Three-dimensional Electrochemical Reactor Research Articles

Application of a fluidized three-dimensional electrochemical reactor with Ti/SnO2–Sb/β-PbO2 anode and granular activated carbon particles for degradation and mineralization of 2,4-dichlorophenol: Process optimization and degradation pathway

A three-dimensional electrochemical reactor with Ti/SnO2–Sb/β-PbO2 anode and granular activated carbon (3DER-GAC) particle electrodes were used for degradation of 2,4-dichlorophenol (2,4-DCP). Process modeling and optimization were performed using an orthogonal central composite design (OCCD) and genetic algorithm (GA), respectively. Ti/SnO2–Sb/β-PbO2 anode was prepared by electrochemical deposition method and then its properties were studied by FESEM, EDX, XRD, Linear sweep voltammetry and accelerated lifetime test techniques. The results showed that lead oxide was precipitated as highly compact pyramidal clusters in the form of β-PbO2 on the electrode surface. In addition, the prepared anode had high stability (170 h) and oxygen evolution potential (2.32 V). A robust quadratic model (p-value < 0.0001 and R2 > 0.99) was developed to predict the 2,4-DCP removal efficiency in the 3DER-GAC system. Under optimal conditions (pH = 4.98, Na2SO4 concentration = 0.07 M, current density = 35 mA cm−2, GAC amount = 25 g and reaction time = 50 min), the removal efficiency of 2,4-DCP in the 3DER-GAC system and the separate electrochemical degradation process (without GAC particle electrode) were 99.8 and 71%, respectively. At a reaction time of 80 min, the TOC removal efficiencies in the 3DER-GAC and the separate electrochemical degradation system were 100 and 57.5%, respectively. Accordingly, the energy consumed in these two systems was calculated to be 0.81 and 1.57 kWh g−1 TOC, respectively. Based on the results of LC-MS analysis, possible degradation pathways of 2,4-DCP were proposed. Trimerization and ring opening reactions were the two dominant mechanisms in 2,4-DCP degradation.

Removal of persistent organic contaminants from wastewater using a hybrid electrochemical-granular activated carbon (GAC) system

A three-dimensional (3D) electrochemical flow-through reactor equipped with GAC packed bed, polarized by the electric field, was evaluated for the removal of persistent organic contaminants from real sewage effluent. The performance of the reactor was investigated for 27 consecutive runs at two anodic current densities, i.e., low current density (LCD) of 15 A m−2, and high current density (HCD) of 100 A m−2. In the HCD experiments, the adsorption ability of saturated GAC was increased, mainly due to the increase in the mesoporosity of GAC. A synergy between electrosorption/adsorption on GAC and electrooxidation was observed in terms of the removal of all target pollutants. DEET presented the highest synergy, ranging from 40% to 57%, followed by iopromide (22–46%), carbamazepine (15–34%) and diatrizoate (4–30%). The addition of GAC decreased the concentrations of toxic chlorate and perchlorate by 2-fold and 10-fold, respectively, due to their electrosorption on GAC. Also, 3D electrochemical system yielded lower concentrations of adsorbable organic iodide (AOI) and adsorbable organic chlorine (AOCl). Thus, addition of low amounts of GAC in electrochemical systems may be a low-cost and simple way of minimizing the formation and final effluent concentrations of toxic halogenated byproducts.

