Enhanced biological phosphorus removal (EBPR) has been used in many wastewater treatment plants, sometimes with mixed success. There is still substantial variability in both the practices applied to achieve EBPR and the results of these practices in terms of phosphorus removal. The
Water Environment Research Foundation commissioned this research project to develop information that will help municipal wastewater treatment plants more efficiently and costeffectively remove phosphorus through processes that involve EBPR. Detailed analysis of water quality and operating
data collected from five facilities throughout the research project showed that reliably meeting low effluent phosphorus limits (under 1 mg/L) with EBPR can be an elusive goal. Facilities that consistently produce effluent with soluble phosphorus concentrations of less than 1 mg/L
augment the EBPR process by providing supplemental volatile fatty acids (VFAs), precipitating phosphorus using metal salts, or both. The study did not reveal any direct correlation between influent BOD:P, COD:P, or VFA:P ratios and EBPR performance. Plants with aeration basin influent BOD:P
ratios greater than 25 milligram BOD per milligram phosphorus generally had the most stable phosphorus removal performance, however plants with lower BOD:P ratios (as low as 10:1) also had stable performance. In situations where BOD:P ratios were less than 25:1, variability in influent BOD:P
had a greater impact on the effluent phosphorus concentration than the absolute value of the ratio. Phosphorus profiles were collected at each facility, and mixed liquor samples gathered to conduct bench-scale uptake and release tests and to examine the process microbiology. The phosphorus
profiles and uptake and release tests both showed that facilities with functioning EBPR populations and low effluent phosphorus concentrations can exhibit a wide range of release rates, uptake rates, and acetate consumption rates. Finally, the study showed that populations of phosphorus accumulating
organisms (PAOs) and glycogen accumulating organisms (GAOs) can coexist in facilities exhibiting stable EBPR, however increases in the GAO population can be an indicator of loss of EBPR.
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