Improved Bioconversion of Volatile Fatty Acids from Waste Activated Sludge by Pretreatment

Batch tests were conducted to analyze the influence of various pretreatment methods including thermo-alkaline, thermo-acid, ultrasonic-alkaline, and ultrasonic-acid on the bioconversion of volatile fatty acids (VFAs) from waste activated sludge. Experimental results showed that total VFAs (TVFAs) increased by 68.2% for ultrasonic-alkaline and 59.1% for thermo-alkaline. The TVFAs bioconversion in the case of the thermo-acid or ultrasonic-acid pretreatment, however, was lower than that without pretreatment. The results of VFA distribution showed that acetic acid was the most prevalent product, with a fraction of 35.5 to 57.2% for all cases. The mechanism of VFA production was then investigated. Results revealed that, in the two alkaline-pretreated slurries, soluble COD and soluble BOD/soluble COD significantly increased to yield more soluble substrate for the subsequent fermentation. Soluble proteins comprised the main substance provided that was converted to VFAs. A further investigation indicated that volatile (organic) solids, including insoluble proteins, in the solid phase of the samples pretreated with these two methods were hardly consumed during the fermentation. Water Environ. Res., 81, 13 (2009).