Achieving high performance for electrocatalytic dechlorination with magnetic Pd/CoFe2O4 particle electrodes

Moveable catalysts in a three-dimensional (3D) electrochemical reactor offer benefits for pollutant dechlorination because of increased active sites and mass transfer, but they suffer from difficulties in catalyst recovery. Herein, we demonstrate that magnetic Pd/CoFe2O4 catalysts are highly active, durable, and recyclable when used in the electrochemical dechlorination of 2,4-dichlorophenol (2,4-DCP). Highly dispersed nano-sized Pd/CoFe2O4 catalysts were successfully synthesized using an easy chemical deposition method. Tests on the effects of the initial solution pH showed that the alkaline condition was favorable for achieving increased dechlorination performance in terms of increased reaction rate and higher current efficiency. Greater amounts of surface-adsorbed atomic H (Hads*) formed and Pd with an electron-rich state as a consequence of metal-support interaction under the alkaline condition may play important roles in the effectiveness. The Pd/CoFe2O4 particle electrodes in the 3D reactor were effective in removing 2,4-DCP with different concentrations. Notably, at a current density of 2.50 mA cm−2, 200 mg L−1 2,4-DCP can be dechlorinated to phenol within 30 min with current efficiency of 64.4%. The findings demonstrate that magnetic Pd/CoFe2O4 catalysts hold distinct promise for application in the 3D electrochemical dechlorination process.

Degradation Pathway and Kinetics of 4-chlorphenol by Sn/Sb-Mn-GAC Composite Particle Electrode

A composite particle electrode Sn/Sb-Mn-GAC was prepared by impregnation with granular activated carbon (GAC) as carrier. The surface morphology, phase composition and electrochemical properties of the particle electrode were characterized by scanning electron microscopy, X-ray diffraction and electrochemical workstation. The results show that the Sn/Sb-Mn-GAC particles have uniform grain size, good dispersity and high oxygen evolution potential. The Sn/Sb-Mn-GAC particle electrode was used to the electrochemical degradation of 4-chlorophenol. It was shown that 4-chlorophenol was almost completely removed after electrolyzing for 60 min. A large number of intermediates were produced during the degradation of 4-chlorophenol in the experimental system. The main intermediate products were benzoquinone, 4-chlorocatechol, hydroquinone, fumaric acid, oxalic acid, etc., eventually mineralized into water and carbon dioxide. The degradation pathway of 4-chlorophenol were preliminarily suggested through the analysis of intermediates in degradation process. The supported Sn/Sb-Mn-GAC particle electrode can be repeated used 4 times in three-dimensional electrochemical reactor and the kinetic model for the electrochemical oxidation of 4-chlorophenol was established. The experimental results show that the degradation process of 4-chlorophenol accords with the first-order kinetic model, the correlation coefficient is 0.98 or more. The kinetic rate constant k of Sn/Sb-Mn-GAC particle electrode is reduced when it is repeated used, but the treatment efficiency of 4-chlorophenol is still better. The results of research show that the three-dimensional electrochemical reactor using Sn/Sb-Mn-GAC particle electrode has promising application prospects in the treatment of phenolic wastewater.

Efficient electrochemical-catalytic reduction of nitrate using Co/AC0.9-AB0.1 particle electrode

In this work, a composite particle electrode (Co/ACx-ABy) was proposed using cobalt as the catalyst, active carbon (AC) as the carrier, and acetylene black (AB) as the conductor. The proposed particle electrodes were applied in a continuous three-dimensional (3D) electrochemical reactor. Based upon the removal efficiency of total nitrogen (TN) and the corresponding energy consumption, the optimum mass ratio of AC to AB was determined to be 0.9:0.1. Scanning electron microscopy (SEM) and energy dispersive system (EDS)-mapping revealed the presence of metal particles on the surface of Co/AC0.9-AB0.1 electrode. Furthermore, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that Co/AC0.9-AB0.1 contained three valence states of Co, namely Co0, Co2+, and Co3+. Additionally, batch experiments showed that 95% of TN removal was achieved under the current of 0.4 A, pH of 7, hydraulic retention time (HRT) of 60 min and the initial TN of 20 mg/L. The addition of Cl− was obviously beneficial to the removal of TN, whereas HCO3−, PO43−, CO32−, and dissolved organic matter (DOM) inhibited the removal of TN. The cyclic voltammetry (CV) curve and the atomic H detected by electron spin resonance (ESR) demonstrated that nitrate was directly reduced by Co0 ions and indirectly reduced by H radicals.

