions, sizes, shapes, paintings and other contaminations. Ina study, user sub-models, which represent the distributed nature of the scrap feed, weredeveloped and integrated into a computational fluid dynamics (CFD) based processmodel of a rotary furnace (Zhou et al., 2006). Aluminum scrap was classified into sev-eral groups depending on their properties, e.g. size, establishing a discretized populationbalance model (PBM). The melting behavior of aluminum scrap was simulated with theexchange of information between the melting sub-model and the CFD calculations. Inaddition, the sub-model for scrap burn-off was also developed and integrated in theCFD framework providing distributed burn-off rates. Simulations of the melting processwere made to model the flow and thermal phenomena in such a furnace and the influ-ence of the scrap size, shape and quality, as well as burn-off rate were studied.

Several models for estimating the potential arising from metal scrap were developedby Melo (1999). The modeling approach consisted of first aggregating metal-containing


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products into end use categories and then employing statistical distributions to describethe service life of products in each category. This statistical approach was applied to theGerman aluminum market. Due to the absence of historical data regarding the age ofproducts upon disposal, it is very difficult to single out a model as being particularlyappropriate for representing lifetime. The choice is made on the basis of considera-tions, such as the degree of complication of the calculations involved using the modeland qualitative information gathered from experts. Naturally, modeling uncertainty onthe basis of subjective judgments by experts is not exempt from criticism. We consid-ered the normal, Weibull and beta distributions as life models. In contrast to the nor-mal, the other two models have the advantage of assuming a wide variety of shapes thatare likely to arise in practice. In terms of analytical tractability, the Weibull distributionis easier to manipulate. The results obtained disclosed that the proposed models yieldbetter estimates of old scrap than commonly used approaches that assume a fixed serv-ice life for products. The fixed lifetime procedures are highly influenced by fluctuationsin the consumption of metal and can significantly underestimate or overestimate thescrap potential. Hence, the information provided by such approaches may naturallyhave a negative impact on the planning of future activities in the secondary and pri-mary industries. Although those models were applied to the German aluminum market,they can easily be extended to other countries and metals as well. A concluding remarkis that more attention should be focused on the development of reliable techniques toestimate metal scrap generation, since they provide valuable assistance in decision-making both in secondary and primary industries.

A robust design method for reducing cost and improving quality in aluminum recy-cling was developed by Khoei et al. (2002). An experimental investigation into theprocess parameter effects was presented to determine the optimum configuration ofdesign parameters for performance, quality and cost. The Taguchi method is appliedinitially to plan a minimum number of experiments. Orthogonal array techniques areused to investigate the simultaneous variation of several parameters and the investiga-tion of interactions between parameters. Matrix experiments using standard L4 andL9 orthogonal arrays were employed to evaluate the effects of parameters in recyclingof aluminum dross and scrap materials. A statistical analysis of signal-to-noise ratiowas followed by performing an analysis of variance (ANOVA), in order to estimate theoptimum levels and determine the relative magnitude of the effect of various factors.Finally, a historical data analysis based on the response surface methodology was car-ried out using a Taguchi orthogonal analysis. Experimental results were shown for anL18 orthogonal array illustrating a good agreement between the optimum factor levelssuggested by the signal-to-noise ratios and those obtained from the response surfaces.

The recycling of the aluminum content of LPM in Germany is actually done at aresource orientated recycling quota of 59%. The presented calculations show that byincreasing the recycling quota to the optimal one concerning energy demand, 27.6%of the energy, which is required now, could be saved. A further increase in the resourceorientated recycling quota over 79% would not be reasonable concerning the overallenergy demand including primary energy as well as the heat content of burnt materi-als. Although remelting of aluminum requires less energy than primary production, at high recycling quotas the results identify a turning point. Above that point,


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methodological and social aspects (like consumer behavior) influence the recyclingpractice and therefore the calculated results. The development of the scenario concen-trates on increasing the recycling quota. Here the new technology of fully automatedsorting is a big step towards highly efficient metal recovery and reduced energyrequirement. At the same time, further fractions of usable materials are won. Reachinghigher sorting selectivity of one of these materials might result in quality losses of theother ones. Also pyrolysis can be identified as an important part of a material efficientprocess chain. Besides the technical improvement, new strategies to increase the over-all recovery rate of secondary raw materials have to be considered. Here the collectionquota appears to be of great potential towards increasing the recycling efficiency. Inthis evaluation, all packaging material which is not utilized by the DSD is assumed tobe collected via municipal waste collection. Besides disposal in landfill sites, one-third of the municipal waste is incinerated. Two-thirds of the incineration slag areprocessed for further utilization, e.g. for road construction. Therefore, the metalliccontent must be extracted. This is done in a slag treatment plant which mainly consistsof a shredder, sieves, a magnetic separator for ferrous metals and an eddy current sep-arator to recover the non-ferrous metals (Figure 15.11). Since most of the metal in theslag is ferrous, the plant is optimized for the extraction of ferrous metal and the non-ferrous metal fraction is a by-product. The non-ferrous fraction consists of aluminum,copper and zinc, which are separated in a sink–float process. The aluminum fractionis molten in a rotary drum furnace (Quinkertz et al., 2001).

Xiao and Reuter (2002) investigated the melting behavior of four different turningscraps. The melting experiments were carried out at 800°C under a nitrogen atmosphere.The basic salt flux used in the experiments contained 70 wt% NaCl, 30 wt% KCl withadditional and varying amount of Na3AlF6. In general, it has proved that scrap distribu-tion, contaminant, type and size of the scrap have a significant effect on the meltingbehavior. The metal recovered from the turning scrap ranges from 84 to 95 wt%, repre-senting the metal content of the scrap if potential reactions of the salt flux with metalwere disregarded. The recyclability of the turning scrap B (95.3 wt% recovered metal)and C (94.5 wt% recovered metal) is better than scrap A (84.3 wt% recovered metal) andD (91.8 wt% recovered metal). By increasing the amount of cryolite in the salt flux, thepercentage of metal recovered was increased but not substantially. The accumulation ofthe metal droplets was improved with increasing cryolite from 5 to 15 wt%. The accu-racy of the classification for the turning scrap is limited due to the characteristics of thescrap shape. For scrap B, the percentage of metal recovered and the accumulationdegree of the metal droplets is increased with turning size. The distributed metal yieldas a function of scrap type and size is the basis for establishing a future statistical modelto ensure better product quality in the recycling industry.

A complete mathematical model for the pyrolysis of coated waste of aluminum wasdeveloped by Marias et al. (2005). It is based on a coupling between two sub-modelsrepresenting:

1 the bed of solids to be reprocessed and the kiln itself2 the gaseous phase where the volatiles are released (as a result of pyrolysis) and

where their oxidation takes place.


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Non-ferrousfraction

Non-ferrousfraction

Ferrousfraction

Slagproduct

Sieve

Magneticextractor

Sieve 1st

Sieve 2nd

Magnet

Eddy currentseparator

Slagproduct

Collectionof municipal

waste

Wasteincineration

Slagtreatment

Is particle size�5 mm?


Sieve

Magneticextractor

Shredder


No

No

No

Yes

Yes

Yes

Figure 15.11 Process chain of slag processing with additional steps of metal recovery (adapted fromQuinkertz et al., 2001)

The first of these sub-models considers the bed of solids as a plug flow reactor wherepyrolysis occurs. It takes into account heat transfer by conduction in the kiln as wellas heat transfer with the surroundings (both ambient air and electrical heaters) andwith the kiln. The second of these sub-models deals with processes occurring within

Ch15-P373654.qxd 10/18/07 6:35 PM Page 974

a gaseous medium where turbulent combustion occurs. Turbulence chemistry wastaken into account. Comparisons with experimental investigation were performed inthe case of particles of covers of cans. They are congruous, at least qualitatively.Indeed, the value of 450°C seems to be the ignition value for which pyrolysis beginsto occur (for the particular coating in question). Moreover, because of the oxidation ofthe volatiles and because of the mode of operation of the furnace (counter-current), ahigh amount of the heat released by combustion is received by the bed in the vicinityof the first heater. This would indicate that perhaps there is no need to preheat the alu-minum to be reprocessed (if the heating rate of a particle is the same). Moreover,because of the value of the ignition temperature, there is probably no need to set thetemperature inside the second heater to 570°C. These kinds of conclusions coulddiminish the cost (from an energy-saving point of view) of the operation of reprocess-ing. Moreover, they could help diminish the level of temperature reached inside thefurnace and then diminish the risk of the oxidation of aluminum.

Rabah (2003) made an attempt to recover standard aluminum–magnesium alloy(s)and some valuable salts from used beverage cans (UBCs). The suggested methodupdated the current recycling technology by augmenting removal of the coating paint,decreasing magnesium loss during the melting process and improving hydrochloric acidleaching of the formed slag. Iron impurity present in the leaching solution was removedby oxidation using oxygen gas or hydrogen peroxide and filtered as goethite. Theobtained results revealed that a mixture of methyl ethyl ketone/dimethyl formamideentirely removes the paint coating at room temperature. The process compared favor-ably to the current methods involving firing or swell peeling. The coating decomposedto titanium dioxide by heating at 750°C for 30 min. Standard compositions of Al–Mgalloys are formulated using secondary magnesium. The extent of recovery (R) of thesealloy(s) is a function of the melting time and temperature and type of the flux. The max-imum (R) value amounts to 94.4%. Sodium borate/chloride mix decreases magnesiumloss to a minimum. The extent of leaching valuable salts from the slag increases withincreasing the molarity, stoichiometric ratio and leaching temperature of the acid used.Removal of iron is a function of the potential of the oxidation process. Stannous chlo-ride has been recovered from the recovered and dried salts by distillation at 700–750°C.

Paper/carton

In spite of synthetic packaging materials and electronic media, internationally paper andboard consumption is increasing steadily. While in 1950, about 50 million tonnes ofpaper were produced worldwide, in 1998, approximately 300 million tonnes were pro-duced. In the year 2010, 400 million tonnes are projected. In Europe, Japan and theUSA, where one-fifth of the world population lives, more than two-thirds of the paper isconsumed. To make this increase in paper production possible and for saving resourcesat the same time, paper recycling has been intensified steadily in the last decades and hasnow reached a high technical level. Most of the products made of paper only have a lifespan of a few days (e.g. newspapers) or a few weeks (e.g. packaging). The increase ofrecovered paper use in industrialized countries is determined by problems of disposal.


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Paper recycling in Europe increased markedly throughout the 1990s. The amount ofpaper collected and recycled at the end of the decade was roughly two-thirds morethan at the beginning. This means that the recycling rate (percentage of recoveredpaper use compared to total paper consumption) was 53.2% in 2003, compared toabout 40% in 1990. Thus, recovered paper is today the most important raw materialfor the production of paper, paperboard and corrugated board. The target by the year2006 was at least 56% of paper and board products consumed in Europe to be recy-cled. Taking into account the expected increases in paper and board, recycled, this ratewould be at least 25% higher than it is today. The prime objective of recovered paperrecycling is to utilize the fibers contained in post-consumed recovered paper. Regardingdisturbances in production, thermoplastic impurities (stickies) must especially be men-tioned. Internal paper recycling (re-use of ‘broke’) describes the recycling of produc-tion waste within a paper mill with a processing line on site. An example is tissue andtowel mills where paper goes directly from the paper machine to rewinders for the pro-duction of bathroom tissue or paper towelling. During this processing, adhesives areused for laminating, for the pick-up of the first sheet on the tube and for the end sheettie down, and the waste, or ‘broke’, created here must be returned to the paper mill.Here, in general, only a relatively small amount of rejects are moved back into thepaper production process. In contrast to adhesives that get into paper mills by externalrecycling and have sources varied and unknown, in internal recycling, there is only arelatively small amount of adhesive and the types used are known exactly. These millsnormally do not have lavish sorting machines. As the additives added to the paper inproduction cannot be sorted out mechanically, most of the time the additives arerequired to be completely water-soluble or redispersible, even if this pollutes theprocess water with impurities. Adhesives that are used in this production are normallyclassified by the European Standard EN 1720 ‘Adhesives for Paper and BoardPackaging and Disposal Sanitary Products Determination of Dispersibility’ or by theAmerican TAPPI standard UM 666 ‘Dispersibility Test for Adhesives’. Nowadaysthere are many adhesives that fulfill the requirements (Onusseit, 2006).

In the pulp and paper industries, environmental problems vary with both the sizeand category of the mill. In recent years, pulp and paper manufacturers have facedadditional constraints to modernization, namely, raw water availability and limitationson wastewater discharge. Additional in-plant water conservation efforts are becomingnecessary to reduce wastewater produced, which is highly contaminated with sus-pended particles, reduce the volume of effluents discharged and to minimize solidwaste for disposal (Miner and Unwin, 1991). In recycling wasted paper mills, zerodischarge is possible through wastewater re-use after suitable treatment. But due topoor or no wastewater treatment and old fiber recovery technologies, the industry isunable to recycle the effluent. The different processes in the plant were operated in anopen circuit manner. Figure 15.12 shows the manufacturing processes, water usageand wastewater discharged. Two scenarios have been investigated: the first being thetreatment of the end-of-pipe and the second being the control and management of pol-lution problems through the application of in-plant control and pollution preventionmeasures. Comparison between the two alternatives, based on a cost-benefit analysisand compliance with National Environmental Laws was done. From this study it was


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DAF Effluent

Freshwater

Paper

Finescreening

Low-densitycleaning

Thickening

Dispersing

Deflaking anddefining

Pressing

Drying

Pulpingwastepaper

Coarsescreening

High-densitycleaning

Sheetformation

Figure 15.12 Process water usage and wastewater discharged from the board paper mill (adapted fromSohair et al., 2006)

apparent that the implementation of the pollution prevention measures, such as therecovery of fiber, reduction of freshwater consumption and optimization of whitewater usage, proved to be very cost effective. All the implemented solutions haveshort payback periods and resulted in great savings compared with the treatment ofthe end-of-pipe (Sohair et al., 2006).

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The pulp and paper industry is responsible for large discharges of highly pollutedeffluents, whose main characteristics are the high toxicity and low biodegradability oftheir tannins, lignins, resins and chlorophenolic compounds. The composition ofthese effluents, which has a great influence on its treatability, may vary considerably,depending on the raw material and manufacturing process utilized (Sierra-Alvarez,1990; Kortekaas et al., 1998; Vidal et al., 2001). Although aerobic treatment systemsare the most widely used methods for treating effluents from pulp, the anaerobicprocess has been successfully applied in the treatment of non-toxic and easilybiodegradable wastewaters from pulp and paper plants, such as the effluents frommechanical pulping, from paper recycling and from evaporator condensates. Buzziniand Pires (2007) evaluated the performance of an upflow anaerobic sludge blanket(UASB) reactor treating diluted black liquor from a Kraft pulp mill, which simulatesan unbleached Kraft plant wastewater under different operational conditions, includ-ing partial recycling of the effluent. The reactor’s performance was evaluated from thestandpoint of COD, pH, volatile acid concentration, alkalinity, concentration ofmethane in the biogas and microbiological examinations of the sludge. Without recir-culation, the reduction of the HRT from 36 to 30 h did not significantly affect the aver-age COD removal efficiency. The average volatile acids concentration in the effluentincreased by 16%. The average COD removal efficiency varied from 80 to 86% (with-out recirculation) and from 7% to 78% with recirculation but, in this latter case, thehydraulic retention time was 30 and 24 h, while without recirculation the HRT was36 h. Thus it can be considered that, under the tested conditions applied in this work,the partial recycle of the effluent did not improve the COD removal efficiency.However, it allowed operating the reactor with lower hydraulic retention time withoutdisintegation of the granules. For the wastewater used in this research and under oper-ational conditions of this work the partial recirculation of the effluent caused the aver-age COD removal efficiency to drop from 80�1% to 75�2% for an HRT equal to30 h. However, when the HRT was reduced from 30 to 24 h, the average COD removalefficiency increased from 75�2% to 78�0.3%. The effluent alkalinity was alwayshigher than the influent one, even though the loading rate increased, which indicatedthat the anaerobic metabolism produced alkalinity. When the recirculation wasapplied, the average effluent alkalinity showed an increase. The concentration ofvolatile acids in the effluent was lower than the influent concentration in all cases. Thereactor presented stable operation even when some granule flotation appeared. After83 days of operation, it was observed that the floating granules were hollow in thecenter. However, after 180 days these hollow granules were no longer observed eitherin the sludge blanket or in the few granules that reached the reactor surface.

