characterization of municipal solid waste of borås of msw an… · municipality; carried out on...

This thesis comprises 30 ECTS credits and is a compulsory part in the Master of Science

with a Major in Technology – Resource recovery, 120 ECTS credits

No. 2/2011

Characterization of

municipal solid waste of

Borås

Mitra Kaeni Moghadam

Parima Haji Karimkhani

i

Characterization of municipal solid waste of Borås

MITRA KAENI MOGHADAM, [email protected], [email protected]

PARIMA HAJI KARIMKHANI, [email protected], [email protected]

Master of sience thesis

Subject Category: Technology, Waste to Energy Technology

University College of Borås

School of Engineering

SE-501 90 BORÅS

Telephone +46 033 435 4640

Examiner: Prof. Tobias Richards

Supervisor,name: Prof. Tobias Richards

Supervisor,address: University of Borås, School of Engineering

Telephone: +4633-4354207 Email: [email protected]

Client: Borås Energy och miljö AB

Date: June 4, 2010

Keywords: Waste management, sorting of waste, biogas, combustion, composting,

waste characterization

mailto:[email protected]





ii

Acknowledgment

This project was performed in collaboration between University of Borås and Borås Energi

och Miljö AB. We would like to acknowledge Professor Tobias Richards for being the

examiner and supervisor of this work. We express our appreciation for his patience and

support from the beginning to the last step of doing this project.

We are very grateful to staffs of Borås Energi och Miljö AB for providing us required

facilities and sharing their useful information and experiences about waste collecting system.

More thanks to Hans Skoglunds and Kenneth Oberg to be our coordinators in Borås Energi

och Miljö AB.

Working on this project brought us the chance to get more familiar with actual waste

collecting and handling system in the municipality. It was not very easy to deal and handle

with the garbage, but we achieved valuable information about people habits and behaviour in

waste production, sorting and separating system in the origin. We cannot forget the terrible

and funny memories of doing this project.

We should also express our thanks to the teachers and staffs of School of Engineering in the

University of Borås. We would like also to say thanks to our friend Abas Mohsenzadeh, for

his help in writing the report. Last but not least, we would like to express our great love to our

parents who always support us long away from Iran.

Mitra Kaeni Moghadam

Parima Haji Karimkhani

September 2010

iii

Abstract

By ever-growing of population of the world, introducing new technologies and instruments to

make easier life and improving the standards of living the consumption of natural recourses

and materials are increasing dramatically during last century. As a consequence the amount of

waste is increasing more and more. Handling of this huge amount of waste is one of the most

important issues in urban areas all over the word. But in treating and managing the waste the

environmental and sustainable development aspects should be concerned. Minimizing

material usage, reusing, recycling, energy recovery and landfilling are important steps in

waste management. According to environmental effect, disposing the waste in the landfill is

limited by recent legislation such as the EU landfill Directive (1999/31/EC). The waste

treatment system in Borås which respects all aspects of sustainability can be considered as

state- of- art and is described briefly in this report.

In order to achieve more information about the waste sorting system in Borås, three different

neighbourhoods are selected to investigate their sorting behaviour. The household waste in

these areas is collected randomly in spring 2010 and analyzed into 21 fractions. The results

are compared with the previous study in 2000, some improvement and some declination

happened in these 10 years.

Keywords: Waste management, sorting of waste, biogas, combustion, composting, waste

characterization

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Contents

1. Introduction ...................................................................................................................... 1 1.1 Waste Management ...................................................................................................... 1 1.2 The city of Borås .......................................................................................................... 3 1.3 Waste treatment in Borås ............................................................................................. 3 1.4 Biogas ........................................................................................................................... 6

1.4.1 Process ................................................................................................................ 6 1.4.2 Utilization of biogas for energy purposes ........................................................... 8 1.4.3 Utilization of digestate as fertilizer..................................................................... 8 1.4.4 Incentives and barriers affecting biogas production ........................................... 8 1.4.5 The municipal and industrial sector .................................................................... 9

1.5 Biogas production in Sobacken .................................................................................. 10

2. Methods and Materials .................................................................................................. 12 2.1 Statistical sampling .................................................................................................... 12 2.2 Collection ................................................................................................................... 12 2.3 Description of sampling areas .................................................................................... 12

2.3.1 Hestra ................................................................................................................ 12

2.3.2 Kristineberg ...................................................................................................... 13 2.3.3 Norrby ............................................................................................................... 13

2.4 Pick Analysis .............................................................................................................. 13 2.5 Concepts and definitions ............................................................................................ 14 2.6 Analysis Equipment ................................................................................................... 15

2.7 Errors .......................................................................................................................... 15

3. Results and discussions .................................................................................................. 16 3.1 Scope of study ............................................................................................................ 16

3.2 Waste Proportion ........................................................................................................ 16

3.3 Analyzing of Black Bags ........................................................................................... 17 3.3.1 Contents of Black bags in Hestra...................................................................... 18

3.3.2 Contents of Black bags in Kiristineberg ........................................................... 18 3.3.3 Contents of Black bags in Norrby .................................................................... 19

3.4 Analyzing of white bags............................................................................................. 20

3.5 Classifying the content of the white bags .................................................................. 21 3.5.1 Classifying the fractions according to manual sorting in houses ..................... 21 3.5.2 Classifying the fractions according to energy recovery values ........................ 23

3.6 Share of each fraction in total household waste ......................................................... 25

4. Comparing results with the previous study ................................................................. 27 4.1 Comparing the weight of bags ................................................................................... 27

4.2 Comparing classification of fractions ........................................................................ 27

5. Conclusions ..................................................................................................................... 30

1

1. Introduction

This report is a study of household waste from three selected neighborhood in Borås

Municipality; carried out on cooperation between Borås energy öch miljo and the University

of Borås. The Project aims to find the characterization of the households‟ wastes of

municipality of Borås by analyzing the household waste of three selected area representing

good, moderate and bad area in accordance of sorting wastes. This survey is part of a larger

project relating to an evaluation of the black and with bags sorting system in Borås completed

in 2000.

This study includes analysis of household waste of three areas during the spring of 2010,

weeks 14-21. The content of the bags are sorted into 21 fractions to quantify the purity of

black bags, organic fraction in white bags, recycling rate of food packaging and presence of

loose waste. Furthermore, comparing the results with previous work to study the changes and

possible improvements is the other goal of this work.

The previous survey conducted the similar method. This allows a comparison between this

and the previous one, but with some caution in the interpretation; because of some differences

and changes during these 10 years.

