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This study constructed a 1000 L modularized MFC system, the largest volume so far, to treat practical municipal wastewater. This MFC system was operated under two different water flow connections in two municipal wastewater treatment plants (MWTP) for more than one year to test their treating abilities for wastewater with both low (average 80 mg L −1 ) and high initial COD concentration (average 250 mg L −1 ). The COD concentration in the effluent from the MFC system remained below 50 mg L −1 with a removal rate of 70–90%, which stably met the level A of the first class in discharge standard of pollutants for MWTP of China. A maximum power density of 125 W m −3 (7.58 W m −2 ) was generated when the MFC system was fed with artificial wastewater, while it lay in a range of 7–60 W m −3 (0.42–3.64 W m −2 ) when treating municipal wastewater. The energy recovery of 0.033 ± 0.005 kWh per m 3 of municipal wastewater was achieved, with a hydraulic retention time (HRT) of 2 h. [ABSTRACT FROM AUTHOR]

Inefficient extracellular electron transfer within bioanode leads to low current production by microbial fuel cell (MFC). In this study, magnetite was sprinkled in electroactive biofilm with the aid of magnet field. Magnetite located inside biofilm (interior-doped biofilm) facilitated the electron delivery of electroactive bacteria far away from electrode surface. Electron transfer efficiency was improved by 12% and 37% compared with that of biofilms with magnetite located at the interface of biofilm/electrode (surface-doped biofilm) and that without any magnetite (control biofilm) respectively. The output power density of MFC with interior-doped biofilm (764 ± 32 mW m −2 ) was greatly increased compared with that of MFCs with surface-doped biofilm (604 ± 22 mW m −2 ) and control biofilm (475 ± 12 mW m −2 ). SEM images showed that magnetite evenly distributed inside the interior-doped biofilm and penetrated the electroactive biofilm, which would facilitate extracellular electron transfer across electroactive biofilms and thus improving the bioelectricity production. [ABSTRACT FROM AUTHOR]

The traditional microbial fuel cell (MFC) sensor with bioanode as sensing element delivers limited sensitivity to toxicity monitoring, restricted application to only anaerobic and organic rich water body, and increased potential fault warning to the combined shock of organic matter/toxicity. In this study, the biocathode for oxygen reduction reaction was employed for the first time as the sensing element in MFC sensor for toxicity monitoring. The results shown that the sensitivity of MFC sensor with biocathode sensing element (7.4±2.0 to 67.5±4.0 mA% −1 cm −2 ) was much greater than that showed by bioanode sensing element (3.4±1.5 to 5.5±0.7 mA% −1 cm −2 ). The biocathode sensing element achieved the lowest detection limit reported to date using MFC sensor for formaldehyde detection (0.0005%), while the bioanode was more applicable for higher concentration (>0.0025%). There was a quicker response of biocathode sensing element with the increase of conductivity and dissolved oxygen (DO). The biocathode sensing element made the MFC sensor directly applied to clean water body monitoring, e.g., drinking water and reclaimed water, without the amending of background organic matter, and it also decreased the warning failure when challenged by a combined shock of organic matter/toxicity. [ABSTRACT FROM AUTHOR]

The use of biosensors for water alert system is critical for providing safe water to the general public. A cathode-shared microbial fuel cell (MFC) sensor array was designed improve the detection credibility by eliminating the cathode performance variation, based on the principle that only the bioanode would be used as the sensing and transducing element. Four integrated MFCs exhibited high parallelism, and independence without the cross contamination or electric signal interference. Two linear ranges were observed (from 0.25 to 0.75 mM and from 1 to 10 mM) for acetate detection. A linear relationship between inhibition ratio ( IR ) and Cu 2+ concentration from 2 to 6 mg/L was recorded. The sensor expressed an immediate voltage decrease when exposed to a pH decrease from 6 to 4. The compact design of the cathode-shared MFC sensor array assure the detection credibility, and the number of the integrated MFC sensors is alterable based on the monitoring requirement. [ABSTRACT FROM AUTHOR]

