THE MECHANISMS OF EBPR WASHOUT AND TEMPERATURE RELATIONSHIPS

In this study the combined effect of temperature and SRT on EBPR performance and the mechanism of EBPR washout were investigated. Two pilot scale UCT systems fed with synthetic wastewater were operated at 5 and 10°C. The results showed that the phosphorus (P) removal performance was optimum at SRT ranges of 16 to 24 days and 12 to 17 days for 5 and 10°C, respectively. Higher SRT values of up to 32 days at 5°C and 25 days at 10°C slightly reduced EBPR performance due to increased extent of endogenous respiration which consumed internally stored glycogen leaving less reducing power for PHA formation in anaerobic stages. The washout SRT of each system was determined as 3.5 days at 5°C and 1.8 days at 10°C. The energy reserves (poly-P) of EBPR bacterial consortium were not completely depleted even at washout points. The inability of EBPR biomass to utilize glycogen to generate reducing power for PHA formation was the major reason for washout to occur. The results not only suggest that glycogen mechanism is the most rate limiting step in EBPR systems, but also show that the glycogen metabolism is an integral part of EBPR biochemistry as proposed originally by Mino and coworkers (1987), and others following that (Pereira et al. 1996, Erdal et al., 2002; Erdal, 2002). The results showed that the aerobic washout SRT values (2.1 and 1.2 days for 5° and 10°C, respectively) of this study did not fit into the linear line developed by Mamais and Jenkins (1992). The reason for the differences perhaps is related to the use of COD limited influent in this study compared to the use of P limited influent in their study.