I. Dinges, I. Depentori, L. Gans, D. Holtmann, S. R. Waldvogel, M. Stöckl
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.
