Bioelectrochemical systems for energy storage: A scaled-up power-to-gas approach.

• Bioelectrochemical systems can be used as power-to-gas technology for energy storage. • A BES prototype was long-term operated to store electric energy in the form of biomethane. • The prototype produced 4.4 L CH 4 m−2 d−1 with an energy storage efficiency of 42–47%. • Electric behavior of BES prototype was simulated to design its electric converter. • Future research increasing current density demand can lead to positive business case. The development and implementation of energy storage solutions is essential for the sustainability of renewable energy penetration in the electrical system. In this regard, power-to-gas technologies are useful for seasonal, high-capacity energy storage. Bioelectrochemical systems for electromethanogenesis (EMG-BES) represent an additional power-to-gas technology to the existing chemical and biological methanation. EMG-BES process can be retrofitted in traditional anaerobic digesters, with advantages in terms of biologic process stability and high-quality biogas production. Nowadays, there are no reported studies of scaled-up EMG-BES plants for energy storage. The present work describes the setup and operation of a medium-scale EMG-BES prototype for power-to-gas, storing energy in the form of biomethane. The prototype was built by stacking 45 EMG-BES cells, accounting for a total volume of 32 L. It was continuously fed with 10 L day−1 municipal wastewater, and it was long-term operated at different voltage and temperature ranges. A steady-state current density demand of 0.5 A m−2 was achieved at 32 °C while producing 4.4 L CH 4 m−2 d−1 and removing 70% of the initial organic matter present in wastewater. Microbial competition between electro-active bacteria and acetoclastic methanogens was observed. Energy storage efficiency was estimated around 42–47%, analyzing surplus CH 4 production obtained when applying voltage to the stack. A first order electric model was calculated, based on the results of a series of electrical characterization tests. The model may be used in the future to design the converter for EMG-BES plant connection to the electrical grid. The obtained results show that energy storage based on EMG-BES technology is possible, as well as its future potential, mixing renewable power overproduction, biomethane generation and wastewater treatment under the circular economy umbrella. [ABSTRACT FROM AUTHOR]