strategic planning of municipal solid waste management planning of municipal solid... · strategic...

Resources, Conservation and Recycling 30 (2000) 111–133

Strategic planning of municipal solid wastemanagement

Juha-Heikki Tanskanen *Finnish En6ironment Institute, PB 140, FIN-00251 Helsinki, Finland

Received 12 July 1999; accepted 1 February 2000

Abstract

A computer model was developed and applied for studying integrated municipal solidwaste management (MSWM) in the Helsinki Metropolitan Area. The model is based on amethod developed for analysing on-site collection systems of waste materials separated at thesource for recovery. The aim of the Helsinki study was to find and analyse separationstrategies fulfilling the recovery rate targets adopted for municipal solid waste in Finland, i.e.50wt.% by the end of 2000 and 70wt.% by 2005. In the present situation (i.e. in 1995), thetotal recovery rate of 27wt.% was achieved in the region. The strategies studied were firstbased on source separation only, resulting in a highest recovery rate of 66wt.%. At the sametime, the costs of MSWM increased by 41% compared to the year 1995. Next, a recovery rateof 74wt.% was attained by combining source separation with central sorting of mixed waste.As a result, the costs of MSWM increased by 30% compared to the present situation. In bothof these strategies, the emissions caused by MSWM were generally reduced. The modeldeveloped proved to be a suitable tool for strategic planning of MSWM. Firstly, the analysisof collection systems helped to identify potential separation strategies and to calculate theamounts of materials collected for recovery. Secondly, modelling of MSWM systems madeit possible to determine the effects of separation strategies on costs and emissions caused bythe whole MSWM. The method and model developed can be also applied in other regions,municipalities and districts. © 2000 Elsevier Science B.V. All rights reserved.

Keywords: Waste management; Municipal solid waste; Recovery rate; Separation; Materials; Costs;Emissions; Models

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* Tel.: +358-0-40300421; fax: +358-0-40300491.E-mail address: [email protected] (J.-H. Tanskanen).

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J.-H. Tanskanen / Resources, Conser6ation and Recycling 30 (2000) 111–133112

1. Introduction

Integrated municipal solid waste management (MSWM) can be defined as theselection and application of suitable techniques, technologies and managementprograms to achieve waste management objectives and goals [1]. Computer modelscan be used as tools in the planning of integrated MSWM systems. During the pastthree decades, models have been developed in accordance with waste managementobjectives, especially waste minimization and emissions control.

The reviews compiled by Gottinger [2] and MacDonald [3] show that earlyMSWM models developed during the 1960s and 1970s focused on studyingindividual functional elements, i.e. determining collection routes or facility loca-tions, capacities or expansion patterns. In the 1980s, the focus was extended tocover MSWM on the system level, resulting in extended system boundaries. Thesemodels were mainly aimed at minimizing the costs of mixed waste management[2,4], and recycling was included in some of them more or less comprehensively[5,6].

In the 1990s, recycling has been extensively included in most models used forstrategic planning of MSWM. Reduced system costs are the most common objec-tive [7–14], but some models study MSWM from the point of view of the size andcharacteristics of waste streams [15,16] or their emissions [17]. In several strategicplanning models, both costs and emissions of MSWM have been included in thestudy [18–22]. In some models, the whole life cycle of products has been studiedinstead of only the waste management system when searching for environmentallyoptimal waste management strategies [23,24].

Despite the development of strategic planning models, the descriptions of sourceseparation strategies of recyclables are usually insufficient to enable calculation ofthe amounts of materials separately collected. The amount of a material separatelycollected in an area depends on two factors: (1) the coverage of a collection systemapplied and (2) the separation activity of waste producers, consisting of participa-tion rate and separation efficiency. The coverage of a collection system is defined asthe ratio of (a) the amount of a material produced in those properties whereseparate collection is available and (b) the amount of the material in questionproduced in all properties of the area. Participation rate is defined as the share ofpeople providing sorted material to bins in those properties where this option isavailable. Separation efficiency is defined as the share of a material which iscorrectly separated by those participating in separation. In several strategic plan-ning models, all of these factors have been ignored and the amounts of materialsseparated at the source are treated as input data [10,13,18–20]. In some models, theamounts of materials separated are calculated on the basis of participation ratesand separation efficiencies [11,12]. However, the analysis of the coverages ofcollection systems has generally been excluded from strategic planning models.

This paper presents the HMA (Helsinki Metropolitan Area) model developed forintegrated analysis of recovery rates, costs and emissions of MSWM. The HMAmodel differs from most earlier models through a method developed to analyse thecoverages of on-site collection systems of waste materials. Thus, the amounts of

J.-H. Tanskanen / Resources, Conser6ation and Recycling 30 (2000) 111–133 113

materials separately collected for recovery can be calculated on the basis of thecharacteristics of source separation strategies and area studied. Costs and emissionsof MSWM are calculated on the basis of waste streams and corresponding unitcosts and unit emissions. The method used in the HMA model can also be appliedto study the effects of separation in other regions, municipalities and districts.

