Feasibility of a Two-Step Culture Method to Improve the CO2-Fixing Efficiency of Nonphotosynthetic Microbial Community and Simultaneously Decrease the Spontaneous Oxidative Precipitates from Mixed Electron Donors

Abstract

When compared with H2, mixed electron donors (MED), comprising S(2-), S2O3 (2-), and NO2 (-), could generally improve the CO2-fixing efficiency of nonphotosynthetic microbial communities (NPMCs). However, a large amount of abiotic precipitates combined with bacteria produced during culture may be unfavorable for the recycling and reuse of bacteria. The main component of the abiotic precipitates is S(0), which influences the enrichment and reuse of bacteria but is not conducive for CO2 fixation in the subsequent step. In this study, a two-step culture method (TSCM), employing H2 and MED, respectively, was verified to be feasible for improving the CO2-fixing efficiency of NPMCs in the second step. In the TSCM, the net-fixed CO2 increased to 854 mg/L and abiotic precipitates were not produced in the medium. Sequence analysis of 16 s rDNA from NPMC indicated the presence of microbial symbioses in the NPMC, supporting the possible applications of TSCM.

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

“…Again, after this period, 70 Na 2 S was supplemented to the medium achieving a high CO 2 consumption of 56%, however, after this, the consumption of both CO 2 and O 2 was disturbed, which can be possibly attributed to the accumulation of abiotic precipitates produced during sulfide oxidation. This phenomenon has also been reported by other authors; for instance, Hu, Wang, Zhang, Le, and Fu (2014) observed the accumulation of precipitates when using Na 2 S as electron donor, the authors reported that these precipitates affected negatively the CO 2 fixation by a marine microbial community, making difficult the cell recirculation and decreasing the CO 2 fixation efficiency. Interestingly, in this study, after the disturbance of gas consumption, CO 2 consumption was restored by Day 19, showing an increasing CO 2 consumption reaching its highest value of 77%.…”

“…For instance, Hu et al. ( 2010a ) reported the use of a gas mixture containing air/CO 2 (80:20% v/v) as substrate for a marine microbial community. The authors evaluated the effect of different electron donors and showed that the use of Na 2 S, Na 2 S 2 O 3 and NaNO 2 increased the CO 2 fixation 100%, 200% and 200%, respectively.…”

“…However, these studies often evaluate unrealistic gas mixtures, with compositions not typically found in waste streams emitted by the cement industry. For instance, Hu et al (2010a) and Hu, Wang, Zhang, Le, and Fu (2014) evaluated the effect of Na 2 S, Na 2 S 2 O 3 and NaNO 2 on the CO 2 fixation under aerobic conditions (air/CO 2 , 80:20% v/v; H 2 /O 2 / CO 2 , 80:10:10% v/v) using marine non-photosynthetic microbial communities. Similarly, Wang et al (2017) assessed the influence of Na 2 S 2 O 3 on carbon fixation by Halothiobacillus neapolitanus from a gas containing CO 2 /O 2 (10:21%).…”

“…For instance, Hu et al. ( 2010a ) and Hu, Wang, Zhang, Le, and Fu ( 2014 ) evaluated the effect of Na 2 S, Na 2 S 2 O 3 and NaNO 2 on the CO 2 fixation under aerobic conditions (air/CO 2 , 80:20% v/v; H 2 /O 2 /CO 2 , 80:10:10% v/v) using marine non‐photosynthetic microbial communities. Similarly, Wang et al.…”