Steering acidogenesis towards selective propionic acid production using co-factors and evaluating environmental sustainability

The major challenge faced during acidogenic fermentation is the specificity in production of an individual biochemical in the fermentation broth. The production of biochemicals with special focus on propionic acid (H-Pr) during acidogenic fermentation experiment was studied using cobalt (Co) and zinc (Zn) divalent ions as cofactors individually and synergistically in eleven different systems (RC1, RC2, R-1-R-7, R-Co and R-Zn). Further, to check the feasibility of H-Pr production at higher scale, the two scale up systems (R-SU1 and R-SU2) were operated with the best observed condition. Life cycle assessment (LCA) was also performed using the results pertaining to the best scale up bioreactor (R-SU2). Supplementation of Co2+ and Zn2+ synergistically enhanced the H(Pr )fraction among other acids in the acidogenic fermentation at their respective optimum concentrations. Biosystem R-2 and its respective scale up reactor (R-SU2) with Co2+/Zn2+ concentration of 0.10/0.16 mM depicted highest H-Pr concentration of 1.03 +/- 0.05 g/L and 1.22 +/- 0.06 g/L, respectively. Although control operated without Co2+/Zn2+ supplementation showed higher total volatile fatty acid (VFA) (3.02 +/- 0.15 g/L) production, H-Pr fraction was observed to be lower in the system. The presence of peaks identified on voltammetric signature corresponding to redox mediator fumarate reductase (+ 0.030 V) and hydrogenase (2H(+)/H-2) (+ 0.421 V) supported higher titres of H-Pr in R-1 (Co2+/Zn2+ : 0.01/0.06 mM) and R-2. Life cycle assessment (LCA) carried out on the performance of H-Pr production (R-SU2) depicted process sustainability with lesser environmental impacts. The results further supported that Co2+/Zn2+ synergistically can drive selective acidogenic fermentation towards H(Pr )production.