Anaerobic digestion, function

The acid-forming and methane-forming bacteria work simultaneously in the anaerobic digestion process. Oxygen is excluded from the digester and various other environmental conditions are controlled so that the methane-formers are maintained in balance with the acid-formers. Otherwise, the methane-formers would be inhibited and in some cases would cease to function entirely. 

There are three major groups of bacteria that function in anaerobic digestion. The first group hydrolyzes large soluble and nonsoluble organic compounds such as proteins, fats and oils (grease), and carbohydrates, producing smaller water-soluble compounds. These are... 

Table 19.5 Typical biogas composition of a normal functioning anaerobic digestion process...

Weld, R.J. and Singh, R. (2011) Functional stability of a hybrid anaerobic digester/microbial fuel cell system treating municipal wastewater. Bioresour. Tedmd., 102 (2), 842-847. 

Several bioreactor designs are used to produce bioproducts, and include, but are not limited to batch reactors, fed-batch reactors, continuous cultivation reactors, plug flow reactors, recycle bioreactor systems, immobilized cell reactors, biofilm reactors, packed bed reactors, fluidized-bed reactors, and dialysis cultivation reactors (Williams 2002). These reactor types can contain either mixed or pure cultures, and can stimulate heterotrophic and/or phototrophic cellular functions depending on the specific reactor design. Additionally, these reactor schemes can be used to produce products directly, or to harvest biomass or other products for downstream processes. Due to the complex nature of bioreactors, particularly anaerobic digesters, the use of metagenomics is helpful to understand the physiology of such systems. 

Process flow diagrams for the MBR option are presented in Figure 7.3. The inclusion of primary clarification and aerobic or anaerobic digestion as a function of flow rate is identical to the CAS-TF case. Also, for all but very small plants, the membranes are immersed into separate tanks from the main bioreactors. This provides more flexibility in isolating membranes for cleaning or maintenance without handling. 

Wang, Q., Peng, L., Su, H., 2013. The effect of a buffer function on the semi-continuous anaerobic digestion. Bioresource Technology 139, 43—49. 

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