The study covers only waste and materials found in waste bins that sanitation‟s staffs

collected from selected area. So, hazardous, chemical and bulky waste collecting at recycling

center or the producer responsibility waste collecting in recycling stations such as paper,

glasses, metal packaging and newspaper are not included.

1.1 Waste Management

By rapid growing of waste production worldwide, treating various streams of waste e.g.

industrial, agricultural and household waste become serious issues for each municipality[1].

The word ‟waste‟ is used to define that ”the substance is not used to its full potential” any

more. By proper treating the substance labelled waste can be change to resource of another

material cycle [2].

For waste treatment, sustainable and environmental friendly methods should be applied to

minimize the environmental impact of waste. The waste hierarchy explains different options

for waste managing system according to their favourability. 3Rs in waste hierarchy (Figure 1)

Reduce, Reuse and Recycle, show the main strategies in waste management regarding to their

importance and desirability[1-2].

2

Figure 1. Waste-hierarchy [3].

Reusing and recycling is the first priority of waste processing. Fuel production and energy

recovery comes after and at the last choice, when there is no other option; some waste such as

hazardous waste can go for waste disposal [4].

According to definition of infra structure, services to improve a system, waste management is

one of the public infra structure to transit the undesired streams labelled “waste” into

desirable materials, renewable fuel, power, electricity and fertilizer.

Very common steps in waste treating organization are collecting from waste production

location, transporting to pre-treating or processing facility, and disposing the remained part.

The waste can be compressed, sorted, separated, dried, packed or stored in pre-treatment step

and get ready for future processing or transportation. It is very common to collect the

household waste once a week in Europe and it depends on the amount of waste production per

inhabitant in that area and waste collection facilities of municipality [5].

These steps should be ordered in sustainable and low environmental impact manner to recover

materials and energy as much as possible and disposing to landfill as less as possible.

Reducing the amount of waste going to landfill and converting the disposals to fuel for

production of power, heat and vehicle fuels demands governments supports, national and

international legislation such as the EU Landfill Directive (1999/31/EC) [5-6]. According to

this agreement disposing of organic waste should be reduced to 75% till 2010, to 50% till

2013 and finally to 35% till 2020, as compared to 1995 levels [6-7].

Converting Waste To Energy (WTE) by thermal treatment (i.e., incineration and gasification)

results in both energy recovery and landfill reduction. In these methods waste is used as

alternative fuels to produce heat, power and electricity. Different kind of solid waste, such as

textile, plastic, biomass and from both municipal and industrial waste stream can be used for

this propose. The waste treatment facility should be designed to fulfil both environmental and

economical desires [1]. Waste treatment trends in different European countries are shown in

Figure 2.

3

Figure 2. Municipal solid waste treatment in European countries in 2007 [1].

1.2 The city of Borås

Borås is located in the south west of Sweden and “was founded by king Gustav II Adolf in

1621” [8]. There are 33 000 households, apartments and houses, in the city with 100 000

inhabitants consisting of Swedish, foreigner students and immigrants [9].

Sobacken the waste management facility of Borås was founded in 1992 and located in sout of

the city. The organization is owned and operated by “Borås Energi och Miljö AB” (BEM) and

is responsible for handling and taking care of industrial and municipal solid waste of the city

[9]. In 2005, the amount of 49000 tones of municipal waste from Borås and surrounding were

treated [5]. Borås Energi och Miljö AB owned by the municipality of Borås and is responsible

to produce district heating, cooling and electricity in the municipality of Borås. BEM has 150

employee, with annual turnover of MSEK 650, and annual production of 650 GWh of district

heating, 8 GWh of district cooling, 11 GWh of Biogas and 180 GWh of electricity [9].

1.3 Waste treatment in Borås

The household wastes in Borås are expected to be sorted in origin. The people should sort

their household waste in kitchens, yards and houses. At the beginning this system started in

small scale (3000 houses) in the late 1980‟s, and after being successful it covered the whole

city. According to Table 1, typical household waste consist of food waste, food packaging

waste, paper, cardboard, backyard and garden waste, electronic waste, chemical and

hazardous waste, cloths and textiles, used kitchen stuffs and furniture. There are different

waste stations for different kind of waste in the city.

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Table 1. Components of household waste stream [10]

Component Contribution

(percentage) News paper/ Magazines 18

Paper/ Cardboard 20

Plastic 4.5

Dense Plastic 4.2

Textile/Leather 3.3

Glass 5.8

Vegetable waste 20.2

Metal/Iron 5.7

Metal/Aluminium 1.0

Wood/Yard Waste 7.3

Grit. Dirt, Misc 10.0

Rubber tires N.A

In Sweden, there are producer responsibility for different kinds of packaging and newspapers.

This means that anyone who manufactures imports or sells packaging or packaged goods are

responsible for collection and recycling them. Producer responsibility formed to contribute a

sustainable society, by replacing materials which previously considered as waste to be useful

as a resource.

Today‟s Borås Energi och miljö manages approximately 80 recycling facilities for collecting

the packaging with producer reasonability. There are six-chamber-recycling stations in each

neighborhood for recycling newspaper, paper, plastic, glass and metal packaging. And also

boxes for collecting small batteries [11].

There are five recycling centers in Borås. Two of them are in Borås, while the others are in

Viskafors, Dalsjöfors and Fristad. These centers are responsible for collecting Electronic

waste, hazardous waste, bulky waste, used furniture and landfill fraction. People are

responsible to carry these types of waste to these stations during opening hours.

The household waste should be sorted in black and white plastic bags in origin (kitchen and

houses). These white and black bags are ordered by Sobacken and produced from recycled

plastic materials. The bags are designed for household waste and distributed free in whole

municipality of Borås. They are in different sizes and can be knotted easily and properly to

prevent loose waste in bins. The black bags are only for food waste. In the past people were

asked to put compostable waste in black bags, but from 2005 only food waste should be

placed in the black bags. The remained part of household waste which, is mostly combustible

materials goes to the white bags.

The black and white bags should be put in the same wheeled refuse bins (for the villas),

especial deposing chambers (for the blocks) or disposal chutes. Schematic of municipal solid

waste collection in Borås is illustrated in Figure 3.

5

Figure 3. Schematic of municipal solid waste collection in Borås [9].

The waste are collected from different areas once or twice a week, or every second week

according to number of inhabitants, production rate of waste in each neighbourhoods and

disposal chambers capacity.

After delivering and loading bags to the production plant in Sobacken, they are sorted to

white and black groups by an optical scanner. Bags with other color than black are considered

as combustible waste [5, 9, 12].

Each group goes to a different processing line. Both biological and thermal treatments are

carried out in Sobacken. Black bags go for biological treatment and fuel production, while the

white ones go or thermal treatment and energy recovery.

