Elevated Cr(VI) reduction in a biocathode microbial fuel cell without acclimatization inversion based on strain Corynebacterium vitaeruminis LZU47-1

Biocathode application in microbial fuel cell has been developed as a sustainable technology for heavy metal reduction. However, most biocathodes require pretreatment with acclimatization inversion. Here, a biocathode MFC based on strain Corynebacterium vitaeruminis LZU47-1 without acclimatization inversion was constructed for hexavalent chromium reduction. The maximum power generation by the biocathode MFC with C. vitaeruminis LZU47-1 increased by 24.5% and 53.4% in inversion and abiotic cathode groups, respectively. Compared with the inversion (72.52%) and abiotic cathode groups (64.75%), the biocathode group achieved a Cr(VI) removal efficiency of 98.63%. Furthermore, electrochemical analysis such as SEM-EDS, XPS and CV test were conducted to elucidate the adsorption-reduction mechanism for Cr(VI) reduction. MiSeq sequencing revealed that Geobacter (51.28%) was enriched on the anode biofilm in the biocathode group than inversion (38.52%) and abiotic cathode groups (31.74%). Therefore, this study provides a convenient and highly effective method for enhancing power output and Cr(VI) reduction in biocathode MFCs.     

Effects of mediator producer and dissolved oxygen on electricity generation in a baffled stacking microbial fuel cell treating high strength molasses wastewater

The effects of Pseudomonas aeruginosa, pyocyanin, and influent dissolved oxygen (DO) on the electricity generation in a baffled stacking microbial fuel cell (MFC) treating high strength molasses wastewater were investigated. The result shows that the influent chemical oxygen demand (COD) of 500–1000 mg l⁻¹ had the optimal substrate-energy conversion rate. The addition of a low density of P. aeruginosa (8.2 mg l⁻¹) or P. aeruginosa with pyocyanin improved the COD removal and power generation. This improvement could be attributed to the enhancement of electron transfer with the help of redox mediators. Influent DO at a concentration of up to 1.22 mg l⁻¹ did not inhibit the electricity generation. Large proportions of COD, organic-N and total-N were removed by the MFC. The MFC effluent was highly biodegradable. Denaturing gradient gel electrophoresis analysis shows that the added pyocyanin resided in the MFC for up to 14 days. An analysis of anode voltage reveals that microbial proton transport to the cathode was importantly responsible for the internal resistance.     

Self-sustainable electricity production from algae grown in a microbial fuel cell system

This paper describes the potential for algal biomass production in conjunction with wastewater treatment and power generation within a fully biotic Microbial Fuel Cell (MFC). The anaerobic biofilm in the anodic half-cell is generating current, whereas the phototrophic biofilm on the cathode is providing the oxygen for the Oxygen Reduction Reaction (ORR) and forming biomass. The MFC is producing electricity with simultaneous biomass regeneration in the cathodic half-cell, which is dependent on the nutrient value of the anodic feedstock. Growth of algal biomass in the cathode was monitored, assessed and compared against the MFC power production (charge transfer), during this process. MFC generation of electricity activated the cation crossover for the formation of biomass, which has been harvested and reused as energy source in a closed loop system. It can be concluded that the nutrient reclamation and assimilation into new biomass increases the energy efficiency. This work is presenting a simple and self-sustainable MFC operation with minimal dependency on chemicals and an energy generation system utilising waste products and maximising energy turnover through an additional biomass recovery.     

Recent advances in constructed wetland‐microbial fuel cells for simultaneous bioelectricity production and wastewater treatment: A review

The coupling of constructed wetlands (CWs) to microbial fuel cells (MFCs) has turned out to be a source of renewable energy for the production of bioelectricity and for the simultaneous wastewater treatment. Both technologies have an aerobic zone in the air‐water interface and an anaerobic zone in the lower part, where the anode and the cathode are strategically placed. This hybridization is a promising bioelectrochemical technology that exerts a symbiosis between plant‐bacteria in the rhizosphere of an aquatic plant, converting solar energy into bioelectricity through the formation of root exudates as an endogenous substrate and a microbial activity. The difference between CW‐MFC and MFC conventional lies in the bioelectricity and substrate production in situ, where exogenous substrates are not required for example wastewater. However, CW‐MFC can take organic content present in wastewater, promoting the removal of some pollutants. Different areas that comprise the study of a CW‐MFC have been explored, including the structures and their operation. This review aims to provide concise information on the state of the art of CW‐MFC systems, where a summary on important aspects of the development of this technology, such as bioelectricity production, configurations, plant species, rhizodeposits, electrode materials, wastewater treatment, and future perspectives, is presented. This system is a promising technology, not only for the production of bioenergy but also to maintain a clean environment, since during its operation, no toxic byproducts were formed.     

