INVESTIGATION OF PAOs AND GAOs AND THEIR EFFECTS ON EBPR PERFORMANCE AT FULL-SCALE WASTEWATER TREATMENT PLANTS IN U.S.

The abundance of Accumulibacter phosphatis (presumed to be polyphosphate polyphosphorus-accumulating organisms, or PAOs), Competibacter phosphatis (presumed to be glycogen-accumulating organisms, or GAOs), and tetrad-forming organisms (TFOs) at six full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants were investigated. Phosphorus removal to effluent P concentrations of less than 1 mg/L was achieved with the co-existence of various levels of PAOs and GAOs. P release to acetate uptake ratios obtained from bench tests varied greatly among plants, ranging from 0.27-0.75 mole/C-mole. Accumulibacter-like PAOs were found to be 5-20% of the total bacterial population and Competibacter-like GAOs were 0-20% of the total bacteria population. TFO abundance varied from non-detect to dominance. An inverse relationship between the phosphorus release to acetate uptake ratio (Prel/HAcup) and the population of TFOs was observed for all but one plant. The plant that did not have TFOs had high levels of Competibacter, which also led to a lower P/HAc ratio as well. Evaluation of full-scale EBPR performance data indicated low effluent P concentration and high (EBPR) process stability did not correspond to higher Prel/HAcup ratios and higher PAO abundance. The plant that had the lowest average effluent P and highest stability rating had the lowest Prel/HAcup and the most TFOs.