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Waste-to-Energy Technologies: a Literature Review
Abstract
Rapid economic development and urbanization has caused rapid increase of waste generation worldwide. The Municipal Solid Waste (MSW) generation is expected to double by 2025. This rapid increase needs to be tackled to reduce the generation rates along with the environmental impacts it imposes. Disposal of waste in landfills results in the generation of huge amounts of Greenhouse Gases (GHG), negative impacts on human health, air and water pollution. Solid waste generation increments, rising demand for energy and preservation of fossil fuels, caused an increase in the popularity of Waste-to-Energy (WTE) technologies as the solution for waste managing problems and energy demands. Waste-to-Energy technologies convert the waste into energy and minimize the amount of waste sent to landfills. The aim of this paper is to present the process and specific aspects of WTE technologies along with their advantages and disadvantages. It illustrates that the waste and process must be closely matched to achieve proper conversion of waste and better efficiency of a WTE technology. This study also highlighted some thermochemical WTE facilities which can recover both energy and materials from waste. The continuous developments being made in process efficiency and process control of WTE facilities are expected to enhance the commercial feasibility of these conversion processes in the near future.
... The advantage of incineration over the other WtE technology is that it uses almost all types of MWS fraction and can reduce the volume of the waste by 80% and the solid mass by 70%. However, the initial costs to invest in such a plant is very high and could eventually lead to air and/or water pollution [14,15]. ...
... During the pyrolysis process, up to 80% of the carbonaceous fraction of the feedstock (here, MSW) used is recovered [14]. There are three types of pyrolysis reactions (slow, fast, and flash pyrolysis) depending on the operating parameters, such as temperature, heating rate, particle size, and residence time [15]. The proportion of each of the three fuels produced from the process depends on the type of pyrolysis used, as seen in the Table 1 [15,17,18]. ...
... There are three types of pyrolysis reactions (slow, fast, and flash pyrolysis) depending on the operating parameters, such as temperature, heating rate, particle size, and residence time [15]. The proportion of each of the three fuels produced from the process depends on the type of pyrolysis used, as seen in the Table 1 [15,17,18]. However, pyrolysis technology has some demerits. ...
Municipal solid waste (MSW) in the Accra region of Ghana has created the need for innovative ways to deal with waste management crises facing the city. The goal of this study is to use the analytical hierarchy process (AHP) to select an appropriate waste-to-energy (WtE) technology for Accra. The AHP methodology is used to assess four WtE technologies, namely landfill biogas, incineration, anaerobic digestion, and aerobic composting. Three main criteria and nine sub-criteria are identified for pair-wise comparison and assessed by 10 experts. The results show that incineration is the most preferred technology, followed by anaerobic digestion and aerobic digestion, with landfilled gas being the least preferred technology. Stakeholders in waste management development in Ghana can utilize the findings of the study to develop implementation strategies for capacity and institutional capabilities for both thermochemical and biochemical processes in the country.
... Similarly, using waste-to-energy techniques, various organic wastes, e.g., the organic portion of municipal solid waste, sewage sludge, food waste, animal manure, etc., can also be subjected to anaerobic digestion [4]. This technique involves the breakdown of organic material in the absence of oxygen, leading to the formation of gases such as methane (CH 4 ), carbon dioxide (CO 2 ), ammonia (NH 3 ), and low-molecular-weight organic acids [5]. ...
... The microbial electrochemical cell (MEC) is one of the rapidly evolving microbial electrochemical technologies and is a component of a broad platform of upcoming sustainable energy and chemical production technologies [10]. Electromethanogenesis can be performed using electrons and the hydrogen produced at the cathode in an MEC via the application of a small voltage to convert CO 2 properly to CH 4 [11]. The MEC system utilizes exoelectrogenic bacterial biofilm on an anode to biodegrade organic material and produce biological hydrogen. ...
Citation: Bhatt, P.; Poudyal, P.; Dhungana, P.; Prajapati, B.; Bajracharya, S.; Yadav, A.P.; Bhattarai, T.; Sreerama, L.; Joshi, J. Enhancement of Biogas (Methane) Production from Cow Dung Using a Microbial Electrochemical Cell and Molecular Characterization of Isolated Methanogenic Bacteria. Biomass 2024, 4, 455-471. https://doi. Abstract: Biogas has long been used as a household cooking fuel in many tropical counties, and it has the potential to be a significant energy source beyond household cooking fuel. In this study, we describe the use of low electrical energy input in an anaerobic digestion process using a microbial electrochemical cell (MEC) to promote methane content in biogas at 18, 28, and 37 • C. Although the maximum amount of biogas production was at 37 • C (25 cm 3), biogas could be effectively produced at lower temperatures, i.e., 18 (13 cm 3) and 28 • C (19 cm 3), with an external 2 V power input. The biogas production of 13 cm 3 obtained at 18 • C was~65-fold higher than the biogas produced without an external power supply (0.2 cm 3). This was further enhanced by 23% using carbon-nanotubes-treated (CNT) graphite electrodes. This suggests that the MEC can be operated at as low as 18 • C and still produce significant amounts of biogas. The share of CH 4 in biogas produced in the controls was 30%, whereas the biogas produced in an MEC had 80% CH 4. The MEC effectively reduced COD to 42%, whereas it consumed 98% of reducing sugars. Accordingly, it is a suitable method for waste/manure treatment. Molecular characterization using 16s rRNA sequencing confirmed the presence of methanogenic bacteria, viz., Serratia liquefaciens and Zoballella taiwanensis, in the inoculum used for the fermentation. Consistent with recent studies, we believe that electromethanogenesis will play a significant role in the production of value-added products and improve the management of waste by converting it to energy.
... Sufficient amount of oxygen is required to ensure complete oxidation of waste with the typical temperature of about 850 °C. This process is very effective in reducing volume of waste and subsequently required landfill space as it accepts wide variety of waste components (Abdallah et al. 2018;Qazi et al. 2018b). Considering the per capita generation rate, Muscat generated around 1837 ton/day of MSW in 2020 (National Centre for Statistics and Information 2020). ...
... Financial feasibility of waste-to-energy technologies for municipal solid waste management… It exposes waste to temperatures ranging between 600 and 1000 °C. The produced syngas can be used in combustion engines to generate electricity (Hadidi and Omer 2017;Qazi et al. 2018b). Gasification is capable to treat unsorted MSW, but to enhance the efficiency of the process sorted MSW should be used; this requires mechanical treatment of MSW, which rejects 72.51% of total MSW for gasification to process (Hadidi and Omer 2017;Alzate et al. 2019;Alsabbagh 2019). ...
Oman has witnessed a rapid growth in the generation of municipal solid waste due to the ever-increasing urbanization and expanding population. This escalation in the generation of municipal solid waste has burdened the existing waste management infrastructure and increased the carbon footprint of the sector. Therefore, the need of an integrated waste management system is rising in Oman and establishing waste-to-energy technologies is becoming an absolute necessity. Therefore, this study investigates the financial feasibility of incineration, gasification and anaerobic digestion technologies in the Muscat governorate of Oman. The potential cost and revenue streams during the economic life of waste-to-energy plants are estimated to evaluate the profitability of projects by a set of financial parameters. Incineration has emerged as the most profitable strategy with the positive net present value of 255 million USD compared to 169 and 97.9 million USD for anaerobic digestion and gasification, respectively. Furthermore, incineration offers higher energy potential at lower cost (0.06 USD/kWh) than gasification (0.11 USD/kWh) and AD (0.16 USD/kWh). However, AD plant turns out more favorable in terms of profitability index, payback period, and internal rate of return and levelized cost of waste, mainly due to the low investment cost. This study concludes that incineration stands out among all options because of the higher profitability, waste treating capacity, energy generation and carbon footprint savings. The sensitivity analysis reveals that change in carbon credit allowance affects the profitability of all waste-to-energy plants, whereas electricity tariff and capital investment affect only incineration and gasification.
Graphic abstract
... Anaerobic digestion is a biochemical technology that converts organic waste into energy with the assistant of anaerobic microorganisms such as yeast. This anaerobic digestion process takes place in a specific reactor with special condition that suits well with the targeted microbes (Bajpai, 2017;Qazi et al., 2018). At the end of the anaerobic digestion process, three main products are generated, which consist of biogas, fiber, and liquid digestate (Chiu et al., 2016). ...
Types and factors of waste accumulation
... Recent studies have examined aspects like technological advancements, policy frameworks, economic viability and the environmental impacts of waste-to-energy conversion or specific waste-to-energy treatment processes [25][26][27]. However, no recent review has provided a comprehensive review of the latest advancements in technological treatments converting FW and FL into energy [28,29]. ...
