Biogas fermentation is accomplished by the co-fermentation of various methanogenic and non-methanogenic bacteria. In the first stage of biogas fermentation, cellulose and starch are hydrolyzed into monosaccharides by anaerobic and facultative anaerobic hydrolytic bacteria or fermentative bacteria, and acetone is further formed; protein is hydrolyzed into amino acids and ammonia of organic acids is further formed; lipids are hydrolyzed into glycerol and fatty acids, and propionic acid, acetic acid, butyric acid, ethanol and so on are further formed. In the second stage, the bacteria producing hydrogen and acetic acid utilize the organic acid produced in the first stage to oxidize and decompose into acetic acid and molecular hydrogen. In the third stage, the bacteria producing methangens are strictly anaerobic. The biogas purification company reminds us that in this complex mixed fermentation system, non-methanogenic bacteria provide the matrix for methanogenic bacteria to grow and produce methane, create appropriate redox conditions and remove toxic substances; methanogenic bacteria release feedback inhibition for the biochemical reaction of non-methanogenic bacteria, create thermodynamic favorable conditions; and the two types of bacteria maintain together. The suitable pH value in the environment. Methane-producing bacteria and non-methanogenic bacteria can form methane efficiently through mutual cooperation.
The whole anaerobic digestion process is a dynamic equilibrium process in which methanogenic bacteria and non-methanogenic bacteria interact and restrict each other. The raw materials used for anaerobic digestion are almost all insoluble organic macromolecules such as carbohydrates, fats and proteins, which can be utilized by hydrogen-producing Acetobacteria and methanogenic bacteria only after they are decomposed into smaller molecules by hydrolytic enzymes, and finally methane is produced.
The hydrolysis process is usually slow, so it is the limited stage of anaerobic degradation of wastewater containing macromolecule organic matter or suspended matter. There are many factors affecting the hydrolysis rate and degree. Whether extracellular enzymes can effectively contact the substrate is the key to affect the hydrolysis rate. Therefore, the degradation of large particles is much slower than that of small particles. Many microorganisms can produce extracellular enzymes, including lipase, protease and cellulase. Their function is to hydrolyze complex macromolecules into monomers that can be assimilated by microorganisms. Hydrolysis is a speed-limiting step in the anaerobic biological treatment of wastes with organic polymers as the majority.
In the past 10 years, it has been found that hydrogen-producing acetic acid bacteria include Mutual Bacillus, Mutual Bacillus, Clostridium, Acinetobacter and so on. These bacteria can degrade various volatile fatty acids into acetic acid and H2. Methanogenic bacteria utilizing acetic acid are Methanothrix soxhlii and Methanococcus Pasteuri, and their growth rates are quite different. In general anaerobic reactors, about 70% of methane is decomposed from acetic acid and 30% from hydrogen to carbon dioxide. In an anaerobic reactor, 70% of methane production is produced by disproportionate acetic acid bacteria. In the reaction, the carboxyl group in acetic acid is separated from the acetic acid molecule, methyl is eventually converted to methane, and carboxyl is converted to carbon dioxide.
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