Improving Biogas Production

Global energy demand is getting higher, and most of this energy is produced through fossil fuels. Recent studies report that anaerobic digestion is an efficient alternative to produce biogas. Moreover, the transformation of complex organic materials into a source of clean and renewable energy reduces the emission of greenhouse gases and can produce as by-product a high-value fertilizer for growing crops. The anaerobic co-digestion is an option to solve the disadvantages of single substrate digestion system, being the chemical composition and properties of the substrates, the operating parameters (temperature, pH, charge rate, etc.), the biodegradability, bioaccessibility, and bioavailability, important parameters to be optimized. The main materials that could be used for biogas production are waste from cities, residues from the production of other biofuels, agro-industrial waste in general, agricultural crops, straws, or microalgae biomass obtained by cultivation in wastewater. However, some of these materials, specially raw materials, need to be treated to improve the biogas production. The aim of this chapter is to review the main materials that could be used for biogas production and the factors to optimize the production.

Anaerobic digestion is an environmentally friendly technology for the stabilization and recovery of biodegradable organic waste, both agroindustrial and urban. Hydrolysis is the first and one of the main steps of the anaerobic digestion process, as it determines the overall biodegradation rate of the substrates. Fibrous materials, for example, although rich in carbon, present sugars protected by lignocellulosic structures, which hinders their biodegradability. Lipid residues present a great energetic potential; however, they are hydrophobic, which hinders their hydrolysis. Residues that have coarse granulometry tend to exhibit long periods of biodegradation due to their small surface areas and difficult solubilization. In this regard, the present chapter will discuss the application of pretreatments of substrates for anaerobic biodigestion by physical, chemical, and biological methods. The aim is to facilitate the hydrolysis and increase the energy and nutritional use of the residues in shorter time intervals, increasing the yield and optimizing the biogas production chain.

Enzymes are biocatalysts present in all living cells and have main function to perform the processes of breaking down complex nutrients into simple nutrients for cellular assimilation. Enzymatic catalysis has advantages over chemical catalysis due to high enzymatic specificity and moderate reaction conditions. Of great industrial interest, the enzymes can be applied in increasing the yield of compound production or in the degradation of unwanted by-products and these characteristics make the knowledge of enzymatic catalysis in biogas production extremely relevant, since the traditional method of biogas production is based on the biodegradation of organic matter by anaerobic digestion, which is produced by the action of a variety of microorganisms and enzymes. In the production of biogas, enzyme-mediated degradation may be the key to a higher quality final product, acting in the steps of hydrolysis, acidogenesis, acetogenesis and methanogenesis, and in the identification of by-products of enzymatic catalysis that may inhibit the process. In this context, the present chapter will be addressed: (i) introduction of enzymes in anaerobic biodigestion; (ii) enzymes as a mediator of biogas yield; (iii) inhibition of biogas production and biodegradability.

Last decade advances on methane microbial ecology in natural environments and man-made systems have introduced possibilities and challenges to biogas-producing processes. Mostly restricted to anaerobic environments, methanogens have also been detected in aerobic desertic soils, and their presence in extreme environments, such as hydrothermal vents, soda lakes, and Antarctic sediments, shows how ubiquitous and adapted they are to different environmental conditions. Most known methanogens belong to Euryarchaeota classes, producing methane from acetoclastic, hydrogenotrophic, or methylotrophic pathways. Recently discovered representatives in Thermoplasmata and Halobacteria classes, as well as in Bathyarchaeota and Vestretearchaeota, Phyla brought new insights on methanogenic diversity and their metabolic pathways. Biotechnological application of methanogens has been studied in bioreactors used for treatment of wastewater and waste. These bioreactors can be operated with acidogenesis and methanogenesis occurring in one stage or, with phase separation, acidogenesis followed by methanogenesis, with suspended and/or attached cells. Several factors have been studied to understand and optimize biogas production in bioreactors, such as temperature, organic load, and type of wastewater input. The biogas-producing communities received special attention following the development of metagenomics, metatranscriptomics, and single-cell genomic approaches. Coupled to the discovery of new methanogenic lineages, these methods revealed the complexity of microbial community structure and functions in both natural environments and bioreactors. However, a comprehensive view of these communities is still needed to improve current biogas-producing processes.

