Dynamic modeling of partial nitrification in a rotating disk biofilm reactor: Calibration, validation and simulation

Partial nitrification to nitrite saves oxygen and organic matter. A dynamic model of a rotating disk biofilm reactor was developed in order to determine optimal operation conditions for partial nitrification. The biofilm model considered the active biomass fraction as a state variable; it was calibrated at steady state using the adjustment of two parameters - μ_max,AOB (1.32d^-1) and k_L (0.44mh^-1) and validated with long-term experiments. The experimental data were attained running the reactor in continuously and in batch modes for more than 700 days at different pH values, oxygen concentrations and nitrogen load rates (NLRs). A good agreement between the measured and modeled results was obtained with a Theil inequality coefficient lower than 0.3 for both calibration and validation. The model predicts that the active biomass fraction does not reach steady-state before 40 operating days, and the active nitrite-oxidizing bacteria fraction is much more sensitive than the ammonia-oxidizing bacteria fraction to the pH. Results demonstrated that nitrite accumulation (β) is strongly influenced by the NLR and the pH. The optimal operation zone for β>70% is reached for NLRs between 8.5 and 11.5gNm^-2d^-1, pH>8 and dissolved oxygen concentration <3mgO₂L^-1.