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(a) Thermogravimetric (TG) profiles of various electrodes studied and (b) the corresponding derivative thermogravimetric curves (DTG).
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The electrode material is one of the key components of a bioelectrochemical system (BES) as the biocatalyst or the electroactive biofilm will develop on this base material and hence plays a pivotal role in regulating the type and rate of electron transfer processes and bioelectrochemical conversions. Microbial electrosynthesis (MES) requires biocom...
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... points per logarithmic decade were taken. The previously referred N'Stat box (Bio-logic) was used to simultaneously connect, polarize, and monitor all the eight working electrodes in the electrochemical cell ( Fig. 2), including the frequency response analysis. The electrochemical system was confirmed for linearity, causality, finiteness, and stability, as described in Dominguez-Benetton et al. (2012). Stability was defined as per variations in current lower than ±10 [[ in a period of 1 h, immediately before the EIS run. Each EIS run took about 53 ...
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... thermal resistance of the electrode materials showed different trends as a function of the presence of functional groups on their surface. E1, E5, E6, E7 and E8 showed one single major degradation, with a maximum in the rate of mass loss (peak in DTG) at relatively high temperatures: 617 C for E5, accounting for a mass loss of 72%; 656 C for E6, accounting for a mass loss of 99%; 696C for E8, accounting for a mass loss of 98%; 600 C for E7, accounting for a mass loss of 72%; and >800 C for E8 (the degradation step was not completed when the upper temperature limit of 800 C had been reached), accounting for a mass loss of 52% ( Figure 2, Table 2). ...
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... the case of E2, a carbon-PTFE composite, two different degradation steps can be distinguished in the DTG traces ( Figure 2b, Table 2). The first degradation step, with a maximum in the rate of mass loss at ca. 540 C, would be mainly related to the decomposition of the PTFE component (through unzipping to tetrafluoroethylene monomer) and to the degradation of functional groups, most likely carboxylic acid groups (Schild, 1993;Figueiredo et al., 1999;Szymanski et al., 2002) and other acid moieties. ...
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... also showed two different degradation steps ( Figure 2, Table 2). The first step, with a peak in DTG at 356 C, may be Please do not adjust margins ...
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... discussed in previous sections, the bacterial settlement on the electrode surface is favored by a surface roughness close to the size of the microbial cells. For instance, electrode E2 shows more dense cell packing than the other electrodes with a roughness factor R a of 1.33 [ which roughly corresponds to the microbial cell size, as can be observed from the SEM results ( Figure SI S2.3). ...
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Electromicrobiology is an emerging field investigating and exploiting the interaction of microorganisms with insoluble electron donors or acceptors. Some of the most recently categorized electroactive microorganisms became of interest to sustainable bioengineering practices. However, laboratories worldwide typically maintain electroactive microorga...
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... However, the application of mixed culture microbes as biocatalyst in MES is mostly preferred as it can be easily implicated at the field-scale. Besides electrotrophic microbes, the type of cathode material also affects the performance of MES since it acts as electron donor for the electrotrophic microbes [47]. Hence, biocompatible cathode possessing a high surface area and high conductivity is desirable for application in MES [45]. ...
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.
... These advanced integrative processes could increase the cumulative wastewater treatment with a stage-wise approach, reducing chemical/reagent usage along with lowering the costs for operational feasibility as compared to conventional AOPs [16,17,41]. Though electrochemical processes have benefits in industrial wastewater treatment, the need to optimize the operational parameters and electrode materials in specified combinations to design a reactor raises the estimated costs for application feasibility [10]. Hence, future research could focus on utilizing biological and renewable energy interventions in electrochemical processes for application to industrial wastewater treatment to decrease the overall environmental impact. ...
... Anodic biofilm attachment and microbial community entities in relation to the synergy with the electrode play a crucial role in complex (pollutants/contaminants/toxins/metals) treatment by metabolically biocatalyzed electrochemical oxidation [61]. Anodic complex degradation in BET usually takes place by the mechanisms of direct anodic oxidation (DAO) and indirect anodic oxidation (IAO) processes [10,20]. DAO involves microbial metabolism utilizing simple organic molecules for electron (e − ) and proton (H + ) production, creating a gradient through their movement to the electrode surface and in situ biopotential generation [7]. ...
