Selection of Waste to Energy Technologies for Municipal Solid Waste Management—Towards Achieving Sustainable Development Goals

Abstract

The Sustainable Development Goals (SDGs) play an essential role, emphasizing responsible resource use, production, and consumption, including waste management. In addition, SDG 3, 7, 11, 12, and 13 are directly/indirectly related to waste management. This study aims to determine a suitable waste-to-energy (WtE) technology in Chittagong City, Bangladesh, focusing on cleaner technology. Anaerobic digestion, gasification, incineration, and landfill gas (LFG) recovery were considered as possible alternatives. Technical, economic, environmental, and social issues have been considered as necessary criteria for evaluation. An analytical hierarchy process was applied to rank these technologies based on stakeholders’ perceptions. The study found that anaerobic digestion (AD) ranked first, receiving 38% of overall weight. The second preferred technology is LFG (27%). Gasification and incineration stood at third and fourth, respectively (21% and 14%). According to a sensitivity study, the decision is only sensitive to the economy. LFG will become the most favoured solution for WtE conversion if the economy prioritizes more than 38%. Subsequently, this study’s findings will help achieve Bangladesh’s SDG agenda.

1. Introduction

Rising per capita energy use and production of waste are two of the largest issues the world is currently experiencing [1,2]. The increasing population, urbanization, and higher living standards around the world are all contributing factors to these problems. Cities all across the world generated about 2 billion tons of MSW in 2016 [2,3]. By 2050, this figure is expected to rise by 70%, reaching 3.40 billion tons [4,5]. Over 90% of waste in developing nations is frequently dumped in uncontrolled landfills or burned in the open [6]. Improperly handled, discarded, or burned waste endangers human health, damages the climate, and prevents economic growth in countries. As far as energy consumption is concerned, global energy consumption will grow by nearly 50% between 2020 and 2050 if present policy and technological trends continue [7]. More than 80% of energy used worldwide comes from fossil fuels of the five primary sources of greenhouse gases (GHGs) [7]. Scientists have warned that the bulk of the planet’s remaining fossil fuels must be kept underground by the year 2050, to avoid the worst effects of climate change [2].

Bangladesh, one of South Asia’s most rapidly urbanizing countries, has been struggling with a sharp rise in energy demand and waste production [8]. Nearly 42% of the generated MSW in Bangladesh is landfilled, which results in the contamination of surface and groundwater by landfill leachate, unpleasant odours, bioaerosol emissions, and toxic organic compounds [9]. The country does not have adequate waste management policies, systems, trash collection services, or government institutions to properly manage their wastes. In the case of energy generation, Bangladesh is also facing difficulty in bridging the gap between energy demand and supply [9]. The country is highly dependent on imported fossil fuels for electricity production. Currently, LNG imports provide more than 70% of Bangladesh’s principal energy source, gas. Bangladesh will have to pay five times more for LNG in 2022 than it did in early 2020 in order to address its energy issue. To offset the high cost of imported LNG, Bangladesh Energy Regulatory Commission has advised boosting electricity prices by 58% [10,11]. It is clearly visible that relying on imported fossil fuels is not helping Bangladesh to achieve sustainable economic growth due to the ongoing depletion of fossil fuel reserves, fluctuating oil and gas prices, and the effects of climate change [10].

As a signatory to the 2030 Plan for Sustainable Development, Bangladesh set a national goal of raising renewable energy’s proportion of overall energy consumption to 20% by 2030 [12]. However, by 2022, the share of renewable energy is 3.1 percent, including off-grid, which indicates that the government is well behind the track in attaining the target. In this situation, the government can consider waste-to-energy generation (WtE) to achieve the target [10,12]. In order to lessen reliance on fossil fuels, US policymakers are encouraging the recognition of WtE as a source of renewable energy. Thus, WtE can help the country to achieve the Sustainable development goal SDG7. The goal of increasing renewable energy’s share in the global energy mix (SDG7) also helps to accomplish the SDG 13, which focuses on taking immediate action to address climate change [13]. Furthermore, WtE implementation will assist the government in achieving goal number 11, which is to make cities inclusive, safe, resilient, and sustainable, as per the following: Reduce cities’ negative per capita environmental effect by 2030, notably by focusing on air quality and municipal and other waste management [12,13].

