Initial Current Density Research Articles

High-rate aqueous zinc-organic battery achieved by lowering HOMO/LUMO of organic cathode

Despite the development of quinone as the potential cathode material for Zn-organic batteries, there are undesired behaviors for the rate and cycling performances. To achieve high-performance Zn-organic batteries, intentional organic molecular design and a deep understanding of the mechanism of Zn-organic batteries are highly essential. Herein, strong electron-withdrawing and conjugating groups (-CN) were introduced to lower the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy on an aromatic Schiff base (Hexaazatrinnphthalene, denoted as HATN). With such a decoration, HATN-3CN exhibits an outstanding rate capacity with retention of 60.7% of the initial capacity at 400 times the initial current density and long cycle life of over 5800 cycles. Besides, the charge storage mechanism was systematically investigated through experiments and density functional theory calculation, showing that CN moieties are the active site for the storage of H+/Zn2+. This strategy and insight provided by molecular orbital theory and kinetics-controlled process offer a feasible pathway of molecular-level design for constructing high-performance Zn-organic batteries.

Combined electrocoagulation and electrochemical oxidation treatment for groundwater denitrification

Electrocoagulation (EC) with an aluminum electrode arrangement as anode-cathode was applied to denitrify groundwater and electrooxidation (EO) was examined as a post-treatment step to remove the produced by-products. Initially, EC experiments were performed under batch operating mode using artificially-polluted tap water to investigate the effects of initial pH (5.5, 7.5, 8.5), initial NO3−-N concentration (25, 35, 45, 55 mg L−1) and applied current density (10, 20 mA cm−2) on process efficiency. The effect of initial solution pH on ammonium cation concentration was also investigated as their generation (as a by-product) is the main drawback preventing wide-scale application of these treatment processes. Experimental results revealed high nitrate removal percentages (up to 96.3%) for initial pH 7.5 and all initial concentrations and current densities, while the final ammonium concentrations ranged between 5.3 and 9.2 mg NH4+-N L−1 (for initial NO3−-N of 25 mg L−1). Therefore, EO was examined to oxidize the ammonium cations to nitrogen gas on iridium oxide coated titanium electrodes (IrO2/Ti) anode surface. The effects of cathode material (aluminum, stainless steel), total current density and anode surface area (3.3–30 mA cm−2 and 12–36 cm2, respectively) were investigated, and lead to NH4+-N percentage removals of between 25% (10 mA cm−2, 12 cm2) and 100% (30 mA cm−2, 24 cm2) for an initial NH4+-N concentration of 10 mg L−1. The optimum EC (20 mA cm−2, natural initial pH 7.5–7.8) and EO parameters (30 mA cm−2, 24 cm2 surface area anode, Al cathode) were combined into a hybrid system to treat two real nitrate-polluted groundwaters with initial NO3−-N concentrations of 25 and 75 mg L−1. Results revealed that the proposed hybrid treatment system can be used to efficiently remove nitrate from groundwaters.

Three-phase composites of NiFe2O4/Ni@C nanoparticles derived from metal-organic frameworks as electrocatalysts for the oxygen evolution reaction

Composite electrocatalysts of carbon and metals or metal compounds with homogeneous active sites can be obtained through the carbonization of metal organic framework (MOF) materials under inert atmosphere. In this work, a three-phase composite electrocatalysts NiFe2O4/Ni@C were prepared via pyrolysis from self-assembled MOF nanosheets aggregates. The excellent electrocatalytic activity of the obtained electrocatalysts with various Ni:Fe ratios is demonstrated. Especially, the NiFe2O4/Ni@C sample with the mole ratio of Ni:Fe = 1:1 can use the overpotential (η) of 330 and 423 mV to drive 10 and 50 mA cm−2 respectively. After 80 000 s/22 h, the current density could retained 90% of the initial current density. The excellent activity and stability of the electrocatalysts are attributed to nickel and iron ions with uniform dispersion at atomic level in the NiFe2O4 phase and the synergistic effect of nickel and NiFe2O4 nanoparticles with amorphous carbon atoms or nanoparticles around.

