Insight of persulfate-based treatments induced stable volatile fatty acids promotion during waste activated sludge anaerobic fermentation in semi-continuous-flow reactors: Focusing on variations of substrate and microbial functional profiles

Waste activated sludge (WAS) is generated continuously in sewage treatment plants (STPs) which requires ongoing treatment mode. Persulfate(PS)-based approaches have been demonstrated to stimulate VFAs production successfully via batch tests but whether they can be suitable to continuous flow is still unknown. Herein, the long-term performance of utilizing Persulfate(PS)-based approaches to promote volatile fatty acids (VFAs) production as well as the potential microbiological mechanisms are investigated and revealed. Results indicated that PS-based treatments stimulated stable acetic acid-enriched VFAs promotion by 3.1- and 14.1-fold that of the blank. The key genes for substrate metabolism (i.e., carbohydrates and amino acid metabolism), pyruvate metabolism (i.e., pdhA and aceE) and fatty acid biosynthesis (i.e., fabB and ACSL) were up-regulated by PS-based treatments via metagenomic analysis. The differential gene expression was primarily attributed to the variation of fermentative bacteria (i.e., Clostridium and Fonticella). Further explorations demonstrated that accompanied with more abundant bioavailable organics, the critical genes encoding oxidative defensive enzymes (i.e., SOD2 and katE) were activated to counteract the oxidative toxicity to anaerobes and maintain high metabolic functions in the PS-based treatment systems. This study provides the foundation for applying PS-based treatment to WAS treatment continuously.