Microbial electrosynthesis of industrially viable chemicals from carbon dioxide and electricity

This master thesis reflected the work done during the internship at Laboratory of Chemical and Environmental Engineering (LEQUIA), a research group of the University of Girona. The research study dealt with biotechnological platforms for CO2 recycling and valorization. In two lab-scale H-type reactors industrially valuable chemicals were produced through microbial electrosynthesis (MES), using only carbon dioxide and electricity. The work was focused on investigating conditions and experimental parameters triggering chain elongation process in MES applications. Plus, the effect of several factors (applied potential, hydraulic retention time and CO2 loading rate) on MES performance was tested. The reactors were run in a three-electrode configuration and connected to a potentiostat. The energy provided to the anode induced water oxidation reaction, which generated the electrons and protons required for the cathodic CO2 reduction into organics catalyzed by microbial cells. In this study, significant acetogenic and solventogenic activity was detected, as well as chain elongation production. The highest concentrations obtained for ethanol, acetic, butyric and caproic acid were 5.28, 12.90, 1.32 and 1.28 g L-1, respectively. For both systems the maximum productivity phase was observed when low nutrient availability was present in the bulk liquid, while CO2 loading rate and applied potential did not represent limiting factors for the overall MES performance. Moreover, the results obtained validated several observations discussed in reference works regarding solventogenic optimal conditions and the influence of production trends on current signal. Finally, the parameters tested in this work showed potential for increasing MES productivity and further combinations should be investigated for the optimization of MES technology towards the production of higher-value organic compounds.