Life cycle impact assessment (LCIA) was combined with economic analysis ofsocial life cycle costs (SLCC) to investigate five alternatives for newspaper wastemanagement (Dahlbo et al., 2007). The alternatives consisted of various recovery andtreatment methods applicable to newspaper in a separately collected paper fractionand to newspaper in mixed waste. LCIA and SLCC were linked to each other at threedifferent stages. First, LCIA was used to rank alternatives and asked how this rankingrelated to the SLCC associated with each alternative. Second, the cost minimizingproblem was solved and asked how this purely economic ranking related to LCIA


Ch15-P373654.qxd 10/18/07 6:35 PM Page 978

ranking. Third, the cost minimizing problem was solved when external costs from theuse of fossil fuels were included and then compared the solution to the LCIA results.All of the comparisons between the environmental and economic impacts of the casestudy clearly show that including both of these two dimensions in the assessment ofwaste management alternatives is crucial for making sustainable decisions. The resultsof the two assessments appear, however, to rank the alternatives in exactly reverseorder. Concentrating solely on the economic aspects seems to lead to the environmen-tally worst alternatives. On the other hand again, the environmentally best solutionresults in highest costs. The LCIA results support energy recovery if the producedenergy replaces energy from fossil fuels, thus earning credits from avoided impacts.Otherwise recycling newspaper for paper production outperforms energy recovery.The differences between energy recovery and material recycling turned out to be rela-tively small, however. Therefore, SLCC provides an important additional qualification:burning separately collected newspaper is always far more expensive than materialrecovery for paper production. In addition to economic gounds, credits from biodiver-sity benefits from replaced harvests reinforce the advantages of newspaper recycling.

A new process for the incorporation of old newspaper fibers into polyolefins, suchas LDPE, HDPE and PP, was developed by Baroulaki et al. (2006) based on the dis-persion of paper fibers in a hot polymer solution and the subsequent precipitation ofthe polyolefins by cooling, which produces a slurry of polymer with paper fibers(Figure 15.13). The technique studied in this work was an alternative to the conven-tional melt compounding and was expected to provide efficient wetting of fibers bythe polymer. The density, hardness and tensile properties of composite specimens pre-pared by compression molding, with filler content ranging from 10% to 40% (w/w),were measured. The tensile strength of HDPE and PP composites presents a slightdecrease at filler concentrations between 10% and 20%, followed by considerabledecrease in the range of 30–40%. On the other hand, the modulus of elasticity did notdisplay a clear dependence on filler content. Composites based on LDPE exhibitedgood retention of tensile strength especially at low filler content, whereas their modu-lus of elasticity at 40% fiber concentration increased by 78%.

Asha Poorna and Prema (2007) optimized the culture condition for the enhancedproduction of extracellular thermostable cellulase-free xylanase from Bacilluspumilus by solid-state fermentation. Batch studies were carried out to evaluate vari-ous agro-industrial residues such as rice bran, rice husk, rice straw, sawdust, coconutpith, sugarcane bagasse and wheat bran for enzyme production by the bacterial cul-ture. The endoxylanase production was highest on wheat bran media (5582 U/gds),which enhanced 3.8-fold (21 431 U/gds) by optimization of cultivation conditions.The enzymatic extracts were used in mixed wastepaper recycling, which resulted in aconsiderable improvement of the paper strength with high drainage and easy dryingup. The results of enzyme application with recycled paper clearly indicated that theeffective use of enzymes in fiber separation could reduce the cost of carton paper pro-duction from 25 to 50% of total production cost. This increase in yield and decreasein production cost is a promising methodology for hyper-production of alkaline ther-mostable xylanase. The results of enzyme application with recycled paper clearlyindicate that the effective use of enzymes in fiber separation can substantially reduce


Ch15-P373654.qxd 10/18/07 6:35 PM Page 979


Dissolution

Polymersolution

Mixing

Coolingco-precipitation

Filtration

Vacuumdrying

Solvent(xylene)

Composite

Solvent(xylene)

Sizereduction

Paperimpregnation

Pulping

Washing

De-inking

Paper fibers

Polymer(LDPE,

HDPE, PP)Paper

Samplemolding

(190–270°C)

Figure 15.13 Polyolefin/newspaper fiber composites preparation and characterization flowsheet(adapted from Baroulaki et al., 2006)

the cost of carton paper production and is a promising alternative in the present sce-nario of biobleaching of Kraft pulp.

Polymers

Biodegradable synthetic copolymers and composites

The continuously increasing extent of pollution of the environment has recently givenrise to demands for novel biodegradable polymers, mainly for applications related to

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food packaging and agriculture (Schnabel, 1981; Huang, 1985; Kumar, 1987). The mainemphasis initially was focused on the synthesis of novel aliphatic polyesters (Schnabel,1981; Chiellini and Solaro, 1992; Vert et al., 1992) due to their higher susceptibility tobiodegradation with regard to other polymers such as polyamides and polyanhydrides(Zhang et al., 1993; Satyanarayana and Chaterji, 1993). Among the aliphatic polyesters,poly (ε-caprolactone) (PCL) (Tokiwa et al., 1983, 1988), poly (β-methyl-δ-valerolac-tone) (Nakayama et al., 1993, 1995), polylactide (Kim et al., 1992, 1993; Vert et al.,1992; Satyanarayana and Chaterji, 1993) and their copolymers (Den Dunnen et al., 1993;Gaymans and de Haan, 1993; Shiaw et al., 1994) have been suggested as the most prom-ising polymers in terms of potential applications. Low glass transitions and low meltingpoints of most polyesters have oriented several researchers toward exploring other poten-tial avenues, such as the direct polymerization of α-amino acids (Wu, 1992; Kiyotsukuriet al., 1992; Yang et al., 1993) or copolymerization of lactams with lactones (Goodman,1984; Goodman and Valavanidis, 1984; Goodman and Vachon, 1984a, b) in an attempt tosynthesize novel polymers with higher thermal resistance. The biodegradability testsconducted on the copolyesteramides were highly promising and in favor of potentialapplications (Huang, 1985; Kumar, 1987). However, the difficulties encountered inproducing high molar mass and environmentally degradable copolyamides have beenthe restrictive factors, in terms of applications, for the copolyamides (Yang et al.,1993; Chen et al., 1993; Bera and Jedlinski, 1993).

Novel biodegradable copolyamides based on diacids, diamines and α-amino acidsThe novel copolyamides, based on adipic acid (AA), 1.6-hexane diamine (1.6-HD),isophorone diamine (IPD), bis(para-aminocyclohexyl)-methane (PACM-20), and var-ious α-amino acids (L-tyrosine, proline, alanine, glycine, glutamic acid), were syn-thesized with a two-stage melt polycondensation (100°C and 250°C for 1 and 2 h,respectively). The semicrystalline and, occasionally, amorphous nature of copolyamidesbased on the salt of 1.6-HD/AA (1:1 mol/mol)/α-amino acids were shown with wide-angle X-ray diffraction. Several biodegradability experiments (burial in soil, alkali andenzymatic hydrolysis) were carried out for testing the susceptibility of these polymersto degradation. The physical properties of the copolymers were investigated before andafter biodegradability testing. The observed gradual increase in Xc of the NaOH-insol-uble fraction of the copolyamides was proportional to their exposure to alkali hydroly-sis. It is thought that the initial gradual dissolution of the amorphous parts results inhigher crystallinity values, similar to what has been reported for the early stages of in vivo and in vitro degradation of poly-(L-lactide) (PLLC), polyglycolide (Chu, 1981)and PCL (Pitt et al., 1981). The degradation process of biodegradable polymers occursin two stages. In the first stage, the chain scission occurs preferentially in the amor-phous regions of the semicrystalline polymer. The initially random chain scissionsresult in a decrease of the degree of entanglement, thus facilitating and even consid-erably promoting the mobility of non-degradable chain segments in these regions. Themobility promotes crystallization, as reflected by the high Xc values. However, fol-lowing dissolution of the amorphous regions, the degradation proceeds to the crys-talline regions. A substantial decrease in the molar masses of the copolymers was


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recorded when the copolymer were exposed to NaOH (10% wt/vol NaOH, 80°C)(Arvanitoyannis et al., 1993, 1994, 1995). The effect of alkali hydrolysis was verypronounced for the copolymers rich in α-amino acids because they underwent a sig-nificant reduction in the molar mass of polymeric chains, thus resulting in numberaverage molecular weights Mn as low as 2100. Tensile strength and tensile modulus ofcopolyamides were shown to undergo a sharp decrease after the copolymer sampleswere treated with alkali solutions for more than 20 h. In fact, a linear dependence oftensile strength on the Mn with regard to the exposure time of alkali hydrolysis wasestablished. The molar mass of copolyamides was not substantially affected when thecopolyamides were buried in soil. Overall, when the content of α-amino acids washigher than 15% in the copolyamides, they turned from semicrystalline to amorphousaccording to the DTA and WAXD measurements. The potential degradability of thesynthesized copolyamides was confirmed by various biodegradability experiments,such as alkali hydrolysis, microbial-bacterial attack (burial in soil) and enzymatichydrolysis. It is envisaged that these copolyamides may find various applicationsbecause of their enhanced susceptibility to biodegradation.

Novel biodegradable copolyesteramides from ε-caprolactone and various nylon saltsThe biodegradation of synthetic polymers is of considerable interest to environmen-talists, industrialists and academic researchers as well (Chen et al., 1993). Aliphaticpolyesters have been long considered as the most promising polymers for applicationsin which biodegradability is a prerequisite (Vert et al., 1992; Kim et al., 1992, 1993;Satyanarayana and Chaterji, 1993). On the other hand, synthetic poly(amino acids)and polyamides, though regarded as the analogs of proteins and natural peptides, havenot yet found the extent of expected applications, mainly because of preparation dif-ficulties (Huang, 1985; Yang et al., 1993). The aliphatic copolyesteramides recentlyhave been suggested and partially investigated as a polymer family with much poten-tial concerning functional performance and susceptibility to degradation (Goodmanand Sheahan, 1990a, b; Arvanitoyannis et al., 1994, 1995). Synthesis of copoly-esteramides has been carried out following a three-stage process: 1.6-HD was mixedwith a diacid (AA, sebacic acid [SA], or octadecanedioic acid [ODA]) and ε-caprolac-tone (ε-CL) and was kept at 120, 180 and 250°C for 2 h, 2 h and 0.5 h, respectively(Arvanitoyannis et al., 1994, 1995). Although the melting points Tm versus ε-CL con-tent showed eutectic curves (minimum at 20/20/60 for SA, ODA, or AA/1.6-HD/ε-CL),similar to other copolymers (Kehayoglou and Arvanitoyannis, 1990), the melting pointsversus the ε-CL content were found to give straight lines (Arvanitoyannis et al., 1994,1995). The substantial difference in the heat of fusion between the ester-rich and theamide-rich copolymers possibly could be attributed to the incompatibility of crystalstructures (monoclinic or triclinic for nylons in contrast to the orthorombic for PCL)(Arvanitoyannis et al., 1994). An increase in ε-CL content resulted in broadening ofpeaks and in decreasing the Tm and Tg values due to the higher flexibility of the poly-meric chain imparted by the incorporation of ε-CL. The total organic carbon (TOC)measurements indicated that only the ester-rich copolyesteramides (�50% ester con-tent) could be considered biodegradable because the TOC values for the amide-rich


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copolyesteramides were very low (Arvanitoyannis et al., 1994, 1995). It was also foundthat the weight loss percentages of the copolyesteramides after their immersion in alkalisolution increased with an increase in ε-CL content. The weight loss rate was greatlyenhanced after the first 10 h, reaching up to about 50% (after 30 h exposure) and wasaccompanied by a substantial decrease in Mn, as determined by GPC. Enzymatichydrolysis was also conducted for studying the degradation products. Nuclear magneticresonance analysis (NMR) of the degradration products showed that cleavage primarilyoccurs at ε-CL–ε-CL labile bonds in the polymer backbone, whereas the amide bonds(O�C–NH–) are characterized by low susceptibility to degradation. The thermal prop-erties (Tg, Tm) showed a linear decrease against the CL content, while the TOC consid-erably increased. Enzymatic and alkali hydrolysis, as well as burial in soil experiments,agreed that an increase in CL content reflected an increase in the susceptibility ofcopolyesteramides to biodegradation.

Novel star-shaped copolylactidesStrong interest in the eventual, and preferably rapid, biodegradation of synthetic poly-mers has developed only in past years, primarily in response to the growing problemof waste disposal of plastics (Lenz, 1993). Polyesters attracted much research interestin view of their satisfactory performance property wise and their inherent biodegrad-ability. PCL and PLLA were the most responsive to biodegradation both in vitro andin vivo (Nishida and Tokiwa, 1992, 1993a, b; Reeve et al., 1994). Apart from thesetwo homopolymers (PCL and PLLA), several copolymers, based on these two compo-nents, have been synthesized in an attempt to ‘tailor’ the properties of the homopoly-mers for special applications (Kricheldorf et al., 1988; Zhang et al., 1993; Mikos et al., 1993). A successful shaping in-situ process has been the main incentive for theintroduction of a soft segment such as poly(ethylene glycol) in PLLA (Kobayashi et al., 1991; Cerrai and Tricoli, 1993). The difficulties encountered in processingPLLA remained the major limiting factor in applications despite the well-acceptedbiocompatibility and biodegradability of PLLA (Leenslag, 1984; Kim et al., 1992,1993). Novel branched star-shaped polymers are envisaged as a potential solution tothe processing problem because they can combine high molecular weight with lowermelt viscosities than the linear PLLA (Aragade and Peppas, 1993; Gijpa andPennings, 1994a, b). The polymerization of L-lactide (LLA) with polyol (i.e. pen-taerythritol, glycerol or sorbitol) was carried out in the presence of two catalysts (stan-nous octoate [Sn, oct], tetraphenyl tin [TPhT]) at 130°C for 4 day (Arvanitoyannis et al., 1995, 1995, 1996). The GPC traces of the LLA/GL or LLA/pentaerythritolcopolyesters (synthesized with Sn octoate) gave monodisperse curves, thus favoringthe occurrence of only one mechanism. In contrast, the biomodal GPC traces,recorded when TPhT was used as the catalyst, support the previously expressed sug-gestion that two mechanisms are in action, one initiated by the polyol and the other viathe catalyst. The DSC results (bimodal traces) further support the suggestion for twomechanisms. The degradation rates of these polyesters were studied by enzymatic andalkali hydrolysis, primarily in terms of changes in weight, Mn, and TOC. NMR analy-sis of degraded products confirmed the suggested cleavage of hydrolyzable bonds of


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star-shaped PLLA. High polyol contents strongly favored extensive cleavage of polymeric chains, thus resulting in an increase of crystallinity. It is noteworthy that the theoretical capability of polyols to act as cross-linking agents was not confirmed by solubility experiments on the synthesized copolyesters (Arvanitoyannis et al., 1995, 1996).

Biodegradable composite materialsThe development of novel polymeric materials that degrade slowly is considered a veryimportant research area, especially in view of their various current and potential applica-tions as environmentally degradable materials (Storey and Shoemake, 1993; Albertssonet al., 1994). Although D, L- or L-lactide and ε-CL seem to be the most popularmonomers, especially in the field of polymeric composite materials (Li et al., 1990a, b, c)mainly related to medical applications, polyamides are another promising class of poly-mer that appeals to a wider range of applications (Consalves et al., 1993). It is anticipatedthat these novel thermoplastic materials have a lot of potential because of their inherentadvantages over the majority of thermoset materials (Arvanitoyannis and Psomiadou,1994) namely, control of their percentage crystallinity (physicochemical properties), easeof processing and ‘friendliness’ to the environment (Arvanitoyannis et al., 1995).Composites, consisting of AA/1.6HD/L-proline or L-glycine and short E-glass fibers,were prepared by the hand lay-up method (Srivastava and Lal, 1991). The crystallinityof the copolyamide matrix was determined from WAXD following the generallyaccepted procedure for constructing the diffraction pattern of a composite material.Determination of percentage of crystallinity in composite materials with DTA is com-plicated by the occurrence of nucleation fronts on the glass fibers, in addition to thestatistical nucleation from the melt, known as transcrystallinity. Therefore, occur-rence of multiple melting peaks should be attributed to different spherulite morpholo-gies (Arvanitoyannis and Psomiadou, 1994). Detection of void content is very criticalin terms of determining the shelf-life and performance of the composite material. Themain reasons for the occurrence of voids in the degradable composite materials arethe following: entrapment of air within pelletized material, residual moisture andshrinkage volume of the core region.

