MOLECULAR MICROBIAL ECOLOGY OF ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL IN AERATED-ANOXIC ORBAL™ PROCESSES

The traditional process for enhanced biological phosphorus removal (EBPR) in wastewater treatment involves an anaerobic zone followed by an aerobic zone. Although there is no strict anaerobic zone in aerated-anoxic Orbal™ processes, phosphorus removal in excess of that required for cell growth does occur. The microbial ecology of polyphosphate accumulating organisms (PAO) in two full-scale Orbal™ wastewater treatment plants was investigated using flow cytometry to physically separate PAO from non-PAO and fluorescent in situ hybridization (FISH) to identify the main bacterial groups in the PAO subpopulation. Although organisms related to Rhodocyclus were present in these full-scale Orbal™ processes, they were not enriched in the PAO subpopulation, suggesting that the operational characteristics of aeratedanoxic processes select for a PAO community significantly different from that observed in traditional EBPR processes.