The HMA model was applied in a case study performed in the HelsinkiMetropolitan Area. The aims of the Helsinki study were: (1) to find separationstrategies fulfilling the recovery rate targets adopted for municipal solid waste inFinland, i.e. 50wt.% by the end of 2000 and 70wt.% by 2005 [25] and (2) todetermine the effects of these strategies on the costs and emissions of MSWM.Separation strategies were largely based on source separation according to thepolicy of the Helsinki Metropolitan Area Council. Recovery rate was determined asthe share of waste which is separated and delivered to material or energy markets.Participation rates and separation efficiencies were expressed as separation activity,because of insufficient input data. The study covered all municipal solid waste fromhouseholds and commercial premises. Wastes generated by e.g. construction anddemolition activities as well as by waste water treatment plants were excluded fromthe study. The preliminary results of the case study have been presented byTanskanen [26,27].

2. Materials and methods

2.1. The modelling concept

The approach used in the HMA model can be divided into six stages (Fig. 1).

Fig. 1. Stages of the approach used in the HMA model.


Firstly, potential separation strategies are formulated for recoverable waste materi-als on the basis of an analysis in which the coverages of different kinds of collectionsystems are determined. Waste producers are divided into groups, e.g. residentialproperties and commercial establishments, so that differences in the amount ofmaterials produced can be taken into consideration when planning separationstrategies. In addition to source separation, strategies may include central sorting ofmixed waste. Secondly, the total recovery rate and the recovery rates of individualmaterials are calculated (Eqs. (1)–(7)). After the second stage, the separationstrategies can be modified if the recovery level is too low.

R=%g

�Rg×

sg

100�

(1)

Rg=%i

�Rg,i×

sg,i

100�

(2)

Rg,i=r1,g,i+r2,g,i (3)

r1,g,i=co,g,i×Po,g,i

100×

eo,g,i

100+cd,g,i×

Pd,g,i

100×

ed,g,i

100(4)

100]co,g,i+cd,g,i (5)

r2,g,i=ei

100×�

cx,g,i+cy,g,i×�

1−Po,g,i

100×

eo,g,i

100�

+cz,g,i×�

1−Pd,g,i

100×

ed,g,i

100�n

(6)

100]cx,g,i+cy,g,i+cz,g,i (7)

where cd,g,i is the coverage of drop-off centre collection of material i in wasteproducer group g (%); co,g,i, coverage of on-site collection of material i in wasteproducer group g (%); cx,g,i, coverage of on-site collection of mixed waste for centralsorting in waste producer group g including properties from which material i is notseparately collected (%); cy,g,i, coverage of on-site collection of mixed waste forcentral sorting in waste producer group g including properties from which materiali is separately collected as on-site collection (%); cz,g,i, coverage of on-site collectionof mixed waste for central sorting including properties from which material i isseparately collected as drop-off centre collection (%); ed,g,i, separation efficiency ofmaterial i in drop-off centre collection in waste producer group g (wt.%); ei,separation efficiency of material i in central sorting plant (wt.%); eo,g,i, separationefficiency of material i in on-site collection in waste producer group g (wt.%); pd,g,i,participation rate of material i in drop-off centre collection in waste producer groupg (%); po,g,i, participation rate of material i in on-site collection in waste producergroup g (%); R, total recovery rate (wt.%); Rg, recovery rate of waste producergroup g (wt.%); Rg,i, recovery rate of material i in waste producer group g (wt.%);r1,g,i, recovery rate of material i in waste producer group g which is achieved with


source separation (wt.%); r2,g,i, recovery rate of material i in waste producer groupg which is achieved with central sorting (wt.%); sg, the share of waste produced bywaste producer group g in total waste (%); sg,i, the share of material i in wasteamount produced by waste producer group g (%).

Thirdly, the sizes of waste streams in the waste management system and theaccumulations of waste types (mixed waste and recoverable materials) at theaverage property and drop-off centre of each waste producer group are calculated.Waste streams and waste types are described by their waste components. Thus, theeffect of separation on the composition of, for example, mixed waste is calculatedby the model. Fourthly, collection systems are planned separately for each wastetype, waste producer group and separation strategy. The types and numbers of binsand containers and collection frequencies are dimensioned on the basis of theaccumulations of waste types at the average collection points. Fifthly, the unit costsand unit emissions of functional elements are determined. The unit costs areconnected to the sizes of waste streams. The unit emissions are determinedseparately for each waste component of a waste stream and expressed, for example,as kg CH4 t−1 of biowaste landfilled. Sixthly, costs and emissions of MSWM arecalculated as a product of the sizes of waste streams and the unit costs and unitemissions (Eqs. (8) and (9)). Finally, the costs and emissions of MSWM can beminimized by iteration, i.e. by replanning separation strategies and collectionsystems.

