There are both organic and inorganic impurities present in the sewage. Organic impurities present in sewage are- (I). Vegetable and fruit peel waste, (ii). Pesticides
Sewage contains a huge amount of organic matters which are toxic. Microorganisms are widely used in the sewage treatment plant for removing this toxic organic matter. Sewage or wastewater treatment plant consists of two stages.
It involves the removal of large or small-sized components in the wastewater through physical processes.
Aerobic microorganisms are inoculated into the sewage treatment plant. These microbes utilize the organic components of the sewage and reduce the toxicity. This can be measured by BOD (Biological oxygen demand).