Kinetics methane fermentation

Many of the important bacteria which mediate the over-all methane fermentation have not been isolated and questions about pathways are still unanswered. The use of thermodynamics may help in suggesting which of the many possible reactions are hkely, as well as helping to explain some of the observations about the process. The thermodynamic and kinetic analysis presented in this paper is apphed to steady-state reactor operation. 

Anaerobic treatment, a multistep complex process, can be described from a kinetic viewpoint as a three-step process involving (1) hydrolysis of complex organic material (2) organic acid production (3) methane fermentation (2). In the first step complex organics are converted to less complex soluble organic compounds by enzymatic hydrolysis. In the... 

Volatile Acids Kinetics. In evaluating the methane fermentation kinetics of the three volatile acids chosen for study, it was necessary to consider the process biochemistry and stoichiometry. According to Barker (19), acetic acid is fermented to methane and carbon dioxide in a single step while both propionic and butyric acids are fermented in two steps. In the first step these acids are fermented to acetic acid and methane by species of methanogenic bacteria. The resulting acetic acid is then fermented by different methanogenic species to methane and carbon dioxide. The stoichiometry of these fermentations is shown by the following equations (19). 

Lipid (Long Chain Fatty Acid) Kinetics. O Rourke (3) evaluated the methane fermentation kinetics of lipids (long chain fatty acids) in a complex waste (municipal sewage sludge). His laboratory scale experiments were operated on a semicontinuous feed basis at several values of 6c and at temperatures of 35°, 25°, 20°, and 15 °C. 

Hydrogen Oxidation Kinetics. Shea et al. (22) studied the kinetics of methane fermentation by an enrichment culture of lithotrophic (autotrophic) hydrogen oxidizing methanogenic bacteria at 37 °C. Reported values of the kinetic coeflScients are as follows (1) Y = 0.043 mg volatile suspended solids per mg of hydrogen COD removed, (2) b = —0.009 day"S (3) k = 24.8 mg hydrogen COD removed per mg volatile suspended solids per day and (4) Ks = 569 mm of mercury, hydrogen pressure. 

Wu B. Integration of mixing, heat transfer, and biochemical reaction kinetics in anaerobic methane fermentation. Biotechnol Bioeng 2012 109(11) 2864-74. 

During microbial action, kinetic isotope fractionations on the organic material by methanogenic bacteria result in methane that is highly depleted in typically with 5 C-values between -110 and -50%c (Schoell 1984, 1988 Rice and Claypool 1981 Whiticar et al. 1986). In marine sediments, methane formed by CO2 reduction is often more depleted in than methane formed by acetate fermentation in freshwater sediments. Thus, typical ranges for marine sediments are between -110 and -60%c, while those for methane from freshwater sediments are from -65 to -50%c (Whiticar et al. 1986 Whiticar 1999). 

In anaerobic treatment, failure of this type is usually evidenced by the near cessation of methane production and decreased COD removal. Several investigators (5, 16, 17) have reported that kinetic failure is also characterized by a build-up in the concentration of long and short chain fatty acids, the predominate precursors of methane. McCarty (7) and O Rourke (3), in laboratory digestion studies on primary sewage sludge conducted at 35 °C, confirmed the fact that the fermentation of short and... 

Mechanism and kinetics in biochemical systems describe the cellular reactions that occur in living cells. Biochemical reactions involve two or three phases. For example, aerobic fermentation involves gas (air), liquid (water and dissolved nutrients), and solid (cells), as described in the Biocatalysis subsection above. Bioreactions convert feeds called substrates into more cells or biomass (cell growth), proteins, and metabolic products. Any of these can be the desired product in a commercial fermentation. For instance, methane is converted to biomass in a commercial process to supply fish meal to the fish farming industry. Ethanol, a metabolic product used in transportation fuels, is obtained by fermentation of corn-based or sugar-cane-based sugars. There is a substantial effort to develop genetically modified biocatalysts that produce a desired metabolite at high yield. 

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