Bacterial community shift and improved performance induced by in situ preparing dual graphene modified bioelectrode in microbial fuel cell

Promoted electrochemical performance by MOF on MOF composite catalyst of microbial fuel cell: CuCo-MOF@ZIF-8 and the comparison between two-step hydrothermal method and dual-solution method

The microbial fuel cell (MFC) is a device that simultaneously achieves electricity generation and sewage degradation. In this study, a novel cathode catalyst metal-organic frameworks (MOFs) have been fabricated by two-step hydrothermal and dual-solution method (CuCo-MOF@ZIF-8). The synthesized trimetal MOFs exhibited a 3D badminton-like structure morphology and porosity. The results of the characterizations showed that CuCo-MOF@ZIF-8 possesses greater surface area porosity and novel functional groups. The Trimetal MOF-on-MOF mode not only demonstrated the stability of the structure but also enhanced its mechanism. Molecular mechanism analysis revealed changes in the organic ligand and metal binding site due to the transformation of Cu2+ to Cu+, Co2+ to Co3+, and Zn-N to Zn-O organic connection. Furthermore, differences between the two fabrication methods were compared. The solid-state single preparation (CuCo-MOF@ZIF-8-1), was synthesized using the two-step hydrothermal method; the liquid mixed preparation material (CuCo-MOF@ZIF-8-2), was synthesized using the dual-solution method; they exhibited completely different chemical structures and morphologies during material testing and characterization. The maximum output power density of CuCo-MOF@ZIF-8-2-MFC was 246.38 mW/m2, about 2.49 times of ZIF-8 (98.72 mW/m2). The output voltage of CuCo-MOF@ZIF-8-1-MFC was measured at 357 mV over 10 d, while that of CuCo-MOF@ZIF-8-2-MFC reached 365 mV over 12 d.

Impact of bioelectricity on DNRA process and microbial community composition within cathodic biofilms in dual-chambered bioelectrode microbial fuel cell (MFC)

The synchronous bioelectricity generation and dissimilatory nitrate reduction to ammonium (DNRA) pathway in Klebsiella variicola C1 was investigated. The presence of bioelectricity facilitated cell growth on the anodic biofilms, consequently enhancing the nitrate removal efficiency decreasing total nitrogen levels and causing a negligible accumulation of NO2- in the supernatant. Genomic analysis revealed that K. variicola C1 possessed a complete DNRA pathway and largely annotated electron shuttles. The up-regulated expression of genes narG and nirB, encoding nitrite oxidoreductase and nitrite reductase respectively, was closely associated with increased extracellular electron transfer (EET). High-throughput sequencing analysis was employed to investigate the impact of bioelectricity on microbial community composition within cathodic biofilms. Results indicated that Halomonas, Marinobacter and Prolixibacteraceae were enriched at the cathode electrodes. In conclusion, the integration of a DNRA strain with MFC facilitated the efficient removal of wastewater containing high concentrations of NO3- and enabled the environmentally friendly recovery of NH4+.

Magnetite-equipped algal-rich sediments for microbial fuel cells: Remediation of sediment organic matter pollution and mechanisms of remote electron transfer

Using the bio-electrochemical methods for the restoration of high algae sediments is full of potential and challenges. How to promote extracellular electron transfer (EET) process in microbial fuel cells (MFC) is the key bottleneck. The study had explored the potential application of magnetite on accelerating electron transfer for improving the output of MFC and sediment pollution remediation. The results indicated that the organic matter degradation rate showed a remarkable increase of 27.45 %, and the voltage output was approximately 1.68 times higher compared to the MFC configured with regular sediment. Abundant electroactive bacteria (EABs), such as Geobacter and Burkholderiaceae, and fermentative bacteria were responsible for these results, accompanied by the enhanced fluorescence of humic substances (HS), increased concentration and activity of cytochrome C (25.05 % and 21.12 %), as well as elevated extracellular polymeric substance content. Moreover, the intrinsic EET mechanisms among Fe-oxides, HS, and EABs were explored. According to the electrochemical analysis and substance transformation, the EET process involved four stages: magnetite-enhanced direct electron transfer via strong conductivity, iron respiration mediating electron transfer to the electrode, the model quinone substance acting as an electron shuttle facilitating EET and iron reduction, and iron cycling mediating electron transfer. This study provides an effective strategy for pollution remediation in algal-rich sediment, which was beneficial for the harmless treatment and resource utilization of both algae and sediment, simultaneously.