Food loss (FL) and food waste (FW) have become severe global problems, contributing to resource inefficiency and environmental degradation. Approximately 6% of greenhouse gas emissions (GHGs) are derived from FW, which is usually discarded in landfills, emitting methane, a gas that is 28 times more harmful than CO2. Diverting the path of FW towards the energy industry represents a promising avenue to mitigate the environmental impact and save resources while generating energy substitutes. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach was utilized to conduct a systematic literature review on 10 different conversion processes used to convert FL and FW into energy. Anaerobic bioconversion integrated with pyrolysis emerges as a potential eco-friendly and promising solution for FW management, nutrient recovery and energy production in various forms, including biogas, heat, biohydrogen and biochar. Despite its potential, the anaerobic digestion of FW still faces some challenges related to the production of intermediate harmful compounds (VOCs, NH3, H2S), which necessitate precise process control and optimization. Nonetheless, converting FW into energy can provide economic and environmental benefits in the context of the circular economy. This review offers insightful information to stakeholders, academics and policymakers who are interested in utilizing FW as a means of producing sustainable energy by summarizing the important findings of ten different waste-to-energy processing methods and their potential for improved energy recovery efficiency.
... Second, a large amount of heat is produced during waste combustion that further promotes renewable energy generation (heat and/or power, gases, etc.) (Francesco et al., 2018;Kamyab et al., 2022). Third, compared to anaerobic digestion and aerobic composting technology, WTE stands out as an optimal approach for efficiently treating MSW in a shorter time, at a lower cost and with well-established technology, and it excels in handling inorganic waste, which anaerobic composting and aerobic digestion technology cannot achieve (LoRe and Hurdle, 2013;Qazi et al., 2018). These advantages of WTE incineration have led to its worldwide popularity in recent decades, contributing greatly to the sustainable development of the circular economy and society (Leckner, 2015;Istrate et al., 2020;Peng et al., 2023). ...
Introduction: Environmental regulation, as a vital component of public regulation in China, plays a crucial role in coordinating regional eco-efficiency, while the traditional hypothesis, Porter hypothesis, and uncertainty hypothesis offer three different perspectives for understanding the relationship between industry performance and environmental regulations.
Methods: Based on the assumption of industry heterogeneity, 81 public-private partnership (PPP) waste-to-energy (WTE) incineration projects are analyzed using panel data from 66 cities within China during the period from 2013 to 2017 with the aims to reveal the underlying mechanism behind environmental regulation and the government subsides of public-private partnership waste-to-energy incineration projects by using multiple regression modeling.
Results: The results show that the impact of environmental regulation on government subsides of PPP WTE projects has demonstrated an “Inverted-U”-shaped relationship with an inflection point, of which an increase in environmental regulation is positively correlated with an increase in subsidies at first then a negative correlation developing later.
Discussion: The findings are significant in setting flexible environmental regulations according to the needs of regional economic and social development. In addition, they also supply a theoretical reference for promoting the WTE incineration industry’s sustainable and healthy development.
... However, their greenhouse gas emissions, energy security concerns, sustainability issues, and high production costs highlight the pressing necessity to develop affordable or cost-free sustainable and renewable technologies as substitutes for fossil energy (Salahi et al., 2023a;Zarei-Jelyani et al., 2023). Biomass is a viable option for producing renewable energy because to its abundance, availability, and ability to create several kinds of energy sources (such as bioliquids and biofuels) via physical, thermal, or biological processes (Qazi et al., 2018). Nevertheless, it has certain disadvantages due to its heterogeneous characteristics, poor grindability index, high O/C ratio, elevated humidity content, and the fact that it only contains 10-40% of the calorific content found in fossil fuels. ...
... Furthermore, there is a need for research in developing effective waste management systems that can be integrated into small and medium-scale farms. This includes the development of cost-effective biogas systems and waste-to-energy technologies (Qazi et al., 2018). In addition to technological research, there is a need for socioeconomic studies. ...
... The incineration process is characterized by its ability to significantly reduce the volume of waste, minimizing the need for extensive landfill spaces [71]. However, a critical aspect of this process lies in its environmental impact, necessitating a detailed examination of emissions, ash management, and the potential release of pollutants [72]. ...
The paper presents a thorough examination of the burgeoning field of utilizing manufacturing waste for sustainable energy generation, aligning with the global imperative for resource efficiency and clean energy solutions. With the manufacturing sector being a significant contributor to waste generation, this study explores innovative approaches to transform waste materials into valuable resources, thereby mitigating environmental impacts and contributing to a circular economy. This work critically reviews current trends, emphasizing technological advancements, policy interventions, and market dynamics shaping the manufacturing waste utilization landscape. Noteworthy developments, such as advanced sorting technologies and the integration of digital solutions, are discussed in detail, showcasing their role in enhancing the efficiency of waste management processes. The study outlines future trends in the field, anticipating a shift towards closed-loop systems guided by circular economy principles. This comprehensive review aims to contribute to the discourse on sustainable waste management and energy generation by providing a holistic perspective on the field's current state and offering insights into the future trajectories that will propel manufacturing waste toward a more sustainable and circular future. The synthesis of technological innovation, collaborative efforts, and evolving regulatory frameworks presents a compelling case for the continued exploration of manufacturing waste as a valuable resource in the pursuit of a more sustainable and energy-efficient world.
... Bioenergy can be considered the most subsistent renewable energy origin because of its economic merits and remarkable capacity to substitute for fossil fuels. Bioenergy is renewable energy generated from biomass materials, and it can be released from various origins and generated with several technologies [2]. Biogas is an example of bioenergy that is produced through anaerobic digestion, and it is flexible to various biodegradable materials. ...
This study examined the possibilities of enhancing methane yield from anaerobic digestion of Xyris capensis and duck wastes based on improved feeding composition and the C/N ratio. Batch anaerobic digestion of Xyris capensis and duck wastes was conducted at mesophilic temperature (37 ± 2 °C) with the mixing ratios of 100:0, 75:25, 50:50, 25:75, and 0:100% of duck wastes: Xyris capensis. The highest methane yield of 301.17 mL CH4/ gVSadded was recorded when the mixing ratio of 50:50% (duck wastes: Xyris capensis) and C/N ratio of 19.26 was digested. The biodegradability (BD) of duck wastes and Xyris capensis were 86.60 and 58.57%, respectively. The BD of duck wastes increases with the addition of Xyris capensis, and it started to decline after a 50:50% mixing ratio. A stronger synergistic influence of co-digestion was noticed compared to monodigestion of the individual of each feedstock. This study showed a better performance of anaerobic co-digestion and can be used to enhance feeding composition and the C/N ratio. In general, methane production from duck wastes co-digested with Xyris capensis is a good strategy to generate renewable energy and minimize waste management challenges.
... WTE with biogas/methane recovery from non-thermal treatment should be obtained with a selective collection system for the biodegradable waste or will need advanced pre-treatment for segregating the bio-decomposable portion from the overall waste. Landfilling should be the option for waste disposal only after a significant volume reduction by either WTE conversions or recycling [75]. A critical evaluation of these processes and parameters is required to assemble the decision-making building blocks, attract potential investment opportunities, influence the marketplace, and regulate environmental policies for MSW disposal. ...
This review on current US municipal solid waste-to-energy trends highlighted regional contrasts on technology adoption, unique challenges of each technology, commonly used decision support tools, and major operators. In US only 13% of MSW is used for energy recovery and 53% is landfilled. There are 86 WTE facilities that mostly use Mass-Burn and Refuse-Derived Fuel technologies and are concentrated in densely populated northeast (predominantly in New York) and the State of Florida. For the rest of the country most of the MSW ends up in landfills equipped with gas recovery, which is supplied to homes or used for electricity generation. However, there are many pilot and experimental systems based on advanced gasification and pyrolysis processes, which are viewed as potential technologies to respond to an issue of landfills nearing full capacity in various US states. These systems are viewed as “cleaner” (65% less toxic residue) than established mass burn technologies but not matured to commercialization due technical and cost hurdles. Operation and maintenance costs between 100 per ton of MSW were reported for gasification systems. The heterogeneous nature of MSW, gas cleaning and air pollution controls are the main disadvantages. Key design and decision support tools used by the scientific community and major operators in US include: Techno-economic analysis, Life cycle sustainability assessment, and Reverse logistics modeling. A conclusion drawn from reviewed studies is that adoption of thermal WTE technologies in US could continue to increase, albeit slowly, in coastal and urban areas lacking suitable lands for new landfills.
Environmental problems and the ever-increasing growth of population dictate the need for new methods to turn the problem into an opportunity. The recycling of agricultural waste is very important to achieve sustainable development of agriculture. Present paper focuses on how the proper disposal and recycling of agricultural waste can significantly reduce greenhouse gas emissions, conserve resources, and improve soil fertility. Hereupon, the specified criteria were determined by relevant organisations. Five final products including composting, biochar, biogas, reuse/recycling, and incineration resulting from the technologies used were investigated using the AHP technique. In addition to the effective management of agricultural waste, these technologies help in the production of electricity, fertiliser, and carbon absorption, which results in the reduction of climate change and the reduction of economy. Among the proposed products, biochar was preferred, and the incineration method was ranked the last. Biochar offers potential environmental benefits in terms of reducing greenhouse gas emissions, increasing the quality and quantity of agricultural products, and preventing soil erosion and degradation as well as water pollution. High rank was assigned to environmental criteria, and the actual waste production sub-criterion was preferred over other criteria with a weight of 0.170. The lowest weight was obtained for the shipping distance (weigh = 0.013).
