Waste-to-Energy

Recently, waste management became a tremendous global concern due to the high rate of waste materials production. This rate leads to wastes accumulation in the environment without proper management or valorization. Consequently, more problems appeared to the surface, such as global warming and other dangerous phenomena on the whole ecosystem. For instance, in 2018, the total municipal solid waste production was 292.4 million tons, only 38.2 wt.% of which were managed mainly through mechanical recycling and composting. The remaining amounts were incinerated for energy recovery (11.8 wt.%) and landfilled (50 wt.%, which accounts for 146 million tons). The massive amounts of landfilled wastes consume large land areas; therefore, more waste valorization techniques should be applied to achieve a zero waste point in the circular economy system. This chapter defines and classifies solid wastes according to their sources and compositions. It also discusses the types of recyclable, hazardous, and hard-to-control wastes besides briefly discussing the efforts to manage them. Additionally, waste production statistics of different countries are presented to give a real figure about waste amounts and emphasize the urgent need for their management. Finally, the circular economy practices and business models that consider the socioeconomic impact on the whole economy are discussed.

Approximately, half a ton of waste is produced per person annually; thus, waste management is essential to avoid environmental issues. The waste management system encompasses the entire set of activities related to treating, handling, recycling, or disposing of waste materials. This chapter aims to represent the history of waste management, as well as the current commonly used methods for waste management, together with their pros and cons. The commonly applied methods, including sanitary landfill, composting, safe disposal of biomedical wastes, recycling of industrial CO₂ emissions, incineration of hazardous wastes, sludge recycling in the cement industry, direct combustion of sludge, wastewater treatment, and construction waste recycling, are discussed. In this chapter, the problems associated with landfills, such as lack of efficient systems for gas utilization from the landfill and lack of proper leachate management and recycling CO₂ from industrial flue gas and wastewater treatment methods, are more highlighted. Also, the need for law enforcement to control the negative environmental impacts properly is highlighted.

The progressively growing patterns of global population, urbanization, industrialization, environmental degradation and associated depletion of natural reserves are paving the way towards the conservation and recycling of resources. Contrary to the traditional linear economy, based on procurement-production-usage-disposal, the novel circular economy model corresponds to sustainable flow of materials, products and energy, in terms of growth-manufacturing-utilization-restoration. Likewise, bioeconomy deals with the production and subsequent conversion of renewable biological residues into bioenergy and value-added products. Accordingly, circular bioeconomy constitutes the integration of circular economy and bioeconomy for the sustainable and cascading use of bioresources into reusable/recyclable bio-based products. In addition to biomass, the organic waste containing plentiful amounts of proteins, carbohydrates, lipids and other essential substances can be efficiently converted into useful and eco-friendly products. Therefore, circular bioeconomy represents a promising and effective strategy for resolving the global issues of food scarcity, constant dependence on fossil fuels, waste management, energy deficit, limited employment opportunities and environmental pollution. Nevertheless, limitations in supply chain, technological advancement, legislative measures and consumer compliance necessitate thorough consideration for the implementation of circular bioeconomy approach in various sectors of socioeconomic significance.

Biofuels have a long history but have recently gained increasing attention and demand as a renewable, environmentally friendly, and sustainable energy source. Different kinds of biofuels can easily replace traditional fossil fuels with positive environmental impact and potential for net-zero or even negative carbon emissions. Hence, biofuel is vital for tackling the current global warming crisis, which has resulted from our overreliance on fossil fuels. The varied types and forms of biofuels include liquid fuel (such as bioethanol, biodiesel, and jet fuel), gaseous fuel (such as biogas, biomethane, syngas, and biohydrogen), and solid fuels (such as charcoal, biochar, briquettes, and pellets). Bioelectricity is also introduced briefly as another source of bioenergy. These biofuels are generated from a range of different biomass feedstocks, which are divided into four generations based on their biochemical composition, typical usage, and cultivation methodologies. This chapter presents an overview of the major aspects of biofuels, including the generations of biomass feedstocks, types of biofuels, and the main conversion technologies applied to generate the biofuels from biomass.

Thermochemical conversion technologies have recently played a significant role in converting energy from waste sources. Thermochemical technologies have promising ways of recycling energy from various waste materials while reducing the environmental impact. This chapter primarily provides the collective information on waste feedstocks used for the thermochemical conversion from the recent review literature. Second, the numerous thermochemical conversion methods are discussed, including direct combustion, pyrolysis, gasification, and hydrothermal liquefaction using various reactors for each technique. It assesses the conversion of multiple wastes to crude bio-oil and the likelihood of converting syngas to bio-oil. Hydrothermal conversions occur at moderate temperatures, but typically at high pressure and in the presence of water. The thermochemical conversion includes the accurate temperature, pressure, and heating rate, which can be accomplished using various reactors. For the large-scale industrialization of biofuels, a greater understanding of the mechanism of conversion, reactors, and feedstock composition is crucial. Moreover, this chapter discusses the various thermochemical conversions of wastes and its bio-oil yield.

