Enhancing ethanol selectivity in microbial electrosynthesis from CO2 via digital process control

The present work aimed to address the challenges of low efficiency and selectivity that are hindering the industrial adoption of microbial electrosynthesis (MES) for producing ethanol from CO2. To this end, an electrically efficient MES cell with a low-gap stack configuration was operated and subsequently integrated into a bench scale system, enabling full control of the operating parameters to optimize ethanol production. In a preliminary test, low pH values (<5) along with low CO2 partial pressure (< 0.2 atm) were identified as key parameters in triggering solventogenesis. Under these conditions, ethanol was produced with 64% selectivity and 57% coulombic efficiency. This resulted in an ethanol:acetic acid molar ratio exceeding 2.0, a final concentration of 3.35 g L−1 and a production rate up to 1.24 g m−2 d−1. A digital process control was then implemented in the automated bench scale system, setting the pH between 4.5 and 4.7, fixing the dissolved CO2 concentration range between 200 and 800 ppm and the total pressure to either 1.6 or 1.8 atm. Ethanol production rate boosted to 5.69 g m−2 d−1 while maintaining a similar production selectivity. Overall, the present work lays the foundation for the digital transformation of microbial electrosynthesis by showcasing the application of automated control systems to accurately regulate the operational parameters required to optimize ethanol production from CO2.