Thermophilic Anaerobic Fermentation of Sludge: Effect of Zero-Valent Iron (ZVI) in Methane Production

In this study, the impact of zero-valent iron (ZVI) on methane production during sludge thermophilic anaerobic fermentation was investigated. The results showed that ZVI addition significantly enhanced cumulative methane production, with an optimum concentration of 5 g/L increasing the biochemical methane potential by 51.4% compared to the control. ZVI primarily promoted the acidogenesis and methanogenesis stages rather than hydrolysis, as indicated by the enhanced production of short-chain fatty acids and increased activities of key enzymes. Specifically, the activity of the methanogenic enzyme F420 increased by 28.09%, which contributed to a higher methane yield. Moreover, the synergistic effect of ZVI and its decomposition products (Fe2+ > Fe3+) facilitated a more reduced environment. Furthermore, ZVI addition enriched acetate-utilizing methanogens, i.e., Methanosarcina, which helps rapidly degrade organic acids, thereby stabilizing the fermentation process. These findings demonstrated the potential of ZVI to improve methane recovery and process stability in thermophilic anaerobic fermentation systems.