Waste management is critical for public health and environmental sustainability, yet traditional methods face inefficiencies and pollution challenges. Recent technological innovations, like IoT sensors and RFID tags, optimize waste collection routes and reduce fuel usage, thus lowering greenhouse gas emissions. Waste-to-energy technologies, such as pyrolysis and anaerobic digestion, convert organic waste into valuable energy sources, reducing reliance on fossil fuels. Robotics, drones, and smart waste bins enhance waste sorting and disposal practices, reducing littering in urban areas. Collaboration among stakeholders is emphasized to drive innovation and adoption of these technologies, fostering a more sustainable and circular economy.
The aim of this third Eng Special Issue is to collect experimental and theoretical re-search relating to engineering science and technology [...]
In recent years, global population and urbanization have experienced significant growth, resulting in the substantial increase in the generation of Municipal Solid Waste (MSW) worldwide. The rise in MSW generation has raised concerns on the significant environmental impacts. However, instead of being viewed as a problem, MSW has been recognized as a valuable resource that can be used for energy generation. One of the most promising technologies for generating energy from MSW is pyrolysis. Pyrolysis of municipal solid waste for energy generation has several advantages including reducing greenhouse gas emissions and potentially providing an alternative to fossil fuels as a cleaner source of energy. Although pyrolysis is a promising technology for energy generation, the implementation of advanced technologies is crucial to minimize the potential environmental impacts, such as air pollution and ash disposal. Thus, it is essential to utilize effective technologies to ensure that generating energy from municipal solid waste via pyrolysis technology is carried out in an environmentally friendly manner. Pyrolysis of MSW also ensures effective municipal solid waste management, which reduces the volume of waste that would otherwise be sent to landfills. Overall, this study discusses how energy is generated from MSW via pyrolysis, and its environmental aspects.
This paper provides a comprehensive review of the environmental impact of plasma gasification technology, and assesses its merits as a sustainable technology fitting within waste management strategies for the circular economy transition. It reviews prior published work on conventional and plasma gasification through an environmental Life Cycle Assessment (LCA) lens, extracting each LCA's impact categories for a systematic review by comparing each LCA's relative difference. Such review method has not been applied for gasification technology before. From the reviewed LCA, it is found that plasma gasification, given its simultaneous energy and materials recovery feature, has more environmental benefits over landfilling and incineration. For example, in terms of global warming potential, 67% and 61% of the reviewed LCA work agrees that plasma gasification is more environmentally sound when compared to landfilling and incineration, respectively. For conventional (non-plasma) gasification, 89% of the reviewed-LCA find it to have lower global warming impact than landfilling; however, only half (56%) of the reviewed LCA find conventional gasification to be beneficial over incineration for the same impact categories. This review has demonstrated the environmental superiority of plasma gasification over other Energy-from-Waste (EFW) technologies, and has presented its alignment with the circular economy principle of circulating products and materials at their highest value with a minimal environmental impact.
Prominent among problems of developing nations are access to affordable and reliable energy as well as clean and livable environment. The abovementioned points coincide with the sustainable development goals 7 (SDG 7) and 11 (SDG 11) of the United Nations (UN), respectively. Adopting waste-to-energy system could leverage on the possibility of reducing the adverse environmental impact occasioned by waste generation and ensuring production of renewable and sustainable energy while achieving circular economy. A review of most commonly used technologies for solid waste management worldwide, such as incineration, pyrolysis, gasification, anaerobic digestion, and landfilling with gas recovery in order to achieve waste-to-energy nexus is presented. A brief discussion on the economic, environmental and social impact as well as the implementation levels, some challenges and possible solutions to the implementation of the mentioned technologies for both developed and developing countries are included. This paper also addresses waste-to-energy (WtE) as a contributor to achieving sustainable development. It is evident from this paper that the waste stream of developing countries contained 50-56% food and garden wastes making anaerobic digestion technology more appropriate for treatment. Incineration is widely adopted in developed countries with more than 1,700 incineration plants operational worldwide. This paper offers to add to the pool of literature while helping researchers and decision-makers to make an informed decision on the feasibility of WtE as a pathway for sustainable waste management and renewable energy generation.
Municipal solid waste (MSW) is a big environmental challenge. However; it is a potential source of recycling materials, heat and energy. In developed countries this waste is used as resource to produce energy and compost; whereas in developing countries like India, collection, transportation and disposal of MSW are a big task. Wastes to energy technologies (WTE-T) play important role in sustainable management of MSW throughout the world. These technologies reduce the amount of waste as well as produce energy, which can be used to generate electricity. These include thermochemical treatment technologies, biochemical treatment technologies and utilization of landfill gas. Thermochemical techniques include Incineration, Gasification, Pyrolysis, Plasma arc gasification and Hydrothermal carbonization. Incineration is the most common technique used for treatment of MSW. It reduces 70% mass and 90% volume of MSW and sterile ash remains as byproduct. Gasification is advantageous over incineration, as gases are not released into atmosphere. Pyrolysis is the anaerobic thermal degradation of MSW, carried out in an oxygen free environment, producing gases (syngas), liquid and solid residuals. Syngas is composed of methane, hydrogen, carbon mono oxide and carbon dioxide. It can be used in engines, boilers, turbines, fuel cells and heat pumps. Plasma arc gasification also involves partial oxidation of MSW. Syngas and high quality producer gas is obtained that can be used as transport fuel, heat and to generate electricity. Hydrothermal Carbonization (HTC) is a complex process through which hydro-char is produced, which is similar to coal and can be used as a solid fuel for heat and power generation. Organic fraction of MSW is biodegradable and has high energy content. Biochemical treatment technologies are designed to utilize this fraction of MSW. Anaerobic digestion of organic waste is performed by microbes in absence of oxygen in a closed container (biogas digester), resulting in the reduction of waste and production of a combustible gas, biogas, a mixture of methane and carbon dioxide. Landfill gas is rich in methane and must be used to produce heat and energy. It usually consists of 50% methane and 50% CO2. Gas is collected by pipes and reaches the wells installed inside the landfills.
The aim of this chapter is to provide an overview of the potential of waste-to-energy (WtE) as a source for future electricity generation from Municipal Solid Waste (MSW) in the context of developing countries. The amount of MSW has been increasingly generated in developing countries due to the improvement of lifestyle, increase of income level, and rapid urbanization. While developed countries have been using advanced technologies for the management of MSW in a sustainable way, developing countries are not well prepared to manage MSW. There are tools and techniques to manage MSW in a sustainable way such as minimization of waste by reducing the use of products. Importantly, advanced WtE technologies for sustainable MSW management such as gasification, incineration, anaerobic digestion, and pyrolysis are not only suitable for recovering materials but also to produce electricity. However, the use of advanced technologies in developing countries is still in infancy level with a few exceptions. This chapter indicates that there is a huge potential of generating electricity from MSW using WtE technologies. The reasons behind the inadequate use of WtE technologies in developing countries may include the lack of adequate institutional arrangements, scarce of skilled people, insufficient investment for sustainable management of MSW, and the lack of satisfactory awareness among city dwellers.
In light of legislative requirements and circular economy principles, valorization of wastes is the best strategy for its management. The biodegradable fraction of industrial wastes is a sustainable source of biomass, thereby optimizing its management by energy valorization, decreasing the quantity of waste that needs to be managed (and its economic costs), minimizing the environmental impact and health risks, and reducing the high dependence of industries on primary sources and fossil energy. Although traditional biomass sources, such as wood, crops, agricultural and forestry residues, and food and municipal wastes, are renewable, sustainable and cost-efficient, they compete with food and their energy processes release waste into the environment. Waste to Energy (WtE) is a recent, efficient and sustainable method of waste management based on the idea that energy sustainability involves both sustainable energy sources and sustainable energy systems. This paper reviews studies that propose industrial waste and by-products as sustainable, renewable and unlimited sources of biomass for use in sustainable energy systems to generate electricity, heat and cold, bioliquids and biofuels. The advantages and disadvantages of various types of resources are presented, and their limitations and the challenges that must be overcome are analyzed and compared.
The need of an integrated municipal solid waste (MSW) management system to maximize resource recovery and simultaneously reduce greenhouse-gas (GHG) emissions is rising in Oman. Therefore, three waste management scenarios are proposed and assessed in this study based on their potential to reduce waste and GHG emissions, and recover energy and recyclables in Oman from 2020 to 2040. The first scenario included recycling, anaerobic digestion (AD), and landfill disposal; while second scenario entailed recycling, incineration, and ash disposal. The third scenario involved incineration and AD plants, and landfilling of residues. The analysis indicated that the disposal of waste in scenario 2 will be the lowest during the entire study period (30–24%), followed by scenario 3 (32–41%) and scenario 1 (94–58%). Moreover, during the assessment period, scenario 3 will generate a total of 47 TWh electricity, higher than scenario 2 (29 TWh) and scenario 1 (4.7 TWh). Disposal of MSW is estimated to produce 309,803 GgCO2e from 2020 to 2040; however, these emissions can be reduced by 53, 94 and 90% by the implementation of scenarios 1, 2 and 3, respectively. Furthermore, the average global warming factors after energy and material recovery further indicate that scenario 2 and scenario 3 result in net GHG emission savings of − 0.4 and – 0.28 GgCO2e/Gg of MSW, except for scenario 1 which will produce 2.37 GgCO2e/Gg of MSW. The analysis showed that in terms of reducing waste disposal and GHG emissions, scenario 2 is the best performing option; however, scenario 3 has the highest energy output.
