Enhanced CO2 fixation by a non-photosynthetic microbial community under anaerobic conditions: optimization of electron donors

Optimization of Magnetic Biochar Preparation Process, Based on Methylene Blue Adsorption

The search for low-cost and effective adsorbents for the removal of organic dyes from contaminated water is urgently needed. The substantial amount of waste mushroom cultivation substrates generated in practical production can serve as an ideal material for the preparation of adsorbents. In this study, we investigated the main control parameters affecting the performance of magnetic mushroom substrate biochar and optimized the process of preparing biochar by using the Plackett-Burman and central composite design methods. Various analytical techniques including SEM, EDX, BET, and VSM were used to characterize the biochar. The results indicate that the carbonization temperature had the most significant impact on the yield and adsorption performance of biochar. Under the conditions of a carbonization temperature of 600 °C, a carbonization retention time of 1 h, and an impregnation ratio of 0.1, the yield and methylene blue adsorption value of magnetic biochar were 42.54% and 2297.04 μg/g, respectively, with a specific surface area of 37.17 m2/g. This biochar effectively removed methylene blue from the solution, demonstrating a high economic efficiency for wastewater treatment and pollution control. Furthermore, the adsorption-desorption cycle studies revealed its excellent stability and reusability. Additionally, based on the response surface methodology, a three-dimensional surface model of the adsorption performance of magnetic biochar under different carbonization conditions was established, providing a theoretical basis for the preparation of magnetic biochar from agricultural wastes.

Effect of electron donors on CO2 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 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.

Key internal factors leading to the variability in CO2 fixation efficiency of different sulfur-oxidizing bacteria during autotrophic cultivation

Variability in the apparent CO₂ fixation yield of four aerobic sulfur-oxidizing bacteria (Halothiobacillus neapolitanus DSM 15147, Thiobacillus thioparus DSM 505, Thiomonas intermedia DSM 18155, and Starkeya novella DSM 506) in autotrophic culturing was studied, and mutual effects of key intrinsic factors on CO₂ fixation were explored. DSM 15147 and DSM 505 exhibited much higher CO₂ fixation yields than DSM 18155 and DSM 506. The differences in CO₂ fixation yield were determined not only by cbb gene transcription, but also by cell synthesis rate, which was determined by rRNA gene copy number; the rRNA gene copy number had a more significant effect than cbb gene transcription on the apparent CO₂ fixation yield. Moreover, accumulation of EDOC was observed in all four strains during chemoautotrophic cultivation, and the proportion of EDOC accounting for total fixed organic carbon (TOC; EDOC/TOC ratio) was much higher in DSM 18155 and DSM 506 than in DSM 15147 and DSM 505. The accumulation of EDOC led to a significant decrease in the cbb gene transcription efficiency during cultivation, and a further feedback inhibitory effect on CO₂ fixation.

Performance and mechanism of carbon dioxide fixation by a newly isolated chemoautotrophic strain Paracoccus denitrificans PJ-1

CO₂ is regarded as a major contributor to the global warming. CO₂ utilization is promising to reduce the CO₂ emissions. Currently, the biofixation of CO₂ using chemoautotrophs has markedly gain interest in CO₂ utilization. In this study, a newly isolated chemoautotroph, Paracoccus denitrificans PJ-1, was used for the biofixation of CO₂ under anaerobic condition. Experimental results revealed that Paracoccus denitrificans PJ-1 achieved a high carbon fixation rate (13.25 mg·L^-1·h^-1) which was ∼10 times faster than the previous reported chemotrophic bacteria using thiosulfate as electron donor. The best CO₂ fixation activity of Paracoccus denitrificans PJ-1 was achieved at the pH value of 9.0 and CO₂ concentration of 20 vol%. Meanwhile, a high CO₂ fixation yield of 106.03 mg·L^-1 was reached. The presence of oxygen was adverse to the biofixation, indicating that strain PJ-1 was more suitable for CO₂ fixation in anaerobic environments. Carbon mass balance analysis revealed that the carbon from CO₂ was mainly fixed into the extracellular organic carbon rather than the biomass. GC-MS analysis and cbbL gene test revealed that Paracoccus denitrificans PJ-1 fixed CO₂ through the Calvin-Benson-Bassham cycle and mainly converted CO₂ to oxalic acid and succinic acid. Overall, the excellent CO₂ fixation capacity of Paracoccus denitrificans PJ-1 suggests that it had potential for CO₂ utilization.

Inhibitory effect of organic carbon on CO₂ fixing by non-photosynthetic microbial community isolated from the ocean

The inhibitory effect of organic carbon on CO(2) fixation (CF) by the non-photosynthetic microbial community (NPMC) and its mechanism were studied. The results showed that different concentrations of glucose inhibited CF to some extent. However, when these microorganisms pre-cultured with glucose were re-cultured without organic carbon, their CF efficiency differed significantly from the control based on the glucose concentration in the pre-culture. ATP as bioenergy and NADH as reductant had no obvious inhibitory effect on CF; conversely, they improved CF efficiency to some extent, especially when both were present simultaneously. These results implied that not all organic materials inhibited CF by NPMC, and only those that acted as good carbon sources, such as glucose, inhibited CF. Moreover, some metabolites generated during the catabolism of glucose by heterotrophic metabolism of NPMC might inhibit CF, while other cumulated materials present in the cell interior, such as ATP and NADH, might improve CF.