WASTE WATER TREATMENT, Physical unit operation, Chemical unit operation, Biological unit operation, Preliminary Treatment, Screening, Comminution, Flotation, Grit Removal, Preliminary treatment, Primary treatment, Secondary treatment, Tertiary/advanced treatment, Biological treatment Processes (Aerobic Process), Activated Sludge, Oxidation ditch, Trickling filter, Biofilter (Biotower), Rotating biological contactor, Facultative Stabilization ponds, Aerated lagoons, Return Activated Sludge (R.A.S), Waste Activated Sludge (W.A.S),