Electro-Fenton,hydrogenotrophic and Fe2+ ions mediated TOC and nitrate removal from aquaculture system: Different experimental strategies

A number of methods for denitrification were studied including Electro-Fenton method, hydrogenotrophic as well as innovative Fe²⁺ mediated denitrification and their technical feasibility in terms of changes in TOC and nitrate concentrations, effect of different Fenton’s reagent dosage, current and the effect of the pH was investigated. This study was carried out using tailor made electrodialytic reactor. It was found that the highest TOC removal was achieved at pH 2.2 and 2.4 (77.1% and 97.8%, respectively) at the anode and the lowest accumulation of 33% at pH of 6.2 at the cathode. The highest TOC removal in terms of using different H₂O₂ concentrations was achieved at 40 mM reaching as high as 97.3%. Regardless experimental strategy, initially nitrates migrated towards the cathode due to the strong hydraulic gradient under the applied electric current. During the course of experiments, nitrates were transported towards the anode where their concentration decreased. The highest nitrate removal was achieved at 0.12 mA cm^?2 electric current density (94.8%) at the anode and a complete removal at the cathode. Hydrogenotrophic denitrification was the highest reaching 92.5%, however, when Fe²⁺ ions as electron donor was used for the destruction of nitrates, only 66.6% removal was achieved. Denitrification using only Fe²⁺ ions was a factor 1.4 less than using electrically generated hydrogen or a Fenton’s reagent.     

A membrane-free baffled microbial fuel cell for cathodic reduction of Cu(II) with electricity generation

A membrane-free baffled microbial fuel cell (MFC) was developed to treat synthetic Cu(II) sulfate containing wastewater in cathode chamber and synthetic glucose-containing wastewater fed to anode chamber. Maximum power density of 314 mW/m³ with columbic efficiency of 5.3% was obtained using initial Cu²⁺ concentration of 6400 mg/L. Higher current density favored the cathodic reduction of Cu²⁺, and removal of Cu²⁺ by 70% was observed within 144 h using initial concentration of 500 mg/L. Powder X-ray diffraction (XRD) analysis indicated that the Cu²⁺ was reduced to Cu₂O or Cu₂O plus Cu which deposited on the cathode, and the deficient cathodic reducibility resulted in the formation of Cu₄(OH)₆SO₄ at high initial Cu²⁺ concentration (500-6400 mg/L). This study suggested a novel low-cost approach to remove and recover Cu(II) from Cu²⁺-containing wastewater using MFC-type reactor.     

Performance and microbial ecology of air-cathode microbial fuel cells with layered electrode assemblies

Microbial fuel cells (MFCs) can be built with layered electrode assemblies, where the anode, proton exchange membrane (PEM), and cathode are pressed into a single unit. We studied the performance and microbial community structure of MFCs with layered assemblies, addressing the effect of materials and oxygen crossover on the community structure. Four MFCs with layered assemblies were constructed using Nafion or Ultrex PEMs and a plain carbon cloth electrode or a cathode with an oxygen-resistant polytetrafluoroethylene diffusion layer. The MFC with Nafion PEM and cathode diffusion layer achieved the highest power density, 381 mW/m² (20 W/m³). The rates of oxygen diffusion from cathode to anode were three times higher in the MFCs with plain cathodes compared to those with diffusion-layer cathodes. Microsensor studies revealed little accumulation of oxygen within the anode cloth. However, the abundance of bacteria known to use oxygen as an electron acceptor, but not known to have exoelectrogenic activity, was greater in MFCs with plain cathodes. The MFCs with diffusion-layer cathodes had high abundance of exoelectrogenic bacteria within the genus Geobacter. This work suggests that cathode materials can significantly influence oxygen crossover and the relative abundance of exoelectrogenic bacteria on the anode, while PEM materials have little influence on anode community structure. Our results show that oxygen crossover can significantly decrease the performance of air-cathode MFCs with layered assemblies, and therefore limiting crossover may be of particular importance for these types of MFCs.     

