Sequential anaerobic and electro-Fenton processes mediated by W and Mo oxides for degradation/mineralization of azo dye methyl orange in photo assisted microbial fuel cells

The intensification of the degradation and mineralization of the azo dye methyl orange (MO) in contaminated water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs) operated sequentially under anaerobic - aerobic processes, in the presence of Fe(III) and W and Mo oxides catalytic species. In this novel process, the W and Mo oxides deposited on the graphite felt cathodes accelerated electron transfer and the reductive decolorization of MO. Simultaneously, the mineralization of MO and intermediate products was intensified by the production of hydroxyl radicals (HO[rad]) produced by (i) the photoreduction of Fe(III) to Fe(II), and by (ii) the reaction of the photochemically and electrochemically produced Fe(II) with hydrogen peroxide, which was produced in-situ during the aerobic stage. Under anaerobic conditions, the reductive decolorization of MO was driven by cathodic electrons, while the partial oxidation of the intermediates proceeded through holes oxidation, producing N,N-dimethyl-p-phenylenediamine. In contrast, under aerobic conditions superoxide radicals (O2[rad]−) were predominant to HO[rad], forming 4-hydroxy-N,N-dimethylaniline. In the presence of Fe(III) and under aerobic conditions, the oxidation of the intermediate products driven by HO[rad] superseded that of O2[rad]−, yielding phenol and amines, via the oxidation of 4-hydroxy-N,N-dimethylaniline and N,N-dimethyl-p-phenylenediamine. These sequential anaerobic and electro-Fenton processes led to the production of benzene and significantly faster oxidation reactions, compared to either the anaerobic or the aerobic operation in the presence of Fe(III). Complete degradation and mineralization (96.8 ± 3.5%) of MO (20 mg/L) with simultaneous electricity production (0.0002 kW h/kg MO) was therefore achieved with sequential anaerobic (20 min) - aerobic (100 min) operation in the presence of Fe(III) (10 mg/L). This study demonstrates an alternative and environmentally benign approach for efficient remediation of azo dye contaminated water with simultaneous production of renewable energy

Electricity generation and bivalent copper reduction as a function of operation time and cathode electrode material in microbial fuel cells

The performance of carbon rod (CR), titanium sheet (TS), stainless steel woven mesh (SSM) and copper sheet (CS) cathode materials are investigated in microbial fuel cells (MFCs) for simultaneous electricity generation and Cu(II) reduction, in multiple batch cycle operations. After 12 cycles, the MFC with CR exhibits 55% reduction in the maximum power density and 76% increase in Cu(II) removal. In contrast, the TS and SSM cathodes at cycle 12 show maximum power densities of 1.7 (TS) and 3.4 (SSM) times, and Cu(II) removal of 1.2 (TS) and 1.3 (SSM) times higher than those observed during the first cycle. Diffusional resistance in the TS and SSM cathodes is found to appreciably decrease over time due to the copper deposition. In contrast to CR, TS and SSM, the cathode made with CS is heavily corroded in the first cycle, exhibiting significant reduction in both the maximum power density and Cu(II) removal at cycle 2, after which the performance stabilizes. These results demonstrate that the initial deposition of copper on the cathodes of MFCs is crucial for efficient and continuous Cu(II) reduction and electricity generation over prolonged time. This effect is closely associated with the nature of the cathode material. Among the materials examined, the SSM is the most effective and inexpensive cathode for practical use in MFCs

Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials

© 2016 Elsevier B.V.The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO4−) and dichromate (Cr2O72−) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy

Correlation between circuital current, Cu(II) reduction and cellular electron transfer in EAB isolated from Cu(II)-reduced biocathodes of microbial fuel cells

The performance of four indigenous electrochemically active bacteria (EAB) (Stenotrophomonas maltophilia JY1, Citrobacter sp. JY3, Pseudomonas aeruginosa JY5 and Stenotrophomonas sp. JY6) was evaluated for Cu(II) reduction on the cathodes of microbial fuel cells (MFCs). These EAB were isolated from well adapted mixed cultures on the MFC cathodes operated for Cu(II) reduction. The relationship between circuital current, Cu(II) reduction rate, and cellular electron transfer processes was investigated from a mechanistic point of view using X-ray photoelectron spectroscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectrometry, linear sweep voltammetry and cyclic voltammetry. JY1 and JY5 exhibited a weak correlation between circuital current and Cu(II) reduction. A much stronger correlation was observed for JY3 followed by JY6, demonstrating the relationship between circuital current and Cu(II) reduction for these species. In the presence of electron transfer inhibitors (2,4-dinitrophenol or rotenone), significant inhibition on JY6 activity and a weak effect on JY1, JY3 and JY5 was observed, confirming a strong correlation between cellular electron transfer processes and either Cu(II) reduction or circuital current. This study provides evidence of the diverse functions played by these EAB, and adds to a deeper understanding of the capabilities exerted by diverse EAB associated with Cu(II) reduction