Ternary synergistic catalyst system of Pt–Cu–Mo2C with high activity and durability for alcohol oxidation

Efficient catalyst system of high activity and durability is urgently required to convert alcohols directly on the anode in the direct alcohol fuel cells technique. Herein, an efficient ternary catalyst system of Pt–Cu–Mo2C catalyst is compositionally optimized and mechanically probed for the oxidation of methanol and ethanol fuels. Outstanding catalytic capabilities including high catalytic activity, stability, fast kinetics and high anti-poisoning ability are found due to the strong electronic effect, ligand effect and multi-oxophilic component synergism. Cu and Mo2C play different roles in the oxophilic functionalities formation as well as the anti-poisoning effect, and the combined advantages of Mo2C and Cu in the catalyst system make this ternary system more efficient for alcohols fuel oxidation compared with the traditional binary catalysts. Specifically, the peak current density of Pt–Cu–Mo2C is 80.31 mA cm−2 for methanol oxidation with a nearly 3.5-fold enhancement compared to the state-of-the-art commercial Pt/C catalyst (23.61 mA cm−2); the highest CO-tolerance ability is demonstrated by the lowest CO-oxidation peak at 0.451 V(117 mV less than Pt/C), and as high as 74.55 and 86.81% of the initial current density are maintained, respectively, after a 1000-cycle accelerated stability test towards methanol and ethanol oxidation for fuel cell reaction.

Gold nanocrystal decorated trimetallic metal organic frameworks as high performance electrocatalysts for oxygen evolution reaction

Electronic states of active sites of catalysts play a key role in determining electrocatalytic performances. Engineering electronic states through decoration of functional entities is an effective way to advance catalyst design. In this work, Au nanocrystal decorated Fe, Co, and Ni based trimetallic metal organic frameworks (MOFs) (termed Au/(FCN)MOFs), grown in-situ on nickel plates (NP), are developed as high performance oxygen evolution reaction (OER) electrocatalysts. At optimal Au nanocrystal decoration, the Au/(FCN)MOF/NP electrode achieves significantly improved OER performances over the (FCN)MOF/NP electrode, lowering η10 and η500 from 242 and 340 mV to 216 and 290 mV, respectively, Tafel slope from 42.1 to 31.7 mV dec−1, and current density decay from 6 to 5% after 50 h operations at an initial current density of 160 mA cm-2. The enhancement is attributed to the significantly elevated oxidation states of Fe, Co, and Ni, induced by decoration of the Au nanocrystals of high electronegativity, as evidenced with high-resolution X-ray photoelectron spectroscopy and in-situ Raman spectroscopy studies. Furthermore, the main active metal centers are identified with in-situ X-ray absorption spectroscopy study to be Ni and Co, with Fe playing a supporting role to help Ni acquire high valence states to realize enhanced OER activities.

Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate.

The electro-oxidation of methanol to formate is an interesting example of the potential use of renewable energies to add value to a biosourced chemical commodity. Additionally, methanol electro-oxidation can replace the sluggish oxygen evolution reaction when coupled to hydrogen evolution or to the electroreduction of other biomass-derived intermediates. But the cost-effective realization of these reaction schemes requires the development of efficient and low-cost electrocatalysts. Here, a noble metal-free catalyst, Ni1- x Fex Se2 nanorods, with a high potential for an efficient and selective methanol conversion to formate is demonstrated. At its optimum composition, Ni0.75 Fe0.25 Se2 , this diselenide is able to produce 0.47 mmolcm-2 h-1 of formate at 50 mAcm-2 with a Faradaic conversion efficiency of 99%. Additionally, this noble-metal-free catalyst is able to continuously work for over 50000 s with a minimal loss of efficiency, delivering initial current densities above 50 mAcm-2 and 2.2 Amg-1 in a 1.0 m KOH electrolyte with 1.0 m methanol at 1.5V versus reversible hydrogen electrode. This work demonstrates the highly efficient and selective methanol-to-formate conversion on Ni-based noble-metal-free catalysts, and more importantly it shows a very promising example to exploit the electrocatalytic conversion of biomass-derived chemicals.

