The effluent after primary treatment will be subjected to secondary treatment. The major goal of this treatment is to remove soluble Organic Pollutants by oxidation & settling. This involves bringing the active microbes in contact with waste water which consume the impurities as food. These organisms; in presence of Oxygen (O2), convert the biodegradable organic matter into Carbon Di Oxide (CO2) water, more cell material and other inert products. With the help of this the total BOD reduction will be 90-95%.