Biogas

The aim of this chapter is to present a short critical overview on the various municipal solid waste management (MSWM) technologies together with a glance at how conducting a feasibility study to choose the most suitable scenario for a particular region. In the first part, a conceptual approach to waste management followed by a valuable laconic review over the global status are presented. Short and must-know explanations about the various waste management technologies are provided in the second part within six subsections, i.e., materials recovery facility (MRF), refuse-derived fuel (RDF)/solid recovery fuel (SRF), landfill, compost, anaerobic digestion (AD), and combustion. Finally, the question of how to conduct a feasibility study to choose the most suitable scenario for a particular region is concisely answered along with a brief elucidation of life cycle assessment (LCA) and financial feasibility, as two of the most important factors.

The information presented in this chapter outlines the current state of biomass utilization for Anaerobic Digestion (AD) and biogas production, whether through the use of municipal solid waste (MSW), agricultural residues (i.e., manures and field wastes), or downstream residues originating from biomass processing. This chapter aims to encompass biogas activities from differing geographic regions (Europe, Africa, North and South America, Asia), and draws on region-specific substrates as examples, describing substrate availability, composition, applicability in AD activities, and future trends. It summarizes biogas potential of a range of substrates, as well as potential use of digested materials as fertilizer. Additionally, a brief discussion is also presented on biogas chain development.

This chapter aims to describe the basic design principles of biogas plants (such as TS, OLR, HRT, etc.) including the impacts that every parameter has in the operation/cost of investment of the plant in accordance with the substrate used and the outcome desired. It also includes description and comparison of the different kinds of anaerobic digestion models with a focus on continuously stirred tank reactor (CSTR). The construction of biogas plants involves different specific issues that have to be taken into consideration when developing in-detailed design. All these aspects contribute to preventing early digesters maintenance, fast wearing of the plant, problems during operation, difficulties with maintenance, and most importantly safety/risk prevention. Various technical details and differences in the designs and equipment used in biogas plants have been well presented and discussed. Some real-world examples of possible design choices to help better understand the design principles have also been illustrated.

Biogas, a mixture of methane and carbon dioxide, is produced by anaerobic digestion of organic waste. Municipal and agroindustrial organic wastes are important feedstocks for producing biogas. Anaerobic digestion is a microbial process. It not only reduces the amount of waste to be disposed, but the methane produced can be burnt as fuel to provide energy. Anaerobic digestion is carried out in various kinds of bioreactors. This chapter is focused on the diverse bioreactor systems, or digesters, that are available for producing biogas. Depending on their design and operation, the different types of bioreactors are suited to different kinds of wastes, processing scenarios and other conditions. The following main types of bioreactors are discussed: the conventional anaerobic digesters (e.g. anaerobic sequencing batch reactor, continuous stirred tank reactor, anaerobic plug-flow reactor); the sludge retention reactors (e.g. anaerobic contact reactor, up-flow anaerobic sludge blanket reactor, expanded granular sludge blanket reactor, up-flow anaerobic solid-state reactor, anaerobic baffled reactor, internal circulation reactor, anaerobic fluidized bed reactor); the anaerobic membrane reactors; the anaerobic biofilm reactors; and the high rate reactors.

Mixed organic wastes are heterogeneous substrates with high moisture content as well as high levels of different contaminations. Therefore, in order to carry out an ideal anaerobic digestion process using this kind of substrates, i.e., highest possible biogas production while avoiding operation complications and failures, pre-treatment is a crucial stage of the whole process. In the present chapter, an overview on the mechanical and thermal pre-treatment technologies, with a focus on plants running on heterogeneous solid wastes, is presented. In general, mechanical pre-treatments are used for size reduction of organic matters to enhance the active surface area of hard-solid substrates as well as for separation of impurities (e.g., plastics, glass, stone, metal, etc.) to lower the cost of operation and maintenance. The current industrially-available mechanical pre-treatment technologies used in AD plants, i.e., hammer mills, impact reactor combined with a reject separation, pulpers, pressing as well as crushing technologies have been discussed. Following mechanical pre-treatment, organic fraction of waste can be further treated at high temperature and/or pressure values in order to disintegrate the structure of hardly-degradable substrates to increase the biogas production rate and/or to pasteurize the organic waste. Different thermal pre-treatment methods have also been presented herein.