Increasing power generation for scaling up single-chamber air cathode microbial fuel cells

Scaling up microbial fuel cells (MFCs) requires a better understanding the importance of the different factors such as electrode surface area and reactor geometry relative to solution conditions such as conductivity and substrate concentration. It is shown here that the substrate concentration has significant effect on anode but not cathode performance, while the solution conductivity has a significant effect on the cathode but not the anode. The cathode surface area is always important for increasing power. Doubling the cathode size can increase power by 62% with domestic wastewater, but doubling the anode size increases power by 12%. Volumetric power density was shown to be a linear function of cathode specific surface area (ratio of cathode surface area to reactor volume), but the impact of cathode size on power generation depended on the substrate strength (COD) and conductivity. These results demonstrate the cathode specific surface area is the most critical factor for scaling-up MFCs to obtain high power densities.     

Layer-by-layer construction of graphene-based microbial fuel cell for improved power generation and methyl orange removal

Development of highly efficient anode is critical for enhancing the power output of microbial fuel cells (MFCs). The aim of this work is to investigate whether modification of carbon paper (CP) anode with graphene (GR) via layer-by-layer assembly technique is an effective approach to promote the electricity generation and methyl orange removal in MFCs. Using cyclic voltammetry and electrochemical impedance spectroscopy, the GR/CP electrode exhibited better electrochemical behavior. Scanning electron microscopy results revealed that the surface roughness of GR/CP increased, which was favorable for more bacteria to attach to the anode surface. The MFCs equipped with GR/CP anode achieved a stable maximum power density of 368 mW m^?2 under 1,000 Ω external resistance and a start time for the initial maximum voltage of 180 h, which were, respectively, 51 % higher and 31 % shorter than the corresponding values of the MFCs with blank anode. The anode and cathode polarization curves revealed negligible difference in cathode potentials but obviously difference in anode potentials, indicating that the GR-modified anode other than the cathode was responsible for the performance improvement of MFC. Meanwhile, compared with MFCs with blank anode, 11 % higher decolorization efficiency and 16 % higher the chemical oxygen demand removal rate were achieved in MFC with GR-modified anode during electricity generation. This study might provide an effective way to modify the anode for enhanced electricity generation and efficient removal of azo dye in MFCs.     

Enhanced wastewater treatment efficiency through microbially catalyzed oxidation and reduction: synergistic effect of biocathode microenvironment

Microbially catalyzed treatment of wastewater was evaluated in both the anode and cathode chambers in dual chambered microbial fuel cell (MFC) under varying biocathode microenvironment. MFC operation with aerobic biocathode showed significant increment in both TDS (cathode, 90.2±1%; anode, 39.7±0.5%) and substrate (cathode, 98.07±0.06%; anode, 96.2±0.3%) removal compared to anaerobic biocathode and abiotic cathode operations (COD, 80.25±0.3%; TDS, 30.5±1.2%). Microbially catalyzed reduction of protons and electrons at cathode will be higher during aerobic biocathode operation which leads to gradual substrate removal resulting in stable bio-potential for longer periods facilitating salts removal. Bio-electro catalytic behavior showed higher exchange current density during aerobic biocathode operation resulting in induced electrochemical oxidation which supports the enhanced treatment. Anaerobic biocathode operation depicted relatively less TDS removal (anode, 16.35%; cathode, 16.04%) in both the chambers in spite of good substrate degradation (anode, 84%; cathode, 87.39%). Both the chambers during anaerobic biocathode operation competed as electron donors resulting in negligible bio-potential development.     

The effect of temperature on the electrochemical properties of copper—DNA membranes

The influence of temperature, electrode plate metals and protamine on the membrane potential of an electrochemically prepared copper—DNA (Cu-DNA) membrane (size, 2.5×6cm; thickness, 80μm; Cu/P molar ratio, 0.4) was investigated. The results obtained showed that the membrane potential increased with temperature as well as with increasing order of ionization tendency of the divalent metals used, and decreased with an increase of protamine bound to the membrane. These results indicated that electrons accumulated on the anode side, and positive holes formed on the cathode side, of a Cu-DNA membrane prepared by electrolysis.     