Natural-synthetic polymer blendsIt has been estimated that approximately 2% of all plastics (mostly non-degradable)eventually end up in the environment, thus contributing considerably to the currentlyacute ecological problem. The current trend toward protection of the environment isexpressed by using degradable polymers and composting or recycling the ‘recalci-trant’ polymers. Blends of natural and synthetic polymers have been considered apromising avenue for preparing polymers with ‘tailor-made’ properties (functionalphysical properties and biodegradability).

Partially degradable blendsStarch-based plastics initially attracted some research interest, but their developmentwas not as expected, mainly because of their inadequacy with regard to mechanicalproperties and water transmission (Otey et al., 1974; Giffin, 1994). In an attempt to


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overcome this problem, synthetic polymers/starch blends were investigated (Shogen,1993; Lawton and Fanta, 1994). The main advantages of these blends could be sum-marized as follows (Scott and Gilead, 1995):

1 property tailoring by proper selection of components and their ratios2 lower cost by using blending (i.e. extrusion, casting) instead of synthetic3 routes for production of novel materials4 ecological factors (environmentally friendly and usage of plastic wastes).

Mixtures of low-density polyethylene (LDPE) with gelatinized potato, rice, wheat andsoluble starch, with or without ethylene acrylic acid (EAA) as a compatibilizer, wereextruded in the presence of 15–20% water. As long as the starch content in the blendsdoes not exceed 20%, the mechanical properties of the LDPE/starch blends still liewithin the operational limits. Typical scanning electron microscopy (SEM) micro-gaphs taken after fracture clearly showed the blend morphology and the distributionof each component (Psomiadou et al., 1998). The wheat starch particles are deformedand interspersed within the LDPE matrix. Although in several previous publicationsthe failure modes of PE were investigated and analyzed, a tentative failure mechanismof PE/starch blends was only recently put forward (Arvanitoyannis et al., 1997, 1998).Brittleness and ductility are the two main failure modes. Whichever of these two pre-vails depends not only on the deformation features and fast or slow crack growth(Stojmirovic et al., 1992; Chudnovsky et al., 1995), but also on conditioning of thesample over certain relative humidity environments. Therefore, the ensuing plasticiza-tion of the LDPE/starch blends could be due to penetration of water and filling ofvoids. Constructing a tentative micromechanical model to depict the geometries,arrangements and interactions of components within a composite material has alwaysbeen a challenging task (Christensen, 1979). The main difficulties arise from inherentstrength variations within the mass of the composite systems and the need for long-term predictions concerning the performance of the composite in terms of themechanical properties. Although a previously described system (Reifsnider, 1994)was initially suggested for fiber-matrix composite materials, it could possibly beapplied in the case of LDPE/EAA/wheat starch composites as well. According to thismodel, deformed starch particles constitute the core material which is surrounded byan LDPE/EAA continuous matrix. Depending on the relative distribution of the EAA,regions of LDPE/starch/EAA vary in their plasticity; a high EAA content promotesgreater plasticity in the matrix, while in regions of lower EAA content, debonding andslipping may occur at the matrix/starch particle interface.

Both LDPE and HDPE were thoroughly investigated with regard to their gas perme-ability (GP) (Yasuda and Stannett, 1962; Van Krevelen, 1990) because of their extensiveuse in food packaging applications. LDPE is a semi-crystalline polymer of both amor-phous (intralamellar, interlamellar and interspherulitic) and crystalline (ribbon-likelamellae) areas (Michaels and Bixler, 1961). The presence of starch particulates asfillers within the LDPE matrix, apart from disturbing the continuity of the LDPE net-work and contributing to the inhomogeneity of the system, enhances substantially the GP of the LDPE/starch composite structure because of their strong hydrophilic


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character. The water is either strongly bound (0–12%) or is capillary moisture(12–30%). The temperature dependence of GP and gas diffusion (GD) of the blendsis described by the well-known Arrhenius equations.

At this point, it is worth emphasizing the importance of the activation energy of dif-fusion because of its involvement in chain separation, which is necessary for the even-tual ‘loosening’ of the structure. Certainly, the incorporation of starch particles disruptsthe LDPE network by imparting some flexibility and mobility and thus reducing therequired energy per unit chain separation. An increase in temperature enhances evenmore the cavity and channel formation, thereby facilitating the diffusivity and perme-ability. The diffusion and the permeation activation energies were found to fall in the fol-lowing order with regard to the permeating gas: ED(N2) �ED(O2) �ED(CO2). Thisorder is in agreement with other reports, assuming that there is no interaction betweenthe permeant gas and the matrix (LDPE/starch). LDPE/starch blends have been com-mercially used for the past 15–20 years. The generally accepted degradation scheme ofa high molar mass polymer consists of the following stages:

O2

p

High MW : Low MW : Organic fragments : CO2 � O2 � Energy :

Energy Biomass : Endogenous respiration, Growth, Cell division

Both soil burial and bioreactor exposure experiments showed a decrease in percentageelongation and considerable weight loss, which could be described as a two-stage process(Krupp and Jewell, 1992). The first stage consists of partial starch removal and only at alater stage does a slow rate of degradation of LDPE occur. Most investigations of LDPEadvocate enzymatic oxidation, dehydrogenation and carbon-carbon breaking processesas the predominant degradation mechanisms of LDPE (Albertsson and Ranby, 1979;Albertsson et al., 1994; Albertsson and Karlsson, 1994). However, the biodegradation rateof LDPE/starch blends can be effectively accelerated only if the starch content is higherthan 10%. Similar conclusions were also reached by other researchers (Gould et al.,1990; Narayan, 1991; Goheen and Wool, 1991; Wool, 1995) who, in addition, applied thepercolation theory (Stauffer, 1985) assisted by computer simulation (Peanasky et al.,1991). In general, the higher the starch content, the worse the performance of the com-posite materials will be (lower tensile strength and modulus, higher GP and water vaportransmission rate), but the higher their biodegradability. An increase in moisture or EAA(whenever used) content of these composite materials induced plasticization of the sam-ples. The degradability of LDPE/starch blends was confirmed by weight loss measure-ments and changes in mechanical properties.

Chitosan-poly (vinyl alcohol) blends

Poly(vinyl alcohol) (PVA) can be prepared by hydrolysis of a variety of poly(vinyl esters)and poly(vinyl ethers) and has many applications in pharmaceuticals, cosmetics and


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the paper and food industries, either alone or in blends with other polymers, such aspoly(3-hydroxy butyrate) (Azuma et al., 1992), polyacrylic acid (Daniliuc and David,1996), β-chitin (Lee et al., 1996) and cellulose (Hasegawa et al., 1992a, b, 1994), amongothers. Chitosan is the deacetylated product of chitin. Next to cellulose, chitin is the sec-ond most abundant polysaccharide in nature (Rathke and Hudson, 1994). Chitin is asso-ciated with other polysaccharides in fungal cell walls, while in animal forms, chitin isassociated with proteins (Muzzarelli, 1977). The production of chitin is possible prima-rily as a secondary activity related to the marine food industry (Zikakis, 1984). Chitosanhas been used in a very wide range of applications, such as prevention of water pollu-tion by chelating heavy metals or radioactive isotopes, in membrane separation (Aiba et al., 1986), in medicine and biotechnology and in the food areas, either as a food pack-aging material because of its antimicrobial action or as dietary fiber and a potential med-icine against hypertension thanks to its scavenging action for chloride ions (Furda andBrine, 1990; Ishikura, 1993; Okuda, 1995; Muzzarelli, 1996). The preparation of chi-tosan/PVA blends was carried out as follows. The PVA solution was added, under vig-orous stirring and heating, to the chitosan solution and then the plasticizer was addedand mixed into the solution for 10–15 min until dispersed. Then the solution was castover plexiglass plates. Low molecular weight compounds added to chitosan/PVA blendsare shown to lower the melting point and the glass transition Tg. Wide-angle X-ray dif-fraction patterns (WAXDP) showed that PVA has a high percentage crystallinity (Xc~54%). The observed reduction in percentage crystallinity in chitosan/PVA blends shouldbe due to ‘crystallization disturbance’ of chitosan in the blend state.

Landfill

Landfill has served mankind for much longer than any alternative disposal option.Landfilling is defined as the disposal, compression and embankment fill of waste atappropriate sites. Landfill for the moment is easy, adjustable with lower cost than therest of disposal methods and stands alone as the only all waste material disposalmethod (Karakasidis, 1997; Clarke et al., 1999). Although landfill was traditionallyselected by many communities because of its low cost, it has become prohibitivelyexpensive. The costs of landfill rose, due to the decreasing number of landfill sites andthe more sophisticated techniques and operating practices (Von Schoenberg, 1995;Adams et al., 1996). Important factors that need to be taken into account for the cor-rect function of the disposal sites are the selection of the site, the design and organi-zation of the site, the operating performance and the life cycle and biodegradability of the wastes (Karakasidis, 1997). The environmental impact of waste landfillingdepends on the design and operational mode of the landfill facility and the nature ofthe waste deposited (Dascalopoulos et al., 1998). The landfill gas generated at landfillsites was considered barely controllable and one of the main disadvantages of thismethod. However, the production of such gas has recently been perceived as a prom-ising source for highly combustible fuel since it is a clean source of fuel (VonSchoenberg, 1995; Clarke et al., 1999).

In order to comply with the EU ELV Directive, an increase in the recycling rate ofautomobiles to 80% by 2006 and 85% by 2015, must be met (EC, 2000). On average,


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the plastic content of a car was 9% (ACORD, 2000) and the average thermoplasticcontent is about 45% polyolefin (40% PP, 4–6% PE). The properties of a blow-moldedbottle prepared from 100% post-consumer high-density polyethylene (HDPE) showedthat this recycled polymer exceeded the materials specifications for virgin plasticdesigns. Similarly, a sample of thermoplastic polyolefin (TPO, 100% polypropylene),obtained entirely from shredder residue (SR) displayed sufficient material strength forfuture separation and reprocessing (Ambrose et al., 2002).

Incineration

An alternative method of waste disposal to landfill is waste incineration. Waste incin-erators use the process of combustion to convert the waste materials into carbon diox-ide and water. Incineration residues usually are small quantities of HCl, S and othervolatile compounds and ash (Waite, 1995). However, it is obvious that not all house-hold waste materials are combustible. Reduction of waste volume by 80–90% isachieved with incineration. Therefore, it should be considered as a means of reducingthe amount of waste to be disposed of by landfill rather than a method of ultimate dis-posal on its own (Von Schoenberg, 1995).

Combustion can be regarded either as a pretreatment method for the waste prior toits final disposal or as a means for increasing value to waste by energy recovery(Dascalopoulos et al., 1998). Incineration became an increasingly popular method ofwaste disposal treatment by the beginning of the 1970s when many incinerators wereconstructed (Waite, 1995). The effect of polymers on the combustion of MSW has notbeen satisfactorily assessed in the past. The Association of Polymer Manufacturers inEurope (APME), in conjunction with academia, launched an in-depth program aimedat understanding the role of polymers in MSW combustors. The program of APME onenergy recovery from used plastics is focused on exploring all technically differentmeans (Mark, 1995). Co-combustion is regarded as one of the most promising meansfor economic and safety reasons. As a result, conversion of polyurethanes togetherwith other materials such as textiles, wood, paper and other plastics into energy in‘state of art’ incinerators, which meet all health and safety requirements and therespective legislative regulations for emissions and environmental standards, wouldbe now and in the future an important process contributing to the economy and envi-ronment (Bastian et al., 1995). Waste combustion with energy recovery is usually costeffective only in large, heavily populated metropolitan areas. This approach becomesless appealing with low fossil fuel cost, strong markets for paper and the necessity fordisposing of a substantial volume of residue, a part of which may be hazardous (Mark,1995). However, the main problems to be addressed prior to extensive utilization ofthis method are the finite risk of contamination, noise, odor, fire and explosion haz-ards, vegetation damage, ground water pollution and air pollution (El-Fadel et al.,1997). The consumption of crude oil, natural gas and pit coal, normally used in dis-trict heating plants, can be substantially lowered by the incineration of plastic waste.Assuming that the efficiency of an incineration plant and a district heating plant is thesame (80%), the incineration of 1 kg LDPE releases 43.3 MJ which correspond to0.08 kg crude oil, 0.07 kg natural gas and 0.25 kg pit coal (Molgaard, 1995). The cost


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for landfill or incineration varies in different countries as well as the treatment routesemployed by different European nations (Simons et al., 1995; Morris et al., 1998; Palinand Whiting, 1998).

Pyrolysis

High molecular weight substances cannot be purified by physical processes like distilla-tion, extraction or crystallization. They can only be recycled by pyrolysis of their macro-molecules into smaller fragments. Pyrolysis can be used to convert mixed plastic wastesto oil products, combustible gas and heavy residues. The pyrolysis products may then besuitable for common petrochemical separation processes. Pyrolysis is the thermaldegradation of macromolecules in the absence of air and generates oils and gases, whichare suited for chemical utilization or generation of energy. In fact, the pyrolysis productsconsist of 34% ethylene, 9% propane, 39.7% oil (mainly aromatic compounds) and1.7% residue (Kaminsky, 1995; Faaij et al., 1998).

The Constantinople composting and recycling plant, constructed in 2001, is one ofthe few composting plants in Turkey. During test operations of the plant, it wasreported that the weight of the oversize materials (OM) above an 80-mm sieve wasabout 40% of the total incoming waste. They mainly consist of plastic bags that werefull of garbage, which resulted in operational problems in the plant. In a study, thecomposition of OM was determined and evaluated, particularly to find the economiclosses in the plant. It was determined that approximately 58% of the OM transferredto the landfill area due to operational failures and interruptions could be used at theplant with improved operational conditions. Otherwise, the plant would realize anannual economic loss of about 640 800 US$. Compost quality in the plant has beensatisfactory, but source separated collection, at least the separation of the wet from thedry fraction, is needed to increase the amount of compost and recovered materials. Toincrease the amount of compost and captured recyclable materials in the plant inConstantinople, all plastic garbage bags should be torn in the first step of the process.However, appropriate waste collection (higher organic and recyclable content) frompotential districts of the city is still an important factor for the plant. The best way toimprove the situation would be source separated collection, at least the separation ofthe wet from dry fractions. In Turkey and some other developing countries, it is diffi-cult to operate plants optimally, especially publicly owned plants, due to investmentand administrative problems. The most important inadequacy in any environmentalmanagement activity in those countries is the operating problems and lack of researchduring operation of the plants (Kanat et al., 2006).

The thermal decomposition of polyalkenes was investigated as a recycling route forthe production of petrochemical feedstock. Low-density polyethylene (LDPE) andpolypropylene (PP) were thermally decomposed individually in a batch reactor at450°C, thus forming oil/wax products. Then these products were dissolved in primaryheavy naphtha to obtain steam cracking feedstock. The selectivity and kinetics ofcopyrolysis for 10 mass% solutions of oil/waxes from LDPE or PP with naphtha in thetemperature range from 740 to 820°C at residence times from 0.09 to 0.54 s were


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studied. The decomposition of polyalkene oil/waxes during copyrolysis was con-firmed. It was shown that the yields of the desired alkenes (ethene, propene), accord-ing to polymer type, increased or only slightly decreased compared to the yields fromnaphtha. In addition to the primary reactions, the secondary reactions leading to cokeformation were also studied. The formation of coke during copyrolysis of LDPE waxwith naphtha was comparable to the coking of pure naphtha. Slightly higher forma-tion of coke was obtained at PP wax solution at the beginning of the measurements,on the clean surface of the reactor. After a thin layer of coke covered the walls, theproduction was the same as that from naphtha. The results confirmed the possibilityof polyalkenes recycling via the copyrolysis of polyalkene oils and waxes with con-ventional liquid steam cracking feedstocks on already existing industrial ethyleneunits (Hajekova and Bajus, 2005). The results obtained proved that the oil/wax frac-tions obtained from the thermal decomposition of polyalkenes at mild conditions canbe added to liquid charges for steam cracking in the amount of 10 mass%. It is notnecessary to separate the oil and wax fractions from each other at this level ofallowance. The separation would unnecessarily increase the costs for preparing theseraw materials. The gases formed on the decomposition of polyalkenes can be burnt,but in the case of fluid cracking of polyalkenes, they can be returned to the process asfluidizing gas. They can also be added to the streams of gases that are formed at thesteam cracking unit and thus the already existing equipment for separation of gasesfrom steam cracking can be utilized. The solution that has a 10 mass% concentrationof oil/waxes does not cause any problems on spreading. Slightly warming up the rawmaterial in the tank is sufficient.

