Process principle of nitrogen and phosphorus removal

Ammonia nitrogen produces nitrite and nitrate through aerobic nitrosation and nitration, and nitrite and nitrate produce nitrogen through anoxic denitrification, which escapes from water.

Phosphorus removal bacteria release phosphorus under anaerobic conditions, then absorb phosphorus excessively under aerobic conditions, and remove phosphorus through sludge discharge.

Biological nitrogen removal mechanism

According to the theory of biological nitrogen removal, biological nitrogen removal mainly includes two biochemical processes, nitrification and denitrification, which are completed by ammoniation, nitrification and denitrification of organic nitrogen and assimilation of microorganisms.

Ammonification refers to the transformation of organic nitrogen compounds in water into ammonia nitrogen under the decomposition of ammonifying bacteria. Generally, the ammoniation process is carried out at the same time as the removal of organic matter by microorganisms, and the ammoniation process is carried out very quickly. When the removal of organic matter is finished, the ammoniation process has been completed, so no special measures are needed.

Nitrification means that under the condition of sufficient oxygen supply, ammonia nitrogen in water is first oxidized to nitrite nitrogen by nitrifying bacteria, and then further oxidized to nitrate nitrogen by nitrifying bacteria. Because of the low growth rate of nitrifying bacteria and nitrifying bacteria, it needs a long sludge age.

Denitrification is a biochemical process completed by denitrifying bacteria. Under anoxic conditions, denitrifying bacteria can reduce nitrite and nitrate nitrogen produced by nitrification to gaseous nitrogen (N2) or N2O andNO. Because denitrifying bacteria are facultative anaerobic bacteria, they can only carry out denitrification under anoxic or anaerobic conditions, so it is necessary to create an anoxic or anaerobic environment for them (the mixed liquor of aerobic tank flows back to anoxic tank).

References:

Simultaneous Nitrogen and Phosphorus Removal _ Baidu Encyclopedia