Enhanced performance and stability in anaerobic digestion of expired makgeolli by adding conductive magnetite particles

Waste makgeolli, a byproduct of Korean rice wine production, has a short shelf life and high organic load, necessitating sustainable disposal solutions. Anaerobic digestion (AD) offers both treatment and energy recovery benefits, but its stability is challenged by volatile fatty acid (VFA) accumulation under high organic loading rates (OLR). Direct interspecies electron transfer (DIET) can enhance AD efficiency, and ethanol, the main organic component of waste makgeolli, is known to promote DIET. This study evaluated the effect of submicron magnetite particles on DIET enhancement in continuous AD reactors treating waste makgeolli. Without magnetite, process failure occurred at 1.5 g COD/L-d OLR, whereas magnetite addition enabled stable operation at 4 g COD/L-d. Enhanced electron transfer between syntrophic bacteria and methanogens improved AD stability and efficiency. These findings highlight the potential of DIET promotion via magnetite addition for optimizing waste makgeolli AD and biogas utilization.