Re-use and recovery

One of the priorities set in most countries over the world is drastic waste reduction.Where waste cannot be avoided, it must be recovered, preferably in an environmen-tally friendly way. This simply means recover and reuse something after its initialfunction has expired. The ways that the recovered material can be used may be simi-lar or dissimilar to the original function (Lemann, 1995). The number of strategiesidentified to help waste prevention includes material life extension, process mana-gement and reduction of material used (Bergner, 1995). The term re-use expresses the identification of the most cost-effective avenue in reusing goods, components and materials. When a product is designed, the requirements of re-use and collectionprocess need to be taken into account (Stahel, 1995). Moreover, the recovery and re-use of waste must not result in an enrichment of hazardous substances within the substance life cycle. All plastic materials interact with ‘products’ to a certainextent. This interaction can either be superficial or more extensive, followed byabsorption into the body of the plastic. Contamination of refillable containers throughmigration of substances (i.e. dyes, flavors) into the plastic could occur at various times of the material shelf-life. Although these substances may not be affected by thewashing process, they might subsequently be released into the food on their re-use,with serious implications regarding both consumer safety and sensory characteristicsof food.


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A plastic container is suitable for refilling when it is resistant to the uptake of chemi-cal and microbiological (toxicological) hazards and taints. Exposure to chronic toxinsis statistically unlikely to occur with contaminated containers, but a single exposure ata high level could be a major issue (Castle, 1994).

Composting

Municipal solid waste composting is an alternative to the disposal of wastes thatattracted interest in the USA and Europe. A study on composting in the USA lists 15facilities that are currently operational and an additional 23 that are under construc-tion, or at planning or designing stages. In Europe, composting facilities are opera-tional or under construction in France, Holland, Switzerland, Italy, Greece and Spain(Renkow and Rubin, 1998). Composting has been officially recognized as a form ofrecycling and is expected to play an even more important role in future waste manage-ment operations. Although composting has been rapidly gaining importance, thedevelopment of the technology still relies on practical experience. Composting stillhas to grow from an art to a well-established technology. Composting refers to a self-heating, aerobic process of organic wastes and other industrial organic compounds inorder to convert them to a mature and plant compatible substrate. If a material is con-sidered compostable, biodeterioration/biodegradation should transform it into com-post (Tokiwa et al., 1989; Narayan and Snook, 1994; Raschle et al., 1995; Blanc et al.,1995). Under optimal degradative conditions, a controlled composting process couldbe completed within 3 months, while under normal conditions within 1 to 2 years(Kaiser et al., 1995). The final product of composting is rich in organic matter but itsconcentration of key nutrients, usually too low for competing with commercial fertil-izers, improves the soil structure through its enrichment with humic substances(Marilley et al., 1995; Masters, 1998). Besides the microflora required for compost-ing, composts can also harbor potentially pathogenic and/or allergenic bacteria andmolds like Aspergillus fumigatus (Lott Fischer et al., 1995). The aim of the compost-ing operation is to obtain, preferably in the short term against limited cost, compostwith a desired product quality. All composting operations should take place undercontrolled, environmentally safe conditions. During the process, gas and heat may bereleased that can be used for energy recovery while, at the same time, volume reduc-tion of the original material up to 40% can be achieved. Furthermore, the process isconsidered to be ‘environmentally friendly’ and financially viable, but only underproper guidance and management. The basic reaction of the composting process is theoxidation of organic matter with oxygen to carbon dioxide and water by employingthermophilic microorganisms. Under normal temperature conditions (i.e. room tem-perature), chemical oxidation plays a minor role. At the same time, there is a releaseof heat resulting in a temperature increase within the composting matter. The processrequires a blend of materials with appropriate physical and chemical properties andpertinent management to ensure that suitable process conditions are maintained. Theprocess takes place at temperatures sufficiently high for destroying pathogens.Municipal solid waste composting treats all readily degradable components of thewaste stream such as paper, food and wood which account for 55–70% (by weight) of


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a community’s residential solid waste. The two basic processes applied in large-scalecomposting are classified as windrow-based and in-vessel technologies. In windrowsystems, waste is conveyed to a central open air facility and formed into windrowsthat are 3–5 feet (1–1.5 m) high. The windrows are turned periodically to maintain a stable temperature and decomposition rate and water is periodically added to main-tain an appropriate level of moisture content. After the targeted decomposition levelhas been attained, the composted product is ready for assembly and distribution to end- users. Vessel systems employ considerably more sophisticated technologieswhich offer a highly controlled enclosed environment for affecting the biologicaldecomposition, thus leading to a high quality product. This system though is morecapital intensive than windrow technologies and the sophisticated techniques requirehighly trained facility operating personnel. Therefore, the composting process isanticipated to play an important ecological role in the promotion of the biological car-bon cycle. Similarly to the recycling of other materials, composting requires highquality raw materials, thereby ensuring that no toxic and hazardous residues areincluded in the product. In addition to compromising product quality, materials thatare resistant to biodegradation may severely affect compost processing. Non-degrad-able plastic films may interfere with the film screening of the composted product byplugging the screen or reduce the degradation of biodegradable materials by blockingthe oxygen flow. The composting process is further affected by temperature, moisture,pH, nutrient supply and oxygen availability while temperature also plays an importantrole in hygiene (Hamelers, 1994; Hanna, 1994; Vos, 1994; Beffa et al., 1995;Siegenthaler, 1995; Peringer et al., 1995; Guneklee and Kubocz, 1995; Neumann,1995; Gajdos, 1995; Schaub and Leonard, 1996). The composting process is shown inFigure 15.14.

Recycling

According to Waite (1995), ‘recycling is a very broad term referring to the conversionof waste into a useful material’. While recycling is second in priority waste manage-ment options, it has gained ground in many European and American countries as anessential ingredient for the reduction of wastes that must be landfilled. Over the lastdecade, the emphasis on the part of municipal solid waste management has been onrecycling due to the introduction of waste management hierarchy. Recycling is a rela-tively old method with a well-recorded history. Metals have been recycled since theirdiscovery because of their high value, rarity and properties that allow near indefinitereprocessing. The recycling of old textiles is equally old since they were used for theproduction of paper. Among the several factors which contributed to improving therecycling process are the decrease in available landfills and the urgent need for rawmaterials recovery that could be used by reducing the amount of natural resourcesconsumed. Moreover, the increasing public interest in environmental protectionenhanced the importance of recycling as an alternative solution to the constantlyincreasing waste problem (Vogas, 1995; Alter, 1997).


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According to NSWA (National Solid Waste Management Association), recyclingconsists of five basic steps:

1 Collection and sorting of recyclable materials from the waste stream2 Raw material reclamation by special treatment, so that they could replace virgin

materials in manufacturing operations3 Marketing of the recycling materials4 Market establishment for recycled materials5 Public involvement in the recycling programs operations6 Collection recycling programs target the useless materials from the waste stream

and treat them in such a way so that they could return to the industries as raw mate-rials for packaging applications (Vogas, 1995).

Any responsible recycling operation has to meet market, economic and environmen-tal requirements. The viability of recycling depends on the following factors:

1 the packaging or product design: since the product should be designed for recy-cling, mixed plastic materials complicating the recycling operations should beavoided


Micro-organisms

Oxygen/air

Organic/compostable wasteUtilizable carbon source

NutrientsN, P, K

New micro-organisms

Death

Heat

Energy Humus/compost

Polymerization

Breakdownproducts

CO2

Moisture

Figure 15.14 Composting process (adapted from Arvanitoyannis, 1999)

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2 the raw materials: it is essential that the product does not contain any non-recyclableraw materials

3 management operations: i.e. identifying distribution channels4 legislation: inspection of legislation for packaging and taxes involved to verify that

it does not interfere with recycling management options5 consumer education concerning recycling: increasing the percentage of informed

and educated consumers concerning recycling further promotes the recycling man-agement scheme

6 the technological advances and their applications: this plays an important role inimproving the recycling processes (Vogas, 1995).

As far as the economic viability of recycling is concerned, it needs to be measuredagainst the alternative waste management operations. The cost of recycling is mainlygoverned by three elements (Pearson, 1996):

1 the cost to collect and to sort2 minus the cost of landfill avoided3 minus the revenue from the recyclable sold by the material recovery facility.

Industrial recycling is so well established that under ordinary commercial practicesmany secondary materials are destined only for recovery or reclamation and not fordiscard and final disposal (Alter, 1997). The percentage of recycling of glass, alu-minum and PET in the European Union and the USA is given in Figure 15.15.

Plastic recyclingThe number of recyclable materials collected through the waste stream is quite largeand consists of glass, plastic, scrap metal, tins, paper and boards, fabrics, oils, con-struction materials, ash and organic substances (Waite, 1995). Plastic makes up


1997 1998 1999 2000 2001 2002 2003

70

60

50

40

30

20

10

0

Year

Per

cent

age

(%)

Figure 15.15 The percentage recycling of glass, aluminum and PET in the European Union and the United States (� PET in EU, � aluminum in EU, * glass in EU, � PET in the USA, X aluminum in theUSA and � glass in the USA) (adapted from http://container-recycling,org/aluminrate/gaphs.thm,http://europa.eu.int/lib/)

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around 8% of the total waste weight out of which nearly 85% are thermoplastics:mainly PET (polyethylene terephthalate), HDPE/LDPE (high-density/low-densitypolyethylene), PVC (polyvinyl chloride) and PP (polypropylene). The recycling ratefor all plastic bottles dropped from 24.5% in 1996 to 23.7% in 1997. PET soda bot-tles represent 26% of total plastic bottle production and 40% of total plastic bottlesrecycled. PET beverage and soda bottles combined represent 44% of total plastic bot-tle production and 48% of total plastic bottles recycled. The recycling rates for PETsoda bottles and for all PET bottles have been in decline for several years in the USA.PET soda bottle recycling rate (36%) was 8% lower than in 1996 and 25% lower thanin 1994. Total PET bottle recycling rate (25%) was 9% lower than in 1996 and 18%lower than in 1994. One reason for the drop in the PET bottle recycling rate is the factthat PET resin production increased 45% between 1994 and 1997. Another is the factthat 60% of the PET soda bottle market is made up of single-serve bottles and most ofthose soda bottles are consumed away from home and away from curbside recyclingbins. If the major soft drink companies were to use 25% recycled content in their PETsoda bottles, they could boost the PET bottle recycling rate from the current rate of36% to 61%, the total PET bottle recycling rate from 25% to 40% and the total plas-tic bottle recycling rate from 24% to 30% (Anon, 1994, 1998).

Statistics show that plastic waste tends to become one of the largest categories in MSW.Although only representing around 4% of total oil consumption, plastics represent a valu-able resource. The 4% of the world’s oil consumption used in plastic products actuallyhelps users of oil (transport, heating, etc.) to become more energy efficient. Therefore,plastic recycling is important to the plastic industry, energy savings and the environment.

In the USA, plastics account for 13% by weight of waste and are handled by MSWmanagement operations. The USA has historically relied on landfilling as its principaldisposal technique. In 1972, approximately 20 000 landfills were operational, while in1990 these were reduced to 6300 landfills in which over 80% of US MSW was dis-posed. The number of landfills is expected to decrease even further to 2100 by the endof 2000, while recycling and other waste management techniques would handle themain quantity of wastes (Anon, 1990; Jenkins, 1991; Liesemer, 1992). In contrast tothe USA, Japan, with a much higher population density, in 1990 employed landfillsfor only 52% of its solid waste and Western Europe about 60%. Incineration, com-bined with energy recovery, was widely used in Japan (47% of MSW) as an importantmethod of solid waste disposal in 1990 (Jenkins, 1991). Currently, in Western Europe,about 75% of plastics are landfilled, while 25% are recovered in the form of eithernew material or useful energy. In 1993, just over 50% of MSW generated in Swedenwas incinerated and the energy recovered was used for district heating (94%) and forelectricity (6%) (Tamaddon et al., 1995). Finally, only 8% of MSW in Canada isincinerated, one of the lowest proportions among developed countries. Canada is theleading country in the amount of waste per capita sent to landfill and has below aver-age rates of diversion to recycling or composting (Gilbert, 1998). Even though recy-cling is becoming increasingly important, not many comparative figures are availableand there are large differences in performance in recycling rates between countries(APME, 1999). The European Community generally recycled by mechanical recy-cling about 7% of the total plastics consumed in 1995.


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In Western Europe, there was a recovery of 25% of the plastics consumed during theperiod 1996–1997 (4 364 000 tons) while, at the same time, there was an 8% increase intotal plastics consumption and a 12% increase of recycling volume in 1996. Eight percentof plastics recovered from Europe’s waste stream was mechanically recycled with agri-culture (31%) and distribution sectors (23%) remaining the two sectors with the largestproportions of mechanically recycled plastics. Feedstock recycling rose by 33% from251 000 tons in 1996 to 334 000 tons in 1997, but this method is used only in Germany.Europe, in 1997, recycled 14–15% of plastic packaging waste, of which 25 million tonswas turned into energy (http://www.apme.org/press/htm/PR030299.htm). In 1995,Germany recycled 60% of consumed plastic of which 20.56% was recycled mechani-cally, 27.85% was sent abroad and 9.56% by feedstock recycling. In 1996, the total recy-cling rate rose by 7.6%. After 1991, when the packaging ordinance was set in Germany,there was an enormous increase in its national recycling rates. In 1991, Germany begana very ambitious plastics recycling plan, the aim of which was to separate and recycle80% of plastic components in packaging waste (Plinke and Kaempf, 1995). In 1994, itwas estimated that 460 000 tons were collected, although there was a recycling capacityof 250 000 tons. Unfortunately, this surplus was dumped in other countries, underminingtheir own recycling industries (Ball and Unsworth, 1995). Italy is the second country inEurope in terms of recycling plastic industries. In 1992, the number of recycling indus-tries that imported recyclable materials from the international market reached a rate of66.5%, while there was a reduction in the imported quantities (Pinetti, 1995). In 1995,Austria and Switzerland mechanically recycled 15% and 11.9% of plastic waste, respec-tively (Mader, 1992; Hertzog, 1995). In Switzerland, 80% of household waste was incin-erated and 20% landfilled in 1990, while 49% of the remaining urban solid waste wassuccessfully recycled in 1993, which accounts for a total of 1 370 000 tons of waste. Outof this waste, 6100 tons of PET (72% of beverage containers) were recycled (Fahrni,1995). Moreover, according to the latest figures from PET Container Recycling Europe,PET recycling had risen by 66% in 1996 throughout Europe. In Switzerland, plasticswere collected early on and also used as regranulate, but the recycling rate in Switzerlandand neighboring countries is disappointingly low at about 5–6%. It is estimated that morethan 700 000 tons were consumed in Switzerland, of which only 400 000 tons were col-lected and returned for recycling and only 35 000 tons of regranulate were used for fur-ther manufacture (http://www.polyrecycling.ch/english/kvs.htm). The USA recycledabout 2% in 1985, less than 5% of total plastic waste in 1994, while there was an increaseof about 4% in recycling plastic in 1996 (Jenkins, 1991; Liesemer, 1992). The officialrecycling rate for the year 1997 increased to 27% of total municipal discards, twicethe rate of a decade ago, while 9.5% is mechanically recycled. Nearly 1.4 billionpounds of post-consumer plastic bottles were recycled in 1997, a 4% increase from1.32 billion in 1996. Even though more plastic bottles were recycled in 1997 than everbefore, the recycling rate for plastic bottles decreased from 24.5% in 1996 to 23.7%in 1997. Recycling of PET soft drink and beverage bottles reached an all-time high of649 million pounds for 1997. The recycling rate for PET bottles was the highest over-all bottle recycling rate of any resin type at 25.4%. HDPE bottle recycling increased7% in 1997 to 704 million pounds. Both natural and pigmented bottle rates saw sig-nificant gains in 1997. In US the percentages of recycled plastics for 2004 were 22, 26


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and 3.2 for PET, HDPE and PP, respectively. As regards US post-consumer bottlesrecycled, in 2005, was 24.3% (www.plasticsresource.com).

