Occurrence of PAOI in a low temperature EBPR system

• At 10 °C and 6 d net aerobic SRT, an enriched GAO culture shifted to PAO I.
• PAO I did not switch to a GAO-like metabolism under P-limiting conditions at 10 °C.
• Low temperature can be used to enrich PAO I cultures for their metabolic research.

The occurrence of Accumulibacter Type I (a known phosphorus-accumulating organism, PAO) has received increased attention due to the potential operating benefits associated with their denitrifying activity in enhanced biological phosphorus removal (EBPR) wastewater treatment plants. In this study, after a shift from an enriched glycogen-accumulating organism (GAO) culture (competitors of PAO) to a PAO-enriched system, Accumulibacter Type I (PAO I) became dominant in an anaerobic–aerobic EBPR system fed with acetate and operated at 10 °C with a net aerobic solids retention time (SRT) of 6 d. Since Accumulibacter Type II (PAO II) were not detected, the low temperature in combination with the net aerobic SRT applied appeared to have suppressed their growth as well. The stoichiometry of PAO I was in agreement with previous metabolic models, suggesting that it was the main PAO organisms present in previous studies operated under similar conditions. Moreover, under poly-P limiting conditions, PAO I were unable to switch to a GAO-like metabolism at low temperatures. These results contribute to increase the understanding of the physiology, microbial metabolism and microbial ecology of PAO I.