Effect of temperature on short chain fatty acids (SCFAs) accumulation and microbiological transformation in sludge alkaline fermentation with Ca(OH)2 adjustment

The effects of temperatures (15-55 degrees C) on the alkaline fermentation of sewage sludge were investigated in semi-continuous stirred tank reactors (semi - CSTR) at the pH of 10. The highest soluble chemical oxygen demand (SCOD) yield was obtained at 55 degrees C (764.2 mg/(gVS L d)), while the highest short chain fatty acids (SCFAs) yield was observed at 55 degrees C (319.8 mg/(gVS L d)), 1.5 times higher than SCFAs yield at 55 degrees C (209.5 mg/(gVS L d)). The proportion of the intercellular organic substances being transferred to the slime layer of sludge flocs increased from 29% at 15 degrees C to 54% at 55 degrees C. But only a small part of soluble organic substances in the slime layers was converted to SCFAs at 55 degrees C. The dewaterability of sludge was better at 35 degrees C than that at 55 degrees C. Microbiological community analysis showed the acid-producing microorganisms at the medium temperatures (25 degrees C and 35 degrees C) were more diverse and abundant than those at the low (15 degrees C) and high temperatures (55 degrees C). Clodtridium and Bacillus in Firmicutes and Gamma proteobacterium in Proteobacteria were the dominant functional bacterial species for high SCFA accumulation. (C) 2014 Published by Elsevier Ltd.