Black plastic bags are opened by some knives and blades. The food wastes go to biogas

digester reactor by means of belt; and convert to biogas as a green fuel for public transport.

After biogas production, the digestate, remained solid parts in the digester, centrifuged to

reduce the amount of water, processed in sequencing batch reactor to remove extra amount of

Nitrogen, deride and screened to produce fertilizers and construction materials.

The white bags are also opened by knives and pressing, shredded to small pieces less than

100mm in a hammer mill, packed and wrapped to be ready for combusting in Borås och

Energy Miljö furnaces, to produce district heating and cooling. The Rya plant was built by

Metso Power in 2005 and has two bubbling fluidized-bed boilers. Each boiler can burn 7

6

tonnes of waste per hour and produce 5MW of electricity. The total capacity of the waste

combustion is 40 MW.

The feed of Borås power plant consist of 70% of industrial waste and the rest are household

combustible waste. Pretreatment process is needed to remove metals and inert materials from

feed stream.

In 2005, 100 000 tonnes of waste was burnt to produce heat and power. By using bag filter

and dry flu gas treatment system, the flue gases are cleaned, and the emossions of the process

are low.

Borås is a pioneer city to convert the waste to the source of energy in both biological and

thermal processing. Biogas production, converting the disposal waste to renewable green

fuel, is very interesting from environmental point view [5, 9, 12].

1.4 Biogas

Considered as a renewable high-quality fuel, biogas is produced as by more than 200 plants in

Sweden. Using biogas production systems reduces emissions of greenhouse gases,

eutrophication, air pollution and improves utilization of crop nutrients. Therefore, compared

to current waste handling methods, using biogas production systems leads to significant

improvements concerning resource efficiency and environmental impacts. A wide range of

raw materials, from organic waste to dedicated energy crops, can be used as feedstock for the

biogas production. Therefore, a number of different barriers and incentives, including energy,

waste treatment and agricultural policies, affects on the biogas production systems. These

incentives and barriers are divided into two categories: those affecting the biogas production,

and those affecting the biogas utilization. While a few types of biogas production systems are

competitive, the majority of them needs increased incentives of different kinds to reach

profitability in Sweden today. Energy, environmental and sustainability issues concerns

motivate these incentives. Concerted efforts are required for the process of implementing

adequate policy instruments. As well as national policies in Sweden, these concerns are

expressed in international such as the Kyoto Protocol which was negotiated within the United

Nations, and the policy documents which have been issued by the European Union regarding

renewable sources of energy, security of energy supply, alternative fuels for road

transportation and green house gas emissions etc.

Furthermore, increase in prices of fossil fuels together with political incentives will improve

competitiveness for biogas production systems in the near future.

1.4.1 Process

Biogas is produced when the organic materials are degraded in absence of oxygen (anaerobic

digestion) by microorganisms. A wide range of raw materials, from organic waste to

dedicated energy crops, can be used as feedstock for the biogas production. As well as small

farm-based units digesting local agricultural feedstocks, large plants using a wide range of

different feedstocks are employed for biogas production (Figure 4)

7

Figure 4. Overview of the biogas systems applied in Sweden [13].

The produced biogas consists of methane (50–80%), carbon dioxide (20–50%) and traces of

hydrogen sulphide (0–0.4%). Besides producing biogas, the added feedstock is transformed

into digestate by anaerobic digestion which can be used as fertilizer in crop production. This

digestate consists of all the non-degradable substances present in the original feedstock. Thus,

plant nutrients remain in the digestate. It should be regarded that any non-biodegradable

contamination in the feedstock will remain in the digestate. In Sweden, almost 60% (3

PJ/year) of the total amount of biogas is produced at biogas plants which are located at

municipal waste water treatment plants. Over the last decades, these biogas plants were built

mainly for stabilizing the sludge. Also, 30% (1.5 PJ/year) of the total biogas is produced in

landfills which contains higher levels of impurities than is normal for biogas. However the

biogas obtained from landfill could be used for energy production, the main purpose of

landfill gas is the reduction of methane emission which is a highly potent green house gas. It

should be noted that biogas production in land fill does not lead to digestate production since

the feedstock is the landfill itself. Industrial organic waste, e.g. from the food industry, has the

potential to produce (3.3 PJ/year) biogas, but approximately 10% of total potential production

is produced at present. The potential of biogas production from urban parks and gardens

organic waste is estimated to be 1.7 PJ. Totally, the contribution of municipalities and

industry wastes is estimated to be 12 PJ of which more than half is unemployed [13]. In

Sweden, the reactor technology of choice is slurry-based tank reactors fed with liquid or

homogenized and diluted feedstock. Liquid feeds with a high particulate content (e.g. manure

and sewage sludge) need no or only simple pretreatment before being diluted. But food

industry waste and restaurant waste should be processed by „„wet‟‟ method. Currently co-

digestion is implemented at 10 biogas plants in Sweden. A quick expansion of the biogas

production through increased co-digestion is possible because the biogas plants located at the

municipal wastewater treatment plants are often over-dimensioned. Furthermore, the slurry

digestion process can be improved. For example, high- temperature digestion (thermophilic)

and enhanced monitoring and control could be implemented. Becoming viable financially,

wet, anaerobic digestion systems which are used currently need centralized and full scale

concepts. Also, state subsidies are needed over a longer period of time to develop the

technology for new feedstocks.

The dry technology is implemented to treat solid feedstocks which require a more costly pre-

treatment in to be slurred, or those which cause process problems such as crust and scum

formation. Currently, the dry digestion in case of municipal solid waste is a proper process

with a variety of available reactor designs. Also, the economy of the process is improved by

the implementation on a farm-scale of innovative and yet simple reactor technology.

8

However, its market share is still limited; the technology commercially available in Europe is

a batch digestion in which the solid feedstock is loaded into several sequentially started

reactor cells [13].

1.4.2 Utilization of biogas for energy purposes

Nowadays produced biogas is employed for the production of heat, CHP, vehicle fuel and

injection into the gas grid. The latter case is yet limited. The biogas is simply flared in some

cases that the energy production is not the main aim such as landfills and in some older

sewage plants. The interest in using of the energy content of biogas has regained recently due

to increase in energy prices and environmental issues. The vehicle fuel production has

increased from 3TJ (in 1996) to almost 500 TJ (in 2004) which is 10% of the current total

biogas production (equals to 0.2% of Sweden‟s total use of petrol and diesel). Often, it is

possible to use an adapted form of technology to produce heat in large as well as small

boilers. Requiring no or limited gas treatment, these boilers developed for natural gas with a

minimum of adjustments. There is a wide range of technologies available regarding CHP such

as converted diesel engines (dual-fuel), gas turbines and Stirling engines. Under current

conditions, the large scale applications are more economical regarding the troubles

concerning the usage of the produced heat. Biogas used as the vehicle fuel produced via two

types of technologies; namely gas upgrading and gas vehicles. The technology employed for

biogas upgrading is being developed for example improving the methods and concerning the

scale for economic feasibility [13].