This study mainly aims to select suitable WtE technologies in the context of Chittagong, Bangladesh. With so many WtE technologies now readily available, picking the best one is difficult since various factors must be considered. There are two studies have been conducted to assess the feasibility of mixed MSW incineration and landfill gas (LFG) recovery in Chittagong, considering their success in developed countries [14,15]. However, what works successfully in developed countries will not perform well in Bangladesh due to differences in waste characteristics. These studies have considered only economic and environmental aspects for evaluating WtE technologies. However, according to Yong et al. [16], technical, economic, environmental, and social factors should all be considered while selecting the appropriate WtE. These studies are also “top-down approach” where stakeholder’s perception-based participatory approach is not considered. Therefore, it is essential to perform a study that considers technological, economic, environmental, and social factors while evaluating all possible WtE technologies through stakeholders’ perception-based participatory approaches. The study’s findings are expected to assist decision-makers in better understanding WtE technologies and choosing the most appropriate WtE for Chittagong, Bangladesh.

To select the most appropriate WtE technology while considering several factors, several researchers have applied the analytic hierarchy process (AHP) method, as shown in

Table 1. Ranking of WtE technologies by various researchers.

References	Yap et al., 2015 [18]	Rahman et al., 2017 [19]	Qazi et al., 2018 [17]	Marzia et al., 2019 [20]	Yong et al., 2019 [16]	Kurbatova et al., 2020 [21]	Alao et al., 2020 [22]	Agbejule et al., 2021 [23]
Method Applied	AHP-BOCR	AHP	AHP	AHP	SWOT	AHP	TOPSIS	AHP
Stake holders	Academic experts	Academic experts	Waste Management Department, Academic experts	-	-	Academics, Waste Professionals, Decision Makers of Federal and Local Authorities, Energy Specialist, Members of International donating agencies in Moscow, Graduate Researchers	-	Academics, Waste Professional, Graduate researchers in bioenergy and waste management on Ghana, Energy Regulator, Decision Maker
Alternatives considered	Incineration, Gasification, AD, LFG, RDF	AD, Plasma Gasification, Pyrolysis	Incineration, gasification, plasma arc gasification, pyrolysis, AD, Fermentation, TDP, HTC	Incineration, AD, LFG	AD, incineration, Plasma gasification, Pyrolysis, LFG	LFG, AD, RDF	Incineration, AD, LFG pyrolysis	Incineration, AD, LFG, Aerobic composting
Factors Considered	Cost, Opportunity, Benefit, risk	Technology, environment, economy	Waste quality and quantity, economy, social acceptance, environment	Cost, benefit, risk	Economy, environment, Technology, social and political	Environment and health, Technical, socio economic,	Technical, economic, environmental	Environment, technical, socio economic

. In Ref. [17], the stakeholders’ perception approach for ranking the WtE technologies was used. After obtaining the ranking, sensitivity analysis was performed by SuperDecisions software in order to investigate the stability of the priorities resulting from the AHP model. The findings of this research are expected to assist decision-makers in better understanding WtE technologies and choosing the most appropriate technique for Chittagong. Yap et al. considered the cost, opportunity, benefit and risk based on the AHP-benefits, opportunities, costs, and risks (AHP-BOCR) method [18]. Rahman et al. [19] and Marzia et al. [20] have applied the AHP method to select proper WtE technology for Dhaka, Bangladesh. This method allows decision-makers to consider and integrate opposing criteria simultaneously. The AHP method decomposes the complex decision problem into small sub-problems. It allows the decision-makers to compare the criteria considered for judgment pairwise. This method also enables the decision-makers to check the inconsistent judgment. Considering the popularity and numerous advantages, this study has applied the AHP method to select suitable WtE technologies for Chittagong. This research first determined the criteria and options for selecting suitable WtE technology in the context of Chittagong, Bangladesh. Potential stakeholders associated with the waste management of Chittagong, Bangladesh were then identified by applying snowball sampling.

