Evaluating the potential of treating organic acid-pretreated mixed fruit waste in a 13-L microbial electrolysis cell

Microbial electrolysis cells (MECs) offer a sustainable approach to producing hydrogen (H₂) from organic waste. However, industrialization of MECs is hindered by a low H₂ production rate (HPR), mainly due to inefficient mass transfer between microbes and electrodes. To overcome this limitation, efficient dual-chamber MEC reactor design and evaluation of various substrate applicability are essential. In this study, we investigated the potential of mixed fruit waste (MFW) as an MEC substrate and its impact on microbial community dynamics in a multi-stack MEC reactor designed for H₂ production. To enhance microbial utilization, MFW was pretreated with eco-friendly organic acids (i.e., citric acid), achieving a high carbohydrate extraction efficiency of 82 %. Physicochemical analyses of MFW before and after pretreatment confirmed effective hydrolysis. MEC operation with 25 % MFW extract achieved a high chemical oxygen demand (COD) removal efficiency of 77 % and a maximum current density of 0.71 A/m² (16.36 A/m³). Organic components in the MFW extract, including 5-hydroxymethylfurfural (HMF) and furan derivatives, were completely decomposed during MEC operation. Notably, microbial community analysis revealed distinct spatial distributions across the anode's vertical positions. Fermentative bacteria predominated in the bottom section, while electroactive genera such as Geobacter and Comamonas dominated the top section, likely due to the upward flow and recirculation of the organic substrate introduced at the bottom. The proposed multi-stack MEC process enhanced substrate utilization and microbial symbiosis interactions, highlighting its potential for industrial-scale applications.