A binder-free, pseudocapacitive anode was fabricated by coating reduced graphene oxide (rGO) and manganese oxide (MnO 2 ) nanoparticles on stainless steel fibre felt (SS). Microbial fuel cell (MFC) equipped with this novel anode yielded a maximum power density of 1045 mW m −2 , 20 times higher than that of a similar MFC with a bare SS anode (46 mW m −2 ). Transient-state regulation (TSR) was implemented to further improve the MFC’s power generation. The optimal TSR duty cycle ranged from 67% to 95%, and the MFC’s power density increased with TSR frequency. A maximum power density output of 1238 mW m −2 was achieved at the TSR duty cycle of 75% and the frequency of 1 Hz, 18.4% greater than that obtained from the steady state operation. The TSR mode delivered better MFC performance especially when the external resistance was small. Long-term operation tests revealed that the current density and power density yielded in the TSR mode were on average 15.0% and 32.7% greater than those in the steady state mode, respectively. The TSR mode was believed to reduce the internal resistance of the MFC while enhance substrate mass transfer and electron transfer within the anode matrix, thereby improving the MFC performance. [ABSTRACT FROM AUTHOR]

A novel anode was developed by coating reduced graphene oxide (rGO) and manganese oxide (MnO 2 ) composite on the carbon felt (CF) surface. With a large surface area and excellent electrical conductivity, this binder-free anode was found to effectively enhance the enrichment and growth of electrochemically active bacteria and facilitate the extracellular electron transfer from the bacteria to the anode. A microbial fuel cell (MFC) equipped with the rGO/MnO 2 /CF anode delivered a maximum power density of 2065 mW m −2 , 154% higher than that with a bare CF anode. The internal resistance of the MFC with this novel anode was 79 Ω, 66% lower than the regular one's (234 Ω). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses affirmed that the rGO/MnO 2 composite significantly increased the anodic reaction rates and facilitated the electron transfer from the bacteria to the anode. The findings from this study suggest that the rGO/MnO 2 /CF anode, fabricated via a simple dip-coating and electro-deposition process, could be a promising anode material for high-performance MFC applications. [ABSTRACT FROM AUTHOR]

The application of microbial fuel cell (MFC)-based toxicity sensors to real-world water monitoring is partly impeded by the limited sensitivity. To address this limitation, this study optimized the flow configurations and the control modes. Results revealed that the sensitivity increased by ∼15–41 times with the applying of a flow-through anode, compared to those with a flow-by anode. The sensors operated in the controlled anode potential (CP) mode delivered better sensitivity than those operated in the constant external resistance (ER) mode over a broad range of anode potentials from −0.41 V to +0.1 V. Electrodeposition of Cu(II) was found to bias the toxicity measurement at low anode potentials. The optimal anode potential was approximately −0.15 V, at which the sensor achieved an unbiased measurement of toxicity and the highest sensitivity. This value was greater than those required for electrodeposition while smaller than those for power overshoot. [ABSTRACT FROM AUTHOR]

Using microbial fuel cells (MFCs) to power a capacitive deionization (CDI) process enables simultaneous removal of salinity and organic matter in wastewater. The desalination performance of an MFC-CDI system can be influenced by not only the capacity of individual components but also the arrangement and operation of the MFC-CDI circuit. Five typical circuits (consisting of serial- or parallel-connected MFCs or CDIs) and two ion-desorption modes (short-circuit and reverse-voltage desorption) were compared. Results showed that the MFC-CDI system could be reasonably modeled (R 2 > 0.967) by a first-order resistor–capacitor circuit. The optimal arrangement of the MFC-CDI circuit depended on the electrical characteristics of selected MFCs and CDIs as well as operating conditions. When the system was powered by two MFCs of a larger internal resistance (146 Ω), the highest salt removal after 60 min ( m 60 ; 7.5 mg) was achieved by paralleling the two MFCs; with MFCs of a smaller resistance (12 Ω) being used, the highest m 60 (16.5 mg) was obtained when the two MFCs were connected in series. Further analysis revealed that the MFC's internal resistance and open-circuit voltage, along with the CDI's internal resistance and capacitance, were the chief factors affecting the charge transfer and accordingly desalination on the CDI electrodes. [ABSTRACT FROM AUTHOR]

