Effect of different acclimation methods on the performance of microbial fuel cells using phenol as substrate.

Single-chamber microbial fuel cells (MFCs) with air-cathode were constructed. MFCs were fed different feedstocks during their inoculation, their role on phenol degradation and MFC performance were investigated. The results showed that the MFC inoculated using glucose exhibited the highest power density (31.3 mW m(-2)) when phenol was used as the sole substrate for MFC. The corresponding biodegradation kinetic constant was obtained at 0.035 h(-1), at an initial phenol concentration of 600 mg L(-1). Moreover, the phenol degradation rates in this MFC with closed circuit were 9.8-16.5% higher than those in MFC with opened circuit. The cyclic voltammograms revealed a different electrochemical activity of the anode biofilms in the MFC, and this led to differences in performance of the MFCs with phenol as sole substrate. These results demonstrated that phenol degradation and power production are affected by current generation and type of acclimation.

A novel core-shell Fe@Co nanoparticles uniformly modified graphite felt cathode (Fe@Co/GF) for efficient bio-electro-Fenton degradation of phenolic compounds.

In this study, a core-shell Fe@Co nanoparticles uniformly modified graphite felt (Fe@Co/GF) was fabricated as the cathode by one-pot self-assembly strategy for the degradation of vanillic acid (VA), syringic acid (SA), and 4-hydroxybenzoic acid (HBA) in the Bio-Electro-Fenton (BEF) system. The Fe@Co/GF cathode showed dual advantages with excellent electrochemical performance and catalytic reactivity not only due to the high electron transfer efficiency but also the synergistic redox cycles between Fe and Co species, both of which significantly enhanced the in situ generation of H2O2 and hydroxyl radicals (OH) to 152.40 µmol/L and 138.48 µmol/L, respectively. In this case, the degradation rates of VA, SA, and HBA reached 100, 94.32, and 100%, respectively, within 22 h. Representatively, VA was degraded and ultimately mineralized via demethylation, decarboxylation and ring-opening reactions. This work provided a promising approach for eliminating typical recalcitrant organic pollutants generated by the pre-treatment of lignocellulose resources.

Coordinated response of Au-NPs/rGO modified electroactive biofilms under phenolic compounds shock: Comprehensive analysis from architecture, composition, and activity.

Electroactive biofilms (EABs) can be integrated with conductive nanomaterials to boost extracellular electron transfer (EET) for achieving efficient waste treatment and energy conversion in bioelectrochemical systems. However, the in situ nanomaterial-modified EABs of mixed-culture, and their response under environmental stress are rarely revealed. Here, two nanocatalyst-decorated EABs were established by self-assembled Au nanoparticles-reduced graphene oxide (Au-NPs/rGO) in mixed-biofilms with different maturities, then their multi-property were analyzed under long-term phenolic shock. Results showed that the power density of Au-NPs/rGO decorated EABs was significantly enhanced by 28.66-42.82% due to the intensified EET pathways inside biofilms. Meanwhile, the electrochemical and catalytic performance of EABs were controllably regulated by 0.3-3.0 g/L phenolic compounds, which, however, resulted in differential alterations in their architecture, composition, and viability. EABs originated with higher maturity displayed more compact structure, lower thickness (110 µm), higher biomass (8.67 mg/cm2) and viability (0.85-0.91), endowing it better antishock ability to phenolic compounds. Phenolic-shock also induced the heterogeneous distribution of extracellular polymeric substances in terms of both spatial and bonding degrees of the decorated EABs, which could be regarded as an active response to strike a balance between self-protection and EET under environmental pressure. Our findings provide a broader understanding of microbe-electrode interactions in the micro-ecology interface and improve their performance in the removal of complex contaminants for sustainable remediation and new-energy development.

Degradation of phenolic compounds with simultaneous bioelectricity generation in microbial fuel cells: Influence of the dynamic shift in anode microbial community.

This study evaluated the feasibility of microbial fuel cells (MFCs) for simultaneous electricity generation and degradation of phenolic compounds. The voltage generation was inhibited by 36.18-63.90%, but the degradation rate increased by 146.15-392.31% when the initial concentration of syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA) increased from 0.3 to 3.0 g/L. The collaboration among the functional microbes significantly enhanced the degradation rate of parent compounds and their intermediates in MFCs systems, while the accumulated intermediates severely inhibited their complete mineralization in fermentative systems. High-throughput sequencing showed that the growth of fermentative bacteria prevailed, but electrogenic bacteria were inhibited in the anode microbial community (AMC) under high concentrations of phenolic compounds (3.0 g/L). These findings provide a better understanding of the dynamic shift and synergy effects of the AMC to evaluate its potential for the treatment of phenolic-containing wastewater.

Increased fermentative adenosine production by gene-targeted Bacillus subtilis mutation.

