1. Theoretical knowledge: Denitrification is carried out in anoxic environment. Generally, urban sewage mainly provides anoxic environment and plays the role of denitrifying bacteria (denitrifying bacteria are facultative bacteria, which can carry out aerobic breathing and harmless breathing), but when dissolved oxygen exists in sewage, it will be preferentially used as an electron donor, which will affect denitrification and ensure anoxic environment (do
2. Common processes of biological denitrification engineering: A/O biological denitrification process, oxidation ditch process, etc.
3. Control elements: sludge reflux ratio R, dissolved oxygen DO and internal reflux ratio R..