Study Area

Chittagong, the study location, is the second largest city in Bangladesh. Figure 1 represents the geographical view of Chittagong, Bangladesh. The city is populated by 6.18% of the country’s urban population while generating 7.67% of its urban waste (Waste Concern, 2014). Under the ministry of local government and engineering department, Chittagong City Corporation (CCC) is responsible for the collection, transportation, and disposal of MSW in Chittagong, with 41 administrative areas named wards. Two dumping sites, namely Halishahar and Arefin Nagar, are being used by CCC for open dumping. In addition, illegal dumping of waste in riverbanks and canals is also common in Chittagong. Like other parts of the country, Chittagong city residents have been suffering due to a poor waste management system.

2. Research Methods

This research methodology is divided into several parts. The overall methodology of this research is shown as a flowchart as follows (Figure 2).

2.1. Identification of Criteria and Alternatives

A thorough literature assessment of waste to energy selection process was undertaken to determine the criteria and options (

Table 2. Criteria selected for the evaluation of the Waste to Energy Technology.

Criteria	Sub-Criteria	Description
Technology	Waste quality and quantity	How much a specific technology is compatible with the composition, calorific value, and quantity of the available waste from the city
	Continuity of supply	Sensitivity of the specific technology to the consistency of supply. The lower the sensitivity better the technology is.
	Waste Segregation	Define how sensitive a specific technology is to the waste segregation process. The lower the sensitivity, the better the technology is.
	Energy generation potential	The amount of electricity produced from waste using a specific technique. It is preferable to generate as much energy as possible from waste.
Environment	GHG emission	Greenhouse gas may be emitted during the operation of a specific technology. The lesser the emission, the better the technology.
	Production of hazardous waste	Various hazardous wastes like dioxin, furan, etc. can be produced during the operation of a specific technology. The lesser the emission, the better the technology.
Economy	Capital cost	This is the initial investment needed for the plant to start. Low-cost technology is recommended.
	O&M cost	The amount of money that will be spent on the plant’s Operation and maintenance over the course of its life. Its worth should be kept to a minimum.
Social	Safety of public health	The specific technology should not impose health hazards during the plant’s operation.
	Social acceptance	Resistance by local people can intensely affect the establishment of waste-to-energy plants inside an area. Innovation with high social acknowledgment is generally preferred.

). Then, for a region like Chittagong, four alternatives, namely anaerobic digestion (AD), incineration, gasification, and LFG were identified. The criteria and sub-criteria used to choose the best WtE technology are technical, economic, social, and environmental considerations. In Table 2, these requirements are concisely discussed and provided.

Some input data associated with this research, like the electricity generation potential of selected alternatives, economic criterion data, and environmental criterion data, were collected from research and journal papers and listed in

Table 3. Inputs considered for selecting WtE Technologies [16,17,25,26,27,28,29].

Options	Process Type	Energy Recovery Potential from Per ton of MSW [16,17,25]	Feedstock Type [16,17]	Moisture Content [16,17]	Capital Cost, (EUR/ton) [26]	O&M Cost (EUR/ton) [26]	GHG Emission (kg eqCO2/t of Waste) [27,28,29]
Incineration	It is a process of burning waste in a controlled environment in the presence of oxygen	2 MJ (electricity)	Biological and synthetic dry waste	25–30%	80–115	180	0.22
Gasification	It is a thermochemical process that converts organic waste into useful syngas in the presence of limited oxygen	2 MJ (Electricity)	Dry mixed MSW without inorganic materials	Below 15%	35–45	30–40	0.114
Anaerobic digestion	It is a process where organic compounds are broken down through microbes without oxygen.	0.04–0.09 MJ (Electricity)	Organic waste without metals and plastics	75%	12–19	10–15	0.2
LFG	Landfill gas (LFG) is produced by anaerobic degradation of the organic fraction of landfilled MSW.	0.003 m3/min (LFG)	Organic waste without metals and plastics	75%	1.4 (China CDM project)	0.3 (China CDM project)	1–1.2

.

2.2. Construction of Hierarchy Structure

As shown in Figure 3, a hierarchy structure is designed for the waste composition of Chittagong, Bangladesh. The essential requirements are found in the uppermost cluster. The second cluster is composed of the sub-criteria considered in this study. The alternatives considered in this study are kept at the bottom of the hierarchy.

