Improving CH4 production and energy conversion from CO2 and H2 feedstock gases with mixed methanogenic community over Fe nanoparticles

Enhanced carbon dioxide biomethanation with hydrogen using anaerobic granular sludge and metal-organic frameworks: Microbial community response and energy metabolism analysis

In this work, metal-organic frameworks (MOFs) were prepared to evaluate its impact on carbon dioxide (CO₂) biomethanization during anaerobic degradation (AD). The results showed that MOFs significantly improved the CO₂ biomethanation efficiency, especially in the AD reactors using a concentration of 1.0 g/L MOFs. Furthermore, MOFs promoted direct interspecific electron transfer and alleviated the hydrogen competition of bacteria. Meanwhile, hydrogenotrophic methanogens were enriched in the AD reactors with MOFs. After the addition of MOFs, there was 3.28 times and 3.41 times increase in the abundance of metabolic functions related to methanogenesis by CO₂ reduction with hydrogen and dark hydrogen oxidation, respectively. There was an increased abundance of all genes that encode the key enzymes used in methane metabolism. However, functional genes involved in nitrate reduction had their expressions inhibited. The work may offer a contribution to helping the industry achieve the carbon capture and utilization policy.

In-situ biogas upgrading assisted by bioaugmentation with hydrogenotrophic methanogens during mesophilic and thermophilic co-digestion

In this study, the effects of bioaugmentation of typically dominant hydrogenotrophic methanogens to CSTR co-digesting cheese whey and manure, under in-situ biomethanation operations were investigated. Reactors working at mesophilic (37 °C) and thermophilic (55 °C) conditions were independently treated and examined in terms of microbial composition and process dynamics. Addition of Methanoculleus bourgensis in the mesophilic reactor led to a stable biomethanation, and an improved microbial metabolism, resulting in 11% increase in CH₄ production rate. 16S rRNA and biochemical analyses revealed an enrichment in syntrophic and acidogenic species abundance. Moreover, nearly total volatile fatty acids conversion was observed. Differently, Methanothermobacter thermautotrophicus addition in the thermophilic reactor did not promote biogas upgrading performance due to incomplete H₂ conversion and inefficient community adaptation to H₂ excess, ultimately favoring acetoclastic methanogenesis. Bioaugmentation constitutes a viable tool to strengthen in-situ upgrading processes and paves the way to the development of more sophisticated and robust microbial inoculants.

Electron transfer from Geobacter sulfurreducens to mixed methanogens improved methane production with feedstock gases of H2 and CO2

In order to solve problems of poor utilization of H₂ and CO₂ in biomethane conversion with mixed methanogens due to multi-channel competition and nondirectional electron transfer, Geobacter sulfurreducens were cocultured with mixed methanogens to promote oriented metabolic pathway of H₂ and CO₂ to produce CH₄. When inoculation volume ratio of G. sulfurreducens to mixed methanogens was 2:4, CH₄ yield increased to 0.24 mL/ml H₂ (close to the maximum theoretical yield of 0.25 mL/ml H₂) and conversion efficiency of H₂ to CH₄ increased from 72 to 96%. Electrochemical detection and three-dimensional fluorescence spectra showed that the co-culture system had an increased metabolic capacity and spectral intensity of fulvic acid-like compounds was enhanced, which mediated direct interspecific electron transfer to produce CH₄. The 16S rRNA gene sequencing showed that relative abundance of G. sulfurreducens and Methanoculleus increased, indicating an established syntrophic relationship between G. sulfurreducens and Methanoculleus.

Reactor Designs and Configurations for Biological and Bioelectrochemical C1 Gas Conversion: A Review

Microbial C1 gas conversion technologies have developed into a potentially promising technology for converting waste gases (CO₂, CO) into chemicals, fuels, and other materials. However, the mass transfer constraint of these poorly soluble substrates to microorganisms is an important challenge to maximize the efficiencies of the processes. These technologies have attracted significant scientific interest in recent years, and many reactor designs have been explored. Syngas fermentation and hydrogenotrophic methanation use molecular hydrogen as an electron donor. Furthermore, the sequestration of CO₂ and the generation of valuable chemicals through the application of a biocathode in bioelectrochemical cells have been evaluated for their great potential to contribute to sustainability. Through a process termed microbial chain elongation, the product portfolio from C1 gas conversion may be expanded further by carefully driving microorganisms to perform acetogenesis, solventogenesis, and reverse β-oxidation. The purpose of this review is to provide an overview of the various kinds of bioreactors that are employed in these microbial C1 conversion processes.