Treatment of phenolic wastewater by anaerobic fluidized bed microbial fuel cell using carbon brush as anode: microbial community analysis and m-cresol degradation mechanism

Anaerobic fluidized bed microbial fuel cell (AFB-MFC) is a technology that combines fluidized bed reactor and microbial fuel cell to treat organic wastewater and generate electricity. The performance and the mechanism of treating m-cresol wastewater in AFB-MFC using carbon brush as biofilm anode were studied. After 48 h of operation, the m-cresol removal efficiency of AFB-MFC, MAR-AFB (fluidized bed bioreactor with acclimated anaerobic sludge), MAR-FB (ordinary fluidized bed reactor with only macroporous adsorptive resin) and AST (traditional anaerobic sludge treatment) were 95.29 ± 0.67%, 85.78 ± 1.81%, 71.24 ± 1.86% and 70.41 ± 0.32% respectively. The maximum output voltage and the maximum power density of AFB-MFC using carbon brush as biofilm anode were 679.7 mV and 166.6 mW/m2 respectively. The results of high-throughput sequencing analysis indicated the relative abundance of dominant electroactive bacteria, such as Trichococcus, Geobacter, and Pseudomonas, on the anode carbon brushes was higher than that of AST, and also identified such superior m-cresol-degrading bacteria as Bdellovibrio, Thermomonas, Hydrogenophaga, etc. Based on the determination of m-cresol metabolites detected by Gas Chromatography-Mass Spectrometry (GC-MS), the possible biodegradation pathway of m-cresol under anaerobic and aerobic conditions in AFB-MFC was speculated. The results showed that m-cresol was decomposed into formic acid-acetic anhydride and 3-methylpropionic acid under the action of electrochemistry, which is a simple degradation pathway without peripheral metabolism in AFB-MFC.

Co-Fe-N@biochar anode for improvment the electricity generation performance of microbial fuel cell

Microbial fuel cells (MFCs) can generate energy while processing organic pollutants, which has a great impact on environmental wastewater treatment applications. In this study, a gel polymer was formed by Co-Fe-N co-doping biochar (Co-Fe-N@BC), which was used as the anode material to improve the electricity generation performance of MFC. The Co-Fe-N@BC material prepared at 900℃ carbonised biomass into more graphitic carbon, and its total resistance (3.56 Ω) was significantly reduced. In the corresponding dual-chamber MFC, the current density was 2.81 A/m2, and the power density reached 1181 mW/m2 at maximum. Among the materials tested, the Co-Fe-N@BC anode MFC had the highest chemical oxygen demand removal rate and coulombic efficiency, reaching 91% and 13%, respectively. It is proved that MFC with Co-Fe-N@BC anode has the best electrochemical performance.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

Enhanced MFC sensor performances and extracellular electron transport efficiency mediated by biochar and underlying biochemical mechanisms

To explore the application of biosensor in real-time monitoring of composite heavy metal polluted wastewater in view of the low performance of MFC sensor, this study used sodium alginate to immobilize biochar to the anode of MFC biosensor, and conducted a study on the sensor performance and related biological processes. The results showed that under the optimal HRT conditions, the output power of the MFC-sensor (BC-300) was 0.432 W/m³ after biochar modification, which was much higher than the highest power density of CG and BC-0 of 0.117 and 0.088 W/m³. The correlation coefficient was greater than that of the control group at the plating wastewater concentration of 0.1-1.0 M and had a wider detection range, and the time to recover the output voltage was 1/3 of that of the control group. The biochar significantly promoted the sensitivity, interference resistance, recovery and anti-interference performance of the MFC-sensor. The intrinsic mechanism was that the composition and structure of biochar lead to a 1.53 fold increase in the abundance of electrogenic microorganisms and the abundance of functional genes such as cytochrome c (MtrABC, CymA, Cox, etc.) and flavin (riba, Rib B, gdh, ushA, IDH, etc.) increased by about 1.03-3.20 times, which promoted the shift of electrons from intracellular to extracellular receptors and significantly improved the electron transfer and the energy metabolism efficiency. The results of this study can provide a reference for the application of MFCsensor to the detection of complex heavy metal effluents.

Bacterial community structure of electrogenic biofilm developed on modified graphite anode in microbial fuel cell

Formation of electrogenic microbial biofilm on the electrode is critical for harvesting electrical power from wastewater in microbial biofuel cells (MFCs). Although the knowledge of bacterial community structures in the biofilm is vital for the rational design of MFC electrodes, an in-depth study on the subject is still awaiting. Herein, we attempt to address this issue by creating electrogenic biofilm on modified graphite anodes assembled in an air-cathode MFC. The modification was performed with reduced graphene oxide (rGO), polyaniline (PANI), and carbon nanotube (CNTs) separately. To accelerate the growth of the biofilm, soybean-potato composite (plant) powder was blended with these conductive materials during the fabrication of the anodes. The MFC fabricated with PANI-based anode delivered the current density of 324.2 mA cm-2, followed by CNTs (248.75 mA cm-2), rGO (193 mA cm-2), and blank (without coating) (151 mA cm-2) graphite electrodes. Likewise, the PANI-based anode supported a robust biofilm growth containing maximum bacterial cell densities with diverse shapes and sizes of the cells and broad metabolic functionality. The alpha diversity of the biofilm developed over the anode coated with PANI was the loftiest operational taxonomic unit (2058 OUT) and Shannon index (7.56), as disclosed from the high-throughput 16S rRNA sequence analysis. Further, within these taxonomic units, exoelectrogenic phyla comprising Proteobacteria, Firmicutes, and Bacteroidetes were maximum with their corresponding level (%) 45.5, 36.2, and 9.8. The relative abundance of Gammaproteobacteria, Clostridia, and Bacilli at the class level, while Pseudomonas, Clostridium, Enterococcus, and Bifidobacterium at the genus level were comparatively higher in the PANI-based anode.

