Biological Nutrient Removal

Biological Nutrient Removal (BNR) is a process used for nitrogen and phosphorus removal from wastewater before it is discharged into surface or ground water.

The rising concentration of harmful nutrient compounds – specifically nitrogen and phosphorus – in municipal wastewater treatment plant discharge causes cultural eutrophication (nutrient enrichment due to human activities) in surface waters. Summer algal blooms are a familiar example of this eutrophication, and can present problems for ecosystems and people alike: low dissolved oxygen, fish kills, murky water, and depletion of desirable flora and fauna.

Because conventional biological processes designed to meet secondary treatment effluent standards typically do not remove total nitrogen (TN) and total phosphorus (TP) to the extent needed to protect receiving waters, wastewater treatment facilities are increasingly being required to implement processes that reduce effluent nutrient concentrations to safe levels. This can be a challenge for wastewater treatment plants because it usually involves major process modifications to a plant, such as making a portion of the aeration basin anaerobic and/or anoxic, which reduces the aerobic volume and limits nitrification capacity.