Intensified degradation and mineralization of antibiotic metronidazole in photo-assisted microbial fuel cells with Mo-W catalytic cathodes under anaerobic or aerobic conditions in the presence of Fe(III)

A novel strategy to intensify the degradation and mineralization of the antibiotic drug metronidazole (MNZ) in water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs). In this system Mo and W catalytic species immobilized onto a graphite felt cathode intensified the cathodic reduction of MNZ under anaerobic conditions and the oxidation of MNZ under aerobic conditions. The aerobic oxidation process was further accelerated in the presence of Fe(III), realizing a combined photo-assisted MFCs and Fenton-MFCs process. The highest rates of MNZ degradation (94.5 ± 1.4%; 75.6 ± 1.1 mg/L/h) and mineralization (89.5 ± 1.1%; 71.6 ± 0.9 mg/L/h), and power production (251 mW/m2; 0.015 kWh/m3; 0.22 kWh/kg COD) were achieved at a Mo/W loading of 0.18 mg/cm2with a Mo/W ratio of 0.17:1.0, in the presence of 10 mg/L of Fe(III) and at an incident photon flux of 23.3 mW/cm2. Photo-generated holes were directly involved into the oxidation of MNZ under anaerobic conditions. Conversely, under aerobic conditions, the photo-generated electrons favored the production of O2[rad]−over [rad]OH, while in the presence of Fe(III), [rad]OH was predominant over O2[rad]−, explaining the intensification of the MNZ mineralization observed. This study demonstrates an alternative and environmentally benign approach for the intensification of the removal of the antibiotic MNZ in water and possibly other contaminants of emerging concern by combining photo-assisted MFCs and Fenton-MFCs in a single process with simultaneous production of renewable electrical energy

Improvement of Water-, Sulfur Dioxide-, and Dust-Resistance in Selective Catalytic Reduction of NO_<i>x</i> with NH₃ Using a Wire-Mesh Honeycomb Catalyst

A novel V₂O₅/WO₃/TiO₂/Al₂O₃/wire-mesh honeycomb (WMH) catalyst was prepared for selective catalytic reduction (SCR) of NO_<i>x</i> with NH₃. The resistances to H₂O, SO₂, and dust were investigated for the WMH catalyst, which were compared with those for ceramic honeycomb (CH) catalysts. The results showed that the WMH catalyst kept above 95% NO_<i>x</i> conversion in the broad temperature window (250–425 °C) and provided nearly 92% NO_<i>x</i> conversion during H₂O and SO₂ durability test, which might be attributed to the unique three-dimensional structure. Furthermore, the WMH catalyst could provide nearly 90% NO_<i>x</i> conversion during 40 h dust exposure experiment owing to the little dust deposition of 2.9 g/m², whereas the amount of dust deposited on the CH catalyst with the same cell density reached 6.7 g/m², which resulted in a decrease of the NO_<i>x</i> conversion from 72% to 58%

Highly Permeable Thin-Film Composite Forward Osmosis Membrane Based on Carbon Nanotube Hollow Fiber Scaffold with Electrically Enhanced Fouling Resistance

Forward osmosis (FO) is an emerging approach in water treatment, but its application is restricted by severe internal concentration polarization (ICP) and low flux. In this work, a self-sustained carbon nanotube hollow fiber scaffold supported polyamide thin film composite (CNT TFC-FO) membrane was first proposed with high porosity, good hydrophilicity and excellent electro-conductivity. It showed a specific structure parameter as low as 126 μm, suggesting its weakened ICP. Against a pure water feed using 2.0 M NaCl draw solution, its fluxes were 4.7 and 3.6 times as high as those of the commercial cellulose triacetate TFC-FO membrane in the FO and pressure retarded osmosis (PRO) modes, respectively. Meanwhile, the membrane showed excellent electrically assisted resistance to organic and microbial fouling. Its flux was improved by about 50% during oil–water simulation separation under 2.0 V voltage. These results indicate that the CNT TFC-FO membrane opens up a frontier for stably and effectively recycling potable water from electrochemical FO process

