Water & Wastewater Treatment is the process to convert water no longer needed or suitable for its most recent use - into an effluent that can be either returned to the water cycle with minimal environmental issues or reused. In other words it is the process of removing contaminants from wastewater. It modifies wastewater characteristics such as its biological oxygen demand (BOD), chemical oxygen demand (COD), pH, etc. Water that has been adversely affected in quality by pollutants is called waste water. Wastewater treatment means removing biological or chemical waste products from water and then there by treated water can be used for other purpose. Wastewater treatment plants include Agricultural wastewater treatment, Sewage treatment and Industrial wastewater treatment. Irrigation with wastewater is both disposal and utilization and indeed is an effective form of wastewater disposal (as in slow-rate land treatment). However, some degree of treatment must normally be provided to raw municipal wastewater before it can be used for agricultural or landscape irrigation or for aquaculture.