EFFECT OF TEMPERATURE ON EBPR SYSTEM PERFORMANCE AND MICROBIAL COMMUNITY

It is well known and firmly established that the rate of chemical and biochemical reactions slow down as temperature decreases. Nevertheless, several studies have reported that the efficiency of enhanced biological phosphorus removal (EBPR) improves as temperature decreases. However, several recent studies have reported that EBPR reaction rates decrease with temperature decrease in accordance with the Arrhenius relationship. This study was designed to more thoroughly investigate this controversy using two UCT plants fed with a synthetic wastewater consisting primarily of acetate as the COD form, and a small amount of supplemental yeast extract. Experiments were performed over temperatures ranging from 5 to 20°C. The results showed that, even though the kinetic rates decrease as temperature decreases, EBPR systems perform better at colder temperatures. The reason for better system performance is apparently related to reduced competition for substrate in the non-oxic zones, which results in an increased population of PAOs and, thus, greater EBPR efficiency. The proliferation of PAOs apparently occurs because they are psychrophilic whereas their competitors are not. The experiments showed that the acclimated EBPR sludges accumulated high concentrations of both PHA and glycogen at 20°C, but accumulated more PHA and much less glycogen at 5°C. Although the results could be interpreted as the consequence of changes in the PAO-GAO competition, comparisons of transmission electron microscopy examinations revealed no indication of the presence of GAO population under any temperature condition. Regardless, mass balances of the glycogen data showed that the involvement of glycogen is less at cold temperature, even though PHA production and EBPR performance was greater. Unlike current EBPR models (e.g., the Mino model, 1987), the results suggest that involvement of glycogen metabolism in EBPR biochemistry is a requirement as suggested by Mino model (Mino et al. 1987) but its involvement depends on the environmental conditions. EBPR stoichiometry was presumed to be insensitive to temperature changes (Brdjanovic et al. 1997). However, this study showed that the stoichiometry of EBPR was sensitive to temperature The results also indicate that temperature not only causes selective pressure on the dominant organisms, but also may force them to use different metabolic pathways as temperature decreases.