Bioelectricity production by using goat (Capra hircus) rumen fluid from slaughterhouse waste in mediator-less microbial fuel cells

Microbial fuel cells (MFCs) grasped an outlook for bioelectricity production under global scenario. Many studies have highlighted the utilization of various wastes for electricity generation by this advantageous technology. In the present investigation, an H-type, two-chambered MFC was designed for bioelectricity production using Capra hircus rumen fluid collected from slaughterhouse, paddy straw as substrate, copper as anode, and zinc as cathode. The power output of single MFC was recorded to a maximum of 5.76 W and 8.49 W/m². Effect of acetic acid as catholyte with concentration range (0.0–2.0%) was compared with air cathode. Acetic acid was found to enhance the power output at 2% concentration. Assessment for increased power output was carried out by connecting the four MFCs in series. MFC series performed well with a maximum power output of 67.24 W at 192 h with acetate as catholyte whereas 54.76 W for air cathode. The maximum power density achieved was 42.11 W/m² for acetate in cathode and 34.39 W/m² for air cathode. The MFCs developed with rumen consortia, hay as substrate, and Cu–Zn electrodes were found to be effective in bioelectricity production.     

A dual photoelectrode-based double-chambered microbial fuel cell applied for simultaneous COD and Cr (VI) reduction in wastewater

Cerium oxide (CeO₂) and cuprous oxide (Cu₂O) were used for the first time as photoanode and photocathode, respectively, in a microbial fuel cell (MFC) for simultaneous reduction of chemical oxygen demand (COD) and Cr(VI) in wastewater. The photoelectrodes, viz. Photoanode and photocathode were separately prepared by impregnating activated carbon fiber (ACF) with the respective metal oxide nanoparticles, followed by growing carbon nanofibers (CNFs) on the ACF substrate using catalytic chemical vapor deposition. The MFC, operated under visible light irradiation, showed reduction in COD and Cr(VI) by approximately 94 and 97%, respectively. The MFC also generated high bioelectricity with a current density of ~6918 mA/m² and a power density of ~1107 mW/m². The enhanced performance of the MFC developed in this study was attributed to the combined effects of the metal oxide photocatalysts, the graphitic CNFs, and the microporous ACF substrate. The MFC based on the inexpensive transition metal oxides-based photoelectrodes developed in this study has a potential to be used at a large scale for treating the industrial aqueous effluents co-contaminated with organics and toxic Cr(VI).     

Effect of dissolved oxygen concentration on nitrogen removal and electricity generation in self pH-buffer microbial fuel cell

A double-chamber self pH-buffer microbial fuel cell (MFC) was used to investigate the effect of dissolved oxygen (DO) concentration on cathodic nitrification coupled with anodic denitrification MFC. It was found that nitrogen and COD removal, electricity generation were positively correlated with DO concentration in the cathode chamber. When total inorganic nitrogen of influent was 202.51 ± 7.82 mg/L at DO 6.8 mg/L, the maximum voltage output was 282 mV and the maximum power density was 149.76 mW/m². After 82 h operation, the highest removal rate of total inorganic nitrogen was 91.71 ± 0.38%. Electrochemical impedance spectroscopy (EIS) test showed that the internal resistance of the reactor with different DO concentration was related to the diffusion internal resistance. The data of bacterial analysis in the cathode chamber revealed that there were not only ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), but also a large number of exoelectrogens. Compared with the traditional biological denitrification and related MFC denitrification research, this method does not need pH-buffer solution and external circulation device through the anion exchange membrane (AEM). It can generate electricity and remove nitrogen simultaneously, and the oxygen utilization rate in the cathode can also be enhanced.     