Municipal solid waste (MSW) generation has been escalated at a global scale and poses drastic impacts on the environment along with many socioeconomic problems. Waste to energy (WtE) technologies have been recognized to convert MSW into useful energy and minimize the problems related to it. This study reviewed different WtE technologies according to the conversion pathways, end-products, and their applications, and assessed statistical values of these technologies based on six different factors, viz., environmental performance, suitable waste fractions, capital and operational cost, efficiency, and complexity of the technology, the skillset of the labor, and favorable geographical location for the plant. The results of this review showed that biochemical and physicochemical WtE technologies are more favorable to convert organic waste, while thermochemical WtE technologies are suitable to process combustible fractions of organic and inorganic MSW. Based on the statistical review of considered factors from the literature, the statistical profiles of concerned WtE technologies were observed. Finally, a general framework in the form of a systematic scheme was proposed for the selection of the most suitable WtE technologies for a sustainable MSW management system. The recommended indicators, methods, and models in the proposed framework were selected after a detailed review of the literature published in well-known scientific journals, and reports of leading international organizations such as the World Bank, International Energy Agency (IEA), and International Labour Organization (ILO). Moreover, the databases to extract the data for the estimation of various recommended indicators have also been presented.
The rapid increase in the generation of solid waste and rising demand for energy and preservation of fossil fuels worldwide caused an increase in the popularity of waste-to-energy (WTE) technologies as the solution for waste management problems and energy demands. WTE technologies convert the waste into energy and thus minimize the amount of waste sent to landfills, which also reduces negative impacts on the surrounding environment. This chapter presents the processes and specific aspects of WTE technologies along with their advantages and disadvantages. It also discusses the important criteria involved to select and ensure efficient operation of WTE technology. Furthermore, popular multi-criteria decision-making techniques are discussed in this chapter, as they have the capability to solve a complex decision problem of selecting the right WTE technology which involves many factors. This chapter illustrates that the waste and process must closely match to achieve proper conversion of waste and better efficiency of a WTE technology. The continuous developments being made in process efficiency and process control of WTE facilities is expected to enhance the commercial feasibility of these conversion processes in the near future.
Waste management in European Union has long being regulated by the 4Rs principle, i.e. reduction, reuse, recycling, recovery, with landfill disposal as the last option. This vision recently led the European Union (especially since 2015) to the introduction of virtuous goals based on the rejection of linear economy in favour of circular economy strongly founded on materials recovery. In this scenario, landfill disposal option will disappear, while energy recovery may appear controversial when not applied to biogas production from anaerobic digestion. The present work aims to analyse the effects that circular economy principles introduced in the European Union context will have on the thermochemical waste treatment plants design. Results demonstrate that indirect combustion (gasification + combustion) along with integrated vitrification of the non-combustible fraction of treated waste will have a more relevant role in the field of waste treatment than in the past, thanks to the compliance of this option with the principles of circular economy.
This paper proposes an overarching review of national municipal waste management systems and waste-to-energy as an important part of it in the context of circular economy in the selected countries in Europe. The growth of population and rising standards of living means that the consumption of goods and energy is increasing. On the one hand, consumption leads to an increase in the generation of waste. On the other hand, the correlation between increased wealth and increased energy consumption is very strong as well. Given that the average heating value of municipal solid waste (MSW) is approximately 10 MJ/kg, it seems logical to use waste as a source of energy. Traditionally, waste-to-energy (WtE) has been associated with incineration. Yet, the term is much broader, embracing various waste treatment processes generating energy (for instance, in the form of electricity and/or heat or producing a waste-derived fuel). Turning waste into energy can be one key to a circular economy enabling the value of products, materials, and resources to be maintained on the market for as long as possible, minimising waste and resource use. As the circular economy is at the top of the EU agenda, all Member States of the EU (including the EEA countries) should move away from the old-fashioned disposal of waste to a more intelligent waste treatment encompassing the circular economy approach in their waste policies. Therefore, the article examines how these EU policies are implemented in practice. Given that WtE traditionally is attached to the MSW management and organisation, the focus of this article is twofold. Firstly, it aims to identify the different practices of municipal waste management employed in selected countries and their approaches in embracing the circular economy and, secondly, the extent to which WtE technologies play any role in this context. The following countries, Estonia, Greece, Italy, Latvia, Lithuania, Norway, Poland, Slovenia, Spain, and the UK were chosen to depict a broad European context.
Vegetables waste is generally utilized through a bioconversion process or disposed of at municipal landfills, dumping sites or dumped on open land, emitting a foul odor and causing health hazards. The presents study deals with an alternative way to utilize solid vegetable waste through a thermochemical route such as briquetting and gasification for its energy recovery and subsequent power generation. Briquettes of 50 mm diameter were produced from four different types of vegetable waste. The bulk density of briquettes produced was increased 10 to 15 times higher than the density of the dried vegetable waste in loose form. The lower heating value (LHV) of the briquettes ranged from 10.26 MJ kg⁻¹ to 16.60 MJ kg⁻¹ depending on the type of vegetable waste. The gasification of the briquettes was carried out in an open core downdraft gasifier, which resulted in syngas with a calorific value of 4.71 MJ Nm⁻³ at the gasification temperature between 889°C and 1011°C. A spark ignition, internal combustion engine was run on syngas and could generate a maximum load up to 10 kWe. The cold gas efficiency and the hot gas efficiency of the gasifier were measured at 74.11% and 79.87%, respectively. Energy recovery from the organic vegetable waste was possible through a thermochemical conversion route such as briquetting and subsequent gasification and recovery of the fuel for small-scale power generation.
The organic content of municipal solid waste has long been an attractive source of renewable energy, mainly as a solid fuel in waste-to-energy plants. This study focuses on the potential to use microbial fuel cells to convert municipal solid waste organics into energy using various operational conditions. The results showed that two-chamber microbial fuel cells with carbon felt and carbon felt allocation had a higher maximal power density (20.12 and 30.47 mW m-2 for 1.5 and 4 L, respectively) than those of other electrode plate allocations. Most two-chamber microbial fuel cells (1.5 and 4 L) had a higher maximal power density than single-chamber ones with corresponding electrode plate allocations. Municipal solid waste with alkali hydrolysis pre-treatment and K3Fe(CN)6 as an electron acceptor improved the maximal power density to 1817.88 mW m-2 (~0.49% coulomb efficiency, from 0.05–0.49%). The maximal power density from experiments using individual 1.5 and 4 L two-chamber microbial fuel cells, and serial and parallel connections of 1.5 and 4 L two-chamber microbial fuel cells, was found to be in the order of individual 4 L (30.47 mW m-2) > serial connection of 1.5 and 4 L (27.75) > individual 1.5 L (20.12) > parallel connection of 1.5 and 4 L (17.04) two-chamber microbial fuel cells . The power density using municipal solid waste microbial fuel cells was compared with information in the literature and discussed.
In China, incineration is essential for reducing the volume of municipal solid waste arising in its numerous megacities. The evolution of incinerator capacity has been huge, yet it creates strong opposition from a small, but vocal part of the population. The characteristics of Chinese municipal solid waste are analysed and data presented on its calorific value and composition. These are not so favourable for incineration, since the sustained use of auxiliary fuel is necessary for ensuring adequate combustion temperatures. Also, the emission standard for acid gases is more lenient in China than in the European Union, so special attention should be paid to the issue of acidification arising from flue gas. Next, the techniques used in flue gas cleaning in China are reviewed and the acidification potential by cleaned flue gas is estimated. Still, acidification induced by municipal solid waste incinerators remains marginal compared with the effects of coal-fired power plants.
Municipal solid waste disposed in landfill sites decomposes under anaerobic conditions and produces so-called landfill-gas, which contains 30%-40% of carbon dioxide (CO2) and 50%-60% of methane (CH4). Methane has the potential of causing global warming 25 times more than CO2. Therefore, migration of landfill-gas from landfills to the surrounding environment can potentially affect human life and environment. Thus, this research aims to determine municipal solid waste generation in Oman over the years 1971-2030, to quantify annual CH4 emissions inventory that resulted from this waste over the same period of time, and to determine the economic and environmental benefits of capturing the CH4 gas for energy production. It is found that cumulative municipal solid waste landfilled in Oman reaches 3089 Giga gram (Gg) in the year 2030, of which approximately 85 Gg of CH4 emissions are produced in the year 2030. The study also found that capturing CH4 emissions between the years 2016 and 2030 could attract revenues of up to US291 million from the carbon reduction and electricity generation, simultaneously. It is concluded that CH4 emissions from solid waste in Oman increases enormously with time, and capture of this gas for energy production could provide a sustainable waste management solution in Oman.