2.3. Stakeholder Identification and Selection

Initially, the literature review identified the local authorities and researchers as stakeholders. The other potential stakeholders were identified by the snowball sampling technique, which is shown in Figure 4. As shown in

Table 4. List of stakeholders.

Stakeholder Groups	Invitation	Response	Responded Agencies
Governmental group (G)	9	6	BPDB, EGCB, PGCB, Chittagong City Corporation, CDA, LGED
Researchers (R)	6	4	Premier university, Chittagong University of Engineering and Technology, Chittagong University, Chittagong medical college.
Private sector (P) (service suppliers, technology suppliers)	2	1	Nirapod Engineering Limited
Community (C) (non-governmental organizations (NGOs), local community and media)	6	4	Seba foundation, Chittagong Television, Bangladesh Betar, Residents near dumpsites.
Total	23	15	65% response

, identified stakeholders were divided into four groups: government, academics, private sector, and society. Since AHP is not a statistics-based strategy, no discussion of the optimum size of the number of stakeholders has been conducted. Stakeholders in high positions (such as renewable energy experts or directors of their organizations) were selected for this analysis, and questionnaires were circulated.

Prior to calling and/or sending e-mails to stakeholders, the study’s overall description was presented, and the prospect of answering questionnaires was inquired about. The questionnaires were then distributed to 23 stakeholders, including 9 government departments, 3 non-governmental organizations, 6 educational institutions, 2 technicians, and three communal organizations. Fifteen responses were received from the 23 invited stakeholders, reflecting a 65 percent response rate. Those stakeholders who expressed concern about the weightings were individually contacted after the questionnaires were distributed.

2.4. Questionnaire Development and AHP Analysis

The purpose of the questionnaire was to obtain stakeholder weightings for WtE technologies. The procedures for carrying out the weightings in pair-wise comparisons were given in the questionnaire. It also contains a series of questions that ask each responder to compare the relative importance of two evaluation items on a scale of 1 to 9 (Appendix A). The pair-wise comparison is based on the four-level hierarchical structure, which is shown in Figure 3. For instance, if the stakeholders believe that “Environmental” criteria is significantly more important than “Technology” criteria, then a pair-wise comparison metric would indicate a scale of “7”.

In this research, AHP analysis was performed using SuperDecisions software [30]. The advantage of this software is that it allows for the integration of tangible factors, intangible factors, and human judgments in decisions. The steps followed for AHP are shown detail in Appendix B.

3. Results and Discussion

3.1. Waste Quality and Quantity

The amount of waste produced, and its composition must be taken into account when choosing an acceptable WtE technology, in addition to sustainability factors [27]. This study provides greater details on the MSW quantity and waste composition in Chittagong, Bangladesh. Primary data on waste quality and quantity of Chittagong, Bangladesh, has been collected by dumpsite visit and sample collection. A sample of MSW weighing around 250 kg was reduced to 15 kg using the coning and quartering technique without affecting the makeup of the solid waste components, which is shown in Figure 5. According to Arunprakas et al. [31], the quartering method’s mixing stage can be carried out accurately if the MSW weights less than about 50 kg. In order to increase precision, MSW is first divided into smaller pieces before being quartered. Two diagonal sections of MSW were combined once more after being divided into four equal sections and chopped into large portions. Figure 5 demonstrates these procedures [32]. The reduced sample was then sorted out manually into food waste, fabric, paper, plastic, wood, metal, and other categories. From this research, it was found that a significant portion of the waste is composed of food (around 80%). Plastic constitutes the seconds largest share (8%) of the waste stream. Figure 6 represents the distribution of collected waste over different categories.

According to the proximate analysis, the sample contained 80% moisture content, 17% volatile matter, 2% ash, and 1 % fixed carbon. In this research, the data on waste disposal per day (from 2016 to 2019) were collected from Chittagong City Corporation Authority. According to the collected data, MSW generation in the city has varied between 2000 Ton per day (TPD) and 2400 TPD, with an overall upward trend.

3.2. Weight Determination by Various Stakeholder Groups

Table 5. Preferences on criteria and sub-criteria.