Methanogenic anaerobic digestion (AD) is known as an alternative green technology, capable of converting different types of biomass and wastes into biogas. Various types of anaerobic reactors have been designed and implemented but regardless of the type of reactor use, it is necessary to thoroughly monitor the performance of such configurations and prevent any drastic change during biogas production process. Parameters such as pH, temperature, volatile fatty acids (VFAs), alkalinity, hydraulic retention time (HRT), organic loading rate (OLR), total solid (TS), volatile solid (VS), inhibitors such as ammonia, mixing and shear stress, etc., could potentially adversely affect the AD process efficiency if not managed. Hence, these parameters should be adjusted within a proper range to guarantee a favorable biogas production rate. The present chapter reviews the effects of major operational and non-operational parameters on AD process and summarize the most recent findings in this regard.

Anaerobic digestion is a biochemical process where complex organic matter such as carbohydrates, proteins, and lipids degrade in the absence of oxygen and are converted into methane and carbon dioxide by the action of different groups of microorganisms. It is a sustainable waste management technology, which reduces and stabilizes organic wastes, recycles its nutrient and water content, while producing energy. Biogas reduces the demand for fossil fuels, since it can be used for the production of electric power and heat, or converted into vehicle fuel. Currently, methane production via anaerobic digestion is a steadily increasing industry in Europe and all over the world. This chapter focuses on the anaerobic digestion process and the parameters affecting its performance. It also describes briefly the current technologies for anaerobic digestion. Finally, since the degradation of organic material requires a synchronized action of different groups of microorganisms with different metabolic capabilities, this chapter also presents recent developments in molecular biology techniques as valuable tools to obtain in-depth understanding about this complex microbiological system.

Nowadays, biogas has been widely produced commercially from different waste materials worldwide. The composition and structure of the raw materials used have a significant effect on the rate and yield of biogas production. Therefore, to optimize the process design and yield, different analytical methods are necessary. In this chapter, the most important analytical methods related to the anaerobic digestion process and produced biogas measurement are presented. More specifically, the methods used for characterizing feedstock including, the determination of total solids (TS) and volatile solids (VS), structural carbohydrates and lignin, elemental composition, and chemical oxygen demand (COD), are discussed. Moreover, the most important standard theoretical and experimental procedures used to obtain biochemical methane potential (BMP) are reviewed.

The fact that most countries do not promote the use of biogas as energy vector via tax incentives entails the need for an optimization of biogas upgrading technologies in order to support a cost-competitive utilization of this renewable energy source. Nowadays, the contaminants present in biogas such as CO₂, H₂S, H₂O, N₂, O₂, siloxanes, and halocarbons are removed through the implementation of costly and environmentally unfriendly upgrading processes. Conventional biogas upgrading is based on physical/chemical technologies leading to CH₄ purities of 88–98% and removal efficiencies of higher than 99% for H₂S, halocarbons, and siloxanes. Unfortunately, their high energy and chemical demands limit the environmental and economic sustainability of these conventional biogas upgrading technologies. In this sense, biological processes have emerged in the past decade as an economic and environmentally friendly alternative to conventional biogas upgrading technologies. Thus, biotechnologies such as microalgae-based CO₂ fixation, H₂-assisted litoautotrophic CO₂ bioconversion to CH₄, enzymatic CO₂ dissolution or fermentative CO₂ reduction have been consistently shown to result in CO₂ removals of 80–100% with CH₄ purities of 88–100%, while allowing the valorization of CO₂ into bioproducts of commercial interest (therefore preventing its release to the atmosphere). Similarly, H₂S removals > 99% are consistently achieved in aerobic and anoxic biotrickling filters, algal-bacterial photobioreactors, and digesters under microaerobic conditions. In addition, recent investigations have shown the potential biodegradability of siloxanes and halocarbons under both aerobic and anaerobic conditions. This chapter constitutes a state of the art comparison of physical/chemical and biological technologies for the removal of CO₂, H₂S, halocarbons, and siloxanes from biogas.