In this study, a microbial fuel cell (MFC) with granular activated carbon packed anode (GAC-MFC) is developed and compared with a MFC with granular graphite packed anode (GG-MFC), to evaluate the adsorptive effect of the granular activated carbon anode on MFC’s performance. The current output of GAC-MFC (11.1 mA, 18.1 mA and 21.6 mA) is much higher than that of GG-MFC (4.87 mA, 12.5 mA and 17.9 mA) at low substrate COD concentrations (∼50, ∼100 and ∼200 mg/L) when a low external resistance (20 Ω) and high circulation flow rate (20 mL/min) are applied. The half-saturation constant ( K s ) of GAC-MFC is about half as much as that of GG-MFC, suggesting that GAC-MFC has more affinity for anode substrate and deliver better kinetic performance than GG-MFC. Internal resistance distribution shows that mass diffusion resistance of GAC-MFC is at least 50% lower than that of GG-MFC when the substrate COD is ∼50 mg/L, indicating that the adsorptive effect of granular activated carbon packed anode helps to effectively facilitate mass transfer at low COD concentrations. Otherwise, the substrates adsorbed on GAC surface also serve to buffer the impact of COD concentration plummeting in bulk solution. [ABSTRACT FROM AUTHOR]

A novel anode is fabricated by electrodepositing manganese dioxide (MnO 2 ) on carbon felt to promote MFC's power production. Compared to the bare carbon felt anode, when the electrodeposition time increases to 60 min, the anode capacitance improves 46 times. The maximum power density of the MFC with the MnO 2 -coated anode reaches 3580 ± 130 mW m −2 , 24.7% higher than that with the bare carbon felt anode (2870 mW m −2 ). MnO 2 is believed to facilitate extracellular electron transfer and accordingly improve the power output. Three anode substrate circulation modes, i.e., flow-through, side-flow, and no-flow, are applied. Electrochemical impedance spectroscopy (EIS) tests reveal that flow-through mode decreases the anode mass transfer resistance by 41.4% compared to the no-flow mode and contributes to the MFC's power production improvement. [ABSTRACT FROM AUTHOR]

Abstract Electron transfer efficiency in electroactive biofilm is the limiting factor for bioelectricity output of bioelectrochemical system. Here, carbon felt (CF) is coated with manganese dioxide (MnO 2) which acts as electron mediator in electroactive biofilm. A wrapping layer of conducting Poly 3,4-ethylenedioxythiophene is developed to protect the MnO 2 and enhance electron transfer efficiency of MnO 2 mediator. The hybrid bioanode (PEDOT/MnO 2 /CF bioanode) delivered the highest electron transfer efficiency (6.3 × 10−9 mol cm−2 s−1/2) and the highest capacitance of 4.78 F, much higher than bare CF bioanode (1.50 ± 0.04 × 10−9 mol cm−2 s−1/2 and 0.42 F). As a result, microbial fuel cells could produce a maximum power density of 1534 ± 13 mW m−2, approximately 57.7% higher than that with the bare carbon felt anode (972 ± 21 mW m−2). Possible mechanisms are proposed to help understanding the different function of the PEDOT and MnO 2 on the anodic layer. This study introduces an effective method for the fabrication of high performance anode. Graphical abstract Unlabelled Image Highlights • A MnO 2 layer acts as electron mediator in electrochemical biofilm. • The wrapping layer of PEDOT helps to enhance electron transfer efficiency. • Electron transfer efficiency improved by ~4 times. • PEDOT/MnO 2 /CF anode increases the maximum power density by 143%. [ABSTRACT FROM AUTHOR]