Dimensionally stable anode (Ti/RuO2) mediated electro-oxidation and multi-response optimization study for remediation of coke-oven wastewater

Electrochemical oxidation by means of dimensionally stable anodes (Ti/RuO2) was executed for the simultaneous elimination of various pollutants (such as COD, phenol, cyanide, and ammonia, etc.) from simulated and real coking-wastewater. A multiparameter variation study was also performed to investigate the operating range of certain operational parameters (such as pH, electrolyte, current density (CD), and H2O2 as a catalyst) and their effects on removal efficiencies of COD and rest of the pollutants of wastewater. To investigate the visual, morphological & elemental features of electrodes FE-SEM and EDX studies were performed before and after the treatment of wastewater. The electrochemical behavior was explored through cyclic voltammetry analysis. Moreover, the degradation and mineralization performance of organic material in wastewater was also investigated through LC-MS and total organic carbon (TOC) studies, respectively. A mathematical equation (model) was also developed to represent the multi-parameter optimization study using central composite design (CCD) through response surface methodology software (RSM tool). At the end of the process, the COD (90.13%), phenol (99.34%), cyanide (96.23%), and ammonia (94.43%) were eliminated within 180 min of reaction at optimum initial pH, NaCl (electrolyte), current density (CD), and H2O2 concentration of 8.0, 1.6 g/L, 24 mA/cm2 and 0.030 M, respectively.

Degradation of triclosan by anodic oxidation/in-situ peroxone process: Kinetics, pathway and reaction mechanism

Triclosan (TCS) is an emerging contaminant that threatens the environment and human health. This study was conducted to investigate TCS abatement by a novel electro-oxidation (EO) process, which used a Ti-based nickel and antimony doped tin oxide (NATO/Ti) anode and a carbon nanotubes (CNTs) doped carbon/PTFE (CNTs-C/PTFE) gas diffusion electrode (GDE) for oxygen reduction reaction (ORR). A comparative study was also performed for TCS degradation by using a traditional EO with a nickel foam cathode, termed as HER-EO. The optimal initial TCS concentration, current density and solution pH for TCS degradation during the ORR-EO and HER-EO were investigated. Results showed that ORR-EO removed more than 98% of TCS in 10–60 min under the concentration of 5–50 mg/L. The TCS degradation followed pseudo-first-order kinetics and its main intermediates were observed during the ORR-EO and HER-EO using liquid chromatography combined mass (LC-MS). The results of FED analysis and toxicity prediction by ECOSAR software showed that less intermediates accumulated during the ORR-EO and the residues were less harmful. The ORR-EO degradation mechanism for TCS was attacking on the ether bond and the benzene ring by •OH. This novel ORR-EO process exhibits a great merit in the field of emerging contaminants abatement.

Electrochemical mineralization of abattoir wastewater with continuous system

This study aims to determine the effects of initial pollutant concentration level (1/1–1/4), flow rate (10–40 mL/min), NaCl concentration (0.1–1 M), pH (3–9) and current density (4.73–23.67 mA/cm2) parameters on the removals of total suspended solids, total organic carbon, chemical oxygen demand, total nitrogen and color for economic treatment of cattle-abattoir wastewater using mesh-type Ti/Pt anodes with continuous EO system. Total suspended solids, total organic carbon, chemical oxygen demand, total nitrogen and color analyses were carried out according to photometric method, catalytic oxidation method, closed reflux colorimetric method, nitrogen cell test method and platinum–cobalt method, respectively. The effluent chloride levels were analyzed according to the argentometric titration method. According to results, all operational parameters had an impact on removal efficiencies but the most effective parameters on energy consumption were NaCl concentration and applied current density. Although two possible system conditions were determined according to removal efficiencies the operating conditions with the lowest energy consumption are considered to be optimal. The optimum operating conditions were determined as NaCl concentration of 1 M, CD of 4.73 mA/cm2, initial pH of 7.03, reaction temperature of 25 °C and FR of 10 mL/min. Under these conditions removal efficiencies (%) for total suspended solids, total organic carbon, chemical oxygen demand, total nitrogen and color were found as; 98.28, 93.03, 97.44, 95.53 and 99.80, respectively. The energy consumption values were calculated as 2.42 kWh/kg COD and 19.43 kWh/m3. The approximate cost to treat 1 m3 wastewater was calculated as $ 6.43. The kinetic behavior abided by a pseudo-first-order model.

