ADAPTATION OF EBPR BACTERIA TO COLD TEMPERATURE THROUGH HOMEOVISCOUS ADAPTATION

摘要

Temperature is one of the key parameters that affects the reaction kinetics andperformance of enhanced biological phosphorus removal (EBPR) systems. Althoughstudies agree that decreases in temperature cause decreases in EBPR kinetic reactionrates, there are contradictory results in the literature regarding the effect of temperatureon EBPR system performance. Early investigators reported better performance withlower temperatures (Sell et al. 1981; Ekama et al. 1984; Daigger et al. 1987), but morerecent 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 speculationhas been that deterioration in EBPR system performance at cold temperatures may beattributed to reduced fluidity and more rigid-like behavior of the cell membranes, whichwould reduce or prevent substrate transport across the membrane. Most cells have theability to alter their membrane fatty acid composition to keep their cellular membrane atnearly the same fluidity despite the temperature changes (Becker et al. 1996). Thisunique ability is known as “homeoviscous adaptation”. In this study, homeoviscousadaptation by EBPR activated sludge was investigated for a series of temperaturesranging from 20oC to 5oC using a lab scale continuous flow EBPR system fed withacetate and supplemental yeast extract. The fatty acid analysis results showed that theunsaturated to saturated fatty acid ratio increased from 1.40 to 3.61 as temperaturedropped from 20 to 5oC. The increased cis-9-hexadecanoic acid (C16:1) at 5oC stronglyindicated 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 solutetransport and proton motive force were operable even at 5oC. It was concluded that lossof EBPR performance at low temperatures is not related to the physical state of thecellular membranes, but is possibly related to the application of unsuitable operationalconditions for the reduced kinetic rates, e.g. SRT less than critical, excessive electronacceptors, low anaerobic detention time, non-acclimated sludge, enzyme inactivation, etc.