ZIF-8-derived Cu, N co-doped carbon as a bifunctional cathode catalyst for enhanced performance of microbial fuel cell

The development of bifunctional catalysts is an effective way to simultaneously address the slow kinetics of oxygen reduction reaction (ORR) on the cathode and biofilm contamination in the microbial fuel cells (MFC). Cu-N/C@Cu composites were synthesized as bifunctional cathode catalysts for MFC by doping, adsorption, and two calcinations by using Cu-ZIF-8 as the precursor. The higher Cu-N_x content confers excellent ORR catalytic activity to the optimized Cu-N/C@Cu-2 catalyst. The half-wave potential for Cu-N/C@Cu-2 in a neutral solution is 0.67 V vs. RHE, which is close to that of commercial 20% Pt/C (0.70 V vs. RHE). The maximum power density of the MFCs assembled with Cu-N/C@Cu-2 reached 581 ± 13 mW m^-2, which is even better than that using Pt/C (499 ± 13 mW m^-2). Moreover, the results of antimicrobial activity and biomass test show that the higher Cu content made Cu-N/C@Cu-2 effective against the contamination of cathode biofilm. And the 16S rDNA results find that the community structure of the biofilm is favorable for the power production and purification of MFC. This work shows that copper-based materials can be used as potential bifunctional catalysts to promote MFC applications in wastewater treatment.

A review on graphene / graphene oxide supported electrodes for microbial fuel cell applications: Challenges and prospects

Microbial Fuel Cell (MFC) has gained great interest as an alternative green technology for bioenergy generation along with reduced sludge production, nutrient recovery, removal of COD and color, etc. during wastewater treatment. However, the MFC has several challenges for real-time applications due to less power output and high ohmic resistance and fabrication (electrode and membrane) cost. Several kinds of research have been carried out to increase energy production by reducing various losses associated with electrodes in the MFC. Though, carbonaceous electrodes (carbon and graphite) are the key materials for the anode and cathode side, since these have a higher surface area, good biocompatibility, low cost, and good mechanical strength. Graphene or graphene oxide-based nanocomposite can be an ideal substitute for electrode modifications and an alternative for an expensive anode and cathode catalyst in MFC. Graphene oxide synthesis from waste material such as waste biomass, agricultural, plastic waste, etc. is added advantages of minimizing the cost of the electrodes. But, the synthesis of graphene is quite expensive and has limitations in economic feasibility for bioelectricity production in MFC. Hence, the present review deals with the anode and cathode electrode modification with graphene-based nanocomposites, synthesis of graphene/graphene oxide from various raw materials, and its application in MFC. The current challenges and future outlook on graphene-based composites on MFC performance are also discussed.

Quorum sensing signals improve the power performance and chlortetracycline degradation efficiency of mixed-culture electroactive biofilms

Electroactive biofilms (EABs) play an important role in bioelectrochemical systems due to their abilities to generate electrons and perform extracellular electron transfer (EET). Here, we investigated the effects of quorum sensing (QS) signals on power output, chlortetracycline degradation, and structure of EABs in MFCs treating antibiotic wastewater. The voltage output of MFCs with C4-HSL and PQS increased by 21.57% and 13.73%, respectively, compared with that without QS signals. The chlortetracycline degradation efficiency in closed-circuit MFCs with C4-HSL and PQS increased by 56.53% and 50.04%, respectively, which resulted from the thicker biofilms, higher biomass, and stronger activities. Additionally, QS signals induced the heterogeneous distribution of EPS for a balance between self-protection and EET under environmental pressure. Geobacter prevailed by the addition of QS signals to resist high chlortetracycline concentration. Our results provided a broader understanding on regulating EABs within electrode interface to improve their performance for environmental remediation and clean energy development.