The effect of anodic potential on bornite dissolution: A key button of copper pollution

The relationship between anodic potential and sulfur film of bornite in acidic electrolyte was investigated by electrochemical experiments and surface analytical techniques. The formation of sulfur film decreased the conductivity of bornite, and the initial current density of bornite was positively correlated with subjected potential due to thermodynamic energy. The higher potential hindered the formation of sulfur precipitates Sn 2-/S0 and forced products of bornite diffuse into electrolyte. The S 2p 3/2 spectrum proved that S2- has been converted to S2 2-, Sn 2-/S0 and SO4 2- during bornite dissolution. Combined with the composition of sulfur film formed on the bornite surface, the passive effect of sulfur film was mainly caused by formed Sn 2-/S0. The solution potential was the primary factor in the bornite dissolution under acidic environment.

Chromium and cadmium removal from synthetic wastewater by Electrocoagulation process

Electrocoagulation (EC) is one of the efficient electrochemical approaches for industrial wastewater treatment. The present work aims to reach optimum conditions for achieving simultaneous removal of chromium and cadmium ions from synthetic wastewater by EC through assessment of different parameters like electrodes material, electrode configuration, initial pH, current density, initial temperature, and initial contaminate concentration. In addition, a comparison between chemical coagulation and EC efficiency for Chromium and cadmium removal was presented. Results showed that the (Fe-Al), an anode and cathode, achieved better removal efficiency than other electrodes configurations (Fe-Fe / Al-Fe / Al- Al). Also, the increase of initial temperature and current density enhanced the removal efficiency. In contrast, the increase in the initial concentration reduced the removal efficiency. The complete removal of Chromium achieved through the use of Fe-Al electrodes and current density was 12.50 mA/cm2 with solution pH of 5.8, temperature was 25oC and an initial concentration of 280 mg/L. On the other hand, Cadmium’s complete removal was achieved through the use of Fe-Allectrodes, at pH of 5.8, applied current 1.4 A and 60oC. Therefore, EC was proved to be better approach than conventional coagulation in case of treatment of wastewater containing different types of heavy metals ions with high initial concentrations.

A Dynamic Self-Clamping Caused by Dynamic Avalanche During the Turn-Off of PT-IGBT

A dynamic self-clamping is found during overstress turn-off of the PT-insulated gate bipolar transistor (IGBT) with a higher carrier lifetime. Theoretical analysis and numerical device simulation reveal that it is caused by the remaining plasma that cannot be completely removed due to dynamic avalanche injection. A 1-D physics-based analytical model for the self-clamping is established, and analytical results indicate that clamped voltage is inversely proportional to the initial turn-off current density and the carrier lifetime. When the dc-link voltage is larger than the clamped voltage of the device at a certain turn-off current, both terminal voltage and terminal current will be clamped, causing the device to lose control of the gate. Simulations of the multicell structure demonstrate that the avalanche-generated current filament under the self-clamping is stationary and may exist for a longer time, which is extremely likely to lead to local overheat and device destruction.

