RELATIONSHIP BETWEEN SEASONAL BIOLOGICAL FOAMING AND LIPASE ACTIVITY IN ACTIVATED SLUDGE

Biological foaming is more likely in warm climates and when the fat loading rate to the activated sludge system is high. We recently described that these two factors are both correlated with the degree of biological foaming at the same activated sludge wastewater treatment system, suggesting that they are part of a single mechanism (Frigon, D., R. M. Guthrie, G. T. Backman, J. Royer, L. Raskin,Wat. Res., in preparation). We hypothesized that the foam-forming bacteria are specialized in consuming fat. If so, since fat needs to be hydrolyzed through the action of lipase enzymes before consumption, the abundance of foam-forming bacteria should be controlled by lipase activity. In this study, it was found that the lipase activity profile of full-scale activated sludge systems changed slightly with the season. The study also aimed at quantifying the temperature dependence of the lipase activity. The activation energy of the lipase activity was found to be approximately 67 kJ/mol. This temperature dependence results in an increase in lipase activity by a factor 4 between winter (10°C) and summer (25°C). This result confirms that the abundance of a population specialized in consuming fat would be very sensitive to temperature variations. It is consistent with the hypothesis that bacteria causing seasonal biological foaming are specialized in consuming fat.