Studies were conducted with 62 Brazilian distilleries during the last nine years to elicit the advantages and disadvantages of continuous and batch fermentation processes. Of these, 51 were batch and 11 continuous. Findings indicate that the batch fermentation process with yeast recycle is superior for the following main reasons. The process parameters are more easier to measure and invariably control and manage. In particular, it is less susceptible to bacterial and wild yeast contamination which otherwise would invite hosts of problems including decrease in productivity. In a case study presented, the increase in output (of 3.3 million litres) through the replacement of a continuous process with a batch process resulted in payback within the year. While the continuous system is relatively cheaper to install, this is negated by poor productivity levels associated with bacterial and wild yeast contamination as it does not lend itself to be cleaned more frequently, the additional costs of antibiotics to address this and yeast shocks when they pass from one fermenter to other where the composition of the substrate (namely alcohol and sugars) and temperature are both different. This suggests why 83% of the Brazilian distilleries have adopted the batch process and new ones are also opting for this as process of choice.
China-the largest developing country in the world-is experiencing both rapid economic maturation and large-scale urbanization. These situations have led to waste disposal problems, and the need to identify alternative energy sources. Waste-to-energy (WTE) conversion processes, a source of renewable energy, are expected to play an increasingly important role in China's sustainable management of municipal solid waste (MSW). The purpose of this research is to investigate the key problems and opportunities associated with WTE, to provide recommendations for the government. This paper begins by describing China's current MSW management situation and analyzing its waste disposal problems. The major challenges associated with China's WTE incineration are then discussed from economic, environmental and social points of view. These include the high costs associated with constructing necessary facilities, the susceptibility of facilities to corrosion, the lower heating value of China's MSW, air pollutant emissions and especially public opposition to WTE incineration. Since discarded waste can be used to produce energy for electricity and heat-thus reducing its volume and the production of greenhouse gas (GHG) emissions-with government policies and financial incentives, the use of WTE incineration as a renewable energy source and part of a sustainable waste management strategy will be of increasing importance in the future. The paper concludes by summarizing the management, economic and social benefits that could be derived from developing the country's domestic capacity for producing the needed incineration equipment, improving source separation capabilities, standardizing regulatory and legal responsibilities and undertaking more effective public consultation processes.
Environmental issues are often neglected until a lapse in the care for environment, which leads to serious human health problem, would then put regulation gaps in the spotlight. Environmental regulations and standards are important as they maintain balance among competing resources and help protect human health and the environment. One important environmental standard is related to municipal solid waste (MSW). Proper MSW management is crucial for urban public health. Meanwhile, the sustainability of landfills is also of concern as increasing volumes of MSW consume finite landfilling space. The incineration of MSW and the reuse of incinerated residues help alleviate the burden on landfilling space. However, the reuse of MSW incinerator residues must be regulated because they may expose the environment to toxic heavy metal elements. The study of environmental standards from different countries applicable to MSW is not widely published, much less those for incinerated MSW residue reuse. This paper compares extant waste classification and reuse standards pertinent to MSW, and explores the unique recent history and policy evolution in some countries exhibiting high environmental regard and rapid changes, policy makers can propose new or revise current MSW standards in other countries.
This paper describe a conceptual framework and methodological tool developed for evaluation of different waste to energy technology suitable for treating municipal solid waste, by introducing the multi criteria decision support method MATLAB computing software and demonstrating its related applicability via test application. The solid waste quantity in the Kolhapur city, Maharashtra, India, per day and calorific value of waste, physical and chemical characteristic of waste etc are evaluated with generation potentiality of energy through. In this work multi criteria exercise, using MATLAB tool is presented for comparing a ranking of 5 selected alternatives for WTE technologies and final result are achieved. In conclusion, multi criteria approach is found to be a practical and feasible method for the integrated assessment and ranking WTE technologies it can help decide, uncertainties in decision making process.
Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The objective of this study is to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process about 1 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600°C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N 2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000 °C – 1100 °C. The tars are cracked into carbon and additional gases. Most of the carbon is subsequently gasified by oxygenated volatiles (CO 2 , H 2 O) from the first stage. In a final step, the temperature of the first stage can be raised and the purge gas switched from N 2 to CO 2 in order to gasify the remaining char in the first stage and the remaining carbon deposits in the second stage. Alternatively, the char can be removed from the first stage and saved as a future source of CO 2 or used to make activated carbon. The product gases from the pyrolyzer will be rich in CO and cannot be vented directly into the cabin. However, they can be processed in a shift reactor or sent to a high temperature fuel cell. A control system based on artificial neural networks (ANNs) is being developed for the reactor system. ANN models are well suited to describing the complicated relationships between the composition of the starting materials, the process conditions and the desired product yields.
This article presents an analysis of possibilities for electrical energy production by using municipal solid waste disposed in the biggest Brazilian cities. Currently, the municipal solid waste in Brazil is collected and disposed of at landfills, but there are also other technologies, which in addition to dealing with the garbage can also provide benefits in terms of energy provision. The following scenarios were studied in this work: electricity production from landfill gas (reference scenario); incineration of all municipal solid waste; anaerobic digestion of organic waste and incineration of refuse-derived fuel fractions after being separated in separation plants. According to this study, the biggest cities in Brazil generate about 18.9 million tonnes of municipal solid waste per year (2011), of which 51.5% is biogenic matter. The overall domestic consumption of electricity is 480,120 GWh y(-1) in Brazil and the municipal solid waste incineration in the 16 largest cities in the country could replace 1.8% of it using incinerators. The city of São Paulo could produce 637 GWh y(-1) with landfill gas, 2368 GWh y(-1) with incineration of municipal solid waste and 1177 GWh y(-1) with incineration of refuse-derived fuel. The latter two scenarios could replace 27% and 13.5% of the residential electrical energy consumption in the city. This shows that thermal treatment might be a viable option of waste-to-energy in Brazil.
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Hydrothermal carbonization (HTC) is a thermochemical process used in the production of charred matter similar in composition to coal. It involves the use of wet, carbohydrate feedstock, a relatively low temperature environment (180 °C-350 °C) and high autogenous pressure (up to 2.4 MPa) in a closed system. Various applications of the solid char product exist, opening the way for a range of biomass feedstock materials to be exploited that have so far proven to be troublesome due to high water content or other factors. Sludge materials are investigated as candidates for industrial-scale HTC treatment in fuel production. In general, HTC treatment of pulp and paper industry sludge (PPS) and anaerobically digested municipal sewage sludge (ADS) using existing technology is competitive with traditional treatment options, which range in price from EUR 30-80 per ton of wet sludge. PPS and ADS can be treated by HTC for less than EUR 13 and 33, respectively. Opportunities and challenges related to HTC exist, as this relatively new technology moves from laboratory and pilot-scale production to an industrial scale. Feedstock materials, end-products, process conditions and local markets ultimately determine the feasibility of a given HTC operation. However, there is potential for sludge materials to be converted to sustainable bio-coal fuel in a Finnish context.
In recent years, waste management systems have been evaluated using a life cycle assessment (LCA) approach. A main shortcoming of prior studies was the focus on a mixture of waste with different characteristics. The estimation of emissions and consumptions associated with each waste fraction in these studies presented allocation problems. Waste-to-energy (WTE) incineration is a clear example in which municipal solid waste (MSW), comprising many types of materials, is processed to produce several outputs. This paper investigates an approach to better understand incineration processes in Spain and Portugal by applying a multi-input/output allocation model. The application of this model enabled predictions of WTE inputs and outputs, including the consumption of ancillary materials and combustibles, air emissions, solid wastes, and the energy produced during the combustion of each waste fraction.
Anaerobic digestion is the method of wastes treatment aimed at a reduction of their hazardous effects on the biosphere. The mutualistic behavior of various anaerobic microorganisms results in the decomposition of complex organic substances into simple, chemically stabilized compounds, mainly methane and CO2. The conversions of complex organic compounds to CH4 and CO2 are possible due to the cooperation of four different groups of microorganisms, that is, fermentative, syntrophic, acetogenic, and methanogenic bacteria. Microbes adopt various pathways to evade from the unfavorable conditions in the anaerobic digester like competition between sulfate reducing bacteria (SRB) and methane forming bacteria for the same substrate. Methanosarcina are able to use both acetoclastic and hydrogenotrophic pathways for methane production. This review highlights the cellulosic microorganisms, structure of cellulose, inoculum to substrate ratio, and source of inoculum and its effect on methanogenesis. The molecular techniques such as DGGE (denaturing gradient gel electrophoresis) utilized for dynamic changes in microbial communities and FISH (fluorescent in situ hybridization) that deal with taxonomy and interaction and distribution of tropic groups used are also discussed.