The increasing energy demands as a consequence of fast-growing global population and higher living standards over the last few decades have triggered huge interest in finding new energy resources. In this context, biomass is an environmentally friendly renewable resource with huge potentials to generate power as well as various useful chemicals and fuels. Biorefineries which are analogous to today’s petroleum refineries are identified as a processing facility that can use biomass as feedstock to produce these value-added products. Although being promising, biorefineries face some serious limitations and constraints as well. For instance, for upscaling biorefineries, a considerable infrastructure would be required to make possible the collection and storage of a large amount of biomass. The economic and sustainable processing of raw materials in biorefineries requires advanced and sophisticated technologies most of which are still at a pre-commercial stage. Food security, high energy demand, production cost, seasonal diversity, land use change effect, etc. are also among the other important topics in question. The objectives of this chapter are to review the concept of biorefinery, introduce different types of biorefineries and their classifications, overview associated barriers and obstacles to biorefineries, and evaluate various potential feedstocks for biorefining process. Finally, the potential of integrating anaerobic digestion to biorefinery platforms is discussed and the advantages and drawbacks are reviewed.

The application of life cycle assessment (LCA) as a systematic approach for identifying the environmental hot spots in waste management strategies has been increasing. Despite some underlying problems, LCA has been shown to be an appropriate approach to quantify the environmental impacts caused by distinctive solid waste management scenarios. Although this approach has long been employed as a decision support tool in waste management, some inconsistency, faulty assumptions, and incorrect methodologies can still be found in some studies on waste LCA leading to scientific errors and erroneous conclusions. This chapter aims at providing insights about the general principles and methodologies of LCA followed by providing short guidelines regarding how to effectively apply LCA in waste management systems.

Farming and forestry residues are predicted to be the main sources of biogas to meet the future feedstock demands. The main constituents of these lignocellulosic feedstocks are cellulose, hemicellulose and lignin. The biological conversion of these feedstocks to biogas suffers from poor yield and slow reactions, and thus, commercial biogas production from lignocelluloses faces with economical infeasibility. The process economy could be enhanced by the application of new pretreatment and digestion technologies. However, the profitability of these new technologies should be evaluated prior to the plant construction phase. Techno-economic analysis includes process development and economic evaluation for such processes. In this chapter, the method for techno-economic analysis including process development and simulation, economic estimations and profitability analysis are presented. Furthermore, the results of techno-economic analysis and the parameters affecting such results are discussed.

By consolidating the principles of both first and second laws of thermodynamics, exergy-based analyses have demonstrated their potential for evaluating the efficiency, productivity, and sustainability of various biofuel production systems including biogas. Exergy-based approaches have been extensively applied in biofuel industry for finding the most thermodynamically, economically, and environmentally sound production, upgrading, refining, and utilization systems. In this chapter, after briefly explaining the concept of exergy, a case study on the application of advanced exergy and exergoeconomic analyses for evaluating two biogas upgrading processes, i.e., high pressure water scrubbing (HPWS) and cryogenic separation (CS) was presented and discussed. According to the results obtained, endogenous exergy destruction and investments costs of most of the elements of both biogas upgrading processes were higher than their corresponding exogenous counterparts, showing a weak economic correlation among those elements. Exergy destruction and investment costs associated with compressors and pumps were avoidable and unavoidable, respectively. While, exergy destruction and investment costs related to heat exchangers and air coolers were found to be unavoidable and avoidable, respectively. Finally, three different strategies were suggested for discounting costs and improving the process performance.

