Investigation of Performance in MBR Operated with Low DO for Low C/N Ratio Wastewater.

This study investigated the effect of low DO operation on the performance of membrane bioreactors (MBRs) in treating wastewater with low carbon to nitrogen ratios(C/N = 3.5), the microbiological communities in them, and on membrane fouling. Two bench-scale MBRs were operated in tandem under different DO regimes: one maintained at an average DO of 0.5 mg/L and the other at 2 mg/L. Both systems exhibited high organic carbon removal efficiencies above 97%, with the low-DO reactor demonstrating a slight advantage. While the low DO conditions limited nitrification due to oxygen depletion affecting nitrifying bacteria, these conditions favored improved total nitrogen removal by achieving simultaneous nitrification and denitrification (SND) process. This improvement is attributed to the facilitation of denitrification and other nitrogen transformations, including the anammox and comammox pathways. Furthermore, the low DO environment was associated with reduced membrane fouling rates, suggesting that reduced aeration does not compromise membrane fouling mitigation. Microbial community analysis revealed that lower DO concentrations significantly increased diversity, as evidenced by alpha and beta diversity metrics. Redanduncy Analysis (RDA) confirmed the proliferation of nitrogen-transforming bacteria under low DO conditions, and the detection of anammox and comammox bacteria in the sludge samples confirmed the operation of these alternative nitrogen removal pathways. [ABSTRACT FROM AUTHOR]