Investigation of enhanced biological phosphorus removal at different temperatures: Microbial competition, kinetics, stoichiometry, and the effects of sludge age

Enhanced biological phosphorus removal (EBPR) is achieved with phosphorus-accumulating organisms (PAOs) under the anaerobic and aerobic (A/O) conditions in sequence. Although EBPR processes have been successfully applied to many full-scale wastewater treatment plants, the lack of stability is a noticeable problem, especially for removing phosphorus from industrial wastewater with temperatures greater than 25°C. This study demonstrated that temperature and sludge age are important factors in determining the stability of EBPR.; At temperatures ≥20°C, the stability of EBPR is the result of the outcome of competition between PAOs and glycogen-accumulating non-poly-P organisms (GAOs). At 20°C and a 10-day sludge age, PAOs were dominant in an A/O sequencing batch reactor (SBR) and were able to consistently remove 40 mg-P/L at the COD/P ratio of 300/40 due to a higher anaerobic acetate uptake rate and aerobic biomass yield; however, at 30°C and a 10-day sludge age, GAOs were able to out-compete PAOs due to their anaerobic acetate uptake. At 30°C and a 5-day sludge age, PAOs and GAOs coexisted in the A/O SBR, resulting in an unstable EBPR performance. After reducing the sludge age from 5 to 3 days, the EBPR efficiency improved significantly, and the EBPR performance stabilized. Temperature and sludge age were found to be important factors in determining the anaerobic acetate uptake kinetics of PAO- and GAO-enriched sludge. In addition, mathematical model simulations demonstrated that the aerobic glycogen formation rate for GAOs was an important metabolic process for determining the dominance of PAOs or GAOs at 30°C and a 3-day sludge age.; At 10°C, increasing the sludge age from 10 to 20 days improved the phosphorus removal efficiency and provided a stable EBPR. The unstable EBPR observed at 10°C and a 10-day sludge age may have been due to the aerobic sludge age (6.1 days) employed in this study, which is close to the minimum required aerobic sludge age calculated for 10°C (5.9 days). A dynamic model was developed to compute the ratio (α_P) of aerobic phosphorus uptake to anaerobic phosphorus release at a wide range of biomass phosphorus content (0.03 to 0.35 mg-P/mg-COD·VSS) and validated with experimental observations.