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Utilization of Agro-Industrial Wastes for Biofuel Generation
Published in Anil Kumar Anal, Parmjit S. Panesar, Valorization of Agro-Industrial Byproducts, 2023
Rajeev K. Sukumaran, Meera Christopher, AthiraRaj Sreeja-Raju, Meena Sankar, Prajeesh Kooloth-Valappil, Valan Rebinro Gnanaraj, Anoop Puthiyamadam, Reshma M. Mathew, Velayudhan Pillai-Prasannakumari Adarsh
Acidogenesis follows the hydrolysis stage, in which the breakdown products from the hydrolysis stage (fatty acids, sugars, amino acids, etc.) are fermented by obligate or facultative anaerobes to short-chain organic acids (primarily volatile fatty acids like acetate, propionate, and butyrate), H2, alcohols, NH3, and CO2 (Gerardi, 2003). In this step, the concentration of the H+ ions formed is a critical determinant of the products of fermentation. Production of Volatile fatty acids (VFAs) is mostly accomplished by anaerobic oxidation reactions where reducing equivalents are directly transferred to hydrogen ions. The reaction is highly susceptible to H2 partial pressures, and low (<10−4 atmos) H2 partial pressures are required for thermodynamic feasibility. In well-maintained anaerobic digesters, low H2 partial pressures are maintained through hydrogenotrophic methanogens and homo-acetogens through interspecies hydrogen transfer (Pavlostathis, 2011).
Biodegradable Waste: Renewable Energy Source
Published in Rouf Ahmad Bhat, Moonisa Aslam Dervash, Khalid Rehman Hakeem, Khalid Zaffar Masoodi, Environmental Biotechnology, 2022
Anaerobic fermentation consists mainly of the following four biochemical stages: Hydrolysis, carried out by bacteria that convert insoluble carbohydrates, proteins, and fats into simple sugars, fatty acids, amino acids, and peptides.Acidogenesis, where acidogenic bacteria transform hydrolysis products into simple organic acids, alcohols, CO2, and hydrogen.Acetogenesis, in which acetogenic bacteria convert fatty acids with more than two carbon atoms into acetate and hydrogen.Methanogenesis, the final step in the anaerobic fermentation process, in which methanogenic bacteria produce biogas from acetic acid or from hydrogen and CO2.
Advanced Biomethane Processes
Published in Eduardo Rincón-Mejía, Alejandro de las Heras, Sustainable Energy Technologies, 2017
Sevcan Aydin, Bahar Yavuzturk Gul, Aiyoub Shahi
In the third step of anaerobic digestion (acetogenesis) the products of acidogenesis are converted into acetate, hydrogen, and carbon dioxide by acetogenic bacteria from which methane can be obtained. Because acetate is the most common and significant precursor of methane production, acetogenic bacteria have an important role for methanogenic microorganisms. Hydrogen-producing or hydrogen-consuming acetogenetic bacteria play a role in the conversion acidogenesis end products of acetate (Aydin et al., 2015). There are two different types of acetogenic mechanisms: acetogenic hydrogenation and acetogenic dehydrogenation. Acetogenic hydrogenation includes the production of acetate from fermentation hexoses or from CO2 and H2. Acetogenic dehydrogenation refers to the anaerobic oxidation of long and short chain volatile fatty acids by obligate hydrogen-producing or obligate proton-reducing bacteria. Acetic acid-producing bacteria are Methanobacterium bryantii, Desulfovibrio Syntrophobacter wolinii, Syntrophomonas wofei, and Syntrophus buswellii, which are the most common acetic acid-producing bacteria (Zahedi et al., 2016).
