Sufian 2007 Waste-Management 1

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Modeling of urban solid waste management system: The case ofDhaka city

M.A. Sufian a, B.K. Bala b,*

a Beximco Synthetics Ltd., Kabirpur, Savar, Dhaka-1344, Bangladeshb Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Accepted 24 April 2006Available online 15 June 2006

Abstract

This paper presents a system dynamics computer model to predict solid waste generation, collection capacity and electricity genera-tion from solid waste and to assess the needs for waste management of the urban city of Dhaka, Bangladesh. Simulated results show thatsolid waste generation, collection capacity and electricity generation potential from solid waste increase with time. Population, unclearedwaste, untreated waste, composite index and public concern are projected to increase with time for Dhaka city. Simulated results alsoshow that increasing the budget for collection capacity alone does not improve environmental quality; rather an increased budget isrequired for both collection and treatment of solid wastes of Dhaka city. Finally, this model can be used as a computer laboratoryfor urban solid waste management (USWM) policy analysis. 2006 Elsevier Ltd. All rights reserved.

1. Introduction

Solid waste consists of the highly heterogeneous mass ofdiscarded materials from the urban community, as well asthe more homogeneous accumulation of agricultural,industrial and mining wastes. The principal sources of solidwastes are residences, commercial establishments, institu-tions, industrial and agricultural activities. Domestic, com-mercial, and light industrial wastes are considered togetheras urban wastes. The main constituents of urban solidwastes are similar throughout the world, but the quantity

generated, the density and the proportion of constituentsvary widely from country to country, and from town totown within a country according to the level of economicdevelopment, geographic location, weather and social con-ditions. In general, it has been found that as the personalincome rises, kitchen wastes decline but the paper, metals

and glass wastes increase; the total weight generatedincreases but the density of the wastes declines (Rao, 1992).

Several disposal methods are being used in various partsof the world and the most prominent of these are: opendumping, sanitary landfilling, incineration and compo-sting. Sanitary landfilling is the main method used in indus-trialized countries and open dumping is very common indeveloping countries like Bangladesh and India.

Open dumping of solid wastes is practiced extensively inBangladesh because it is cheap and requires no planning.Generally, the low-lying areas and outskirts of the towns

and cities are used for this purpose.Sanitary landfilling is a controlled engineered operation,designed and operated according to acceptable standards.It may be defined as a controlled method of disposing ofrefuse onto or into land while minimizing nuisances or haz-ards to public health or safety. The operation is carried outwithout environmental damage and in areas alreadyspoiled or in need of restoration.

Incineration involves the burning of solid wastes at hightemperatures. If incineration is to become an economicalmethod for solid waste disposal, useful materials and

0956-053X/$ - see front matter 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.wasman.2006.04.011

* Corresponding author. Tel.: +880 91 55518; fax: +880 91 55810.E-mail address:[email protected](B.K. Bala).

www.elsevier.com/locate/wasman

Waste Management 27 (2007) 858868
mailto:[email protected]:[email protected]


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energy must be recovered by the process. Heat can berecovered by putting a waste heat boiler or some otherrecovery device on an existing solid waste incinerator.The heat so recovered can be utilized for generating elec-tricity or for space heating purposes. In general, solid wastehas about one-third the heating value of coal, but unlike

coal it has a very low sulfur content. All types of incinera-tors produce air pollution. The contributions to globalwarming by incineration is much less than those of landfillbut comparable to those by composting (Sonesson et al.,1997, 2000).

In contrast to a sanitary landfill, composting of refuse isan aerobic method of decomposing solid waste. Manytypes of microorganisms already present in the waste bio-stabilize the organic matter in the waste and produce a soilconditioner as a result of the process. The organismsinclude bacteria, which predominate at all stages, fungi,which often appear after the first week, and actinomycetes,which assist during the final stages.

Solid wastes contain significant amounts of valuablematerials like steel, aluminum, copper and other metalswhich, if they are recovered and reused, would reduce thevolume of the wastes to be collected and at the same timewould yield significant salvage and resale income. In addi-tion, better reclamation techniques will help to save valu-able natural resources and turn wastes, which could bedangerous, into useful products. Some important solidwastes that have been successfully reclaimed are paper,plastics, glass and metals.

In Bangladesh, analysis of the composition of the urbansolid waste is not generally carried out on a regular basis by

the municipalities. The results of composition analyses ofthe solid waste generated in Dhaka city are shown inTable 1.

On average, constituents are 18% inorganic matter and82% organic matter (Khan, 1999). The density of domesticsolid waste of Dhaka city is 0.35 tonne/m3 (Alam, 2001).

