ADAPTATION OF EBPR BACTERIA TO COLD TEMPERATURE THROUGH HOMEOVISCOUS ADAPTATION

Temperature is one of the key parameters that affects the reaction kinetics and performance of enhanced biological phosphorus removal (EBPR) systems. Although studies agree that decreases in temperature cause decreases in EBPR kinetic reaction rates, there are contradictory results in the literature regarding the effect of temperature on EBPR system performance. Early investigators reported better performance with lower temperatures (Sell et al. 1981; Ekama et al. 1984; Daigger et al. 1987), but more recent ones have reported partial or complete loss of EBPR functions at low temperatures (McClintock et al. 1991; Brdjanovic et al. 1997; Beatons et al. 1999). One speculation has been that deterioration in EBPR system performance at cold temperatures may be attributed to reduced fluidity and more rigid-like behavior of the cell membranes, which would reduce or prevent substrate transport across the membrane. Most cells have the ability to alter their membrane fatty acid composition to keep their cellular membrane at nearly the same fluidity despite the temperature changes (Becker et al. 1996). This unique ability is known as “homeoviscous adaptation”. In this study, homeoviscous adaptation by EBPR activated sludge was investigated for a series of temperatures ranging from 20°C to 5°C using a lab scale continuous flow EBPR system fed with acetate and supplemental yeast extract. The fatty acid analysis results showed that the unsaturated to saturated fatty acid ratio increased from 1.40 to 3.61 as temperature dropped from 20 to 5°C. The increased cis-9-hexadecanoic acid (C16:1) at 5°C strongly indicated the presence of homeoviscous adaptation in the EBPR bacterial community. Thus the cell membranes of the EBPR community were still in a fluid state, and solute transport and proton motive force were operable even at 5°C. It was concluded that loss of EBPR performance at low temperatures is not related to the physical state of the cellular membranes, but is possibly related to the application of unsuitable operational conditions for the reduced kinetic rates, e.g. SRT less than critical, excessive electron acceptors, low anaerobic detention time, non-acclimated sludge, enzyme inactivation, etc.