Effect of Addition of Zero-Valent Iron (Fe) and Magnetite (Fe3O4) on Methane Yield and Microbial Consortium in Anaerobic Digestion of Food Wastewater

Direct interspecies electron transfer (DIET), which does not involve mediation by electron carriers, is realized by the addition of conductive materials to an anaerobic digester, which then activates syntrophism between acetogenic and methanogenic microorganisms. This study aimed to investigate the effect of the addition of two conductive materials, zero-valent iron (ZVI) and magnetite, on the methane production and microbial consortium via DIET in the anaerobic digestion of food wastewater. The operation of a batch reactor for food wastewater without the addition of the conductive materials yielded a biochemical methane potential (B-u), maximum methane production rate (R-m), and lag phase time (lambda) of 0.380 Nm(3) kg(-1)-VSadded, 15.73 mL day(-1), and 0.541 days, respectively. Upon the addition of 1.5% ZVI, B-u and R-m increased significantly to 0.434 Nm(3) kg(-1)-VSadded and 19.63 mL day(-1), respectively, and lambda was shortened to 0.065 days. Simultaneously, Methanomicrobiales increased from 26.60% to 46.90% and Methanosarcinales decreased from 14.20% to 1.50% as the ZVI input increased from 0% to 1.50%. Magnetite, at an input concentration of 1.00%, significantly increased the B-u and R-m to 0.431 Nm(3) kg(-1)-VSadded and 18.44 mL day(-1), respectively. However, although magnetite improves the efficiency of methanogenesis via DIET, the effect thereof on the methanogen community remains unclear.