Ashish
Soni
a,
Sonu Kumar
Gupta
b,
Natarajan
Rajamohan
c and
Mohammad
Yusuf
*de
aCentre for Additive Manufacturing, Chennai Institute of Technology, Chennai, Tamil Nadu 600069, India
bDepartment of Civil Engineering, School of Engineering and Technology, Sandip University, Nashik, MH 422212, India
cChemical Engineering Section, Faculty of Engineering, Sohar University, Sohar PC-311, Oman
dClean Energy Technologies Research Institute (CETRI), Faculty of Engineering & Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada. E-mail: mohd.yusuf@uregina.ca
eUTE University, Faculty of Architecture and Urbanism, Architecture Department, TCEMC Investigation Group, Calle Rumipamba S/N and Bourgeois, Quito, Ecuador
First published on 21st May 2025
The huge generation of municipal solid waste along with the reliance on natural resources to meet the ever-increasing demand of energy has stimulated the world towards the exploration of novel methods for the recovery of energy and resources by using the generated waste. Despite the numerous advantages of waste-to-energy (WtE) technologies, these techniques are not widely implemented. The review has summarized the various aspects of WtE techniques including advantages and limitations, techno-economic analysis, challenges and prospects, framework and implementation. The review has identified that the WtE techniques are more efficient than conventional waste management practices. The characteristics of municipal solid waste (MSW) vary with geographical conditions, living standards, socio-economic conditions, etc. Therefore, no particular WtE technique is equally feasible for the treatment of MSW. The strict environmental strategies, policies, and guidelines can assist in selecting the best WtE practice. The thermal treatment methods can effectively reduce the volume of generated waste by up to 90%. Techno-economic analysis has revealed that WtE techniques are economically feasible with suitable measures. The life-cycle assessments have found that WtE techniques can recover up to 27.40% of energy. The food and agriculture waste constitutes 50–56% of the generated waste stream in developing countries thereby highlighting the significance of anaerobic digestion. The implementation of WtE techniques can considerably reduce the emission of greenhouse gases and is beneficial to environmental health. The potential of WtE techniques for effective waste management and promotion of sustainability is underscored. The review contributes to the implementation of more effective measures for MSW management and promotes a circular economy.
There are various techniques available for the treatment of municipal solid waste to reduce landfilling, and each technique has its perspectives and consequences.8 The transformation of waste into electrical energy is an effective approach to overcome the issue of increasing waste generation and it promotes the production of sustainable energy.9 The improvement in energy efficiency and reduction in the emission of toxic contaminants from gases are the current anxieties. Gasification, incineration, pyrolysis, and digestion are the alternative approaches for the generation of electricity in urban areas, with each approach requiring specific methods for the generation of electricity.10 The research community is dealing with these problems by finding economically feasible techniques to decrease the liability of urban waste.11 Thermal treatment including pyrolysis, gasification, incineration, and plasma gasification is the most commonly employed technique for the generation of energy in different forms and waste-to-wealth creation.12 In terms of energy and resource recovery capacity, pyrolysis is recognized as a more promising alternative when compared to incineration.
Combined heat and power (CHP) is commonly employed as an alternative source of energy with a good energy conservation rate and is generally employed in incineration or anaerobic digestion plants.13 The feasibility of incineration and gasification for the conservation of energy through a stable source has recognized incineration as an effective approach to transforming urban waste into electrical energy by using a steam turbine. Consequently, the generation of solid waste and air pollution due to combustion are critical issues.14 To reduce the emission of harmful gases from the incineration of waste, several post-treatment processes like carbon capture are employed with waste-to-energy facilities.15 The relatively high efficiency, ability of quick startup and shutdown, and economy of combustion processes have made them a popular choice. The operating condition, structural design, and rate of fuel consumption are the factors that influence the generation of power. The gas turbine and micro gas turbine are employed for the generation of electricity from municipal solid waste.16 The gas turbine utilizes combustion as a stable source to heat the compressed air, which improves the efficiency of energy production by the inlet gas. The micro gas turbine utilizes the syngas produced by the gasification of municipal solid waste with a high caloric value in the inlet gas. Biodiesel derived from different discarded oils can be a suitable alternative to petroleum-based diesel as a fuel for engines.17 Besides combustion, fuel cells are a source of power generation from urban waste but their sensitivity to impurities like chlorides, sulfides, and particulates within syngas generated by municipal solid waste requires a purification system to maintain the service and life of the fuel cell.18 Due to their low sensitivity, matching operating conditions and favorable operating environments solid oxide fuel cells (SOFCs) have drawn attention. The microbial fuel cell relies on the anode of respiring bacteria allowing the production of electricity by using organic waste.19 Through their metabolic action, these bacteria release electrons from organic waste, and these electrons then flow through a circuit to the cathode and generate electricity leaving behind water and CO2 as the by-products. Although the technique is less polluting and reduces the issue of organic waste, it is still not commercialized. Moreover, the hybridization of solar panels and wind turbines in a hybrid microgrid system can improve trustworthiness and efficacy by giving numerous energy sources.20
The recycling and reuse of feedstock, and the elimination of waste in landfills are the prerequisites for an ideal circular economy. The waste-to-energy sector provides various business opportunities when strict pollution standards are being enforced by the governments.21 Despite the low energy recovery efficiency of incineration, there are many feasible pathways for the recovery of energy through incineration.22 Although not every conversion technique is economically feasible, optimum pathways depend on the characteristics of the local supply connection. The wastes are collected, transported, sorted, preheated, and finally transformed into a value-added product or energy, and the by-products are disseminated and eventually disposed of. An optimized supply chain can reduce the impact on the environment and cost incurred in the recovery of energy while increasing the income from sales.
A smooth flow of products, waste, and by-products between supply points is of paramount importance.23 Techno-economic aspects considering technical viability and cost-effectiveness can be evaluated. An evaluation of the technical performances of different processes can assist in identifying a suitable technology for the attainment of higher return and efficiency.24 Therefore, the economic feasibility and technical performances are combined for a complete assessment of WtE techniques. In general, the environmental considerations of the waste-to-energy process cannot be ignored, particularly with the growing focus on global carbon neutrality.25 Global warming is one of the primary indexes to qualify the influence of greenhouse gases against carbon dioxide. The waste-to-energy conversion of MSW is crucial for the attainment of net-zero pledges as it addresses the increasing rate of waste generation associated with economic growth.26 There are different economically feasible approaches available for the recovery of energy having less environmental impact for each type of municipal waste.
