Microbial electrosynthesis (MES) from CO2 is resilient to fluctuations in renewable energy supply

Abstract

Microbial electrosynthesis (MES) allow CO2 capture and utilization for the electricity-driven bioproduction of organics such as acetic acid. Such systems can be coupled to any renewable electricity supply, especially those derived from solar and wind energy. However, fluctuations or even absence of electricity may cause damages or changes in the microbial community, and/or affect the performance and robustness of MES. Therefore, the transformation of gaseous CO2 into organic products in a MES was assessed continuously during 120 days of operation. Time-increasing power outages, from 4 h to 64 h, were applied in order to evaluate the effects of electric energy (current) absence on microbial community, organics formation, production rates and product accumulation. Acetic acid was the main product observed before and after the power outages. A maximum titer and production rate of 6965 mg L−1 and 516.2 mg L−1 d−1 (35.8 g m−2 d−1) of acetic acid were observed, respectively. During the absence of power supply, it was observed that acetic acid is oxidized back to CO2 which suggests microbial activity and/or pathway reversal. However, the electro-autotrophic activity recovered after the power gaps, and acetic acid production was restored after reconnecting the energy supply, reaching a current density of −25 A m−2. The microbial community of the biofilm responsible for this behavior was characterized by means of high-throughput sequencing, revealing that Clostridium, Desulfovibrio and Sporomusa accounted for 93% of the total community attached onto the cathodic biofilm. Such resilience of electrotrophic microorganisms reinforces the opportunity to couple bioelectrochemical systems to renewable energy, overcoming the eventual electrical power fluctuations.