What is a biological nutrient removal (BNR) system designed to do?

A biological nutrient removal (BNR) system is specifically designed to remove nutrient pollutants, particularly nitrogen and phosphorus, from wastewater through biological processes. This is critical because excessive nitrogen and phosphorus in water bodies can lead to eutrophication, which results in algal blooms, depletion of oxygen in the water, and harm to aquatic life.

BNR typically employs a combination of anaerobic, anoxic, and aerobic conditions to facilitate the growth of specific microorganisms that effectively metabolize these nutrients. During the anaerobic phase, certain bacteria can take up organic matter and release phosphorus, while in the aerobic phase, nitrogen is converted to a gaseous state (often as nitrogen gas) that is released into the atmosphere. This comprehensive biological approach not only helps in nutrient removal but also promotes the sustainability of wastewater treatment by minimizing reliance on chemical additives.

The other options do not accurately describe the primary function of a BNR system. Reducing the volume of wastewater, while a potential outcome of efficient treatment processes, is not the main objective of BNR. Enhancing the chemical composition does not pertain to the nutrient removal focuses of BNR systems, and controlling odor emissions in treatment facilities, while important, falls within the realm of different treatment technologies rather than the biological nutrient