Performance and Bacterial Communities in Conventional Activated Sludge and Membrane Bioreactor Systems with Low C/N Ratio Wastewater for Nitrogen Removal

Membrane-based pretreatment can recover organic matter from the sewage and further reduce energy consumption, and the remaining wastewater often contains low C/N ratio. Anoxic/oxic membrane bioreactor (MBR) is considered as the effective way to remove nutrients from low C/N ratio wastewater. However, information on microbial community related to this process is limited. In this study, performance and bacterial communities in two systems, anoxic/oxic MBR, and anoxic/oxic conventional activated sludge (CAS), were compared after being fed with the organic matter-recovered sewage. The MBR system performed better than the CAS system at nitrogen removal when operated at all loading rates (5-12.5 L/day) and recirculation ratio (1 and 2). Higher bacterial diversity and a larger number of novel operational taxonomic units were found in the MBR system at a loading rate of 10 L/day. Proteobacteria clones were most abundant, followed by Bacteroidetes and Actinobacteria clones in all reactors, but the clone ratio within each phylum and the class of Proteobacteria were different. Larger differences were observed at the genus level in Proteobacteria in both systems. In the denitrification reactors, Tolumonas, Dokdonella, and Thauera genera were identified in the CAS system and Tolumonas, Accumulibacter, and Dechloromonas genera were identified in the MBR system. More genera, including Paracoccus, Woodsholea, Dechloromonas, Azospira, and Inhella, were identified in the nitrification reactor of the MBR system than the CAS system, in which only the genera, Leptothrix and Hirschia, were detected. These results identified different bacterial communities responsible for the stable performance of CAS and MBR systems.