Effects of the applied voltage on electroactive microbial biofilm viability and hydrogen production in a recalcitrant organic waste-fed single-chamber membrane-free microbial electrolysis cell performance

The microbial electrolysis cell (MEC) is a future clean technology with a wide range of applications in energy recycling fields, particularly for hydrogen production. Applied voltage governs the electrochemically active microbial activities in MEC and further affects hydrogen production. Therefore, this study investigated the im-pacts of the applied voltages on MEC performance and anodic biofilm viability during the biotransformation of straw waste biomass into green hydrogen energy in an anaerobic environment. The results revealed that the COD removal efficiency and bioH2 yield increased with the augmentation of the applied voltage and beyond 0.8 V started decreasing. Among the performed protocols MEC0.8 depicted the best performance with a maximum H2 production of 6.017 mmoles H2/g-COD which was-28.2 % and-9.8 % higher than that of MEC0.5 and MEC1.0 respectively. Moreover, it also achieved a maximum COD removal of 73.4% and a coulombic efficiency (CE) of 68.4%. Consistently, the anodic biofilm viability and bacterial cell shape in the MECs performed with 0.5 V and 0.8 V were less affected but largely damaged in a high potential operated protocol (MEC1.0), suggesting that the mixed electroactive consortia were so sensitive to high potentials. Furthermore, MEC1.0 displayed a high charge transfer resistance of 16.06 & omega; which was-22.1 %, and-73.7 % higher than that of MEC0.8, and MEC0.5 respectively. Based on our novel study's results, the optimal applied voltage for the best performance of MEC was 0.8 V; and this information will be a pillar for future MEC operations prior to maintaining its industrial practice.

Automated summary

The study investigated the impacts of applied voltages on the performance of microbial electrolysis cells (MECs) used for converting straw waste biomass into green hydrogen energy. The results showed that increasing the applied voltage improved COD removal efficiency and bioH2 yield up to a certain point, beyond which it decreased. Among the tested protocols, MEC0.8 displayed the best performance with the highest H2 production, COD removal, and coulombic efficiency. The viability of the anodic biofilm and bacterial cell shape were less affected at lower voltages but significantly damaged at higher voltages.