The literature presents considerable work on the management of MSW and less work is available on WtE techniques while there is an absolute dearth of work dedicated to the techno-economic analysis, prospects, and limitations of waste-to-energy techniques. The present work is aimed at providing an overview of the different aspects of waste-to-energy techniques. The novelty of the review stems from the thorough analysis of the environmental impact and economic feasibility of WtE conversion plants across different regions of the globe. The review explores different aspects of municipal solid waste including techno-economic analysis, benefits and limitations of waste-to-energy techniques, generation of solid waste, implementation of waste-to-energy techniques, etc. Moreover, the review summarizes state-of-the-art municipal waste-to-energy techniques, aiming to identify future research prospects rather than delving deep into a single aspect. The study highlights the prospects of municipal solid waste for energy recovery by implementing waste-to-energy techniques. The review emphasizes the positive impact of energy recovery of promising waste-to-energy recovery techniques. This work is crucial to overcome the detrimental effects of municipal solid waste. The work is significant for the recovery of energy through waste and the implementation of the circular economy. The review will assist the decision makers and policymakers to advance towards the attainment of the sustainable development goal. The review findings are intended to function as a scientific framework to deliberately allocate resources to the WtE pathways.
The remaining part of the review is organized as follows: Section 2 gives the status of municipal solid waste and treatment methods. Section 3 discusses the waste-to-energy conversion techniques in detail. Techno-economic analysis is provided in Section 4, while Section 5 discusses the framework for waste-to-energy techniques. Section 6 is dedicated to the challenges of waste-to-energy techniques. The discussions on prospects of waste-to-energy techniques in terms of energy, environment, economy, and society are provided in Section 7. Section 8 is the conclusion section where concluding remarks are provided, and then finally, in Section 9 the outlook of the work is presented.
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Fig. 1 Solid waste generation in different regions of the world.44 |
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Fig. 2 Characteristics of municipal solid waste.44 |
To overcome the issues of municipal solid waste management, it is essential to advance an eco-friendly method for the management of municipal solid waste. Recycling, landfill gas recovery, and waste-to-energy techniques have gained considerable attention for minimizing municipal solid waste.45 The different waste-to-energy methods are the most beneficial as they reduce the reliance on fossil fuels and mitigate associated emissions. The waste-to-energy technologies can assist in the promotion of a circular economy.46 The waste-to-energy methods are influenced by environmental, location-related, geographical, and socio-economic considerations.47 A thorough analysis of the waste-to-energy techniques is required for the large-scale implementation of waste-to-energy techniques in developing countries.48 The advantages and limitations of the waste-to-energy technique must be discussed before adopting any waste-to-energy technique as different WtE techniques have their benefits and limitations (Table 1). Municipal solid waste can be used in different ways and therefore can be considered as a source of resources for the conservation of energy.49 A few of the methods based on the quality and composition of the waste can offer several opportunities. The collection of waste is a critical step before the treatment and utilization of waste. The collection and transportation of municipal solid waste constitute a considerable part of the overall waste management.50 The model for solid waste management indicates that a part of the collected waste is utilized in the generation of energy and recovery of material and the remaining is directly disposed of in a landfill (Fig. 3).
Feedstock | Treatment | Target | Power generation technology | Description and power capacities | Benefits | Limitations | Ref. |
---|---|---|---|---|---|---|---|
MSW | Combustion | Steady heat source | Steam turbine | >250 kW | Integrated power generation | MSW contains various kinds of wastes and a high content of moisture | 60 and 61 |
• Organic ranking cycle | |||||||
Biomass and MSW | Combustion or gasification (rarely) | Stable heat source | Stirling engine | A flue gas flow of 730 g s−1 and temperature of 980 °C corresponding to 24.5 kW of power generation | Appropriate for constant, small- to medium-scale power generation by utilizing biomass and MSW | Combustion and gasification of biomass and MSW face challenges such as operational conflicts and complex emission control requirements. | 62 |
Electric efficiency ≈ 30% | |||||||
Biomass and MSW | Gasification | Syngas | Internal combustion engine (ICE), spark ignition engine (SIE), compressed ignition engine (CIE) | Efficiency is prominently influenced by the type of fuel and the equivalent ratio 0.5–5.8 kg kW−1 h−1 | Flexibility in utilizing dissimilar forms of internal combustion engines for power production | The efficiency is highly adjustable, and largely influenced by various fuel and equivalent ratios | 63 |
Biomass and MSW | Gasification | Syngas | Gas turbine | Efficiency up to 65% in combined cycle configurations | Attain high efficacy | The system complications and cost increase significantly | 64 |
Biomass and MSW | Gasification | Syngas | Micro gas turbine (MGT) | 25 kW to 2 MW | Appropriate for an extensive range of uses | The comparatively low efficacy of 26–33% may hamper its effectiveness | 5 |
Efficiency of 26–33% | |||||||
Biomass and MSW | Gasification and purification | Hydrogen | Fuel cell | Electric efficiency of 35–65% | It promotes the production of clean energy | Variations in electric efficacy (35–65%) may influence the overall steadiness | 65 |
Biomass | Gasification | Syngas | Hybrid SOFC/MGT cogeneration | Electric efficiency of 35% and cogeneration efficiency of 88% | High efficacy combined system | The system's performance is dependent on the efficiency of both SOFC and MGT | 66 |
Organic waste | Microorganisms | Hydrogen | Microbial fuel cell | The MFC capability could reduce up to 95% of food waste degradation efficiency | Proficiently transform organic waste into hydrogen | Inadequate due to the specific conditions and effectiveness of the microbial processes involved | 67 |
Organic waste | Microorganisms | Hydrogen | Microbial fuel cell | Generated more energy (24.47 mW m−2) | Higher power density | Integrated WTP system | 68 |
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Fig. 3 Model for municipal solid waste management.69 |
Nowadays, the methods for storage and separation of waste, such as door-to-door collection, drop-off points, storage in mixed waste, etc., are performed without separation.51 It is observed that in the door-to-door collection of waste, people put their recyclable waste in non-recyclable plastic bags which creates difficulties in the separation of waste and restricts the implementation of the techniques.52 In the curbside system for collection of waste, the waste is placed in the container placed at a certain distance generally 50 to 100 (meters) apart.53 Besides, at the drop-off points the people deposit the waste in big containers placed at intervals of 500 to 1000 (meters) at the side of the street.54 In the mixed collection, the municipal solid waste is kept in a container without any separation; the separation is performed later at a recycling facility where the person involved separates the waste, which is then transported to a transfer station and finally to a disposal center.51 The present system of waste collection is classified as formal, informal, and formalized modalities. In the traditional method of waste collection, the separation of waste is performed by the citizens while the collection is carried out by the standard private or municipal personnel, whereas in the informal model, the separation of waste is performed by the recyclers and there is no formalization; the formalized model is the combination of the formal and informal models.55 Different strategies have been employed to enhance the separation and collection of waste. The economic and technical aspects in the collection of municipal solid waste including waste generation, financial parameters, composition settlement structure, database for infrastructure nature, etc. have been improved by the different mathematical models and life cycle assessments.56 The different factors such as the number of bins and houses, cycle for waste collection, vehicle trips, seasonal variations, and working hours have increased the complexity of the model.57 The artificial intelligence system, mathematical programming, and geographic information systems have been employed to optimize the collection of municipal solid waste.58 Nowadays, the replacement of manual sorting of waste by a robot with artificial intelligence has facilitated the automation of municipal solid waste.59 The subway collection of waste by a vacuum-assisted system is another emerging solution for the collection of municipal solid waste.