Insight into synergies between ozone and in-situ regenerated granular activated carbon particle electrodes in a three-dimensional electrochemical reactor for highly efficient nitrobenzene degradation

This study compared the removal and mineralization of nitrobenzene (NB) by electrolysis using granular activated carbon (GAC) as three-dimensional (3D) electrodes, ozonation, and the combination of electrolysis, GAC, and ozone (E-GAC-O3). A highly synergetic effect was demonstrated by combining electrolysis, ozone, and GAC, and able to achieve 95.58% of TOC removal within 120 min due to abundant production of OH in the E-GAC-O3 process. Interestingly, further study revealed 92.30% of NB removal was due to the oxidation of OH, and the E-GAC-O3 process could achieve a much higher energy efficient ratio for OH production compared with other processes. Besides, the mechanism of OH generation was explored through quantitatively estimating the contribution of different reaction paths involved in E-GAC-O3 process. Results demonstrated that electrochemical oxidation of hydroxyl ion, peroxone reaction, GAC catalyzed ozone reaction, and electro-reduction of ozone reactions were responsible for 12.50%, 37.50%, 8.75%, and 31.25% of OH generation, respectively. Moreover, the durability of GAC in E-GAC-O3 process was systematically investigated by reusing GAC for 50 times. It is worth noting that GAC possessed a very stable activity for transforming ozone into OH with almost unchanged functional groups and pore texture during long consecutive recycles in E-GAC-O3 process, while the cathode insulation experiment revealed that replenishing of free electrons from both cathode and inside of GAC was critical for maintaining the stability of GAC. These findings should be widely considered in the combination of electrolysis using 3D electrodes and ozone technologies to obtain further improvement of their potential and applicability in industrial practice. Finally, the removal efficiency of other ozone-refractory organics, Ibuprofen (IBP), Benzotriazole (BTA), and N,N-Dimethylformamide (DMF) were also investigated while the effects of different water matrices on NB removal in E-GAC-O3 process was studied. All the results suggest that the E-GAC-O3 process was efficient and sustainable for refractory organic wastewater treatment.

A pilot-scale three-dimensional electrochemical reactor combined with anaerobic-anoxic-oxic system for advanced treatment of coking wastewater

Coking wastewater is highly concentrated and extremely toxic, greatly challenging the treatment technologies. Conventional biological technology such as anaerobic-anoxic-oxic (A2O) system is inefficient, since various biological reactions are inhibited by toxicants in coking wastewater. In this work, a pilot-scale three-dimensional electrochemical reactor (3DER) is integrated into the A2O system as a pretreatment unit to improve the treatment efficiency of coking wastewater. The results indicate that 3DER pretreatment increased the biodegradability of coking wastewater, promoting the degradation of coking wastewater in A2O system. The integrated 3DER-A2O system can remove 94.4% of COD and 76.2% of TN from coking wastewater, and the energy consumption was only 0.22 kWh/kg COD and 4.69 kWh/kg TN. The components of coking wastewater were significantly simplified and the acute toxicity was reduced from 99% to 12% after the treatment. The integrated 3DER-A2O system provides a new solution for coking wastewater treatment, showing a promising application potential.

Co-doping polymethyl methacrylate and copper tailings to improve the performances of sludge-derived particle electrode

