Enhanced disintegration of waste activated sludge by ruminal microorganisms: Insights into structural disruption, microbial communities and functional genes.

Compared to other sludge disintegration methods, bio-disintegration of waste activated sludge (WAS) offered the advantages of lower cost and stable operation of the subsequent digestion system. This study used rumen fluid as an external biological source for hydrolytic pretreatment and cell wall disruption of WAS, and compared its cell disruption effect with that of anaerobic sludge (AS), and explored the mechanism by which ruminal microorganisms (RM) disrupted WAS cell walls. Experimental results showed that the release concentrations of SCOD and NH+ 4 from the RM reactor were 2.2 times and 1.7 times higher than those in the AS reactor, respectively. VFAs maintained high concentrations during cell wall disruption. The 2D-FTIR and EEM results demonstrated that the RM reactor exhibited more pronounced hydrolysis performance and enhanced protein release. SEM, AFM, CLMS provided direct evidence of cell disintegration of WAS in the RM reactor. The RM reactor harbored abundant hydrolytic and fermentative bacteria, among which Bacteroidota (14.1%) and Bacillota (25.9%) were dominant. Proteiniphilum (1.8%) and Petrimonas (7.4%) present in RM formed a stable and efficient hydrolytic network with genera such as Proteiniclasticum in WAS. Genes associated with cell wall disruption, such as lysozyme, mepA, and mepH were more abundant in the RM reactor. The abundance of polysaccharide hydrolases, proteases, and peptidoglycan hydrolases was higher in the RM reactor. Thus, the addition of RM promoted the hydrolysis of sludge EPS, thereby depriving cells of their protective layer and allowing hydrolytic enzymes to directly attack the cell surface, leading to cell disintegration.