Contribution of nitrification and denitrification to nitrous oxide turnovers in membrane-aerated biofilm reactors (MABR): A model-based evaluation

As a novel and sustainable technology, membrane-aerated biofilm reactors (MABR) performing simultaneous nitrification and denitrification face the challenge of undesirable nitrous oxide (N2O) emission. Thereby, a comprehensive analysis of N2O turnover pathways and the affecting parameters in MABR are demanded for N2O mitigation strategies. In this work, a mathematical model describing three N2O turnovers pathways was studied to uncover the underlying mechanisms and the impacts of operational conditions on N2O turnovers in MABR system performing simultaneous nitrification and denitrification. The modeling results demonstrate that higher oxygen surface loading, longer hydraulic retention time (HRT) and lower influent chemical oxygen demand (COD) significantly induce higher N2O production factor (0.18%–3.3%). N2O turnovers are mainly regulated by the hydroxylamine (NH2OH) pathway and heterotrophic bacteria (HB) denitrification, accounting for 76%–87% and 10%–21%, respectively. In contrast, the thicker biofilm (i.e., 400–600 μm) causes lower N2O production factor (