The Production of Short-Chain Fatty Acids and Constituents with Primary Sludge as Fermentation Substrate under Different pHs

This paper investigated the influence of pH on short-chain fatty acids (SCFAs) production and constituents with anaerobic fermentation of primary sludge from a Chinese wastewater treatment plant (WWTP). Controlled and uncontrolled pH experiments were conducted in ten completely mixed bench-scale reactors. Results showed that pH significantly influenced on the SCFAs yields and constituents from primary sludge as a potential fermentation substrate. At about 25°C, the alkaline pH owned more benefit of generating SCFAs than that at other pHs or in the blank test. At pH 10 SCFAs significantly increased in the 4-6 d of fermentation, from the initial of 12.2 to 319.9 (mg COD/g VSS). At pH 11, however, only 316.6 (mg COD/g VSS) of SCFAs were produced even at the fermentation of 10 d. At any pH value investigated, acetic, propionic and n-butyric acid were the three main products on the 4th day, they complied with the order of acidic pH > alkaline pH > neutral pH except at pH 5. The percentage of acetic, propionic, n-butyric acid and the rest three acids was, respectively, 45, 21, 15, 18% at pH 10.