Effect of supplementation levels of magnetite (Fe3O4) as an interspecies direct interspecies electron transfer (DIET) on methane production in a biochemical methane potential (BMP) test using an inoculum from anaerobic digestate adapted to food waste

Recent studies have investigated the enhancement of anaerobic digestion (AD) efficiency through direct interspecies electron transfer (DIET) using organic waste like food wastewater (FW).However, when FW is used as the sole substrate, its high organic loading rate may cause initial inhibitory reactions, reducing AD efficiency and limiting the DIET effect.This study examined the effect of magnetite (Fe 3 O 4 ) supplementation levels, a DIET-promoting material, on AD performance in biochemical methane potential (BMP) tests where FW serves as the primary substrate.Anaerobic digestate adapted to FW is used as the inoculum.The BMP test included treatments with different supplementation levels of magnetite: 0 mM (control), 10 mM, 20 mM, 30 mM, 60 mM, 120 mM, and 150 mM, with AD conducted at 38C over a period of 60 days.Methane potential (B u ) and chemical oxygen demand (COD) removal rates were higher in most treatments compared to the control, except for the 10 mM and 150 mM (p<0.05).The maximum methane production rate improved in the 10-60 mM treatments but declined in the 120 and 150 mM treatments compared to the control (p<0.05).Additionally, the time to reach the maximum methane production rate was extended in the 10-60 mM treatments compared to the control, while it was shortened in the 120 and 150 mM treatments.These findings suggest that AD efficiency in BMP test using FW as a substrate can be enhanced by supplementing magnetite at levels ranging from 20 to 60 mM.