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There has been a considerable increment in the atmospheric CO2 concentration, which has majorly contributed to the problem of global warming. This issue can be extenuated by effectively developing microbial electrosynthesis (MES) for the sequestration of CO2 with the concurrent production of biochemical and biofuels. Though the MES technology is in...
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... Increasing global atmospheric CO 2 concentration is a major environmental issue and to mitigate the same, scientists are toiling hard to develop efficient carbon capture and sequestration technologies [1]. Bioelectrochemical CO 2 sequestration through microbial electrosynthesis (MES) is one such futuristic technology, which employs microbes as catalysts to sequester CO 2 and produce multi-carbon organic compounds, primarily acetic acid [2]. The technology of MES is at the embryonic stage and hence, researchers are toiling hard to overcome the hurdle associated with this innovative technology so that it can be efficaciously applied in the field to alleviate real world problems [3]. ...
The embryonic technology of microbial electrosynthesis (MES) possesses the potential to alleviate global CO2 concentration with concomitant recovery of valuables. However, due to the significant bottlenecks of inferior yield of valuables and higher capital cost, its potential has not been fully realized at a larger scale till date. With the aim of bridging this lacuna, a first of its kind pilot-scale MES (PSMES) was designed and operated to yield acetic acid from biogas. The PSMES was able to produce 70.55 g m−2.day of acetic acid in its extraction chamber with the coulombic efficiency of 77.8% for an imposed cathode potential of −1.0 V vs. standard hydrogen electrode. Moreover, life cycle assessment (LCA) and economic analysis of the PSMES was also conducted to elucidate the economic and environmental feasibility of the same. From the LCA and economic analysis of the PSMES, it was inferred that acrylic sheet and carbon felt used during the fabrication of PSMES were the major culprit in terms of both environmental and economic sustainability and thus should be replaced with greener but cost-effective materials. Therefore, these results would guide the budding scholars in designing more economical and environment friendly scaled-up MES, thus paving towards the commercialization of this ingenious technology.
... Typically, MES for CO2 hydrogenation into formate involves two distinct reaction chambers, namely, the abiotic anodic chamber and the biotic cathodic chamber, separated by a proton exchange membrane (PEM) that enables the migration of protons from the anodic to the cathodic compartment. Notably, the anodic chamber can also be biotic, facilitating the microbial oxidation of organic substrates such as acetate, which supplies essential reagents (electrons and protons) for the cathodic reaction [82] . The basic difference between the natural metabolic hydrogenation of CO2 to formate and MES is the supply of electrons and protons. ...
... MES can be categorized into two types based on the electrode process: homogeneous and heterogeneous. Homogeneous systems comprise suspended microorganisms in electrolyte solution, normally in buffer solution, requiring the presence of an electron mediator (commonly known as MET) to facilitate electrical communication between the microorganisms and the electrode because many microorganisms cannot directly accept or donate electrons to the electrode [82] . In contrast, heterogeneous MES setups involve microbial organisms that are either grown or immobilized on the electrode surface, allowing for direct electron transfer (DET) between microorganisms and the electrode. ...
... In contrast, heterogeneous MES setups involve microbial organisms that are either grown or immobilized on the electrode surface, allowing for direct electron transfer (DET) between microorganisms and the electrode. Additionally, hybrid MES for CO2 hydrogenation exhibits a distinct feature from homogeneous or heterogeneous MES configurations, wherein microorganisms or electron mediators can be immobilized on the electrode surface to facilitate the efficient reduction of CO2 into formate [82] . Furthermore, combination homo-and heterogeneous MES may also be applied together in hydrid MES. ...
The increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to the use of fossil fuels, pose a significant threat to the environment and necessitate urgent action to mitigate climate change. Carbon capture and utilization technologies that can convert CO2 into economically valuable compounds have gained attention as potential solutions. Among these technologies, biocatalytic CO2 hydrogenation using bacterial whole cells shows promise for the efficient conversion of CO2 into formate, a valuable chemical compound. Although it was discovered nearly a century ago, comprehensive reviews focusing on the utilization of whole‐cell bacteria as the biocatalyst in this area remain relatively limited. Therefore, this review provides an analysis of the progress, strategies, and key findings in this field. It covers the use of living cells, resting cells, or genetically modified bacteria as biocatalysts to convert CO2 into formate, either naturally or with the integration of electrochemical and protochemical techniques as sources of protons and electrons. By consolidating the current knowledge in this field, this review article aims to serve as a valuable resource for researchers and practitioners interested in understanding the recent progress, challenges, and potential applications of bacterial whole cell catalyzed CO2 hydrogenation into formate.
... Low production yield and difficulty in scaling up the process due to high capital cost are one of the drawbacks of this system (S. Das et al., 2020;Sarkar et al., 2017). ...
Azo dyes are the most commonly produced dyes worldwide, characterized by their distinct azo groups (-N––N-) in their chemical structure. These dyes are xenobiotic and notably resistant to degradation. Approximately 20 % of all water body contamination is caused exclusively by textile effluents, which are released into the environment either deliberately or accidentally, leading to significant environmental toxicity. While numerous physical and chemical treatment methods are available, they each have their own drawbacks. Therefore, this comprehensive review explores the role of various microbes, including bacteria, bacterial consortia, fungi, algae, and lichens, along with their limiting factors. The review also delves into the role of various microbial enzymes and their encoding genes, as well as the molecular mechanisms involved. This study emphasizes the potential of
microbial bioremediation as a cost-effective and eco-friendly tool for treating azo dye-contaminated water, in comparison to other techniques
... Among them, with its high productivity and efficiency, S. ovata is the best biocatalyst for acetate production in MES. 130,131 S. ovata exhibits the highest conversion rates (51.1 g/m 2 /d) in pure culture. 131 Through the development of cathode materials and optimization of MES reactor configuration to increase H 2 availability, 115,117,118 as well as bio-printing of synthetic biofilm to reduce the time for biofilm formation on the electrode, 114,116 acetate production rates and titers have been significantly improved. ...
... 130,131 S. ovata exhibits the highest conversion rates (51.1 g/m 2 /d) in pure culture. 131 Through the development of cathode materials and optimization of MES reactor configuration to increase H 2 availability, 115,117,118 as well as bio-printing of synthetic biofilm to reduce the time for biofilm formation on the electrode, 114,116 acetate production rates and titers have been significantly improved. The highest acetate titer reached 11 g/L 115 , with an outstanding acetate production rate of 1697.6 mmol/m 2 /d from CO 2 ( Table 4). ...
The pressing climate change issues have intensified the need for a rapid transition towards a bio-based circular carbon economy. Harnessing acetogenic bacteria as biocatalysts to convert C1 compounds such as...
... This observation of higher amounts of hydrogen gas associated with increasing current density was 292 previously noted when the applied voltage was increased from 2.5 V to 3. was not a goal of this study, its production rate was still higher than those in many other studies (Bian et 302 al., 2020a; Das et al., 2020;Giddings et al., 2015) due to the efficient cell architecture. 303 ...
... Microbial electrosynthesis (MES) is a bioelectrochemical process in which CO 2 is converted into multi-carbon organic compounds, also referred as the electrocommodities employing anaerobic electrotrophic microbes as biocatalysts [44]. A typical MES consists of a biotic cathodic chamber under anaerobic conditions and an abiotic anodic chamber separated by PEM, which facilitates the migration of protons from the anodic to the cathodic chamber ( Fig. 8.4). ...
... Microbes that are employed in MES to convert CO 2 into electro-commodities are chemolithoautotrophic and can be attached to the cathode as biofilm or can be planktonic or both simultaneously. Generally, direct and mediated electron transfer between microbes and cathode surface takes place for microbes present in the form of biofilm and planktonic cells, respectively [44,45]. Mainly acetogens and methanogens as biocatalysts in the form of both pure and mixed microbial cultures have been extensively explored in MES for converting CO 2 into electro-commodities [46]. ...
