China
Africa
Explore chapters and articles related to this topic
Technical and Economic Assessment of Biogas and Liquid Energy Systems from Sewage Sludge and Industrial Waste
Published in Vladimir Strezov, Hossain M. Anawar, Renewable Energy Systems from Biomass, 2018
Hossain M. Anawar, Vladimir Strezov
The microbial community has a significant role in conversion of organic materials to methane and carbon dioxide, plus small amounts of hydrogen sulphide in anaerobic digestion through four main reactions: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. A few enzymes depolymerize carbohydrates, lipids, and proteins into soluble compounds in the hydrolysis process of anaerobic degradation. The acetogenic bacteria produce acetate from hydrogen and carbon sources in the acetogenesis reaction (Daniel et al., 1993). Methanogens belong to the Archaeal phylum Euryarchaeota (Anderson et al., 2009), and methane is produced in the last step of the anaerobic process. The methane-producing microorganisms, which usually dominate in biogas reactors, are the acetoclastic methanogens (Zinder, 1993). The primary substrate for methane production by the hydrogenotrophic methanogens is carbon dioxide and hydrogen, and this group consists of several methanogenic orders: Methanobacteriales, Methanococcales, and Methanomicrobiales (Garcia et al., 2000; Liu and Whitman, 2008).
Implication of Anaerobic Digestion for Large-Scale Implementations
Published in Arindam Kuila, Sustainable Biofuel and Biomass, 2019
Anaerobic digestion (AD) is a chain of natural biological process that takes place in the absence of oxygen where the organic materials are broken down to produce mainly methane and carbon dioxide. This is achieved due to the interaction of a wide range of microorganisms (hydrolysers, acidogens, acetogens, and methanogens) with the substrate fed in the reactor. It involves four stages, that is, hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Fig. 12.1). Hydrolysis is a primary stage where the complex macromolecules mainly carbohydrates, proteins, and lipids are broken down into sugars, amino acids, and fatty acids, respectively, with the help of hydrolytic bacteria.Acidogenesis is performed by acidogenic bacteria. Here, sugars, amino acids, and fatty acids produced in the previous step act as substrates which are converted to CO2, ammonia, organic acids, and hydrogen.Acetogenesis is the process of generation of acetic acid along with other components such as CO2 and hydrogen using the previously produced organic acids by acetogenic bacteria.Methanogenesis is the final stage which includes two different pathways, that is, acetoclastic methanogenesis and hydrogenotrophic methanogenesis. The end products for both are methane and CO2 using acetic acids for the former and CO2 and hydrogen for the latter.
Identification of sulfate-reducing and methanogenic microbial taxa in anaerobic bioreactors from industrial wastewater treatment plants using next-generation sequencing and gene clone library analyses
Published in Journal of Environmental Science and Health, Part A, 2020
Krittayapong Jantharadej, Wuttichai Mhuantong, Tawan Limpiyakorn, Skorn Mongkolsuk, Kwanrawee Sirikanchana, Benjaporn Boonchayaanant Suwannasilp
In the acetogenesis process, the dominant acetogenic bacteria in the samples included Syntrophobacter, Syntrophus, Syntrophomonas, unclassified genus in family Syntrophorhabdaceae, and unclassified genus in family Syntrophaceae. The relative abundances of acetogenic bacteria in the samples (A–I) were in the range of 9.7–23.1% of the total sequences. Syntrophobacter spp. and Syntrophus spp., which belong to Deltaproteobacteria, were the main acetogenic bacteria found in the anaerobic bioreactors treating wastewater (Samples A–H). In contrast, Syntrophomonas in the phylum Firmicutes were the dominant acetogenic bacteria in the anaerobic sludge digester (Sample I) with relative abundances of 12.6% of the total sequences.
