Municipal Solid Waste to Energy Generation in Bangladesh : Possible Scenarios to Generate Renewable Electricity in Dhaka and Chittagong City

Increased generation of methane (CH 4 ) from municipal solid wastes (MSW) alarms the world to take proper initiative for the sustainable management of MSW, because it is 34 times stronger than carbon dioxide (CO 2 ). Mounting land scarcity issue around the world brands the waste to energy (WtE) strategy for MSW management in urban areas as a promising option, because WtE not only reduces the land pressure problem, but also generates electricity, heat, and green jobs. The goal of this study is to evaluate the renewable electricity generation potential and associated carbon reduction of MSW management in Bangladesh using WtE strategies. The study is conducted in two major cities of Bangladesh: Dhaka and Chittagong. Six different WtE scenarios are evaluated consisting of mixedMSW incineration and landfill gas (LFG) recovery system. Energy potential of differentWtE strategy is assessed using standard energy conversion model and subsequent GHGs emissions models. Scenario A 1 results in highest economic and energy potential and net negative GHGs emission. Sensitivity analysis by varying MSW moisture content reveals higher energy potential and less GHGs emissions from MSW possessing low moisture content. The study proposes mixed MSW incineration that could be a potential WtE strategy for renewable electricity generation in Bangladesh.


Introduction
The agitated race of human society towards modern urban life around the world generates tremendous amount of municipal solid waste (MSW) [1], because the generation rate is mounting even faster than the rate of urbanization [2].Global MSW generation showed a twofold increase just only within 10 years from 0.68 billion tons per year in 2000 to 1.3 billion tons per year in 2010.Moreover, it is projected to reach 2.2 billion tons per year by 2025 and 4.2 billion tons per year by 2050 [2].This humongous waste load of urbanized world if not managed properly will certainly have a negative impact on sustainable living style, local environment, and human health [3].Severe MSW management problems are reported in a number of cities of different countries like China [4], India [5], Malaysia [6], Thailand [7], and Bangladesh [8], because of rapid population growth, fast industrialization, and urbanization.
Tremendous generation of MSW because of fast population growth and ongoing economic development is already blamed for significant environmental glitches in Bangladesh [8][9][10].Bangladesh has enjoyed tremendous growth in its economy over the last few years, and this persuades a great influx of village workforce to cities [11][12][13].In this circumstance, for sustainable MSW management population and economy growth should be constructively transformed, because they are the major drivers of wastes generation [6,14].Around the world to ensure sustainable MSW management, four options are now considered, such as thermal treatment, biological treatment, landfilling with energy recovery, and recycling [15], as presented in Figure 1.Among them, thermal treatment, biological treatment, and landfilling with energy recovery are based on the theme of energy recovery option of MSW management hierarchy [16].
Waste treatment process generating energy in the form of electricity, heat, or transport fuels is considered as waste to energy (WtE) option.Each year 2.3 billion tons of MSW will be generated by 2025, and this is equivalent to 2.58×10 23  for the future because with this amount of energy 10% of global annual electricity need can be satisfied [17].In fact, by the world economic forum report "Green Investing: Towards a Clean Energy Infrastructure" published in 2009, WtE is identified as one of the eight technologies having significant potential to contribute to future low-carbon energy system [18].According to some estimation, WtE option by 2022 will treat at least 261 million tons of MSW per year to produce 283 terawatt hours (TWh) of electricity and heat [17].The most two common practices for WtE method are mixed MSW incineration and landfill gas (LFG) recovery system [19], but the most economically feasible solutions to be used in the future energy system are mixed MSW incineration [20].A general overview of major WtE technologies is presented in Table 1.
Large-scale WtE option, mostly incineration of mixed MSW as a means of sustainable MSW management, has been implemented in the countries like Denmark, Germany, Netherlands, Sweden, and UK [20]; Malaysia [19]; Indonesia, China, Japan, and Korea [21]; and USA [22].Globally more than 800 WtE incineration plants are now operating in approximately 40 countries.Most of them located in Europe (472), Japan (100), and USA (86) [23].In China, operational or under construction WtE incineration plants are expected to be over 300 by the end of 2015 [4,24], with the aim of building the world largest WtE incineration plant in Shenzhen [25].
On the other hand, sustainable MSW management in Bangladesh is still a dilemma in spite of continuous government effort [8,9].This has been reflected in the available scientific literature related with MSW management in Bangladesh.A number of studies have been conducted covering a number of aspects related with MSW management issues in Bangladesh, such as characterization and factor of the MSW generation [10,[26][27][28][29], disposal status and management problems [8,[30][31][32][33][34][35], peoples willingness to pay for different wastes management option [36,37], composting aspects [26,38,39], and recycling aspects [33,40].A few studies have been conducted to estimate electricity generation potential [41][42][43], but none of the studies is conducted to comprehensively assess the feasibility of WtE strategies in terms of energy conversion and carbon reduction from MSW management in Bangladesh.
Energy availability greatly stimulates the economic and social development as well as living standard in a society [44,45].Bangladesh is an energy deficit country and the energy source is not sustainable because of the major share of fossil fuel in the energy mix [46,47].Moreover, to overcome this energy deficit situation, Bangladesh government recently aims to reduce gas-based electricity generation and gradually shift to coal-fired power plant, which will certainly increase national carbon footprint [48][49][50].Bangladesh is an energy dependent country, and an increase in the energy supply has a positive impact on economic development [51][52][53].In these circumstances, WtE for MSW management in Bangladesh can be a viable option for alternative and renewable electricity generation.Such strategy will also avoid significant GHG emissions by replacing the equivalent fossil fuels electricity.Moreover, deploying WtE strategy will help Bangladesh to move towards zero waste society and to adopt circular economy principle at the national level.
In view of the above-mentioned contexts, this study is conducted with the goal to assess the potential of WtE   Typical characterization of MSW in Dhaka and Chittagong city by different study is presented in Table 3. From Table 3, it can be clearly stated that the solid wastes of Dhaka and Chittagong consist of mainly organic and inorganic fraction like food waste, paper, textile, rubber, plastic, glass, metals, and wood.The major fraction (75%) of MSW in Bangladesh is food waste [28,31], whereas it is 50% in China [4], 40% to 60% in Malaysia [6,44], and 20% to 30% in US and European countries [42].