... Mainly acetogens and methanogens as biocatalysts in the form of both pure and mixed microbial cultures have been extensively explored in MES for converting CO 2 into electro-commodities [46]. Different pure microbial strains, namely Clostridium and Sporomusa, and mixed microbial culture have been reported in the literature to synthesize organic compounds like acetate, formate, methane, butanol, propanol, etc. [44]. In particular, pure microbial culture leads to the selective production of valuables, while in mixed culture, the formation of side products takes place due to the presence of different microbes in mixed culture by initiating non-targeted reactions. ...
The world today is experiencing adverse effects of climate change due to the escalated levels of greenhouse gases such as CO2 in the atmosphere. Consequently, there is an urgent need for minimizing the CO2 level to tackle climate change. Utilization of CO2 for synthesizing valuable commodities, such as biofuel and biochemical, is an effective strategy toward mitigating climate change as well as the energy crisis. Moreover, the conversion of CO2 into valuable products is also a promising step for achieving carbon neutrality and exemplifying a circular economy. In this regard, several methods, such as physical, chemical, and biological, are available for the utilization and conversion of CO2. However, biological methods for the conversion of CO2 into biofuels and biochemicals are more sustainable as they are environmentally friendly and cost-effective compared to the chemical methods. Thus, in this chapter, different CO2 bioconversion processes with their efficacy and their limitations have been discussed. Besides this, future developments in terms of CO2 bioconversion have also been presented for alleviating the limitations, so that the production of biocommodities from CO2 can be achieved at a large scale.
... The direct supply of electrons and the absence of Fe 2+ may stimulate the generation of EPS, similar to a survival strategy to adapt environmental stresses. It has been reported for other microorganisms that EPS plays a significant role in extracellular electron uptake [86], and it can improve the efficiency of electron transport [87]. This is consistent not only with our transcriptome and metabolome joint analysis data, but also with the SEM image ( Figure 4E). ...
Acidophiles are capable of surviving in extreme environments with low pH. Acidithiobacillus ferrooxidans is a typical acidophilic bacterium that has been extensively studied when grown chemoautotrophically, i.e., when it derives energy from oxidation of Fe²⁺ or reduced inorganic sulfur compounds (RISCs). Although it is also known to grow with electrons supplied by solid electrodes serving as the sole source of energy, the understanding of its electroautotrophic growth is still limited. This study aimed to compare the growth characteristics of A. ferrooxidans under electroautotrophic (ea) and chemoautotrophic (ca) conditions, with an attempt to elucidate the possible mechanism(s) of extracellular electron flow into the cells. Jarosite was identified by Raman spectroscopy, and it accumulated when A. ferrooxidans used Fe²⁺ as the electron donor, but negligible mineral deposition occurred during electroautotrophic growth. Scanning electron microscopy (SEM) showed that A. ferrooxidans possesses more pili and extracellular polymeric substances (EPSs) under electroautotrophic conditions. A total of 493 differentially expressed genes (DEGs) were identified, with 297 genes being down-regulated and 196 genes being up-regulated in ea versus ca conditions. The genes known to be essential for chemoautotrophic growth showed a decreased expression in the electroautotrophic condition; meanwhile, there was an increased expression of genes related to direct electron transfer across the cell’s outer/inner membranes and transmembrane proteins such as pilin and porin. Joint analysis of DEGs and differentially expressed metabolites (DEMs) showed that galactose metabolism is enhanced during electroautotrophic growth, inducing A. ferrooxidans to produce more EPSs, which aids the cells in adhering to the solid electrode during their growth. These results suggested that electroautotrophy and chemoautotrophy of A. ferrooxidans have different extracellular electron uptake (EEU) pathways, and a model of EEU during electroautotrophic growth is proposed. The use of extracellular electrons as the sole energy source triggers A. ferrooxidans to adopt metabolic and subsequently phenotypic modifications.