Long‐Life,High‐Rate Lithium–Sulfur Cells with a Carbon‐Free VN Host as an Efficient Polysulfide Adsorbent and Lithium Dendrite Inhibitor

Lithium–sulfur (Li‐S) batteries are a promising next‐generation energy‐storage system, but the polysulfide shuttle and dendritic Li growth seriously hinder their commercial viability. Most of the previous studies have focused on only one of these two issues at a time. To address both the issues simultaneously, presented here is a highly conductive, noncarbon, 3D vanadium nitride (VN) nanowire array as an efficient host for both sulfur cathodes and lithium‐metal anodes. With fast electron and ion transport and high porosity and surface area, VN traps the soluble polysulfides, promotes the redox kinetics of sulfur cathodes, facilitates uniform nucleation/growth of lithium metal, and inhibits lithium dendrite growth at an unprecedented high current density of 10 mA cm^?2 over 200 h of repeated plating/stripping. As a result, VN‐Li||VN‐S full cells constructed with VN as both an anode and cathode host with a negative to positive electrode capacity ratio of only ≈2 deliver remarkable electrochemical performance with a high Coulombic efficiency of ≈99.6% over 850 cycles at a high 4 C rate and a high areal capacity of 4.6 mA h cm^?2. The strategy presented here offers a viable approach to realize high‐energy‐density, safe Li‐metal‐based batteries.     

Sodium Sulfide Cathodes Superseding Hard Carbon Pre‐sodiation for the Production and Operation of Sodium–Sulfur Batteries at Room Temperature

This study demonstrates for the first time a room temperature sodium–sulfur (RT Na–S) full cell assembled based on a pristine hard carbon (HC) anode combined with a nanostructured Na₂S/C cathode. The development of cells without the demanding, time‐consuming and costly pre‐sodiation of the HC anode is essential for the realization of practically relevant RT Na–S prototype batteries. New approaches for Na₂S/C cathode fabrication employing carbothermal reduction of Na₂SO₄ at varying temperatures (660 to 1060 °C) are presented. Initial evaluation of the resulting cathodes in a dedicated cell setup reveals 36 stable cycles and a capacity of 740 mAh g_S^?1, which correlates to ≈85% of the maximum value known from literature on Na₂S‐based cells. The Na₂S/C cathode with the highest capacity utilization is implemented into a full cell concept applying a pristine HC anode. Various full cell electrolyte compositions with fluoroethylene carbonate (FEC) additive have been combined with a special charging procedure during the first cycle supporting in situ solid electrolyte interphase (SEI) formation on the HC anode to obtain increased cycling stability and cathode utilization. The best performing cell setup has delivered a total of 350 mAh g_S^?1, representing the first functional full cell based on a Na₂S/C cathode and a pristine HC anode today.     

High Voltage Operation of Ni‐Rich NMC Cathodes Enabled by Stable Electrode/Electrolyte Interphases

The lithium (Li) metal battery (LMB) is one of the most promising candidates for next‐generation energy storage systems. However, it is still a significant challenge to operate LMBs with high voltage cathodes under high rate conditions. In this work, an LMB using a nickel‐rich layered cathode of LiNi_0.76Mn_0.14Co_0.10O₂ (NMC76) and an optimized electrolyte [0.6 m lithium bis(trifluoromethanesulfonyl)imide + 0.4 m lithium bis(oxalato)borate + 0.05 m LiPF₆ dissolved in ethylene carbonate and ethyl methyl carbonate (4:6 by weight)] demonstrates excellent stability at a high charge cutoff voltage of 4.5 V. Remarkably, these Li||NMC76 cells can deliver a high discharge capacity of >220 mA h g^?1 (846 W h kg^?1) and retain more than 80% capacity after 1000 cycles at high charge/discharge current rates of 2C/2C (1C = 200 mA g^?1). This excellent electrochemical performance can be attributed to the greatly enhanced structural/interfacial stability of both the Ni‐rich NMC76 cathode material and the Li metal anode using the optimized electrolyte.     

