Effect of electron donors on CO2 fixation from a model cement industry flue gas by non-photosynthetic microbial communities in batch and continuous reactors

Abstract

The aim of this work was to evaluate the effect of different inorganic compounds as electron donors for the capture of CO₂ from a model cement flue gas CO₂ /O₂ /N₂ (4.2:13.5:82.3% v/v) using a non-photosynthetic microbial community. The inoculum obtained from a H₂ -producing reactor was acclimated to CO₂ consumption achieving 100% of CO₂ removal after 45 days. Na₂ S, MnCl₂ , NaNO₂ , NH₄ Cl, Na₂ S₂ O₃ , and FeCl₂ were used as energy source for CO₂ fixation by the acclimated microbial community showing different efficiencies, being Na₂ S the best electron donor evaluated (100% of CO₂ consumption) and FeCl₂ the less effective (28% of CO₂ consumption). In all treatments, acetate and propionate were the main endpoint metabolites. Moreover, scaling the process to a continuous laboratory biotrickling filter using Na₂ S as energy source showed a CO₂ consumption of up to 77%. Analysis of the microbial community showed that Na₂ S and FeCl₂ 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 CO₂ fixing pathways used by the microbial community in all treatments were the 3-hydroxypropionate-4-hydroxybutyrate cycle and the Wood-Ljungdahl pathway.

FIGURE 1

Schematic overview of the biotrickling filter reactor (modified from Muñoz‐Páez & Buitrón, 2022). Blue lines indicate the gas flow, and red lines indicate the aqueous phase flow.

FIGURE 2

(A) Kinetics of CO₂ and O₂ consumption and (B) metabolite production during the acclimation of the inoculum to CO₂ fixation. Arrows represent the addition of gas and electron donor.

FIGURE 3

Effect of different inorganic electron donors on CO₂ fixation. (A) CO₂ and O₂ consumption, and (B) metabolite production in each treatment. The red (CO₂) and blue (O₂) horizontal lines represent 100% of gas available. Means not sharing any letters are significantly different (p < 0.05). Letters a‐d correspond to CO₂ consumption, and letters from e‐h correspond to O₂ consumption.

FIGURE 4

(A) Non‐metric multidimensional scaling (nMDS) ordination of microbial communities of treatments using different electron donors based on the Bray–Curtis dissimilarity. (B) Chao 1 and (C) Shannon diversity estimators for the microbial communities. Means not sharing any letters are significantly different (p < 0.05). (D) Relative abundance of the most significant taxa from each microbial community according to the similarity percentages (SIMPER) analysis. On the horizontal axis, the name of each electron donor followed by the replicate number.

FIGURE 5

Canonical correspondence analysis (CCA) showing the ordination of taxa, gas consumption, and metabolites produced during carbon fixation.

FIGURE 6

Kinetics of CO₂ and O₂ consumption during the operation of the biotrickling filter reactor. Grey arrows represent the addition of 30 mM Na₂S, and black arrows represent the addition of 70 mM Na₂S.