Many studies have been reported on strategies toachieve municipal solid waste management (Pawan et al.,

1997; Salvato, 1992; Kum et al., 2005). Linear program-ming, inputoutput analysis, expert system (a methodologythat uses expert knowledge to solve problems of a complexsystem) and system dynamics have been applied to aid deci-sion makers in planning and management of solid wastemanagement systems (Everett and Modak, 1996; Clayton

and McCarl, 1979; Barsi, 2000; Ming et al., 2000; Heikki,2000; Mashayekhi, 1992; Sudhir et al., 1997). Morerecently,Dyson and Chang (2005)emphasized the capabil-ity of system dynamics for prediction of solid wastegeneration.

Alam and Bole (2001) analyzed the electrical energyrecovery potential from urban solid waste of Dhaka cityand its economic feasibility and emphasized that the 1.28million tonnes of municipal waste generated annually inthe Dhaka city could potentially produce about 71 MWof electricity.

Heating values of solid wastes depend on the types ofwastes and moisture contents of the wastes. Themelis

et al. (2002)reported that the heating values of the differenttypes of wastes decrease as the moisture content increases.Fig. 1shows the variation of the heating values of differenttypes of solid wastes based on Themelis et al. (2002). Theheating values of residential, industrial and commercialwastes are 9.20 MJ/kg, 5.67 MJ/kg and 6.94 MJ/kg andthe corresponding percentages of the wastes by weightare 44.2%, 14.7% and 17.7%, respectively with street sweep-ing of 23.4% (Alam and Bole, 2001). Since street sweepingsare not under consideration, the new percentages of wastesin the above sectors are 57.70%, 19.19% and 23.11%,respectively. Based on these data, the calorific value of

the solid waste generated in Dhaka city is estimated as8.0 MJ/kg.

The purpose of this study is to develop a system dynam-ics model of solid waste management systems to predictsolid waste generation and electrical energy recovery from

Table 1Composition of solid waste of Dhaka (wt%)

Constituent Khan (1999) Ahmed and

Rahman (2000)

Alam

(2001)Residential Industrial

Plastic 1.74 1.48 5 2.3Paper 5.68 7.22 4 10.0Glass 6.38 10.22 0.25 1.4Metal 0.13 0.5Textile 1.83 1.59 Food stuff

and kitchen84.37 79.49 70

Food waste 18.0Wood/grass 0.16 2.1Garden waste 11Ash/soil 40.0Other 5 23.0

Total 100.00 100.00 95.54 97.3

Fig. 1. Variation of heating values of different types of solid wastes with

moisture contents (Source. Themelis et al. (2002)).

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the solid waste of the Dhaka city and also to assess differ-ent policy options for solid waste management.

2. System dynamics modeling of urban solid waste

management system

Planning of USWM has to address several interdepen-dent issues such as public health, the environment, the elec-tricity generation potential from the urban solid wastegenerated, and present and future costs to society. TheUSWM is a complex, dynamic and multi-faceted systemdepending not only on available technology but also uponeconomic and social factors. Experimentation with anactually existing urban solid waste management systemcontaining economic, social, technological, environmentaland political elements may be costly and time consumingor totally unrealistic. Simulating an USWM by a computermodel one can conduct a series of experiments. Computermodels clearly are of great value to understand the dynam-

ics of such complex systems (Bala, 1999). Owing to theintrinsically complex nature of USWM problems, it isadvantageous to implement USWM policy options onlyafter careful modeling analyses. The analysis involves theuse of different modeling techniques such as optimization,econometrics, inputoutput analysis, multi-objective analy-sis and system dynamics simulation. Forresters systemdynamics methodology provides a foundation for con-structing computer models to do what the human mindcannot do (Forrester, 1968), that is rationally analyze thestructure, the interactions and mode of behavior of com-plex socio-economic, technological, and environmental sys-

tems. Hence, the system dynamics approach is the mostappropriate technique to handle this type of complexproblem.

The methodology used in the development of the solidwaste management model discussed in this paper is systemdynamics. A detailed description of the methodology isgiven inForrester (1968) and Bala (1998, 1999). It has beenused in many areas including global environmental sustain-ability (Forrester, 1971; Meadows et al., 1992), environ-mental sustainability in an agricultural developmentproject (Saysel et al., 2002), modeling strategies for pro-moting agricultural development (Drew, 1990), regionalsustainable development issues (Saeed, 1994; Bach andSaeed, 1992), environmental management (Mashayekhi,1990; Sudhir et al., 1997) and ecological modeling (Sayseland Barlas, 2001).