T=%f%g%i(uf,g,i×mf,g,i) (8)

Oc=%f%g%i%j(hc, f,g,i, j×mf,g,i, j) (9)

where hc, f,g,i, j is the unit emission c of functional element f resulting from treatmentof waste component j which is a part of waste type i in waste producer group g (e.g.mg CH4 t−1); mf,g,i, amount of waste type i in waste producer group g which istreated with functional element f (t year−1); mf,g,i, j, amount of waste component jin waste type i produced by waste producer group g and treated with functionalelement f (t year−1); Oc, total amount of emission component c (e.g. t CH4 year−1);T, costs of MSWM (EUR year−1); uf,g,i, unit cost of functional element f for wastetype i produced by waste producer group g (EUR t−1).

The modelling concept described above is based on an analysis of the coveragesof on-site collection systems and corresponding accumulations of waste materials atthe properties. The analysis of the coverages is based on the fact that largeproperties are usually obliged to participate in on-site collection of recoverablematerials before smaller ones. Thus, the coverages of on-site collection systems canbe determined on the basis of the size distribution of properties. In Finland, theminimum size of a property obliged to participate in on-site collection of a material,termed on-site obligation limit, is determined on the basis of the number ofhouseholds in residential properties and on the basis of the amount of a materialproduced in commercial establishments. For example in the Helsinki study, 50 185


residential properties and 17 597 commercial establishments were included in theanalysis in which the size distributions of these properties were calculated.

The modelling concept developed can be applied to all regions, municipalitiesand districts provided that:� The properties from which source-separated materials are collected on-site are

selected on the basis of their size, e.g. the number of households.� Adequate input data are available.

2.2. The HMA model

The HMA model was developed for integrated analysis of separation strategiesand their effects on recovery rates, costs and emissions of MSWM (Fig. 2, Table 1).Waste producers were divided into three groups: (1) residential properties smallerthan five households (detached houses and small terraced houses), (2) residentialproperties larger than or equal to five households (terraced houses and apartmenthouses) and (3) commercial establishments. In addition to mixed waste, sourceseparation of seven materials was included in the model: paper, cardboard,biowaste, energy waste, glass, metal and liquid packaging board, e.g. juice cartons.Energy waste may consist of paper, cardboard, plastics, liquid packaging board andmiscellaneous combustible waste components. These combustible waste compo-nents can be also sorted and processed centrally for energy recovery. The collectionsystems of source-separated materials include both on-site collection and drop-offcentres, which are defined on the basis of coverage, participation rate and separa-tion efficiency. The HMA model is a static and linear simulation model in theformat of an Excel spreadsheet (version 5.0).

Nine emission components from collection, backyard composting, central com-posting and landfilling were included in the HMA model (Table 1). The individualemission components were expressed as four groups of emissions as follows:1. nutrient load (O2 consumption) consisting of COD, NOx, NH4 and NH3;2. greenhouse gas load (CO2 equivalents) consisting of CO2, CH4 and N2O;3. acid load (SO2 equivalents) consisting of SO2, NOx and NH3;4. ozone formation (C2H4 equivalents) consisting of VOCs.

The coefficients needed to convert the individual emission components to theequivalents of emission groups were selected to correspond to the Scandinavianenvironmental conditions by Pelkonen et al. [28] from the data compiled by theNordic Council of Ministers [29].

2.3. Study area and input data

The Helsinki Metropolitan Area consists of four municipalities, i.e. Espoo,Helsinki, Kauniainen and Vantaa, covering a total of 764 km2. The number ofinhabitants in the region was 891 000 in 1995 and the amount of municipal solidwaste produced 520 000 t (585 kg person−1 year−1).


Fig. 2. Graphic presentation of the HMA model (C, bins and containers; CO, collection; Tr, transporta-tion; Ts, transfer station).

In 1995, five types of materials were collected separately in the Helsinki region.Paper was collected on-site from residential properties bigger than or equal to fivehouseholds and paper and cardboard from commercial establishments in which theproduction of these materials was more than 50 kg week−1. Separate collection ofbiowaste was carried out in one-quarter of the region with on-site obligation limitsof 10 households and 50 kg week−1. In addition, there were drop-off centres for


paper, cardboard, glass and liquid packaging board. Waste types were collected in0.12–0.6 m3 bins or with 1.3–6.0 m3 containers and compacting collection vehicles.There was one transfer station, one composting plant and one landfill in the region.Nine percent of residential properties composted their biowaste on the spot.

The calculation bases of the input data used in the Helsinki study have beenpresented in details by Tanskanen [26] and by Pelkonen et al. [28]. The input datacan be divided into the following three groups:1. The data needed to calculate the waste amounts and recovery rates (Table 2).

These data were based on unpublished statistics compiled by the HelsinkiMetropolitan Area Council and by Statistics Finland. In addition, an earlierstudy of waste composition in the Helsinki region was utilized [30].