Study on power generation and Congo red decolorization of 3D conductive PPy-CNT hydrogel in bioelectrochemical system

In this paper, a polypyrrole-carbon nanotube hydrogel (PPy-CNT) with 3D macroporous structure was prepared by secondary growth method. This self-supporting material with good conductivity and biocompatibility can be directly used as anode in a microbial fuel cell (MFC). The prepared material had a uniform structure with rich 3D porosity and showed good water retention performance. The effect of the mass ratio of PPy and CNT in the hydrogel were also investigated to evaluate the electrical performance of MFC. The MFC with 10:1 PPy-CNT hydrogel anode could reached the maximum power density of 3660.25 mW/m3 and the minimal electrochemical reaction impedance of anode was 5.06 Ω. The effects of Congo red concentration, external resistance and suspended activated sludge on decolorazation and electricity generation were also investigated in the MFC with the best performance hydrogel. When the Congo red concentration was 50 mg/L and the external resistance was 200 Ω, the dye decolorization rate and chemical oxygen demand (COD) removal rate could reach 94.35% and 42.31% at 48h while the output voltage of MFC was 480 mV. When activated sludge was present, the decolorization rate and COD removal rate could be increased to 99.55% and 48.08% at 48 h. The above results showed that the porous hydrogel anode had broad application prospects in synchronous wastewater treatment and electricity production of MFC.     

Utilizing acid-rich effluents of fermentative hydrogen production process as substrate for harnessing bioelectricity: An integrative approach

Lower substrate degradation is one of the limiting factors associated with fermentative hydrogen production process. To overcome this, an attempt was made to integrate microbial fuel cell (MFC) as a secondary energy generating process with the fermentative hydrogen (H₂) production. The acid-rich effluents generated from the acidogenic sequential batch biofilm reactor (AcSBBR) producing H₂ by fermenting vegetable waste was subsequently used as substrate for bioelectricity generation in single chambered MFC (air cathode; non-catalyzed electrodes). AcSBBR was operated at 70.4 kg COD/m³-day and the outlet was fed to the MFC at three variable organic loading rates. The final outlet from AcSBBR was composed of fermentative soluble acid intermediates along with residual carbon source. Experimental data illustrated the feasibility of utilizing acid-rich effluents by MFC for both additional energy generation and wastewater treatment. Higher power output (111.76 mW/m²) was observed at lower substrate loading condition. MFC also illustrated its function as wastewater treatment unit by removing COD (80%), volatile fatty acids (79%), carbohydrates (78%) and turbidity (65.38%) effectively. Fermented form of vegetable wastewater exhibited higher improvement (94%) in power compared to unfermented wastewater. The performance of MFC was characterized with respect to polarization behavior, cell potentials, cyclic voltammetry and sustainable power. This integration approach enhanced wastewater treatment efficiency (COD removal, 84.6%) along with additional energy generation demonstrating both environmental and economic sustainability of the process.     

Power generation from furfural using the microbial fuel cell

Furfural is a typical inhibitor in the ethanol fermentation process using lignocellulosic hydrolysates as raw materials. In the literature, no report has shown that furfural can be utilized as the fuel to produce electricity in the microbial fuel cell (MFC), a device that uses microbes to convert organic compounds to generate electricity. In this study, we demonstrated that electricity was successfully generated using furfural as the sole fuel in both the ferricyanide-cathode MFC and the air-cathode MFC. In the ferricyanide-cathode MFC, the maximum power densities reached 45.4, 81.4, and 103 W m⁻³, respectively, when 1000 mg L⁻¹ glucose, a mixture of 200 mg L⁻¹ glucose and 5 mM furfural, and 6.68 mM furfural were used as the fuels in the anode solution. The corresponding Coulombic efficiencies (CE) were 4.0, 7.1, and 10.2% for the three treatments, respectively. For pure furfural as the fuel, the removal efficiency of furfural reached up to 95% within 12 h. In the air-cathode MFC using 6.68 mM furfural as the fuel, the maximum values of power density and CE were 361 mW m⁻² (18 W m⁻³) and 30.3%, respectively, and the COD removal was about 68% at the end of the experiment (about 30 h). Increase in furfural concentrations from 6.68 to 20 mM resulted in increase in the maximum power densities from 361 to 368 mW m⁻², and decrease in CEs from 30.3 to 20.6%. These results indicated that some toxic and biorefractory organics such as furfural might still be suitable resources for electricity generation using the MFC technology.     

