Advancing microbial electrolysis cells (MECs) for efficient wastewater-to-energy conversion

The global energy crisis and fossil fuel impacts highlight the need for sustainable energy carriers such as hydrogen. Microbial electrolysis cells (MECs) can generate hydrogen from organic waste, but their optimization under complex feedstock conditions remains challenging. Accordingly, this study focused on optimizing key parameters to enhance MEC performance. Variation in flow velocity (0.2 and 0.8 mm/s) in Geobacter sulfurreducens and Shewanella oneidensis co-culture biofilms, cultivated in a microfluidic bioelectrochemical system, showed that S. oneidensis exhibited a pronounced flow-dependent response. Higher shear stress produced thinner but more electroactive biofilms, linked to biofilm formation through mechanosensing pathways. To further evaluate system performance, the effects of substrate concentration (20–60%), pH (5–8), and applied anodic potential (−0.2 to +0.4 V vs standard hydrogen electrode SHE), in a cylindrical microbial electrolysis cell (Cylindrical-MEC) were also studied. Optimal performance was achieved at 40 % hydrolysate, pH 8, and +0.4 V vs. SHE, yielding a mean current density of 3.4 A/ m² and coulombic efficiencies (CE) of 95 %. Metagenomic and PCA analyses revealed that high anodic potential and alkaline pH enriched Geobacter-dominated communities while suppressing methanogens. In a 10-L rotating disk bioelectrochemical reactor (RDBER), operation at 0.4 V vs. SHE achieved a hydrogen production rate of 30.57 L/m²·d with minimal methane formation. The hydrogen produced under these conditions was subsequently utilized for the autotrophic synthesis of acetoin.