Biogas production from organic wastes is a complex, dynamic, nonlinear, multivariable, and uncertain biological process whose underlying mechanisms are still unclear. Accordingly, this process is not amenable to conventional mathematical and phenomenological modeling and optimization approaches. Advanced soft computing techniques are considered as powerful tools for dealing with the complexity, nonlinearity, dimensionality, and uncertainties of complicated ill-defined biological processes like biogas production. For this reason, advanced soft computing techniques are extensively employed in biogas applications due to their higher efficiency, generalization, and simplicity. In this chapter, after introducing the soft computing techniques and briefly describing their theoretical backgrounds, an overview is presented of the most important applications of these approaches for modeling and optimization of biogas production processes. This chapter is arranged into four main sections. In the first section, artificial neural network (ANN) is introduced and its applications in biogas production processes are reviewed and discussed. In the second part, fuzzy logic systems like Sugeno and Mamdani systems are presented in detail and their related applications in biogas production processes are summarized and analyzed. The third section covers evolutionary algorithms including Genetic Algorithm (GA), Ant Colony Optimization (ACO), and Particle Swarm Optimization (PSO) and their applications for optimizing biogas production processes. Hybrid models like Neuro-fuzzy, Fuzzy-Neural, and Neuro-Evolutionary approaches are discussed in the last section and their applications in anaerobic digestion systems are also summarized and scrutinized.

Biogas production from wastes and residues is classified among the versatile, energy-efficient, and environmentally beneficial strategies considered to gradually replace fossil fuels in the future. Nevertheless, biogas production from different resources is faced with many technical, efficiency, and cost challenges, and therefore, optimization of the various aspects of the process, including feeding, mixing, microbial community, as well as process monitoring and control are vital to enhance process efficiency. The microbial community structure and functions exert vital effects on the process stability and biogas yield. However, due to the lack of optimized culture media and conditions for most of the organisms involved in biogas production, the majority of the participating microbes as well as their genes and metabolic pathways during the process are yet to be well known. Recent developments in culture independent “omics” and next generation sequencing technologies (NGS) have provided excellent opportunities for exploring microbial communities and their factions during the anaerobic digestion process. Therefore, this chapter has focused on recent applications of new “omics”, including NGS-based whole genome sequencing, metagenomics, meta-transcriptomics, meta-proteomics, and met-metabolomics in characterization of microbial flora, their genes and encoded transcripts, proteins, and metabolites, as well as the metabolic pathways contributing to the anaerobic digestion process. Recent findings have confirmed that the revolutionary innovations and developments in these domains will help to enhance the efficiency of biogas production from a diverse range of organic matters with complex structures in the near future.

A considerable portion of the populations living in the rural areas of developing countries mostly solely rely on traditional biomass for cooking, lighting and heating purposes. The prime concerns with such conventional energy dependency include deforestation, environmental degradation, ecological imbalance, sanitation and other public health issues and socioeconomic difficulties. Therefore, implementing small-scale biogas plants at household level could be accompanied with positive and synergistic effects in mitigating such integrated global problems. Moreover, promoting and executing small-scale biogas technology in both rural and urban areas, using generally freely available local organic resources, could result in more sustainable national energy demands and reduce the use of traditional biomass and imported fossil fuels. Doing so, the targets of renewable energy generation, mitigation of GHGs emissions and sustainable waste management could be fulfilled. In this chapter, different small-scale biogas plants including their history, designs, operation, etc. are presented and discussed.

Biogas and biomethane deserve particular attention and support among renewable energy sources as these low-carbon technologies promote closed loop waste-energy systems. The industry can significantly contribute to further development of rural areas. The use of biogas in stationary engines for various agricultural operations (milling, grinding, powering water pumps and chaff cutters, etc.) also shows that it has the capacity to be a profitable business that can generate ample opportunities for employment in rural areas. Given the potential of biogas in off-grid, rural areas to meet household energy requirements and, to a small extent, rural industry requirements, the future prospects of biogas remain high. Global trends such as the increased rural to urban migration are limiting the potential of biogas in off-grid, rural areas. Increasingly, farmers are depending more on farm mechanization which is leading to a lower number of cows. This chapter presents various case studies from India, Nepal, Vietnam, Cambodia and Rwanda that illustrate the prospects for the medium and long term of the biogas industry in the agriculture sector.