Effects of temperature on hydrolysis performance and short-chain fatty acids production during thermophilic micro-aerobic fermentation of waste activated sludge

摘要

Rapid hydrolysis of waste activated sludge (WAS) can be achieved by improving activities of extracellular enzymes under proper temperature conditions. As short-chain fatty acids (SCFAs) accumulation is always consumed by methanogens under anaerobic conditions, and considering that the micro-aerobic condition can inhibit the activities of methanogens, in this study, effects of temperature (55-75 degrees C) on thermophilic micro-aerobic fermentation of WAS were investigated. Results showed that the highest soluble chemicaloxygen demand (SCOD) yield was obtained at 60 degrees C (4,407 +/- 80mg/L, 36h), 2.0 times higher than that obtained at 75 degrees C (2,180 +/- 40mg/L, 36h), the corresponding hydrolysis rate was 0.6689d(-1). The highest SCFAs yield was 2,928 +/- 12mgCOD/L at 60 degrees C and 36h, 4.9 times higher than that obtained at 75 degrees C (594 +/- 10mgCOD/L, 36h). The analysis of SCFAs composition showed that acetic acid (HAc) accounted for the most percentage (>40%), followed by n-valeric (n-HVa) (20-25%), and propionic acids (HPr) (10-15%). Total suspended solids removal efficiency reached 18.7% after 192-h fermentation at 60 degrees C. These results suggested that the optimal thermophilic micro-aerobic conditions for WAS hydrolysis and SCFAs accumulation from WAS were 60 degrees C and 36-h fermentation time.