Three-dimensional electrochemical reactor (3DER) is a highly efficient technology for refractory wastewater treatment. Particle electrodes filled between anode and cathode are the core units of 3DER, determining the treatment efficiency of wastewater. However, particle electrodes deactivation due to catalytic sites coverage seriously impedes the continuous operation of 3DER. In this work, granular sludge carbon (GSC) particle electrodes being resistant to deactivation are fabricated by pyrolyzing the mixture of waste sludge, polymethyl methacrylate (PMMA), and copper tailings, whose performances are evaluated by degrading rhodamine B (RhB) wastewater in a continuous-flow 3DER. Results indicate that hierarchical-pore structure comprising macro-, meso-, and micropores is developed in GSC-10-CTs by doping 10 g PMMA and 5 g copper tailings into 100 g waste sludge. PMMA contributes to construct macropores, which is essential for the mass transfer of RhB into GSC particle electrodes of centimeter-size. Copper tailings promote the formation of meso- and micro-pores in GSCs, as well as improving the electrochemical properties. Consequently, GSC-10-CTs packed 3DER exhibits the highest removal efficiency and lowest energy consumption for RhB treatment. In addition, the compressive strength of GSC-10-CTs is enhanced by copper tails, that is crucial to fill into 3DER as particle electrodes. The high-efficient and cost-effective GSC-10-CTs fabricated by waste materials have the potential of substituting commercial granular activated carbon catalysts in the future, consequently promoting the application of 3DER in wastewater treatment.

Electrochemical Degradation of Reactive Black 5 Using Three-Dimensional Electrochemical System Based on Multiwalled Carbon Nanotubes

The removal of Reactive Black 5 (RB5) dye and chemical oxygen demand (COD) was investigated using a three-dimensional (3D) electrochemical (3DE) reactor with multiwalled carbon nanotubes (MWCNTs). The experiments were performed according to a Taguchi design model, with the variables being the solution pH (2–9), current density (10–25 mA/cm2), reaction time (15–60 min), MWCNT concentration (25–200 mg/L), and RB5 concentration (25–100 mg/L). The best conditions for optimum removal of RB5 and COD were pH 3, MWCNT concentration 200 mg/L, current density 15 mA/cm2, RB5 concentration 100 mg/L, and reaction time 60 min. Among the main factors, the solution pH for removal of COD and RB5 and the current density for energy consumption had the highest impact. The 3D system generated more H2O2 and OH radicals compared with a two-dimensional (2D) system because the MWCNTs act as microelectrodes in the optimal conditions. In the 3D process, the production of high levels of reactive species led to an increase in the degradation of RB5 into aromatic compounds and various acids.

Electrochemical removal of acid red 18 dye from synthetic wastewater using a three-dimensional electrochemical reactor

Electrochemical removal of acid red 18 dye from synthetic wastewater using a three-dimensional electrochemical reactor

Electrocatalytic hydrodechlorination of 4-chlorophenol on Pd supported multi-walled carbon nanotubes particle electrodes

A series of Palladium (Pd) supported multi-walled carbon nanotubes (Pd/MWCNTs) were synthesized via modified impregnation of Pd2+ followed by in situ chemical reduction with ethanol, NaBH4, and H2 as the reducing agent (referred as Pd/MWCNTs-E, Pd/MWCNTs-B, and Pd/MWCNTs-H, respectively). The electrocatalytic hydrodechlorination of 4-chlorophenol (4-CP), a highly toxic, cancerigenic, and bio-refractory contaminant, was investigated in a three-dimensional electrochemical reactor with Pd/MWCNTs as the particle electrodes. Nearly 100% of 4-CP could be efficiently dechlorinated and completely converted into phenol within 30 min under optimized conditions. Transmission electron microscope (TEM) and X-ray diffraction (XRD) results indicated that the small Pd nano-particles (6.4–13.1 nm) were uniformly supported on the surface of MWCNTs and formed face centered cubic (fcc) structure in all as-prepared catalysts. The removal efficiency of 4-CP was significantly affected by the size of loaded Pd nano-particles, where Pd/MWCNTs-B (100%, 6.4 nm) > Pd/MWCNTs-E (60%, 9.5 nm) > Pd/MWCNTs-H (29%, 13.1 nm). Effects of current density, initial pH, and initial dissolution oxygen (DO) on the 4-CP removal were also investigated. Scavenger experiments confirmed that indirect reduction by atomic H∗ was responsible for the reductive dechlorination of 4-CP. The stability of Pd/MWCNTs-B for the 4-CP dechlorination was also exhibited in repetitive experimental cycles.

