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ANAEROBIC DIGESTION

Definition

The anaerobic breakdown of complex organic materials to simple substances which include a high proportion of gaseous and soluble products; it involves a diverse range of bacteria whose metabolic pathways are closely interrelated, and it occurs in benthic muds, in the rumen, in certain types of sewage treatment plant, etc. The process of anaerobic digestion results in an appreciable reduction in the bulk of biodegradable solids, with the conversion of organic carbon to methane forming an important part of the carbon cycle. In sewage treatment (and in the treatment of other organic wastes - e.g. agricultural and food-industry and fish farm effluents) anaerobic digestion can yield a rich, relatively odourless agricultural fertilizer (rich in microbial biomass) and a useful fuel gas (biogas - also called marsh gas, sewer gas, sludge gas ) which may contain 50% or more methane; ca. 30-70% of solids may be converted to gases.

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