Lignin‐derived carbon nanofibers‐laminated redox‐active ‐mixed metal sulfides for high‐energy rechargeable hybrid supercapacitors

The design of inexpensive, binder-free electrodes with high energy densities from naturally occurring compounds poses an interesting challenge for the construction of high-performance supercapacitors. In particular, the synthesis of highly conductive carbon electrodes starting from miscanthus-derived (silver grass) lignin with inorganic active sites is of interest for hybrid supercapacitors. In this work, Ni-Mn sulfide nanograin networks are embedded on lignin-derived carbon nanofibers (LCNFs) by electrospinning, followed by either direct vapor-phase sulfidation or peroxidation-induced sulfidation in an inert atmosphere. After either of the two different sulfidation processes, the direct transformation of Ni-Mn sulfide on carbon nanofibers results in highly mechanically flexible freestanding electrodes, with a good specific capacity of 652.3 C g−1 at 1 A g−1, excellent current rate properties (73.6% capacity retention at 20 times the initial current density), and a cycling stability of 91.3% after 5000 cycles, even at the high current density of 10 A g−1. These outstanding properties are attributed to the rational design of surface-embedded Ni-Mn sulfide nanograins on the 3D LCNFs and the fascinating synergetic and graphitic nature of the fibrous web, which increases conductivity, influences the interfacial contact, and promotes highly electrochemically active sites on the electrode surface. Furthermore, an aqueous hybrid supercapacitor assembly of LCNFs-NiMnS//activated carbon (AC) is demonstrated, with a maximum energy density of 52.4 W h kg−1 at a power density of 800 W kg−1, as well as 92.3% capacitance retention even after 10 000 cycles. This work not only establishes a high-capacity anode but also provides an ideal strategy for designing flexible and conductive heterostructure network for various energy storage applications.

Preparation and electrochemical treatment application of Ti/Sb–SnO2-Eu&rGO electrode in the degradation of clothianidin wastewater

This work investigated the preparation of Ti/Sb–SnO2 electrode co-doped with graphene and europium and the electrochemical degradation of clothianidin in aqueous solution with Ti/Sb–SnO2-Eu&rGO electrode. The physicochemical properties of different electrodes were characterized by using the scanning electron microscopy, X-ray diffraction, oxygen evolution potential and cyclic voltammetry tests. The results indicated that the Ti/Sb–SnO2-Eu&rGO electrodes have a compact structure and fine grain size and have a higher oxygen evolution overpotential than Ti/Sb–SnO2-None, Ti/Sb–SnO2-Eu and Ti/Sb–SnO2-rGO electrodes. Among the four electrodes, the Ti/Sb–SnO2-Eu&rGO electrode showed the highest efficiency and was chosen as the experimental electrode. The main influence factors on the degradation of clothianidin, such as initial pH, electrolyte concentration, current density and initial concentration of clothianidin, were analyzed. The results showed that the removal rate of clothianidin can reach 96.44% under the optimal conditions for 120 min treatment. Moreover, a possible degradation pathway including the fracture of internal bonds of clothianidin such as the N–N bond, the C–N bond that connects nitroguanidine to the thiazole ring and mineralization was elucidated by intermediate products identified by HPLC-MS method and Fourier transform infrared spectroscopy (FTIR). This paper introduces the Ti/Sb–SnO2-Eu&rGO electrode into an electrocatalytic degradation system and could provide basic data and technique support and guidance for the clothianidin wastewater pollution control.

Reduced graphene oxide coated graphite electrodes for treating Reactive Turquoise Blue 21 rinse water using an indirect electro-oxidation process

The present study deals with the decolourization of synthetic Reactive Turquoise Blue 21 (RTB21) dye-based model wastewater using an indirect electro-oxidation process and enhanced by modified graphite electrodes. Graphene oxide (GO) was successfully synthesized and deposited on the surface of pre-treated graphite electrodes. It was further reduced to form reduced graphene oxide (rGO). The resultant newly developed anode electrodes were designated as (Gr)0, (rGO/Gr)1, and (rGO/Gr)2 and used for the treatment of wastewater. Electrodes, thus developed, were characterized using Fourier-transform infrared spectroscopy, X-ray diffractions, Field emission scanning electron microscopy, and Contact angle (CA). The effect of process parameters such as initial pH, current density, electrolyte concentration, and temperature on the performance of novel anode electrodes was investigated. The colour removal efficiency was increased significantly almost 25.80% in the presence of a modified electrode with the highest efficiencies of about 96.69% in a natural pH environment, 200 A/m2, 2 g/L NaCl concentration, 30 °C temperature, and 15 min process time for 50 ppm RTB21 dye concentration for (rGO/Gr)2 electrode. The RTB21 decolourization by indirect electro-oxidation process follows the pseudo-first-order kinetics, and the activation energy was estimated to be 23.42 kJ/mol. The stability of (rGO/Gr)2 electrode was also examined. The rGO coated electrode was a superior electrode for the indirect electro-oxidation process, giving enhanced colour removal (%).