Data Collection.
The field work of this study was conducted in Dhaka city and Chittagong city (Figure 3) for a total time period of five months.Detailed survey was conducted during this period by a group of data collectors.Detailed survey covers basically direct observations, interviewing the officials of MSW management authority of both cities, and segregation of MSW at the solid waste disposal sites (SWDS).Segregation of MSW was performed at the primary level (source), secondary level (dustbin along the street), and third level (SWDS) to identify and quantify different MSW categories.Quantification and percentage of different MSW were computed from 5 kg sample.MSW generation and disposal data for both the cities from 2000 till 2015 were collected from authority of both the cities.An extensive literature review was also performed to compare the composition and characteristic of MSW of both cities.MSW projection models through ( 1) and ( 2) were used to predict the future MSW in Dhaka and Chittagong city (Section 3.2), ( 6) and ( 7) were used to model the energy generation through MSW incineration plant (Section 3.4), and ( 8) were used to model the CH 4 emissions from landfill (Section 3.4).Equations ( 10) and ( 11) were used to model the net carbon emission (Sections 3.6 and 3.7).Different WtE options were analyzed under six different scenarios to find the optimum solution.A sensitivity analysis was performed to evaluate the effects of moisture content of MSW on the energy potential and GHGs emissions.The methodological framework of the study is presented in Figure 4.

3.2.
Projected Future MSW Generation.Future MSW generation was projected for Dhaka and Chittagong city using ( 1) and (2).A brief sketch about these two approaches is given here: (i) Historical trend: annual growth rate of population in the respective city was computed from census data [62], and average growth rate in the per capita waste generation was computed from historical waste generation (2001 to 2015).Projected waste generation was calculated using Here, PWG is projected wastes generation in a year (tons); PBY is population in baseline year; AGP is annual growth rate of population; PCWB is per capita wastes generation in baseline year (kg/cap/day); AGW is average growth rate in the per capita waste generation.(ii) Compound annual growth rate (CAGR), gross annual product (GAP), and income spending approach: Dhaka city