2. The unit costs of the functional elements (Tables 3 and 4). The unit costs weremainly calculated on the basis of the charges levied in the Helsinki region in1995 and the empirical cost functions supplied by the Helsinki MetropolitanArea Council. Both fixed and operational costs were included in the calcula-tions. The unit costs of waste collection were updated between the strategiesstudied (Table 8) on the basis of the changes in the accumulations of waste typesat the collection points.

3. The unit emissions of the functional elements (Tables 5 and 6). The coefficientsused to convert the unit fuel consumption to unit emissions were the following[28]: 154.5 g O2 l−1 for nutrient load, 2.7 g CO2 l−1 for greenhouse gas load,18.1 g SO2 l−1 for acid load and 2.7 g C2H4 l−1 for ozone formation.

Table 1Functional elements, costs and emission components of MSWM included in the HMA model

Functional element Costs Emission components

Waste collectionYesBins and containers at the properties –

Containers at drop-off centres Yes –Structures of collection points –YesCollection work at the collection area Yes CO2, NOx, SO2, VOCsTransportation CO2, NOx, SO2, VOCsYes

Yes –Transfer stationYes CO2, CH4, N2O, NH3, VOCsBackyard compostingYesCentral composting COD, CO2, CH4, N2O, NH3, NOx

a, NH4,SO2

a, VOCsProcessing of source separated energy –Yes

wasteYesCentral sorting and processing of mixed –

wasteYesLandfilling

Decomposition of waste COD, NH4, CO2, CH4, VOCsCO2, NOx, SO2, VOCsLandfill compactorsCO2, NOx, SO2,VOCsRecovery of landfill gas

YesWaste tax –Re6enues from reco6ered materials Yes –

a Emissions from the production of energy needed in composting.


Table 2Data used in the calculation of waste amounts and recovery rates

CommercialParameter Residentialestablishmentsproperties

891 000 –Number of inhabitants412 000–Number of employees

0.6900.265Waste generation rate (t person−1 year−1)Waste composition (wt.%)

29 20Paper17Cardboard 13028Biowaste

24Glass34Metal

7 7Plastics–Liquid packaging board 225Textiles

16 16Miscellaneous combustibles3Miscellaneous non-combustibles 4

See Fig. 4Co6erages of on-site collection systems and corresponding See Fig. 3accumulations of materials

Current separation acti6ities (wt.%)On-site collection 50–75 50–75

–20–50Drop-off centre collectionTarget separation acti6ities (wt.%)

60–90 70–90On-site collectionDrop-off centre collection 50 –

90Separation efficiency of the central sorting plant (wt.%) 90

3. Results

3.1. Formulation of separation strategies

A total recovery rate of 27wt.% was attained with the separation strategy used inthe Helsinki region in 1995 (termed Strategy I). The analysis done proved that highcoverages were reached in the on-site collection of paper and cardboard with thepresent on-site obligation limits of five households and 50 kg week−1 (Table 7,Figs. 3 and 4). However, three major weak points were identified in the separationstrategy applied. Firstly, energy waste and metal were not separately collected.Secondly, separate collection of biowaste was applied in only one quarter of theregion, resulting in coverages of 19% for residential properties and of 23% forcommercial establishments with the present on-site obligation limits of 10 house-holds and of 50 kg week−1. Thirdly, the present separation activities, 20–75 %,were far from the estimates of the highest achievable activities, 50–90%.

Following the analysis above, two different separation strategies were formulatedand studied with the HMA model (Table 8). The waste management system used in1995 (Strategy I) was studied to serve as the point of comparison. Strategy II wasbased on source separation only and it was formulated by amending the presentstrategy in the following phases:


� Separate collection of biowaste was extended to cover the whole region ofHelsinki with the current on-site obligation limits. As a result, the total recoveryrate rose from the present 27 to 36wt.%.

� Separate collection of energy waste started, increasing the total recovery ratefrom 36 to 47wt.%. The on-site obligation limits used in this calculation were fivehouseholds and 50 kg week−1.

� Separate collection of metal and glass from commercial establishments werestarted with an on-site obligation limit of 50 kg week−1. Also, drop-off centrecollection of metal was started. The total recovery rate increased from 47 to48wt.%.

� The present separation activities were replaced by the target activities, resultingin a total recovery rate of 60wt.%.

