When nitrifying ammonia, maintaining adequate DO in the mixed liquor is important to prevent what?

Maintaining adequate dissolved oxygen (DO) in the mixed liquor during ammonia nitrification is critical because it directly influences the biological processes involved in converting ammonia to nitrite and then to nitrate. When sufficient DO is present, nitrifying bacteria, such as Nitrosomonas and Nitrobacter, thrive and effectively carry out this conversion process.

If the DO levels fall below the optimal range, it can result in conditions that favor denitrification. Denitrification is a process where nitrate is converted back to nitrogen gas under anaerobic conditions, which not only reduces the efficiency of the nitrification process but also can lead to increased nitrogen loading in the effluent. Additionally, low DO levels can potentially contribute to sludge bulking in the secondary clarifier, as the growth of filamentous organisms may be encouraged in such conditions, leading to settling problems.

Thus, ensuring adequate DO in the mixed liquor is vital for successful nitrification and for maintaining proper solid-liquid separation in secondary treatment processes.