The current world demand for bioethanol is increasing as a consequence of low fossil fuel availability and a growing number of ethanol/gasoline flex-fuel cars. In addition, countries in several parts of the world have agreed to reduce carbon dioxide emissions, and the use of ethanol as a fuel (which produces fewer pollutants than petroleum products) has been considered to be a good alternative to petroleum products. The ethanol that is produced in Brazil from the first-generation process is optimized and can be accomplished at low cost. However, because of the large volume of ethanol that is produced and traded each year, any small improvement in the process could represent a savings of billions dollars. Several Brazilian research programs are investing in sugarcane improvement, but little attention has been given to the improvement of yeast strains that participate in the first-generation process at present. The Brazilian ethanol production process uses sugarcane as a carbon source for the yeast Saccharomyces cerevisiae. Yeast is then grown at a high cellular density and high temperatures in large-capacity open tanks with cells recycle. All of these culture conditions compel the yeast to cope with several types of stress. Among the main stressors are high temperatures and high ethanol concentrations inside the fermentation tanks during alcohol production. Moreover, the competition between the desired yeast strains, which are inoculated at the beginning of the process, with contaminants such as wild type yeasts and bacteria, requires acid treatment to successfully recycle the cells. This review is focused on describing the problems and stressors within the Brazilian ethanol production system. It also highlights some genetic modifications that can help to circumvent these difficulties in yeast.
This study focuses on the use of restaurant waste for production of ethanol. Food wastes (corn, potatoes, and pasta) were converted to ethanol in a two-step process: a two-part enzymatic digestion of starch using α-amylase and glucoamylase and then fermentation of the resulting sugars to ethanol using yeast. Because of the low initial composition of starch in the food waste, low ethanol concentrations were achieved: at best 8 mg/mL ethanol (0.8% by mass). Ethanol concentration increased with increasing enzyme dosage levels. Calculations were conducted to evaluate whether waste heat from restaurant waste could be used to drive flash vaporization to purify ethanol. If the solution produced by fermenting food waste is flashed at a temperature of 99.7°C, 77% of the ethanol is recovered in a vapor stream with 1.14 mol % ethanol (2.87 mass %). Waste heat could provide over a third of the energy for this vaporization process. If 4 mol % ethanol could be produced in the fermentation step by increasing the initial starch content in the waste solution and improving the fermentation process, then a single flash at 98.9°C will recover nearly 99% of the ethanol, giving a mass concentration of ethanol of 10.3%, which is similar to that achieved in industrial grain fermentation. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1280–1283, 2013
This paper proposes an overview of waste-to-energy conversion by gasification processes based on thermal plasma. In the first part, basic aspects of the gasification process have been discussed: chemical reaction in gasification, main reactor configuration, chemical conversion performances, tar content in syngas and performances in function of the design and the operation conditions (temperature, pressure, oxidizing agent…). In the second part of the paper are compared the performances, available in the scientific literature, of various waste gasification processes based on thermal plasma (DC or AC plasma torches) at lab scale versus typical performances of waste autothermal gasification: LHV of the syngas, cold gas efficiency and net electrical efficiency. In the last part, a review has been done on the various torch technologies used for waste gasification by plasma at industrial scale, the major companies on this market and the perspectives of the industrial development of the waste gasification by thermal plasma. The main conclusions are that plasma technology is considered as a highly attractive route for the processing of waste-to-energy and can be easily adapted to the treatment of various wastes (municipal solid wastes, heavy oil, used car tires, medical wastes…). The high enthalpy, the residence time and high temperature in plasma can advantageously improve the conditions for gasification, which are inaccessible in other thermal processes and can allow reaching, due to low tar content in the syngas, better net electrical efficiency than autothermal processes.
The study aimed to analyze potential environmental burdens of different waste-to-energy technologies through LCA model. LCA model is developed by SimaPro software by considering Eco- indicator 99 method. Landfill, Incineration, Pyrolysis-Gasification and Anaerobic Digestion are analyzed by considering emission to the atmosphere per unit electricity generation. Results show that, Landfill and Incineration have the highest climate change impact among the four WTE options. Incineration and P-G has the significant impact on respiratory inorganics and acidification categories. AD has the lowest impacts on respiratory inorganics and acidification. AD and P-G have found as least environmental impact causing technology for waste-to-energy options. therefore, P-G and AD are more favorable waste-to-energy options for municipal solid waste management.
In this paper a review and assessment of the Hot Temperature Plasma Processing of Waste is presented. The environmental advantage of this method over incineration is clearly demonstrated. The present technology of Plasma Arcs and the Modern Plasma Torches Applications are also shown. An Assessment of the Heavy Duty Gasification Combined Cycle Turbines, Gasification Process, Magmavication/Vitrification process, and Environmental Engineering Protection are also described.
a b s t r a c t A new waste-disposal technology named Plasma Gasification Melting (PGM) was developed. A pilot PGM reactor was constructed in northern Israel. The reactor is an updraft moving-bed gasifier, with plasma torches placed next to air nozzles to heat the incoming air to 6000 °C. The inorganic substances of the feedstock are melted by the high-temperature air to form a vitrified slag in which undesirable materials such as heavy metals are trapped. The residual heat in the air supplies additional heat for the gasification process. A series of tests were conducted to study the performance of PGM gasification. The plasma power was varied from 2.88 to 3.12 MJ/kg of municipal solid waste (MSW), and the equivalence ratio (ER) was varied from 0.08 to 0.12. For air and steam gasification, the maximum steam/MSW mass ratio reached 0.33. The composition of the syngas product was analyzed in all tests; the lower heating value (LHV) of the syngas varied from 6 to 7 MJ/Nm 3 . For air gasification, the syngas LHV decreased with increasing ER, whereas the gas yield and energy efficiency increased with ER. When high-temperature steam was fed into the reactor, the overall gas yield was increased significantly, and the syngas LHV also increased slightly. The positive effect may be attributed to the steam reforming of tar. In air and steam gasification, the influence of increased ER on syngas LHV was negative, while the effect of increased plasma power was positive. The maximum energy efficiency of the tests reached 58%. The main energy loss was due to the formation of tar.
In this paper, life cycle assessment (LCA) of waste to energy (WtE) treatment plants for electricity generation
in twelve selected cities of Nigeria is studied with the aim of evaluating their electricity generation
potential, global warming potential (GWP), acidification potential (AP) and dioxin/furan emission potential.
The WtE plants are: landfill gas to energy (LFGTE), hybrid of incineration and anaerobic digestion
(INC/AD) and hybrid of incineration and landfill gas to energy (INC/LFGTE). The benefits of the WtE plants
are thereafter compared to the landfilling (waste management without intention of energy recovery) in
each of the locations in order to determine the option that best fit the locations in an environmentally
sustainable manner. To achieve this, the waste profile of each of the locations is determined using per
capita waste generation and the population data obtained from national population commission (NPC).
Some of the key results reveal that the hybrid of INC/AD is potentially viable compared to other methods
in terms of GWP and ecosystem potential measured by AP. However, LFGTE technology is the best in
terms of carcinogenic reduction potential measured by dioxin/furan emissions. The hybrid of INC/AD
has the potential of reducing GWP in the range of 75.7–93.3% compared to land filling without energy
recovery. Similarly, hybrid of INC/LFGTE provided a reduction in the range of 75.3–84.8% while LFGTE
could reduce the GWP by 75%. This paper could serve as a source of scientific information for decision
making on environmental sustainability in waste-to-energy projects in Nigeria.
Basics of anaerobic digestion process is presented in this chapter. Principal reactions are Hydrolysis, Fermentation Acetogenesis/dehydrogenation, Methanogenesis. The critical step in the anaerobic digestion process is Methanogenesis.
The influences of temperature and residence times on the conversion and product distribution during hydrothermal carbonisation of municipal solid wastes were investigated. Analysis of variance and reaction severity were used to comprehensively analyse the experimental results. Analysis results showed both reaction temperature and residence time had varying degrees of impact on production distribution and hydrochars characteristic, while the effect of combine temperature and time was negligible. It is novel to find that the products yield was a linear function of the logarithm of the reaction ordinate. Base on comprehensive consideration, 240 °C to 260 °C and 50 min to 60 min would be the optimised reaction region to achieve relatively better economic benefits for hydrothermal carbonisation of municipal solid waste. By employing the analysis results and estimated models of high heating value and solid yield established in this article, predicting the product characteristics that have not been explored experimentally become possible.
