Search

Graphical abstract Highlights • The acetate production rate with fluidized GAC was 2.8 times that of control. • Fluidized GAC provide a high electrode surface and a favorable mass transport. • Fluidized GAC likely promoted the enrichment of electrochemically active bacteria. • Fluidized GAC electrode is a promising strategy to improve MES efficiency. Abstract The electricity-driven bioreduction of carbon dioxide to multi-carbon organic compounds, particularly acetate, has been achieved in microbial electrosynthesis (MES). MES performance can be limited by the amount of cathode surface area available for biofilm formation and slow substrate mass transfer. Here, a fluidized three-dimensional electrode, containing granular activated carbon (GAC) particles, was constructed via MES. The volumetric acetate production rate increased by 2.8 times through MES with 16 g L−1 GAC (0.14 g L−1 d-1) compared with that of the control (no GAC), and the final acetate concentration reached 3.92 g L−1 within 24 days. Electrochemical, scanning electron microscopy, and microbial community analyses suggested that GAC might improve the performance of MES by accelerating direct and indirect (via H 2) electron transfer because GAC could provide a high electrode surface and a favorable mass transport. This study attempted to improve the efficiency of MES and presented promising opportunities for MES scale-up. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal organic frameworks (MOFs) significantly promote CO 2 biomethanation with H 2. • MOFs promote direct interspecific electron transfer between microorganisms. • Hydrogenotrophic methanogens were enriched in the anaerobic reactors with MOFs. • MOFs alleviated the hydrogen competition of bacteria. • MOFs increase the abundance of functional gene for CO 2 biomethanation with H 2. In this work, metal–organic frameworks (MOFs) were prepared to evaluate its impact on carbon dioxide (CO 2) biomethanization during anaerobic degradation (AD). The results showed that MOFs significantly improved the CO 2 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 CO 2 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. [ABSTRACT FROM AUTHOR]

Background: Microbial electrosynthesis (MES) is a biocathode-driven process, in which electroautotrophic microorganisms can directly uptake electrons or indirectly via H2 from the cathode as energy sources and CO2 as only carbon source to produce chemicals. Results: This study demonstrates that a hydrogen evolution reaction (HER) catalyst can enhance MES performance. An active HER electrocatalyst molybdenum carbide (Mo2C)-modified electrode was constructed for MES. The volumetric acetate production rate of MES with 12 mg cm−2 Mo2C was 0.19 ± 0.02 g L−1 day−1, which was 2.1 times higher than that of the control. The final acetate concentration reached 5.72 ± 0.6 g L−1 within 30 days, and coulombic efficiencies of 64 ± 0.7% were yielded. Furthermore, electrochemical study, scanning electron microscopy, and microbial community analyses suggested that Mo2C can accelerate the release of hydrogen, promote the formation of biofilms and regulate the mixed microbial flora. Conclusion: Coupling a HER catalyst to a cathode of MES system is a promising strategy for improving MES efficiency. [ABSTRACT FROM AUTHOR]

The effects of N 2 , CO 2 and H 2 O dilutions on the two-dimensional (2D) temperature and concentration fields of OH in methane Bunsen flames were investigated by employing two-line planar laser-induced fluorescence (PLIF) thermometry and bi-directional PLIF technique, respectively. The spatial resolution of the measured temperature and concentration fields of OH radical was 41.7 μm. It was found that the measured temperature fields in methane Bunsen flames with different diluents exhibited a non-uniform and a symmetrical structure. In terms of decreasing the flame temperature, the CO 2 diluent achieved a good result compared with N 2 and H 2 O diluents. The total uncertainties in PLIF thermometry measurements were estimated to be ±8.44%, ±8.17% and ±8.27% for each diluent, respectively. The OH peak absorption cross sections at different heights were obtained in methane Bunsen flames with different diluents. Finally, the 2D absolute OH concentration filed in methane Bunsen flames diluted with three different diluents were obtained by using bi-directional PLIF technique. The peak absolute OH number densities in the flames with H 2 O, N 2 and CO 2 diluents were 9.84 × 10 17 cm −3 , 8.57 × 10 17 cm −3 and 7.84 × 10 17 cm −3 , with the overall uncertainties of ±20.56%, ±19.04% and ±23.43%, respectively. The numerical simulations of chemical kinetics were performed by using a physical model of one-dimensional laminar premixed flame and a detail methane reaction mechanism of GRI-Mech 3.0 so as to investigate the difference between the simulation results and experimental values. The comparison results for the temperature and OH concentration indicated that the reaction mechanism of GRI-Mech 3.0 might underestimate the chemical effects of CO 2 and H 2 O diluents on the production of OH radical in premixed methane flames. [ABSTRACT FROM AUTHOR]