In Situ Formation of Protective Coatings on Sulfur Cathodes in Lithium Batteries with LiFSI‐Based Organic Electrolytes

Development of sulfur cathodes with 100% coulombic efficiency (CE) and good cycle stability remains challenging due to the polysulfide dissolution in electrolytes. Here, it is demonstrated that electrochemical reduction of lithium bis(fluorosulfonyl)imide (LiFSI) based electrolytes at a potential close to the sulfur cathode operation forms in situ protective coating on both cathode and anode surfaces. Quantum chemistry studies suggest the coating formation is initiated by the FSI(‐F) anion radicals generated during electrolyte reduction. Such a reduction additionally results in the formation of LiF. Accelerated cycle stability tests at 60 °C in a very simple electrolyte (LiFSI in dimethoxyethane with no additives) show an average CE approaching 100.0% over 1000 cycles with a capacity decay less than 0.013% per cycle after stabilization. Such a remarkable performance suggests a great promise of both an in situ formation of protective solid electrolyte coatings to avoid unwanted side reactions and the use of a LiFSI salt for this purpose.     

Bioelectricity generation enhancement in a dual chamber microbial fuel cell under cathodic enzyme catalyzed dye decolorization

Enzymatic decolorization of reactive blue 221 (RB221) using laccase was investigated in a dual-chamber microbial fuel cell (MFC). Suspended laccase was used in the cathode chamber in the absence of any mediators in order to decolorize RB221 and also improve oxygen reduction reaction in the cathode. Molasses was utilized as low cost and high strength energy source in the anode chamber. The capability of MFC for simultaneous molasses and dye removal was investigated. A decolorization efficiency of 87% was achieved in the cathode chamber and 84% COD removal for molasses was observed in the anode chamber. Laccase could catalyze the removal of RB221 and had positive effect on MFC performance as well. Maximum power density increased about 30% when enzymatic decolorization was performed in the cathode chamber.     

A Lithium–Sulfur Cell Based on Reversible Lithium Deposition from a Li2S Cathode Host onto a Hostless‐Anode Substrate

The development of lithium–sulfur batteries necessitates a thorough understanding of the lithium‐deposition process. A novel full‐cell configuration comprising an Li₂S cathode and a bare copper foil on the anode side is presented here. The absence of excess lithium allows for the realization of a truly lithium‐limited Li–S battery, which operates by reversible plating and stripping of lithium on the hostless‐anode substrate (copper foil). Its performance is closely tied to the efficiency of lithium deposition, generating valuable insights on the role and dynamic behavior of lithium anode. The Li₂S full cell shows reasonable capacity retention with a Coulombic efficiency of 96% over 100 cycles, which is a tremendous improvement over that of a similar lithium‐plating‐based full cell with LiFePO₄ cathodes. The exceptional robustness of the Li₂S system is attributed to an intrinsic stabilization of the lithium‐deposition process, which is mediated by polysulfide intermediates that form protective Li₂S and Li₂S₂ regions on the deposited lithium. Combined with the large improvements in energy density and safety by the elimination of a metallic lithium anode, the stability and electrochemical performance of the lithium‐plating‐based Li₂S full cell establish it as an important trajectory for Li–S battery research, focusing on practical realization of reversible lithium anodes.     

Electricity generation from model organic wastewater in a cassette-electrode microbial fuel cell

A new highly scalable microbial fuel cell (MFC) design, consisting of a series of cassette electrodes (CE), was examined for increasing power production from organic matter in wastewater. Each CE chamber was composed of a box-shaped flat cathode (two air cathodes on both sides) sandwiched in between two proton-exchange membranes and two graphite-felt anodes. Due to the simple design of the CE-MFC, multiple cassettes can be combined to form a single unit and inserted into a tank to treat wastewater. A 12-chamber CE-MFC was tested using a synthetic wastewater containing starch, peptone, and fish extract. Stable performance was obtained after 15 days of operation in fed-batch mode, with an organic removal efficiency of 95% at an organic loading rate of 2.9 kg chemical oxygen demand (COD) per cubic meter per day and an efficiency of 93% at 5.8 kg COD per cubic meter per day. Power production was stable during this period, reaching maximum power densities of 129 W m(-3) (anode volume) and 899 mW m(-2) (anode projected area). The internal resistance of CE-MFC decreased from 2.9 (day 4) to 0.64 Omega (day 25). These results demonstrate the usefulness of the CE-MFC design for energy production and organic wastewater treatment.     