Sensitivity analysis
Varying moisture content ±30% compound annual growth rate (CAGR) of population in the respective city was calculated at first using census data [62].Gross annual product (GAP) growth rate of Bangladesh was assumed as 4%, and 70% of income is assumed to be used for expenditure to bear the personal consumption in Bangladesh [30].Waste generation growth factor is calculated as 0.028 (4%× 70%).Projected waste generation was calculated using Here, PWG is projected wastes generation in a year (tons In (3),  is moisture fraction of MSW (%),  is initial weight of the sample which belongs to an individual class, and  is weight of an individual class after drying.
In (4),  is dry weight fraction of MSW (%),  is wet weight fraction of MSW (%), and  is moisture content (%).The physical and chemical characteristics of the MSW of Dhaka and Chittagong city are presented in Table 4.

Energy from MSW by Waste Incineration.
Energy content of MSW highly influences the waste combustion processes in an incinerator to generate the electricity.For generation of electricity by combusting MSW, unsegregated wastes feed stock combusted in a furnace or boiler, under high temperature (980 to 1090 ∘ C) conditions with excess oxygen.MSW feed stock is converted into heat, flue gases and particulates, and incinerator bottom ash.The heat is used to produce steam and based on the Rankine cycle principle in steam turbine electricity is generated [19,60,61].Under ideal situation MSW combustion processes chemical reaction is represented using [19] Organic matter + Excess air The energy content of MSW is usually expressed by its lower heating value (LHV).In this study, the approximate LHV of MSW of Dhaka and Chittagong city is computed by ultimate analysis and compositional analysis.Under the ultimate analysis, LHV of MSW of Dhaka and Chittagong city was estimated using the mathematical correlation of the modified Dulong equation, as shown in (6) [19,60].
Under the compositional analysis, LHV of MSW of Dhaka and Chittagong city was estimated using the typical heat values of MSW components and using (7).Typical heat values of MSW components are presented in Table 5 [61].
The values of the variables in (6), such as C org , C iorg , and MC (moisture content), are presented in Table 4.
In (7), HV  is typical heat values of MSW component  and DW  is dry weight fraction (%) of component .

CH 4 Generation in Landfill.
Estimation of methane (CH 4 ) emission from SWDS was done using a simple and straightforward method called the intergovernmental panel on climate change (IPCC) methodology [63].The global warming potential (GWP) of CH 4 was taken as 34 [64].Methane emission from SWDS was estimated using (8), and adopted parameters are presented in Table 6.

GHGs
Avoidance.This study quantified the GHGs avoidance from equivalent CO 2 emission avoidance from coal electricity.Bangladesh now is establishing all the coal based power plant to ensure constant supply of electricity in the future [48].Hence, electricity generated using MSW in Dhaka and Chittagong city under different scenarios using WtE strategy was assumed to replace electricity generated from coal and so CO 2 emission avoidance was computed using In (11), EP MSW is electricity production from MSW using WtE projects or LFG and CF EC is carbon emission factor of per KWh electricity production from coal.Carbon emission factor of 1.001 kg CO 2 /KWh was considered in this study [67].[19,44].

Results and Discussion
Figure 6 presents the energy potential through electricity generation from WtE strategy.As mentioned earlier, the energy of MSW in Dhaka and Chittagong city can be recovered through mixed MSW incineration plant and LFG recovery.As shown in Figure 6, the electricity generation from mixed MSW incineration and LFG recovery is estimated to increase from 2001 to 2050 because of increasing generation rate of MSW.In Dhaka and Chittagong city an estimated 1444 and 1394 GWh electricity can be produced, respectively, by 2050 through MSW incineration, under the context of ultimate analysis derived energy value and historical MSW generation rate.The electricity generation potential through MSW incineration was even higher when MSW was projected under CAGR approach, which was 2132 GWh for Dhaka and 1556 GWh for Chittagong.From WtE analysis, it was observed that MSW incineration has a higher electricity generation potential in both cities compared to LFG recovery.Other similar WtE potential assessment study also reported mass MSW incineration as highest power yielding option than the other WtE option like RDF and biomethanation and incineration with recycling [71] and LFG recovery [72].

