Enhancing sludge fermentation and anaerobic digestion by mechanical cutting pretreatment

A new sludge pretreatment approach was developed to disintegrate waste activated sludge by mechanical cutting in this study, and the effect of mechanical cutting pretreatment on sludge fermentation and anaerobic digestion was analysed. The study results showed that a sludge disintegration degree of 6.7 % was achieved when the sludge was mechanically cut for 8 min. Moreover, the sludge fermentation was promoted by mechanical pretreatment. After the pretreatment, the soluble COD (SCOD) production in the sludge fermentation system was as high as 3052 mg/L, which was 2.28 times higher than that of the control group. More short-chain fatty acids (SCFAs), especially acetic acid, were observed in the pretreatment group. The mechanical pretreatment accelerated the sludge digestion process and increased biogas production, resulted in a maximum yield of 539.30 mL and 3.06 times higher than that of the control group. High-throughput sequencing results indicated that the microbial community composition in the sludge fermentation system was affected by the mechanical pretreatment, and these changes were conducive to sludge fermentation. The composition of methanogens in the anaerobic digestion reactors was changed by mechanical pretreatment, the relative abundance of Methanosaeta in the control group was 52.70 %, while that in the pretreatment group was as high as 94.05 %. The methanogens in the sludge anaerobic digestion system involving and without involving pretreatment was 5.47 x 10(7) and 5.12 x 10(7) copies/g, respectively. Overall, the mechanical pretreatment was beneficial for the enrichment of methanogens, especially acetotrophic Methanosaeta, and it increased methane production.