System dynamics methodology is based on the feedbackconcept of control theory and the feedback loops simulatedynamic behavior (Bala, 1999). Two basic building blocksin system dynamics studies are stock or level and flow orrate. Stock variables (symbolized by rectangles) are statevariables and stocks represent accumulation in the system.Flow variables (symbolized by valves) are the rate ofchange in the stock variables and flows represent the activ-ities and decision function in the system. Converters (repre-

sented by circles) are intermediate variables used for

miscellaneous calculations. Finally, the connectors (repre-sented by simple arrows) represent cause and effect linkswithin the model structure (Bala, 1999). The flow diagramof the urban solid waste management system is shown inFig. 2. The original computer model was developed as apart of a thesis (Sufian, 2001) and it was constructed using

STELLA Research software (HPS, 1996) designed fordynamic feedback modeling of complex systems. Fulldetails are available inSufian (2001).

The model described here is a theoretical frameworkfor examining urban solid waste generation and its man-agement system in Dhaka city and also to assess electricalenergy generation potential to meet the electrical energyconsumption requirements of Dhaka city. There is a largegap between the waste generation and management sys-tem, which results environmental pollution. Both theuncollected waste and unhygienic disposal of waste createenvironmental pollution, which gives rise to increase pub-lic annoyance and anger and hence public concern devel-

ops to reduce waste generation and source separation ofrecyclable waste. But, waste generation increases withincreased population and GDP, as well as per-capitaincome. Hence, the electrical energy generation potentialfrom the urban solid waste also increases. On the otherside, composite index shows the lack of waste collection(uncleared waste). A higher composite index increasesmanagement perception, which increases fund allocationfor solid waste management. The composite index isdefined as:

Composite Index w1 UNCL w2 UNTR POPR

1

where w1, w2 is the weighting factor (w1= 0.5 andw2= 0.5), UNCL is the ratio of the uncleared waste atany point of time to the base value, UNTR is the ratioof the untreated waste at any point of time to the base va-lue, POPR is the ratio of the population at any point oftime to the base value.

A higher value of composite index indicates a progres-sive deterioration in health and environmental quality.

In Dhaka city, normal practice is that the householdersput their solid wastes at different collection points on thestreet. The Dhaka city corporations personnel collect the

wastes at a particular time and transport them to the dis-posal site. The disposal method is open dumping in anunhygienic manner. The Dhaka city corporation does notundertake any sanitary landfilling, incineration, compo-sting or recycling. A portion of the recyclable solid wasteof Dhaka city is used in recycling industries (plastics,paper, glass, metals, etc.), but this amount is very smalland is undertaken informally.

Although the Dhaka city corporation does not have anyelectricity generation plant fueled by urban solid waste norany scientific disposal facilities, the electrical energy gener-ation potential from urban solid waste at Dhaka city and

the controlled disposal of a portion of collected wastes as

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landfill, and treatment of waste (incineration, composting,etc.) are included in this model. The heating value of the

generated waste is considered to be 8.0 MJ/kg. Figs. 2(a)

and 2(b) show the STELLA flow diagram of a systemdynamics model used to analyze the Planning for USWM

of the Dhaka city.

Fig. 2(a). STELLA flow diagram of the system dynamics model of urban solid waste management system.



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The model consists of two sectors and these are wastegeneration and waste management. The waste generationsector inFig. 2(a)consists of population, solid waste gen-eration, electricity generation, public concern, compositeindex and stock levels of cleared, uncleared, treated,

untreated, recyclable and non-recyclable wastes, while the

waste management sector consists of waste collection, eco-nomics of waste collection and waste treatment issues. Thewaste generation sector and waste management sector haveinterrelations and these two sectors are interconnected bySTELLA symbol ghost, a means of tidy presentation of

interconnections. For example, dotted disposal in

Fig. 2(b). STELLA flow diagram of the system dynamics model of urban solid waste management system.



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Fig. 2(b)is the ghost of disposal inFig. 2(a), and it showsthe connection of disposal to landfill rate.

3. Results and discussion

The authors considered various ways of validating a sys-

tem dynamics model, such as comparing the model resultswith historical data, checking whether the model generatesplausible behavior and checking the quality of parametervalues. Some of the parameters have been derived fromstudies in other areas and some were the results of expertguesswork. To judge the plausibility of the model, thebehavior of the key variables in the base run were examinedby the authors.