Economic Analysis. The design capacity of mixed MSW incineration plant to generate electricity in Dhaka and
Chittagong city is assumed as 1200 tons/day.The electricity generated is assumed to replace coal electricity in Bangladesh.Since the economic life of existing as well as proposed coal power plants in Bangladesh is assumed to be 30 to 50 years, for WtE incineration plant economic life was also taken as 35 years.For the economic analysis of this study, capital costs of incineration plant to generate electricity in Dhaka and Chittagong city are assumed as $36 per ton of MSW per day [73], and operation and maintenance costs as $60 per ton of MSW [74].On the other hand, landfill with LFG recovery system is assumed to have a capacity of greater than 1000 tons mixed MSW/day for a period of 35 years.
For the economic analysis of this study, capital costs of landfill with LFGs recovery system in Dhaka and Chittagong city are assumed as $14 per ton of MSW per day, and operation and maintenance costs as $10 per ton of MSW [74].Carbon credit revenue is assumed as $15.2 per ton of CO 2 [75].Electricity sales revenue is taken from the residential tariff rate ($0.13/KWh) of Dhaka Power Distribution Company Limited (DPDC), because the generated electricity is assumed to consume at the residential sector.
The economic analysis based on electricity sales, carbon credits, and the capital and operating cost for MSW incineration plant and LFG recovery in Dhaka and Chittagong city is shown in Figure 7. Higher electricity production from MSW incineration plant increased the revenue as a result of higher electricity sales and associated claiming of carbon credits due to higher avoidance of CO 2 from coal based power plant.Approximately US $535 million and US $251 million of revenue can be generated from the sales of electricity and claiming of carbon credits from MSW incineration and LFG recovery, respectively, in Dhaka and Chittagong city under the CAGR approach of MSW projection in 2050, while under the historical MSW generation rate based MSW projection resulted in US $412 million and US $188.92 million of revenue in Dhaka and Chittagong city in 2050.However, incineration requires higher capital and operating costs than LFG recovery system, and revenue from MSW incineration is much lower when the LHV value calculated by compositional analysis was used as shown in Figure 7.  8).The scenario analysis was performed using the LHV value of MSW estimated by ultimate analysis.The scenario analysis results of energy potential and net GHGs emissions for different WtE strategy in Dhaka and Chittagong city are presented in Figure 8.The net GHGs emission for all scenarios ranged from −0.29 to 0.81 tCO 2 equivalent/tMSW.The negative value in net GHGs emission represents the idea that this respective strategy avoided more CO 2 than its process emission.With the same composition of MSW, the net GHGs emissions from LFG recovery system were noticeably higher than MSW incineration.BaU  All the MSW will be incinerated to generate electricity under the WtE project.Scenario A 2 All the MSW will be landfilled to generate electricity from LFG, under the WtE project.
Scenario A 3 50% MSW will be incinerated and 50% MSW will be utilized through LFG recovery system for integration of WtE (landfill and incineration) strategy.
Scenario A 4 70% MSW will be incinerated and 30% MSW will be utilized through LFG recovery system for integration of WtE (landfill and incineration) strategy.
Scenario A 5 30% MSW will be incinerated and 70% MSW will be utilized through LFG recovery system for integration of WtE (landfill and incineration) strategy.
A scenario (scenario A 0 ).So operating costs represent the current costs for managing (collection to disposal) the MSW in Dhaka and Chittagong city.In Dhaka, the operating costs for the ongoing MSW management practices are approximately BDT 626.24 ($7.97)/ton of MSW [1] and in Chittagong it is BDT 439 ($5.59)/ton of MSW [31].Hence, these costs were considered as operating cost for BaU scenario (scenario A 0 ). Figure 9 represents the cost and profit analysis of different WtE strategy for this study under different scenario.BaU scenario resulted in negative net profit as expected, because no effort is currently implemented in both cities to recover energy or generation of revenue from MSW. Scenario A 1 was the best WtE strategy with the highest profit of US $16.73/ton of MSW.Scenario A 1 can be considered as the optimal scenario, with the highest energy potential, best economic benefit, and GHGs emission reduction.The next best WtE strategy was scenario A 4 , with the second highest profit of US $11.87/ton of MSW.

