The Biochemical Pathway in the Nitrification Process

At the biochemical level the nitrification process is more complex than simply the sequential oxidation by Nitrosomonas of ammonia into nitrite, and the subsequent oxidation by Nitrobacter, of nitrite to nitrate. Various reaction intermediates and enzymes are involved in this processes. In soils, streams and treatment plants, conditions permitting the oxidation of ammonia and nitrite can be created by a variety of micro-organisms. Table 3.2 show some of the factors influencing the nitrification.

Table 3.1 Some characteristics of nitrifying bacteria and biological nitrification.




Cell shape Cell size Motile Gram test Cell weight

Estimated generation time hours


Dissolved oxygen requirements to nitrify


Maximum growth rate at 20 °C

Nitrogen oxidation rate mg N/g VSS at 20 °C

Yield constant mg vss/mg N


Long-term temperature constant susp. culture, °C"1 0,05

Long-term temperature constant att. culture, °C"1

Temperature range for process °C

Reaction Kinetics used in literature

Saturation constant, mg N/liter

Saturation constant, mg 02/liter

Ovoid to rod-shaped 1 x 1,5|im may or may not be negative

8-36 Obligate

Strict Aerobe


Monod, zero order first order

Ovoid to rod-shaped 0,5 x1,0nm may or may not be negative

12-59 Facultative

Strict Aerobe

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