Livestock productions are changing with scale production increasing and concentration in some geographical areas. As a consequence, the activity environmental sustainability is under concern especially for manure and carcass management, disposal, or treatment. The livestock production system has its own particularities for each rearing process, resulting in residues with different characteristics. News technologies for pre-treatment and treatment for these residues have been established. Anaerobic digestion is an alternative for treatment due to this process combines the waste stabilization producing renewable energy and biofertilizer. The different components of manure excreted by livestock could be influenced on the biodegradation and biogas production. Previous studies are corroborated in this chapter and highlighted the importance of process control and digestate application when the carcass and manure are digested. For the evaluation of the efficiency of treatment processes, reduce environmental risks, and sanitary aspects, the choice of biomarkers is imperative. This chapter presents an approach and review to legislation about the conditions and criteria for the use of manure and carcasses in biodigesters and subsequently biofertilizer.

There is high interest in applying anaerobic digestion to organic wastes for the recovery of biogas as a renewable energy source. In the case of protein-rich residues, the performance of anaerobic digesters might be affected by the accumulation of ammonia and volatile fatty acids. High concentrations of these compounds impact negatively on the activity of the acetotrophic methanogenic archaea (AMA). This limitation can be overcome by promoting the enrichment within digesters of syntrophic acetate-oxidizing bacteria (SAOB) in conjunction with certain groups of hydrogenotrophic methanogenic archaea (HMA). These two microbial populations have a relatively high tolerance towards the aforementioned inhibitory compounds. Hence, when the partial pressure of hydrogen is low enough, SAOB metabolize acetate to carbon dioxide and hydrogen, which are syntrophically consumed by HMA. Once the organic matter has been biodegraded, the remaining nitrogen can be biologically removed from digester supernatants by the anaerobic ammonium oxidation (anammox). This pathway consists of the simultaneous conversion of ammonium and nitrite to (di)nitrogen gas, and, therefore, a previous partial oxidation of ammonium to nitrite under aerobic conditions is required. Interestingly, the whole process constitutes a completely autotrophic nitrogen removal strategy. This chapter compiles the current knowledge on the syntrophic oxidation of acetate and on the anaerobic oxidation of ammonium, mostly focusing on technological aspects in view of a sequential bioreactor implementation.

Bio-hydrogen is generated by renewable feedstocks from biological, chemical, thermochemical and photolytic methods. Biological methods such as dark fermentation have been suggested as a feasible alternative to produce this gas and obtain a sustainable energy source. Bio-hydrogen is not a primary energy source, but it is compatible with electrochemical and combustion processes for energy conversion; this gas can be stored, transported and utilised to fulfil energy needs, and it also contributes to minimise carbon-based emissions reducing environmental pollution and climate change. In the present manuscript, a review is performed about the state of the art of the dark fermentation process and its integration with other processes in an attempt to increase the efficiency of substrate conversion. The two-stage configurations studied involve the bioprocesses for hydrogen production and waste treatment by coupling the dark fermentation process with an alternative biological route such as anaerobic digestion, microbial electrochemical systems or photo-fermentation to promote an efficient stabilisation and use of the organic matter.

Besides their use in human treatments, antibiotics have been extensively used to control animal diseases and, in some countries, still used to promote animal growth in livestock industry. To attempt human diet necessities, concentrated animal feeding operations (CAFOs) are necessary, increasing antibiotics consumption and manure production. Once antibiotic active agents and its metabolites are excreted in urine and feces, these substances are present in manure and can reach the environment. Around the world, especially in rural areas, manure is the main substrate for biogas production. This chapter presents a review about fate of antibiotics, with special focus on livestock by-products, and effects during the anaerobic digestion (AD). The antibiotic interaction has two important emphases addressed: (a) inhibition on the biogas and methane production process by the presence and action of these compounds and metabolites in the digester and (b) the ability of AD to degrade the molecules of antibiotics and thereby reduce the adverse effect caused by these compounds on the environment.

