A sewage treatment process generally involves 3 steps. First is the primary step where solids, grit, oil and grease are physically separated out. Second one is the biological step were the beneficial microbes in sewage treatment plant degrade the dissolved pollutants present in it. The third stage is a disinfection stage where the harmful biological load from the treated water is reduced by chlorination, U.V or ozonation after which the water is discharged in fresh water.