Conductive materials supplement alters digestate dewaterability during anaerobic co-digestion of food waste and sewage sludge and promotes follow-up indigenous peroxides activation

Despite growing interest in conductive materials amended anaerobic co-digestion of food waste and sewage sludge and demonstrated process improvement, little information is available on how conductive materials affect the digestate dewaterability. This study traced the dewaterability and physicochemical properties of digestate in anaerobic co-digestion process by supplying three representative conductive materials (i.e., zero-valent iron (ZVI), magnetite, and biochar) and evaluated the practicability of indigenous peroxides activation to improve digestate dewaterability. Results showed that supplying conductive materials, especially ZVI and biochar performed the higher methane yield (enhanced by > 23.1%) and better digestate dewaterability (specific resistance of filtration reduction > 57.1%). The mechanism exploration demonstrated that the ZVI and biochar supplement in the anaerobic co-digestion system effectively changed the microbial community probably related to organics degrading bacteria, causing the reduction of hydrophilic tyrosine-like/tryptophan-like components (> 13.2%) and protein secondary structure (the reduction value of alpha-helix/(beta-sheet + random coil) > 46.9%) in extra cellular polymeric substances. Accordingly, the water-bound energy and hydrophilicity of digestate were significantly weakened, thus promoting digestate dewaterability. The downstream dewatering experiments indicated that the residual ZVI in digestate could more efficiently active peroxides for further enhancing dewaterability with economic advantage. These findings pioneer the potential application of the conductive materials assisted anaerobic co-digestion combined with coagulants/peroxides conditioning technology for advantages of environmental sustainability.

Automated summary

This study investigates the effect of conductive materials on the dewaterability of anaerobic co-digestion digestate. The results show that the addition of zero-valent iron (ZVI) and biochar can enhance methane production and improve the dewaterability of the digestate. Mechanism exploration suggests that the addition of ZVI and biochar changes the microbial community and reduces the hydrophilic components and protein secondary structure in extracellular polymeric substances, thereby promoting digestate dewaterability.