Metagenomic characterization of the enhanced performance of anaerobic digestion of waste activated sludge with CaO2 addition under ambient condition: Fatty acid biosynthesis metabolic pathway and CAZymes

Abstract This study investigated the chemical and genetic mechanisms of the ambient anaerobic digestion of waste activated sludge (WAS) with the addition of CaO2. The microbial community structures, key microorganisms, functional profiles and related carbohydrate-active enzymes were further revealed according to metagenomic sequencing combining with microbial diversity sequencing. Results showed that the prolonged period of alkaline condition generated from CaO2 contributed significantly to the continuous destruction of WAS, and the oxidative environment caused by CaO2 further enhanced flocs dissolution. This synergistic effect also significantly changed the microbial community. Oxidation contributed more than the alkaline condition to the decline of microbial diversity, while the change of microbial community structure was mainly due to the alkaline condition. The key enhanced genes associated with fatty acid biosynthesis pathways with CaO2 addition were highlighted. Three kinds of high-abundance acetyl-CoA carboxylase genes and eleven kinds of synthetase, hydrolase, lyase and oxidoreductase genes promoted by CaO2 were distributed throughout each branch of fatty acid biosynthesis pathway (ko00061). Moreover, carbohydrate binding modules (CBMs) and glycoside hydrolases (GHs) were the top two carbohydrate-active enzymes (CAZymes) improved by CaO2 addition. CaO2 can also effectively promote the function of lysozyme and the metabolism of several monosaccharides. This work provides a deep insight into the advantage of CaO2 in promoting sludge solubilization and acidification at the genetic levels, thus expanding the application of CaO2 in sludge treatment and resource recovery.