1.4.3 Utilization of digestate as fertilizer

From the economic and the practical point of view, making use of digestate as fertilizer in

agriculture is essential for developing biogas systems. Thus, a general acceptance for this

should be among farmers, the food industry, consumers and other actors involved. Due to

frequent alarm reports that it contains undesirable substances, there has been a debate on the

agricultural utilization of sewage sludge from wastewater treatment plants in Sweden.

Consequently, the Federation of Swedish Farmers has recommended that the members should

not utilize the sewage sludge as fertilizer in food and fodder crop production. Thus, a clear

distinction has been developed between the sewage sludge and digestate in certification

criterions and legislation for the agricultural use of these products regarding these historical

obstacles. Also, a set of rules and voluntary agreements accepted such as controlling of the

feedstocks origin and content, managing the digestion process and sanitation of the feedstock

[13].

1.4.4 Incentives and barriers affecting biogas production

In Sweden, the potential expansion of biogas systems is influenced by a number of factors

regarding energy supply, environmental goals and sustainability issues expressed in various

policies. The Swedish parliament, on national level, has agreed on 15 national, environmental,

quality objectives such as limited influence on climate change, natural acidification only and

zero eutrophication. Except those are regarding climate change, each objective is meant to be

achieved by the year 2020. Without the implementation of appropriate policies such as taxes,

subsidies and regulations, international and national objectives and activities have a limited

effect.

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1.4.5 The municipal and industrial sector

During the recent years waste treatment has been drastically under discussion especially in

modern countries. Released statistics show that in 2004, municipal solid waste was chiefly

handled by incineration (47%), material recirculation (33%) and landfilling (9%). Apart from

aforesaid treatment methods, roughly 10% of waste generated by municipalities was treated

biologically by anaerobic digestion (1/5) and composting (4/5).

However, there are various competitive treatment methods in hand among those incineration

is most preferred in Sweden. Even though incineration has acted as an obstacle to biogas

production, its counteractive effect on biogas production is on the decline on account of a

proposed taxation policy on the fossil fraction of incinerated waste. Such taxes are imposed

with the intention of promoting biological waste treatment methods.

The tendency to biological treatment was strengthened more than ever after setting a

provisional target as a national environmental objective, stating that 35% of municipal food

waste and all uncontaminated food waste from food industries should be treated biologically

by the year 2010.

According to the target, considering the fact that in 2004 only 20% of all municipal food

waste went through the biological treatment, therefore, by 2010 the amount of biologically

treated waste must undergo an increase by 75% in order to accomplish the target [14].

Composting could be defined as another blockade to biological treatment. However,

composting cannot dramatically hinder the promotion of biological treatment owing to

detrimental emissions of ammonia, methane and nitrous oxide which are said to be inevitable

during composting.

According to a report, in 1999 [15], the net treatment cost for organic food processing waste

in centralized biogas plants in Denmark was estimated to be 1.4 € /ton (exchange rate 1€ = 7.7

DKK). It was assumed that the feed consists of 20% waste and 80% manure. At the time in

question, the gate fees charged at centralized biogas plants were 7–8 € /ton compared to 26–

39 € /ton for waste that was incinerated. Therefore, under Danish conditions, waste treatment

in centralized biogas plants was extremely favorable. In Sweden, waste treatment in

centralized biogas plants is probably very favorable for the biogas plants when the gate fees

charged for industrial waste in Sweden with those charged in Denmark are compared.

Increasing the biogas production capacity and competition make treatment within biogas

plants more favorable for the different waste producers. This may lead to reduced gate fees

[13].

Choosing a specific kind of waste treatment for individual companies and industries is

influenced by the gate fees charged by the waste treatment plants. Since in Sweden the gate

fees charged for incineration of industrial waste are based on negotiations, they are normally

not publicly available. However, a gate fee is charged for incineration of slaughterhouse

waste of 43 € /ton compared to 4–32 € /ton for slaughterhouse waste treated in centralized

biogas plants (RVF, 2005b) (exchange rate, 1 € = 9.3 SEK). The gate fees charged for

incineration of municipal waste are 27–54 € /ton compared to 43–80 € /ton for municipal

waste treated in the centralized biogas plants. Currently there are no economic incentives to

persuade waste companies to deliver municipal organic waste to centralized biogas plants

because the municipal waste is separated at source in centralized biogas plants [13, 15].

10

1.5 Biogas production in Sobacken

In 1995, Borås started to produce biogas from waste. Although the first processing plant was

not successful, but by applying some improvements and using a one-stage thermophilic

process, it continued to produce fuel and in 2004, 30 000 tonnes of biodegradable waste was

successfully converted to biogas. There are different feedstocks that can be operated in this

system:

Solid food waste from restaurants and food factories

Liquid waste

Liquid waste from slaughter houses (After being sterilized in 70°C)

Household waste

There are plastic bags and other inert material in domestic and solid food waste which should

be removed from these waste streams in pre-treatment unit. These materials might cause

mechanical problems in future processing of the sludge.

The plastic bags containing food waste are opened by means of knives and blades, and by

addition of water, separation of inert materials takes place by gravity. Small pieces of metals,

stones and other hard and heavy materials settle down and the light plastic bags stay at top. As

illustrated in Figure 5, The mixture of food waste and water are pumped to a storage tank.

Every day about 100 m3 of waste from the storage tank are fed into the digester and the same

amount of digestate is pumped out. Digester has a volume of about 3000 m3.

To ensure that

the Sobacken biogas plant is no disease-causing all material in the digester are heated to at

least 52 ° C during 10 hours. The environment in the digester is anaerobic and decomposition

of the material takes place in a complex interaction between different micro-organisms.The

micro-organisms work in various stages and the final product, methane gas, is formed by

specialist methanogenesis. The mixture of gases, called raw gas, contains mainly methane and

carbon dioxide [9, 13].

Figure 5. Pre-treatment of biogas production in Sobacken

11

By increasing the degradation rate of feed over 70%, about 15 000 tonnes of waste processed

to produce 1.1 million Nm3 of raw biogas in 2005. The raw biogas is compressed and treated

to be suitable as vehicle fuel in public transportation.