Electrocatalytic oxidation of tetracycline by Bi-Sn-Sb/γ-Al2O3 three-dimensional particle electrode

In this work, highly efficient Bi-Sn-Sb/γ-Al2O3 particle electrodes were prepared for effectively degrading tetracycline. The effects of a mass ratio (Sn: Sb), the mass ration of Bi:(Sn + Sb), impregnation times, calcination temperature, and calcination time on the electrocatalytic oxidation capacity of Bi-Sn-Sb/γ-Al2O3 particle electrode was investigated. Conditions in which mass ratio of (Sn: Sb) = 10:1, the mass ratio of Bi:(Sn/Sb) = 1:1, impregnation times 2 h, calcination temperature 500 °C., and calcination time 3 h were considered as optimal preparation conditions for Bi-Sn-Sb/γ-Al2O3 particle electrode. It was cherecterized by infrared spectroscopy (IR), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-Ray Diffraction (XRD), and X-ray fluorescence (XRF) techniques to conforming that the triclinic Bi2O3 formed in the preparation conditions has superior electrocatalytic activity. The electrocatalytic oxidation mechanism of tetracycline by Bi-Sn-Sb/γ-Al2O3 particle electrode is proposed by determining degradation intermediates through LC-MS detection. Electrocatalytic oxidation experiments by adding tert-butyl alcohol indicate that the formation of OH is the primary responsibility for degradating tetracycline. Electrocatalytic degradation of tetracycline at different initial concentration shows that the degradation of tetracycline meets the pseudo first-order kinetics. Results suggest that the three-dimensional electrochemical reactor with Bi-Sn-Sb/γ-Al2O3 particle electrodes could be an alternative for the pretreatment of antibiotic wastewater before biological treatment.

Zn-Fe-rich granular sludge carbon (GSC) for enhanced electrocatalytic removal of bisphenol A (BPA) and Rhodamine B (RhB) in a continuous-flow three-dimensional electrode reactor (3DER)

Recycling sewage sludge from wastewater treatment plants is one of the most challenging environmental problems. In this work, we develop a one-step facile synthesis method of converting iron-rich sewage sludge into granular sludge carbon (GSC), further applying as particle electrodes in three-dimensional electrochemical reactor (3DER) for wastewater treatment. Iron in sludge and zinc in activator are in-situ loaded on particle electrodes as catalytic ingredients. The prepared GSC under different pyrolysis temperature are characterized to investigate the physical, chemical and electrochemical properties. The treatment performances of GSC as particle electrodes are evaluated by degrading bisphenol A (BPA) and Rhodamine B (RhB) in a continuous-flow 3DER. The stability of the GSC are evaluated and possible reaction mechanism are explored. Results indicate that GSC fabricated are typical macroporous material, exhibiting good electrocatalytic activity. The 500 °C/GSC packed 3DER shows the best performances in contaminants removal, that was attributed to larger specific surface and superior electrochemical properties with cooperation of iron oxide and zinc oxide components. The 500 °C/GSC prepared are proved to be suitable for utilizing as particle electrodes in 3DER. Our work offers a new strategy for sewage sludge reuse and provides a promising future for 3DER applications.

Electrochemical degradation of diclofenac using three-dimensional electrode reactor with multi-walled carbon nanotubes.

