In the sewage treatment plant, sewage water is first allowed to pass through bar screens or a grit chamber where large solids are removed. Which is followed by aeration/mixing in a tank and then primary sedimentation where suspended solids settle down. Primary treatment involves the addition of a coagulant which helps to remove grits, coarse solids, oil, and grease if present. Effluent from primary treatment consists of unstable organic matter which undergoes secondary treatment where the organic matter in sewage is converted into stable forms through biological activities, resulting in secondary sedimentation. Where common approach like the activated sludge method involves the addition of a mixture of active microorganisms to sewage, followed by aeration and agitation. The aerobic conditions and microbial actions oxidize the organic solids resulting in coagulation, flocculation and settling of solids. Activated sludge produces a clear liquid without foul odour. The effluent then undergoes tertiary treatment such as sand filters and reverse osmosis process to remove the dissolved solids which may be used followed by disinfection by incorporation of UV radiation or chlorination, the treatment scheme depends upon the nature of the sewage and the effluent from secondary treatment.