MODELING OF NITRIFICATION UNDER SUBSTRATE-INHIBITING CONDITIONS

A mathematical model was developed for the biological-nitrification process. The model assumed two consecutive oxidation steps occurring under a substrate-inhibiting condition. The mathematical model was calibrated using data obtained from batch experiments performed on the contents of five chemostats operated to steady-state on a feed containing 1,000 mg/L of ammonia-nitrogen. In the batch experiments, initial ammonia concentrations ranging from 100 to 1,000 mg-N/L were used. Time-varying concentrations of ammonia and nitrite were collected until the oxidation of these constituents was complete. Parameter sets that optimized the fit on the mathematical model to the experimental data were obtained by nonlinear-regression analyses. The oxidation of ammonia to nitrite was well represented by the Haldane-inhibition model. The Haldane-inhibition model did not satisfactorily describe the oxidation of nitrite to nitrate. It was observed that the simultaneous presence of both nitrite and ammonia led to the inhibition of nitrite oxidation. Modification of the model to consider a revised inhibition mechanism that accounted for the observed behavior was quite successful for the interpretation of the nitrite-oxidation data. © ASCE.