Anaerobic Digestors, Sludge Digestion, Sewage Sludge, Primary Treatment, Secondary Treatment, Biochemical Oxygen Demand, Methane

Anaerobic digestors (sludge digestion)

	Anaerobic digestors (sludge digestion) These are used to process the sludge. Generally slower but saves energy compared to treatment processes requiring forced aeration. Some anaerobic treatment systems also generate biogas which is a useful fuel. The simplest anaerobic system is the septic tank. Large scale anaerobic digestion is used for further processing the sewage sludge produced by primary and secondary treatments.
Hence they are used for processing settled sewage sludge and for treatment of some very high BOD industrial effluents. Conventional anaerobic digestors are large fermentation tanks designed for continuous operation under anaerobic condition. The digestor contains large amounts of suspended organic matter (20-100g/l) with a considerable part of this suspended material forming the bacterial biomass. Fungi and protozoa do not playa significant role in anaerobic digestion. Anaerobic digestion involves two steps: 1. Complex organic materials (microbial biomass) are de-polymerised and converted fermentatively to fatty acids, carbon dioxide and hydrogen (non-methanogenic anaerobic bacteria).
2. Methane is generated by the direct reduction of methyl groups to methane or by reduction of CO₂ to methane by molecular hydrogen or by other reduced fermentation products such as fatty acids, methanol or carbon monoxide. Some examples are Methanobacterium bryantii, M. thermoautotrophicum, M. mobile and M. formicicum. It takes 3-4 weeks for complete sludge digestion and the residue is inoffensive, sticky and tarry mud which will dry readily and form an excellent manure.

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Anaerobic digestors (sludge digestion)