Tuning membraneless microbial electrolysis cells operation alters efficiency and anodic microbiome toward scalable hydrogen production from sludge-hydrolysate

The practical implementation of microbial electrolysis cells (MECs) is hindered by challenges in optimizing system performance with complex substrates. This study addresses that gap by evaluating MECs fed with hydrolysate, an appealing substrate rich in organic-acids. Through systematic variation of substrate concentration (20–60 %), pH (5–8), and applied anodic potential (−0.2 to +0.4 V vs standard hydrogen electrode [SHE]), the optimal operational conditions were defined as 40 %-hydrolysate, pH 8, and +0.4 V vs SHE, yielding a mean current density of 3.4 A/m 2 and coulombic efficiencies (CE) of 38 % and 96 % based on total organic carbon (TOC) and total volatile fatty acids (VFAs), respectively. Scalability was demonstrated using a 10 L rotating disk bioelectrochemical reactor (RDBER) at 0 and 0.4 V vs SHE, achieving a maximum hydrogen production rate of 30.57 L/m 2 /d and minimal methane formation at 0.4 V. These findings offer a framework for optimizing MECs under real-feedstock conditions. • Microbial electrolysis cell output was optimized with primary-sludge hydrolysate. • Optimal conditions were 40 %-hydrolysate, pH 8, and anodic potential of 0.4 V vs SHE. • Optimal operation enriched Geobacter and suppressed methanogens in the biocoenosis. • Scale-up to a 10 L reactor achieved 30.57 L-H 2 /m 2 . d under optimized conditions. • Anodic potential of 0.4 V increased H 2 production without improving economic gain.