The inoculum effect on the ammonia-oxidizing bacterial communities in parallel sequential batch reactors

Three identical sequential batch reactors (SBRs) were each inoculated with sludge from a full-scale wastewater treatment plant (WWTP) treating a waste stream of different origin, i.e. a hospital, a meat processing company, and a municipal WWTP. The SBRs were run in parallel for 84 consecutive days to investigate whether the reactors would become more phylogenetically similar or stay separated concerning their functionality and microbial communities. Overall, the nitrification functionality was high throughout the experiment, and the size and structure of the sludge flocs were very similar. The total bacterial and ammonia-oxidizing bacterial (AOB) communities were analyzed by PCR-DGGE. Cluster analysis demonstrated very distinct bacterial communities in the three SBRs, not showing any trend becoming more similar. The carrying capacity, dynamics and functional organization of the communities were assessed by DGGE analysis and based on these patterns the range-weighted richness, moving window analysis, and constructing Pareto-Lorenz evenness distribution curves were calculated. Between the SBRs, highly comparable internal structure and dynamics of the AOB communities were observed, although they had only one AOB DGGE band in common. These observations indicate that community characteristics such as the extent of biodiversity and dynamics are more important indicators of good microbial functionality than the presence of certain specific species.