Criteria	Group Priority on Criteria				Sub Criteria	Priority Factor				Global Weight
	G.	R.	C.	P.		G.	R.	C.	P.	G.	R.	C.	P.
Technology	0.351	0.276	0.156	0.351	Waste quality and quantity	0.2	0.073	0.25	0.2	0.07	0.02	0.039	0.07
					Continuity of supply	0.2	0.498	0.25	0.2	0.07	0.138	0.039	0.07
					Waste segregation	0.2	0.366	0.25	0.2	0.07	0.101	0.039	0.07
					Energy potential	0.4	0.063	0.25	0.4	0.14	0.018	0.039	0.14
Environment	0.189	0.498	0.462	0.189	GHG emission	0.667	0.5	0.667	0.667	0.126	0.249	0.308	0.126
					Production of Hazardous waste	0.333	0.5	0.333	0.333	0.063	0.249	0.154	0.063
Economic	0.351	0.045	0.088	0.351	Capital cost	0.333	0.25	0.5	0.333	0.117	0.011	0.044	0.117
					O&M cost	0.667	0.75	0.5	0.667	0.234	0.034	0.044	0.234
Social	0.109	0.181	0.294	0.109	Safety of public health	0.5	0.75	0.5	0.5	0.055	0.136	0.147	0.055
					Social acceptance	0.5	0.25	0.5	0.5	0.055	0.045	0.147	0.055

shows the priorities on criteria and sub-criteria set by various stakeholders. All stakeholders, except private groups, have placed a high emphasis (more than 40%) on the environment. On the other hand, private groups have prioritized economy and technology as the essential criterion, each of them 35% of the total weight. A WtE plant, according to this group, cannot be developed without techno-economic feasibility. The government group also gave the economy a quarter of the weight. Because they claimed that economic viability was a major factor in selecting whether or not to pursue WtE initiatives in the past. On the other hand, the community and researchers have given the economy the lowest priority. These two groups placed a greater emphasis on social issues and technology than economics. Overall, the environment has gotten the most priority (42%), followed by technology (25%). The social aspect was only 1% more important than the economics (16%).

In terms of sub-criteria, almost all stakeholders (excluding researchers) have given “GHG emission” more priority than “hazardous waste production,” according to Table 5. The majority of stakeholders perceive “operating costs” to be more significant than “capital costs” in economics. The government and researchers agreed that “public health safety” is more important than “public approval.” The other two groups, on the other hand, have given equal weight to these two sub-criteria.

However, unlike other sub-criteria, stakeholders’ opinions on technological sub-criteria have varied. While the governmental group and the private group have given their highest priority on “energy recovery potential”, researchers put more emphasis on “waste segregation” and “continuity of waste supply”. On the other hand, the community has given equal weight to all sub-criteria under technological aspects. This variation in the opinion of the stakeholders is because of their backgrounds and experience. In addition, no workshop or group discussion between stakeholders was conducted in this study due to the COVID-19 situation.

3.3. Ranking of Alternatives

By aggregating stakeholder opinions on sub-criteria, the preferences of each stakeholder group on alternatives were determined. According to Figure 7a, all groups judged AD to be the best alternative for “waste quality and quantity”. Due to a higher organic fraction in Chittagong MSW, stakeholders believe AD is the best option for treating this waste. Stakeholders also agreed that AD emits fewer GHG and Hazardous waste, has relatively cheaper capital and operating and maintenance costs, and is more socially acceptable.

However, AD obtained the least preference from almost all the stakeholders in terms of “waste segregation”, indicating that AD is highly sensitive to this sub-criterion. Some previous incidents also support the stakeholder’s point of view. Lucknow Municipal Corporation, for example, constructed a 5-MW anaerobic digestion plant to treat 500–600 tons of municipal waste daily [33,34]. However, because of the high level of inert compounds in the trash, the plant was unable to run at total capacity for even a single day and was shut down [33,34].

On the other hand, LFG received the highest ranking from all the stakeholder groups as they feel that the LFG recovery project would be the most cost-effective to deploy in existing landfills. While the majority of the stakeholders picked gasification as the greatest option in terms of “GHG emission potential,” incineration was chosen as the best alternative in terms of “energy recovery potential” and “waste segregation” (Figure 7a). The final priorities of alternatives are derived after aggregating the local priorities of all sub-criteria, criteria, and alternatives, as shown in Figure 7b.

