Effect of electron donors on CO 2 fixation from a model cement industry flue gas by non-photosynthetic microbial communities in batch and continuous reactors.

The aim of this work was to evaluate the effect of different inorganic compounds as electron donors for the capture of CO 2 from a model cement flue gas CO 2 /O 2 /N 2 (4.2:13.5:82.3% v/v) using a non-photosynthetic microbial community. The inoculum obtained from a H 2 -producing reactor was acclimated to CO 2 consumption achieving 100% of CO 2 removal after 45 days. Na 2 S, MnCl 2 , NaNO 2 , NH 4 Cl, Na 2 S 2 O 3 , and FeCl 2 were used as energy source for CO 2 fixation by the acclimated microbial community showing different efficiencies, being Na 2 S the best electron donor evaluated (100% of CO 2 consumption) and FeCl 2 the less effective (28% of CO 2 consumption). In all treatments, acetate and propionate were the main endpoint metabolites. Moreover, scaling the process to a continuous laboratory biotrickling filter using Na 2 S as energy source showed a CO 2 consumption of up to 77%. Analysis of the microbial community showed that Na 2 S and FeCl 2 exerted a strong selection on the microbial members in the community showing significant differences (PERMANOVA, p = 0.0001) compared to the control and the other treatments. Results suggest that the CO 2 fixing pathways used by the microbial community in all treatments were the 3-hydroxypropionate-4-hydroxybutyrate cycle and the Wood-Ljungdahl pathway.