Anaerobic fermentation technology is one of the effective ways to produce biogas energy from biomass waste. Biomass anaerobic fermentation is the effective conversion of organic matter in biomass under the assimilation of anaerobic bacteria, and finally produces methane and part of carbon dioxide with economic value, which can be used for combustion and power generation. Biomass resources such as crops, oil crops, agricultural organic residues, forest trees, and forest industrial residues usually provide energy. This paper reviews the research achievements of biogas production by anaerobic fermentation of biomass waste resources at present, and analyzes the progress of biogas production by means of different organic wastes such as agricultural waste, urban waste, forestry waste, mixed fermentation of different wastes and adding exogenous catalyst. The use of aquatic plants such as duckweed to produce biogas is also highlighted. Based on the above analysis, the economic feasibility of using different kinds of biomass waste was evaluated. This paper provides valuable reference for the production of biogas from material waste by anaerobic fermentation.

Biological fermentation engineering is an important part of biological engineering. Carbohydrates are used to produce various industrial solvents and chemical raw materials by microorganisms, among which energy production through biotransformation is a very important research field. In this chapter, the common organic wastes, including typical rural solid wastes, forestry solid wastes, and naturally-grown aquatic plants such as duckweed, as well as urban waste are discussed as potential feedstock for liquid bioenergy including bioethanol, biobutanol, and bio-olefin. The pretreatment technology and fermentation modes of these wastes as well as the microbial species used are compared and discussed in depth. Duckweed was used as a typical example to evaluate the potential of producing ethanol, butanol, higher alcohols, and biodiesel via fermentation pathways. Moreover, the economic feasibility of producing liquid biofuel through fermentation from different waste feedstocks is evaluated. This chapter provides an important reference and insight for future research on organic waste fermentation.

Biodiesel, a promising alternative fuel to diesel, has recently attracted worldwide attention due to its low toxicity, biodegradability, and eco-friendly nature. This fuel can solely be used in diesel engines or blended with diesel without complicated modifications to the engine. Generally, biodiesel is produced from edible and non-edible oil crops, lipidic wastes, and algae. Previous reports indicate that more than 75% of the overall cost of biodiesel production is related to feedstock. In this regard, feedstock selection for biodiesel production is of significant importance. Therefore, this chapter aims to provide an overview of biodiesel production through esterification and/or transesterification from diverse lipid-rich resources, especially the low-cost wastes. The potential of biodiesel production from various feedstocks and the impact of fatty acids profiles on biodiesel quality are discussed. The effect of different process conditions such as pretreatment and downstream processing for enhanced production of biodiesel is reviewed. Finally, the economic feasibility of biodiesel production from wastes is estimated and discussed.

Microbial fuel cell (MFC) is a kind of device that uses electricity-producing microorganisms as anode catalysts to directly convert chemical energy in organic matter into electrical energy. It has broad application prospects in the field of wastewater treatment and new energy development. This chapter aims to discuss the concept, reaction mechanism, and application prospect of bioelectrochemical systems using wastes for electricity generation. The types, properties, and activity parameters of microbe for MFC are discussed. In addition, the design and optimization of MFCs devices for enhanced efficiency are evaluated. Particularly, critical discussions are provided on application of MFCs technology for different types of wastewater as well as corresponding key bottlenecks. Besides, the recent progress in wastewater treatment and seawater desalination, as well as the possibility of the combination between wastewater treatment and seawater desalination integrated with biomass production is evaluated. This chapter also discusses the limitations and challenges of MFCs industrialization and large-scale applications. The advantages and inadequacies of MFCs compared with other technical solutions for waste utilization are analyzed in detail. Moreover, the economic feasibility, future research perspectives in order to enhance the MFCs performance in large-scales are presented.

The nuisance of algae blooms can cause serious ecological and socio-economic damage and can incur a huge cost in their proper disposal. Therefore, it is imperative to research technological solutions that can value algal biomass and minimize its harmful effects on the environment. In this sense, the purpose of this chapter is to compile information about energy recovery from nuisance algal blooms and residues. Here, general issues about algae biology are described. The harmful effect of excessive algal proliferation and the prevention, control, and mitigation strategies are outlined. This chapter also presents an overview of environmental issues, including aspects of eutrophication and life cycle assessment. Finally, the potential applications of biomass as biofuels, bioenergy, and other uses are presented and discussed.

