Enhancing hydrogen production from anaerobic sludge fermentation via sodium dichloroisocyanurate pretreatment: Performance and mechanisms

Sodium dichloroisocyanurate (DCCNa), a widely applied disinfectant and oxidant, has recently aroused significant attention in waste activated sludge (WAS) treatment, but its influence in enhancing anaerobic dark fermentation for hydrogen (H₂) production remains unexplored. Accordingly, this work aims to cover above research gap and reveal the corresponding mechanism of DCCNa pretreatment for hydrogen recovery from WAS. Batch tests showed that DCCNa dosages of 50–250 mg/g volatile suspended solids (VSS) significantly increased H₂ yield, with the optimal dosage at 200 mg/g VSS achieving a maximum yield of 10.3 ± 0.3 mL/g VSS, a 9.4-fold enhancement over the blank (without DCCNa addition). Mechanistic analysis revealed that DCCNa benefited the disintegration of WAS, simultaneously enhanced the biodegradability of the solubilized organics. While DCCNa slightly inhibited the microbial activity related to hydrogen production, it caused stronger inhibition on hydrogen consumers and promoted the activity of hydrolytic microorganisms, which is conductive to hydrogen accumulation. Microbial analysis further confirmed the enrichment of hydrolytic bacteria (e.g., Bacteroides and Macellibacteroides ), while the overall abundance of hydrogen producer (e.g., WS6_(Dojkabacteria) , SJA-28 and Christensenellaceae_R-7_group ) and consumers (e.g., Dechloromonas , Rhodobacter and Methanospirillum ) significantly decreased. This work elucidated the novel role and mechanism of DCCNa in promoting hydrogen recovery from sludge, providing a theoretical basis for expanding its application in sludge treatment and bioenergy recovery.