Explain the term 'biological nutrient removal' (BNR).

Biological nutrient removal (BNR) refers specifically to the process through which certain biological methods are employed to effectively remove nitrogen and phosphorus from wastewater. This is essential because these nutrients, when released into water bodies in excessive amounts, can lead to eutrophication, resulting in harmful algal blooms and the degradation of water quality.

In BNR systems, microorganisms play a crucial role. For nitrogen removal, processes like nitrification and denitrification are utilized, where ammonia is converted to nitrate and then to nitrogen gas, which is released into the atmosphere. For phosphorus removal, specific bacteria can uptake phosphorus and store it in their cells, which is then removed during the waste sludge process.

This process emphasizes the importance of using biological activity to manage nutrient levels, which is more sustainable and environmentally friendly compared to chemical treatments. Understanding BNR is critical for wastewater treatment operators, as it aligns with modern practices aimed at protecting water resources from nutrient pollution.