Several waste management systems are developed by using the Internet of Things such as pello, recycling robots, solar power compactors, and pneumatic waste pipes besides some government initiatives. Pello is a novel technology that has been developed to assist in the efficient management of waste and decrease the environmental impact. The system monitors the level of trash cans and generates real-time information on the location; therefore the system can alert users regarding the contamination of the container. Recycling robots can be programmed for a rapid and accurate response to differentiate the materials. The implementation of recycling robots allows for an efficient sorting of waste and decreases landfills. Pneumatic waste pipes can directly deliver the waste to the processing centers and eliminate the requirement of waste collection thereby minimizing the harmful emissions and overflowing of the waste. Furthermore, solar-powered trash compactors compress the trash to increase the capacity of the bin. They consist of sensors that can transmit data on the fill level of the waste bin which facilitates scheduling pickups and streamlining the collection of waste. There are several recycling apps available to assist the individual in developing a sustainable and circular economy.
The advantages of incineration are as follows: (i) it can reduce the quantity of waste by 80% to 90% and mass by nearly 70% to 80%; (ii) it can reduce the landfill spaces significantly; (iii) it is helpful in mitigating the hazardous substances due to elevated temperature; (iv) even low-technique and low-skilled manpower may be sufficient to minimize the mass and volume for any type of waste through the incineration process; (v) incineration produces hot fuel gas as a by-product which can be useful to produce steam in a boiler; and (vi) the extracted energy can be used for various purposes to meet the energy requirements of a community. However, the advantages of incineration are not feasible as the incineration of solid waste promotes the formation of dangerous carcinogenic complexes such as dioxins, furans, particulate substances, and acidic gases such as SO2, HF, and NOx which produce waste containing plastics.79 The extracted fuel gases are a combination of gases and compounds of heavy metals. The control and mitigation of hazardous emissions require intricate and expensive pollution controller technologies. The incineration is performed under high temperatures and produces corrosive gases which can damage the equipment and lead to costly maintenance. The incineration waste disposal method leads to various public health issues.
The gasification method can be adopted for homogeneous carbon-based organic materials having a high heating value. The pre-treatment with densification homogenizes the MSW which improves the efficiency of energy recovery.88 The various gasifiers such as fixed bed, fluidized bed, entrained-flow, moving grate, and plasma are useful for solid waste gasification.80 To fulfill the requirement for gasification a commercial MSW gasification plant is required in large numbers. The gasification method exhibits low emission when compared to conventional combustion and converts biomass gas into synthesis gas which is generally recognized as an environmentally friendly source of energy.89 The process requires a limited supply of oxygen, thereby reducing the development or reformation of dioxins and furans. It is potentially useful for low-cost applications and efficient for green hydrogen production. Gasification technology is efficient for the removal of fine metal particulates which promotes the formation of dioxins and furans.90 Syngas is considered a resource by the manufacturing sector. It can be an alternative source to produce electricity through graded composting which is an acceptable economic solution. The efficiency of the gasification process depends on the treatment of MSW and its characteristics and handling. The requirement of sophisticated equipment for high heat transfer efficacy is the limitation of the gasification process. Advancements in the design of the gasification process and the use of catalysts are important for the future advancement of the MSW disposal methodologies.91
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Fig. 4 Mechanism of the pyrolysis process and products (with permission from Elsevier, copyright 2021).106 |
Biochar shows promise as a cement replacement to advance the structural characteristics of concrete and building materials.111 Hydrothermal carbonization can efficiently process the waste having high moisture content and no pre-drying is required. The process is beneficial for the treatment of organic waste which is normally wet.112 The process yields biochar which can be utilized as a soil amendment to enhance the fertility of soil, carbon sequestration, and water retention. The biochar is a valuable material for application in water treatment as a carbon-rich material. Hydrothermal carbonization faces challenges in optimizing and scaling up the process due to the need for control of pressure, temperature, and reaction time.