Supplementary information files for: A light-management film layer induces dramatically enhanced acetate production in photo-assisted microbial electrosynthesis systems

Supplementary files for article A light-management film layer induces dramatically enhanced acetate production in photo-assisted microbial electrosynthesis systems.  A light-management system consisting of a Al-doped ZnO (AZO) film layer was combined for the first time with different bio-photocathodes (Serratia marcescens Q1 electrotroph immobilized on g-C3N4, MnFe2O4 or MnFe2O4/g-C3N4) to significantly enhance acetate production from bicarbonate in photo-assisted microbial electrosynthesis systems (MES). The AZO light-management system exhibiting optical properties independent of the light incident angle mitigated the shielding effect of light by electrotrophs, increasing light trapping and decreasing light reflection, ultimately allowing higher rates of photon absorption and redistributions of photons over the photo-active layers. As a result, more reducing equivalents as H2 produced up to 242% (g-C3N4/AZO-filter) and 543% (g-C3N4/AZO) increase in acetate production at coulombic efficiencies of 70% (g-C3N4/AZO-filter) and 81% (g-C3N4/AZO). The record high solar-to-acetate efficiency obtained with the MnFe2O4/g-C3N4/AZO biocathode was 3.20%. The light-management system proposed in this study opens a new promising way to construct efficient bio-photocathodes for inorganic carbon reduction in photo-assisted MES. </p

A light-management film layer induces dramatically enhanced acetate production in photo-assisted microbial electrosynthesis systems

A light-management system consisting of a Al-doped ZnO (AZO) film layer was combined for the first time with different bio-photocathodes (Serratia marcescens Q1 electrotroph immobilized on g-C3N4, MnFe2O4 or MnFe2O4/g-C3N4) to significantly enhance acetate production from bicarbonate in photo-assisted microbial electrosynthesis systems (MES). The AZO light-management system exhibiting optical properties independent of the light incident angle mitigated the shielding effect of light by electrotrophs, increasing light trapping and decreasing light reflection, ultimately allowing higher rates of photon absorption and redistributions of photons over the photo-active layers. As a result, more reducing equivalents as H2 produced up to 242% (g-C3N4/AZO-filter) and 543% (g-C3N4/AZO) increase in acetate production at coulombic efficiencies of 70% (g-C3N4/AZO-filter) and 81% (g-C3N4/AZO). The record high solar-to-acetate efficiency obtained with the MnFe2O4/g-C3N4/AZO biocathode was 3.20%. The light-management system proposed in this study opens a new promising way to construct efficient bio-photocathodes for inorganic carbon reduction in photo-assisted MES.</p

Enhancement of Catalytic Activity Over the Iron-Modified Ce/TiO₂ Catalyst for Selective Catalytic Reduction of NO_<i>x</i> with Ammonia

A series of iron-modified Ce/TiO₂ catalysts with different Fe/Ti molar ratios were prepared by an impregnation method and used for selective catalytic reaction (SCR) of NO_<i>x</i> with NH₃. The Fe–Ce/TiO₂ catalyst with a Fe/Ti molar ratio of 0.2 had good low-temperature activity and sulfur-poisoning resistance compared with the Ce/TiO₂ catalyst. The introduction of Fe could increase the amount of Ce³⁺ and chemisorbed oxygen species on the catalyst surface and thereafter generate more ionic NH₄⁺ and in situ formed NO₂, respectively. In addition, the dispersion of cerium oxide could be improved by the addition of iron, and no visible phase of iron oxide could be observed at low Fe/Ti molar ratios (≤0.2). All of these factors played significant roles in the enhanced catalytic activity, especially the low-temperature activity. Furthermore, mechanisms of the SCR reaction and the SO₂ poisoning of the Fe(0.2)–Ce/TiO₂ catalyst were studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. Coordinated NH₃ and ionic NH₄⁺ species as well as adsorbed NO₂ might be the key intermediates in the SCR reaction in the relatively low-temperature range. The formation of ammonium sulfate appeared to be the dominant cause for the catalyst deactivation in SO₂-containing gases