Abstract A new photoelectrocatalytic (PEC) and microbial fuel cell (MFC) process was developed and applied to simultaneously remove refractory organic pollutants (i.e., phenol and aniline) from wastewater while recovering energy for in-situ utilization. The current generated by the MFC process was applied to drive the PEC reaction. Compared with single PEC or MFC processes, the PEC-MFC combined process showed higher pollutant and chemical oxygen demand (COD) removal capacities and electricity production. Over 95% of the phenol or aniline was removed by these process, even at high initial concentrations. The COD removal efficiencies for phenol and aniline were ca. 96% (from 700 to 29 mg L−1) and 70% (from 165 to 49 mg L−1), respectively. Although the PEC process showed a limited contribution to phenol and aniline removals (16.5% and 43%, respectively), the utilization of PEC-treated phenol or aniline streams resulted in a MFC with higher voltage output, higher coulombic efficiency, maximal volumetric power density, and lower internal resistance as compared to untreated water. High-performance liquid chromatography coupled with mass spectrometry measurements revealed quinones/hydroquinones and low molecular weight organic acids to be produced as intermediates after the PEC process, which could improve the production of electricity in the MFC. Highlights • A new process composed of photoelectrocatalysis (PEC) and microbial fuel cell (MFC) was developed. • PEC-MFC may simultaneously remove pollutants and recover energy for in-situ utilization. • The (hydro)Quinones and low-molecular-weight organic acid as products from PEC increase electricity production of MFC. • A consecutive, dynamic adsorption and degradation process in MFC supply stable current to drive PEC. [ABSTRACT FROM AUTHOR]

An early warning system is important to guarantee human health and ecological safety. Microbial fuel cell (MFC) sensor can achieve a self-sustainable monitoring without additional transducer or power sources. It would not limited by the main bottleneck of other contemporary MFC technologies, i.e., the low current density output, and is believed one of the most promising applications in the niche market of MFC technologies. This review is limited to MFC sensors for water quality early warning systems only, with emphasis on biochemical oxygen demand (BOD) and toxicity sensors. A comprehensive summary and discussion on sensor fabrication, operation, data representation, and optimization are provided. The MFC sensor is particularly promising to serve as a self-powered sensing device for in-situ and on-line environmental monitoring, as proved both in laboratory and field test. In addition, the main hurdles and future perspectives are discussed, as well as potential future research, which includes the following: separately lowering the detection limit or improving the concentration range dependent on the application of MFC for organic matter monitoring; further improving the sensitivity as well as lowering the recovery time of biofilm after a certain shock; developing the kinetic and/or empirical model in combining with the detection algorithm to distinguish the signal interference of complex aquatic environment, especially when the shock of BOD and toxicity occur simultaneously. [ABSTRACT FROM AUTHOR]

Microbial desalination cells are considered a low-energy-consumption, clean technology to simultaneously purify wastewater and desalinate saline water by utilizing the in situ energy source contained in wastewater. To enhance desalination performance and achieve an optimal membrane stack configuration, an enlarged stacked microbial desalination cell (SMDC) has been developed and tested with 6–14 desalination cells. The cross-membrane area of the enlarged SMDC is 100 cm 2 . The anode and cathode volumes are both 200 mL. To reduce internal resistance, the width of desalination cells is kept as <0.5 mm. The optimal configuration with 10 desalination cells achieves the highest total desalination rate (TDR) of 423 mg/h and the highest charge transfer efficiency (CTE) of 836% when treating the 20 g/L NaCl solution. During this process, the junction potential across membranes increases from 0 to 374 mV, and occupies up to 74% of the total potential loss inside the SMDC. This shows that the SMDC used in this work achieves the highest TDR and CTE among the reported studies, and the junction potential should be effectively controlled to achieve the desired desalination performance in future practical applications. [ABSTRACT FROM AUTHOR]

A homogeneous carbon membrane with multi-functions of microfiltration, electron conduction, and oxygen reduction catalysis was fabricated without using noble metals. The produced carbon membrane has a pore size of 553 nm, a resistance of 6.0 ± 0.4 Ω cm 2 /cm, and a specific surface area of 32.2 m 2 /g. After it was assembled in microbial fuel cell (MFC) as filtration air cathode, a power density of 581.5 mW/m 2 and a current density of 1671.4 mA/m 2 were achieved, comparable with previous Pt air cathode MFCs. The filtration MFC was continuously operated for 20 days and excellent wastewater treatment performance was also achieved with removal efficiencies of TOC (93.6%), NH 4 + –N (97.2%), and total nitrogen (91.6%). In addition, the carbon membrane was much cheaper than traditional microfiltration membrane, suggesting a promising multi-functional material in wastewater treatment field. [ABSTRACT FROM AUTHOR]

