Augmenting succinic acid production by bioelectrochemical synthesis: Influence of applied potential and CO2 availability

Abstract

Bioelectrochemical synthesis offers a promising solution to transform organic and inorganic carbon to high-value added products using microorganisms under a constant applied potential (AP). In the present study, Citrobacter amalonaticus a facultative anaerobic bacterium exhibited its applicability as a biocatalyst in a bioelectrochemical system (BES) for the production of a reduced end product, succinic acid (SA). Influence of decreasing AP from −0.7 to −0.9 V (vs. Ag/AgCl) on SA production was evaluated and external applied potential induced significant enhancement in SA concentration. Highest SA production of 14.4 gL-1 was observed at an AP of −0.8 V and a further increase in AP led to a decrement in SA concentration. Reductive catalytic currents obtained in chronoamperometry analysis allowed to further acknowledge the influence of AP on electrocatalytic activity and product formation. BES system was comparatively evaluated with a control system (FControl) lacking electrode assembly and 1.29 fold increment in SA production was observed in BES system. Since CO2 is fixed during SA formation, the influence of its availability on SA yield was studied. Absence of CO2 resulted in the formation of higher acetic acid (6.34 gL−1) and lactic acid (6.13 gL−1), revealing a direct dependency of SA production on availability of CO2. In addition, use of carbonate as a source of CO2 was also investigated and positive effect on SA concentration (13.6 gL−1) was observed. The results suggest that electro fermentative approach could be employed to steer the distribution of reduced metabolic products, which are obtained through valorization of organic substrates and sequestration of CO2, via potentiostatic regulation of redox potential.