Adenosine, which is produced mainly by microbial fermentation, plays an important role in the therapy of cardiovascular disease and has been widely used as an antiarrhythmic agent. In this study, guanosine 5'-monophosphate (GMP) synthetase gene (guaA) was inactivated by gene-target manipulation to increase the metabolic flux from inosine 5'-monophosphate (IMP) to adenosine in B. subtilis A509. The resulted mutant M3-3 showed an increased adenosine production from 7.40 to 10.45 g/L, which was further enhanced to a maximum of 14.39 g/L by central composite design. As the synthesis of succinyladenosine monophosphate (sAMP) from IMP catalysed by adenylosuccinate synthetase (encoded by purA gene) is the rate-limiting step in adenosine synthesis, the up-regulated transcription level of purA was the potential underlying mechanism for the increased adenosine production. This work demonstrated a practical strategy for breeding B. subtilis strains for industrial nucleoside production.

Enhanced Bio-Electro-Fenton degradation of phenolic compounds based on a novel Fe-Mn/Graphite felt composite cathode.

Phenolic compounds are problematic byproducts generated from lignocellulose pretreatment. In this study, the feasibility degradation of syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA) by Bio-Electro-Fenton (BEF) system with a novel Fe-Mn/graphite felt (Fe-Mn/GF) composite cathode were investigated. The nano-scale Fe-Mn multivalent composite catalyst with core shell structure distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. Accordingly, the maximum power density generated with Fe-Mn/GF cathode was 48.1% and 238.9% higher than Fe/GF and GF respectively, which further enhanced the in situ generation of H2O2 due to the superiority of nano-scale core shell structure and synergistic effect of Fe and Mn species. The degradation efficiency of the three phenolic compounds in the BEF system could reached 100% after optimization of influencing parameters. Furthermore, a possible SA degradation pathway by BEF process in the present system was proposed based on the detected intermediates. These results demonstrated an efficient approach for the degradation of phenolic compounds derived from lignocellulose hydrolysates.

[Utilization of Copper (â ¡) Wastewater for Enhancing the Treatment of Chromium (â ¥) Wastewater in Microbial Fuel Cells].

The effect of copper (Ⅱ) wastewater addition on the treatment of chromium (Ⅵ) wastewater in dual-chamber microbial fuel cells (MFCs) was investigated for different Cr(Ⅵ)/Cu(Ⅱ) concentration ratios (2:1, 1:1, 1:2, 1:4) and external resistances (10, 500, 1000, 2000 Ω). The results demonstrated that the addition of Cu(Ⅱ) and Cr(Ⅵ) into the cathode chamber of MFCs could enhance the Cr(Ⅵ) removal efficiency. The Cr(Ⅵ) removal efficiency increased with the increase in the Cr(Ⅵ)/Cu(Ⅱ) concentration ratio. The Cu(Ⅱ) on the Cr(Ⅵ) removal efficiencies increased with the decrease of external resistance. The highest Cr(Ⅵ) removal efficiency achieved was 91.00% in MFC at the Cr(Ⅵ)/Cu(Ⅱ) concentration ratio of 1:4 and external resistance of 10 Ω, which was 132.57% higher than the MFC with Cr(Ⅵ) only (39.13%). The scanning electron microscopy with coupled energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) analyses of the cathode electrode at the end of the experiments indicated that Cr(Ⅵ) reduced to non-conductive Cr(Ⅲ) deposits (Cr2O3) on the cathode electrode, resulting in cathode deactivation which blocked the electron transfer. However, the addition of Cu(Ⅱ) could improve the electrical conductivity of the cathode due to its conductive reduzates (copper and Cu2O) on the cathode which could reduce the cathode deactivation and subsequently enhance the Cr(Ⅵ) removal efficiency.

[Effect of Activated Carbon Addition on the Anaerobic Fermentation of Corn Straw in Mesophilic and Thermophilic Conditions].

In order to improve the methane production and concentration, effect of activated carbon addition on the anaerobic fermentation of corn straw under the conditions of mesophilic temperature (38℃) and thermophilic temperature(50℃) was investigated in this study. The results showed that the addition of activated carbon could significantly promote methane production. Compared with the control group in mesophilic and thermophilic conditions, cumulative methane production could be increased by 63% and 96% in test groups. By DGGE analysis, the bacterium enriched by addition of activated carbon was mainly Clostridiales bacterium, compared to Bacillus (without adding activated carbon) in the thermophilic system, while the differences in fermentation with adding activated carbon and without adding activated carbon was not significant in the mesophilic system. With addition of activated carbon, the archaea enriched in the fermentation liquid was mainly Methanosaeta concilii in the mesophilic system, whereas the archaea enriched in the fermentation liquid was mainly Methanosarcina acetivorans in the thermophilic system. The archaea enriched on activated carbon was mainly Methanosaeta concilii at mesophilic temperature, while the archaea enriched on activated carbon was mainly Methanosarcina thermophila at thermophilic temperature.

Bio-Electron-Fenton (BEF) process driven by microbial fuel cells for triphenyltin chloride (TPTC) degradation.