Computer projections of population, solid waste gener-ation, waste collection capacity, and electrical energy gen-eration potential from the solid waste for Dhaka city areshown inFig. 3. Dhaka city had a population of 4.375 mil-lion in 1995, approaching 12.082 million by 2025. The pop-

ulation growth rate of the city is higher than the averagevalue of the whole country. This might be due to the factthat for job opportunities or other attractive factors, thereis a rapid population inflow into the city. More populationmeans more waste, and more waste means more resourcesfor waste management and more potential for electricitygeneration. The waste generation increases from 1.027 mil-lion tonnes in 1995 to 4.257 million tonnes in 2025. An esti-mate of waste generation is crucially important tocollection services and disposal facilities. The collectioncapacity needed increases from 483,000 tonnes in 1995 to2,412,500 tonnes in 2025. The existing collection capacity

is far below the needed collection capacity. However, it isinteresting to note that the electrical energy generationpotential increases from 456,900 MWh in 1995 to1,894,400 MWh in 2025, and the electrical energy recovery

from urban solid waste generation of Dhaka city can sup-ply a significant portion of the consumption requirement ofelectrical energy of the city. Hence, adoption of the policyfor electricity from urban solid waste of Dhaka city shouldbe dictated by the economy of adoption of the technologyof electricity generation from the solid waste and environ-

mental implications.Fig. 4 shows simulated uncleared waste, untreatedwaste, composite index and public concern for a time hori-zon of 30 years. It is clear from this figure that unclearedwaste increased from 559,200 tonnes in 1995 to3.45e + 007 tonnes in 2025, and untreated waste increasesfrom 376,300 tonnes in 1995 to 1.70e + 007 tonnes in2025. The uncleared waste of Dhaka city is increasing withtime because of an inadequate collection capacity to trans-port the wastes to the dumpsites as a result of small fundallocation for USWM. Untreated waste is also increasingwith time due to the lack of treatment facilities. As a result,composite index and public concern increase with time.

The composite index increases from 0.86 in 1995 to127.43 in 2025. The rapid increase in composite index withtime means that the quality of the environment is deterio-rating rapidly with time. The public concern increases from1 in 1995 to 6.78 in 2025, and this means that the public ismore concerned about the environment.

Fig. 5shows simulated uncleared non-recycling, uncle-ared recyclable waste, recyclable stock waiting for recy-cling, treatment capacity and landfill capacity. Unclearednon-recycling stock increases from 519,600 tonnes in1995 to 3.340e + 007 tonnes in 2025. Uncleared recyclablewaste stock increases from 395,00 tonnes in 1995 to

1.075e + 006 tonnes in 2005, and recyclable stock waitingfor recycling increases from 5,900 tonnes in 1995 to1.088e + 006 tonnes in 2025. Uncleared non-recycling isincreasing rapidly, but the uncleared recyclable waste stock

Fig. 3. Population, solid waste generation, collection capacity and electricity generation potential from solid waste of Dhaka city.



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and proposed desired landfill capacity, respectively. Logi-cally, the total fund required increases from Tk4.660e + 008 in 1995 to Tk 19.27e + 008 in 2005, and thetotal fund required for solid waste management increasesfrom Tk 1.18e + 008 in 1995 to Tk 6.16e+008 in 2005.Thus, increased funds are needed for both collection andsolid waste management.

Fig. 7 shows the simulated desired number of trucks,number of trucks used, surplus or deficit total budget,

surplus or deficit budget for collection and percent offund available for collection for a time horizon of 30years. The desired number of trucks increases from 575

in 1995 to 2384 in 2025, whereas the number of trucksused increases from 230 in 1995 to 1148 in 2025. Thereis always a gap between the desired number of trucksand number of trucks used. Thus, the collection serviceat Dhaka city is deteriorating rather than improving.Moreover, the transportation of the waste to the dumpsiteis not properly managed. Wastes are seen flying from thetrucks during transport. Since the population and wastesgenerated are increasing with time, the desired number

of trucks is also increasing. The number of trucks neverequals the desired number of trucks, since the policywas to reduce the shortage in number of trucks, which

Fig. 6. Simulated total fund required for collection, fund required for disposal, fund required for processing, total fund required and fund for USWM fora time horizon of 30 years (one US $ = Taka 70.00).

Fig. 7. Simulated desired number of trucks, number of trucks used, surplus or deficit budget, surplus or deficit budget for collection and percent of fund

available for collection for a time horizon of 30 years.



