Insight in the mechanism of alkali treatment methods effecting dewatered sludge fermentation from microbial characteristics

This study explored the mechanisms of alkali treatment methods (pretreatment and process treatment) on volatile fatty acids (VFAs) yield of dewatered sludge (DS) fermentation. Three fermentation groups were conducted with two alkali treatments and high-throughput sequencing was conducted to reveal the mechanism. The results showed that alkali process treatment improved VFAs accumulation and the maximum VFAs and acetic acid yields were 3.55 and 2.11 times higher than that of the alkali pretreatment group. The concentrations of soluble chemical oxygen demand (sCOD), protein and carbohydrate were 3100.72, 1256.46, and 308.78 mg/L with alkali process treatment. The microbial community analysis revealed that alkali process treatment reduced microbial diversity and richness compared with alkali pretreatment. Bacteroidetes and Proteobateria were the dominant bacteria in alkali pretreatment group, while Firmicutes was the dominant bacteria for alkali process treatment. Meanwhile, alkali process treatment promoted the enrichment of Clostridia compared to the alkali pretreatment. Tisierella, Proteniborus, Acetoanerobium, Rikenellaceae, and Burkholderiaceae occurred only in alkali process treatment. Besides, the abundances of carbohydrate and amino acid metabolisms in alkali process treatment exceeded alkali pretreatment, which promote the accumulation of VFAs. This study offers an effective microbial strategy for improving VFAs production from AF of DS.