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Fig. 5 Consecutive stages of anaerobic digestion (reproduced with permission from Elsevier, copyright 2021).106 |
Biogas is mainly composed of methane (CH4) and carbon dioxide (CO2) at about 55–75 vol% and 25–45 vol%, respectively.116 Biogas requires the removal of CO2 through physical absorption by using caustic soda, silica gel, and activated carbon before being supplied to internal combustion engines for the generation of electricity or can be used as a fuel in automobiles by using combined heat and power generation.117 Digestate is an additional valuable product of anaerobic digestion that can be utilized as a soil conditioner or an organic amendment.118 The production of biogas, methane content, and stability of the digestion are influenced by operating factors like pH value, carbon–nitrogen ratio, operating temperature, and substrate composition.119 The biodegradable ingredients are the appropriate raw feed for the generation of biogas in an anaerobic breakdown process. The plant biomass and manure are commonly used in biogas plants in rural areas, while food waste and sewage sludge are the feedstock for the production of biogas in municipality areas.120 Although anaerobic digestion is an important technique for the treatment of waste and favors sustainability and carbon neutrality, the process has limitations of high-capital investment and requires safety regulations and maintenance.
The shortage of land is a challenge for the allocation of new dumpsites in advanced nations. Landfill gas recovery technology (LFGR) can be employed by using an internal combustion engine for the generation of electricity by utilizing the gas emitted from landfills.125 Energy recovery from landfills offers a chance to generate income by selling electricity and earning credits in carbon markets. The generation of methane is influenced by biodegradation which is affected by the requirement of moisture for bacterial growth. The implementation of bioreactors has accelerated the degradation of waste in the landfill and enhanced the production of landfill gas.126 The biodegradation of waste in a bioreactor landfill is increased by the recirculation and distribution of aqueous effluent. The biocell technology of is an advanced method for the optimization of biogas recovery from landfills.127 It is an upgraded bioreactor landfill process in which biological breakdown takes place in three consecutive stages: anaerobic, aerobic, and mining. In the first stage, landfill gas is produced by recirculating the leachate as in a bioreactor and after that air is pumped into the solid matrix to facilitate compost formation. In the last stage, the biocell recovers materials that can be recycled and creates space for reuse and therefore is considered an important source of wealth for sustainable growth.
A techno-economic analysis of the generation of biogas from organic municipal solid waste was conducted by considering six different scenarios including plant size, upgrading methods, digester type, and the addition of biogas from the treatment of wastewater. Aspen Plus® was employed for the simulation of the process. The evaluation of the economic performance was performed by using the Aspen process economic analyzer. The economic feasibility and technical performances of six (06) different circumstances for the generation of biogas from municipal solid waste in Boras, Sweden, were assessed by varying the cost of municipal solid waste between −200 and 200 US $ per ton. Scenario 6 provided the optimum profit in terms of economic performance, energy efficiency, and consumption. The minimum price of compressed biogas for the base scenario and scenario 6 was 1.15 and 0.76 (US$ per L), respectively. It was concluded that utilizing upgraded methods with increased capacity will produce greater profits. Municipal solid waste has a significant influence on the economy, but there exists an uncertainty in the cost of collection and conveyance. The techno-economic analysis of municipal solid waste in Brazil has identified biogas from landfills and incineration of municipal solid waste as the primary two scenarios for the generation of electricity.133 Electricity is generated by using biogas from landfills by passing it through an internal combustion engine. Initially, the biogas having equal fractions of CH4 and CO2 is purified and then it is passed into the incineration unit where it is burned at a high temperature of about 870–1200 (°C) and a high pressure is created in the incinerator which drives the gas turbine to generate electricity.134 The net profit value, cash flow, and internal rate of return are the indicators of the economic feasibility of municipal solid waste. Besides, the consumption of municipal solid waste is related to the energy indicator CH4. The different waste-to-energy techniques such as incineration, anaerobic digestion, and landfill gas recovery are the most prominent methods for the management of solid waste. The advancement of WtE techniques has led to an improvement in efficiency and reduced the environmental impact with the progression of years (Table 2). The implementation of waste-to-energy techniques has reduced the dependency on fossil fuels in developed countries whereas in developing countries these practices are not effectively performed.88 The inadequate technical expertise and lack of funding have hampered the widespread adoption of waste-to-energy conversion practices. Despite the challenges developing countries are facing to produce sufficient energy, the waste is dumped instead of being transformed into a valuable form.
Year | Method | Electricity generation | Cost | Environmental impact | Remark | Sources |
---|---|---|---|---|---|---|
2019 | Anaerobic digestion and incineration | 4165 GW h per year | — | Reduces the GHG emissions by 1.7 Mt per year | New South Wales produces 5.9% of the overall power | 135 |
2018 | Incineration | 1471 GW h per year | — | Emits 0.18 kg per s of CO2 | Improves the waste management in Jitabarang | 136 |
2018 | Combustion | 277.17 GW h per year | — | — | Reduces the dependency on oil and other non-renewable energy sources. Decreases the emission of GHG to minimize the global warming and eliminates the contamination of water and air | 137 |
Gasification | 177.39 GW h per year | — | — | |||
Anaerobic digestion | — | — | — | |||
2013 | Combustion | 8500 GW h per year | — | Reduces the emission of CO2 by 11 Mt per year | The results of the simulations indicate the potential to meet 0.5% of the electricity requirement in Turkey by 2023 | 138 |
2017 | Incineration | 113 GW h per year | 150 USD per MW h | — | Optimizes the powder generation through wastes | 139 |
2017 | Landfill, anaerobic digestion and composting | 1229 GW h per year | 10 USD per ton | Reduces the emission of CO2 by 1.8 Mt per year | Decreases the emission of greenhouse gases | 140 |
2020 | Incineration | 11![]() |
128![]() |
— | Produces 4.3% of the power requirement of the country. Decreases the challenges of environmental pollution | 141 |
2013 | Landfill | 1.5 GW h per year | 250![]() |
— | Production of energy by using landfill is the economical way, good quality fertilizers can be produced. | 142 |
Incineration | 2 GW h per year | — | Transmission of diseases can be prevented by sanitary landfills | |||
2022 | Incineration | 170 GW h per year | 2.36 million USD per year | — | A systematic waste to energy practice transfers 20 MW of energy to the network | 143 |
The recovery of energy systems for households having three (03) inhabitants was put into perspective by using economic indicators. Considering a population of 100000, a negative net profit value and an internal revenue rate of 0.4% were calculated. The zero net profit was obtained at the selling price of 82.60 US$ per MW h. Besides, the net positive value was 3
004
678 US$ and 8
793
264.25 US$ for a population of 500
000 and 1
000
