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Microbial fuel cells (MFCs) have gained considerable importance for the production of bioelectricity and other value-added products recovery along with the concomitant treatment of wastewater. However, the poor power output of MFC as a result of sluggish oxygen reduction reaction (ORR) remains one of the major setbacks of this green technology. Application of metal composite as cathode catalyst has shown tremendous potential in this regard to the augmentation of power generation through MFC. Thus, this review article pivots around the role of bimetallic catalysts in boosting the ORR and critically evaluates different metal composites employed in lab-scale as well as field-scale MFCs chiefly in terms of power generation. In this regard, bimetallic catalyst such as Cu-Sn have shown the maximum power density of 470.2 ± 27.3 mW/m2 and coulombic efficiency of 36.4 ± 2.1% compared to the power density obtained by the MFC with Pt/C as cathode catalyst (465.3 ± 27.1 mW/m2), which shows that bimetallic catalysts possess excellent ORR activity and are more sustainable with respect to expensive Pt based catalyst. Similarly, Cu–Zn bimetallic catalysts have shown the competence for application in both lab- and field-scale. Moreover, the effect of synthesis procedure, structural morphology, and electrochemical behavior of bimetallic catalysts has been scrutinized and summarized in this review. Therefore, this review is an attempt to fill the existing knowledge void on composite metal catalysts and would aid budding scholars in carrying out influential research work in the future. [ABSTRACT FROM AUTHOR]

Microbial fuel cell (MFC) is a type of bio-electrochemical system, which harvests bioelectricity by oxidizing the organic material present in the wastewater. Performance of a MFC relies on the both anodic and cathodic reaction kinetics. The oxygen reduction reaction (ORR) occurring on the cathode is a sluggish reaction, which majorly diminishes the power generation of a MFC. In this context, the use of metal organic frameworks (MOFs) is appropriate as a cathode catalyst to boost the ORR kinetics, thus enhancing the power generation of MFCs. The higher specific surface area, excellent catalytic activity and precise permeable structure of MOFs render them suitable for the application as cathode catalysts to enhance ORR in MFCs. Hence, there is a wide scope of implementation of different low-cost MOF-based cathode catalysts in MFCs, which would not only enhance its performance but also would diminish the fabrication cost of field-scale MFCs. This review therefore provides the detailed understanding on both the synthesis methods and structural characteristics of MOFs and also explains the mechanism of ORR, role of cathode catalysts and application of MOFs as cathode catalysts in MFCs. [ABSTRACT FROM AUTHOR]

There is a dire need to replace the chemical buffers that regulate the redox environment in single-stage anaerobic digestion of food waste. Hence, the applicability of grass clippings as an eco-friendly buffering agent and biomass during the anaerobic co-digestion of food waste was explored. A focus was primarily given on the effects of grass clippings on the redox environment and acidogenesis. Concomitantly the production of volatile fatty acids, hydrogen and methane in mesophilic conditions was monitored. Organic load and substrate-to-inoculum ratio were kept constant in all the experiments, and no chemical buffer was used. The results revealed that the redox environment was regulated with 10% grass clippings by inhibiting rapid pH drop in the digester. The addition of 2, 4, and 6% grass clippings promoted acidogenesis with increased production of acetic and butyric acids, whereas 8 and 10% grass clippings promoted solventogenesis with ethyl alcohol production. Hydrogen generation from the experiments with grass clippings was in the range of 27–30% of the total biogas, which was marginally higher than the control (25%). Methane concentration was negligible in the biogas generated from all experiments. The acidification rate, VFA production/consumption rate, specific hydrogen yield, hydrogen conversion efficiency, and volatile solids removal were maximum and minimum in the reactors with 6 and 10% grass clippings, respectively. From the above results, it can be concluded that adding grass clippings to food waste would regulate the sudden pH changes and enhance the production of value-added biochemicals, making the process cost-effective. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) is an innovative technology, which can yield valuable organic chemicals with concomitant CO2 sequestration by employing microbes as biocatalysts. The mode of operation has an imperative role in the performance of MES, thus, affecting the yield of synthesized organic chemicals from the MES. However, to the best of our knowledge, the optimal mode of operation for MES has not been determined till date. Hence, in the present investigation, two MES were operated: one in batch mode (MES-B) and another in continuous mode (MES-C), and their performance was monitored. The MES-B exhibited 31%, 33.5% and 44% higher production rate of acetate, propionate and butyrate, respectively, in comparison to MES-C. Moreover, the performance of MES-B also stabilized faster, and microbiome in the cathodic chamber of MES-B was able to accept 26% more electrons supplied to it externally, which were employed as reducing equivalents to reduce CO2. The enactment of MES-B was superior to that of MES-C due to the higher retention of CO2 and hydrogen in cathodic chamber of MES-B. Therefore, operating MES in batch mode would aid in yielding more organic chemicals through CO2 sequestration. [ABSTRACT FROM AUTHOR]