In Australia, recycling comprised about 11% of the semi-rigid and rigid plasticsdisposal operations in 1992 and recycled about 42% of HDPE, 29% of PET, and 6%of vinyl polymers in 1996. As far as Japan is concerned, in 1995, 28% of total plasticwaste was recycled: 11% mechanically and 17% by thermal recycling, 35% of plasticwent for incineration and 37% was dumped on reclaimed land without any prior recy-cling. Furthermore, it was expected that by the beginning of 2000, more than 90% ofplastics would be recycled in Japan (20% mechanically and 70% by thermal recy-cling), while landfilling would account for less than 10% in waste management oper-ations. Hong Kong recycles much of its industrial and commercial paper and plasticswith this taking place entirely on the basis of existing market prices. However, in thecase of domestic solid wastes, the level of recycling is generally low. Although alu-minum cans are nearly 100% recovered, only small amounts of consumed plastics andpaper are recycled (Okawa, 1995; Barron and Ng, 1996). In the EEC, it is expectedthat 50–65% of packaging materials would be recovered and 25–45% would be recy-cled by a minimum for each material of 15% by weight. In developing countries suchas India, the problem of waste becomes a major issue since the collection, transporta-tion and disposal are unscientific and chaotic. Since formal investment on infrastruc-ture is not increasing, most of these countries have to rely on private sector initiativesfor waste disposal (Dasgupta and Sharma, 1995; Gupta et al., 1998).

Collection of recyclable materials In most countries, the collection of MSW falls underthe jurisdiction and direction of local authorities. Such authorities could be districtcouncils, municipalities, or county councils. Each waste collection authority isresponsible for organizing the collection of MSW for its area and delivering the wasteto a point of disposal as directed by each country’s ministry or responsible nationwideauthority. This is an enormous task for the authorities because communities have to learnhow to transform the collection to an economically viable enterprise. Traditionally,trash has been collected at the curbside of the homeowner. In such cases, it is possibleto obtain 70% or more of the recyclables from the household wastes. In contrast, vol-untary drop-off and payback approaches to gathering the recyclables from householdwastes amounts to only 20% and 10%, respectively. In several cases, a mixed systemof collection has been endorsed (Chiellini, 1994; Chang et al., 1995). As far as haz-ardous household waste is concerned, several countries have already introduced nationallegislation for centralized collection schemes. It has been estimated that plastics consti-tute about 40% of the total volume of hospital waste. Many pilot plants have been set invarious hospitals because it was proven that packaging waste is more easily collectedand recycled in hospitals than private households provided the required infrastructureand management are in place. Research and commercial experience clearly show thatthe more complicated the job becomes for the householder, the less recyclable materialsare likely to be obtained. Since the capital cost for equipment to collect material at thecurb and the labor associated with getting the material into the truck represent about70% of total collection costs, which equals to 50% of total handling cost, it is essentialfor the authorities to design a highly efficient collection system (OECD, 1987; Gordon,


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1991; Young and Gordon, 1991; Gellenbeck, 1995; Beattie and Kerell, 1995; Wather-Mausuchat, 1995; Lamber et al., 1995).

Drop-off centers This is the simplest method for collection of recyclable materials. Thesystem operates by placing specially designed buckets of large capacity at strategic spotsin the municipality. The public is asked to collect the recyclable materials and transferthem by their own means to the drop-off centers. Then the local authorities are responsi-ble for delivering the materials to the waste operation facilities. Basic advantages are thelow capital cost necessary and the possibility for a 24-hour operation. Usually, the lack ofpublic cooperation in that collection scheme is the main disadvantage of this method. Itis quite inconvenient for the public to collect and dispose the materials at the drop-offcenters, while there is also the contamination problem of the recyclable materials. It isdifficult for the collection scheme to result, by itself, in high recycling rates. Many localauthorities that operated such drop-off centers have concluded that:

1 Sites must be selected to provide maximum access but minimum nuisance to neighbors

2 All centers should be frequently emptied to ensure that there is always capacity todeposit delivered materials

3 It is essential to maintain sites and to manage the littering problem thus avoidingany health implications (NSWA, 1990).

Payback centers These are centers where the consumer deposits the recyclable mate-rials and receives a compensation to ensure that cooperation will be maintained. Thebasic advantage is the high quality of obtained material and high public involvementrates. Long distances between consumers and these centers make the operation of thismethod rather difficult (Vogas, 1995; Pearson, 1996).

Combination of systems There are numerous examples of how an appropriate combina-tion of the abovementioned methods resulted in viable and successful results (Brandrup,1992). The method that each local authority will use depends on waste collection opera-tions, experience obtained by other municipalities, possibilities provided by the particu-lar site, population characteristics, convenience to the consumer, recycling goals, numberof individual materials, contamination issues, capital and operational costs, raw materialsmarket, public behavior, current working positions, available technology, legislation,weather conditions, hygiene issues and political factors. It is important to realize thatrecycling is not only a collection and recovery method of waste, but the last part of thelife cycle of the materials in which the consumer/recycler is a key factor (Vogas, 1995).

SortingAfter collection, the recyclables are conveyed to a facility for processing into a formsuitable for sale as raw materials. Plastic and glass can first be separated from eachother by mechanical or manual means and then once more according to their type.Sorting is carried out in specially designed sorting plants which employ semi- or fullyautomatic processes, depending on the type, size and technical standards of the plant.The introduction and use of automated plastic sorting systems have lowered processing


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cost and improved the purity of the separated plastics over the past few years, therebyincreasing the quantity utilization of recycled plastics.

Various separation systems are used in different countries with varying capacityand sensor types implemented, such as the OTTO system (Germany), PET recyclingSchweiz (Switzerland), P & R environmental (USA) and Ipia (Novate Milanese). Thetechnologies for separating post-consumer plastics into their appropriate componentsfall into two categories: macro-separation and micro-separation.

Macro-separation involves removing discarded materials from waste and separat-ing them into different components by handling manually or automatically the indi-vidual items. Macro-separation allows separation of a wide range of materials fromeach other. The following techniques and methods fall under these categories:

1 Gravity/centrifugation2. Methods based on the shape of the individual fragments (manual, 3D measuring

devices)3 Optical (X-ray, IR, NIR, fluorescence, etc.)4 Metal detectors5 Sonic techniques (ultrasonic technique).

Micro-separation involves separating polymers by type after they have been shreddedand chopped down to small pieces of approximately 1/8 to 1/4 inch (0.3–0.6 cm) indiameter. This category comprises techniques based on:

1 geometry (air classification, micronization)2 density (hydrocyclon, swim/sink)3 melting point (heated rolls)4 electrostatic5 mechanical (peeling)6 solving behavior (temperature gradient).

Gravity and centrifugal techniques make use of different density (specific gravity) of thematerials. Such a system is employed by Duales System, where the mixed plastics, afterbeing cleaned, are suspended in water and enter the centrifuge as a suspension. Particleswith a higher density of water precipitate down to the centrifuge bowl while the lighterparticles float on the surface and are extracted. Sorting out specific types of plastic isfeasible but the process has to be repeated with several centrifuges. Other methodsemploy rotating disks and inclined belts. The principles of plastic flotation show that itis more flexible than other techniques and could prove useful in separating mixtures ofplastics, but more research needs to be carried out for its successful implementation inthe industry. Separation according to shape can be conducted manually. As far as theoptical methods are concerned, these are based on IR, UV and visible spectroscopy,laser-induced plasma spectroscopy, X-ray spectroscopy, fluorescence and near infrared(NIR) detectors. Infrared spectroscopy uses the way different materials respond toinfrared light for identification. Although infrared spectroscopy is very selective andrapid, it is rather expensive and unsuitable for industrial applications, apart from specially


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sorting installations, because only thin-film specimens can be scanned. X-ray spectro-scopic processes that are commonly used are fast, reliable techniques, but are appro-priate only for PVC detection since they depend heavily on the layer thickness whilesources of radiation are objective, comparatively expensive and of limited applicabil-ity. This process is usually combined with infrared spectroscopy. Some of the latestmethods employ NIR systems which are proven to be more advanced compared to theIR because of its fast response and higher detectability. In this area, a tremendousamount of research has been carried out over the past few years. A system using NIRwas developed by Buhler and launched by late 1993. The system, named NIRIKS,enormously increased the measuring speed and was designed as a pure industrial unit.

The system was flexible, rapid and quite accurate. Another system using NIR wasdeveloped by Bayer and employs fluorescence spectroscopy (XFS) for identifyinghalogens and heavy metals. Short wave near infrared spectroscopy uses low wave-length infrared light for polymer identification. The technology is quite limited but theequipment is easy to use, compact and portable. Fourier Transform Mid InfraredSpectroscopy (MIR) uses the light reflected from a plastic for identification. The mainsystems available need a relatively smooth surfaced plastic to be effective. MIR sys-tems are accurate, but the polymer to be identified needs to be close to the sensor forat least a second and identification takes a few seconds more. Systems which use UVand visible spectroscopy are also used for polymer identification. Electrical chargesvaporize the plastic’s surface and the analysis of the emissions gives an accurate iden-tification regardless of the color or coating. Computer software is essential in a devicethat employs this technique. Another technique is based on laser induced plasma spec-troscopy where lasers are used to vaporize the plastic’s surface and the emissions areanalyzed by a spectrometer. The device is highly accurate, additives can also be identi-fied and the method is quite rapid. Raman spectroscopy is a method under developmentthat is expected to become one of the most reliable identification technologies. This sys-tem uses lasers to generate light from the sample which provides identification uponanalysis. Laser impulse thermography is another identification technique that uses laserbeams. A carbon dioxide laser generates two ‘spots’of energy onto a sample. The rise intemperature is measured, as is the cooling rate which both differ based on materials.Although fast, it is still under development because of current limitations. Mass spec-troscopy may also be used in identification. Finally, color images can be identified withspecial digital cameras to recognize different colors for sorting mixed plastics or remov-ing contaminants. In addition, another system uses people to identify and sort itemspassing on a conveyor belt simply by their touching the image of selected items on avideo screen. Electrostatic techniques are based on the electrical properties of plastics.

Plastics have a range of electrical properties and any differences can be used both toidentify and separate them. The existing devices based on electrostatic properties areportable and cheaper than many other systems. Unfortunately, they are only really effec-tive at differentiating plastics with distinctly different characteristics, which is a limita-tion factor regarding their applicability. Any water in the system can also causeproblems. A project funded in Germany called ‘optical recycling’ aimed at developing areasonably priced process in which a single compact device would detect the type ofplastic by using NIR, the color with color cameras, the shape by using a 3D measuringdevice and any impurities and residues present in the package with an X-ray module.


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Strongly charged particles of plastics are deflected in free fall in a high-voltage field(120 000 V) towards the electrode and are separated. This method of sorting is basedon electrostatic differences between polymers and it is independent of density, size orshape. The advantages of this technique are its effectiveness and the low energyrequired, but it is still on the pilot scale and the presence of additives makes the sepa-ration difficult.

Another technique is the use of tracers (i.e. fluorescent) for identification and sortingof plastics. A European project, set for the implementation of tracers on an industrialscale, concluded that it is a fast and reliable identification technique. Furthermore,marking by tracers can differentiate between grades of generic type plastics and also bydestination, e.g. one specific tracer used for plastics not to be recycled. The ultrasonictechnique is based on the use of ultrasound attenuation measurements which weredeveloped for medical diagnostic analyses by Langton. A specialized computer wasdesigned for this specific application and patented by Hull and Langton in order to assistthe classification and identification of polymer waste. The ultrasonic analysis offers acheap reliable technique able to be used both on and off line.

By air classification, it is quite easy to distinguish a thick walled from a thin walledpolymer such as LDPE and HDPE. Any small and big fragments can be effectivelyidentified by micronization. This method is usually applied to separate PET and PVC.The different specific densities of plastic are used in some sorting plants for develop-ing automatic sorting techniques as long as the mixed plastics to be sorted are not tooheavily contaminated. The hydrocyclone is an old technique based on this property. Ina hydrocyclone, the shredded and washed plastic fragments are separated in a cen-trifugal field according to their density resulting in purity of more than 99%. Anotherdevice recently demonstrated is based on solubility of polymers. It is thus possible toseparate six or more polymer categories by dissolving them all in a solvent system andtaking advantage of the different temperature dissolving point (each polymer dis-solves at a different temperature). This method proved to be effective both in labora-tory analysis and industrial applications. This is a very promising technique sincemodern packages usually employ several polymers in order to achieve the desiredproperties. Finally, molded-in codes can be used for identification and sorting of plastic waste. Molding in bar codes appears to be the simplest, most cost-effectiveapproach, but the main disadvantage resides in the possibility that any damage occur-ring to the label, which is likely to happen, would render the code illegible. The analy-sis on the composition and properties of plastic waste and the physical properties ofplastics demonstrate that, although several separation technologies can be applied toseparate mixed plastics, their applicability is still very limited (Soler, 1992; Brown,1993; Hull et al., 1994; Eisenreich et al., 1995; Schudel and Koller, 1995; Riess,1995; Lambert, 1995; Kenny, 1995; Saetti and Peroni, 1995).

The techniques used for separation of different kinds of plastics are based on dif-ferences in density, shape, color, physicochemical properties and solubility. The solu-bility-based processes (SDP) include stages of dissolving a series of incompatiblepolymers in a common solvent at various temperatures or in different solvents, so thatone polymer is separated each time. These processes differ in the method employed torecover the polymer after the dissolution stage. So far, the SDP have been successfullyapplied in a laboratory scale for the recycling of PP pipes, rigid PVC bottles, PS waste


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foam, LDPE film from greenhouses and HDPE bottles from agrochemical packaging(Poulakis and Papaspyrides, 1995; Pappa et al., 2001). The technique involves the fol-lowing steps, shown graphically in Figure 15.16:

1 Cutting the waste into smaller pieces and, if necessary, washing with water2 Preliminary separation of the initial mixture to two or more mixtures by flotation in

water or another liquid3 Addition of a solvent (S) that selectively dissolves only one of the polymers at cer-

tain conditions4 Filtration to remove the non-dissolved polymers5 Addition of an anti-solvent (AS) to precipitate the dissolved polymer6 Filtration and drying of the precipitated polymer7 Separation of the S/AS mixture by distillation for re-use8 Application of the same procedure for each polymer of the mixture.

In this study, the SDP method was applied for the separation of mixtures consisting ofpolyolefins – low-density polyethylene (LDPE), high-density polyethylene (HDPE),polypropylene (PP) – in both laboratory and pilot scale. Excellent recoveries wereachieved and the quality of the recycled polymers remained practically intact. Thefeasibility study of the method for a high capacity unit, based on the scale up of thepilot one, showed that the cost of the recycled polymer is comparable to the commer-cial price of the virgin one.

Dodbiba et al. (2002) studied the separation of polyethylene terephthalate (PET)-polyethylene (PE) and polyethylene terephthalate (PET)-polypropylene (PP) mixturesin order to improve the grade of the raw input used in PET bottle recycling. First, PETbottles and their caps (made of PE or PP) were shredded and the floatability of eachpolymer was tested. Even with the addition of the wetting reagents dodecylamineacetate (DAA) or polyvinyl alcohol (PVA), the results did not suggest that therequired 99.995% purity of PET plastic could not be achieved by flotation. Second,the mixtures were separated with a sink–float process using a drum separator. Finally,as the required purity of PET could not be obtained by either technique alone, a sys-tem utilizing a combination of the two processes was developed. This system easilyachieved the desired PET gade. Finally, some sink–float experiments were performedwith a medium of magnesium sulfate (dense medium separation).