000, respectively. It is observed that all the situations have a negative net profit and as a result decreased economic feasibility. In Brazil, the techno-economic analysis of electricity generation by using gasification was carried out.144 The net profit value, yearly rate of interest, internal revenue rate, and net profit value are the economic indicators, whereas power, efficiency, and generation of electricity are considered as the technical indicators. The generation of electricity is influenced by the size of the population. A decision model for techno-economic analysis of waste-to-energy conversion techniques from municipal solid waste was developed.145 A suitable model for the municipalities can assist in making decisions on the conversion of waste into useful energy. Composting is the cheapest way to generate energy, and the cost of conversion is about 77 US$ per ton. The integration of gasification with composting generates electricity which requires an amount of 42–72 (US$ per ton) for the waste generation of 50
000–150
000 tons per year.146 The sensitivity analysis of gasification has observed the selling price of biofuels and electricity as the dominating factor impacting the feasibility of the technique.147
The generation of energy by using municipal solid waste through pyrolysis has been identified as an intermediate step for the conversion of solid waste into fuel gas and organic oil. The efficiency of the combined heat and power is estimated to be 60% for a plant having a processing capacity of 5 tons per h and capital investment of 27.61 million pounds at an efficiency of 0.063 lb per kW h.148 The energy created from the gas and diesel engines and the data were collected from the pilot experiments of the plant. The profitability of the plant was influenced by the capital cost, feedstock cost, energy productivity, and plant maintenance. The thermo-socioeconomic assessment was performed by studying the thermo-kinetics of municipal sewage sludge through pyrolysis. The comparison of the production of biogas, biochar, and bio-oil through pyrolysis shows an optimum performance due to a higher internal revenue rate, return on investment, and net profit value considering the social and economic aspects.149 The researcher has studied the environmental and economic aspects of the valorization of municipal solid waste by taking seven different conventional waste processing units and found that the least-cost solution reduces the cost and greenhouse emissions by 26%. The plasma gasification process has shown feasibility under higher electricity prices.150
The techno-economic analysis of municipal solid waste for supercritical and critical Indian coal was carried out.151 The co-combustion of municipal solid waste can overcome the issues of low calorific values of municipal solid waste. It is demonstrated that the combustion of municipal solid waste and coal in a ratio of 1:
3 has a lower levelized cost of energy of 73.47 US$ per MW h and 69.7 US$ per MW h for high and low ash coal, respectively, when compared to that for the municipal solid waste at 80 US$ per MW h. Thermal economic analysis of a novel mechanical–biological treatment system that generates heat, power and hydrogen from municipal solid waste was performed.152 In mechanical–biological treatment, the mechanical sorting of the municipal solid waste is performed and then it is converted into wet organic fractions for the generation of electricity and heat while the remaining part of the waste is disposed of as a landfill. However, the discarded material can be effectively converted into some valuable products by a gasification unit.153 The integration of three techniques of waste-to-energy techniques including pyrolysis, anaerobic digestion, and solar PV has generated an annual revenue of $41.6 million. The commercial waste-to-energy plant can process about 1000 tons of waste plastics daily and generate about 19.7 MW of electricity. The capital investment and annual operating cost are $102.2 million and $12.2 million, respectively.154 The investigations of the three different scenarios of the production of electricity and fuel have shown that the generation of electricity and fuels has attained a net profit value of EUR 13 million and a payback period of 12 years. Therefore, hybrid systems have gained great interest and thermal economic analysis plays an important role in selecting a suitable waste treatment method.
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Fig. 6 Strategies for effective municipal solid waste management.167 |
Global energy developers and consultants, countries experienced in waste-to-energy techniques, literate, global financial institutions, etc., are the sources of data for the revenues and expenses of waste-to-energy techniques.25 The approaches for economic analysis such as present value, reimbursement time, and international rate of yield can be used in the development of waste management approaches. A thorough analysis of the initiatives for financial needs and earnings is required.156 The evaluation of the present status of the waste-to-energy technique and the prediction of the characteristics of municipal solid waste are performed through technical evaluations.157 The identification of the most efficient and appropriate waste-to-energy techniques considering both prospects and limitations can be performed by comparing the different waste-to-energy techniques which can be done through an intangible but inclusive design that assesses the rational cost and project timeline for various waste-to-energy techniques.158 The assessment of the cogeneration potential and heat generation is essential to optimize the energy yield.159 The technical feasibility is evaluated by estimating the quantity of recycled waste, suitability of thermal treatment of wastes, efficiency of the technology, and the time required for the operation of the facility.160 The environmental assessment will be performed for the selected waste-to-energy technique by collecting the different ecological baselines for this process such as information on the ecological and geographical area.161 An assessment of the potential contamination of noise, air, soil, surface, and groundwater must be carried out.
A list of potential solutions must be developed and estimations of the time and cost must be determined.162 A social assessment is important for assessing the social context of the project, ensuring its success. The recycling of municipal solid waste and the construction of plants must be carried out in proper time. The conventional and non-conventional waste-to-energy techniques must be favored for the recycling of materials while landfilling must be minimized.163 The anaerobic digestion and composting are followed for organic waste, whereas the non-recyclable waste can be processed by hydrothermal technologies and gasification. Decentralized waste-to-energy facilities can be a feasible approach for a continuous supply of municipal solid waste.164 The handling of solid waste must be performed carefully, and a huge amount of municipal solid waste can be treated instead of landfilling which is not a viable approach for waste treatment. To make non-conventional waste-to-energy methods more cost-effective, facilities should be equipped to produce valuable by-products such as organic acids, syngas, and pyrolysis-derived materials.165
Hydrogen, fuels, and chemical compounds are the valuable end products. The improvement in the capacity of plants by feeding by-products such as slag in plasma gasification, development of methodology of lean manufacturing, and assimilating energy to reduce energy costs are the cost-cutting techniques that can be implemented for waste management.166 There is a need for the feasibility analysis of vital processes and design configuration. The generation of products and the economy of the process must be improved by effective process design, critical decision, optimization, and modifications in the technological stages. These investigations are significant before their implementation at the industrial level and must be performed with the support of academia and industry at the pilot and laboratory scales. It is essential to support a range of stakeholders such as industry, local governmental bodies, and investment corporations for the acceptance of waste-to-energy systems by the customers and community.
