What can be an effect of reduced DO levels in a wastewater treatment system?

Reduced dissolved oxygen (DO) levels in a wastewater treatment system can lead to promoted denitrification. This is because denitrification is an anaerobic process, meaning it occurs in environments with low or no oxygen. During denitrification, bacteria convert nitrate (NO3-) into nitrogen gas (N2) or other nitrogenous gases, releasing them into the atmosphere. This process is essential for removing excess nitrogen from wastewater, which can be harmful to aquatic environments if discharged in high concentrations.

In environments where DO levels are low, facultative bacteria that are capable of both aerobic and anaerobic respiration can thrive, utilizing nitrate as an electron acceptor instead of oxygen. This shift in metabolic activity enhances the denitrification process, allowing for more effective nitrogen removal from the wastewater.

By contrast, enhanced nitrification typically requires sufficient DO levels because nitrifying bacteria need oxygen to convert ammonia into nitrate. Improved sedimentation and increased organic loading might refer to conditions in the system, but they do not specifically relate to lower DO levels affecting biological processes in the same direct manner as denitrification.