Performance and underlying mechanisms of zero-valent iron and percarbonate co-regulation for improved volatile fatty acids production from food waste anaerobic fermentation

Anaerobic biorefining of food waste (FW) into volatile fatty acids (VFAs) is typically limited by substrate recalcitrance and acid-induced stress. In this study, co-regulation with percarbonate (SPC) and zero-valent iron (ZVI) resulted in a maximum VFAs concentration of 28,317.9 mg COD/L, compared to only 3,986.4 mg COD/L in the control. SPC/ZVI treatment facilitated FW solubilization, enhanced substrate biodegradability, and alleviated acid inhibition. These changes promoted the enrichment of functional bacteria (e.g., Megasphaera and Clostridium) and stimulated key metabolic pathways and gene expression (e.g., fabG and por) involved in VFAs biosynthesis. Together with the provision of bioavailable organics and improved fermentation conditions, activation of stress defense systems in functional bacteria (e.g., katG and kdpA) counteracted the acid and oxidative stress in the SPC/ZVI system, thereby preserving metabolic activity for VFAs production. This study presents a dual modulation strategy to enhance FW fermentation, offering valuable insights for efficient resource recovery from FW.