... Hence, the electrochemical integration of these biological processes using conductive materials and electron flux regulation is a necessity to enhance their productivity. The presence of electron-withdrawing groups on the surface of conducting materials effectively promotes electron transfer, thereby crucially contributing to surface-catalyzed bioelectrochemical reactions [10]. A porous and amenable surface morphology is crucial for biofilm formation, which encourages bioelectrochemical reduction reactions [77,88]. ...
Advancements in biological wastewater treatment with sustainable and circularity approaches have a wide scope of application. Biological wastewater treatment is widely used to remove/recover organic pollutants and nutrients from a diverse wastewater spectrum. However, conventional biological processes face challenges, such as low efficiency, high energy consumption, and the generation of excess sludge. To overcome these limitations, integrated strategies that combine biological treatment with other physical, chemical, or biological methods have been developed and applied in recent years. This review emphasizes the recent advances in integrated strategies for biological wastewater treatment, focusing on their mechanisms, benefits, challenges, and prospects. The review also discusses the potential applications of integrated strategies for diverse wastewater treatment towards green energy and resource recovery, along with low-carbon fuel production. Biological treatment methods, viz., bioremediation, electro-coagulation, electro-flocculation, electro-Fenton, advanced oxidation, electro-oxidation, bioelectrochemical systems, and photo-remediation, are summarized with respect to non-genetically modified metabolic reactions. Different conducting materials (CMs) play a significant role in mass/charge transfer metabolic processes and aid in enhancing fermentation rates. Carbon, metal, and nano-based CMs hybridization in different processes provide favorable conditions to the fermentative biocatalyst and trigger their activity towards overcoming the limitations of the conventional process. The emerging field of nanotechnology provides novel additional opportunities to surmount the constraints of conventional process for enhanced waste remediation and resource valorization. Holistically, integrated strategies are promising alternatives for improving the efficiency and effectiveness of biological wastewater treatment while also contributing to the circular economy and environmental protection.
... The anode can act as an electron mediator, which will help to optimize electro-fermentation performance [33]. Similar to other BES technologies, carbon-based materials are the most widely used to prepare the electrodes due to their porosity, high surface area and conductivity, which favors redox reactions, good biocompatibility, which promotes biofilm growth, and their lower cost compared to metal-based electrodes [34]. The following sections comprise the most common reactor designs used to bioelectrochemically produce different types of biogases and/or organic acids which include the reactor configuration, electrode material, type of membrane, nature of the substrate and inoculum as well as the type of polarization of the electrodes. ...
The energy crisis and climate change are two of the most concerning issues for human beings nowadays. For that reason, the scientific community is focused on the search for alternative biofuels to conventional fossil fuels as well as the development of sustainable processes to develop a circular economy. Bioelectrochemical processes have been demonstrated to be useful for producing bioenergy and value-added products from several types of waste. Electro-fermentation has gained great attention in the last few years due to its potential contribution to biofuel and biochemical production, e.g., hydrogen, methane, biopolymers, etc. Conventional fermentation processes pose several limitations in terms of their practical and economic feasibility. The introduction of two electrodes in a bioreactor allows the regulation of redox instabilities that occur in conventional fermentation, boosting the overall process towards a high biomass yield and enhanced product formation. In this regard, key parameters such as the type of culture, the nature of the electrodes as well as the operating conditions are crucial in order to maximize the production of biofuels and biochemicals via electro-fermentation technology. This article comprises a critical overview of the benefits and limitations of this emerging bio-electrochemical technology and its contribution to the circular economy.
... This is because electrodes made up of titanium are usually known for their chemical stability and resistance to deterioration over time, factors which are essential in microbial electrochemical systems (MESs) [26]. Carbon felt is a porous carbon material commonly used as an electrode in MESs as it has a high surface area, low cost, good electrical conductivity along with good biocompatibility [190]. Larger effective surface area of the carbon felt usually means greater attachment of microbial species which in turn enhances the capture of extracellular electron transfer processes and other bioelectrochemical conversions. ...
