Durability and mass loss effect of heat-treated stainless-steel cathode for methane production from organic and inorganic carbon in a bioelectrochemical system

• Iron-assisted electron transfer was stimulated on cathode. • Consistent 92–95 % CH 4 in biogas with heat-treated stainless-steel cathode. • Methanobacterium and Methanosarcina dominated on cathode. • Mass loss of cathode was controlled at low voltage. • Maximum 59 % soluble organic matter removal was achieved. A key factor in biogas production via bioelectrochemical systems (BES) is the stability of electrodes in long-term operation, especially under limited applied energy and varying levels of organic and inorganic carbon content during wastewater treatment. Heat-treated stainless-steel (HTSS) has emerged as a potent cathode for methane (CH 4 ) production in BES for scaling up the technology. In this study, a BES reactor with HTSS electrodes was operated in on-off voltage conditions at different carbon levels in wastewater to evaluate CH 4 evolution through bioelectrosynthesis and controlled microbial corrosion on cathode. Results demonstrated that a low cathodic potential enriched the biofilm with hydrogenotrophic methanogens as Methanobacterium and Methanosarcina . Despite low current generation at lower applied cathodic voltage, biogas with 92–95 % CH 4 content was achieved. Electrochemical impedance spectroscopy test indicated an increased biofilm capacitance, supporting enhanced carbon dioxide (CO 2 ) reduction to CH 4 . The mass loss rate of cathode reached 3.1·10 −14 mg·cm −2 ·d −1 after 133 days of operation, confirming the durability of HTSS cathode. Controlled microbial corrosion showed positive effect on CH 4 production due to iron mediated electron transfer in energy-limited conditions. These findings strengthen the potential of HTSS cathode as a durable and efficient cathode in scaling up BES reactors for CH 4 production.