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is dynamic. This indicates that more funds are required tomitigate the shortage of trucks and to meet the collectioncost. The patterns of the change in the budget deficit andthe budget for collection decrease with time but the per-cent of fund available for collection increases from almost34% in 1995 to 39% in 2000, then gradually to 43.5% in

2005, and then almost remains constant. Thus, there ishigh shortage of fund for collection particularly for trucksfor collection.

Fig. 8 shows the simulated percent of fund increaserequired for only total waste collection and total USWMfor a time horizon of 30 years. Initially the required budgetfor collection is 291%. The budget requirement for collec-tion decreases from 291% to 254% sharply within 5 years,then it gradually decreases to a constant value of 238%within 10 years and it continues up to 25 years. After 25years, it decreases gradually. But for total urban solidwaste management, the required budget for total wastemanagement is 415%. Then, the budget requirement

decreases gradually from 415% to an almost constant valueof 340% within 10 years. The initial jumps of the budgetsfor total waste collection and total urban solid waste man-agement are due to the introduction of treatment plant andlandfills for solid waste disposal.

In order to obtain insight into the effect of the alterna-tive policy options, the following two policy options areconsidered:

Policy 1:Increasing the collection capacity and assessingits impact on uncleared waste, untreated waste, number oftrucks and composite index.

Policy 2: Increasing collection capacity, treatment

capacity, and landfill capacity and assessing its impact onuncleared waste, untreated waste, number of trucks andcomposite index.

Policy 1: Fig. 9 shows the simulated uncleared waste,untreated waste, number of trucks and composite indexfor increase in collection capacity for a time horizon of30 years. From the figure it is observed that if we increasethe collection capacity by doubling truck increase rate, theuncleared waste decreases and untreated waste increases,

but the composite index remains unchanged as comparedwith the base scenarios discussed earlier. This means thatincreasing collection capacity alone does not improve theenvironmental quality because composite index is the indi-cator of environmental quality.

Policy 2: Fig. 10shows the simulated uncleared waste,untreated waste, number of trucks used and compositeindex with increase in collection capacity, treatment capac-ity and landfill capacity for a time horizon of 30 years.FromFig. 10, it is observed that if we increase collectioncapacity, treatment capacity and landfill capacity by dou-bling the truck increase rate, treatment capacity increaserate and landfill capacity increase rate, respectively, the

uncleared waste decreases in a similar fashion as in Policy1; but untreated waste and the composite index alsodecrease as compared to Policy 1. Increased compositeindex is the sign of environmental quality deterioration,and decreased composite index is the sign of environmentalquality improvement. This implies that the increased bud-get allocation for both clearing and treating the wastes isessential for improving the environmental quality ofDhaka city.

Energy from the waste and from the incinerationreduces greenhouse gas emission. An analysis of CO2equivalent emission per kWh of electricity produced by

energy from waste showed that the global warming poten-tial of emission from waste is less than coal, fuel and evennatural gas.

Fig. 8. Simulated percent of fund increased required for only total waste collection and total USWM for a time horizon of 30 years.



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4. Conclusions

Solid waste generation, waste collection capacity, andelectrical energy generation potential from the solid wastefor Dhaka city are increasing with time. Adoption of thepolicy for electricity from the urban solid waste of Dhakacity should be dictated by the economy of adoption of thetechnology of electricity generation from the waste andthe level of adverse environmental impacts. Uncollectedwaste, untreated waste, composite index and public con-cern are increasing with time. Uncleared non-recycling is

increasing rapidly but the uncleared recyclable waste

and recyclable stock waiting for recycling are increasinggradually with time. With the current trend of fund allo-cation for USWM of Dhaka city, it is not possible tomanage the solid waste. More funds are required to mit-igate the shortage of trucks and to meet the cost of collec-tion of all generated waste. If the current budget forUSWM is used only for collection, the deficit budgetfor collection will improve, but a zero balance or surplusfund is not realized. Increasing collection capacity alonedoes not improve the environmental quality. An increasein the budget allocation for both collection and treating

the wastes is essential for improving the environmental

Fig. 9. Simulated uncleared waste, untreated waste, number of trucks and composite index with increase in collection capacity for a time horizon of 30years.

Fig. 10. Simulated uncleared waste, untreated waste, number of trucks and composite index with increased collection capacity, treatment capacity andlandfill capacity for a time horizon of 30 years.



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quality of Dhaka city. The model has the potential toassess the treatment facilities to achieve a desired environ-mental quality improvement. Solid waste management hasinterwoven and interdependent issues, which are to beaddressed from a system perspective. Finally, this modelcan be used as a tool or resource to support USWM pol-

icy analysis.

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