Nitrification and denitrification which is anaerobic and which is aerobic

Denitrification.

The process by which denitrifying bacteria reduce nitrate under anoxic conditions, releasing molecular nitrogen (N2) or nitrous oxide (N2O). Microorganisms and plants absorb and utilize nitrate for two completely different purposes, one is to use the nitrogen in it as a source of nitrogen, called assimilatory nitrate reduction: NO3-→NH4+→organic nitrogen.

Many bacteria, actinomycetes and mycobacteria can utilize nitrate as nitrogen nutrition. Another use is to utilize NO2- and NO3- as the final electron acceptors for respiration, reducing nitrate to nitrogen (N2), called denitrification or denitrification: NO3-→NO2-→N2↑.

Uses

Microorganisms and plants absorb and utilize nitrate for two completely different purposes, one is to use the nitrogen in it as a source of nitrogen, called assimilatory nitrate reduction: NO3-→NH4+→organic nitrogen. Many bacteria, actinomycetes and mycobacteria can utilize nitrate as nitrogen nutrition. Another use is to utilize NO2- and NO3- as the final electron acceptors for respiration, reducing nitrate to nitrogen (N2), called denitrification or denitrification: NO3-→NO2-→N2↑. Can carry out denitrification only a few bacteria, this physiological group called denitrifying bacteria.

Reference: Baidu Encyclopedia-Denitrification Reaction