Environmental factors also have a significant effect on the kinetic rates of denitrifier growth and nitrate removal. Temperature, pH, carbon concentration and substrate concentration are considered below. A combined kinetic expression considering factors that affect denitrification is proposed.
As in the case of nitrification the Monod Kinetic, equation (4.28), has also been proposed to explain the rate of conversion of nitrate to nitrogen gas, by several investigators, for example Henze and Harremoes (1972) and Moore and Schroeder (1970).
HD = growth rate for the denitrifier, day"1.
hnax.D = rriaximum growth rate for the denitrifier, day"1.
Sdenjt = concentration of substrate to be denitrified (nitrate nitrogen) in mg/l.
Kd = saturation constant mg/l nitrate nitrogen.
Even though the Monod Kinetics is used by several investigators to explain the denitrification, the suspended denitrification process with methanol as carbon source is often described in the literature as zero order with respect to nitrate and methanol. The equation used in following this approach is presented as (4.36).
Denitrification filters appear to conform very well to the laws of biofilm kinetics. Because of the low saturation constant, Ks < 1 mg N03" -N / liter, the intrinsic reaction in the biofilm is zero order. This becomes a half-order reaction in thick biofilms owing to diffusional resistance in the biofilm. Where the substrate concentration in the bulk liquid is high enough, the biofilm is penetrated fully, and the overall process becomes zero-order (Harremoes 1982).
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