In Figure 6 different methods and strategies that are used to treat and process different waste

streams from whole municipality come to Sobacken is schematically illustrated.

Figure 6. Different waste streams management in Borås [9].

.

There are four biogas stations to distribute the produced biogas in Borås; which one of them is

located in Sobacken for Borås Energy och Milijö‟s vehicles. Nowadays, 40 busses and 10

waste collecting vehicles use the biogas produced from waste [5, 9].

12

2. Methods and Materials

2.1 Statistical sampling

Three different residential areas were selected to represent the various types of

accommodations, villa and apartment buildings, and various types of sorting / handling of

waste according to a previous sorting study: one good, one moderately and one bad area [16].

The selection unit is wheeled bin, for both houses and apartment blocks. Independent random

sample (IRS) is used for villas and houses, and stratified sampling used for apartment

buildings where each flat constitutes a stratum. If filling in a wheeled bin is less than 50% is

not representative of the multi-housing unit. Instead, another bin was selected randomly.

This study provides answers to how households in three neighborhoods, representing different

categories, sort their waste. By making this division we can receive more detailed knowledge

of waste generation comparing to the information which can be achieved by an unbound

random sampling of the whole municipality. With the survey results as a basis, there is

possibility to do further calculations to the entire municipality of Borås, but not the precise

one.

2.2 Collection

Collection of samples takes place early in the morning before regular collection. Garbage

bags discharge in paper bags labeled with the area code. In most of apartment blocks area

samples have been collected from the waste bins. The volume of all waste in area has

recorded, so an approximate of total volume can be calculated. In villas area samples have

been collected from the bins.

2.3 Description of sampling areas

Three neighborhoods have been chosen on the criterion to create an image of how waste

separation works in Borås. The selected neighborhoods, Hestra, Kristineberg and Norrby,

represent different categories of accommodations and different types of problems that might

arise from the establishment of the source sorting system. These three areas are the same areas

as in previous work [16]. They are selected to represent different categories of waste sorting

in a city. Therefore, they cannot used as statistical representativeness of the whole

municipality of Borås. There are some limitations to use the survey results of calculations of

the outcome for the entire municipality.

2.3.1 Hestra

Hestra is a villa area in the outskirts of Borås mostly 121 houses mostly built in 1980-90.

Approximately 80% of them have 130-liter waste bin and the others have 190-liter waste bin.

Bins are emptied every two weeks in this area. A small number of households reporting that

they compost their food waste. The nearest recycling center is located just over 1 km into the

center of Borås.

13

2.3.2 Kristineberg

In Kristineberg, many of 70‟s Residential are leading into this area with a central road and it

has tall apartment buildings and short ones. Four of these short buildings, with 11-13

staircases and 5-9 apartments per staircase, totally 330 apartments are included in the study.

The houses have refuse disposal chutes, with either a 400 or 600-liter waste bins. Bins are

emptied once a week. In the central area, 200 m away from short buildings, is a small

recycling facilities is located and 400 m away, at the entrance to the area, there is a complete

recycling center.

2.3.3 Norrby

Norrby has mainly houses from 70's residential; three blocks of flats are under study. Each

house has two staircases with refuse disposal chutes. The garbage room is equipped with four

pieces of 600-liter garbage bins. The bins are emptied once a week .The distance from there to

the nearest recycling station is about 200 m. In total, the survey consists of 155 households

which is major part of immigrants‟ families; they include crowded and big households, in

single and small households.

2.4 Pick Analysis

The ccollection analysis was preceded by weighing the bags using an electronic wave balance

(Tanita, max. 50 kg) with a measurement accuracy of 50 grams as a control measure. Weights

and other information was recorded manually on prepared forms. The address and date of

collecting the samples were recorded in the forms. The numbers of black and white bags

were counted, and the weights of loose weight were recorded. Then all white bags of each

wheeled big bins were opened, analyzed and sorted into 21 smaller bins in order to analyze

the waste into 21 different fractions. Afterwards, the weight of each fraction was calculated

by weighting the small bins. The same procedure was repeated for black bags.

Collection analysis follows the following order:

• Count the number of black and white bags

• Weight the black and white bags

• Weight loose waste and sort into 21 fractions.

• Open the white bags, analyze and sort into 21 fractions.

• Open the black bags, analyze and sort into 21 fractions.

• Weigh bags for each fraction afterwards they become filled.

14

2.5 Concepts and definitions

The following 21 fractions are used in the study for the analysis of waste bags:

Hard Plastic Packaging of more than 50% of hard plastic. Hard plastic

can be bent or broken. This also includes plastic cutlery,

plastic cups and medical charts

Soft Plastic Bags and packaging of more than 50% soft plastic

Paper Writing paper, books, magazines, brochures, catalogues,

advertising, envelopes, receipts / invoices and etc

Paper packaging Packaging of more than 50% paper

Tetra Pack Packaging Multi-layers paper packaging for drinks and liquids.

Other Food packaging Multi-layers packaging, foam and plastic packaging in

which there was doubt about which plastics faction they

belonged.

PET Bottle of PET with Deposit. Plastic bottles without a

deposit belonging to hard plastics

Diapers and Tissues Baby diapers, adult diapers, sanitary towels and tampons,

tissues and napkins

Metal Packaging Packaging of over 50% metal. Metal that is not packing

fraction belonging to scrap

Metal Packaging with Deposit Metal packaging with deposit which are mostly beverage

and beer cans.

Glass packaging Packaging made of glass, drinking glasses, glass bowls,

window glass, etc.

Glass packaging with Deposit Glass bottles with deposit.

Metals scarp Metals which are not packaging such as nail, aluminium

foil, etc.

Combustible Waste that burns without fuel addition; such as vacuum

cleaner bags, towels, highly contaminated plastic or paper

containers, wood, sticks, textiles and other combustible

waste. Plastic which is not a package is placed in

combustible waste. Tea bags and filters of coffee maker

machines are placed in this group too.

Food Waste Only food and cooking residues, potted plants, pickling

liquid in glass, plastic or metal containers.

Electronic Waste Electrical and electronic equipment.

Hazardous Waste Waste that is classified as hazardous under the Regulation

(1996:971) on hazardous waste. Chemical, medicine and

drugs paint and colour.

Bulb Light bulbs, Fluorescent lamps are placed in hazardous

waste

Batteries Different kind of batteries and also the packaging of the

waste and electronic equipment containing batteries.

Cardboard Corrugated board and cartons.