All the stakeholders favoured AD over other technologies, according to the findings. Researchers and the community assigned AD more than a fifth of the total weight. However, only around 2% more weight was given to AD than the LFG recovery by private and government organizations. This is because the community and researchers are more concerned about the environment, and AD outperformed LFG in this criterion. On the other hand, the private and public sectors are more concerned with the economy, with LFG receiving the most preference. Incineration, on the other side, received the least amount of support because of its severe environmental impact.

3.4. Sensitivity Analysis

Sensitivity analysis was carried out in order to verify the results. This analysis evaluated the stability of the priorities by changing one of four main criteria while keeping the others in the same percentage. Figure 8 represents the results of the sensitivity analysis. According to the analysis, the only criterion influencing AD’s leading position is the “economy”. LFG would become the first choice for waste-to-energy production if the economy’s weight increased by more than 38%, as shown in Figure 8a. According to Figure 8b, when the weight of environmental criteria increases, the preference of gasification and anaerobic digestion rises, while the priority of LFG recovery and incineration decreases. If the importance of the environment increases over 0.5, gasification will replace LFG as the second most important option. On the other hand, the position of AD is unaffected by the environment; whether it increases or decreases, the position of AD remains unchanged.

The priority of AD and LFG recovery increases as the social criterion’s weight increases, according to the sensitivity analysis of the social criterion (Figure 8c). The importance of incineration and gasification, on the other hand, works in the other direction. However, throughout the investigation, the overall rating of these technologies has remained unaltered. Sensitivity analysis on technology, represented in Figure 8d, shows that the first position occupied by AD is insensitive to this criterion. However, incineration would become the second preferred choice if the priority on this criterion rises over 0.67.

4. Conclusions

In conclusion, this study aims to select the most appropriate WtE for Chittagong city through the stakeholders’ perception-based participatory approaches. It was found that Anaerobic Digestion (AD) is the most preferred technology for Chittagong, Bangladesh. This finding is closely agreed with the results of [17,35,36,37,38], who used the AHP approach to determine the optimum waste treatment option for their respective cities/countries. Stakeholders considered AD as the best option due to the waste quality and quantity of the city, cost-effectiveness, limited environmental footprints, and high potential for energy recovery. This research has also found that the majority of the stakeholders have preferred the environment over other criteria while evaluating the technologies. Sensitivity research has revealed that, if this preference changes and the preference on economy rises above 0.038, LFG will emerge as the best alternative. However, WtE is well positioned to support existing objectives for renewable energy and sustainable cities, as outlined in SDGs 7 and 11. Subsequently, ensure healthy lives and promote well-being for all at all ages, and ensure sustainable consumption and production patterns as a part of the goal of SDGs 3 and 12. Wider adoption of these technologies may be hampered by a variety of factors. Hence, further research is required to identify those negative factors and solve them.

This study is unique in that it incorporated the opinions of each stakeholder group while ranking WtE technologies in Chittagong, Bangladesh. All studies on ranking WtE technologies in the context of Bangladesh follow a “top-down” approach, ignoring stakeholder perspectives and participatory approaches. The spontaneous involvement of diverse stakeholder groups in selecting appropriate WtE technologies can result in the effective implementation of the chosen technology in the city. In addition, no detailed research has yet been conducted to rank suitable WtE technologies in the concept of Chittagong. Although Chittagong City Corporation planned to build a WtE plant in 2018, they failed to implement it because of insufficient knowledge on WtE technologies. This research is expected to assist decision-makers in better understanding WtE technologies and choosing the most appropriate WtE for Chittagong.

However, this study had some limitations, including the following: (a) the impact of seasonal variation on MSW was not taken into account; (b) the unwillingness of some stakeholders to participate due to a lack of time; (c) the knowledge and experience of some stakeholders being insufficient; (d) the workshop or group meeting not being held due to COVID 19; and (e) the majority of the stakeholders did not recognize the significance of waste segregation while ranking the alternatives, although the example of the failure of the AD plants due to this was given to them.

This study recommends that (a) MSW sampling be done at different times during the year; (b) to enhance stakeholder consistency, seminars and community meetings would be helpful; and (c) authorities should consider waste segregation as an important issue while implementing AD. Source-separated organic fraction of MSW should only be fed to the AD plant for proper operation.