Secondary
Treatment
Microbial
Biodegradation - To achieve an acceptable reduction in the BOD, In this treatment a small portion of the dissolved organic matter is mineralised, and the large portion is converted to removable solids. By now the original sewage BOD is reduced to 80. 90percent.
Secondary treatment relies on microbial activity, may be aerobic or anaerobic, and is conducted in large variety of devices. Since this step is microbial process, accidental introduction of a toxic chemical is very dangerous.
