Mechanism insights into enhanced treatment of wasted activated sludge by hydrogen-mediated anaerobic digestion.

In the current study, different forms of added gas including H, CO, and mixed gas (V:V = 4:1), as well as different hydrogen partial pressures (0.10, 0.30, and 0.50 atm) were investigated for the influence on anaerobic performance in waste activated sludge (WAS) treatment. The mixed gas significantly improved methane production by over 20%, which positively correlated with the hydrogen partial pressure. However, pure H (0.5 atm) heavily inhibited methane production by 76.5%. Combined with the microbial metabolic activity study, H accelerated the hydrolysis process. Afterward, mixing with CO accelerated H and organic consumption, thus promoting WAS degradation and methane production. Based on the most extra release of organics, the mixed group exerted the superior performance with hydrogen partial pressure at 0.3 atm. The microbial community analysis evidenced that mixed gas enriched proteolytic and homoacetogenic bacteria and hybrid-trophic methanogens. By metagenomics study, hydrolysis, acetogenic, and methanogenesis pathways were all enhanced via the exogenous addition of H and CO, sustainably transforming WAS towards CH. This study discovered the mechanism of the enhanced conversion from WAS to CH by exogenous H and provided a promising approach for WAS reduction and energy recovery.