Enhancing energy recovery from expired rice wine via microbial electrolysis of supernatant and anaerobic digestion of concentrate after gravity settling

Abstract

Makgeolli is a traditional Korean rice wine with a short shelf life, making the management of expired makgeolli (EM) challenging. Meanwhile, its organic- and nutrient-rich nature renders EM a promising bioconversion substrate. To explore the potential to enhance energy recovery and profitability from EM, the concentrate (MC) and supernatant (MS) separated from EM by gravity settling were utilized for hydrogen production in microbial electrolysis cells (MECs) and methane production through anaerobic digestion (AD), respectively. MS demonstrated superior electron and hydrogen recovery compared to EM in MECs, with greater enrichment of exoelectrogenic Geobacter. In the AD tests, MC exhibited faster and more stable methane production with higher yield than EM. This separate processing of MS and MC was predicted to produce 18-21 % more energy (2,210 MJ/m3 EM) and 6-180 % higher revenue (101 USD/m3 EM) than processing whole EM using either MEC or AD alone, warranting further research for optimization.