1.Introduction of SND

Simultaneous nitrification and denitrification technology (SND) simultaneously produces nitrification, denitrification and carbon removal reactions in the same reactor. It breaks through the traditional view that nitrification and denitrification cannot occur at the same time, especially under aerobic conditions, denitrification can also occur, making simultaneous nitrification and denitrification possible.

2.Three perspectives on the possibility of SND technology

1).Macro-environmental perspective: This view believes that a completely uniform mixing state does not exist. The uneven distribution of DO in the reactor can form aerobic, anoxic and anaerobic areas, which can occur under the same bioreactor anoxic/anaerobic environmental conditions Denitrification reaction, combined with the removal of organic matter in the aerobic environment in the zone and the nitrification of ammonia nitrogen, SND is achievable.

2)Micro-environment perspective: This view believes that the hypoxic micro-environment in the microbial floc is the main reason for the formation of SND, that is, due to the limitation of oxygen diffusion (transmission), there is a dissolved oxygen gradient in the microbial floc, which is conducive to simultaneous nitrification and denitrification. Microenvironment.

3).Biological point of view: This view believes that the existence of special microbial populations is considered to be the main reason for the occurrence of SND. Some nitrifying bacteria can perform denitrification in addition to normal nitrification. Some Dutch scholars have isolated that can perform aerobic nitrification. Sulfococcus pantotrophic, which can also perform aerobic denitrification; and some bacteria cooperate with each other to carry out sequential reactions and convert ammonia into nitrogen, which provides the possibility to complete biological denitrification in the same reactor under the same conditions