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

Abstract

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.