Inoculation and alkali coeffect in volatile fatty acids production and microbial community shift in the anaerobic fermentation of waste activated sludge

•We use inocula in acidification of waste activated sludge in alkaline condition.•Inocula were paper mill anaerobic granular sludge and dying mill anaerobic sludge.•Inoculation increase volatile fatty acid production at pH 9 but not at pH 10.•Inoculum make the microbial community shift at pH 9 but not at pH 10.•Inoculation will decrease alkaline dosage in waste activated sludge acidification.

Batch fermentations of waste activated sludge (WAS) at alkaline pH with different inocula were performed. Paper mill anaerobic granular sludge (PAS) and dyeing mill anaerobic sludge (DAS) were used as inocula. At pH 10 the inoculation did not increase the volatile fatty acids (VFAs) production compared to the non-inoculated samples fermented in the same conditions, and the maximal VFAs yield of non-inoculated WAS was higher than inoculated WAS. However, at pH 9 the inoculation with PAS increased the sludge hydrolysis and VFAs production was 1.7-fold higher than that in non-inoculated WAS (yield 52.40 mg/g of volatile solid). Denaturing gradient gel electrophoresis analysis revealed that 3 bacterial species, identified as Proteocatella, Tepidibacter, and Clostridium, disappeared when inoculated with PAS at pH 9 or at pH ⩾ 10. The results showed that the inoculation with PAS can be helpful to achieve a relatively high VFAs production from WAS in a moderate alkaline environment.