Critical role of bicarbonate in Zero-Valent iron for hydrogen generation and biogas upgrading in anaerobic digestion

This study investigates the role of Zero-Valent Iron (ZVI) in anaerobic digestion, emphasizing the critical influence of bicarbonate and feeding regimes. Abiotic tests revealed that higher bicarbonate concentrations enhanced hydrogen production. However, two-cycle experiments with ZVI and bicarbonate showed reduced hydrogen in the second cycle due to ZVI passivation. A similar phenomenon was observed when anaerobic granular sludge (AGS) was introduced into the system. Glucose at 4, 8, and 16 g/L was tested with AGS, with ZVI containing samples achieving superior methane production, exceeding 95 % methane and CO₂ levels below 0.5 % after 85 days in the 16 g/L reactor. In-situ ZVI addition using cheese whey reached ∼ 90 % methane without lag phases, outperforming ex-situ systems. Tests with Stainless Steel (SS316) showed no significant impact on methane or microbial profiles. This study highlights the novel role of bicarbonate in enhancing ZVI's effectiveness, providing new insights to optimize biogas upgrading in anaerobic digestion systems.