The current practices of waste management are ineffective due to the high quantity of waste production. It is reported that nearly 30–90% of the waste is disposed of in landfills, with Latin America, Africa, and the Caribbean as the leading generators.170 Due to the emission of greenhouse gases, the improper collection and disposal of waste is a major threat to the environment; besides, urbanization and industrialization are creating problems for the available land. The valorization of waste is an effective approach that can effectively deal with the issues of energy crisis, climatic changes, and available land, thereby ensuring effective waste management. Moreover, the strategy can reduce the emission of toxic gases from landfills and mitigate health-related issues that arise due to the contamination of soil, air, and land.171 The majority of the developed countries have successfully implemented waste-to-energy management techniques, but the financial, technical, logistics and socio-eco-technical constraints are still hampering the implementation of waste-to-energy techniques in emerging nations (Fig. 7).48 The lack of waste segregation, poor logistic support, and insufficient waste collection facilities are the challenges to the adoption of waste-to-energy techniques in emerging nations.
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Fig. 7 Techno-economic and social challenges for WtE implementation (reproduced with permission from Elsevier, copyright 2021).106 |
The physical and chemical nature of waste is crucial for estimating the calorific value of municipal solid waste. Insufficient knowledge about the characteristics of waste results in an improper selection of equipment and techniques and eventually a waste of time and effort.163 The waste-to-energy techniques are expensive and require sophisticated equipment; also the developing countries are facing the problem of initiating investigations on the process of waste-to-energy conversion.88 The cost of construction and maintenance of incineration facilities may be uneconomical and unreasonable for emerging nations; e.g. the high maintenance cost suspended incineration in Malaysia.172 The financial incentives can promote investment in waste-to-energy sectors, making waste-to-energy technologies more attractive. The policies and regulatory framework must be introduced through legislative action to motivate the public–government partnership in the waste-to-energy sector.173 The availability of feedstock is decisive for the effective execution of waste-to-energy systems. The authorities at regional and national levels across the countries must enforce strict penalties and sanctions on waste disposal as landfilling to maximize waste diversion from landfills and ensure the availability of feedstock for the implementation of waste-to-energy techniques.174 The separation of waste can increase the calorific value and require less operating cost in comparison to the mixed waste type. The separation at source can ensure homogeneity in wastes and increase the practices of waste management at the community level and the cost-effectiveness of the waste-to-energy techniques.175 The adoption of sustainable waste management practices through the implementation of waste-to-energy techniques is facing numerous challenges. The challenges arise from the different aspects of waste to energy chain, method of energy recovery, power generation, energy analyses, and techno-economic analyses.176 The challenges associated with waste-to-energy techniques must be effectively addressed to promote a sustainable circular economy.
The shift towards a viable circular economy where the generated thrash is regarded as a valuable resource denotes a considerable footrace. A comprehensive waste management system is required to recover the recyclable and reusable materials from the generated waste.177 The initiatives, policies, and government regulations are important factors in the establishment of waste-to-energy facilities.25 However, these initiatives often face social restrictions due to public concerns. Siddiqi et al. have highlighted the challenges in the estimation of waste-to-energy chains to integrate economic and social benefits.178 Thermal treatment methods such as pyrolysis, incineration, and gasification for municipal solid waste treatment are encountering several environmental challenges. Although incineration is a widely adopted technique, it suffers due to the low efficiency and high emissions which lead to the generation of toxic pollutants. Additionally, managing pollution effectively remains a major challenge in the incineration process.179 However, pyrolysis and gasification are more effective and less polluting but they necessitate a primary investment and precise control of the condition to optimize the quality of syngas and minimize the production of tar.180 Despite the potential of plasma gasification to treat the generated waste, its implementation is restricted due to operational cost and energy consumption, and the requirement for advanced material for handling extreme conditions.181
Rajendran et al. have discussed the economic barriers to the implementation of waste-to-energy technologies.155 The uncertainty in economic returns, particularly within the public sector, is intensified due to the limited monetary support and the inadequate risk distribution mechanisms, posing major challenges to capital investment.153 The environmental implications of the traditional waste-to-energy conversion technique are also a cause of concern. The researchers have demonstrated that the waste-to-energy technique significantly contributes to greenhouse gas emissions.51 The effectiveness of waste-to-energy technologies in improving environmental conditions depends on the local conditions and specific processes; therefore, no particular waste-to-energy technique can be established as the standard.182 The high moisture content in municipal solid waste poses a challenge for stable heat production, and blending it with high-heating fuels like coal can reduce this issue, but it increases the emission of toxic substances and air pollution.183 The work has demonstrated that the integration of innovative technologies such as plasma gasification and chemical looping combustion presents implementation challenges.184
Parameters | Waste-to-energy technique | ||||
---|---|---|---|---|---|
Anaerobic digestion | Landfill gas recovery technology | Incineration | Landfill gas | Pyrolysis | |
Waste type | Organic fraction | Mixed waste | Mixed waste | Homogeneous waste | Homogeneous waste |
Technical | |||||
Technology maturity | Very high | Very high | Extremely high | Emerging | Emerging |
Waste volume reduction | 45–50% | Low | 75–90% | 75–90% | 50–90% |
Technology complexity | Low | Low | Low | High | High |
System efficiency | 50–70% | 10% | 50–60% | 70–80% | 70% |
Residence time | 15–30 days | Years | 2 s | 10–20 s | Seconds to weeks |
Labor skill requirement | Low | Low | Low | High | High |
Land requirement | Large | Very large | Small | Small | Small |
Pre-treatment | Required | Not required | Not required | Required | Required |
Future potential | High | High | Moderate | High | High |
Economic | |||||
Capital cost | Medium-high | Low | Medium-high | High | High |
Operation and maintenance costs | Medium-high | Low | Medium-high | High | High |
Pre-treatment cost | Medium | None | None | High | High |
Social and environmental | |||||
GHG emissions | Least | High | Extremely high | Low | Low |
Dioxin and furan emission | Extremely low | Extremely low | Very high | Very low | Very low |
Social opposition | Very less | Less | Extremely high | High | High |
WtE techniques offer several benefits for resource recovery and materials management by the transformation of waste into energy, decreasing the landfills, and supporting circular economy while lowering the environmental impacts. The advantages of WtE include the following: (i) decrease landfill reliance: WtE technologies, such as incineration and anaerobic digestion, can significantly reduce the landfill and therefore can conserve valuable land resources; (ii) energy recovery: WtE technologies can recover usable heat, electricity or fuel from waste materials and therefore provide an alternative source of energy and decrease the reliance on fossil fuels; (iii) resource recovery: WtE techniques facilitate the recovery of valuable resources and therefore promote circular economy; (iv) environmental benefits: WtE techniques assist in the minimization of carbon and methane emissions from landfill as well as soil pollution; (v) circular economy: WtE techniques support circular economy by transforming waste into a valuable resource and as a result reduce the generation of waste and promote resource efficiency; (vi) production of sustainable energy: by transforming waste into energy, WtE techniques contribute to the production of sustainable energy and reduce the environmental impact of traditional practices of waste management. WtE techniques enable the recovery of resources and energy, reduce waste, and create economic benefits. The techniques that divert the waste from landfilling reduce the environmental impact and are favorable for the recovery of energy and resources. The WtE techniques generate electricity and heat which provides an alternative source of energy. Moreover, the techniques can create jobs in the waste management sector and therefore provide economic benefits. The technique integrates a circular economy for a closed-loop system where the waste is recognized as a valuable resource, reducing the extraction of new resources.