Waste-to-Energy (WtE) plants constitute one of the most common waste management options to deal with municipal solid waste. WtE plants have the dual objective to reduce the amount of waste sent to landfills and simultaneously to produce useful energy (heat and/or power). Energy from WtE is gaining steadily increasing importance in the energy mix of several countries. Norway is no exception, as energy recovered from waste currently represents the main energy source of the Norwegian district heating system. Life-cycle assessments (LCA) of WtE systems in a Norwegian context are quasi-nonexistent, and this study assesses the environmental performance of a WtE plant located in central Norway by combining detailed LCA methodology with primary data from plant operations. Mass transfer coefficients and leaching coefficients are used to trace emissions over the various life-cycle stages from waste logistics to final disposal of the ashes. We consider different fractions of input waste (current waste mix, insertion of 10% car fluff, 5% clinical waste and 10% and 50% wood waste), and find a total contribution to Climate Change Impact Potential ranging from 265 to 637gCO2eq/kg of waste and 25 to 61gCO2eq/MJ of heat. The key drivers of the environmental performances of the WtE system being assessed are the carbon biogenic fraction and the lower heating value of the incoming waste, the direct emissions at the WtE plant, the leaching of the heavy metals at the landfill sites and to a lesser extent the use of consumables. We benchmark the environmental performances of our WtE systems against those of fossil energy systems, and we find better performance for the majority of environmental impact categories, including Climate Change Impact Potential, although some trade-offs exist (e.g. higher impacts on Human Toxicity Potential than natural gas, but lower than coal). Also, the insertion of challenging new waste fractions is demonstrated to be an option both to cope with the excess capacity of the Norwegian WtE sector and to reach Norway's ambitious political goals for environmentally friendly energy systems.
From the days of civilization, humans and animals have used the natural resources to support life and to dispose off wastes. In early times, the disposal of wastes did not pose a significant problem due to less population and meagre amount of waste generation and availability of abundant land for the assimilation of wastes. Problems with the disposal of wastes can be identified from the days when humans first began to congregate in communities and generation of wastes became a consequence of life. Solid waste material arises from various human and industrial activities. The solid waste is normally highly heterogeneous mass discarded as useless or unwanted. It is generated from the urban community as well as the more homogeneous accumulation of agricultural, industrial and mining wastes. The wastes are of two forms viz. Solid waste and Liquid waste. Among the wastes, solid waste is predominant in present day world. Solid waste may contain the following (a) Human pathogens – municipal and hospital solid waste, (b) Animal pathogens – waste from pets and other animals and (c) Soil pathogens – garden and agricultural waste. The solid waste comes mainly from industry, agriculture and mining and the rest is municipal solid waste. Some part of the solid waste is recycled or reused and the rest is dumped. After air and water pollution, the solid waste, is often referred as 3rd pollution. The solid waste generation has several adverse effects on environment. Some problems associated with waste include: (a) Inadequacies of existing systems for handling and safe disposal, (b) Environmental pollution – pollution of land, water and air, (c) Breeding flies and rats, (d) Emission of green house gases mainly CH4 and CO2 and (e) Non-availability of land for landfills close to source.
The conversion of agricultural, food, biofuel and forestry residues into value-added products via pyrolysis represents many advantages. Bio-char is created during pyrolysis and to a minor extent from gasification and imperfect combustion processes. Bio-char can be applied to soil as a means to improve soil health, to filter and retain nutrients from percolating soil water. Two business cases have been developed to provide an indication of the state of commercialization of pyrolysis technology in agriculture. Manpower costs constitute the most significant part of the operating costs of a stationary pyrolysis plant. Increasing the throughput of the pyrolysis process with constant manpower improves the business case. Mobile pyrolysis plants may successfully reduce raw material and product transportation costs but are subject to increased labour and set-up costs, depending on how often and how far the unit are moved. Ultimately, the probability of success of both mobile and stationary pyrolysis business models will heavily depend on the steady availability of feedstock and on mitigating raw material costs. Improvements in pyrolysis technologies can further increase yields and process energy efficiency increasing the probability of a strong business model.
Although there are numerous studies suggesting hydrothermal carbonization is an environmentally advantageous process for transformation of wastes to value-added products, a systems level evaluation of the environmental impacts associated with hydrothermal carbonization and subsequent hydrochar combustion has not been conducted. The specific objectives of this work are to use a life cycle assessment approach to evaluate the environmental impacts associated with the HTC of food wastes and the subsequent combustion of the generated solid product (hydrochar) for energy production, and to understand how parameters and/or components associated with food waste carbonization and subsequent hydrochar combustion influence system environmental impact. Results from this analysis indicate that HTC process water emissions and hydrochar combustion most significantly influence system environmental impact, with a net negative GWP impact resulting for all evaluated substituted energy-sources except biomass. These results illustrate the importance of electricity production from hydrochar particularly when it is used to offset coal-based energy sources. HTC process water emissions result in a net impact to the environment, indicating a need for developing appropriate management strategies. Results from this analysis also highlight a need for additional exploration of liquid and gas-phase composition, a better understanding of how changes in carbonization conditions (e.g., reaction time and temperature) influence metal and nutrient fate, and the exploration of liquid-phase treatment.
Copyright © 2015 Elsevier Ltd. All rights reserved.
The increasing amounts of municipal solid waste produced accompanied with the rising need for energy has caused a growth in the popularity of waste-to-energy (WTE) facilities as waste and energy solutions for many regions in Canada. The recent commercially viable WTE facilities across Canada show that the main technologies used in Canada are incineration, gasification, and plasma gasification. The aim of this study is to present these WTE technologies through the examination of case studies taken from the existing facilities across Canada. Background information on case studies, information on the WTE process, and a comparison highlighting the differences between the facilities are discussed.
Scientific and industrial experiences, together with economical and policies changes of last 30 years, bring anaerobic digestion among the most environmental friendly and economically advantageous technologies for organic waste treatment and management in Europe. In this short review, the role of anaerobic digestion of organic wastes is discussed, considering the opportunity of a territorial friendly approach, without barriers, where different organic wastes are co-treated. This objective can be achieved through two proposed strategies: one is the anaerobic digestion applied as a service for the agricultural and farming sector; the other as a service for citizen (biowaste, diapers and wastewater treatment integration). The union of these two strategies is an environmental- and territorial-friendly process that aims to produce renewable energy and fertiliser material, with a low greenhouse gas emission and nutrients recovery. The advantage of forthcoming application of anaerobic digestion of organic wastes, even for added value bioproducts production and new energy carriers, are finally discussed. Among several advantages of anaerobic digestion, the role of the environmental controller was evaluated, considering the ability of minimising the impacts exploiting the biochemical equilibrium and sensitivity as a quality assurance for digestate.
© The Author(s) 2015.
The investigation of the effect of moisture on the release and enrichment of heavy metals during pyrolysis of municipal solid waste is essential. This is important owing to: (i) the increasing amount of metals in the solid product of pyrolysis beyond the normalised level; (ii) the effect of moisture on the overall cost of pyrolysis process; and (iii) the utilisation of pyrolysis products. Seven metals were selected for evaluation: arsenic, cadmium, chromium, mercury, nickel, lead, and vanadium. Pyrolysis experiments were conducted in a steel retort at 650 °C. The municipal solid waste samples with moisture contents of 0, 30, and 65 wt% were investigated. The relative enrichment index and release of heavy metals were evaluated individually for liquid and solid fractions. A consistent trend was observed for the majority of metals investigated. Reductions of relative enrichment index and release, i.e. an increase of volatility, were observed for arsenic, chromium, cadmium, nickel, and vanadium, with an increase of municipal solid waste moisture. Whereas divergent results were obtained for lead and mercury. The effect of moisture on the relative enrichment index and release was greater at 65 wt% moisture than at 30 wt% for lead, and more remarkable at 30 wt% than at 65 wt% for mercury.
© The Author(s) 2015.
The novel concepts Enhanced Waste Management (EWM) and Enhanced Landfill Mining (ELFM) intend to place landfilling of waste in a sustainable context. The state of the technology is an important factor in determining the most suitable moment to valorize – either as materials (Waste-to-Product, WtP) or as energy (Waste-to-Energy, WtE) – certain landfill waste streams. The present paper reviews thermochemical technologies (incineration, gasification, pyrolysis, plasma technologies, combinations) for energetic valorization of calorific waste streams, with focus on municipal solid waste (MSW), possibly processed into refuse derived fuel (RDF). The potential and suitability of these thermochemical technologies for ELFM applications are discussed. From this review it is clear that process and waste have to be closely matched, and that some thermochemical processes succeed in recovering both materials and energy from waste. Plasma gasification/vitrification is a viable candidate for combined energy and material valorization, its technical feasibility for MSW/RDF applications (including excavated waste) has been proven on installations ranging from pilot to full scale. The continued advances that are being made in process control and process efficiency are expected to improve the commercial viability of these advanced thermochemical conversion technologies in the near future.
With increasing automobile ownerships in China, the number of end-of-life vehicles has also rapidly increased. However, the automobile shredder residue generated during the dismantling of end-of-life vehicles in China is not treated properly and has caused great resource waste and environmental problems. In this work, automobile shredder residue from a domestic end-of-life vehicles dismantling company was comprehensively studied through element analysis, combustion heat experiment, proximate analysis, and thermogravimetric analysis. The feasibility of using pyrolysis combined with gasification to treat and recycle automobile shredder residue was investigated. The produced gas, oil, and residue yield was measured and the correlation between their yield and the experimental temperature and ratio of air to automobile shredder residue feed was studied. It is found that when ratio of air and experimental temperature are 1.5 mol kg(-1) and 900 °C, respectively, the heat energy of the gas produced per kilogram treated automobile shredder residue reaches a maximum value of 11.28 MJ. The characteristics of pyrolysis oil and solid residue were studied. The solid residue takes up 4.65%~5.57% of the original end-of-life vehicles weight. This greatly helps to reach the target of a 95% recycling rate.
