How exogenous influent communities and environmental conditions affect activated sludge communities in the membrane bioreactor of a wastewater treatment plant.

In this study, the residual population of influent and activated sludge (AS) communities was defined based on their occurrence frequency and relative abundance through long-term and fine-scale sampling from the membrane bioreactor (MBR) of a wastewater treatment plant (WWTP). There were 481 OTUs defined as the residual OTUs, which taken up 67.90 ± 9.36% of relative abundance in the influent community. Besides, 6.76 ± 5.71% of the residual population migrated to and remained in the AS community. Additionally, the residual populations were more likely to be anaerobes and microaerobes. As the most predominant genus from residual community, the relative abundance of Arcobacter was reduced from 15.78 ± 3.58% in the influent to 1.15 ± 1.35% in the AS. The residues that migrated from the influent have increased the richness and evenness of AS community, as well as the dissimilarities among samples over long-term. The rank-abundance distribution showed identical pattern for the residual species between influent and AS. By adopting the analysis of neutral model, 2766 out of 7491 shared OTUs between influent and AS communities were identified as neutral OTUs, which respectively made up 53.9% and 41.8% of the total relative abundance of influent and AS communities. These indicated that the AS community was to some extent, but not entirely assembled by neutral process. For the residual community in the AS, dissolved oxygen (DO) was positively associated with several aerobic genera, meanwhile influent chemical oxygen demand (COD) had positive relationship with genus Pseudomonas. Last but most importantly, the influent community could not inoculate the nitrifiers in the AS, but instead, was able to inoculate the denitrifiers; as well as enhance the biodiversity and the ability of resisting external disturbance for the AS community in MBR.