Microbial fuel cell performance of multiwall carbon nanotubes on carbon cloth as electrodes

Microbial fuel cell (MFC), which can produce electricity during treatment of wastewater, has become one of the emerging technologies in the field of environmental protection and energy recovery. Of all parts of MFC, the electrode materials play a crucial role in the electricity generation. In this study, we investigate the performance of carbon nanotube (CNT) modified carbon cloth electrodes in single-chamber MFC. The MFC is first inoculated with bacteria in wastewater and then its capability of using acetate sodium as fuel is examined. The results show that the MFC with CNT coated onto carbon cloth electrode improves the power density. In this study, the obtained maximum power density is 65 mW m⁻², the highest chemical oxygen demand (COD) removal efficiency is 95%, and the maximum Coulombic efficiency is 67%. Compared with other reported studies, the CNT/carbon cloth composite electrode has demonstrated high potential for the use of MFC.     

Electricity generation by a baffle-chamber membraneless microbial fuel cell

Microbial fuel cells (MFCs) for organic waste and wastewater treatment represent innovative technologies for pollution control and energy generation. The research reported here considers the influence of reactor configurations designed to mitigate the impact of oxygen transport on electricity generation by a baffle-chamber membraneless MFC. The reactor was constructed to reduce mixing in the vicinity of the cathode and facilitate thick (>1 mm) biofilm formation on the cathode by adding anaerobic biomass/sludge (4330 ± 410 mg COD L⁻¹), resulting in an overall coulombic efficiency of more than 30% at glucose concentrations ranging from 96 to 960 mg COD L⁻¹, compared to previously reported efficiencies <10% in a completely mixed membraneless MFC. Efficiencies in the absence of anaerobic sludge dropped to 21.2 ± 3.7%, suggesting that the importance of pH buffering provided by the biomass in improving electron transport to the anode. However, the anaerobic sludge itself provided very limited power (approximately 0.3 mW m⁻²) and power generation was primarily associated with glucose degradation (e.g., 129 ± 15 mW m⁻²).     

Facile preparation of binder-free NiO/MnO2-carbon felt anode to enhance electricity generation and dye wastewater degradation performances of microbial fuel cell

Binder-free NiO/MnO₂-carbon felt electrode is prepared with a facile two-step hydrothermal method. The NiO self-grown on the carbon felt is used as the skeleton structure to support the in-situ growth of MnO₂. Both the core and shell materials are excellent pseudocapacitance materials. The compositing of such pseudocapacitance metal oxides can produce synergistic effects, so that the modified electrode has a high capacitance. NiO/MnO₂-carbon felt electrode also possesses a high specific surface area, super hydrophilicity and good biocompatibility, which are conducive to the enrichment of typical exoelectrogen Geobacter. As the anode, NiO/MnO₂-carbon felt electrode can effectively improve the electricity generation and methyl orange (MO) wastewater degradation performances of microbial fuel cell (MFC). The highest output voltage and the maximum power density of MFC with NiO/MnO₂-carbon felt anode are respectively 652 mV and 628 mW m^?2, which are much higher than those of MFC with MnO₂-carbon felt anode (613 mV, 544 mW m^?2), NiO-carbon felt anode (504 mV, 197 mW m^?2) and unmodified carbon felt anode (423 mV, 162 mW m^?2). The decolourization efficiency and the chemical oxygen demand (COD) removal rate of MO for MFC with NiO/MnO₂-carbon felt anode are respectively 92.5% and 58.2% at 48 h.     

Electricity generation in microbial fuel cell systems with Thiobacillus ferrooxidans as the cathode microorganism

Microbial fuel cells (MFC) are systems that enable biochemical activities of bacteria to generate the electricity. These systems are of great interest because of their designs that enable biological activity in organic wastes to be transformed into direct electrical energy. In order to increase the commercial usage of MFCs, it is necessary to increase the power output of the system. So as to improve MFC performance, used material selection, the pH value of the used bacterial medium and the choice of the appropriate substrate are very important. In this study, oxidation bacteria Thiobacillus ferrooxidans on the cathode and mixed culture bacteria on the anode of MFC were used. Different anode and cathode pH values were examined in MFC. Best open circuit potential result (0.8 V) was obtained at anode pH 8 and cathode pH 2 conditions. In addition, three different substrates had been used in the anode. In the conditions of acetate the most stable and high valued curve was obtained. The open circuit potential had reached 0.726 V, and power density had reached 0.88 mW/cm².     

Electrophoretic deposition of graphene oxide on carbon brush as bioanode for microbial fuel cell operated with real wastewater

Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm^?2 to 381 mWm^?2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.     