Electron Irradiation Effects and Defects Analysis of the Inverted Metamorphic Four-Junction Solar Cells

The degradation of inverted metamorphic four-junction (GaInP/GaAs/In0.3Ga0.7As/In0.58Ga0.42As, IMM4J) solar cells irradiated by 1-MeV electrons was investigated via their spectral responses and the characterization of their electrical properties. As in the case of traditional three-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties ( I sc, V oc, and P max) decrease with the logarithmic change of the electron fluence. The degradation of open-circuit voltage ( V oc) is slightly more pronounced than that of I sc in IMM4J solar cells because of the sum rule for V oc and the limit rule for I sc. The spectral response analysis showed that an In0.3Ga0.7As subcell was the most damaged subcell in the irradiated IMM4J solar cell, but an In0.58Ga0.42As subcell had the lowest initial short-circuit current density (Jsc), which was maintained throughout the irradiation test. We therefore focused on the In0.58Ga0.42As subcell. Deep-level transient spectroscopy (DLTS) experiments were realized to study emission and capture processes in two special full configurations of In0.58Ga0.42As and In0.3Ga0.7As subcells of the IMM4J solar cell. DLTS measurements reveal a dominant electron trap at 0.52 eV below the conduction band (Ec) of In0.58Ga0.42As, and the electron trap gradually evolved into Ec-0.46eV and Ec-0.58eV after 1-MeV electron irradiation. Based on the first-principles calculation, Ec-0.46 eV and Ec-0.58 eV can be assigned as ${\bf V}_{{\bf Ga}}^{\bf 0}/{\bf V}_{{\bf Ga}}^{{\rm{ - }}1}$ and ${\bf V}_{{\bf In}}^{\bf 0}/{\bf V}_{{\bf In}}^{{\bf - 1}}$ , respectively. However, only one shallow level Ec-0.03eV was observed within the bandgap of In0.3Ga0.7As after irradiation with DLTS detection. We summarize the issues faced for the space application of IMM4J solar cells by comparing the spectral responses of IMM3J, IMM4J, and TJ solar cells. Finally, the optimization of the design and fabrication of IMM solar cells are proposed.

α-Ni(OH)2 electrodeposition from NiCl2 solution

Abstract α-Ni(OH)2 was synthesized from a NiCl2 solution by electrodeposition method. In order to conduct a systematic study on the effects of experimental parameters, a series of electrolyte initial pH values, current densities, electrodeposition temperatures, and electrodeposition time were used. Cyclic voltammetry results demonstrated a side reaction of Ni2++2e→Ni. The X-ray diffraction analysis, Fourier-transform infrared spectrum, and the color of the product showed that pure α-Ni(OH)2 could be obtained in the initial pH value range of 2–5.86, current density range of 10–25 mA/cm2 electrodeposition temperature range of 25–35 °C, and electrodeposition time range of 1.0–3.0 h. When electrodeposition temperature increased to 45 °C, a mixture of α-Ni(OH)2 and metallic Ni was obtained. A current density higher than 30 mA/cm2 resulted in the sample with features of β-Ni(OH)2. A small amount of metallic Ni existed in the as-prepared sample when current density decreased to 5 mA/cm2. A slight increase of electrolyte pH was observed with increasing initial solution pH and current density. Electrodeposition mass revealed a slight decrease with initial pH decreasing and showed an almost linear increase with current density increasing. The slope of the curve for electrodeposition mass versus electrodeposition time remained stable in the first 2.0 h and then decreased.