Other materials Waste which goes to landfill such as porcelain, ceramics,

glass, cat litter, stones and gravel

15

There are some expressions and abbreviations used in this report that are explained as

following:

Black bags, black bags for food waste

White bags, white or colored bags for other waste, i.e. non-black bags

kg / hh / v kg per household per week

2.6 Analysis Equipment

Following instruments and software programme are used in this study:

Electronic Scale, TANITA model BSE, capacity 50 kg ± 0.05 kg

Software EXCEL 2010 for random number generation

2.7 Errors

Like all other systems and experiments, there are several source of unavoidable errors in this

study as explained below:

Systematic Error (Instrumental error)

This error is related to the means of measurement, for example if the scale device was

not regulated properly and shows higher or lower amount.

Personal Errors

Physical and mental conditions cause this kind of error. Some examples of personal

error in this study are probable neglecting in using the measurement devices properly

or reading of numbers correctly, or neglecting to sort or count the loos waste which

was produced in opening of bags and sorting them. Another personal error in this

study is neglecting the amount of food waste sticking in packaging and was difficult to

remove. Mistakes in calculation belong to this group as well.

Sampling error or estimation error:

This kind of error causes by observing a sample instead of the whole population, same

case in this study.

Random error

This error caused by uncontrollable and random effects in measured results across a

sample. [16]

16

3. Results and discussions

3.1 Scope of study

During week 14-21 the waste samples from the three selected areas in Borås were collected.

Since there is no long holiday or any national day during this period of time, waste generation

during this season are stable and can be considered generally acceptable for most of the year.

About 2450 kg of waste which is equal to about 20 m3

were analyzed and sorted to 21

fractions. More information about the total weight of collected samples and individual weight

of white and black bags from each area is presented in Table 2.

Table 2. Collected samples in the different areas

Hestra

(Kg)

Kristineberg

(Kg)

Norrby

(Kg) Black Bags White Bags Black Bags White Bags Black Bags White Bags

Number 273 501 239 607 259 582

Weight 370.25 436.24 252.08 517.55 317.63 545.61

Total Weight 809.09 770.40 870.56

3.2 Waste Proportion

The proportions of the waste generation based on weight are shown in Table 3 for each area.

Hestra has a rather low amount of waste to be a residential area with a household size of 3.1

persons / household. Because usually people are not at home during the day and they eat out,

and of course good recycling rate in this area is another reason. The slightly high amount of

waste of Norrby probably can be explained by an inverse explanation.

Table 3. Waste Proportion of three selected areas

Hestra

(Kg)

Kristineberg

(Kg)

Norrby

(Kg) White Bags 53.92% 67.18% 62.67%

Black Bags 45.76% 32.72% 36.49%

Loose Waste 0.32% 0.10% 0.84%

Loose waste is probably caused by the unknotted bags discarded in the garbage, which in this

case mainly stripped because of their heavy content. The loose wastes were consisting of

different materials in different areas. In Hestra was mostly paper and hard plastic, in

Kristineberg other food packaging, glass and paper, while in Norrby it was consisting of

combustible fraction, diapers and papers.

The average weight of plastic bags are calculated and shown in Table 4 . According to this,

the weight of the black bags is higher than white bags. This is because food waste has a

higher density and this represents the largest fraction of the waste. The weight of the bags

differs somewhat between regions, which mostly depends on two factors, recycling rate, and

17

the way to dispose the waste. An easier and more convenient to dispose the waste results in

less weight of each individual bag. The higher weight of white bags in Norrby is an

indication of lower sorting rate in this area and higher amount of food waste with higher

density putting incorrectly in white bags.

Table 4. Average weight of the collected plastic bags

Hestra

(Kg)

Kristineberg

(Kg)

Norrby

(Kg) White Bags 0.87 0.85 0.94

Black Bags 1.36 1.05 1.23

3.3 Analyzing of Black Bags

Interfering extraneous materials in the black bag, such as glass and metal and cat litter,

causing wear and operating problems in the biogas plant, and also degrade the quality of the

finished compost soil. To get a measure of the extent of the problems, the black bags were

inspected and sorted into 21 Fractions. The results are given in Table 5.

Table 5. Contents of black bags in different areas

Hestra Kristineberg Norrby

Hard Plastic 0.14% 0.55% 1.32%

Soft Plastic 0.37% 1.22% 2.52%

Paper 0.33% 1.51% 2.68%

Paper packaging 0.11% 0.70% 0.73%

Tetra Pack Packaging 0.00% 0.37% 0.69%

Other Food packaging 0.07% 0.32% 0.63%

PET 0.00% 0.00% 0.03%

Diapers and Tissues 4.16% 6.00% 9.92%

Metal Packaging 0.00% 0.34% 0.54%

Metal Packaging with Deposit 0.00% 0.28% 0.13%

Glass packaging 0.00% 1.83% 1.41%

Glass packaging with Deposit 0.00% 0.00% 0.00%

Metals scarp 0.01% 0.12% 0.07%

Combustible 4.96% 1.94% 2.90%

Food Waste 89.73% 79.32% 75.48%

Electronic Waste 0.00% 0.09% 0.00%

Hazardous Waste 0.00% 0.00% 0.00%

Bulb 0.00% 0.02% 0.02%

Batteries 0.00% 0.01% 0.02%

Cardboard 0.04% 0.06% 0.62%

Other materials 0.00% 5.13% 0.14%

Weight of plastic bags 0.07% 0.19% 0.16%

18

3.3.1 Contents of Black bags in Hestra

Total amount of impurities in black bag of Hestra is 10 percent which is acceptable. As

illustrated in Figure 7, the impurities were mostly diapers and tissues (4%) and combustible

materials (5%). The combustible part consisted of tea bags and coffee filters (filter and coffee

residual together). These materials are biodegradable and they do not despoil the quality of

compost. In the past the black bag was for compostable materials and people were allowed to

put tissues, tea bags and coffee filters in it. But since 2005, to improve the quality of produced

compost and avoid mechanical problems in bio gas producing process, the name and contents

of black bags were changed, only food waste are expected to place in black bags.

No hazardous waste, batteries or bulbs are found in black bags, and only 1% belongs to

different kind of packaging. There were considerable numbers of black bag which were sorted

completely correct.

Diapers &

Tissues

4% Combustible

5%

Food Waste

90%

Hestra

Figure 7.Contents of Black bags in Hestra.

3.3.2 Contents of Black bags in Kiristineberg

Total amount of impurities in black bag of Hestra is 20 percent which is fairly acceptable. As

illustrated in Figure 8, the varieties of impurities in black bags are more in comparison with

the case in Hestra. The share of diapers and tissues is 6 percent; the considerable amount of 5

percent of other materials was because of presence of cat litter sands which were wrongly

sorted in black bags. The same as previous area, the combustible part mostly consisted of tea

bags and coffee filters (filter and coffee residual together). Some batteries and bulbs are found

in black bags, although the amount is very small (0,03%) but the heavy metals in these

materials may despoil the quality of final compost or have some impacts in biogas production.