Shen and coworkers (2002) found that the floatability of all the plastics decreasedwith the addition of the surfactant, but they are different in floatability and follow theorder POM�PVC�PMMA�PET�PC�ABS�PS. From the separation test resultsof several plastic mixtures, it was shown that the Gamma flotation method not onlycan be used to separate plastics mixture with different density, such as separation ofPOM and PVC from PC, POM and PVC from PS and ABS, PET and PMMA from PSand ABS, but also can be used to separate plastics mixture with similar density, suchas separation of PMMA from PC. Products with grade higher than 99% and recoveryhigher than 97% can be obtained for the separation of some plastic mixtures. It wasfound that the depressing effect of surfactant 15-S-7 on the plastics is mainly due to


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Waste M


1003

FlotationPolymerwaste

Cutting Washing

Polymersolution

SolventDissolution

vesselFilter

FilterAnti-

solventDistillation

columnS/AS mixture

Solvent

Purepolymer

Precipitationvessel

Wetpolymer

Dryer

Transfer

Figure 15.16 Flow diagram of the selective dissolution/precipitation method for the separation of polymer mixtures (adapted from Pappa et al., 2001)

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the reduced liquid surface tension and flotation selectivity for the plastics with identi-cal particle size is dominated by contact angle, particle density and shape.

Over recent years, several experimental studies have been reported describing theseparation of plastics by froth flotation. In principle, selective flotation separation ofplastics can be achieved by:

1 Gamma flotation using a liquid medium with a specific value of the surface tension2 chemical conditioning using adsorption of wetting agents3 physical conditioning, e.g. plasma treatment or wet oxidation4 hydrophobic modification using a chemical conditioning agent such as a plasti-

cizer, for example, diisodecylphalate on PVC.

In general, all these methods emphasize the modification of the plastic surface or theflotation medium and, in many cases, this can be successfully achieved on different plas-tics leading to high flotation selectivity with mixtures. From the results, it was shownthat plastics flotation is dominated not only by surface chemical factors, but also signif-icantly by gravity factors. It is suggested that plastics flotation is a combination of frothflotation and gravity separation. According to this relation, the idea of particle controlwas first applied for the separation of plastics mixtures. From the separation results, itwas deduced that this method can greatly increase the separation efficiency for flotationseparation of plastics mixtures. The particles in cutting products are not uniform in sizeand shape. Cutting products of PMMA and POM have a relatively wide size distributionand contain a considerable amount of particles of less than 1 mm which are difficult todepress by wetting agents. PVC and PS give an intermediate size distribution with anintermediate left tail but a small right tail. Finally, ABS, PC and PET gave a relativelynarrow particle size distribution. Particle shape tends to be more irregular in the fine sizefractions. The equation and the experimental results showed that particle size and shapecontrol is important for plastics flotation. It is an effective way to improve the separationefficiency for plastics flotation (Shen et al., 2001).

The dry separation of a mixture of three plastics by combining air tabling and tri-boelectric separation has been described (Dodbiba et al., 2005). While air tabling iseffective for particles of different density, the triboelectric separation can be used forseparation of particles of similar density. Before commencing the separation tests, theeffectiveness of the separating devices was evaluated by analyzing the effects of theparticle size and the difference in density between components of the mixture. A two-stage process has been proposed for separation of mixed plastics prior to recycling.Polypropylene (PP), polyethylene terephthalate (PET) and polyvinyl chloride (PVC)were selected for investigation as they are widely used in the manufacture of everydayproducts. An air table was employed for the first stage of the process to collect a PP-rich low-density fraction and a PET/PVC high-density fraction. In the second stage,the PET/PVC fraction was separated by means of a triboelectric separator utilizingdifferences in surface charge. A mixture of PP, PET and PVC was selected for inves-tigation. Each component amounted to one-third of the total mass of the mixture.Thus, high-density plastics (i.e. PET and PVC) amounted to approximately 67% ofthe total. Before commencing the separation tests, the effectiveness of the techniques


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was evaluated by investigating the effects of the particle size and the difference indensity between components of the mixture. The triboelectric separation was effectivefor separation of materials of similar density. However, an upper limit of the particlesize was set after considering the magnitude of the surface potential attained by plas-tics and the maximum electric field strength that the triboelectric separator could cre-ate without causing electric breakdown. The air tabling was effective if the densitydifference between particles was at least 450 kg/m3 and the feed was properly sized. Ageneral schematic flowsheet of the dry process for separating mixtures of three plas-tics is shown in Figure 15.17.


Product2

Product1

PP, PET,PVC

Product3

Shredding

Screening I

Screening II

Air table

Triboelectriccyclone separator

Is screening Iappropriate?

No

YesScreening II

Air table

Is screening IIappropriate?

No

Yes

Figure 15.17 A general scheme flowsheet of the dry process for separating mixtures of three plastics(adapted from Dodbiba et al., 2005)

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The plastic waste samples (PET, HDPE and PP) were taken from an MSW separat-ing and composting plant (Araraquara, SP, Brazil). The PET consisted predominantlyof carbonated soft drink bottles, plus a few water and vegetable oil bottles. The HDPEand PP are mainly packaging materials from cleaning, personal hygiene, utensils,food and automotive mineral oil products. The polyolefins were mixed in a proportion9:1 (HDPE:PP) according to a recent study on MSW composition (Mancini et al.,2000). Owing to the heterogeneity of the contamination of these wastes, one lot (ca.40 kg) for each of these materials (PET and polyolefins) was ground in a knife milland then mixed and homogenized in an appropriate bag. Afterwards, three samples ofabout 3 kg each were taken from these lots and cleaned independently in order toachieve three typical samples of wastewater generated during the cleaning processesof these plastics (Santos et al., 2005). Since polyolefins and PET have different char-acteristics, the conditions used during the washing process also differed from eachother. Specifically for PET, a step that encloses the separation of labels and capsresidue by differences in density is necessary. Furthermore, the susceptibility of PETduring processing step to adhesive residues also requires more aggressive conditionsin the washing step in order to maximize the adhesive removal (Sanko, 1999). Carewas taken not to use high alkalinity content. As an alternative, increments on the bathtemperature are recommended. Ordinary tap water without addition of any chemicalwas used for the pre-washing step. Caustic soda was then used in the washing step forboth plastics, though surfactant was used only for PET. No significant differences inthe effluent characteristics were found between the two types of plastic studied andbetween the pre-washing and washing steps, except those differences intrinsic to thecleaning processes (temperature, surfactant, caustic soda concentration). Some spe-cific unit differences are necessary depending on the type of plastic used due toextrapolation of emission limits of oil and grease in the polyolefins pre-washing stepand Pb excess in the PET washing step.

Cryo-comminution of plastic waste was recently introduced by Gente and coworkers(2004). Laboratory comminution tests were carried out under different conditions oftemperature and sample pre-conditioning adopting CO2 and liquid nitrogen as refriger-ant agents. The temperature was monitored by thermocouples placed in the millingchamber. Moreover, different internal mill screens have been adopted. A proper proce-dure has been set up in order to obtain a selective comminution and a size reduction suit-able for further separation treatment. Tests have been performed on plastics comingfrom medical plastic waste and from a plant for recycling spent lead batteries. Resultscoming from different mill devices have been compared taking into consideration dif-ferent indexes for representative size distributions. The results of the performed testsshowed cryo-comminution improved the effectiveness of size reduction of plastics,promotes liberation of constituents and increases specific surface size of comminutedparticles in comparison to a comminution process carried out at room temperature.

Flame treatment was effectively used towards modifying the surface of plastics toallow water-based coatings to be attached. The effect of the treatment was to producehydrophilic species on the surface of the plastic. The process is therefore potentiallyuseful for the separation of plastics by froth flotation, provided that the production ofthe hydrophilic surface can be achieved selectively. Polyvinyl chloride (PVC) and


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polyethylene terephthalate (PET) were selected for investigation as they were foundas a co-mingled product from the recovery of beverage containers (Pascoe andO’Connell, 2003). A simple, but effective, flame treatment method for flaked plasticswas developed. The treatment involved the use of an acceleration chute that deliversthe flakes through the flame of an angled burner. In experiments with virgin plastics,the PVC was found to be less susceptible to surface modification than PET, as indi-cated by contact angle measurement. Separation of the treated virgin plastic by frothflotation was found to be possible, using careful control of frother addition. The tech-nique was then considered for the treatment of post-consumer plastic bottles. It wasdemonstrated that flame treatment was effective in rendering the surface of both plas-tics hydrophilic, although the process alone was not sufficiently selective. Hydrophobicrecovery of the PVC, but not the PET, was achieved by raising the temperature of thematerial to 140°C for a period of 10 min. A two-stage flotation process was tested forthe separation of the plastics. In the first stage, PET was floated away from the PVCcapitalizing on differences in particle thickness and surface contamination. The floatproduct was then subjected to flame treatment and hydrophobic recovery prior to thesecond stage of flotation. In this stage, the PVC was conveyed to the float productleaving a PET-rich sinks fraction.

Hearn and Ballard (2005) developed two sorting techniques using the electrostaticproperties of materials to produce separate material streams for the purposes of recy-cling. Trials were undertaken using typical common items of waste packaging givingencouraging results. Early results indicate reliable operation under a range of environ-mental conditions, however, the effects on sorting efficiency of extremes of surfacecontamination, moisture, temperature and humidity have yet to be quantified. It is rec-ognized that the presence of high levels of surface contamination on the waste itemsto be streamed may cause problems, particularly for the triboelectric sensor probe.Preliminary examination of material from an MRF, however, suggests that these mate-rials are generally not heavily contaminated with anything other than moisture. Thepresence of surface water does significantly influence both charge generation and tri-boelectrification. MRFs and plants where these techniques are likely to be appliedlend themselves to the application of driers or air curtains which could be installedupstream of the electrostatic sorting area. It is also recognized that this technique maynot be appropriate for all polymer types but can be used in conjunction with othertechniques. Such techniques may include an optical sensor to separate PVC fromHDPE and Fourier transform infrared spectroscopy (Hearn, 2003) to sort the streamcontaining PET/PETE and PS. Difficulties may be encountered with certain packag-ing geometries and the presence of labels and coatings. On all of these issues the useof the small triboelectric probe is an advantage as it can be directed at an area of pack-aging most likely to constitute exposed polymer.

Preparation for recyclingAfter the materials have been collected and sorted, they must be converted into ahomogeneous purable bulk material which is easy to transport and store and is suit-able for recycling. The quality criteria are: high bulk density, defined grain size, lowchlorine content and low dust content. These properties can usually be achieved


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within the frame of the agglomeration process. The agglomeration process is followedby the shredding and separating steps, thus reducing the mixed plastics to a grain sizeof less than 50 mm and producing a more or less homogeneous material. The target ofagglomeration is to convert mixed plastics into a product with specific properties suit-able for recycling. The final product should be pure and easily processable. In thisprocess, the pre-shredded mixed plastics were fed into rotating blades and heated to135–140°C. As a result, small pieces of film sheeting cake together and can then beprocessed into compact plastic granules. Moreover, inpelletizers are also employed sothat plastics compacted by means of pressure are cut off by cutters and subsequentlypelletized. However, agglomeration is considered a ‘young’ technology requiring fur-ther research and development work (Pearson, 1996).

Mechanical recyclingThe purpose of mechanical recycling is to process post-consumer plastics and recovera secondary raw material for the production of new items (Pearson, 1996). Packagingmaterial sorted into individual fractions is either melted down directly and moldedinto a new shape or melted after being shredded into flakes and processed into gran-ules called regranulate. There are several mechanical recycling processes: extrusionand intrusion, injection molding, transfer molding process and regranulation(http://ww/eps.co.uk/mechanical.html). In the extrusion process, the regranulate isheated and melted into a plastic mass which is then transferred to molds for simpleproducts such as profile section or sheets. The only difference between extrusion andintrusion processes is that, in the latter, impurities such as glass fragments, sand andwooden pieces can remain in the plastic melt. The extruder is designed in a way so thatimpurities are embedded in the plastic melt. The molten mass is pressed directly intomolds such as honeycomb-type paving stones. Circulation of cold water speeds up thehardening process of the paving stones which can be removed from the molds after ashort time. The molten plastic mass, during the injection molding process, is injectedinto a mold under high pressure. Similar to the intrusion process, the machines aredesigned for processing mixed plastics containing impurities. The molten plastic ispushed by the piston into the mold for the article to be produced. The pressure on thepiston remains constant until the tray has cooled down and can safely be removedfrom the mold (Pearson, 1996). During the molding process, mixed plastics areshaped into finished products by means of direct melting and molding, either withoutor after only coarse pre-shredding. Finally, in the regranulation process, the post-con-sumer plastics are sorted into different fractions, heated and regranulated. The pro-duced plastic is applicable in various sectors such as construction (frame sections,cable insulation, piping, insulating materials, etc.), packaging and logistics (filmsheeting, hollow containers, transport containers, pallets) and industry (shaped partsfor the car industry). Recycled films can be manufactured from used PE films. Filmsof recycled materials and virgin material can be permanently joined to produce framesections of film sheeting by co-extrusion (http://www.environment97.org/text/reception/r/techPapers/Papers/g19htm). It is estimated that the recycling rate for foamedpolystyrene can reach 100%. The material is broken down to its components and


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either added to new foamed polystyrene packaging or regranulated to produce thestarting material polystyrene which is utilized for the manufacture of injectionmolded parts. In Germany, a recycling rate of 40% has already been achieved.However, it should be mentioned that current standards and regulations prevent sec-ondary plastics from being used to an even greater extent. For instance, packaging forfoodstuff may only be manufactured from virgin polymers. Similarly, the productionof certain types of piping prohibits the use of regranulate. In principle, most of the9.1 M tons of plastic utilized in packaging in Western Europe could be recycled byremelting and extrusion or molding into films.

Actually in 1996, 53% of the plastic sales for packaging were recycled mechani-cally and more than 90% has been recycled in Germany since 1997. Therefore, themechanical recycling process is an important technique despite the following prob-lems that have been encountered in practice (Halle, 1994): the high cost of collectionand separation equipment, the lack of a substantial and reliable market for the recy-cled material and limited applications (i.e. exemption of food packaging materials)for the recycled materials. The implications of mechanical recycling have partiallyinfluenced packaging design. The three predominant trends can be summarized as fol-lows: the increased need for simple structures consisting of a single polymer or atleast a single polymer type instead of complex multilayer structures, which are diffi-cult to be separated into individual materials. Recent predictions for the packagingfilm market suggest the replacement of PS and PVC with PP.

Therefore, the use of compatibilizers – chemical additives that assist the blendingof various polymer types – helps to alleviate some of the problems of blended poly-mers. The addition of 5% of a vinyl acetate EVA film grade polymer of 28% VA con-tent substantially improved the properties of 85/15 LLDPE/PP mixtures (Teh et al.,1994). Furthermore, several new linear ethylene polymers have been successfullyused to increase the recyclable content of post-consumer recycled polyolefins to highlevels, while maintaining good film properties (Begley and Hollifield, 1993). Safetyand contamination considerations and current legislative standards are the mainobstacles for an extensive use of mechanically recycled polymers by the food packag-ing industry. Nevertheless, pack designers and polymer scientists can facilitate therecyclability of food packs so they can be easily used for other applications. The obvi-ous dominance of the food sector within the overall packaging market suggests that aresponse of this kind by the food packaging industry is expected to have a key influ-ence on the future of plastic recycling.

The increasing consumption of polymeric blends results in a great environmentalimpact because the used plastics are discarded in nature in a non-rational form. Facingall these problems, recycling becomes a powerful strategy regarding the reduction ofthe environmental impact caused by plastic waste. Polymeric blends were preparedwith mechanical recycling and characterized. LDPE/Al residues from cartoned pack-aging were blended with recycled HDPE/LDPE and virgin PE resins. It was observedthat processability, mechanical properties, chemical resistance and water absorptionare dependent on the blend compositions. Also, an aluminum film was found toremain as isolated particles in the polymeric matrix and the mechanical behavior ofthe blend depends on the aluminum dispersion. Either, the blend water absorption


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depends on recycled material contamination, mainly polyamides. Finally, the amountof recycled material added to the blends determines both chemical stability and ther-mal characteristics (Paula et al., 2005).