Considering the thermodynamic performance, economic performance, and environmental performance simultaneously, the thermo-environmental optimization for a series dual-pressure organic Rankine cycle (STORC) and a cascaded organic Rankine cycle (CORC) has been investigated. The effects of key operating parameters on the thermal and economic performance of the system were analyzed. Based on a 3 kW ORC experimental prototype, the heat exchanger performance of different mixtures has been studied and compared. Five different proportions of working fluids were selected, respectively, R123, 0.33R123/0.67R245fa, 0.5R123/0.5R245fa, 0.67R123/0.33R245fa, and R245fa. The comparison between the experimental test and simulation result without considering the pressure drop was addressed. Results indicate that R245fa/R152a is the best candidate working fluids for CORC LT-Loop. The evaporator heat transfer coefficients of R245fa are highest, followed by the R245fa/R123 mixture and while R123 shows the lowest evaporator heat coefficients. The measured thermal efficiency of 0.67R123/0.33R245fa is the highest, which is 7.33% and the maximum simulated thermal efficiency is14.55%.

Carbon-di-oxide (CO₂) is inevitable in most of the anthropogenic activities of wider range from household to energy sector. Global CO₂ emissions are always monitored and stringent regulations are constantly being made by different countries to mitigate its level, as the exceedance is linked to severe health problems. Carbon dioxide capture and utilization (CCU) is an effective method to mitigate and balance the ever-raising CO₂ levels in the atmosphere. For instance, CO₂ utilization by microalgal biomass is shown to be significantly effective, which serves the dual purpose of reducing atmospheric CO₂ and effective biomass production. On the other hand, synthetic fuel production by forming isobutanol through sequential utilization of CO₂ along with hydrogen from electrolysis of water is a significant emerging approach. Carbon from waste CO₂ emission can also be effectively utilized to produce polymers like plastic with various innovative technologies in recent years. Thus, the utilization of waste carbon for energy production is vast and scattered. This chapter aims to consolidate the basics, advancements, carbon footprint and promising directions in this field to provide greater insights for cutting down the proportion of CO₂ accumulation in greenhouse emissions.

Plastics are a type of synthetic organic polymer that is widely used in modern society and has a significant environmental impact because of its slow degradation. In addition, toxic substances are released into the soil when plastic bags perish under sunlight. Plastic waste can be converted into hydrogen, diesel, crude oil, and Sulfur using conventional methods. Plastic recycling to energy will have a significant positive impact on the global economy and waste management. It is possible to convert plastic into fuels using modern technology and systematic approaches, which will help in plastic waste management and its recycling to fuels. The most common methods for converting plastic waste into fuel are hydrothermal processing and pyrolysis. In addition, the microbial and enzymatic biodegradation of synthetic plastics got increasing attention in recent years, offering the possibility of developing biological treatment technology for plastic waste. Many enzymes that can degrade plastic and convert it into biofuel have been isolated and studied. However, there are numerous limitations in the degradation of plastic by microbes and its conversion into fuels. This chapter provides an overview of global plastic use, conventional plastic recycling, and the harmful effects of plastic recycling. In addition, the microbial conversion of plastic to energy has been briefly described. Microbial pathways and enzymes involved in the transformation of plastics into fuels have been investigated. Finally, the economic feasibility of bioconversion of plastic into energy has been discussed.

Insects are the most prolific animals in the world due to their broad adaptability to a great variety of food feedstocks. Many insect species exhibit high conversion rates for organic wastes such as food waste, animal byproducts, and agricultural waste. Fly larvae are considered as a promising source of high-value substances due to their richness in proteins and lipids, where their biomass can be utilized being protein supplements and bioenergy substrates the black soldier fly, house fly, and yellow mealworm has been extensively studied with corresponding to high suitability for biodegradation involving organic waste. The maggots of flesh fly and blowfly are found to develop well in meat production waste. Moreover, large-scale industrial larvae production from organic waste comprises plenty of technological obstacles. Likewise, current international legislation about scaling-up of insect rearing. In this chapter, we summarized the methods, advantages, and limitations of using insects during waste conversion regarding global legislation. The information could strengthen the capacity of waste industrial transformation to larval proteinaceous and lipidic biomass.