� Finally, the on-site collection systems of paper, biowaste and energy waste wereextended to cover all residential properties and the on-site obligation limits of all

Table 3Types of bins and containers and unit costs of waste collection in the strategies studied

Costs of waste collection (EUR t−1)Waste type Type of bin orcontainer (m3)

Strategy I Strategy II Strategy III

Residential properties (]5 households0.60Mixed waste 66.3 71.3 71.0

Paper 46.846.848.60.60155.2154.4 149.30.24Biowaste

– 117.7Energy waste 117.70.60Residential properties (B5 households)Mixed waste 0.15 98.7 131.2 103.6Paper –210.9–0.12

0.12 –Biowaste 742.5 ––402.6–Energy waste 0.12

Commercial establishments59.0Mixed waste 65.10.60 64.1

30.431.830.9Paper 0.60100.9104.3102.30.24Biowaste

Energy waste –6.00 132.9 122.3119.26.00Cardboard 133.0122.9

0.60 125.0143.6Glass –74.0 67.3Metal 0.60 –

Drop-off centres42.4Paper –4.00 42.4

223.5–223.5Cardboard 4.00Glass 74.71.30 74.7 74.7

4.00 44.4Metal 44.4–58.2–58.26.00Liquid packaging board


Table 4Unit costs of functional elements and revenues from recovered materials

Unit cost (EUR t−1)Functional element

10.9Transfer of mixed waste1.7Transfer of glass5.2Transport of mixed waste from transfer station to landfill

13.5Transport of glass from transfer station to marketsTransport of energy waste from processing to markets 8.4Backyard composting

95.0Residential properties]5 households645.0Residential propertiesB5 households42.0Central composting33.6Processing of source-separated energy waste33.6Central sorting and processing of mixed waste15.1Waste tax for final disposal

Landfilling7.9Strategy I (380 000 t year−1)

Strategy II (180 000 t year−1) 10.914.3Strategy III (135 000 t year−1)

Re6enues from reco6ered materials44.4Paper42.0Cardboard1.7Biowaste

20.2Energy waste8.4Glass0Metal

Liquid packaging board 25.2

materials were reduced from 50 to 20 kg week−1. As a result, the total recoveryrate increased from 60 to 66wt.%.

In Strategy III, Strategy II was complemented with central sorting of mixedwaste, resulting in a total recovery rate of 74wt.%. At the same time, Strategy IIwas modified by stopping separate collection of paper and energy waste fromresidential properties smaller than five households and separate collection ofbiowaste from properties smaller than 10 households. For commercial establish-ments the on-site obligation limits of all materials were raised from 20 to 50 kgweek−1. Also, drop-off centre collection of paper, cardboard and liquid packagingboard was started.

Strategies II and III represent different, partly alternative and partly complemen-tary choices to aim at the Finnish recovery rate targets of 50wt.% (in 2000) and70wt.% (in 2005). Strategy II can be regarded as an ultimate strategic goal in sourceseparation in the Helsinki region. For this reason it was selected for furtheranalysis, despite the fact that the recovery rate attained was four percentage unitsbelow the target of 70wt.%.


3.2. Costs and waste streams of MSWM

The costs of MSWM increased by 41% in Strategy II and by 30% in Strategy IIIcompared to the year 1995 (Fig. 5). In Strategy II, residential properties smallerthan five households caused 45% of the increase in the total costs. However, theshare of these properties of the increase in the total recovery rate was only 10%. InStrategy III, the increase in the costs of MSWM was mainly caused by residentialproperties bigger than or equal to five households and by commercial establish-ments. In 1995, the costs of MSWM were 41 400 000 EUR in the Helsinki region(79.3 EUR t−1 waste and 46.5 EUR inhabitant−1).

The most important functional element increasing the costs of MSWM was wastecollection (Table 9). The increase in the costs of waste collection was smaller inStrategy III than in Strategy II because in Strategy III recoverable materials wereno longer collected separately from residential properties smaller than five house-holds. Central sorting of mixed waste was an important functional element increas-ing the total costs in Strategy III. Processing of source-separated energy waste andcentral composting increased the total costs both in Strategy II and in Strategy III,

Table 5Unit fuel consumption of waste collection in the strategies studied

Waste type Unit fuel consumption (l t−1)

Strategy I Strategy II Strategy III

Residential properties (]5 households)12.312.3Mixed waste 8.8

9.2Paper 10.7 9.2Biowaste 15.717.817.8

16.5 16.5–Energy wasteResidential properties (B5 households)

21.0Mixed waste 24.4 22.2Paper – 20.6 –Biowaste –122.9–

56.1 ––Energy wasteCommercial establishments

14.08.9 12.6Mixed waste4.9Paper 5.4 5.9

9.3Biowaste 10.0 8.85.6Energy waste 6.3–

Cardboard 9.9 11.2 9.5Glass – 7.510.1

6.69.3Metal –Drop-off centres

– 5.25.2Paper25.5 – 25.5Cardboard

11.211.2Glass 11.2– 6.0Metal 6.0

6.9–Liquid packaging board 6.9


Table 6Unit emissions of backyard composting, central composting and landfilling

Functional element Unit emissions

Nutrient load Greenhouse gas load Acid loada(kg Ozone formationSO2 t−1) (kg C2H4 t−1)(kg CO2 t−1)(kg O2 t−1)