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The voltage output of MFCs was enhanced with the addition of QS signals

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QS signals increased the bioelectrochemical degradation efficiency of CTC

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EABs exhibited heterogeneity in composition and interaction by the QS signals

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QS signals induced a balance between self-protection and EET of EABs

Improving oxygen reduction reaction of microbial fuel cell by titanium dioxide attaching to dual metal organic frameworks as cathode

In this study, a two-step simple distributed feeding method was used to prepare the core-shell nanocomposite dual metal organic frameworks (D-MOFs, TiO₂@ZIF-67/ZIF-8). There were three obvious peaks (011), (112), (222) interface in D-MOFs core, which fully showed that ZIF-67/ZIF-8 crystal core was successfully synthesized. The morphology of composite material was core-shell structure with a rough surface, and Ti, Co, Zn, Al were uniformly distributed on the surface. TiO₂@ZIF-67/ZIF-8 also had excellent electrochemical activity and the maximum power density of TiO₂@ZIF-67/ZIF-8 microbial fuel cell (MFC) was 341.506 mW/m², which was 1.30 times of ZIF-67/ZIF-8-MFC (262.144 mW/m²) and 2.07 times of ZIF-67-MFC (164.836 mW/m²). And the continuous output voltage of TiO₂@ZIF-67/ZIF-8-MFC was 413.43 mV, which could maintain stable voltage output for 8.3 days. D-MOFs as the core of composites ensured the integrity, stability and high activity of materials; Rough TiO₂ as the surface of the material provided surface area and reaction center.

Rumen Inoculum Enhances Cathode Performance in Single-Chamber Air-Cathode Microbial Fuel Cells

During the last decade, bioprospecting for electrochemically active bacteria has included the search for new sources of inoculum for microbial fuel cells (MFCs). However, concerning power and current production, a Geobacter-dominated mixed microbial community derived from a wastewater inoculum remains the standard. On the other hand, cathode performance is still one of the main limitations for MFCs, and the enrichment of a beneficial cathodic biofilm emerges as an alternative to increase its performance. Glucose-fed air-cathode reactors inoculated with a rumen-fluid enrichment and wastewater showed higher power densities and soluble chemical oxygen demand (sCOD) removal (Pmax = 824.5 mWm⁻²; ΔsCOD = 96.1%) than reactors inoculated only with wastewater (Pmax = 634.1 mWm⁻²; ΔsCOD = 91.7%). Identical anode but different cathode potentials suggest that differences in performance were due to the cathode. Pyrosequencing analysis showed no significant differences between the anodic community structures derived from both inocula but increased relative abundances of Azoarcus and Victivallis species in the cathodic rumen enrichment. Results suggest that this rarely used inoculum for single-chamber MFCs contributed to cathodic biofilm improvements with no anodic biofilm effects.

Microbial fuel cells and their electrified biofilms

Bioelectrochemical systems (BES) represent a wide range of different biofilm-based bioreactors that includes microbial fuel cells (MFCs), microbial electrolysis cells (MECs) and microbial desalination cells (MDCs). The first described bioelectrical bioreactor is the Microbial Fuel Cell and with the exception of MDCs, it is the only type of BES that actually produces harvestable amounts of electricity, rather than requiring an electrical input to function. For these reasons, this review article, with previously unpublished supporting data, focusses primarily on MFCs. Of relevance is the architecture of these bioreactors, the type of membrane they employ (if any) for separating the chambers along with the size, as well as the geometry and material composition of the electrodes which support biofilms. Finally, the structure, properties and growth rate of the microbial biofilms colonising anodic electrodes, are of critical importance for rendering these devices, functional living 'engines' for a wide range of applications.

Study of membrane fouling mechanism during the phenol degradation in microbial fuel cell and membrane bioreactor coupling system

This study evaluated the feasibility of phenol degradation in microbial fuel cell (MFC) and membrane bioreactor (MBR) coupling system, and explored the mechanism of MBR membrane fouling. Four aspects were researched in open and closed circuit conditions: the degradation capacity of the coupling system, the increase of trans-membrane pressure (TMP), and the adhesion of phenol degradation products and microorganisms on the membrane. The results showed that the degradation of phenol and COD in the closed circuit coupling system was higher than that in the open circuit. The micro-electric field can inhibit the growth of TMP and keep dodecamethylcyclohexasiloxane away from the membrane, meanwhile can also reduce the abundance and species diversity of microorganisms. Nevertheless, the micro-electric field could not completely eliminate the membrane fouling due to the fact that the phenol degradation product of ethanethiol, microorganisms of Proteobacteria and Actinobacteria were more favorable on the membrane.

Bacterial community composition of internal circulation reactor at different heights for large-scale brewery wastewater treatment

This study analyzed bacterial community structure for large-scale brewery wastewater treatment at different heights in internal circulation (IC) reactor. Proteobacteria, Bacteroidetes and Chloroflexi were dominant bacteria, which accounted for 64.17%, 64.04%, 59.87% and 55.79% in phylum level, respectively. The unidentified bacteria were accounted for a large proportion in genus level, available data showed that Longilinea, Desulfomicrobium, Caldithrix, Geobacter and Syntrophorhabdus were relatively abundant. Organic fermentation, hydrolysis, and acidification were mainly completed at the bottom, and production of hydrogen and methane were completed in the upper and middle part of reactor. Alpha diversity and cluster distance analysis showed the bacterial community could be divided into bottom, middle and upper part of IC reactor. The IC reactor possessed the COD_Cr removal efficiency of 80% - 84.09%, and BOD₅ of 77.50% - 86% for brewery wastewater. This study would provide bacterial analysis references of IC reactor for industrial wastewater treatment in future.

