Effect of temperature shock to thermophilic granules

Abstract

Effects of temperature shock to the activity of thermophilic biogranules in two upflow anaerobic sludge blanket (UASB) reactors were investigated. Treating wastewater containing 9450 mg litre −1 of sucrose, equivalent to 10000 mg litre −1 of COD (chemical oxygen demand) at 55°C and 24 h of hydraulic retention time (corresponding to a loading rate of 10 g-COD litre −1 day −1, both reactors consistently removed 85–90% of COD. The temperature in Reactor-I was raised to 65°C for 8 days, while that in Reactor-D was lowered to 37°C for 16 days. The temperature shocks significantly reduced the reactors' performance: COD removal efficiencies were lowered to 60% for Reactor-I and to only 40% for Reactor-D. Sludge yields during temperature shock were lowered by 25%. In addition, the temperature shock also caused severe biomass washout, lowering of pH and accumulation of fatty acids, in particular propionate. However, both reactors were able to fully recover their efficiencies within 18 days, after the pH was rectified by the addition of alkaline and the temperature was re-adjusted to the normal 55°C. Results of specific methanogenic activity (SMA) tests show that acetotrophic methanogens were not as sensitive to the temperature shock as other bacteria.