Malodorous surface water is an important worldwide environmental concern. Current remediation methods, such as aeration or the addition of chemicals, are not eco-friendly due to their high energy consumption or secondary pollution. This study proposed a modified columnar air-cathode microbial fuel cell as a sustainable and effective remediation module to improve water quality. The excellent and economic sheet air-cathode (activated carbon and carbon black as the catalyst layer) and a carbon brush anode were applied in the columnar air-cathode microbial fuel cell (MFC). The results after 48 h showed that by providing the anode as an electron acceptor and enriching electrochemically-active bacteria, MFCs with different external resistances (5 k Ω, 30 Ω, and 2 Ω) exhibited the much better capacity to improve water quality than the Blank group. The maximum COD and sulfide removal rates in the MFCs were approximately 86.3% and 100%, respectively, which were higher than those of the Blank group by 30% and 35%, respectively. The MFCs also showed maximum sulfate increments from 28 mg L−1 to 98 mg L−1 compared with the sulfate reduction to 10 mg L−1 in the Blank group. The oxidation reduction potential (ORP) of the MFCs dramatically increased from −281.2 mV to −135.7 mV after 24 h, whereas the ORP of the Blank group decreased to −287.7 mV. The enrichment of the aerobic bacteria Acinetobacter on the anodes and chemolithoautotrophic sulfide oxidation bacteria Sulfuricurvum, Thiovirga and Thiobacillus in the MFCs could also contribute to COD and sulfide removal. Cathode reduction, which could produce small amounts of hydroxyl radicals, might assist with the ORP elevation and the complete oxidation of dissolved sulfide to sulfate. Unlabelled Image • A modified columnar air-cathode MFC is designed for remediation of overlying water in malodorous surface water. • MFC significantly improves COD and sulfide removal rates with sulfate accumulation. • MFC elevates ORP in simulated overlying water dramatically. • MFC enhances the enrichment of chemolithoautotrophic sulfide oxidation bacteria. • Hydroxyl radicals detected in MFC is one possible contributor for remediation. [ABSTRACT FROM AUTHOR]

As a viable wastewater treatment and energy recovery technology, microbial fuel cell (MFC) requires more research with regard to the simultaneous achievement of high-quality effluent and high power generation. In this study, a novel flow-through carbon-based composite anode configuration is proposed, which combines the carbon cloth of two-dimensional anode with wooden granular activated carbon of three-dimensional anode. The proposed configuration enhances the performance of power production and chemical oxygen demand degradation by promoting the mass transfer, reducing internal resistance and increasing bioburden. Microbial fuel cell with the composite anode exhibited the highest maximum power density (1300 ± 50 mW m−2) and the highest chemical oxygen demand removal rate constant (0.155 ± 0.007 h−1) compared with the microbial fuel cell using the carbon cloth anode (1136 ± 46 mW m−2 and 0.072 ± 0.008 h−1) or the wooden granular activated carbon anode (1045 ± 32 mW m−2 and 0.129 ± 0.009 h−1). Meanwhile, at a lower chemical oxygen demand concentration (about 48 mg L−1), the microbial fuel cell with the composite anode maintained a current density of 2.4 A m−2, which is 18% higher than the wooden granular activated carbon anode (2.04 A m−2) and 400% higher than the carbon cloth anode (0.48 A m−2). The cyclic voltammetry and electrochemical impedance spectroscopy tests confirmed that the composite anodes displayed better electrochemical performance. Improving the flow rate and reducing the external resistance could effectively enhance the power production and chemical oxygen demand removal performance of microbial fuel cells, while the computational fluid dynamics simulation intuitively demonstrated the positive effect of the composite anode on chemical oxygen demand degradation. These results suggest that the flow-through composite anode provides a feasible strategy to simultaneously enhance the power generation and improve the effluent quality. Image 1 • A composite anode was constructed by optimizing 2D and 3D carbon anode materials.. • Flow-through composite anode MFC had higher power generation and COD removal rate. • Flow-through composite anode MFC maintained high power generation at low COD. • Reducing external resistance and improving flow rate enhanced the MFC performance. • Flow-through composite anode MFC was proved better COD removal in CFD simulation. [ABSTRACT FROM AUTHOR]