Enhanced electrochemical performance by nickel-iron layered double hydroxides (LDH) coated on Fe3O4 as a cathode catalyst for single-chamber microbial fuel cells

The improvement of cathode performance has always been the bottleneck and research hot spot for microbial fuel cells (MFCs). An Fe₃O₄@NiFe-LDH composite with a nanoscale core-shell structure containing an Fe₃O₄ magnetic core and a layered double hydroxide (LDH) shell was prepared by the hydrothermal method. The Fe₃O₄@NiFe-LDH was characterized by FT-IR, XRD, SEM and EDS. The characterization results showed that the composite had a unique cauliflower-like nanoflake structure and special pore size distribution, which greatly improved the ORR performance. Moreover, the use of the synthesized Fe₃O₄@NiFe-LDH core-shell structure as an electrode in an MFC was characterized by CV and LSV, which showed that the Fe₃O₄@NiFe-LDH exhibited excellent ORR catalytic properties. The voltage output of the Fe₃O₄@NiFe-LDH MFC was maintained at approximately 0.39 V, with insignificant variations over 110 h. The maximum power density was 211.40 ± 2.27 mW/m², which was 34 times that of the blank control group MFC and was caused by the many electroactive sites, good rate capability and remarkable cycling stability of LDH. This study provides the possibility for using Fe3O4@NiFe-LDH in cathodes to operate continuously and at low cost in fuel cells.

Diversity and Bioactivity of Endophytes From Angelica sinensis in China

Plant seeds are not merely reproductive organs, they are also carriers of microorganism, particularly, inherent and non-invasive characteristic endophytes in host plant. Therefore, in this study, the endophytic diversity of Angelica seeds was studied and compared with endophytes isolated from healthy leaves, stems, roots, and seeds of A. sinensis using 20 different media. The metabolites of endophytic strains were evaluated with six different methods for their antioxidant activity and the paper disc diffusion method for antimicrobial activities. As a result, 226 endophytes were isolated. Compared with the biodiversity and abundance of uncultured fungi from Angelica seed, the result showed that the most frequent endophytic fungi were Alternaria sp. as seen in artificial media; moreover, compared with artificial media, the pathogenic fungi, including Fusarium sp. and Pseudallescheria sp., were not found from the Angelica seed, the results suggested it may not be inherent endophytes in plants. In addition, bacteria from seven phyla were identified by high-throughput sequencing, while five phyla of endophytic bacteria were not isolated on artificial media including Proteobacteria, Actinobacteria, Bacteroidetes, Microgenomates, and Saccharibacteria. Furthermore, the sample JH-4 mycelium displayed the best antioxidant activity, and the active constituent may be a flavonoid as determined by total phenol and flavonoid content. Moreover, YH-12-1 mycelium had strong inhibitory activity against the five tested strains and the minimum inhibitory concentration (MIC) against Pseudomonas aeruginosa and Streptococcus pneumoniae was found to be 25 μg/mL. Our results confirm that plant endophytes are rich in biodiversity and contain important resource of many uncultured microorganisms.

Bacterial community structure and gene function prediction in response to long-term running of dual graphene modified bioelectrode bioelectrochemical systems

This work studied bacterial community structure and gene function prediction in long-term running of dual graphene modified bioelectrode bioelectrochemical systems (LT D-GM-BE BES, 2 year). The maximum power density of LT D-GM-BE BES was 99.03 ± 3.64 mW/m², which was 3.66 times of dual control BES (D-C-BE BES), and the transfer resistance of LT GM-BE was just approximately 1/4 of control bioelectrode (C-BE). Proteobacteria and Firmicutes were dominant bacteria in long-term modified bioanode (LT GM-BA, 30.03% and 45.64%), and in long-term modified biocathode (LT GM-BC) was Armatimonadetes (47.14%) in phylum level. The dominant bacteria in LT GM-BA was Clostridium (30.56%), in GM-BC was Chthonomonas (47.14%) in genus level. Gene function related with substrate, energy metabolism and environmental adaptation were enriched. LT GM-BE was tended to enrich dominant bacteria and enrich gene to adapt to micro-environmental changes. This study would provide metagenomics information for long-term running of BES in future.