Spatial distribution of major bacterial species and different volatile fatty acids in a two-phase anaerobic biofilm reactor with PVA gel beads as bio-carrier
Published in Preparative Biochemistry and Biotechnology, 2019
Siddhartha Pandey, Sudipta Sarkar
From the foregoing discussions, it is evident that many of the complex set of reactions occurring during the anaerobic digestion process are sequential in nature and definite groups of microbes are associated with each reaction. These microorganisms differ widely in terms of physical characteristics, growth rates, substrate degradation kinetics, nutritional requirements and sensitiveness towards environmental conditions,[20] but they depend on each other either for substrates or for evacuation of reaction byproducts. Therefore, it is expected that in a biofilm-type reactor in plug-flow configuration, starting from the inlet point, the different processes of anaerobic digestion should take place at different locations of the reactor. Due to the necessary interdependence related to interspecies hydrogen transfer and conversion to methane, it is expected that hydrogenotrophic methanogenesis shall take place along with fermentation and acetogenesis process. The process of methanogenesis, presumably aceticlastic methanogenesis, is reported to be the slowest among all other processes that constitute the whole anaerobic process for wastewater containing simple organic molecules.[21] In order to ensure greater overall stability and control, it may be more rational to physically separate the process into two phases: in the first phase, faster and interdependent reactions such as hydrolysis, fermentation, acetogenesis and hydrogenotrophic methanogenesis would take place, while the slowest process of aceticlastic methanogenesis would take place in the second phase. A great deal of research in the recent past has been undertaken to effectively separate the overall anaerobic process into two phases.[22] This separation also allowed for better performance, tolerance to perturbations in operating conditions such as organic loading rate and higher methane production.[23] Process optimization of the phases, specifically acetogenesis process has been studied under different operating conditions with varying nature of substrates, both simple and complex.
Anaerobic Co-digestion of Food Wastes, Algae, Pond Sludge and Cow Dung for Biogas Yield Enhancement as a Potent Approach to Reduce Carbon Footprints
Published in Australian Journal of Mechanical Engineering, 2023
Sonam Sandhu, Rajneesh Kaushal
The AD process has a huge potential to generate biogas which contains 50–70% CH4, 25–40% CO2 and trace gases (1–5%), making it a sustainable energy source (Atelge et al. 2020b). Agricultural waste, industrial waste, food waste, crop waste, keratin waste, and landfilled organic waste are some of the feedstock’s that can be used to produce biogas, depending on their abundance and availability (Atelge et al. 2020a). In the absence of oxygen, AD is a complex mechanism involving a vast community of bacteria in the sequential reduction of organic waste into simple molecules (Bautista Angeli et al. 2021). The mechanism can generally be divided into the following four steps: hydrolysis, acidogenesis, acetogenesis and methanogenesis (as depicted in Figure 2).Complex organic molecules (such as glucose, protein, and fat) are transformed into soluble organic molecules (such as sugar, amino acid and fatty acid) during the hydrolysis process. Small organic molecules are then converted into volatile fatty acid in the process of acidogenesis. Thereafter, acetogenesis is the process of converting volatile fatty acids into acetic acid and carbon dioxide. These products are transformed into methane by microorganisms in the methanogenesis process. AD has the following main advantages: it can generate financial returns and it can benefit the environment. Its specific advantages and disadvantages are outlined below. Odour-AD can reduce the odour of farm slurries by up to 80%.Pollution-AD can reduce the biological oxygen demand (BOD), which is a measurement of a material’s polluting strength, in the feedstock to less than 40% of the digestate. However, the BOD of digestate is still significantly high when compared to wastewater discharge standards for wastewater.Fertiliser-Compared to undigested slurry, digestate nitrogen is more available immediately available as a plant nutrient.Mechanical separation of the digestate contributes to the management of plant nutrients. Plant nutrients in the fibre fraction can be sold as a soil conditioner or processed further into granular organic fertiliser or combustible fuel.During the usual storage and use of farm slurries, methane is released into the atmosphere. Methane is 23 times more potent than carbon dioxide as a greenhouse gas. AD collects methane and thus represents a carbon-neutral source of renewable energy.When used to generate power, biogas generates a direct financial return.