... This is because stabilizing the pH in a weakly acidic environment provides thermodynamic advantages for converting CO 2 into acetate, enhancing substrate availability for the biocatalyst [162] . Furthermore, maintaining a relatively low pH ensures a reducing environment in the cathode chamber, which favors the synthesis of long-chain compounds [163] . For example, an MES system successfully generated long-chain compounds such as C4 and C6 by regularly injecting gaseous CO 2 to maintain the pH of the catholyte to approximately 5.0 [164] . ...
The consumption of non-renewable fossil fuels has directly contributed to a dramatic rise in global carbon dioxide (CO2) emissions, posing an ongoing threat to the ecological security of the Earth. Microbial electrosynthesis (MES) is an innovative energy regeneration strategy that offers a gentle and efficient approach to converting CO2 into high-value products. The cathode chamber is a vital component of an MES system and its internal factors play crucial roles in improving the performance of the MES system. Therefore, this review aimed to provide a detailed analysis of the key factors related to the cathode chamber in the MES system. The topics covered include inward extracellular electron transfer pathways, cathode materials, applied cathode potentials, catholyte pH, and reactor configuration. In addition, this review analyzes and discusses the challenges and promising avenues for improving the conversion of CO2 into high-value products via MES.
... The current density of the biofilm-driven MES could be enhanced by selecting efficient electroactive bacteria, modification of electrode materials, and optimization of reactor designs. [11][12][13] Through dedicated efforts in the past decade, scientists have made significant progress in maximizing the current density of cathodic biofilm-driven MES, bringing it to the upper bounds observed for electro-active biofilms, ranging from 10 to 100 A/m 2 . 14 In contrast, non-biofilm-driven microbial MES utilizes suspended bacteria and electrolytically generated H 2 to facilitate CO 2 reduction. ...
The low current density impedes the practical application of microbial electrosynthesis (MES) for CO2 fixation. Engineering the reactor design is an effective way to increase the current density, especially for H2-mediated MES reactors. The electrolytic bubble column MES reactor has shown great potential for scaling up, but the mixing and gas mass transfer still need to be enhanced. Here we introduced an inner draft tube to the bubble column to tackle the problem. The addition of draft tube resulted in a 76.6% increase in the volumetric mass transfer coefficient (kLa) of H2 and a 40% increase in the maximum current density (337 A/m2). The computational fluid dynamics (CFD) simulations showed that the addition of draft tube enhanced mixing efficiency by enabling a more ordered cyclic flow pattern and a more uniform gas/liquid distribution. These results indicate that the electro-bubble column reactor with draft tube holds great potential for industrial implementation.
... Acetogenic enrichments and single acetogenic strains have been tested in bioelectrochemical systems. Sporomusa ovata so far leads to the highest conversion rates (51.1 g of acetate m À2 d À1 ) in pure culture (Das et al., 2020;Madjarov et al., 2022), while enrichments are usually dominated by Acetobacterium (Philips, 2020). ...
Acetogens share the capacity to convert H2 and CO2 into acetate for energy conservation (ATP synthesis). This reaction is attractive for applications, such as gas fermentation and microbial electrosynthesis. Different H2 partial pressures prevail in these distinctive applications (low concentrations during microbial electrosynthesis [<40 Pa] vs. high concentrations with gas fermentation [>9%]). Strain selection thus requires understanding of how different acetogens perform under different H2 partial pressures. Here, we determined the H2 threshold (H2 partial pressure at which acetogenesis halts) for eight different acetogenic strains under comparable conditions. We found a three orders of magnitude difference between the lowest and highest H2 threshold (6 ± 2 Pa for Sporomusa ovata vs. 1990 ± 67 Pa for Clostridium autoethanogenum), while Acetobacterium strains had intermediate H2 thresholds. We used these H2 thresholds to estimate ATP gains, which ranged from 0.16 to 1.01 mol ATP per mol acetate (S. ovata vs. C. autoethanogenum). The experimental H2 thresholds thus suggest strong differences in the bioenergetics of acetogenic strains and possibly also in their growth yields and kinetics. We conclude that no acetogen is equal and that a good understanding of their differences is essential to select the most optimal strain for different biotechnological applications.