In 2010, the total generated municipal solid waste (MSW) in Ghana was 4.5 million tons. About 90% of the total MSW generated is not effectively managed but dumped in unauthorized places creating serious burden on human health. With a population growth rate of about 3.4% per year, Ghana is predicted to face big challenges in waste management. One effective way of managing solid waste is to recover the potent energy from them through waste-to-energy (WTE) plants such as engineered landfilling and controlled incineration. Cost assessment of power generation based on MSW in Ghana showed that the average cost of electricity for landfill gas power plants with already existing closed engineered landfill emerged as the cheapest (USD 0.039/kWh) compared to landfilling without engineered sites and controlled incineration. Moreover, the average domestic employment per megawatt energy generated is higher at approximately 185 for existing engineered landfills compared to the other technologies. Engineered landfill sites are under construction in Ghana whose average power extraction would be between 1 and 2 MW. Thus a potentially sustainable way of managing MSW in Ghana is through the construction of WTE plants to generate electricity.
In this paper a Hierarchical Analytical Network Process (HANP) model is demonstrated for evaluating alternative technologies for generating electricity from MSW in India. The technological alternatives and evaluation criteria for the HANP study are characterised by reviewing the literature and consulting experts in the field of waste management. Technologies reviewed in the context of India include landfill, anaerobic digestion, incineration, pelletisation and gasification. To investigate the sensitivity of the result, we examine variations in expert opinions and carry out an Analytical Hierarchy Process (AHP) analysis for comparison. We find that anaerobic digestion is the preferred technology for generating electricity from MSW in India. Gasification is indicated as the preferred technology in an AHP model due to the exclusion of criteria dependencies and in an HANP analysis when placing a high priority on net output and retention time. We conclude that HANP successfully provides a structured framework for recommending which technologies to pursue in India, and the adoption of such tools is critical at a time when key investments in infrastructure are being made. Therefore the presented methodology is thought to have a wider potential for investors, policy makers, researchers and plant developers in India and elsewhere.
The two main wastes generated from secondary fibre paper mills are rejects (composed mainly of plastics and fibres) and de-inking sludge, both of which are evolved from the pulping process during paper manufacture. The current practice for the disposal of these wastes is either by land-spreading or land-filling. This work explores the gasification of blends of pre-conditioned rejects and de-inking sludge pellets with mixed wood chips in an Imbert type fixed bed downdraft gasifier with a maximum feeding capacity of 10 kg/h. The producer gases evolved would generate combined heat and power (CHP) in an internal combustion engine. The results show that as much as 80 wt.% of a brown paper mill’s rejects (consisting of 20 wt.% mixed plastics and 80 wt.% paper fibres) could be successfully gasified in a blend with 20 wt.% mixed wood chips. The producer gas composition was 16.24% H2, 23.34% CO, 12.71% CO2 5.21% CH4 and 42.49% N2 (v/v%) with a higher heating value of 7.3 MJ/Nm3. After the removal of tar and water condensate the producer gas was of sufficient calorific value and flow rate to power a 10 kWe gas engine. Some blends using rejects from other mill types were not successful, and the limiting factor was usually the agglomeration of plastics present within the fuel.
Municipal solid waste (MSW) incineration is a greenhouse gas (GHG) emitter; however, if GHG reductions, achieved by accounting for waste-to-energy, exceed GHG emissions, incineration can be considered as a net GHG reducer. In Japan, only 24.5% of MSW incineration plants perform energy recovery despite 80% of MSW being incinerated; therefore, there is great potential to extract more energy from MSW. In this study, the factors that should be considered to achieve net GHG reductions from incineration were analysed from a life cycle perspective. These considerations were then applied to the energy supply requirements in seven Japanese metropolises. Firstly, the carbon footprints of approximately 1500 incineration plants in Japan were calculated. Then, the incineration plants with negative carbon footprint values were classified as net GHG reducers. Next, the processes that contribute to the carbon footprint were evaluated, and two processes-plastic burning and electricity savings-were found to have the greatest influence. Based on the results, the energy supply requirements were analysed and discussed for seven metropolises (Sapporo, Tokyo, Nagoya, Osaka, Kobe, Takamatsu and Fukuoka) taking into account the energy demands of households. In Kobe, 16.2% of the electricity demand and 25.0% of the hot water demand could be satisfied by incineration to realise a net GHG reducer, although urban design for energy utilisation would be required.
Published national and state reports have revealed that Australia deposits an average of 16 million Mg of solid waste into landfills yearly, of which approximately 12.6% is comprised of food. Being highly biodegradable and possessing high energy content, anaerobic digestion offers an attractive treatment option alternative to landfilling. The present study attempted to identify the theoretical maximum benefit of food waste digestion in Australia with regard to energy recovery and waste diversion from landfills. The study also assessed the scope for anaerobic process to utilize waste for energy projects through various case study scenarios. Results indicated anaerobic digestion of total food waste generated across multiple sites in Australia could generate 558 453 dam(3) of methane which translated to 20.3 PJ of heating potential or 1915 GW(e) in electricity generation annually. This would contribute to 3.5% of total current energy supply from renewable sources. Energy contribution from anaerobic digestion of food waste to the total energy requirement in Australia remains low, partially due to the high energy consumption of the country. However its appropriateness in low density regions, which are prevalent in Australia, may allow digesters to have a niche application in the country.
After investigating the application of the mesophilic and thermophilic processes in completely stirred, batch, and plug-flow reactors, in this study the authors consider the anaerobic fermentation of source-sorted organic municipal solid wastes in psychrophilic conditions (14−22 °C) without pH control. The pilot-scale reactor was operated in a batch mode, with a hydraulic retention time of 4−4.5 d. The production of soluble COD from the particulate matter was (on average) 0.27 gCOD per gram of total volatile solids fed to the reactor when operating with a total solids content of 20−35 g/L. The volatile fatty acids (VFA) were 15% of the soluble COD produced after 4 d of reaction. These values are far lower than those found in mesophilic and thermophilic conditions, where the production of soluble COD ranged from 0.5 up to 0.9 gCOD/gTVSfed and volatile fatty acids could reach 90% of soluble COD. Further, the first-order reaction constant for the hydrolysis process, Kh, for the psychrophilic conditions was found equal to 0.11 d-1 at 20 °C, while it was in the range 0.2−0.4 d-1 when operating in mesophilic or thermophilic conditions. Conclusively, the study of the psychrophilic fermentation process allowed for completing the scenario of different options of anaerobic solid-state fermentation of organic waste. Though mesophilic and thermophilic processes resulted in being more effective in dissolution of particulate matter, psychrophilic processes can be of some interest because they are simpler and energy saving. In particular, psychrophilic processes can be useful for the production of rough soluble COD to be used, e.g., for sustaining the biological nutrients removal processes in wastewater treatment.
The slow pyrolysis of biomass in the form of pine wood was investigated in a static batch reactor at pyrolysis temperatures from 300 to 720°C and heating rates from 5 to 80 K min−1. The compositions and properties of the derived gases, pyrolytic oils and solid char were determined in relation to pyrolysis temperatures and heating rates. In addition, the wood and the major components of the wood—cellulose, hemicellulose and lignin—were pyrolysed in a thermogravimetric analyser (TGA) under the same experimental conditions as in the static batch reactor. The static batch reactor results showed that as the pyrolysis temperature was increased, the percentage mass of solid char decreased, while gas and oil products increased. There was a small effect of heating rate on product yield. The lower temperature regime of decomposition of wood showed that mainly H2O, CO2 and CO were evolved and at the higher temperature regime, the main decomposition products were oil, H2O, H2, hydrocarbon gases and lower concentrations of CO and CO2. Fourier transformation infra-red spectroscopy and elemental analysis of the oils showed they were highly oxygenated. The TGA results for wood showed two main regimes of weight loss, the lower temperature regime could be correlated with the decomposition of hemicellulose and the initial stages of cellulose decomposition whilst the upper temperature regime correlated mainly with the later stages of cellulose decomposition. Lignin thermal decomposition occurred throughout the temperature range of pyrolysis.
Since the energy crises of the 1970s, many countries have become interest in biomass as a fuel source to expand the development of domestic and renewable energy sources and reduce the environmental impacts of energy production. Biomass is used to meet a variety of energy needs, including generating electricity, heating homes, fueling vehicles and providing process heat for industrial facilities. The methods available for energy production from biomass can be divided into two main categories: thermo-chemical and biological conversion routes. There are several thermo-chemical routes for biomass-based energy production, such as direct combustion, liquefaction, pyrolysis, supercritical water extraction, gasification, air–steam gasification and so on. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Pyrolysis liquid is referred to in the literature by terms such as pyrolysis oil, bio-oil, bio-crude oil, bio-fuel oil, wood liquid, wood oil, liquid smoke, wood distillates, pyroligneous tar, and pyroligneous acid. Bio-oil can be used as a fuel in boilers, diesel engines or gas turbines for heat and electricity generation.