Backyard compostingBiowaste 3.0125.6 0.1083.9Central composting

(windrow)Biowaste 15.8 0.05 0.102.2Landfillingb

−0.21 0.10246.43.7Paper296.84.4 −0.26 0.11Cardboard

Biowaste −0.139.9 0.06164.70 000Glass

00 0 0Metal0.02 0Plastics 0 3.3

3.3 0.020 0Liquid packagingboard

Textiles 214.5 −0.18 0.0924.5221.7 −0.19Miscellaneous 0.082.9

combustibles0 3.3 0.02 0Miscellaneous

non-combustibles

a The negative values result from the utilization of landfill gas in energy production to replace fossilfuels.

b The unit emissions from landfilling were limited to cover 15 years after disposal.

because of the greater amount of waste treated. The costs caused by landfilling andby the governmental waste tax decreased because of the reduced amount ofwaste disposed of to the landfill. The revenues from recovered materials alsoincreased.

The costs of waste collection increased from Strategy I to Strategy II and toStrategy III, although the amount of waste collected did not change. This was dueto the following two reasons: (1) separate collection of new types of materials(energy waste and metal) and (2) extended on-site collection of materials. Thesemeasures divided mixed waste into several separate waste streams at the properties,resulting in reduced amount of waste collected per pickup. Consequently, thepickup times increased and the efficiency of waste collection was reduced (Fig. 6).Pickup time is the time used at the collection area per tonne of waste collected. Theamount of waste collected per pickup affects the pickup time because the time usedfor preparations before loading at a property and the driving time betweenproperties do not depend on the amount of waste collected.


The separation strategies studied increased the recovery rates of all wastematerials and affected the waste streams in the Helsinki region (Table 10). Theamount of waste directly disposed of to the landfill was reduced from 380 000 tyear−1 in Strategy I to 180 000 t in Strategy II and to 135 000 t in StrategyIII. The composition of waste disposed of to the landfill, for example in Strategy II,was as follows: biowaste 35wt.%, miscellaneous combustible waste 15wt.%,textiles 10wt.%, miscellaneous non-combustible waste 10wt.%, paper 9wt.%, plastics6wt.%, cardboard 5wt.%, metal 5wt.%, glass 4wt.% and liquid packaging board1wt.%.

Table 7Analysis of the separation strategy used in the Helsinki region in 1995 (Strategy I)

Coverage of the collection system (%)Material

Commercial establishmentsaResidential properties

Drop-off centre collectionOn-sitecollection

Paper 89188219 –Biowaste 23

Cardboard 87– 100– 100Glass –

Liquid packaging –– 100board

–––Energy waste– –Metal –

a Only on-site collection is applied.

Fig. 3. Coverage of on-site collection of waste materials and average amount of waste produced perproperty in the residential properties larger than or equal to the on-site obligation limit in the Helsinkiregion.


Tab

le8

Sepa

rati

onst

rate

gies

stud

ied

wit

hth

eH

MA

mod

elin

the

Hel

sink

ire

gion

Des

crip

tion

ofse

para

tion

stra

tegy

Stra

tegy

Mat

eria

lD

rop-

off

cent

reO

n-si

teob

ligat

ion

limit

Sepa

rati

onac

tivi

tya

colle

ctio

nR

esid

enti

alpr

oper

ties

(no.

ofC

omm

erci

ales

tabl

ishm

ents

(kg

per

wee

k)ho

useh

olds

)

Pap

er50

–75

550

IY

es50

–B

iow

aste

b50

1020

–75

Car

dboa

rd–

50Y

es40

Gla

ss–

–Y

esY

es20

––

Liq

uid

pack

agin

gbo

ard

20–

190

Pap

erII

60B

iow

aste

120

–C

ardb

oard

90–

–20

70E

nerg

yw

aste

120

– Yes

50–7

0G

lass

–20

50–7

0M

etal

–20

Yes

50–9

0Y

es50

IIIc

5P

aper

Bio

was

te60

1050

–C

ardb

oard

50–9

0–

50Y

es50

70–

5E

nerg

yw

aste

50–7

0G

lass

–50

Yes

Yes

50–7

0M

etal

–50

––

Yes

50L

iqui

dpa

ckag

ing

boar

d

aT

heup

per

limit

isus

edfo

ron

-sit

eco

llect

ion

and

the

low

erlim

itfo

rdr

op-o

ffce

ntre

colle

ctio

n.b

On-

site

oblig

atio

nlim

its

wer

eon

lyap

plie

din

one

quar

ter

ofth

ere

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.c

Inad

diti

onto

sour

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para

tion

,m

ixed

was

teis

sort

edce

ntra

llyfo

ren

ergy

reco

very

.


Fig. 4. Coverage of on-site collection of paper and the average amount of paper produced per propertyin the commercial establishments larger than or equal to the on-site obligation limit. Paper is shown asan example.

Fig. 5. Share of various waste producer groups of the change of the costs of MSWM in Strategies II andIII compared to Strategy I.