Formation of methane in the anodic chamber of a microbial fuel cell (MFC) indicates an energy inefficiency in electricity generation as the energy required for electrogenesis gets redirected to methanogenesis. The hypothesis of this research is that inhibition of methanogenesis in the mixed anaerobic anodic inoculum is associated with an enhanced activity of the electrogenic bacterial consortia. Hence, the primary objective of this investigation is to evaluate the ability of chloroform to inhibit the methanogenesis at different dosing to enhance the activity of electrogenic consortia in MFC. A higher methane inhibition and hence an enhanced performance of MFC was achieved when mixed anaerobic sludge, collected from septic tank, was used as inoculum after pre-treatment with 0.25% (v/v) chloroform dosing (MFC-0.25CF). The MFC-0.25CF attained a maximum power density of 8.51 W/m3, which was more than twice as that of MFC inoculated with untreated sludge. Also, a clear correlation between the chloroform dosing, methane inhibition, wastewater treatment, and power generation was established, which demonstrated the effectiveness of the technique in enhancing power generation in MFC along with adequate biodegradation of organic matter present in wastewater at an optimum chloroform dosing of 0.25% (v/v) to inhibit methanogenesis. [ABSTRACT FROM AUTHOR]

Proton exchange membranes (PEMs) were synthesized in polyvinyl alcohol (PVA) matrix by impregnating TiO2-Si or SrTiO3-Si as proton exchanger for microbial fuel cells (MFCs). These PEMs were physically characterized, which approved the presence of hygroscopic oxides like SiO2 to increase the proton transfer due to the formation of Si-H along with the water channelling through TiO2 or SrTiO3 induced microstructural modifications. Chemical characterization techniques further illustrated their comparable performance to the commercially available Nafion-117 and superior performance than bare PVA membrane. Polarization curves for MFCs using TiO2-Si- or SrTiO3-Si-based PVA membranes exhibited a power density of 6.16 ± 0.31 W m−3 and 5.39 ± 0.27 W m−3, respectively. Power density of MFC with TiO2-Si membrane was comparable to that of the MFC using Nafion-117 (6.50 ± 0.33 W m−3). Thus, comparable properties and 30-folds less synthesis cost of the fabricated TiO2-Si-impregnated PVA membrane in comparison to Nafion, demonstrate its potential for real-life applications in MFC. [ABSTRACT FROM AUTHOR]

Sodium dodecyl sulfate (SDS) is a widely used anionic surfactant, which finds its way to the receiving water body due to the incapability of conventional wastewater treatment systems to completely remove it. A hybrid treatment system consisting of upflow microbial fuel cell (MFC) with titanium dioxide (TiO2) as a photocathode catalyst was developed for treating synthetic wastewater spiked with SDS (10.00 ± 0.46 mg L−1). Effluent from anodic chamber of MFC was passed through raw laterite soil filter followed by the photo-cathodic chamber with TiO2-coated cathode irradiated with the UV spectrum. This hybrid system was operated under varying hydraulic retention time (HRT) in anodic chamber of MFC. The SDS removal efficiency of more than 96% along with organic matter removal efficiency of more than 71% was obtained by this hybrid system at different HRTs. The MFC having cathode coated with TiO2 could generate a maximum power density of 0.73 W m−3 and 0.46 W m−3 at the HRT of 12 h and 8 h, respectively, showing the adverse effect of increased SDS loading rate on the electrical performance of MFC. This investigation highlighted the importance of HRT in anodic chamber of MFC and offered solution for effective removal of surfactant from wastewater. [ABSTRACT FROM AUTHOR]

The fish market wastewater, which is rich in ammonium concentration, was investigated to explore its ability of in situ suppression of methanogenesis in the anodic chamber of microbial fuel cell (MFC) while treating it and to ensure non-reoccurrence of methanogenic consortia in the anodic chamber during its long-term operations. A lower specific methanogenic activity (0.097g chemical oxygen demand (COD)CH4/g volatile suspended solids (VSS). day) with a higher power density (3.81 ± 0.19 W/m3) was exhibited by the MFC operated with raw fish market wastewater as compared to the MFC fed with synthetic wastewater (0.219g CODCH4/g VSS. day and 1.75 ± 0.09 W/m3, respectively). The enhanced electrochemical activity of anodic biofilm of MFC fed with raw fish market wastewater than the MFC fed with synthetic wastewater further advocated the enhanced electrogenic activity and suppression of methanogenesis, because of the presence of higher ammonium content in the feed. This, in response, reduced the internal resistance (55 Ω), enhanced the coulombic efficiency (21.9 ± 0.3%) and normalized the energy recovery (0.27 kWh/m3) from the MFC fed with fish market wastewater than the MFC fed with synthetic wastewater (92 Ω, 15.7 ± 0.3% and 0.13 kWh/m3, respectively). Thus, while treating the fish market wastewater in the anodic chamber of MFC, any costly and repetitive treatment procedures for anodic microorganisms are not required for suppression of methanogens to ensure higher activity of electrogenic bacteria for higher electricity harvesting. [ABSTRACT FROM AUTHOR]

