Coupling of CO2 Electrolysis with Parallel and Semi-Automated Biopolymer Synthesis – Ex-Cell and without Downstream Processing

Abstract

Important improvements have been achieved in developing the coupling of electrochemical CO₂ reduction to formate with its subsequent microbial conversion to polyhydroxybutyrate (PHB) by Cupriavidus necator. The CO₂ based formate electrosynthesis was optimised by electrolysis parameter adjustment and application of Sn based gas diffusion electrodes reaching almost 80 % Faradaic efficiency at 150 mA cm⁻². Thereby, catholyte with the high formate concentration of 441±9 mmol L⁻¹ was generated as feedstock without intermediate downstream processing for semi-automated formate feeding into a fed-batch reactor system. Moreover, microbial formate conversion to PHB was studied further, optimised, and successfully scaled from shake flasks to semi-automated bioreactors. Therein, a PHB per formate ratio of 16.5±4.0 mg g⁻¹ and a PHB synthesis rate of 8.4±2.1 mg L⁻¹ OD⁻¹ h⁻¹ were achieved. By this process combination, an almost doubled overall process yield of 22.3±5.5 % was achieved compared to previous reports. The findings allow a detailed evaluation of the overall CO₂ to PHB conversion, providing the basis for potential technical exploitation.