Recycling of mixed plastic wastes composed of low-density polyethylene (LDPE)matrix and polypropylene (PP) was carried out by compounding using single-screw ortwin-screw extruders. Blends of virgin polymers were prepared to compare mechani-cal properties of both virgin and regenerated materials. First, a model composition ofvirgin LDPE/PP blend was prepared to study the effect of process parameters and thatof different types of compatibilizers. Second, the results were applied to plastic wastescoming from industrial post-consumer plastic wastes. The mixture of plastic wasteswas purified in a pilot plant with steps of grinding, washing and separating. The detailed treatment is shown in Figure 15.18. By adding compatibilizing agents such asethylene-propylene-diene monomer, ethylene-propylene monomer, or PE-g-(2-methyl-1,3-butadiene) graft copolymer, elongation at break and impact strength wereimproved for all blends. The effect of these various copolymers was quite differentand was in relation to their chemical structure. The recycled blends exhibited suitableproperties leading to applications that require good mechanical properties (Bertin andRobin, 2002).

Feedstock recyclingThe main purpose of feedstock recycling is to convert prepared post-consumer plas-tics into their basic components, such as oil, gas, naphtha, and to use them as second-ary feedstocks in refineries or petrochemical industries for the production of newplastics, paints or adhesives. Post-consumer plastics may also be utilized as a substi-tute for valuable raw materials like oil. Plastics can be effectively applied in the pro-duction of steel. Currently, the carbon and hydrogen molecules bound in plastics areused for the reduction of iron oxide. A single industrial-scale plant for feedstock recy-cling has a capacity of 100 000 tons of post-consumer plastic per year. The techniquesemployed consist of hydrogenation, BASF process, etc. and are of crucial importancein the recycling of plastics (Caluori, 1995).

Steel and iron have been overtaken after a period of 3000 years as the most used andmost versatile materials by the different kinds of plastics and this in a period of only50 years. Feedstock recycling is one of the greatest challenges for the recycling ofplastics and various technologies have been successfully demonstrated and continueto be developed. Kaminsky and coworkers (2004) investigated different processessuch as degradation of plastics to monomers, pyrolysis into monomers and oil, gasifi-cation into syngas. Pyrolysis of mixed plastic wastes and elastomers is a cost-effectiveprocess to recover feedstocks for the petrochemical industry. The Hamburg process,using an indirectly heated fluidized bed, can be varied to produce mainly monomers,aliphatic hydrocarbons or aromatics. At temperatures of 450°C, poly(methyl methacry-late) (PMMA) is depolymerized to more than 98% of the monomer. However, theinfluence of fillers on the monomer yield has been studied. Polystyrene as feed givesup to 75% of styrene and 10% of oligomers. First demonstration plants are runningfor feedstock recycling of PMMA in a fluidized bed.


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Waste M


1011

Wetgrinding

Plasticswaste

ConveyingMetal

detection

Filtrate

Purematerials

Filtration

Lightfraction

Polyolefins Drying FiltrationHeavyfraction

PVCPETPS

Hydrocloning II(d � 1)

Slugsfibers

Water

MetalsStonesGlasses

Hydrocloning I(d � 2)

Figure 15.18 Flowsheet of the recycling pilot plant (adapted from Bertin and Robin, 2002)

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Schemes such as the Duales System Deutschland in Germany (‘green dot’) haveaddressed feed recycling, but there remains the high energy and process costs of thefeedstock recycling technology. Thermal and catalytic cracking, although effective,require significant operating temperatures and are strongly endothermic, leading tolarge adiabatic temperature falls across reactors. Oxidation methods, energeticallymore favorable, are at high temperature and have associated difficulties such as dan-gerous emissions, product quality and expensive materials of construction. Hydro-cracking studies have been limited to date and merit further study since the process is exothermic and can be carried out at significantly lower temperatures (Garforth et al., 2004). Total plastic waste generated and recovered in Western Europe is givenin Figure 15.19.

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeriagreenhouses (Spain) towards valuable hydrocarbon mixtures was studied over severalacid catalysts (Serrano et al., 2004). The plastic film waste was mostly made up of ambi-ent degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA)copolymer, the vinyl acetate content being around 4 wt%. Nanocrystalline HZSM-5zeolite (crystal size ~60 nm) was the only catalyst capable of degrading completely therefuse at 420°C despite using a very small amount of catalyst (plastic/catalyst mass ratioof 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike asoccurred with virgin LDPE, showed fairly close conversions to that of thermal cracking.Nanocrystalline HZSM-5 zeolite led to 60 wt% selectivity towards C1-C5 hydrocarbons,mostly valuable C3-C5 olefins, that would improve the profitability of a future industrialrecycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite wasascribed to its high content of strong external acid sites due to its nanometer dimension,which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline


25 000

20 000

15 000

10 000

5000

01993 1995 1997 1999 2001 2003

Year

Tota

l pla

stic

was

te

Figure 15.19 Total plastic waste generated and recovered in Western Europe (� total plastics waste, � total plastics waste recovered, — energy recovery, � mechanical recycling and � feedstock recycling)(adapted from Garforth et al., 2004)

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HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recyclingprocess by catalytic cracking.

Hydrogenation in the Kohleol-Anlage Bottrop The hydrogenation process in theKohleol-Anlage Bottrop serves to recover synthetic crude oil and gases that can beused for industrial purposes. At the beginning of the 20th century in Germany, workwas initiated on the development of feedstock recycling techniques and technologiesin order to enhance the recovery of energy and raw materials. Initially, the purpose ofhydrogenation was to recover oil from coal. At the beginning of the 1950s, the utiliza-tion of this form of hydrogenation ceased because of its high cost. Only after the sec-ond oil crisis was interest in development work on hydrogenation techniquesrekindled (Kohleol-Anlage, Bottrop). In the second half of the 1980s, industrialresidue was processed to an increasing extent in Bottrop because of the detoxifyingeffect that hydrogenation has on various types of contaminated residue, such as oilcontaining chlorine. Since hydrogenation occurs at very high pressure, the plasticshave to be liquefied first to make them suitable for pumping. The solid liquefaction ofhydrocarbons is called depolymerization and is applicable to the long polymericchains resulting in fragmented short and mobile units. Cracking may occur when theplastics are heated for a longer period of time. After liquefaction, high-pressurepumps compress the mixture at a pressure of 15–250 bar. Finally, the liquid mass isheated to 440–480°C and is transferred to a high-pressure column reactor where theactual hydrogenation takes place. The carbon chains are cracked to an even greaterextent and hydrogen is bound at the fragments. Hydrogenation occurs in three seriesof connected column reactors and then the product is exposed to a lower pressure sothat solid, non-usable components are removed. The final products consist of syntheticcrude oil and gases (mixture of methane, ethane, propane, butane, pentane andhexane). Utilization of a closed system is advantageous because there are no harmfulemissions to the environment (Ball and Unsworth, 1995; Pearson, 1996).

Production of gas Several gasification techniques are used worldwide by companiessuch as Thermoselect, TEES, Texaco, BCU, etc. The plastics fed into the process forthe production of gas are converted into a gas mixture (mainly carbon monoxide andhydrogen) at 800°C or higher by adding oxygen and steam. Similar to hydrogenation,any chlorine containing compounds present in the plastic waste (such as PVC) aredecomposed by the high temperatures used in the process and are converted to a moreuseful product. Heavy metals and mineral substances are melted into a vitreous slagto be used in road construction work at later stages of the procedure. This process ofbinding heavy metals and minerals is known as vitrification. The obtained crude gasis cooled very abruptly in order to prevent the formation of harmful substances suchas dioxins and furanes. Tars and solids are first separated in a further step of the process and then the liquid tars, consisting of carbon and hydrogen, can be converted into gas by employing a special gasifier for liquid products. The productionof methanol from waste materials still remains of major importance worldwide(Pearson, 1996).


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Coal can be replaced by a thermal equivalent of this gas in the rotary kiln or can beeffectively used in gas engines. The mineral raw materials can probably be used forthe production of a special cement. Several research groups have taken an interest dueto the importance of this recycling method and the necessity for further research.Therefore, in BCU (Bundrer Cementwerke AG, Switzerland), various gasificationprocesses are currently being studied, tested and compared. Among others, for example, the fluidized-bed method was studied, by using air as a gasifying medium,for the thermoselect process which gasifies with pure oxygen. This latter method,according to BCU, has numerous advantages, such as higher gasification temperature,much smaller volume of gas of very high quality and clean and slag which can bedrawn off as fluid. Its only disadvantage resides in its high initial investment.

During the thermoselect process, the material is compressed to about one-tenth ofits original volume without any prior treatment. The material is pressed into compactplugs which are fed into an air-tight heated degassing duct. The organic componentsare driven off and converted into carbon by increasing the heat in the duct. The carbonforms a continuous renewed active carbon filter which absorbs any pollutant. Afterbeing mixed with inorganic components, such as metals and minerals, it is fed into areactor where gasification occurs in the presence of oxygen at temperatures above2000°C. At these temperatures, the metallic, mineral components and chlorinatedhydrocarbons are completely decomposed. The reformation of dioxins and furanes isprevented by rapid cooling of the hot gas. This gas, which represents about 10% of theamount of gas for a refuse incineration plant, undergoes thorough cleaning and can beutilized as an energy carrier. The liquefied slag components are fed into a secondhigh-temperature reactor where the mineral components, with the addition of oxygen,gas and propane at the temperature of 1800°C, are converted into raw materials.Metals are separated and made available to the metal industry (Caluori, 1995). Inmost gasification systems, environmental emission controls are significantly reducedsince the volume of gas emitted is much smaller than in traditional incineration sys-tems. Furthermore, these systems have low emissions of dioxins, acid gases and otherpollutants because of the relatively high quality of the fuels combusted.

Another research study conducted by De Stefanis et al. (1995) under the supervi-sion of ENEA (Italian National Agency for New Technology, Energy and theEnvironment) focused on the observation of plant operations, data collection andextensive sampling of the produced gas. Several more studies have been conducted inthis area over the last 10 years (Rijpkema, 1995; Seddon-Brown, 1995; Redepenning,1995; Carlsson, 1995; Brunner and Fey, 1995; Steiner, 1995; Edlinger, 1995;Trauberg, 1995; Calamius, 1998).

BASF process BASF was quick to realize that mechanical recycling can only be but apartial solution. The task of the BASF pilot plant was to convert used plastics intopetrochemical products which can be used in the BASF plant network as raw materi-als. The agglomerates are delivered in silo trucks to BASF and pneumatically conveyed with nitrogen to the storage silos of the pilot plant. The agglomerates are then converted into petrochemicals by means of a three-stage process (Wanjek,1995). Similar to hydrogenation, the BASF process also starts with liquefaction of the


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plastics at about 30°C in the absence of air and simultaneously a dehydrochlorinationof the PVC present in the plastic mixture occurs. The released hydrochloric acid isabsorbed and reprocessed in the hydrochloric acid unit of the plant. In the second step,the liquefied plastics are cracked into petrochemical feedstocks without the additionof hydrogen. At temperatures above 400°C, the polymer chains are fragmented downto shorter length chains and various oils and gases are formed. The gases are compressed and used as feedstock in a steamcracker. In the third step, the mixture isfractionated producing a sulfur-free product similar to crude oil (naphtha), shorthydrocarbon molecules and aromatic compounds. All these products can be used bythe network of chemical plants available at BASF in Ludwingshafen. For instance,gaseous molecules such as ethylene and propylene are recovered from naphtha in thesteamcracker. After separation (distillation), these can be directly used for polymerproduction (polyethylene, polypropylene, etc.). The oils, which only boil at high temperatures, are gasified and processed into methanol. About 5% of residues is themaximum amount to be obtained. The process runs pressure-free in a closed systemthus generating practically no toxic emissions to the environment (Wanjek, 1995;Pearson, 1996).

Reduction process At Bremer Stahlwerke (steelworks in Bremer), plastic agglomerateis used as a substitute for heavy oil, one of the materials needed for operation of theblast furnace. During steel production in a blast furnace, the chemically bound oxy-gen must be separated from the iron fed into the furnace. Reduction, which is theremoval of oxygen, is the reaction of carbon, carbon monoxide or hydrogen with oxy-gen. These reactions require energy input for it to take place, whereas combustionreleases heat. The gases are formed when plastic is injected into the furnace at2000°C, melts at the bottom of the blast furnace and undergoes abrupt gasification.Since plastic and oil have a very similar chemical composition, one kilogram of oilcan be replaced by one kilogram of plastic in this process. As the gas migratesupwards through the long blast furnace shaft, more than 80% of the reduction poten-tial of the gas produced from the plastic is utilized. A mixture of slightly combustiblegas, carbon monoxide and steam, which is known as blast furnace gas, is obtained andused in the steelworks (Pearson, 1996).

Chemical recyclingChemical conversion processes can be used for the recycling of plastic waste, butchemical recycling of polymers requires plastics of almost uniform chemical compo-sition and sufficient purity. With regard to the potential cost, this type of recycling canbe performed on an economical basis only with the more expensive engineering plas-tics, such as polyurethanes. The target of any chemical recycling process is to depoly-merize polyurethane and recover those materials that can be reused. The numerousdeveloped processes that are widely applicable are the following: hydrolysis, hydro-genation, pyrolysis, aminolysis, glycolysis, hydroglycolysis, chemolysis and ammo-nolysis. The processes differ greatly in terms of quality of the plastic feed, complexityof the process and final products. The plastic, however, must be adapted to chemical


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recycling processes by liquefaction. A degradative extrusion has been suggested as apretreating process for chemical recycling of plastic with satisfactory effects (Lentzand Mormann, 1992; Michaeli and Lackner, 1995; Seyfarth et al., 1995; Marechal et al., 1995; Cassey et al., 1995).

Chemical plastic recycling processes may find application in recycling of PVC/PET blend where sorting operations are either not possible or prohibitively expensive.The advantage of such a process is the possibility to ‘tailor’ the end product to the application requirements. Since this approach is innovative, energy and materialeconomics need further elaboration (Lusinchi et al., 1998). Ammonolysis ofpolyurethanes has been reported in only a few studies among which the oldest is apatent dating from 1955. Two more patents, assigned to the McDonnell DouglasCorporation, claim ammonia to act as co-reagent in the alcoholysis of polyurethanes.Another representative example is ammonolytic cleavage of urenane and urea bondsof a polyurethane elastomer and flexible foam based on methylenebis (phenyl iso-cyanate) (MDI) and polyetherpolyol under supercritical conditions producing polyols,amines and substituted urea (Lentz and Mormann, 1992).

The glycolysis, as approached by ‘waterilly’, is carried out by charging compactedpellets into a stirred batch reactor containing diethylene glycol (DEG). A catalyst isadded and the reactor is heated to 200°C. The pellets dissolve within 1 h and the reac-tion finishes in 2 h. The stirrer of the reactor is stopped and the reaction mixture isallowed to separate into two layers. The top layer consists of DEG and flexible polyolwith a small quantity of impurities. The bottom layer consists primarily of DEG andaromatic compounds derived from the isocyanate in the foam. The two layers are sep-arated for further processing. The top layer is washed with more DEG either in thebatch reactor or in a liquid/liquid extraction column. After the final wash, DEG isremoved by vacuum stripping yielding pure flexible polyol. Following purification,the obtained flexible polyol undergoes a split phase glycolysis so it can be used toreplace virgin polyol completely. Propylene oxide (PO) is added to the bottom layer toform an aromatic polyol rich in DEG. This mixture is heated under vacuum to reactand distill off any residual PO. Excess of DEG is also removed and is suitable forbeing reused at any stage of the process (Marechal et al., 1995; Cassey et al., 1995).

A new recycling technique has been developed which utilizes a natural solvent, d-limonene, to shrink expanded polystyrene (EPS). The new recycling system con-sists of EPS shrinking equipment and a recycling plant for separation of limonenesolution. There are two types of EPS shrinking equipment developed: a mobile (truck)and a static EPS shrinking apparatus. The final product is polystyrene and not EPSbecause PS cannot be used to produce EPS by the thermal shrinking method (Noguchiet al., 1998a, b, c).