Microbial fuel cell (MFC) is a bioelectrochemical system, which treats wastewater with simultaneous recovery of bioelectricity. Costly proton exchange membrane, like Nafion-117, brings a serious bottleneck towards the sustainable scaled-up application of this technology. For an appropriate field-scale demonstration of MFC, the fabrication cost needs to be reduced drastically. This can be achieved by using low-cost proton exchange membrane (PEM) in MFCs, which would demonstrate equivalent performance as commercially available expensive PEMs. Such a novel PEM constituting 5% goethite and natural clay as a base material was synthesized, named as G-5, and it was used in MFC as a separator. This G-5 membrane was estimated to be five folds cheaper than the commercially available Nafion-117 membrane, which is popularly used in MFC. Membrane properties, like water and acetate uptake, and proton conductivity of the G-5 membrane, were evaluated and compared with Nafion-117. A power density obtained from the MFC using G-5 as PEM (112.81 ± 8.74 mW/m2) was slightly higher than the MFC with Nafion-117 as PEM (106.95 ± 5.52 mW/m2). Chemical oxygen demand removal and Coulombic efficiency for MFC with G-5 membrane were found to be 22% and 8.6% higher, respectively, in comparison with that of the MFC with Nafion-117 as PEM. Thus, low-cost G-5 membrane demonstrated the potential to be used for scaling-up of MFCs to reduce fabrication cost for successful field-scale implementation of MFCs. [ABSTRACT FROM AUTHOR]

In developing countries, like India, there is no systematic approach for septage management. Treatment and possibility of methane recovery from this septage has not been explored previously. Hence, possibility of recovering methane from septic tank sludge in an anaerobic digester was explored with and without ultra-sonication pre-treatment in laboratory scale reactors and a 2 m3 pilot anaerobic digester was operated on raw septic tank sludge over a period of 1 year. Methane production potential of the raw septic tank sludge was 298.88 ± 9.7 L kg VS destroyed, which increased to 409.96 ± 13.25 L kg VS destroyed after sonication pre-treatment. Methane content in biogas increased from 73.15 to 81.83% upon sonication pre-treatment of the sludge. A first-order kinetic model best predicted biogas production from pilot digester fed with raw septic tank sludge, with minimum errors. Laboratory scale studies proved the feasibility and economic benefit of using sonicated sludge in the digester, with a net energy gain of 1.67 W-h/L of sludge digested. The kinetic constants derived from the laboratory experiments can be used for design of digester for field application using sonicated sludge to enhance digestion rate and methane recovery from septic tank sludge for better energy conservation. [ABSTRACT FROM AUTHOR]

Fermentation distilleries produce a considerable volume of high-strength wastewater, known as stillage, having unconvertible organic fractions, lower pH and high percentage of dissolved organic and inorganic matters. Molasses stillage comprises higher level of chemical oxygen demand of 80-140 g/l, biochemical oxygen demand of 40-65 g/l, inorganic impurities and dark brown colour. Grain stillage contains comparatively lower chemical oxygen demand of 40-60 g/l. This stillage is acidic in nature (pH of 3.4-4.1) and exhibits considerable pollution potential upon discharge of untreated or partially treated wastewater into water body. Physical, chemical, biological and integrated processes for treatment of distillery stillage, which have been established by several researchers, are discussed in this review article. These treatment methods are discussed with focus on process details and current challenges, prospect and opportunities of future research and development. By utilizing distillery stillage as substrate in microbial fuel cell or integrated or combined fungal aerobic treatment followed by microbial fuel cell system, encouraging observations are demonstrated recently in terms of achieving the required treatment efficiency to meet the discharge standards, simultaneous bioelectricity generation and value-added products recovery. Such treatment system can offer a suitable solution for treatment of distillery wastewater in coming days. [ABSTRACT FROM AUTHOR]

Wastewater treatment coupled with electricity recovery in microbial fuel cell (MFC) prefer mixed anaerobic sludge as inoculum in anodic chamber than pure stain of electroactive bacteria (EAB), due to robustness and syntrophic association. Genetic modification is difficult to adopt for mixed sludge microbes for enhancing power production of MFC. Hence, we demonstrated use of eco-friendly plant secondary metabolites (PSM) with sub-lethal concentrations to enhance the rate of extracellular electron transfer between EAB and anode and validated it in both bench-scale as well as pilot-scale MFCs. The PSMs contain tannin, saponin and essential oils, which are having electron shuttling properties and their addition to microbes can cause alteration in cell morphology, electroactive behaviour and shifting in microbial population dynamics depending upon concentrations and types of PSM used. Improvement of 2.1-times and 3.8-times in power densities was observed in two different MFCs inoculated with Eucalyptus-extract pre-treated mixed anaerobic sludge and pure culture of Pseudomonas aeruginosa, respectively, as compared to respective control MFCs operated without adding Eucalyptus-extract to inoculum. When Eucalyptus-extract-dose was spiked to anodic chamber (125 l) of pilot-scale MFC, treating septage, the current production was dramatically improved. Thus, PSM-dosing to inoculum holds exciting promise for increasing electricity production of field-scale MFCs. [ABSTRACT FROM AUTHOR]