Flexible Quasi‐Solid‐State Sodium‐Ion Capacitors Developed Using 2D Metal–Organic‐Framework Array as Reactor

Achieving high‐performance Na‐ion capacitors (NICs) has the particular challenge of matching both capacity and kinetics between the anode and cathode. Here a high‐power NIC full device constructed from 2D metal–organic framework (MOFs) array is reported as the reactive template. The MOF array is converted to N‐doped mesoporous carbon nanosheets (mp‐CNSs), which are then uniformly encapsulated with VO₂ and Na₃V₂(PO₄)₃ (NVP) nanoparticles as the electroactive materials. By this method, the high‐power performance of the battery materials is enabled to be enhanced significantly. It is discovered that such hybrid NVP@mp‐CNSs array can render ultrahigh rate capability (up to 200 C, equivalent to discharge within 18 s) and superior cycle performance, which outperforms all NVP‐based Na‐ion battery cathodes reported so far. A quasi‐solid‐state flexible NIC based on the NVP@mp‐CNSs cathode and the VO₂@mp‐CNSs anode is further assembled. This hybrid NIC device delivers both high energy density and power density as well as a good cycle stability (78% retention after 2000 cycles at 1 A g^?1). The results demonstrate the powerfulness of MOF arrays as the reactor for fabricating electrode materials.     

微生物电解池阳极生物膜功能菌群构建及群落特征分析

【目的】微生物电解电池(MEC)是近几年快速发展的利用电极呼吸微生物快速降解有机质,通过较小的辅助外加电压直接生成氢气的新工艺。MEC能够有效地富集高效率电子传递功能菌群,是未来工艺放大和快速启动的关键。【方法】采用不同驯化方法构建MEC电极微生物菌群,通过单链构象多肽性技术(Single-strand conformation poly-morphism,SSCP)快速检测分析启动后电子传递功能菌群特征。【结果】阳极生物膜接种MEC可以实现2 d的快速启动,库仑效率达到20%以上,7 d获得稳定产氢,氢气转化率达到30%,能量回收效率达到90%以上。通过SSCP群落分析发现,采用微生物燃料电池阳极生物膜构建的MEC主要电子传递功能相关的菌群包括Pseudomonas sp.、Flavobacterium sp.、Ochrobactrum sp.,而直接由产氢MEC阳极生物膜新启动的MEC功能菌群组成丰度更大,包括电子传递效能更高的Desulfovibrio、Pseudomonas和Shewanella成为主要优势电子传递菌群。通过稳定产氢运行,MEC阳极生物膜优势菌群中存在的较大比例的厌氧菌与电子传递辅助菌对体系的快速稳定运行十分重要。【结论】与MFC阳极生物膜相比,MEC生物膜作为启动菌源能够获得多样性更丰富的电极功能菌群,其库仑效率和产氢效率更具优势。     

The effects of copper on the microbial community of a coral reef sponge

Marine sponges often harbour communities of symbiotic microorganisms that fulfil necessary functions for the well-being of their hosts. Microbial communities associated with the sponge Rhopaloeides odorabile were used as bioindicators for sublethal cupric ion (Cu2+) stress. A combined strategy incorporating molecular, cultivation and electron microscopy techniques was adopted to monitor changes in microbial diversity. The total density of sponge-associated bacteria and counts of the predominant cultivated symbiont (alpha-proteobacterium strain NW001) were significantly reduced in response to Cu2+ concentrations of 1.7 microg l(-1) and above after 14 days of exposure. The number of operational taxonomic units (OTUs) detected by restriction fragment length polymorphism (RFLP) decreased by 64% in sponges exposed to 223 microg l(-1) Cu2+ for 48 h and by 46% in sponges exposed to 19.4 microg l(-1) Cu2+ for 14 days. Electron microscopy was used to identify 17 predominant bacterial morphotypes, composing 47% of the total observed cells in control sponges. A reduction in the proportion of these morphotypes to 25% of observed cells was evident in sponges exposed to a Cu2+ concentration of 19.4 microg l(-1). Although the abundance of most morphotypes decreased under Cu2+ stress, three morphotypes were not reduced in numbers and a single morpho-type actually increased in abundance. Bacterial numbers, as detected using fluorescence in situ hybridization (FISH), decreased significantly after 48 h exposure to 19.4 microg l(-1) Cu2+. Archaea, which are normally prolific in R. odorabile, were not detected after exposure to a Cu2+ concentration of 19.4 microg l(-1) for 14 days, indicating that many of the microorganisms associated with R. odorabile are sensitive to free copper. Sponges exposed to a Cu2+ concentration of 223 microg l(-1) became highly necrosed after 48 h and accumulated 142 +/- 18 mg kg(-1) copper, whereas sponges exposed to 19.4 microg l(-1) Cu2+ accumulated 306 +/- 15 mg kg(-1) copper after 14 days without apoptosis or mortality. Not only do sponges have potential for monitoring elevated concentrations of heavy metals but also examining changes in their microbial symbionts is a novel and sensitive bioindicator for the assessment of pollution on important microbial communities.     