Improved bio-electricity production in bio-electrochemical reactor for wastewater treatment using biomass carbon derived from sludge supported carbon felt anode

Microbial fuel cell (MFC), a promising bio-electrochemical reactor could decompose organics in wastewater by redox processes of electro-active microorganism in anode and produce bio-energy, and the total MFC performance could mainly rely on electrochemical performance anode. Here, biomass carbon derived from municipal sludge was employed as low-cost and high-performance bio-anode for enhancing bioelectricity generation and wastewater treatment in MFC simultaneously. The electrochemical tests demonstrated that the large electrochemical active surface area, strong conductivity, and good biocompatibility in sludge carbon (SC) electrode resulted in higher power density (615.2 mW m^-2) and lower power loss (5.4%) than those of none carbon (NC) electrode in long term operation. After 30-cycle of continuous running, the low loss of chemical oxygen demand (COD) removal was achieved up to 5.2%, which was smaller than that of NC electrode (14.1%), indicating that the MFC with SC anode could effectively treat wastewater and keep stable redox processes in anode electrode. After the formation of biofilm, the charge transfer resistance of SC electrode (16.38 Ω) was 72.4% lower than that of NC electrode (59.35 Ω). High-throughput analysis of biofilm exhibit Proteobacteria was the dominant electro-active bacteria, and the modification of SC could slightly change the bacterial community. Therefore, resource utilization of natural wastes provided the novel concept of anode catalyst fabrication for MFC in enhancing electron transfer, power output and wastewater decomposition.

Enhanced degradation of diclofenac with Ru/Fe modified anode microbial fuel cell: Kinetics, pathways and mechanisms

A microbial fuel cell (MFC) was constructed with a Ru/Fe-modified-anode prepared by reduction and coating for enhancing diclofenac (DCF) degradation. Results showed that Ru⁰ and Fe⁰ were dispersed uniformly on Ru/Fe-modified-electrode surface, and Ru/Fe existed as an alloy structure. Due to catalysis of Ru/Fe, both electrochemical activity and DCF-degradation performance of Ru/Fe-modified-anode-MFC (Ru/Fe-MFC) were enhanced compared to carbon-felt-anode-MFC (CF-MFC). The maximum power density of Ru/Fe-MFC reached 0.600 W m^-2, and DCF-degradation in Ru/Fe-MFC followed the pseudo-first-order-kinetic model with k_obs of 0.711 d^-1 which was 1.08, 1.34 and 2.21 times higher than that of Ru-modified-anode-MFC (Ru-MFC), Fe-modified-andoe-MFC (Fe-MFC) and CF-MFC, respectively. Results also showed that DCF-degradation and power generation would compete for electrons in Ru/Fe-MFC. Ru/Fe-modified-anode accelerated the enrichment of electro-active bacteria and DCF-degrading bacteria such as Geobacter, Clostridium, Sedimentibacter, Pseudomonas and Desulfovibrionaceae. Stepwise dechlornation occurred for DCF-degradation mainly due to synergistic reaction of Ru/Fe and DCF-degrading bacteria within Ru/Fe-MFC.

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.

Enhanced sulfate reduction accompanied with electrically-conductive pili production in graphene oxide modified biocathodes

This study aimed to investigate the graphene oxide (GO) conversion by the sulfate-reducing biocathode and its modified effects on performance of the microbial electrolysis cell (MEC). Biocathodes were acclimated with autotrophic sulfate-reducing cultures using medium containing 500 mg L^-1 sulfate. Sulfate reductive rate in the MEC was 230 and 135 g m^-3 d^-1, respectively, with and without 30 mg L^-1 GO addition. Raman measurements showed that GO was efficiently reduced to graphene by the biocathode within 24 h. Higher electrochemical activity and smaller charge transfer resistance were detected on biofilm with GO affected. With high electrical conductivity of 307 ± 36 μS cm^-1, pili substance were observed on GO affected biofilm. As dominated by Desulfovibrio sp., the biocathode could use GO as the sole electron acceptor and maintained high activity. The results from this study should provide useful information for applications of nanomaterials in the biocathode MEC.

Bacterial community shift in response to a deep municipal tail wastewater treatment system

In previous studies, ozone oyster shell fixed-bed bioreactor and membrane bioreactor (OFBR-MBR) were developed for municipal tail wastewater treatment, and qualified good effects. This study mainly discussed the bacterial community shift in response to the treatment process of OFBR-MBR. Proteobacteria, Chloroflexi, Planctomycetes, Actinobacteria and Firmicutes were dominant bacteria after ozone treatment in phylum level in OFBR-MBR; Aciditerrimonas, Blastopirellula, Pasteuria, Planctomyces, Paracoccus, Caldilinea and Defluviicoccus were adapted and enriched after ozone treatment in genus level in OFBR-MBR. Ozone played key role in the species selection of bacteria in OFBR-MBR. The chemical oxygen demand (COD), ammonium and total phosphorus (TP) removal efficiency possessed by OFBR-MBR were 79.05%, 98.74% and 38.10%, which due to the function of ozone and these enriched bacteria. OFBR-MBR has exhibited huge potential for municipal tail wastewater, and it would also provide an alternative and promising technology for other kinds of tail wastewater recycling in future.

