What is BNR?
BNR stands for Biological Nutrient Removal (BNR). This process uses microorganisms to remove the elements nitrogen (N) and phosphorus (P) from wastewater. Nitrogen and phosphorus are essential to the growth of plants and therefore are known as nutrients.
What are the forms of N and P in wastewater?
In untreated wastewater, nitrogen comes in the forms of organic nitrogen and ammonia; phosphorus is in the form of orthophosphate, polyphosphate and organic phosphate.
Origins of N and P in wastewater:
Domestic wastewater typically contains approximately 35 ppm (parts per million) ammonia and 7 ppm phosphorus. Some industries may produce wastewater with high nitrogen and phosphorus concentrations.
Reasons to remove N and P:
Treated effluent with a high concentration of nitrogen and phosphorus can be detrimental to aquatic life as well as the function of waterbodies.
Nitrogen in the form of ammonia is toxic to fish. The discharge of nitrogen and phosphorus will stimulate the growth of algae and aquatic plants in lakes and reservoirs and deplete dissolved oxygen in waters, which is also toxic for aquatic life.
The presence of algae and aquatic plants may also appear unsightly, interfering with uses of waterbodies for recreation, water supplies and fish propagation, etc.