Synergic effects of free ammonia and sodium percarbonate for enhancing short-chain fatty acid production during sludge fermentation: Effectiveness assessment and mechanism elucidation

The production of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) via anaerobic fermentation is typically restricted by poor sludge decomposition capacity and low substrate-availability. Therefore, the free ammonia (FA)‑sodium percarbonate (SPC) technology was presented to successfully overcome the limitation while addressing unsatisfactory acidogenic fermentation pretreated with sole FA or SPC. It revealed that FA + SPC co-pretreatment could boost the SCFA concentration to 347.1 mg COD/g VSS at 180 mg/L FA and 0.15 g/g TSS SPC. In-depth studies demonstrated that FA + SPC pretreatment greatly improved sludge disintegration, biodegradability of substrates and acidification of hydrolysis products. Furthermore, FA + SPC co-pretreatment stimulated the activity of hydrolytic and acidogenic enzymes but inhibited methanogenic enzymes while changing the microbial structure and promoting the enrichment of fermentation microorganisms. The synergistic effect of FA and SPC in this work improves the yield of SCFAs from WAS and facilitates the study of WAS carbon resource recovery.