The short-chain fatty acids (SCFAs) are generated in the acidogenesis step of the anaerobic digestion, and their production is very important for the global process and efficient biogas production. SCFA production takes place inside the cells of fermentative microorganisms, which are the first ones to start the complex soluble carbon degradation. The SCFA reactions are the most energetic among the anaerobic digestion steps, which means that this step will hardly be limiting for biogas production in normal conditions—except if the previous hydrolysis is rough or impaired. The SCFAs produced are subsequently converted to acetic acid, which is effectively converted to methane by methanogenic acetoclastic archeas. Nevertheless, acetic acid production from SCFA releases a large amount of hydrogen in the medium, and in some situations, it will reduce the process pH to inhibitory levels for methanogenic archeas and consequently suppress biogas production. This chapter will focus on these events, approaching SCFA formation, the functional microorganisms involved, and their importance for the global process.

Nowadays, it is a well-accepted fact that greenhouse gases (GHG) contribute to the global warming of the planet and that they are a very real and very serious threat to the whole world. It is estimated that 10% of total GHG emitted is from sources in the agricultural sector and over 3% from waste management. Most countries agreed to reduce GHG emissions through the mitigation of GHG sources and application of technologies to stop global warming; however, there is much work to do as GHG are increasing every year. Among these technologies, anaerobic digestion appears as a well-established technology in most countries that can contribute to mitigate GHG emissions from organic wastes. Capture of these gases from uncontrolled organic wastes processes from municipal solid wastes, human excreta, wastewaters, tanneries, distilleries and other industries discharged in public swears is necessary to reduce these emissions and to profit methane from this biogas; otherwise, they are a source of fugitive GHG contributing to the global warming. Anaerobic digestion has the potential for global warming savings, due to the potential substitution of fossil fuel by biogas, also from carbon storage in soil and inorganic fertilizer substitution through use of the digestate as a fertilizer.

The increasing demand for food, energy and natural resources has stimulated the use of anaerobic biodigestion, aiming at the treatment of biomass derived from anthropic activities with potential for biogas production. Digestate is rich in nutrients for soil fertilization purposes, with a potential direct impact on the safety of human, animal and environmental health, within the “One Health” scope. “One Health” deals with the set of strategies applied to human and animal medicine, combined with the conservation of the environment. This chapter will address the management and recycling of digestate in agriculture, considering chemical and microbiological contaminants (pathogens) from an One Health approach.

Management of human and animal wastes is among the major constraints towards the sustainable development of human settlements, where we demand increasing amounts of clean water, food, and energy. The aim of most sanitation solutions is to keep waste away from the generation site, such as households or animal stalls. The misconception that wastes have no useful purpose has resulted in unsustainable systems. However, the recovery of energy and agricultural use of the organics and nutrients contained in excreta and solid waste can improve soil structure and fertility, increasing productivity, reducing the dependency of resource-demanding chemical fertilizers, and thus contributing to food security. Treatment plants for waste anaerobic biodigestion can be applied in that context, moving from “treatment” plants to become “resource recovery” plants. The recovery of biogas in those plants for energy production is highly valuable, and added value can be obtained by the recycling of the biodegradation products—accumulated sludge and digestate. Those fractions should be treated sufficiently to inactivate pathogens to a certain extent. The quantitative microbial risk assessment is an effective approach to estimate risks, which can be applied to any scenarios of recycling liquid fractions from biogas reactors in agriculture.

Biogas is a renewable energy source that can be generated from the digestion of a variety of organic materials and waste. Organic wastes used for biogas include animal manure, human excreta and other agricultural wastes, slaughterhouses and food industries residues or even urban solid waste. However, in some developed countries it has been used corn, barley, sunflower and sorghum as other energy sources. Biogas systems differ strongly between locations, form, cost structure and usage patterns. This difference is mainly related to the development condition of the country. When implemented properly, biogas systems can serve multiple purposes. Digesters are considered a clean and alternative technology that can help distant communities with their energy necessities by improving living conditions or even economical source. Considering this, the present chapter will be addressed: (i) Biogas production around the world; (ii) Feeding material used in different continents to generate biogas; (iii) usage of biogas produced.

Worldwide, biogas production has been successfully happening in rural and urban areas, catering to livestock and industry. However, there are great obstacles to be overcome and public policies to be developed aiming at the materialization of biogas plants for green energy purposes and recycling of nutrients. In this context, this chapter will discuss the main challenges encountered worldwide in the biogas chain, highlighting the scenario and innovations on biogas chain and the legal and administrative framework/incentives for biogas production and uses.