Anaerobic Fermentation of Excess Sludge at Different Phs: Characterize by Acidogenesis Capability and Microbial Communities Structure Shift

MiSeq high-throughput sequencing and quantitative polymerase chain reaction was applied to characterize the shift of microbial communities in a bench-scale anaerobic reactor for excess sludge fermentation. Without pH adjustment, no significant change occurred in the diversified microbes that originally existed in the excess sludge. When pH was adjusted to 10, the bacterial diversity in the sludge clearly decreased. The disappearance of 99% original bacteria was accompanied by the stimulated growth of acidogenesis bacteria, especially Bacillus and Anaerobacillus (which collectively constituted 71% of relative dominance) contributing to high short-chain fatty acids (SCFAs) yields. This extinction and regrowth process of bacteria in pH 10 reactor was quickly achieved on the first day of fermentation. Compared with operating without pH adjustment, the optimum fermentation at pH 10 resulted due to: first, the predominance of acidogenesis bacteria for the maximized SCFAs production and second, low consumption of substrates by other bacteria.