CHAPTER X. 



DENITRIFICATION. 



Denitrification and Reduction of Nitrates and 

 Nitrites. In the process of nitrification ammonia or its 

 compounds are first oxidized to a nitrite, and finally to a 

 nitrate by certain specific organisms, as already described 

 in the previous chapter. Many bacteria are known 

 which carry on processes of reduction the reverse of 

 this, oxygen being removed from nitrates to a greater 

 or lesser extent. The reduction may be of several 

 kinds, namely : 



1. The nitrates may be reduced to nitrites and no 



further. 



2. The oxygen may be taken from nitrates and 



nitrites, with the ultimate formation of 

 ammonia. 



3. Nitrates and nitrites are sometimes reduced with 



the evolution of nitric (NO) and nitrous 

 oxides (N 2 O). 



4. The nitrates and nitrites may be reduced with 



the final production of free nitrogen. 

 Although the term denitrification has been sometimes 

 loosely employed to denote all these forms of reduction, 

 it is now more strictly applied to the decompositions of 

 nitrates and nitrites, which result in the evolution of free 

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