Development of membrane bioreactor for conversion of flue Gas-CO2 to C1 and C2 biomolecules

• Novel membrane bioreactor produces acetate and methane from flue gas-CO 2. • Bio-inhibition of capture agent was eliminated, increasing the potential of BICCU. • CO 2 conversion rate was 92% of rates when CO 2 was supplied as gas from headspace. • Biological enhancement of the CO 2 flux across the membrane by a factor of 3.1 ± 0.3. The capture and utilization of CO 2 (CCU) from flue gases constitute a novel carbon feedstock for producing renewable chemicals and fuels. To lower the energy demand of CCU, Bio-Integrated Carbon Capture and Utilization (BICCU) was recently presented, where CO 2 -consuming microorganisms simultaneously desorb and convert CO 2 captured from flue gas by methyl diethanolamine (MDEA) with H 2 from water-electrolysis as the electron donor. The limiting factor is the microbial toxicity of MDEA, which restricts the capacity of the process. Furthermore, producing soluble molecules like the C2 platform molecule acetate is not possible without contaminating the product with capture agent. To resolve both challenges, we here propose a three-phase membrane system, where the MDEA and microorganisms are separated by a CO 2 -permeable membrane. Biological batch experiments with a mixed mesophilic culture confirmed the increased capacity of the BICCU-process for producing both methane and acetate when introducing a CO 2 -permeable membrane to the system to alleviate microbial inhibition by the capture agent and avoid contamination of soluble bioproducts. When using O 2 -rich flue gas from a biogas combustion engine, the CO 2 conversion rate decreased by 18.0 % compared to a clean 20:80 CO 2 :N 2 gas mixture, yet anaerobic metabolisms were still active in the mixed inoculum. Abiotic experiments furthermore showed that the microbial CO 2 consumption maintained the gradient across the membrane and enhanced the CO 2 -flux by a factor of 3.1 ± 0.3. The membrane-based BICCU concept is expected to hold great promise particularly for producing acetate from flue gas-CO 2 , as the in situ separation eliminates the need for costly downstream separation.