Bacterial community shift and antibiotics resistant genes analysis in response to biodegradation of oxytetracycline in dual graphene modified bioelectrode microbial fuel cell

This study explored the biodegradation mechanisms of oxytetracycline (OTC/O) and electrochemical characteristics from the perspective of bacterial community shift and OTC resistance genes in dual graphene modified bioelectrode microbial fuel cell (O-D-GM-BE MFC). In phylum level, Proteobacteria was accounted to 95.04% in O-GM-BA, Proteobacteria and Bacteroidetes were accounted to 59.13% and 20.52% in O-GM-BC, which were beneficial for extracellular electron transport (EET) process and OTC biodegradation. In genus level, the most dominant bacteria in O-GM-BA were Salmonella and Trabulsiella, accounting up to 83.04%, moreover, representative exoelectrogens (Geobacter) were enriched, which contributed to OTC biodegradation and electrochemical performances; abundant degrading bacteria (Moheibacter, Comamonas, Pseudomonas, Dechloromonas, Nitrospira, Methylomicrobium, Pseudorhodoferax, Thiobacillus, Mycobacterium) were enriched in O-GM-BC, which contributed to the maximum removal efficiency of OTC; coding resistance genes of efflux pump, ribosome protective protein and modifying or passivating were all found in O-GM-BE, and this explained the OTC removal mechanisms from gene level.

Biodegradation of oxytetracycline and electricity generation in microbial fuel cell with in situ dual graphene modified bioelectrode

A three-step method to prepare dual graphene modified bioelectrode (D-GM-BE) in microbial fuel cell (MFC) in previous studies. This study explored the biodegradation of oxytetracycline (OTC) and electricity generation in O-D-GM-BE MFC. The OTC removal efficiency of graphene modified biocathode and bioanode (O-GM-BC, O-GM-BA) was 95.0% and 91.8% in eight days. The maximum power density generated by O-D-GM-BE MFC was 86.6 ± 5.1 mW m^-2, which was 2.1 times of that in OTC control bioelectrode (O-C-BE) MFC. The Rct of O-GM-BA and O-GM-BC were decreased significantly by 78.3% and 76.3%. OTC was biodegraded to monocyclic benzene compounds by bacteria. O-GM-BA was affected strongly by OTC, and Salmonella and Trabulsiella were accounted for 83.0%, while typical exoelectrogens (Geobacter) were still enriched after the maturity of biofilm. In O-GM-BC, bacteria related with OTC biodegradation (Comamonas, Ensifer, Sphingopyxis, Pseudomonas, Dechloromonas, etc.) were enriched, which contributed to the high removal efficiency of OTC.

Anode modification by biogenic gold nanoparticles for the improved performance of microbial fuel cells and microbial community shift

In this study, carbon cloth anodes were modified using biogenic gold nanoparticles (BioAu) and nanohybrids of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) to improve the performance of microbial fuel cells (MFCs). The results demonstrated that BioAu modification significantly enhanced the electricity generation of MFCs. In particular, BioAu/MWCNT nanohybrids as the modifier displayed a better performance. The MFC with the BioAu/MWCNT electrode had the shortest start-up time (6.74 d) and highest power density (178.34 ± 4.79 mW/m²), which were 141.69% shorter and 56.11% higher compared with those of the unmodified control, respectively. These improvements were attributed to the excellent electrocatalytic activity and strong affinity towards exoelectrogens of the BioAu/MWCNT nanohybrids on the electrode. High throughput sequencing analysis indicated that the relative abundance of electroactive bacteria in the biofilm community, mostly from the classes of Gammaproteobacteria and Negativicutes, increased after anode modification.

Novel AgNWs-PAN/TPU membrane for point-of-use drinking water electrochemical disinfection

The safety of drinking water remains a major challenge in developing countries and point-of-use (POU) drinking water treatment device plays an important role in decentralised drinking water safety. In this study, a novel material, i.e. a silver nanowires-polyacrylonitrile/thermoplastic polyurethane (AgNWs-PAN/TPU) composite membrane, was fabricated via electrospinning and vacuum filtration deposition. Morphological and structural characterisation showed that the PAN/TPU fibres had uniform diameters and enhanced mechanical properties. When added to these fibres, the AgNWs formed a highly conductive network with good physical stability and low silver ion leaching (<100 ppb). A POU device equipped with a AgNWs-PAN/TPU membrane displayed complete removal of 10⁵ CFU/mL bacteria, which were inactivated by silver ions released from the AgNWs within 6 h. Furthermore, under a voltage of 1.5 V, the bacteria were completely inactivated within 20-25 min. Inactivation efficiency in 5 mM NaCl solution was higher than those in Na₂SO₄ and NaNO₃ solutions. We concluded that a strong electric field was formed at the AgNW tips. Additionally, silver ions and chlorine compounds worked synergistically in the disinfection process. This study provides a scientific basis for research and development of silver nanocomposite membranes, with high mechanical strength and high conductivity, for POU drinking water disinfection.