3.3. Emissions of MSWM

The amount of emissions caused by MSWM reduced from Strategy I to StrategiesII and III as follows: nutrient load by 23 and 28%, greenhouse gas load by 37 and53% and ozone formation by 17 and 33% (Fig. 7). The reason for the reduction inthe amount of emissions was the decreased amount of waste disposed of to the landfill.In Strategy I, the total nutrient load was 3100 t year−1 expressed as O2 consumption,the total greenhouse gas load was 75 300 t year−1 expressed as CO2 equivalents andthe total ozone formation was 36 t year−1 expressed as C2H4 equivalents.


The amount of acid load increased by 125% in Strategy II and by 114% inStrategy III compared to Strategy I (Fig. 7). The reason for the increase wasenhanced recovery which reduced the amount of landfill gas available for energyproduction to replace fossil fuels. The acid load was smaller in Strategy III than inStrategy II because emissions caused by waste collection reduced from Strategy IIto Strategy III. In Strategy I, the amount of acid load caused by MSWM was 46t year−1 expressed as SO2 equivalents.

The emissions caused by waste collection increased by 30% from Strategy I toStrategy II and by 16% from Strategy I to Strategy III because of increased pickuptimes. The changes in the amount of emissions caused by composting were simply

Table 9Share of various functional elements in the change of the costs of MSWM from Strategy I to StrategiesII and III

Functional element Change of total costs (%)

Strategy II Strategy III

+22Waste collection +450Central sorting and processing of mixed waste +17

+6+7Processing of source separated energy waste+6Central composting +6

0Backyard composting 0−2Landfilling −2

Waste tax −7 −9−8 −10Revenues from recovered materials

Total +30+41

Fig. 6. Interdependence between the amount of waste collected per pickup (expressed as the number ofbins) and the pickup time. Separate collection of paper from residential properties larger than or equalto five households is shown as an example. Unit times used for compacting collection vehicle were basedon data compiled by the Association of Finnish Civil Engineers [31].


Table 10Recovery rates of waste materials in the strategies studied

Recovery rate (wt.%)Material

Strategy IIIStrategy I Strategy II

69 87 98Paper988364Cardboard96Energy waste 0 689770Liquid packaging board 20

5812 51Biowaste46510Metal

4927 44Glass

Total 66 7427

Fig. 7. Effect of various functional elements on the change of the total emissions of MSWM in StrategiesII and III compared to Strategy I.

due to changes in the amount of biowaste treated. In this study, the emissions fromthe landfill were limited to cover 15 years after disposal and the emissions occurringafter this period were ignored. This limit was applied because emissions fromcollection and composting are generated with much shorter delays than emissionsfrom landfills and it is difficult to compare present and future emissions. However,the effects of unlimited decomposition time on the amount of emissions was studiedin the sensitivity analysis (Table 11).

3.4. Uncertainty and sensiti6ity analysis

The potential sources of errors in the Helsinki study are the following:� the system boundary of the HMA model,� the linearity of the HMA model,� the input data used in the study.


Tab

le11

Eff

ect

ofch

ange

sin

the

inpu

tda

taon

the

follo

win

gre

sult

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the

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y:(1

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rate

of66

wt.

%in

Stra

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74w

t.%

inSt

rate

gyII

I;(2

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sein

the

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from

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from

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37%

from

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from

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III

Cha

nge

inth

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put

data

Eff

ect

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sult

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the

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erce

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sts

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SWM

Cha

nge

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ount

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ouse

Tot

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III

Stra

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IISt

rate

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rate

gyII

ISt

rate

gyII

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––

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−0.

9Sh

are

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aste

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sing

the

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Sepa

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93.

39

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ion

(EU

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the

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ial

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alle

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geby9

20%

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rate

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I,II

and

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––

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–U

nit

cost

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lso

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98.

69

50%

inSt

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3.7

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even

ues

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aste

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and

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III


The HMA model was planned according to the waste management system usedin the Helsinki region in 1995 and to the waste policy of the Helsinki MetropolitanArea Council. Thus, the system boundary of the model is broad enough to studyMSWM in the Helsinki region with good reliability. The linearity of the HMAmodel was taken into consideration by studying MSWM systems as single simula-tions, for which the unit costs and unit emissions were individually calculatedaccording to the characteristics of the strategies studied.

Most of the input data used can be modified without significant changes in therelative superiority of Strategies II and III because of the similarity of thesestrategies. However, the changes concerning combustible waste components, resi-dential properties smaller than five households and central sorting of mixed wasteare of major importance. In the sensitivity analysis, the effects of changes in theseinput data on the total recovery rate and on the change of the costs and greenhousegas load of MSWM were studied (Table 11).