Life cycle assessment (LCA) has emerged as a useful tool to estimate and associate the environmental impacts of waste-to-energy technologies and assist in the optimization of the parameters to decrease greenhouse emission and carbon footprints. Technological and environmental factors significantly affect the LCA of WtE techniques (Fig. 8). The integration of LCA into policy-making confirms that the consideration of the environment is prioritized in the planning and implementation of waste-to-energy projects (Table 4).189 The estimation of carbon emission by additive-subtractive integrated hybrid manufacturing (ASIHM) has found a reduction in carbon emission by 80% in comparison to the conventional subtractive manufacturing technique.190 The pretreatment of municipal solid waste decreases the moisture content thereby improving the combustion properties. The exploration of alternative methods for power generation such as fuel cells and gasification can decrease the dependency on coal and fossil fuels.183 The implementation of hybrid power generation arrangements that integrate numerous technologies can decrease emission and improve overall efficiency.191 To identify the improvement and optimization a detailed analysis of the energy and exergy for the different waste-to-energy technologies is important.184 The investigation of the integration of technologies in waste-to-energy systems offers the implementation of best practices and improves the efficiency of waste-to-energy facilities. The LCA system boundary is the interface between the environment and the waste management system. The life of any product ends up being a waste once the product is discarded. The mechanical-biological treatment systems that generate refuse derived fuel (RDF) offer renewable energy sources and reduce landfills. The ash produced in thermal treatment is dumped in a landfill. Material recovery allows for the extraction of various reusable materials, reducing the amount of waste that ends up in landfills (Fig. 9). The sensitivity analysis and cost–benefit analysis can be carried out for LCA.192 A systematic and comprehensive approach consisting of financial incentives, regulatory support, technological advancement, and regulatory support is essential to address the challenges in waste-to-energy systems. The communities, governments, and private sectors must work together to form a sustainable framework that can effectively optimize waste management practices and offer economic and environmental advantages of waste-to-energy technologies.193
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Fig. 8 Factors that affect the life cycle assessment (reproduced with permission from Elsevier, copyright 2021).106 |
Source | Dong et al.51 | Demetrious and Crossin198 | |||||
---|---|---|---|---|---|---|---|
WtE technology | Incineration | Pyrolysis | Gasification | Gasification with ash melting | Landfill | Incineration | Gasification–pyrolysis |
Feedstock | Residual MSW | MSW, industrial sludge, sewage sludge | Solid refuse fuels | MSW | Mixed paper and mixed plastics | ||
Feedstock LHV | 10.307 GJ per ton | Mixed paper: 14.1 MJ kg−1; mixed plastics: 30.8 MJ kg−1 | |||||
Primary product/output | Electric power | Electricity | |||||
Net electricity recovery efficiency | 17.70% | 17.70% | 27.40% | 16.70% | 35% | 15.84% | 32% |
System boundary | Waste pre-processing, thermal transformation, energy capturing, air pollution control (APC), and solid residue management | Waste processing, electricity production, and disposing byproducts/waste | |||||
Functional unit | Thermal treatment with electricity recovery of one (1) ton MSW | Thermal treatment with electricity recovery of one (1) kg MSW | |||||
Additional information | — | Mixed paper: 10% newspaper and 90% packaging paper containing an average moisture of 11.2%, carbon composition of 40%, nitrogen composition of 0.3% and sulfur composition of 0.1% | |||||
Mixed plastics: average moisture of 15.3%, carbon composition of 63%, nitrogen composition of 0.6% and sulfur composition of 0.1% | |||||||
LCA software | Gabi 8.0 | SimaPro 8.0.4 | |||||
Life cycle impact assessment method | CML 2001 method | — | |||||
GWP (kg CO2 eq. per unit) | 172 | 151 | 104 | 422 | Mixed paper: 1.56 | Mixed paper: 1.03 | Mixed paper: 1.02 |
Mixed plastics: 1.51 | Mixed plastics: 8.98 | Mixed plastics: 1.87 |
Source | Khoo, H. H.199 | |||||||
---|---|---|---|---|---|---|---|---|
WtE technology (% of total waste) | Material recovery: 7% incineration: 93% | Material recovery: 11% incineration: 89% | Material recovery: 7% incineration: 89% pyrolysis: 4% | Material recovery: 7% incineration: 84% gasification: 9% | Material recovery: 7% incineration: 80% pyrolysis: 4% gasification: 9% | Material recovery: 10% incineration: 77% pyrolysis: 4% gasification: 9% | Material recovery: 10% incineration: 83% pyrolysis: 7% | Material recovery: 11% incineration: 71% gasification: 18% |
Feedstock | Mixed plastic waste | |||||||
Feedstock LHV | — | |||||||
Primary product/output | Electricity | |||||||
Net electricity recovery efficiency | — | |||||||
System boundary | Waste production and centralized collection, circulation of plastic wastes to various recycling and WtE options, and byproducts/waste disposal | |||||||
Functional unit | Thermal processing with electricity recovery of one (1) kg MSW | |||||||
Additional information | Mixed plastic waste composition: 40% PE, 17% PVC, 12% PP, 4% PS, 4.8% PET, and 22.2% other mixed fractions | |||||||