The indiscriminate disposal of industrial waste has aggravated environmental pollution problems and is an imminent concern for industrial facilities. These issues can be circumvented by conventional effluent treatment techniques, however, there are several bottlenecks associated that make them unattractive. Given this scenario, phycoremediation can be an alternative and are under scrutiny by researchers, developers, and industrialists. Microalgae-mediated processes are a promising approach for the direct removal of polluting compounds from residues, such as organic matter, phosphorus, and nitrogen. Microalgae are also responsible for producing biomass and obtaining various valuable bioproducts. However, some factors have limited the choice of the ideal microalgae cultivation system, which can complicate biomass recovery. Thus, the adoption of cell immobilization techniques can be an economically and environmentally favorable option for removing waste from effluents. In this sense, the objective of this chapter is to present the role of microalgae in waste management and energy production as phycoremediation agents. The main highlights of the chapter include an overview of microalgae and culture conditions, phycoremediation, microalgae in wastewater treatment systems, biological immobilization systems, and the cultivation of immobilized microalgae. Finally, the potential bioenergy products from microalgae and some recommendations are introduced and discussed.

The population growth and the new consumption models contribute significantly to a greater generation of waste, which is generally incorrectly managed because a large percentage of the waste generated is sent to landfills. Waste to energy (WtE) plants play a fundamental role in managing and treating municipal waste because they reduce the amount of waste sent to landfills and reduce dependence on imported fossil fuels; however, these facilities can also cause negative impacts. This case study evaluates the technical–economic feasibility of an incineration plant by using a social cost–benefit analysis, which considers economic, social, and environmental impacts taking into account the 3 pillars of sustainability and allowing policymakers to have a complete view of the impacts generated by the facility. The WtE facility is in Barcelona (Spain). It produces energy from municipal solid waste (MSW) with a total capacity of more than 350,000 tons of waste treated per year, which means the generation of more than 180,000 MWh of electricity and 110,000 tons of steam per year. The positive and negative impacts generated by this facility are identified, discussed, and monetarily valued to carry out this economic analysis. Some of the impacts considered are the sale of energy, the decrease in waste disposal in landfills, the reduction of greenhouse gas (GHG) emissions, and the generation of dioxin emissions. The results show that the facility is profitable from a private point of view (BP = 15.97) and an economic, environmental, and social perspective (BT = 37.48). Finally, the same impacts can be considered by researchers in future economic analyzes of other WtE projects or waste management systems.

This chapter aims to discuss the potential and future prospective of waste-to-energy in arid and semi-arid regions. The main focus will be on the conversion of waste biomass and organic matter to biofuel and biochar through thermochemical and biological processes. The chapter starts by identifying the various types of waste biomass sources that are particularly pertaining to these regions. This will be followed by providing the most recent data on the quantities of waste biomass in some identified worldwide arid and semi-arid regions. Systematic assessment of the biomass and organic matter characteristics (physical, chemical, and thermal) will be presented to evaluate their potential for biofuels and biochar production. Apart from the great potential of biofuels as renewable energy sources, this chapter demonstrates the environmental benefit of biochar in countering land degradation, improving soil fertility, besides highlighting the potential of the by-product water in stretching the limited water resources to support the growth of plants and animal life in arid and semi-arid regions. The chapter concludes by stating the main challenges and recommendations for sustainable bioenergy technologies in arid and semi-arid regions.

Many conversion technologies and processes for bioenergy generation from wastes have been reported and discussed in the previous chapters. These conversion technologies are being selected and applied depending on the type of wastes, chemical composition of the available waste and the desired energy vector. For example, anaerobic digestion (AD) is used for biogas production from mixed biological wastes with varied chemical compositions. Fermentation for bioethanol production is used for wastes that are rich in simple sugars and/or starch. Pyrolysis, combustion and gasification are used for crude bio-oil and/or syngas production from a wide range of wastes, especially those that contain high lignocellulosic compounds. These are environmentally friendly technologies for waste management and bioenergy production, but their economic feasibility is usually limited using a process of a single conversion route. Recent research and prospects suggested that integrating processes for bioenergy production from waste could increase the efficiency of the system in terms of economy, energy recovery and beneficial impact on the environment. This chapter discusses waste biorefinery as a recent trend towards circular bioeconomy. The chapter provides suggestions for future integrated systems for the simultaneous production of multiple energy vectors and high-value chemicals from different types of wastes. In the integrated system, the by-products from the first conversion process are used as substrates for the subsequent conversion process and so on. The importance of catalysis in offering flexibility in an integrated biorefinery system by providing novel routes and downstream environmental solutions for flue gas and exhaust gas cleaning was also covered in the chapter. The chapter concludes with a discussion of the role of models with bioenergy and biomass resource decision making, with focus on bioenergy from waste case studies. This includes assessment of the key issues that determine the economic feasibility and environmental impacts of feedstock choices and technology options. Also covering the social and political frameworks that will enable and drive transitions towards increased bioenergy from waste activities. The chapter presents policy case studies from the EU, China, USA and India, and highlights how social acceptance will be key to the success of any bioenergy from waste sector.