Sensitivity Analysis.
To evaluate the impact of moisture content on overall energy potential and GHG emissions, a sensitivity analysis was performed by varying the moisture content of MSW within the range of ±0 to 30%.Scenario A 1 performance was evaluated, because it was identified as best option for WtE strategy for the management of MSW in Dhaka and Chittagong city, Bangladesh.The results of the sensitivity analysis varying the moisture content of MSW are presented in Figure 10.The results show that the overall GHG emission and energy generation were highly effected by the moisture content of MSW.With the increase or decrease of moisture content, the energy content, electricity generation, and GHGs emissions have changed reversely with a magnitude of 2%, 4.3%, and 9.5%, respectively.So it can be said that preheating of MSW to reduce the moisture content will increase the energy potential in Dhaka and Chittagong city and also reduce GHGs emissions.

Future Direction
This study is an attempt to inform the policy maker of Bangladesh regarding the potentiality of MSW as renewable source of energy in two megacities of Bangladesh, namely, Dhaka and Chittagong.Increasing demand for energy and unsustainable MSW management along with ever-growing shortage of available land space have necessitated the need for formulating a national WtE strategy.Bangladesh is trying to diversify its energy base by deploying a broad energy mix.On the other hand, energy security issue is one of the four security issues addressed in "National Adaptation Action Plan to Climate Change (NAPA), 2009" [76].In spite of growing concern regarding energy security, Bangladesh is still not stepping forward for the expansion of renewable energy technologies and yet relying on merely fossil fuel resources, with the small target to generate 5% and 10% of electricity using renewable energy technologies by 2015 and 2020, respectively [77].This study senses the urgency of reforming this policy because of global concern on GHGs footprint from fossil fuels and MSW generation.In the submitted intended nationally determined contributions (INDCs) to the UNFCCC, Bangladesh stated a voluntary 5% GHGs emission reduction from industry, energy, and transport sectors by 2030.Today or tomorrow, developing countries like Bangladesh will be also under the strict regulation for GHGs emission reduction, due to uncertainty regarding climate sensitivity [78].Two selected WtE technologies, such as mixed MSW incineration and LFG recovery, were evaluated in this study, based on MSW characteristics and generation.The selected WtE strategy has validated the prospects of mixed MSW incineration in Bangladesh to mitigate GHGs emissions and to generate considerable revenue from electricity sales and carbon credit.

Conclusion
Based on the recognized energy conversion model and net carbon emission model, the WtE analysis in Dhaka and Chittagong city has been performed focusing on potential electricity production, GHGs emissions avoidance, and higher economic profit.Six alternative scenarios for WtE in Dhaka and Chittagong city of Bangladesh were assessed.Scenario A 1 provided the highest net profit with better energy potential and net GHG emissions reduction.The total estimated economic profit in 2050 from two cities could be US $170.76 million and US $128.87 million, respectively, under the CAGR approach and historical rate of MSW projection for scenario A 1 .The estimated economic profit US $170.76 million is about 10 times higher than the income of the financial year 2013-14 (US $16.45 million) of CCC [79] and about 4 times higher than the income of the financial year 2012-13 (US $40.82 million) of Dhaka South City Corporation (DSCC) [80].
Sensitivity analysis revealed that some sort of preheating of MSW to reduce moisture can boost the energy recovery as well as GHGs emission reduction for the selected WtE strategy in Dhaka and Chittagong city.WtE strategy for the management of MSW in Dhaka and Chittagong city is vital to initiate nationwide circular economy principle and industrial ecology concept.This WtE strategy will also ensure availability of cheaper and greener energy, which will certainly reduce the energy crisis problem to a certain extent and can generate green jobs.The life of the WtE plant is chosen considering the economic life the coal based power plant on the ground that electricity generated will replace coal electricity.However, shorter life span like 20 years or less may alter the economic perspective of the chosen WtE scenario.The study concludes that WtE strategy based on mixed MSW incineration to generate electricity will deliver environmental benefits nationally and globally and will warrant comprehensive MSW management for the sustainable development in Bangladesh.

Figure 2 :
Figure 2: MSW disposal site in Dhaka and Chittagong city.(a-b) Amin Bazar and (c-d) Matuail dumping site in Dhaka; Matuail open dumping sites named as sanitary landfill (red circle in (d)), with the aim of converting it to sanitary landfill site in the future, but open dumping is practiced now.Kalurghat open dumping sites (e-f) and Ananda Bazar open dumping sites (g-i) in Chittagong.