19

Hard

Plastic

1%

Soft

Plastic

1%

Paper

2%

Paper packaging

1%

Diapers &

Tissues

6%

Glass packaging:

2%

Food Waste

79,32%

Combustible

2%

Other

materials:

5%

Kristineberg

Figure 8. Contents of Black bags in Kiristineberg.

3.3.3 Contents of Black bags in Norrby

As shown in Figure 9, there are 25% of impurities and materials that are wrongly placed in

black bags in Norrby. The presence of high amount of diapers and tissues (10%) in black bags

in this area is an evidence of poor sorting rate. All kind of materials and packaging except

hazardous material were found in the black bags. The presence of heavy metals in bulbs and

batteries may affect the further processing.

Figure 9. Contents of Black bags in Norrby.

20

3.4 Analyzing of white bags

The results of analyzing and sorting the contents of white bags in to 21 fractions are presented

in Table 6 and Figure 10.

The proportion of food waste in white bags is about 15% in Hestra which can be considered

acceptable. The food waste fraction is mostly consisting of foods stack to the packaging such

as jam, margarine, fast food, etc. On the other hand, one third of the contents of white bags in

Norrby consist of food waste. In a comparison with the previous study Norrby still represents

the category of bad area. Most white bags contain some food waste and there are very few of

them that contain only combustible waste.

According to previous study, the share of diapers in bags reflects the density of children in

each area. Adult diapers and feminine hygiene products are also placed in the diapers

fractions but the main proportion belonged to infant diapers.

Table 6. Contents of white bags in different areas


Hard Plastic 7.24% 4.83% 4.06%

Soft Plastic 5.91% 4.79% 5.55%

Paper 7.01% 10.36% 9.35%




PET 0.03% 0.14% 0.21%






Metals scarp 1.89% 1.03% 0.80%

Combustible 20.58% 6.92% 10.69%

Food Waste 13.85% 27.13% 32.86%



Bulb 0.07% 0.04% 0.04%

Batteries 0.06% 0.08% 0.08%

Cardboard 1.23% 2.28% 2.09%



21

Figure 10. Contents of white bags in different areas

3.5 Classifying the content of the white bags

Analyzing the wastes into 21 fractions gives the opportunity to know detailed information

about the characterization and chemical fractions of household waste. But by classifying the

fractions to small number of groups, the results can be more transparent and comparable. The

classification can be done according to different properties and characterizations of materials.

Regarding to waste hierarchy, after reusing, recycling is the most important method in waste

management. Afterwards waste can be considered as source of energy.

3.5.1 Classifying the fractions according to manual sorting in houses

Current developments in technology make the industry to be able to recycle and reuse the

waste- materials losing their desire properties- in new material cycle. Materials made of glass,

plastic, metal and paper are recyclable with available technology. Producers are responsible to

recycle these products.

Although some products and materials are recyclable, but in the classification of different

fractions, the actual satiation of sorting the waste in household by ordinary people with little

information about the recyclability of materials should be considers. The classification should

be also simple and trouble free. Following factors affect the sorting system in households:

22

Some stuffs and packaging have complex structure and are made of several different

materials that make doubt and uncertainty to put them in which recycling fraction.

These are placed in other food packaging and other material fraction in this study.

People are more informed and requested to recycle the packaging. So they care more

about sorting different kind of packaging and newspaper instead of sorting their waste

according to material sorting.

People always prefer to select the simplest way of dealing with waste.

Considering all above mentioned items, 21 fractions of wastes can be classified in to

following 4 groups according to manual sorting and recycling knowledge of ordinary people.

Recyclable (recycling at recycle stations and recycle centers) includes hard plastic,

Soft plastic, paper, paper packaging, tetra pack packaging, cardboard, metal

packaging, metal packaging with deposit, glass packaging, glass packaging with

deposit, PET bottle packaging with deposit and electronic waste fractions

Food Waste (putting in black bags) includes food waste fraction.

Hazardous waste (should always take care to avoid environmental impacts) and

includes hazardous waste, bulbs and batteries fractions.

Other waste or combustible waste (putting in white bags) includes diapers and tissues,

metal scraps, combustible, other materials, and other food packaging fractions.

The classification schematically is explained in Table 7.

Table 7. Classifying the fractions according to manual sorting in houses

23

From the results of classifying the waste into smaller number of groups which are presented

in Figure 11 clearly can see only half of the contents of white bags in Hestra, sorted correctly

and the rest should not place there. The case is worse in Kristinberg, and worst in Norrby.

Only one third of the contents of white bags are sorted correctly and tow third should be

recycled, or placed in black bags.

Figure 11.Classifying the fractions according to manual sorting in houses

3.5.2 Classifying the fractions according to energy recovery values

As described in waste-hierarchy the former strategy, after recycling is energy recovery.

According to the heat value of different materials, moisture and the amount of energy they

release in combustion (Table 8), they can divide in other 4 groups as follow.

Combustible waste (materials with high heat value content) includes hard plastic, soft

plastic, paper, paper packaging, tetra pack packaging, PET bottles, other food

packaging, diapers and tissues, combustible and plastic bags fractions

Bio Waste (putting in black bags) include food waste fraction

Landfilling (materials with very low heat value) includes metal packaging, metal

packaging with deposit, glass packaging, glass packaging with deposit, metal scrap.

Electronic waste and other materials fractions

Hazardous waste ( should always take care to avoid environmental impacts) and

includes hazardous waste, bulbs and batteries fractions

24

Table 8. Heat value of different materials [10].

Component Heat value

(MJ/kg, dry) Moisture

(percentage)

Newspaper/Magazines 20.7 30

Paper/Cardboard 20.7 32

Plastic 27.91 0

Dense Plastic 38.85 0

Textile, leather 20.93 20

Glass 0 0

Vegetable waste 19.07 55

Metal-iron 0 0

Metal-aluminum 0 0

Wood/Yard waste 19.54 40

Grit, dirt, misc 0 55

Rubber tires 34.98 0

The results of this classification are presented in Figure 12.

Figure 12. Classifying the fractions according to energy recovery values

25

3.6 Share of each fraction in total household waste

One of the interesting results of this study is the total share of each fraction in both black and

white bags which can be calculated by the sum of the weight of each fraction in black and

white bags and loose waste derived by total weight of black and white bags and loose waste.