... Carbon cloth, carbon fiber, carbon paper, and graphite rod-based electrode materials need to be further modified to enhance the processability, surface area, and electron conductivity. In this regard, granular carbon and granular graphite materials were applied to develop fuel cell electrodes [130][131][132]. To enhance the surface area, graphite or carbon structures must be cut down into fine small segments. ...
Fuel cell efficiency can be improved by using progressive electrodes and electrolytes. Green nanomaterials and green technologies have been explored for the manufacturing of high-performance electrode and electrolyte materials for fuel cells. Platinum-based electrodes have been replaced with green materials and nanocomposites using green fabrication approaches to attain environmentally friendly fuel cells. In this regard, ecological and sustainable electrode- and electrolyte-based membrane electrode assemblies have also been designed. Moreover, green nanocomposites have been applied to form the fuel cell electrolyte membranes. Among fuel cells, microbial fuel cells have gained research attention for the incorporation of green and sustainable materials. Hence, this review essentially focuses on the potential of green nanocomposites as fuel cell electrode and electrolyte materials and application of green synthesis techniques to attain these materials. The design of and interactions with nanocomposites have led to synergistic effects on the morphology, impedance, resistance, power density, current density, electrochemical features, proton conductivity, and overall efficiency. Moreover, we deliberate the future significance and challenges of the application of green nanocomposites in electrodes and electrolytes to attain efficient fuel cells.
... Bacteria that are able to exchange electrons with electrodes easily attach to their surface and easily transfer electrons what stimulates their metabolism. The electrode should be made of a high performance electrocatalyst material [148]. For this purpose, different materials as electrodes have been tested. ...
... 34,35 Adequate surface area creates accessible active sites both for electrocatalysis and bacterial affinity. [36][37][38] Structural stability guarantees the stationarity of overall performance in the long-term running process. ...
Abstract Upgrading of atmospheric CO2 into high‐value‐added acetate using renewable electricity via electrocatalysis solely remains a great challenge. Here, inspired by microbial synthesis via biocatalysts, we present a coupled system to produce acetate from CO2 by bridging inorganic electrocatalysis with microbial synthesis through formate intermediates. A 3D Bi2O3@CF integrated electrode with an ice‐sugar gourd shape was fabricated via a straightforward hydrothermal synthesis strategy, wherein Bi2O3 microspheres were decorated on carbon fibers. This ice‐sugar gourd‐shaped architecture endows electrodes with multiple structural advantages, including synergistic contribution, high mass transport capability, high structural stability, and large surface area. Consequently, the resultant Bi2O3@CF exhibited a maximum Faradic efficiency of 92.4% at −1.23 V versus Ag/AgCl for formate generation in 0.5 M KHCO3, exceeding that of Bi2O3/CF prepared using a conventional electrode preparation strategy. Benefiting from the high formate selectivity, unique architecture, and good biocompatibility, the Bi2O3@CF electrode attached with enriched CO2‐fixing electroautotrophs served as a biocathode. As a result, a considerable acetate yield rate of 0.269 ± 0.009 g L−1 day−1 (a total acetate yield of 3.77 ± 0.12 g L−1 during 14‐day operation) was achieved in the electrochemical–microbial system equipped with Bi2O3@CF.
... Various measures such as reactor configuration, electro-catalytically efficient electrode materials, and lowering of electrolyte, membrane and electrode resistances have been proposed to address the low energy efficiency issue of bioelectrochemical systems (Sharma et al., 2019;Prévoteau et al., 2020). For instance, the use of saline (i.e., high ionic conductive) electrolytes instead of non-saline (i.e., low ionic conductivity) ones commonly used in MES studies has been invoked and proposed as a promising way to address the ohmic resistance issue (Lefebvre et al., 2012;Prévoteau et al., 2020). ...
