Optimization of simultaneous wastewater treatment and methane recovery via tubular upflow bioelectrochemical reactor outfitted with heat-treated steel electrodes.

• Simultaneous methane production and wastewater treatment were tested. • More than 90% methane concentration resulted from upflow bioelectrochemical reactor. • Maximum 40.7% SCOD removal was obtained. • Heat-treated steel electrodes show potential for long-term methane recovery. Bioelectrochemical systems (BES) have gained widespread attention for environmental remediation and biosynthesis of various products. However, scaling up BES faces challenges related to the electrode lifespan and system stability. Steel electrodes are shown to be a cost-effective alternative with good biocompatibility, but require corrosion control for their durability. This study investigated heat-treated steel cathode for efficient biogas recovery from wastewater treatment, and assessed the performance of heat-treated steel as anode material in the system. An experiment in a tubular upflow BES reactor was executed in two phases with the aim of optimizing the operational conditions, and perform the optimal parameters to increase the methane (CH 4 ) content in biogas, and ensure stable CH 4 production for a longer period of operation. Despite initial challenges, such as abrupt anodic corrosion in the initial stage of phase 1, the final stage of phase 1 resulted in up to 97 % CH 4 content in biogas. Increasing the voltage to -0.8 V vs. SHE, led to dominance of acetic acid production up to 1160 mg · L − 1 . Application of -0.6 V vs. SHE in phase 2, resulted in 14.93 L · L − 1 · m cat − 2 · d − 1 biogas recovery, containing higher than 90 % CH 4 , which is the highest amount achieved with HTSS316 cathode. A maximum 40.73 % SCOD removal was obtained with the upflow BES reactor, while protecting anode from corrosion. The microbial analysis showed that Clostridia and Methanobacterium dominated in the microbial community. This research highlights critical insights for optimizing surface modified steel electrodes in BES, displaying their potential for efficient wastewater treatment and CH 4 recovery in long term operation.