Effects of different hypochlorite types on the waste activated sludge fermentation from the perspectives of volatile fatty acids production, microbial community and activity, and characteristics of fermented sludge

The effects of different hypochlorite types (namely Ca(OCl) 2 and NaOCl) on the waste activated sludge (WAS) anaerobic fermentation, and microbial community and activity were investigated. The results indicated that both Ca(OCl) 2 and NaOCl contributed to volatile fatty acids (VFAs) production by simultaneously enhancing the solubilization, hydrolysis and acidification processes. The maximal VFAs was respectively 1379.5 (at 10 d) and 1621.5 (at 8 d) mg COD/L at the optimal dose of NaOCl and Ca(OCl) 2 while it was merely 157.4 (at 6 d) mg COD/L in the control. However, the Ca(OCl) 2 might affect the anaerobic process in a continuous mode while the NaOCl was relatively transient, which caused distinctive influences on the microbial structure and activity, and subsequently VFAs production in WAS fermentation systems. Moreover, Ca(OCl) 2 treatments showed advantages over NaOCl on WAS dewatering and VSS reduction, implying the superiority of utilizing Ca(OCl) 2 as additives for WAS disposal.