Residence Time Reduction in Anaerobic Reactors: Investigating the Economic Benefits of Magnetite-Induced Direct Interspecies Electron Transfer Mechanism

Existing research on direct interspecies electron transfer (DIET) has predominantly focused on the types and concentrations of conductive materials across diverse anaerobic digestion. However, insufficient understanding of the impact of residence time, a critical economic factor, prompted this investigation. Magnetite, a conductive material, was introduced into the anaerobic digestion of food wastewater, leading to a significant increase in ultimate methane production (B-u) with 25 mM-Fe3O4 (p < 0.05). Despite a subsequent decline in methane production efficiency from 388.9% to 7.1% over the 15- to 65-day anaerobic digestion period, the initial impact of increased methane production due to magnetite addition was evident. Control's maximum methane production rate (R-m) was 27.5 mL/day, reaching its highest point at 37.4 mL/day with 15 mM-Fe3O4, accompanied by a noteworthy 56.6% reduction in the attainment day of R-m (Rm-day), shortened to 8.2 days. Even with 100 mM-Fe3O4, while B-u showed no significant difference, Rm-day exhibited a substantial reduction of 22.8. Despite the lower overall anaerobic digestion efficiency under some magnetite input conditions, this study confirmed a substantial shortening of Rm-day, suggesting that the DIET mechanism induced by conductive materials such as magnetite could reduce the residence time in continuous-type anaerobic reactors, contributing to improved economic feasibility.