The intensive use of triphenyltin chloride (TPTC) has caused serious environmental pollution. In this study, an effective method for TPTC degradation was proposed based on the Bio-Electron-Fenton process in microbial fuel cells (MFCs). The maximum voltage of the MFC with graphite felt as electrode was 278.47% higher than that of carbon cloth. The electricity generated by MFC can be used for in situ generation of H2O2 to a maximum of 135.96µmolL-1 at the Fe@Fe2O3(*)/graphite felt composite cathode, which further reacted with leached Fe2+ to produce hydroxyl radicals. While 100µmolL-1 TPTC was added to the cathodic chamber, the degradation efficiency of TPTC reached 78.32±2.07%, with a rate of 0.775±0.021µmolL-1h-1. This Bio-Electron-Fenton driving TPTC degradation might involve in SnC bonds breaking and the main process is probably a stepwise dephenylation until the formation of inorganic tin and CO2. This study provides an energy saving and efficient approach for TPTC degradation.

An integrated aerobic-anaerobic strategy for performance enhancement of Pseudomonas aeruginosa-inoculated microbial fuel cell.

Microbial fuel cell (MFC) is a promising device for energy generation and organic waste treatment simultaneously by electrochemically active bacteria (EAB). In this study, an integrated aerobic-anaerobic strategy was developed to improve the performance of P. aeruginosa-inoculated MFC. With an aerobic start-up and following an anaerobic discharge process, the current density of MFC reached a maximum of 99.80µA/cm2, which was 91.6% higher than the MFC with conventional constant-anaerobic operation. Cyclic voltammetry and HPLC analysis showed that aerobic start-up significantly increased electron shuttle (pyocyanin) production (76% higher than the constant-anaerobic MFC). Additionally, enhanced anode biofilm formation was also observed in the integrated aerobic-anaerobic MFC. The increased pyocyanin production and biofilm formation promoted extracellular electron transfer from EAB to the anode and were the underlying mechanism for the MFC performance enhancement. This work demonstrated the integrated aerobic-anaerobic strategy would be a practical strategy to enhance the electricity generation of MFC.

Electrophoretic deposition of multi-walled carbon nanotube on a stainless steel electrode for use in sediment microbial fuel cells.

Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. In order to improve electrode materials and enhance their effect on the performance, we deposited multi-walled carbon nanotube (MWNT) on stainless steel net (SSN). Electrophoretic deposition technique as a method with low cost, process simplicity, and thickness control was used for this electrode modification and produced this novel SSN-MWNT electrode. The performances of SMFCs with SSN-MWNT as electrode were investigated. The results showed that the maximum power density of SMFC with SSN-MWNT cathode was 31.6 mW m(-2), which was 3.2 times that of SMFC with an uncoated stainless steel cathode. However, no significant increase in the maximum power density of SMFC with SSN-MWNT anode was detected. Further electrochemical analysis showed that when SSN-MWNT was used as the cathode, the cathodic electrochemical activity and oxygen reduction rate were significantly improved. This study demonstrates that the electrophoretic deposition of carbon nanotubes on conductive substrate can be applied for improving the performance of SMFC.

Construction and operation of microbial fuel cell with Chlorella vulgaris biocathode for electricity generation.

In this study, a modified microbial fuel cell (MFC) with a tubular photobioreactor (PHB) configuration as a cathode compartment was constructed by introducing Chlorella vulgaris to the cathode chamber used to generate oxygen in situ. Two types of cathode materials and light/dark cycles were used to test the effect on MFC with algae biocathode. Results showed that the use of algae is an effective approach because these organisms can act as efficient in situ oxygenators, thereby facilitating the cathodic reaction. Dissolved oxygen and voltage output displayed a clear light positive response and were drastically enhanced compared with the abiotic cathode. In particular, carbon paper-coated Pt used as a cathode electrode increased voltage output at a higher extent than carbon felt used as an electrode. The maximum power density of 24.4 mW/m(2) was obtained from the MFC with algae biocathode which utilized the carbon paper-coated Pt as the cathode electrode under intermittent illumination. This density was 2.8 times higher than that of the abiotic cathode. Continuous illumination shortened the algal lifetime. These results demonstrated that intermittent illumination and cathode material-coated catalyst are beneficial to a more efficient and prolonged operation of MFC with C. vulgaris biocathode.

Construction and operation of microbial fuel cell with Chlorella vulgaris biocathode for electricity generation.

In this study, a modified microbial fuel cell (MFC) with a tubular photobioreactor (PHB) configuration as a cathode compartment was constructed by introducing Chlorella vulgaris to the cathode chamber used to generate oxygen in situ. Two types of cathode materials and light/dark cycles were used to test the effect on MFC with algae biocathode. Results showed that the use of algae is an effective approach because these organisms can act as efficient in situ oxygenators, thereby facilitating the cathodic reaction. Dissolved oxygen and voltage output displayed a clear light positive response and were drastically enhanced compared with the abiotic cathode. In particular, carbon paper-coated Pt used as a cathode electrode increased voltage output at a higher extent than carbon felt used as an electrode. The maximum power density of 24.4 mW/m2 was obtained from the MFC with algae biocathode which utilized the carbon paper-coated Pt as the cathode electrode under intermittent illumination. This density was 2.8 times higher than that of the abiotic cathode. Continuous illumination shortened the algal lifetime. These results demonstrated that intermittent illumination and cathode material-coated catalyst are beneficial to a more efficient and prolonged operation of MFC with C. vulgaris biocathode.