Bacterial Community Composition Dynamics in a Full-Scale Activated Sludge

Activated sludge processes use a consortium of bacteria to oxidize, reduce, and sequester pollutants to prevent water quality degradation in receiving water bodies. Environmental engineers studying these systems have long explored the activity and composition of bacterial communities that comprise it. Several of these studies have drawn broad conclusions using single or a few samples collected from wastewater treatment plants. While such studies have identified several significant bacterial community members, they provide a somewhat myopic view of activated sludge bacterial community composition (BCC) because they do not capture the variation in community structure over time scales of months to years. In this study, we explore the natural BCC dynamics in a full-scale activated sludge tank at the Nine Springs Wastewater Treatment Plant (Madison, WI). To perform this analysis, a bacterial community fingerprinting technique called automated ribosomal intergenetic spacer region analysis (ARISA)was used to quantify community differences in the BCC over one year. We discovered that the BCC differs across seasons. Additionally, a semi-cyclical pattern was observed over the yearlong study when the data were ordinated using a correspondence analysis. The implications of these results are that significantly different bacteria are present across seasons and that changes in treatment performance between seasons might be correlated with these changes rather than simple temperature effects on kinetics as assumed.