Simultaneous organics removal and bio-electrochemical denitrification in microbial fuel cells

Simultaneous organics removal and bio-electrochemical denitrification using a microbial fuel cell (MFC) reactor were investigated in this study. The electrons produced as a result of the microbial oxidation of glucose in the anodic chamber were transferred to the anode, which then flowed to the cathode in the cathodic chamber through a wire, where microorganisms used the transferred electrons to reduce the nitrate. The highest power output obtained on the MFCs was 1.7 mW/m(2) at a current density of 15 mA/m(2). The maximum volumetric nitrate removal rate was 0.084 mg NO(3)(-)-N cm(-2) (electrode surface area) day(-1). The coulombic efficiency was about 7%, which demonstrated that a substantial fraction of substrate was lost without current generation.     

Coordination Engineering of N,O Co-Doped Cu Single Atom on Porous Carbon for High Performance Zinc Metal Anodes

Traditional challenges of poor cycling stability and low Coulombic efficiency in Zinc (Zn) metal anodes have limited their practical application. To overcome these issues, this work introduces a single metal-atom design featuring atomically dispersed single copper (Cu) atoms on 3D nitrogen (N) and oxygen (O) co-doped porous carbon (CuNOC) as a highly reversible Zn host. The CuNOC structure provides highly active sites for initial Zn nucleation and further promotes uniform Zn deposition. The 3D porous architecture further mitigates the volume changes during the cycle with homogeneous Zn²⁺ flux. Consequently, CuNOC demonstrates exceptional reversibility in Zn plating/stripping processes over 1000 cycles at 2 and 5 mA cm⁻² with a fixed capacity of 1 mAh cm⁻², while achieving stable operation and low voltage hysteresis over 700 h at 5 mA cm⁻² and 5 mAh cm⁻². Furthermore, density functional theory calculations show that co-doping N and O on porous carbon with atomically dispersed single Cu atoms creates an efficient zincophilic site for stable Zn nucleation. A full cell with the CuNOC host anode and high loading V₂O₅ cathode exhibits outstanding rate-capability up to 5 A g⁻¹ and a stable cycle life over 400 cycles at 0.5 A g⁻¹.     

Tuning Dopant Distribution for Stabilizing the Surface of High-Nickel Layered Oxide Cathodes for Lithium-Ion Batteries

Layered oxide cathodes with a high-nickel (Ni ≥ 0.9) content exhibit great potential for enabling high-energy-density lithium-ion batteries. However, their practical feasibility and cycle life are hampered by severe surface reactivity with the electrolyte. A LiNi_0.90Co_0.05Al_0.05O₂ cathode is presented enriched with Al on the surface (S-NCA) and benchmark it against a LiNi_0.90Co_0.05Al_0.05O₂ cathode obtained by a conventional co-precipitation method that has a uniform Al distribution throughout the bulk (B-NCA). The S-NCA cathode greatly outperform with an impressive capacity retention of 84% after 1000 cycles in pouch full cells with graphite anode compared to 62% retention for B-NCA. Advanced surface characterization methodologies, including time-of-flight secondary-ion mass spectrometry, reveal that the Al-enriched surface morphology facilitates the formation of a robust, thin electrode-electrolyte interphase (EEI), effectively suppressing the oxidative decomposition of the electrolyte, gas generation, and metallic dead lithium formation on graphite anode. The results illustrate that surface reactivity with the electrolyte is the primary factor limiting the cycle of cells with high-Ni cathodes. The work provides valuable insights toward the practical viability of ultrahigh-Ni cathodes in lithium-ion batteries.