Rational design of bimetallic metal–organic framework composites and their derived sulfides with superior electrochemical performance to remarkably boost oxygen evolution and supercapacitors

Developing highly efficient and stable multi-functional metal–organic framework electrochemical materials is of prime importance for renewable energy technologies and electrocatalytic applications. Herein, a novel series of bimetallic metal–organic framework (MOF) hybrid materials were successfully designedly fabricated through an in-situ growth and MOF-on-MOF strategies, namely as NiFeMOF/NF, NiCoMOF/NF, FeMOF/NiMOF/NF, and CoMOF/NiMOF/NF. Benefiting from the synergistic effect of bimetallic centers, conductive substrate and unique fabrication, they exhibit remarking electrochemical performance. Among them, FeMOF/NiMOF/NF composite with ultrathin nanosheets displays the best electrochecatalytic performance with ultralow overpotentials of 293 mV at 50 mA cm−2 and 359 mV at 100 mA cm−2 for oxygen evolution reaction (OER), and remarking electrochemical stability with high current density of 100 mA cm−2 after testing for 24 h, that 88% of initial current density can be remained. Based on these fabricated bimetallic MOF hybrid materials as precursors, the corresponding MOF-derived nano sulfides were obtained with massive exposure of active sites. As an excellent supercapacitor electrode, NiCoS/NF-1 converted from CoMOF/NiMOF/NF shows admirable specific capacitance of 2815.4 F g−1 at 1 mA cm−2 and a remarkable rate capability of 82%.

Electrocoagulation of kraft pulp bleaching filtrates to improve biotreatability

Bleached kraft pulp mills generate large volumes of effluents usually treated by biological processes that don´t remove recalcitrant organic constituents. The present study was undertaken to evaluate the potential of electrocoagulation of acid (AcF) and alkaline (AlF) kraft pulp bleaching filtrates with Al and Fe electrodes to improve their biotreatability. Response surface methodology was used to predict the effects of initial pH, current density, and electrolysis time on biodegradability (BOD/COD). Biodegradability increases of 1.7–2.1-fold were obtained using optimized experimental conditions for each electrode-filtrate combination: AcF-Al (pH 7.9, 128 A/m², 49 min), AcF-Fe (pH 4.6, 104 A/m², 40 min), AlF-Al (pH 3.8, 150 A/m², 52 min) and AlF-Fe (pH 6.3, 101 A/m², 42 min). Electrocoagulation with Al electrodes was more efficient in removing color, phenols and estrogenic activity, but required longer reaction time and higher current density, while treatment with Fe electrodes resulted in lower toxicity to Daphnia similis. Electrocoagulation of both filtrates before combining them for biological treatment led to 88 % dissolved organic carbon (DOC) removal in a five-day biodegradability test, compared to only 27 % DOC removal from combined raw filtrates. The potential to increase overall pulp mill wastewater treatment efficiency using electrocoagulation prior to biological treatment was demonstrated.

Mean-Field Dynamo Model in Anisotropic Uniform Turbulent Flow with Short-Time Correlations

The mean-field model is one of the basic models of the dynamo theory, which describes the magnetic field generation in a turbulent astrophysical plasma. The first mean-field equations were obtained by Steenbeck, Krause and Rädler for two-scale turbulence under isotropy and uniformity assumptions. In this article we develop the path integral approach to obtain mean-field equations for a short-correlated random velocity field in anisotropic streams. By this model we analyse effects of anisotropy and show the relation between dynamo growth and anisotropic tensors of helicity/turbulent diffusivity. Considering particular examples and comparing results with isotropic cases we demonstrate several mean-field effects: super-exponential growth at initial times, complex dependence of harmonics growth on the helicity tensor structure, when generation is possible for near-zero component or near-zero helicity trace, increase of the averaged magnetic field inclined to the initial current density that leads to effective Lorentz back-reaction and violation of force-free conditions.