Anaerobic Digestion Steps

Waste stabilization ponds are shallow basins into which wastes are fed for biological decomposition. The chemical reactions involved are the same as those that occur in the other biological processes. Aeration is provided by the wind, and anaerobic digestion may also occur near the bottom of deeper ponds. The ponds are very commonly used for sewage treatment and dilute industrial wastes. Waste stabilization ponds are normally used as the final treatment step for effluents because they are not effieient enough to be used on their own. 

Figure 19.20. Flowsketches of two processes employing fermentation, (a) Process for enzyme production, showing the use of growing trays, growing drums and stirred tank. Purification steps are the same for all three modes of culture growth, (b) Production of methane-rich gas by anaerobic digestion of finely divided waste solids in a 10-20% slurry. Residence time in the digester is five days [D.M. Considine (Ed.), Energy Technology Handbook, McGraw-Hill, New York, 1977].

Anaerobic digestion is a natural microbiological process in soils, streams, and oceans. The objective of sewage treatment is to confine the natural organisms in a man-made system and to optimize the rates and extents of the natural reactions in such a way that the polluting substances can be destroyed. Three basic steps are involved in anaerobic digestion ... 

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