Chemical recycling refers to the decomposition of the macromolecular structure togenerate low molecular weight compounds. This is typically carried out under hightemperature and in the presence of various types of catalysts. This approach consumeslarge amounts of energy and, in many cases, results in rather low value products.Probably the type of chemical recycling having the highest potential value involvesdepolymerization. In this case, the resulting monomer can then be utilized to regener-ate more polymeric material (Burillo et al., 2002).


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Radiation technologyOne technological barrier to polymer recycling is the incompatibility of differentpolymer types. When an attempt is made to mold a product using a polymer mixture,the materials typically form separate phases, resulting in poor properties. Anotherproblem is degradation that may be present in the recycled material: properties areaffected by changes in molecular structure caused by environmental factors duringuse, including UV light, thermal-oxidative processes, attack by pollutant gases, chem-ical interaction with liquid contents and others. Ionizing radiation offers unique pos-sibilities for application to the problem of recycling polymers (Clough, 2001), due toits ability to cause cross-linking or scission of a wide range of materials without dis-solving the sample. Possibilities for using radiation in recycling include:

1 enhancing the mechanical properties of recovered materials or blends2 decomposition of polymers.

Radiation-included oxidation of PE prior to blending with recycled polyethyl-eneterephthalate (PET) was particularly beneficial; this enhanced the miscibility ofthe PE with the more polar PET (Burillo et al., 2000).

Recycling of butyl rubber from inner tubes, using irradiation of cryogenicallyground rubber crumb, is a commercial process in China (Yang et al., 1998) whichleaves few refining wastes. A limited amount of work has been reported on the use ofradiation in chemical recycling (degradation) of polymers, yielding liquids of mixedcomposition for potential use in the petrochemical industry. Radiation can be usefulin lowering the energy requirements for chemical recycling, as well as providing ameans of controlling the nature of the products (Zhao et al., 1996). Another studyreported that when particles of radiation-cross-linked polyethylene were incorporatedas an additive into a melt of uncross-linked polythylene, an enhancement of elasticitywas obtained (Matusevich and Krul, 1999; Matusevich et al., 1999).

Radiation may potentially provide major benefit either for material recycling or forchemical recycling. A success in material recycling could constitute a major break-through in demonstrating an energy-efficient and economically attractive recyclingtechnology. Due to its ability to penetrate solids, including opaque materials, and toinduce chemistry in the solid phase, radiation may be uniquely suited to this purpose.Since radiation can also result in degradation of materials, depending on polymer typeand environmental conditions, it may likewise be of utility in reducing energy costs bypretreatment of polymers to promote chemical recycling. Studies over the past twodecades have established that irradiation can be very useful in the processing of poly-mer blends. Nearly all of this work has involved virgin (i.e. non-recycled) samples.

Polyethylene and polyamide The blends of polyethylenes with polyamide-6 (PA-6) arenormally immiscible. The use of polyethylene (PE) (chemically functionalized by intro-duction of polar groups through irradiation) to prepare miscible blends with PA-6 hasbeen reported by several workers. Spadaro et al. (1992, 1993, 1996) used this method toproduce uniform blends of LDPE, HDPE and LLDPE (linear low-density polyethylene)with PA-6. Blending of LDPE with PA-6 led to lower values of tensile strength and


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higher values of Izod impact strength (Valenza et al., 1992, 1993). The irradiated blendswith the stabilized morphology can then be conventionally processed, including conven-tional curing. These blends include NR/EPDM, SB/EPDM and BR/EPDM (NR, naturalrubber; SBF, styrene-butadiene copolymer; BRF, polybutadiene). In another study, theprocessability of HMWPP/EPDM (HMWPP, high molecular weight polypropylene)blends was found to improve on irradiation (van Gisbergen, 1989) and the radiation-induced cross-links stabilized the morphology of this blend during injection molding.Gamma irradiation under an inert atmosphere of mixed compositions of PET and PP,which had been coextruded, was reported to show modest improvement in propertiesat low dose (50 kgy) as a result of material cross-linking, though the data were notconclusive; significantly degraded properties were seen at higher doses (300 kgy)(Revyakin et al., 1999). The addition of agents which undergo cross-linking uponradiation exposure to compositions representing recovered waste materials, has beeninvestigated. Mixed materials containing HDPE, PP and PS, with triallyl cyanurate(TAC) added, showed significant improvement in modulus at a dose of B200-350 kgy.Some positive effect was seen at 2% TAC; substantial improvement was found at 10%TAC (Fujii and Nomura, 1986). Czvikovszky and coworkers have reported a numberof studies in which recycled, reinforced polymer systems were prepared using PP from reprocessed car bumpers (Czvikovszky et al., 1999; Czvikovszky andHargitai, 1999).

Gamma irradiation of butadiene-containing polymers in the presence of oxygencaused the material to exhibit a decrease in the onset temperature for mass loss, com-pared to unirradiated material or material irradiated in the absence of oxygen, whenthe samples were subjected to thermogravimetric analysis (TGA) (Schnabel et al.,1999). There is a large and successful industry based on the radiation-degradation ofTeflon powder, which renders the material able to be incorporated into inks, lubricantsand other formulations (Lunkwitz et al., 2000).

The issue of contamination on recycling

After sorting and washing, the waste polymer is likely to contain polymeric, particu-late and chemical contaminants that might render the recycled material unsuitable forfood applications. In general, recycled materials are not allowed to be used for foodpackaging applications. Food packaging in contaminated recycled materials is a seri-ous problem and well understood scientifically (Franz et al., 1994, 1997; Blakistone,1994; Allen and Blakistone, 1995; Miltz et al., 1997; Devliegehere et al., 1998). Themain drawback with old plastics comes from mass transfer that takes place during itsprevious use (Feigenbaun et al., 1997; Yoda, 1999) and that old plastics, exhibitingpotential contamination (by contact with harmful substances), cannot be in contactwith the food (Perou et al., 1999). One of the most interesting approaches consists ofreusing the wasted plastic as the core of the new material, a layer of virgin polymerbeing placed between the recycled and the food (Feigenbaun et al., 1997). Based ondata of hundreds of known chemicals, the FDA considered the risk linked to the inges-tion of an unknown chemical amounting to 10 ppb migrated substance (Bayer et al.,


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1995). Usage of the abovementioned virgin polymer retards considerably the migra-tion of the contaminant, which tends to be uniformly distributed through the bilayerpackaging into the food. In view of the current state of the art only a predictiveapproach can be of help in deciding whether recycled plastics, although possibly pol-luted, can be used safely (Harmati et al., 1995).

The marketing of unsafe materials is likely to be a barrier to more extensiveexploitation of recycling of plastics. Exclusion of recycled materials from food packaging applications is likely to limit further advances in plastic recycling. Therefore,it is crucial for the industry to function within a frame of a clear and scientificallysound legislation. It has been suggested that the best strategy is to allocate virgin poly-mers to food contact uses and recycled materials to other applications. Many researchgroups are currently carrying out further investigation on this topic in order to ensurethe veracity of such suggestions. Another proposal involves the use of multilayer PETaccording to which the recycled PET layer is ‘sandwiched’ between two layers of vir-gin PET. This technique is supposed to be efficient both for the protection of food andthe environment as well. Therefore, the difficult problem of isolating any possiblecontaminants present in the recycled PET film is reduced to blocking the transport ofthe contaminants across the virgin layers.

US and EU regulators have tried to harmonize worldwide regulations concerningthe use of recycled materials in food packaging. The Food and Drug Administration(FDA) in 1992 considered several suggested uses of recycled plastic for food pack-ages and commented favorably on the use of recycled plastic in the following applica-tions: expanded polystyrene for foam egg cartons; HDPE for grocery bags; PE and PPfor harvesting crates; PET for quart- and pint-size baskets for fruits; regenerated PETfor soda beverage bottles. Several processes for recycled PET for food packagingapplications have been approved by regulatory agencies outside the USA. In 1992, theUK, the Ministry of Agriculture, Fisheries and Food (MAFF) approved the methanol-ysis process and the same process was approved by the European Union as well.Japan, in 1992, also approved methanolysis as a recycling process for PET that isgoing to be used for soft drink bottles. In 1993, Australia approved the multilayer proposal and was followed in 1994 by New Zealand, Sweden and Switzerland (Hopeet al., 1992; Moser and Dudler, 1995; Van Rijwijk, 1995; Kaiser, 1995).

Environmental impacts of waste management processesAny recycling operations wishing to be considered responsible have to meet both themarket and environmental requirements. Recycling seems to be the most popularoption for the reduction of packaging waste. The EEC discussed a directive whichshould harmonize the different national regulations at the European level. Therefore,any assessment of plastic recycling processes has to take into account their environ-mental impacts and compatibility in addition to the actual recycling cost.

Consequently, the life cycle analysis is a system describing environmental andresource impacts of a product in its entire life cycle. It is a research instrument for anyenvironmental parameters with the background of technical and economical specifi-cations. For that purpose, the raw material, energy, emissions, wastewater and wastebalances are carried out throughout the entire life cycle. An ecoprofile is based on the


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same theory as life cycle assessment (LCA) but describes environmental and resourceimpact in a way which makes possible the ranking of different processes. The descrip-tion of the system studied is the first step for preparing a life cycle analysis or an eco-profile. The next step is an inventory of all emissions and resource consumptioncaused by the processes in the life cycle and standardization of the emissions is the third step for a thorough life cycle assessment. Normalization of the equivalents is essential and is considered as a fourth step. The equivalents are normalized bydividing them with the average annual emission per inhabitant. For global effects, theequivalents are divided with the annual emission per inhabitant in the world and forregional effects the equivalents are divided with the annual emission per inhabitant inthe region. The units of normalized equivalents are called person equivalents (PE).Only after normalization of the equivalents would it be possible to evaluate and spec-ulate on the significance of the environmental contributions. LCA, sometimes, mayinclude a fifth step which is the improvement analysis.

In Germany, within the frame of ‘LCA of recycling and recovery of plastics wastepackaging materials from households’, three research institutes studied the variousfeedstock and mechanical recycling techniques with respect to their consumption ofresources, the greenhouse effect, pollution and the production of municipal and haz-ardous waste. All steps involved in the recycling techniques and the fabrication ofrecycled products were thoroughly investigated. The most important conclusionreached in the LCA is that there is often more than one ecologically safe method forrecovery of plastics. On the contrary, feedstock recycling, mechanical recycling orenergy recovery techniques may be selected depending on the particular situation.From an ecological point of view, the most important is the best possible utilization ofthe chemical and physical properties and the energy content of the post-consumerplastics. All aspects of products should be taken into account so that there are no erro-neous results. There have been many examples of published ‘eco-balance’ studies ofvarious packaging systems. The German Institute for Market Research on Packagingstudied the impacts of replacing PVC with other plastics. It was concluded that thetotal tonnage of single-layered films would remain the same were PVC to be replaced.However, because of the PVC superior barrier properties compared to other plastics,the amount of composite films would increase by 25%. This would result in anincrease of waste production (almost 10% by weight) because composites are difficultto recycle while PVC is molded.

A joint application of Life Cycle Assessment and Energy Synthesis, named EnergyLife Cycle Assessment, is shown to provide information about input and output materialflows as well as about the environmental support to the system, in order to facilitatechoices and policymaking towards Zero Emission Strategies and Techniques. Resultsshow that increasing the complexity of the system as well as the use of co-productshelps to achieve a better performance and an optimum use of available resources. Thecase study is only based in the performance comparison of two power plants, which doesnot entail all the possible ways for complexity increase. In fact, if a plant (or any otherproduction system) is really integated within the local productive structure, it is nolonger just a point source of electricity, hot water and released chemicals. Other cycles


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can be involved (water and wastewater, fuel from urban and biomass waste, use of sulfur from fuel purification, etc.), which could generate further non-negligible eco-nomic and environmental advantages. In order to do this, the input of informationneeded may take the form of landscape planning and alternative option explorationand lead to the construction of infrastructures capable of linking all the possible part-ners involved in co-product/raw material exchange and use. This new framework forthe evaluation of production activities, the so-called Zero Emission Strategy, wasfound to be in very good agreement with Lotka-Odum’s Maximum Power Principle inecosystems. The two strategies/statements are, in principle, equivalent. Zero-emissiontechnologies guide the way human-dominated systems can achieve maximum poweroutput in times of scarce resources, like natural ecosystems have already learned to beover their evolutionary trajectories (Ulgiati et al., 2006).

The Life Cycle Assessment approach was used to determine whether a recycle andre-use strategy for plastics-based packaging system that substantially reduces thequantity of waste to landfill would also reduce its overall environmental burden. Thefollowing conclusions were deduced:

1 the life cycle impacts in all categories examined were less for the proposed EPS-HIPS/PE shrink-wrap packaging than for a present EPS/PE packaging. This is dueto its lighter weight and also to the innovative recycling/re-use strategy for the newpackaging system

2 the life cycle oil consumption for the proposed EPS-HIPS/PE shrink-wrap packag-ing is about one-third less than the present EPS/PE shrink-wrap packaging.However, for both packagings, the consumption of oil accounts for a relativelysmall proportion of the over-all energy consumption

3 both packaging options contribute to photochemical oxidant problems in Sydneyand Melbourne. However, the EPS/PE packaging contributes more nitrogen oxidesand volatile hydrocarbon precursors than the proposed EPS-HIPS/PE packaging andwill therefore have a greater marginal impact

4 recycling or, better still, re-use of plastic products can significantly reduce theenergy required across the life cycle because the high energy inputs needed toprocess the requisite virgin materials greatly exceeds the energy needs of the recy-cling or re-use process steps (Ross and Evans, 2003).

Therefore, if a product requires a large input of energy derived from fossil fuels dur-ing primary production, as is the case for plastic-based products derived from virginmaterials, then recycling is likely to reduce a product system’s environmental burden(Patel et al., 2000). It was also found that the energy consumed during transportationis negligible when compared to the overall energy consumption of the system. This istrue even with the additional transport needs of the recycling and re-use steps. This isimportant, because transport emissions are often cited as a reason for not pursuingrecycling possibilities (Pearce, 1997). The raw material, energy, emissions, waste-water and waste balances are carried out throughout the total life cycle as presented inFigure 15.20 and Figure 15.21.


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1022W

aste Managem

ent for the Food Industries

Sorting

Processing/recycling

Bottle fractionFilm fraction

Hydrogenation

Films tocable

conduits

Collection ofsales

packaging

Householdwaste

Films tofilms

Bottles tobottles

Blastfurnaceprocess

ThermolysisFixed bed

gasificationFluidized bedgasification

Mono-combustion

Wasteincineration

Mixed plastic fraction

Sorting residues

Figure 15.20 Scope of life cycle analysis for mechanical and feedstock recycling processes as well as energy recovery techniques

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Waste M


1023

EnergyRaw materials

AirWater

Solid wastesAir emissions

Water effluentsWaste heat andenergy recovery

Recycling Remanufacturing Product re-use

Materialsprocessing

Raw materialsacquisition

Productmanufacturing

Packaging anddistribution

Product use Disposal

Productive life cycle

Figure 15.21 The life cycle of a product, including clarification of the terms re-use and recycling

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e-addresses

http://www.raymond.com/rates97htmhttp://www.epa.gov/epaoswer/non-hw/muncpl/factbook/internet/mswfhttp://www.britglass.co.uk/recycling/glassrec.htmlhttp://www.britglass.co.uk/recycling/stats97.htmlhttp://www.esp.co.uk./machanical.htmlhttp://www.environment97.org/text/reception/r/techPapers/Papers/g19htmhttp://www.polyrecycling.ch/english/kvs.htmhttp://www.grn.orghttp://www.apme.org./environment/htm/0.4.htmhttp://www.apme.org/environment/htm/sustainable.future.pdfhttp://www.thesite.org.ukhttp://www.world-aluminium.org/applications/index.htmlhttp://www.world-aluminium.org/applications/packaging/index.htmlhttp://container-recycling.org/aluminated/gaphs.htmhttp://europa.eu.int/lib/http://www.plasticsresource.com/s-plasticsresource/docs/1900/1874.pdf


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waste management for the food industries || waste management in food packaging industries

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