Characterization of microbial community structure in a hybrid biofilm-activated sludge reactor for simultaneous nitrogen and phosphorus removal.

The microbial communities in a hybrid biofilm-activated sludge reactor (HY) for nitrogen and phosphorus removal were characterized by 16S rRNA-based clone libraries and phylogenetic analysis. The hybrid reactor removed over 90% of COD, 92% of total nitrogen (TN) and 95% of total phosphorus (TP) from the municipal wastewater, respectively. The mean removal rates of COD, TN, and TP in the conventional suspended activated sludge reactor were above 80%, 80% and 94%, respectively. Community structures were determined by phylogenetic analyses of six clone libraries (each nearly 100 clones). The dominant bacterial group with which clones were affiliated to the beta subclass of the Proteobacteria (31% to approximately 77%), following the Bacteroidetes group (10% to approximately 34%). In addition, several clone groups affiliated with unknown bacterial assemblages were identified in the clone libraries. Acinetobacter sp., which was thought to had played an important role in phosphate removal systems, was scarcely represented by clone sequences in both libraries. Differences in community structure were observed between the hybrid reactor and activated sludge reactors. Such differences may account for the differing wastewater treating capabilities of the two different systems.