Figure 3 :CO 2
Figure 3: Generalized map of the studied city of Bangladesh and its location in Bangladesh.

Figure 4 :
Figure 4: Methodological approach of the study.

Figure 5 :
Figure 5: Actual and projected waste generation (a) and associated GHG emission (b) in Dhaka and Chittagong city.Actual wastes generation is from 2001 to 2015, and 2015 onwards represents projection.The legends of the figure are given at the bottom of (a) and (b).

Figure 6 :
Figure 6: WtE assessments in terms of electricity generation potential (actual and projected) for Dhaka and Chittagong city from year 2001 to year 2050.(a) represents the projection using historical MSW generation rate and (b) represents the projection using CAGR approach.The legends of the figure are given at the bottom of (a) and (b).

4. 4 .
Scenario Analysis 4.4.1.Energy Potential and Net GHG.Six scenarios with varying WtE strategies were chosen to evaluate the impacts of MSW utilization for energy conversion and GHGs emissions (Table

Figure 7 :
Figure 7: Economic analysis (actual and projected) for LFG recovery system and waste incineration in Dhaka and Chittagong from year 2000 to year 2050.Carbon credit and electricity sales summed as revenue.(a) represents the projection using historical MSW generation rate and (b) represents the projection using CAGR approach.

Table 1 :
Overview of major WtE technologies.

Table 2 :
MSW disposal site and their salient features in Dhaka and Chittagong city.

Table 3 :
Typical MSW characteristics of Dhaka and Chittagong city.
). PBY is population in baseline year.CAGR is compound annual growth rate of population.PCWB is per capita wastes generation in baseline year (kg/cap/day).WGG is waste generation growth factor.
, MSW is total waste generation (tones/year); MSWF is waste fraction disposed to SWDS;  is 16/12, a conversion factor for converting C to CH 4 .The following are several coefficients involved to adopt the IPCC model to estimate the CH 4 emission for this study.
aged sanitary landfills, MCF = 1; for uncategorized SWDS, MCF = 0.6; for open dump with >5 m waste height, MCF = 0.8; and for open dump with <5 m waste height, MCF = 0.4 [44, 63, 65].As reported in Table4all the existing open dumping SWDS in Dhaka and Chittagong are of height greater than 5 m, so MCF value was taken as 0.8.

Table 4 :
Physical and chemical properties of MSW of Dhaka and Chittagong city considered in this study.

Table 5 :
[61]cal heat values of MSW components considered in this study[61].: a the values are converted from Btu/lb dry weight to KJ/Kg dry weight. Note

Table 6 :
Parameters adopted for IPCC default method in this study.WF  is dry weight fraction of waste component ; C iorg  is anthropogenic carbon fraction of component ; OF  is oxidation factor, with the default value of 1 for MSW;  = C to CO 2 conversion factor, with the value of 44/12; and  is component of MSW incinerated.
[61]61].Because the combustion of MSW for WtE project though CO 2 is emitted, it avoids the use of fossil fuels and the release of CH 4 from SWDS.This type of WtE project can also account for carbon credit, because combustion of MSW and associated electricity generation avoid CO 2 emission from fossil fuel  (WF  C iorg  × OF  ) × .

Table 7 :
WtE analysis parameter adopted for this study.
[19,[68][69][70] MSW of Dhaka and Chittagong city was 0.71 MJ/kg and 1.06 MJ/kg, respectively.Ultimate analysis of MSW in both cities resulted in a higher LHV value.Heat recovery efficiency of mixed MSW incineration plant is reported as 80 to 90%[19,[68][69][70].In this study, heat recovery efficiency of mixed MSW incineration plant in Dhaka and 2 /tMSW and 0.12 tCO 2 /tMSW, respectively.Landfill generated CH 4 is assumed to have a density of 0.667 kg/m 3 , LHV of 17 MJ/m 3 , and electricity generation factor of 0.2775 KWh/MJ

Table 8 :
Scenario description for the WtE option in Dhaka and Chittagong, Bangladesh.
Sensitivity analysis of MSW moisture contents on WtE performance and GHG emission.