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On the denitrification process in activated sludge process

Time : 2020-04-15

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On the denitrification process in activated sludge process


Biological denitrification reactions include amination reaction, nitrification reaction, and denitrification reaction, in which the amination reaction can be carried out under aerobic and anaerobic conditions, the nitrification reaction can only be carried out under aerobic conditions, and the denitrification reaction is under anoxic and Under anaerobic conditions, the reaction formulas are as follows:
  

Ammonia (ammonification): The nitrogen-containing organic matter in sewage is oxidized and decomposed into ammonia nitrogen by aerobic or anaerobic heterotrophic microorganisms during biological treatment。
  
Oxygenation deamination reaction formula is:
RCHNH2COOH+O2RCOOH+CO2+NH3
  
The reaction formula of hydrolytic deamination is:
RCHNH2COOH+H2O→RCHOHCOOH+NH3


After the organic nitrogen in the domestic sewage is hydrolyzed or oxygenated, the produced ammonia (NH3) is dissolved in the water to produce ammonia nitrogen NH4-N in the sewage.
  
Nitrification: The process in which ammonia nitrogen (NH4 + -N) in sewage is converted into NO2- and further NO3- under the action of nitrifying bacteria (aerobic autotrophic microorganisms). The oxygen consumption in the whole process is not The oxygen consumption of the balanced nitrosation process is about 3 times that of the nitrification process;

Nitrosification reaction formula:
NH4++1.5O2NO2-+H 2O+2H+
  
Nitrification reaction formula:
NO2-+0.5O2NO3-
  
Total reaction formula:
NH4++2O2NO3-+H2O+2H+
  
Denitrification: NO2- and NO3- in sewage are reduced to N2 and released into the air under the action of denitrifying bacteria (facultative heterotrophic bacteria) under anoxic conditions.
  
Denitrification reaction formula:

NO2-+3H+(organic donor electron)0.5N2+ H2O+OH-

NO3-+5H+(organic donor electron)0.5N2+ 2H2O+OH-


In the wastewater treatment activated sludge process, the completion of the above three reactions is a complete denitrification reaction process.