Secondary treatment removes 85 to 90% of BOD, TSS, and the small portion of nitrogen, phosphorus, and heavy metals from wastewater. Tertiary treatment of wastewater is the third stage of the wastewater treatment and is also known as an advanced treatment. Tertiary treatment removes the load of nitrogen and phosphorus present in the water.

It includes processes like filtration, ion exchange, activated carbon adsorption, electrodialysis, nitrification, and denitrification. Treatment options in tertiary treatment depend upon the characteristics of effluent after secondary treatment and what kind of water is needed at the end of the treatment. For example, if we need potable water then filtration and disinfection are to be done on the wastewater.