Changes in the share of combustible waste components affect the total recoveryrate attained in Strategy III more than the recovery rate attained in Strategy II.However, moderate changes do not markedly affect the recovery rates obtained ifthe share of non-recoverable waste does not increase. The total recovery rate inStrategy III is not sensitive to changes in the separation efficiency of the centralsorting plant. The unit cost of central sorting is of major importance from theperspective of total costs in Strategy III because of the great amount of mixed wastesorted. The greatest change in the amount of emissions occurred when the unitemissions of final disposal were determined on the basis of infinite decompositiontime instead of only 15 years. However, the effect of this change on the differencebetween Strategy II and Strategy III was small because both of these strategies wereaffected.

4. Discussion and conclusions

The case study performed in the Helsinki region demonstrated that the HMAmodel is a suitable tool for the strategic planning of integrated MSWM. Firstly, theanalysis of collection systems helps to identify potential separation strategies and tocalculate the amounts of materials collected for recovery. Secondly, modelling ofMSWM systems makes it possible to determine the effects of separation strategieson the costs and emissions caused by the whole MSWM.

The HMA model differs from most earlier strategic planning models by reason ofa method developed to analyse the on-site collection systems used for wastematerials separated at source for recovery. As a result, the HMA model has thefollowing major advantages compared to most other models: (1) The coverages ofon-site collection systems of materials can be adapted to the characteristics of astudy area; (2) The recovery rates and sizes of waste streams can be calculated onthe basis of the characteristics of the separation strategies instead of giving them asinput data; (3) The unit costs and unit emissions of waste collection can be updatedbetween separation strategies because the changes in the amounts of materialsseparated at the properties are known.


The modelling concept developed can be applied to all regions, municipalitiesand districts to study the effects of separation on MSWM provided that:� the properties from which source-separated materials are collected on-site are

selected on the basis of their size, e.g. the number of households;� adequate input data are available.

The Helsinki study indicates that the national recovery rate target of 70wt.%adopted for municipal solid waste in Finland can only be achieved by addingcentral sorting of mixed waste to source separation strategies. A recovery rate of66wt.% was reached by a source separation strategy in which separate collection ofrecoverable materials covered all residential properties and 93% of commercialestablishments. In addition, the estimates of the highest attainable separationactivities were used in calculations. At the same time, the costs of MSWM increasedby 41% compared to the present situation. By supplementing source separation withcentral sorting of mixed waste, a recovery rate of 74wt.% was attained and theincrease of total costs was 30% compared to the present situation.

The separation strategies studied reduced the nutrient load, greenhouse gas loadand ozone formation caused by MSWM. The reason for this was the reducedamount of waste disposed of to the landfill. The acid load increased for the samereason, because less landfill gas was available for energy production to replace fossilfuels than in the present situation. The combination of source separation andcentral sorting resulted in a smaller amount of emissions than source separationalone. This was because the central sorting reduced both the amount of wastelandfilled and collection work.

Universal conclusions about the effects of separation of individual waste materi-als on the costs and emissions of MSWM cannot be drawn on the basis of thisstudy for two reasons. Firstly, the effects of source separation vary depending onseveral factors, e.g. characteristics of the region in question, the type of materialsseparated and the collection method applied. Secondly, this study did not cover allemissions caused by MSWM, e.g. emissions caused by burning of energy waste.

Acknowledgements

This work was carried out at the Finnish Environment Institute. The study wasfinanced by the Helsinki Metropolitan Area Council, a joint municipal organisationwith overall responsibility for waste management in the Helsinki region, and by theMinistry of the Environment, Finland. Special thanks are extended to JukkaPaavilainen and Jarmo Nurmivaara of the Helsinki Metropolitan Area Council forvaluable information and successful cooperation during the study. I acknowledgeMarkku Pelkonen and Elisa Rauta of the Helsinki University of Technology forproducing most of the unit emissions and the weighting factors. The author alsoacknowledges Professor Matti Melanen of the Finnish Environment Institute andJuha Kaila Dr. Tech. of the Helsinki Metropolitan Area Council for providingconstructive comments that greatly improved the paper. The language of themanuscript was revised by Virginia Mattila.


Appendix A. Key definitions

Coverage of a collection system: in an area the ratio of (a) the amount of amaterial produced in those properties where separate collection is available and(b) the amount of the material in question produced in all properties of the area.On-site obligation limit: the minimum size of a property obliged to participate inon-site collection of a material in an area.Participation rate: the share of people providing sorted material to bins in thoseproperties where separate collection is available.Pick-up time: the time used at the collection area per tonne of waste collected.Recovery rate: the share of waste which is separated and delivered to material orenergy markets.Separation activity: the share of a material which is correctly separated in thoseproperties where separate collection is available. Separation activity consists ofparticipation rate and separation efficiency.Separation efficiency: the share of a material which is correctly separated by thepeople who participate in separation. Also, the share of a material which iscorrectly separated in a central sorting plant.Waste stream: separate waste output of, e.g. a property, functional element orstudy area.Waste type: mixed waste and recoverable waste materials.

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