Secondary Treatment, Primary Sedimentation Tank, Biochemical Oxygen Demand, Fixed Film Sewage Treatment, Suspended Cell Sewage Treatment

Secondary Treatment

Secondary Treatment
The effluent from the primary sedimentation tank, still contains a proportion of organic matter in solution or colloidal state and numerous living organisms. Its BOD is high hence it is subjected to aerobic oxidation by various methods. It is necessary to oxidize the organic matter present in the effluent before it is being discharged into the body of water (diluting). This oxidation is either carried out on land (naturally) or in bacterial beds (artificially) such as trickling filter or aerators.

The preliminary treatment reduces the BOD while the secondary treatment satisfies the demand of BOD with the help of bacterial beds. Secondary treatment relies on microbial activity. Since these oxidation processes are carried out by microorganisms, they are called as 'biological oxidators' There are four different types of oxidation processes:

1. Fixed film sewage treatment
2. Biological filters or trickling filters
3. Rotating biological contractor or biodisc system
4. Suspended cell sewage treatment
5. Oxidation ponds
6. Activated sludge process

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Secondary Treatment