Effects of the inclusion of a mixed Psychrotrophic bacteria strain for sewage treatment in constructed wetland in winter seasons

Constructed wetlands (CWs) have been used globally in wastewater treatment for years. CWs represent an efficient ecological system which is both energy-saving and low in investment for construction and operational cost. In addition, CWs also have the advantage of being easy to operate and maintain. However, the operation of CWs at northern latitudes (both mid and high) is sometimes quite demanding, due to the inhibitory effect of low temperatures that often occur in winter. To evaluate the wastewater treatment performance of a culture of mixed Psychrotrophic bacteria strains in an integrated vertical-flow CW, the removal rates of ammonia nitrogen (NH₃-N), chemical oxygen demand (COD), nitrite nitrogen [Formula: see text], nitrate nitrogen [Formula: see text] and total phosphorus (TP) were quantified at different bacterial dosages to determine the best bacterial dosage and establish kinetic degradation models of the mixed strains. The bacterial culture was made up of Psychrobacter TM-1, Sphingobacterium TM-2 and Pseudomonas TM-3, mixed together at a volume/volume ratio of 1 : 1 : 1 (at bacterial suspension concentrations of 4.4 × 10⁹ ml^-1). Results showed that the organic pollutants (nitrogen and phosphorus) in the sewage could be efficiently removed by the culture of mixed Psychrotrophic bacteria. The optimal dosage of this mixed bacteria strain was 2.5%, and the treatment efficiency of COD, NH₃-N, [Formula: see text], [Formula: see text], total nitrogen and TP were stable at 91.8%, 91.1%, 88.0%, 93.8%, 94.8% and 95.2%, respectively, which were 1.5, 2.0, 2.1, 1.5, 2.2 and 1.3 times those of the control group. In addition, a pseudo-first-order degradation model was a good fit for the degradation pattern observed for each of these pollutants.

Hydrogen peroxide generation in microbial fuel cells using graphene-based air-cathodes

Utilization of two-electron oxygen reduction reaction (ORR) in bioelectrochemical systems (BES) is a novel way to generate H₂O₂ 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 H₂O₂ productions than plain graphene cathode respectively in an abiotic reactor and an MFC. GO showed nearly no H₂O₂ production in the tests. XPS revealed that oxygen atomic fraction of oxidized graphene reached 5.7%, mostly in the form of COC. These results show that oxidized graphene had good catalytic performance for H₂O₂ production, and oxygen-containing functional groups, especially COC could significantly enhance its performance, but overoxidation worked adversely. Meanwhile, using oxidized graphene air-cathode could realize simultaneous wastewater treatment, power output and H₂O₂ generation in MFCs.

Energy recovery from tubular microbial electrolysis cell with stainless steel mesh as cathode

In comparison to the transportation and storage of hydrogen, methane has advantages in the practical application, while the emerging product termed as 'biohythane' could be an alternative to pure hydrogen or methane in a new form of energy recovery from microbial electrolysis cell (MEC). However, the cathodic catalyst even for biohythane still bothers the performance and cost of total MEC. Herein, we fabricated the MEC reactor with surrounding stainless steel mesh (SSM) to investigate the feasibility of stainless steel mesh as an alternative to precious metal in biohythane production. The columbic efficiency (CE) of anode was around at 80%, representing the SSM would not limit the activity of anodic biofilm; the SEM image and ATP results accordingly indicated the anodic biofilm was mature and well constructed. The main contribution of methanogens that quantified by qPCR belonged to the hydrogenotrophic group (Methanobacteriales) at cathode. The energy efficiency reached more than 100%, reached up to approximately 150%, potentially suggesting the energetic feasibility of the application to obtain biohythane with SSM in scale-up MEC. Benefiting from the likely tubular configuration, the ohmic resistance of cathode was very low, while the main limitation associated with charge transfer was mainly caused by biofilm formation. The total performances of SSM used in the tubular configuration for biohythane production provide an insight into the implementation of non-precious metal in future scale-up pilot with energy recovery.

Bacterial community shift and incurred performance in response to in situ microbial self-assembly graphene and polarity reversion in microbial fuel cell

In this work, bacterial community shift and incurred performance of graphene modified bioelectrode (GM-BE) in microbial fuel cell (MFC) were illustrated by high throughput sequencing technology and electrochemical analysis. The results showed that Firmicutes occupied 48.75% in graphene modified bioanode (GM-BA), while Proteobacteria occupied 62.99% in graphene modified biocathode (GM-BC), both were dominant bacteria in phylum level respectively. Typical exoelectrogens, including Geobacter, Clostridium, Pseudomonas, Geothrix and Hydrogenophaga, were counted 26.66% and 17.53% in GM-BA and GM-BC. GM-BE was tended to decrease the bacterial diversity and enrich the dominant species. Because of the enrichment of exoelectrogens and excellent electrical conductivity of graphene, the maximum power density of MFC with GM-BA and GM-BC increased 33.1% and 21.6% respectively, and the transfer resistance decreased 83.8% and 73.6% compared with blank bioelectrode. This study aimed to enrich the microbial study in MFC and broaden the development and application for bioelectrode.