Moderate potassium ferrate dosage enhances methane production from the anaerobic digestion of waste activated sludge
Published in Environmental Technology, 2022
Yongqi Sun, Mengyu Zhang, Ting Song, Suyun Xu, Liwen Luo, Jonathan Wong, Xuefeng Zhu, Hongbo Liu
Anaerobic digestion involves a series of steps, i.e. hydrolysis, acidogenesis (fermentation), acetogenesis, and methanogenesis. About 50–60% and 2-20% of organic matters mainly existed in EPS and microbial cells, respectively in WAS. During the anaerobic fermentation, these substances are released from the solid phase to the liquid phase, and this experiment showed that the addition of PF effectively promoted this process. As indicated in Figure 2(a), the original TOC concentrations in liquid phase were positively correlated to the PF dosages, in which the maximum TOC concentrations were found in 500 g-K2FeO4/ kg-TS. The main components of EPS are proteins and polysaccharides, which can be directly utilized by microorganisms, and changes can directly reflect the dissolution and utilization of degradable organic matters in WAS by microorganisms [24,25]. As shown in Figures 2(b and c), the variation trend of proteins and polysaccharides concentration in the process of AD was generally consistent with the variations of TOC. The concentrations of soluble protein and polysaccharides increased with the increase of PF dosages. Initially, the highest values appeared in 500 g-K2FeO4/kg-TS, i.e. 386.9 ± 6.1 mg/L and 1113.1 ± 3.8 mg/L, respectively, which were 2.88 and 6.03 times the control group.
Effect of solid concentration on biogas production through anaerobic digestion of rapeseed oil cake
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
B. Deepanraj, N. Senthilkumar, J. Ranjitha
Anaerobic digestion occurs in four distinct stages, namely hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Chynoweth, Owens, and Legand 2008; Tambone et al. 2013). These stages occur through the effects of syntrophy by microbial consortia. In the first stage, monocarbonates and polycarbonates (fatty acids, amino acids, and monosaccharides) are produced from organic polymers (lipids, proteins, and carbohydrates). In the subsequent acidogenesis stage, volatile organic acids (acetic acid, butyric acid, propionic acid and valeric acid), hydrogen and carbon dioxide are produced. In the acidogenesis stage, acetic acid, hydrogen and carbon dioxide, which are substrates for methanogenic microorganisms, are produced. In the final methanogenesis stage, methane and carbon dioxide are formed as the primary products of the metabolic process (Appels et al. 2008; Deepanraj, Sivasubramanian, and Jayaraj 2017a, 2015).
Packed-bed biofilm reactor for semi-continuous anaerobic digestion of olive mill wastewater: performances and COD mass balance analysis
Published in Environmental Technology, 2020
Ghizlane Enaime, Abdelaziz Baçaoui, Abdelrani Yaacoubi, Stephan Berzio, Marc Wichern, Manfred Lübken
Olive mill effluent typically harbors phenolic compounds, which are known resistant to biodegradation and are partially responsible for the toxicity of OMWW [14]. The presence of phenolic compounds may inhibit anaerobic digestion by altering the kinetics of organic degradation and the activity of methanogens, which may lead to an imbalance in the simultaneous process of acidogenesis and methanogenesis causing the accumulation of acids and as a consequence the acidification of the system. Many studies were focused to bring out the inhibitory effect of phenolic compounds during anaerobic digestion. Sayadi et al. [42] showed that the high molecular mass fraction of phenolic compounds inhibited the production of lignin peroxidase in the white rot fungi P. chrysosporium and caused a drop in COD and phenols removal efficiencies. Beccari et al. [43] reported that in a two-stage anaerobic digestion process (acidogenic-methanogenic), only some phenolic compounds were degraded in the methanogenic stage. In another study, Sorlini et al. [44] reported that among the three groups of bacteria (hydrolytic, acetogenic and methanogenic); hydrolytic bacteria were not sensitive to phenolic compounds, acetogenic bacteria were sensitive to caffeic acid at concentrations >0.25 g/L, while methanogenic bacteria were sensitive to caffeic, ferulic and coumaric acids at concentrations exceeding 0.12 g/L. Kouroutzidou et al. [45] demonstrated that anaerobic microorganisms can decompose gallic acid at concentrations higher than 1 g/L.