Microbial electrosynthesis (MES) has been proposed as a sustainable platform to simultaneously achieve wastewater treatment, renewable energy generation and chemicals production. Currently, the CO 2 valorization via MES is restricted by the low production rate, while that via electrochemical reduction is limited by the production of C1 products with high efficiency and selectivity. The electrocatalyst-assisted MES could potentially solve these bottlenecks of both MES and electrochemical reduction technology by increasing the production rate and expanding the product range. Here, four types of metals were evaluated for mixed culture-based, electrocatalyst-assisted MES with the fabrication of electrical-biological hybrid cathodes. Cathodes based on In, Zn, Ti and Cu showed high parallelism at 30 A/m2. However, no parallelism was observed at 50 A/m2, and only Zn experienced a further increase of the maximum acetic acid production rate (1.23 ± 0.02 g/L/d, 313 ± 5 g/m2/d) and titer (9.2 ± 0.1 g/L), with the highest value of the production rate normalized to the project area of the fiber cathodes. Other volatile fatty acids and ethanol were below 0.5 g/L. Moreover, it was the sharp H 2 generation, which mainly caused the fluctuation of coulombic efficiency. The application of such Zn-based electrical-biological hybrid system shall provide a more efficient route for CO 2 valorization. Image 1 • Electrocatalysts (In, Zn, Ti, Cu) were evaluated for electrocatalyst-assisted MES. • Zn based electrical-biological hybrid cathode can be steadily operated at 50 A/m2. • It has the highest record of fiber cathodes (1.23 ± 0.02 g/L/d, 313 ± 5 g/m2/d). • Sharp H 2 generation mainly caused the catholyte alkalization and CE fluctuation. [ABSTRACT FROM AUTHOR]

Cost-effective cobalt oxides were synthesized at mild condition as alternatives to platinum catalyst for oxygen reduction in microbial fuel cells (MFCs). The catalysts were prepared by heating Co(NO 3 ) 2 above its decomposition temperature together with carbon black (CB). At a catalyst loading of 5 mg/cm 2 , cobalt oxide cathodes with a Co(NO 3 ) 2 to CB ratio of 0.732:1 produced a maximum power density of 1220 mW/m 2 , which was slightly lower than that of Pt/C cathodes (1360 mW/m 2 ). Further increase in the loading of cobalt oxides resulted in an increase in performance. The maximum power densities produced by cobalt oxide cathodes increased to 1400 mW/m 2 at a catalyst loading of 20 mg/cm 2 and 1540 mW/m 2 at 30 mg/cm 2 , which outperformed the Pt/C control. The durability of cobalt oxide catalysts was comparable to that of Pt/C in single-chamber MFCs with biological contamination. The costs of cobalt oxide catalysts were much lower than that of Pt/C catalyst, even when the loading of cobalt oxides was several times higher than Pt/C catalyst. These findings show that the facilely synthesized cobalt oxides were cost-effective catalysts for oxygen reduction in air-cathode MFCs. [ABSTRACT FROM AUTHOR]

A microbial fuel cell (MFC), as a cleaner wastewater treatment process, can recover electricity from organic wastes. However, high power production and high quality effluent are difficult to achieve simultaneously. In this study, a novel filtration composite anode (FCA), which combined carbon fiber brush and carbon textile was proposed to enhance COD removal and power generation performance of MFCs. The COD removal rate constant of MFCs with the filtration composite anode (FCA-MFC) was 0.33 h −1 , much higher than that of MFCs with single brush anode (FB-MFC) (0.23 h −1 ) or textile anode (FT-MFC) (0.18 h −1 ) in the recirculation mode, and also exceeded that of CA-MFC in non-recirculation mode (0.12 h −1 ). FCA-MFC delivered a maximum power density of 1140 mW m −2 at a recirculation rate of 2 mL min −1 , which was higher than the FB-MFC (990 mW m −2 ) and the FT-MFC (80 mW m −2 ) and its counterparts in non-recirculation mode (1000 mW m −2 ). Moreover, the FCA-MFC maintained a higher current density (4.0 A m −2 ) than the other two MFCs until the COD decreased to 40 mg L −1 at an external resistance of 100 Ω. CV and EIS tests verified a higher electrochemical performance of the filtration composite anode. These results demonstrated higher COD removals and power generation of the composite anode at ambient temperature, resulting from the filtration effect that facilitated mass transfer, increased microbial colonization, and improved electrochemical activity. Considering the high-quality effluent and high power generation, the filtration composite anode configuration promises a great potential for sustainable wastewater treatment application. [ABSTRACT FROM AUTHOR]

