Mathematical model for simultaneous nitrification and denitrification (SND) in membrane bioreactor (MBR) under Low Dissolved Oxygen (DO) concentrations

Activated Sludge Model no. 1 (ASM1) was modified and applied to Simultaneous Nitrification and Denitrification (SND) in oxygen-limited MBR. In order to calibrate the model correctly, the parametric sensitivity was performed using AQUASIM 2.0 to find the most important coefficients. The most sensitive coefficients in the model of oxygen-limited MBR were related to the growth of heterotrophic biomass. While the total autotrophic biomass concentration (X_BA) was decreased by decreasing DO concentration, there was an increase in the nitrite-oxidizing biomass concentration by a small amount. This model also showed that over 97% of permeate Soluble Chemical Oxygen Demand (S_COD) was the Soluble Inert (S_I). The model showed the change in the ammonia-oxidizing and nitrite-oxidizing biomass was decreased by decreasing DO concentration. However, there was an increase in the nitrite-oxidizing biomass concentration by a small amount due to the biomass retained in the bioreactor with membrane. It is contradictory to the reported observations for conventional activated sludge process.