Modeling and simulation study of simultaneous nitrification–denitrification in membrane aerated bioreactor

Abstract

This study introduces a two-dimensional multi-species biofilm model to investigate the mechanisms of simultaneous nitrification–denitrification (SND) in membrane aerated bioreactors. We focus here on the effect of bulk concentration of oxygen, ammonium, and acetate on the SND performance, biofilm composition, and SND mechanism. The simulation results revealed that the oxygen distribution within the biofilm plays a determining role in achieving simultaneous nitrification and denitrification in MABR. The distribution of the autotrophs and heterotrophs within the biofilm is not clearly stratified due to the combined impact of cell diffusion and cross-diffusion of different species. The nitrification rate increases with the increase in bulk ammonium and oxygen concentrations while remaining relatively steady when the biofilm thickness increases. Biofilm thickness and acetate concentration have been substantiated as two regulating factors affecting the denitrification of MABR biofilm. High bulk oxygen and ammonium concentrations can significantly delay the establishment of the denitrification capacity of the biofilm but their impact on the denitrification rate drastically diminishes after the biofilm grows to a certain thickness. According to the modeling results, to achieve a quick establishment of denitrification capacity of the MABR biofilm, the bulk ammonia nitrogen and acetate concentrations should be in a range greater than 25 and 12 [gm−3], respectively, while the oxygen partial pressure on the gas side should be less than 0.342 bar. Thus, this study provides extensive insight into the impact of the bulk oxygen, ammonium, and acetate on the SND performance and biofilm composition and structure of MABR.