Utilization of two-electron oxygen reduction reaction (ORR) in bioelectrochemical systems (BES) is a novel way to generate H 2 O 2 from wastewater, and cathode catalyst is a key factor affecting ORR performance. Here, the catalytic performance of plain graphene, oxidized graphene and graphene oxide (GO) in microbial fuel cells (MFCs) and the influence of oxygen-containing functional groups are reported. Oxidized graphene air-cathode had 78% and 131% higher H 2 O 2 productions than plain graphene cathode respectively in an abiotic reactor and an MFC. GO showed nearly no H 2 O 2 production in the tests. XPS revealed that oxygen atomic fraction of oxidized graphene reached 5.7%, mostly in the form of C O C. These results show that oxidized graphene had good catalytic performance for H 2 O 2 production, and oxygen-containing functional groups, especially C O C could significantly enhance its performance, but overoxidation worked adversely. Meanwhile, using oxidized graphene air-cathode could realize simultaneous wastewater treatment, power output and H 2 O 2 generation in MFCs. [ABSTRACT FROM AUTHOR]

In this study, nitrogen-doped carbon nanotube (N-CNT) membrane compared with Pt-coated CNT (Pt-CNT) membrane and pristine CNT membrane were utilized as air cathode as well as filtration material of microbial fuel cells (MFCs). The MFCs were continuously operated for 39 days to investigate their power generation, organics removal, proton transfer, and fouling behavior under various influent concentrations and hydraulic retention times (HRTs). During operation, the N-CNT filtration MFC achieved the best effluent quality and power generation, with efficient removal of total organic carbon (TOC) (95.2%) and NH 4 + -N (97.7%), and maximum power density and current density of 408 mW/m 2 and 2.36 A/m 2 respectively. The excellent performance of the N-CNT MFC was mainly attributed to its special morphology and rich N-functional groups. The N-CNT membrane has a nanotube diameter of 37 ± 4 nm, pore size of 95 ± 33 nm, and porosity of 79.9%, which was even better than traditional microfiltration membrane as a filtration material for pollutant removal. The high nitrogen content (2.12 at%) and high specific surface area (93.5 m 2 /g) due to its network structure also enhanced O 2 reduction. In addition to the excellent performance of N-CNT cathode, the filtration operation enhanced cathode O 2 reduction by increasing mass transfer in cathode micro-pore and improving proton transfer with water flowing from anode to cathode. Moreover, a separate experiment also demonstrated that the cathode fouling could be mitigated under high current operation. [ABSTRACT FROM AUTHOR]

A novel stacked microbial fuel cell (MFC) which had a total volume of 72 L with granular activated carbon (GAC) packed bed electrodes was constructed and verified to present remarkable power generation and COD removal performance due to its advantageous design of stack and electrode configuration. During the fed-batch operation period, a power density of 50.9 ± 1.7 W/m 3 and a COD removal efficiency of 97% were achieved within 48 h. Because of the differences among MFC modules in the stack, reversal current occurred in parallel circuit connection with high external resistances (>100 Ω). This reversal current consequently reduced the electrochemical performance of some MFC modules and led to a lower power density in parallel circuit connection than that in independent circuit connection. While increasing the influent COD concentrations from 200 to 800 mg/L at hydraulic retention time of 1.25 h in continuous operation mode, the power density of stacked MFC increased from 25.6 ± 2.5 to 42.1 ± 1.2 W/m 3 and the COD removal rates increased from 1.3 to 5.2 kg COD/(m 3 d). This study demonstrated that this novel MFC stack configuration coupling with GAC packed bed electrode could be a feasible strategy to effectively scale up MFC systems. [ABSTRACT FROM AUTHOR]