In this way more information about characterizations of whole household waste of the city

can be achieved. The results of this calculation are presented in Table 9. The share of each

fraction is more or less the same in three areas. Except other materials fraction, there is not

very big difference among different areas. The difference of other materials fraction is related

to presence of considerable amount of cat sand litter in tow collected samples in Kristineberg.

Since there is not big deviation among the percentages of each fraction in different areas, the

average amount of each fraction in three areas may present a trustworthy characterization of

waste of households in Borås.

Table 9. Share of each fraction in total household waste


Hard Plastic 4.05% 3.42% 3.08%

Soft Plastic 3.41% 3.62% 4.47%

Paper 4.07% 7.46% 6.94%




PET 0.02% 0.09% 0.14%






Metals scarp 1.02% 0.73% 0.52%

Combustible 13.37% 5.28% 7.97%

Food Waste 48.53% 44.18% 48.17%



Bulb 0.04% 0.03% 0.03%

Batteries 0.03% 0.06% 0.06%

Cardboard 0.68% 1.55% 1.62%



An interesting scenario is the perfect sorting, where all waste is sorted perfectly according to

today's requirements. It means to recycle all packaging with producer responsibility in

recycling stations, recycle hazardous materials, electronic waste, bulbs and batteries in

recycling centers, sort food waste in black bags and the rest as combustible in white bags. 21

26

fractions using in this study are summarized in 4 groups considering ideal and perfect sorting

as follow:

Waste going to recycling stations: packaging and products with producer

responsibility includes hard plastic, soft plastic, paper, paper packaging, tetra pack

packaging, cardboard, metal packaging, metal packaging with deposit, glass

packaging, glass packaging with deposit, PET bottle packaging with deposit.

Waste going to recycling center: this group includes electronic and hazardous waste,

bulbs and batteries

Waste sorting in black bags: food waste is the only acceptable fraction

Waste sorting in white bags: the remained fractions including diapers and tissues,

metal scrap, combustible and other food packaging and other materials

Results of perfect sorting of total waste in both black and white bags are presented in .this

means about one forth of waste collecting in boras should be recycled, which is on forth of

weight of the waste but higher based on volume. The volume of recyclable materials which

are mostly packaging is higher in comparison whit food waste and combustible waste. Food

waste is known as high density waste with high content of moisture.

Figure 13. Perfect sorting of household waste in Borås

27

4. Comparing results with the previous study

Although similar methods are implemented in this study and the previous one, but some

changes happened within 10 years. Previous study was about the waste generation of

households in the city and focusing only in white bags, while this study is about waste

characterizations of whole household waste focusing both on black and white bags. So there

are some other results only for white bags that can be compared with recently achieved

results.

The main important revolution was biogas production which stared 2004, and consequently

the definition of black bags, as raw material of biogas production, was changed. Black bags

were for compostable materials, and include all biodegradable materials such as tissues and

napkins. But after starting production of biogas, to improve the quality of product and avoid

mechanical problems in process, only food waste are expected to place in black bags.

4.1 Comparing the weight of bags

The average weights of bags are calculated in both study, and the results are compared in

Table 10.

Table 10. Comparing the average weight of bags

Hestra

2000

Hestra

2010

Kristineberg

2000

Kristineberg

2010

Norrb

y

2000

Norrby

2010

White Bags 0.84 0.87 0.71 0.85 0.71 0.94

Black Bags 1.65 1.36 1.04 1.05 1.08 1.23

Since the main purposes of present and previous study are not exactly the same, and they

focused on different goals, there are some small differences between the fractions. Therefore,

it is better to compare classification according to manual sorting, and energy recovery results

instead of comparing each individual fraction.

4.2 Comparing classification of fractions

Recent results of classification regarding manual sorting, and energy recovery are compared

with previous work respectively in Figure 14 and Figure 15.

From the charts easily can be seen some improvements in white bags in Hestra according to

both manual sorting and energy recovery point of view. The amounts of recyclable materials

are reduced and amount of materials with good heat value for energy recovery is increased.

Furthermore the amount of biowaste is reduced about 10 percent in white bags in Hestra

which is a good improvement. Of course some part of this reduction is due to changing of

biodegradable to biowaste. It means in previous work napkins and tissues were considered as

biodegradable and biowaste, but in this work only food waste are placed in this category. No

significant changes can be seen in Norrby. The amount of biowaste is reduced only 2 present

which can be explained by the same explanation.

28

Kiristnebrg showed worst results, higher amount of food waste and lower amount of

combustibles in the white bags.

Figure 14. Comparing manual sorting classification

29

Figure 15. Comparing classification according to energy recovery

30

5. Conclusions

The overall obtained result from waste analysis in this project shows that the waste generation

of the people living in different neighbourhoods in the city of Borås is more or less similar,

but even in a small city like Borås there are big differences in sorting and recycling behaviour

of people living in different neighbourhoods. These differences provide evidences to show the

importance of effectual factors like education, welfare, legislation, penalties and promotions.

Less than half (44%-48%) of the waste of households is food waste. The nutrition exist in

food waste is used in biogas production, and the remained part is used for producing compost.

But unfortunately, by wrong sorting of this valuable waste, the actual production capacities of

the biogas and compost are lower than the potential production capacities.

Comparing the waste generation in three areas shows that the share of black bags and food

waste in Hestra is about 10% higher than other areas, because people in Hestra are more

conscious about recycling of the waste. They collect their waste in individual garbage bin

which can be controlled more easily comparing to two other areas which collect their waste in

unspecific and share bins. Furthermore the amount of immigrants and uneducated is less in

Hestra. The higher average weight of black bags in Hestra is an evidence of higher purity of

black bags in this neighbourhood.

About half of the food waste (41%, 42%) is places in inaccurate bags in Kristineberg and

Norrby, and instead of using this source of nutrient in biogas production; it would be burnt for

energy recovery.

Diapers and tissue are the main and considerable impurities of black bags in all three areas.

Although from 2005 the black bags are considered only for food waste and no longer for

biodegradable waste, but still people continue to put some biodegradable waste in the black

bags. It shows more announcements and information still is needed to bring up to date the

public.

The results show that about a quarter (20 % in Hestra and 25% in Kristineberg and Norrby) of

the total waste of households (both in black and white bags) should be placed in recycling

centres instead of disposing in garbage bin. And also about one third of the waste in the white

bag in all three areas should be recycled.

Although there were lot of announcements and propaganda about the dangerous of disposing

the batteries in garbage bins and there are especial considered places for collecting the used

batteries, but still considerable number of batteries are found in households‟ garbage bins,

even in Hestra as a good neighbourhood. The heavy metals exist in the batteries spoil and

cause defects in the quality of produced compost.

31

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