Impact of the rotational speed and counter electrode configuration on the performance of a rotating disc bioelectrochemical reactor (RDBER) operated as microbial electrolysis cell

A 10 L Rotating Disc Bioelectrochemical Reactor (RDBER) was operated as a microbial electrolysis cell (MEC) under different rotational speeds and counter electrode configurations. Increasing the anode's speed from 0.25 to 1 rpm raised the anodic current density from 0.55 ± 0.14 to 1.00 ± 0.07 A m⁻² while increasing hydrogen production rates from 0.05 ± 0.01 to 0.18 ± 0.01 L_H₂ L_R⁻¹ d⁻¹. Higher speeds provided no further benefit. Moving the counter electrodes to the upper reactor half reduced observed hydrogen shuttling. The modified RDBER reached current densities of 1.98 ± 0.11 A m⁻² and 0.99 ± 0.03 L_H₂ L_R⁻¹ d⁻¹ hydrogen production. Optical coherence tomography confirmed biofilm morphology changes but no significant increase in biovolume or substratum coverage. Hydrogen recovery remained below 50 %. While the RDBER achieved high volumetric current densities and volumetric hydrogen production rates compared to other MEC pilots, improvements in anodic current density and cathodic hydrogen recovery are required for practical application.