Integrating engineering design improvements with exoelectrogen enrichment process to increase power output from microbial fuel cells

Microbial fuel cells (MFC) hold promise as a green technology for bioenergy production. The challenge is to improve the engineering design while exploiting the ability of microbes to generate and transfer electrons directly to electrodes. A strategy using a combination of improved anode design and an enrichment process was formulated to improve power densities. The design was based on a flow-through anode with minimal dead volume and a high electrode surface area per unit volume. The strategy focused on promoting biofilm formation via a combination of forced flow through the anode, carbon limitation, and step-wise reduction of external resistance. The enrichment process resulted in development of exoelectrogenic biofilm communities dominated by Anaeromusa spp. This is the first report identifying organisms from the Veillonellaceae family in MFCs. The power density of the resulting MFC using a ferricyanide cathode reached 300 W m⁻³ net anode volume (3220 mW m⁻²), which is about a third of what is estimated to be necessary for commercial consideration. The operational stability of the MFC using high specific surface area electrodes was demonstrated by operating the MFC for a period of over four months.     

Modification of graphite felt using nano polypyrrole and polythiophene for microbial fuel cell applications-a comparative study

Microbial fuel cells (MFC) are bio-electrochemical devices used for the generation of electricity from biomass. A single chamber membrane less air-breathing cathode microbial fuel cell (SCMFC) with two different anode configurations was investigated for energy generation using shewanella putrifaciens as bio-catalyst. The graphite felt (GF) anode was modified with 0.008 g/cc polypyrrole nanoparticles (Ppy-NPs) and 0.024 g/cc polythiophene nanoparticles (PTh-NPs) by conventional method. The nanoparticles coating improved the properties such as thermal characteristics and electron transfer capabilities of the anodes, which was confirmed by Thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS) and cyclic voltametry (CV). The variation in the cell potential with time under open circuit condition resulted in voltages of 0.842V and 0.644 V for Ppy-NP and PTh-NP modified GF respectively. A maximum power density (1.22 W/m²) was obtained for Ppy-NP modified GF than PTh-NP modified GF (0.8 W/m²). The results showed that GF coated with nano conductive polymers such as Ppy and PTh are the promising candidates for the best performance of a MFC.     

Microalgae-microbial fuel cell (mMFC): an integrated process for electricity generation,wastewater treatment,CO2 sequestration and biomass production

The world today is facing a crisis of energy and environmental pollution. Conventional or photosynthetic microbial fuel cell (MFC) is an advanced “green” energy technology that utilizes living microorganisms to convert biochemical or light energy into electricity through metabolic reaction and photosynthesis, offering a potential solution for the above-mentioned crisis. Further incorporating microalgae into MFC, microalgae-microbial fuel cell (mMFC) integrates electricity generation, wastewater treatment, CO₂ sequestration and biomass production in a single, self-sustainable technology. This review first describes the fundamentals of MFC as well as its applications in treating domestic, municipal, agricultural and industrial wastewaters. Then, mMFC-based configurations and applications with its advantages compared with MFC are explained in particular, together with the parameters governing its performance. Lastly, the opportunities and challenges involved in the development of mMFCs are also explored.     

Generation of electricity by the degradation of electro-Fenton pretreated latex wastewater using double chamber microbial fuel cell

A double chamber microbial fuel cell (MFC) reactor with anode and cathode chamber separated by a Nafion proton exchange membrane was developed and performance was evaluated for treatment of electro Fenton pretreated latex processing and production wastewater containing chemical oxygen demand of 2660 and 780 mg L⁻¹, respectively. After 12 days, MFC treatment, the COD reduced to 133 mg/L (96%) and 86 mg/L (88.5%) for latex processing and production wastewater respectively. The MFC treatment system generated electrical energy of 1.57 and 1.04 Wh L⁻¹ for latex processing and production wastewaters respectively that was utilized to drive the electro-Fenton reactor. These results indicated that effective wastewater treatment, energy production, and discharge standards could be obtained in the system.     

Study of electrochemical process conditions for the electricity production in microbial fuel cell

The aim of this study was to focus on the optimization of various process parameters such as time (days), pH, and electrode type on electricity production by a microbial fuel cell (MFC). The efficiency of MFC was examined based on the current (A) and potential (V) measurements. In MFC, the anode section was filled with 500 mL of rumen fluid, slaughter house waste, and 2 g of hay as substrate. The cathode section was filled with distilled water, which acted as the air cathode. The results obtained confirmed that copper anode explores the maximum efficiency compared to stainless steel and aluminum. The biofilm attached to the electrode is electrochemically active as per the redox potential shown in cyclic voltammogram results.