LCA software | GaBi | |||||||
Life cycle impact assessment method | ReCiPe | |||||||
GWP (kg CO2 eq. per unit) | 0.940 | 0.921 | 0.929 | 0.911 | 0.900 | 0.866 | 0.902 | 0.872 |
Source | Maghmoumi et al.182 | Ramos and Rouboa156 | |||||
---|---|---|---|---|---|---|---|
WtE technology (% of total waste) | Incineration: 100% | Landfilling: 100% | Incineration: 50% landfilling: 30% material recovery: 20% | Incineration: 30% landfilling: 50% material recovery: 20% | Incineration | Gasification | Plasma gasification |
Feedstock | MSW | MSW | |||||
Feedstock LHV | 8.4 MJ kg−1 | — | |||||
Primary product/output | Electricity | Electricity | |||||
Net electricity recovery efficiency | 21% | — | |||||
System boundary | — | MSW processing, gas cleaning, power production, waste/byproduct disposal | |||||
Functional unit | Treatment with electricity recovery of one (1) tonne MSW | Thermal treatment with electricity recovery of one (1) tonne MSW | |||||
Additional information | GHG emanations was calculated using the IPCC method and complete mechanical treatment analysis | Waste composition (wt%): organic (37.57%), paper (10.47%), plastics (12.10%), metals (2.45%), glass (5.53%), textiles (16.46%), others (15.42%) | |||||
LCA software | — | GaBi | |||||
Life cycle impact | — | CML 2001 | |||||
GWP (kg CO2 eq per unit) | −85.67 | 41.42 | −97.98 | −72.56 | −170.9 | 27 | −31 |
Source | Dastjerdi et al.41 | |||||
---|---|---|---|---|---|---|
WtE technology | Landfilling | Incineration | Food waste: anaerobic digestion | Food waste: anaerobic digestion combustible: incineration | Food waste: anaerobic digestion combustible: incineration plastic waste: recycling | Food waste: anaerobic digestion combustible: gasification plastic waste: recycling |
Combustible and non-combustible: landfilling | Non-combustible: landfilling | Non-combustible: landfilling | Non-combustible: landfilling | |||
Feedstock | Residual MSW | |||||
Feedstock LHV | 8.91 MJ kg−1 | |||||
Primary product/output | Electricity | |||||
Net electricity recovery efficiency | — | |||||
System boundary | Residual MSW treatment, electricity production, and byproducts/waste disposal | |||||
Functional unit | Treatment with electricity recovery of one (1) tonne residual MSW | |||||
Additional information | — | |||||
LCA software | OpenLCA 1.9 and by employing Ecoinvent V3.5 | |||||
Life cycle impact assessment method | ReCiPe 2016 midpoint and endpoint hierarchist methods | |||||
GWP (kg CO2 eq per unit) | + | − | + | − | − | − |
Source | Zhao et al.181 | ||||
---|---|---|---|---|---|
WtE technology | Rotary kiln incinerator | Pyrolysis incineration | Plasma melting | Steam sterilization | Microwave sterilization |
Feedstock | Medical waste | ||||
Feedstock LHV | — | ||||
Primary product/output | Electricity | ||||
Net electricity recovery efficiency | — | ||||
System boundary | Medical waste treatment, flue gas purification, energy recovery, and byproducts/waste disposal | ||||
Functional unit | Disposal of one (1) tonne medical waste (MW) | ||||
Additional information | Electricity consumption: 172.10 kW h per ton MW | Electricity consumption: 151.91 kW h per ton MW | Electricity consumption: 539.64 kW h per ton MW | Electricity consumption: 539.64 kW h per ton MW | Electricity consumption: 127.88 kW h per ton MW |
LCA software | — | ||||
Life cycle impact assessment method | — | ||||
GWP (kg CO2 eq per unit) | 420 | 187 | 686 | 165 | 135 |
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Fig. 9 Life cycle assessment of municipal solid waste.197 |
Integrating technologies such as biopolymer production, large-scale biomass conversion, and waste-to-energy systems can be an effective approach to treat municipal solid waste for the generation of electricity.194 The development of biorefineries for the recovery of municipal solid waste is an essential aspect of sustainability.195 The waste-to-energy method provides a feasible approach for municipal solid waste; and offers various environmental and economic advantages. The waste-to-energy system minimizes the volume and mass of disposal of municipal solid waste by 90% and 80%, respectively.196 The waste-to-energy system offers sustainability through the recovery of energy and reduces the fraction of landfills.
The review suggests that advanced thermochemical techniques particularly combined with recycling increase the volume of energy recovery besides reducing landfilling. Sustainability in waste management can be achieved without any dependency on incineration. The work has provided insight into the qualification of waste management practices. The effectiveness of waste management practices can be demonstrated by the recovery of the resource, decreased landfilling, and enhanced production efficiency. The review has provided vital information to assist in the development of more sustainable practices of management waste and paves the way towards a circular economy to potentially increase the recovery of energy.
ASIHM | Additive-subtractive integrated hybrid manufacturing |
CHP | Combined heat and power |
CIE | Compressed ignition engine |
ICE | Internal combustion engine |
LCA | Life cycle assessment |
LCOE | Leveled cost of electricity |
LFGR | Landfill gas recovery technology |
LHV | Lower heating value |
MGT | Micro gas turbine |
MSW | Municipal solid waste |
MW | Medical waste |
RDF | Refuse derived fuel |
SIE | Spark ignition engine |
SOFC | Solid oxide fuel cell |
WtE | Waste-to-energy |
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