Using saline electrolytes in combination with halophilic CO2-fixing lithotrophic microbial catalysts has been envisioned as a promising strategy to develop an energy-efficient microbial electrosynthesis (MES) process for CO2 utilization. Here, an enriched marine CO2-fixing lithotrophic microbial community dominated by Vibrio and Clostridium spp. was tested for MES of organic acids from CO2. At an applied Ecathode of -1V (vs Ag/AgCl) with 3.5 % salinity (78 mScm-1), it produced 379 ± 53 mg/L (6.31 ± 0.89 mM) acetic acid and 187 ± 43 mg/L (4.05 ± 0.94 mM) formic acid at 2.1 ± 0.30 and 1.35 ± 0.31 mM day-1, respectively production rates. Most electrons were recovered in acetate (68.3 ± 3 %), formate (9.6 ± 1.2 %) besides hydrogen (11 ± 1.4 %) and biomass (8.9 ± 1.65 %). Notably, the bioproduction of organic acids occurred at a high energetic efficiency (EE) of ∼ 46 % and low Ecell of 2.3 V in saline conditions compared to the commonly used non-saline electrolytes (0.5-1 mScm-1) in the reported MES studies with CO2 (Ecell: >2.5 V and EE: <34 %).
... The common electrode materials used in MES are carbonaceous materials (biochar, activated carbon, carbon nitride, carbon nanotubes, graphene, reticulated vitreous carbon, and carbon cloth/brush/rod), metallic materials (metal oxide, stainless steel, and metals like Fe, Pt, Pd, Au, Mo, Ni, etc.), and carbon-metallic materials (metal and metal oxides coated with carbonaceous materials, and carbonaceous materials coated with metals or metal oxide) [14]. However, biocompatible carbon-metallic materials are relatively more advantageous in terms of good catalytic effect and harvesting high power density [15]. ...
Over the last few years, mitigation of global warming has become a challenge for researchers. Therefore, CO2 conversion into energy-rich valuables and fuels can become a crucial strategy for abating the growing global CO2 emission. However, the CO2 molecule is highly stable, which requires large over potential for converting it to valuable chemicals; thus, making its reduction quite difficult. In this regard, technologies, such as microbial electrochemical technology (MET), photocatalytic and electrochemical technologies triggered considerable interest in the reduction of CO2. These technologies can help in solving the global climate issue based on mitigating the CO2 into the desired product like formic acid, methanol, methane, and other valuables with low energy consumption and minimal carbon emission. Thus, the objective of this review is to provide an updated critical discussion on the recent progress in application of biological and non-biological technologies for CO2 reduction and wastewater treatment. Moreover, the mechanism governing the microbial, photocatalytic, and electrocatalytic CO2 reduction and pollutant removal from wastewater along with a detailed discussion of catalysts used in these technologies are also highlighted. Further, brief prospective and future recommendations on the development of efficient CO2 reduction technologies have also been elucidated in this article, which could be vital for enhancing the conversion efficiency of CO2 in the reduction system.
... A detailed list of these materials can be found in the study by Aryal et al. [11]. Overall, the reasons behind favouring C-based materials are their low price, high specific surface area, good corrosion resistance and electrical conductivity, biocompatibility, and flexible manufacturing in a variety of forms [12]. In addition, cathode electrode materials often -and most promisingly in up-scaled technologiesneeds to include additional catalyst (e. g. platinum coating) in order to provide hydrogen at sufficient rate for the bioelectrosynthesis [13]. ...
Microbial electrosynthesis cells (MES) are devices with demonstrated capability to treat CO2-containing gaseous streams and alongside, generate certain valuable chemical products, particularly methane gas, carboxylic acids, alcohols, etc. Although there are many varieties of MES with their own individual characteristics, all systems have a lot in common, starting from their design and operational features to the underlying microbiological phenomena. With the support of literature publications and related numerical data, this paper reviews and analyses the most important features of MES to identify general tendencies and practical recommendations pertaining to their design (electrodes, membranes), operation (cathode potential, CO2 feeding, temperature, pH) and biocatalysts ensuring an enhanced performance. As a result, several key-issues are provided to (i) successfully implement MES setups as well as to (ii) outline the perspectives of the technology towards the further promotion and development of this CO2-refinery process.
