Roles of bacterial and epistylis populations in aerobic granular SBRs treating domestic and synthetic wastewaters

Aerobic granular sludge (AGS) has been recently studied and developed as a way to circumvent the poor settling and biomass retention capacity of conventional activated sludge. While it is known that AGS allows the simultaneous presence of oxic and anoxic zones on the surface or within granules, respectively, the actual composition dynamics of those granules in relation to their underlying wastewater influent have receive little attention. The main goal of this study is thus to assess the relationship between wastewater composition, microbial community structure and epistylis abundance. Two SBRs (sequencing batch reactors) comprising the same inoculum and fed with either domestic or synthetic wastewater were used in this regard. The more complex composition of domestic wastewater promoted a higher bacterial richness than their synthetic counterparts. Indeed, the vast majority of the bacterial community in the SBR fed with synthetic wastewater was dominated by the genus Thauera. The SBR fed with domestic wastewater also showed a more thorough granulation and greater treatment efficiency. Surprisingly, the abundance of epistylis was positively correlated with remaining suspended solids, hinting that ciliates might be responsible for SS (suspended solids) removal and would be a desirable trait to include in wastewater treatment plants. In sum, our study gives insight into the differing population dynamics shaped by domestic and synthetic wastewaters inoculated with the same initial consortium, along with their overall pollutant removal efficiency.