Modeling of membrane-aerated biofilm: Effects of C/N ratio, biofilm thickness and surface loading of oxygen on feasibility of simultaneous nitrification and denitrification

A multipopulation model of a membrane-aerated biofilm (MAB) considering heterotrophic bacteria (HB), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) was constructed with the simulation software AQUASIM 2.1 to corroborate the process concept of the membrane-aerated biofilm reactor (MABR) and to reveal an operational range for high chemical oxygen demand (COD) and nitrogen removal efficiencies. The modeling results confirm that simultaneous nitrification and denitrification (SND) is feasible in the MAB but not in a top-down aerated biofilm (conventional biofilm) due to the absence of oxygen for AOB and NOB. The model precisely predicts the COD, NH₄⁺-N, and T-N removal efficiencies and determines operating parameters like COD/nitrogen (C/N) ratio, biofilm thickness and surface loading of oxygen, which significantly affect SND efficiency. High nitrogen removal efficiency (more than 70%) is attained at ranges of C/N ratio from 3.0 to 5.25 and of biofilm thickness from 600 to 1200 μm. In addition, it was clearly demonstrated that nitrogen removal not via nitrate but via nitrite could be achieved by controlling the relative surface loadings of oxygen and ammonia, supporting the feasibility of short-cut SND with MABs.