The electro-oxidation treatment of aqueous solution containing diclofenac (DCF) on a Ti/RuO2-TiO2 electrode in the presence of multi-walled carbon nanotubes (MWCNTs) was studied in a three-dimensional electrochemical (3DE) reactor. The response surface methodology (RSM) based on central composite design (CCD) was utilized to determine the influence of different factors. The results revealed that the obtained polynomial experimental model had a high coefficient of determination (R2 = 0.9762) based on analysis of variance. The optimum condition for the removal of DCF by the 3DE process was obtained with the initial pH of 3.8, the initial DCF concentration of 4mg/L, the current density of 20mA/cm2, the particle electrode concentration of 70mg/L, and the electrolysis time of 85min. The quadratic model developed for DCF removal and subsequently the analysis of the F value illustrated that the initial pH was the most important factor in the removal of DCF. The comparative experiments between electrochemical processes showed the high electrocatalytic activity and removal efficiency of the 3DE reactor with the MWCNT particle electrode. The results also showed that the Ti/RuO2-TiO2 electrode, in addition to its high stability, had a very good electrocatalytic activity in the 3D reactor. The stability and reusability test proved that MWCNTs, as a particle electrode, had a potential to improve the long-term electrocatalytic degradation of DCF in the aqueous solutions. Based on the identified intermediate compounds along with the results of other studies, a possible pathway for the electrochemical oxidation of DCF by the 3DE process catalyzed with MWCNTs was proposed.

Multiple response optimization for high efficiency energy saving treatment of rhodamine B wastewater in a three-dimensional electrochemical reactor

The removal of high-concentration rhodamine B (RhB) wastewater was investigated in a three-dimensional electrochemical reactor (3DER) packed with granular activated carbon (GAC) particle electrodes. Response surface methodology (RSM) coupled with grey relational analysis (GRA) was used to evaluate the effects of voltage, initial pH, aeration rate and NaCl dosage on RhB removal and energy consumption of the 3DER. The optimal conditions were determined as voltage 7.25 V, pH 5.99, aeration rate 151.13 mL/min, and NaCl concentration 0.11 mol/L. After 30 min electrolysis, COD removal rate could arrive at 60.13% with an extremely low energy consumption of 6.22 kWh/kg COD. The voltage and NaCl were demonstrated to be the most significant factors affecting the COD removal and energy consumption of 3DER. The intermediates generated during the treatment process were identified and the possible degradation pathway of RhB was proposed. It is worth noting that 3DER also showed an excellent performance in total nitrogen (TN) removal under the optimal condition. The activated chlorine generated from chloride had great contributions to eliminate carbon and nitrogen of RhB wastewater. The treatment effluent had a good biodegradability, which was suitable for subsequent biological treatment.

Electrocatalytic removal of humic acid using cobalt-modified particle electrodes

Humic acid (HA) is a complex polymer compound with no definite chemical formula. It seriously affects water quality and is one of the main precursors of producing disinfection by-products. In the present study, column granular electrodes (Φ×H = 4 × 3 mm) were prepared using cobalt loaded powder active carbon (PAC). The electrodes were applied in a continuous three-dimensional (3D) electrochemical reactor to remove HA. The crystal structure, morphology, surface chemical bonds, and pore structure of as-prepared material were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption isotherms. Furthermore, parameters affecting the removal of HA and energy consumption (namely, current, electrolyte type and concentration, and initial pH) were examined. Intermediate products were analyzed using ultraviolet-visible (UV–vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy. The results showed that CoO was well loaded in the PAC carriers. The CoO loaded granular electrodes (GAC-Co) had the surface area of 782.6 m2/g, pore volume of 0.6709 cm3/g, and average pore diameter of 3.429 nm. The 95.3% of chemical oxygen demand (COD) removal was obtained under the current of 0.3 A, hydraulic retention time (HRT) of 8 min, influent pH of 7.0, electrolyte of 0.01 mol/L Na2SO4, and initial concentration of 200 mg/L. A large number of H∙ radicals were involved in the electrochemical processes, which were observed using electron spin resonance (ESR) spectroscopy. The analysis of intermediate products indicated that the GAC-Co electrodes showed high electrocatalytic activity for the degradation of HA, in which HA with large molecular weight was decomposed to small molecular weight in the 3D electrochemical system.

TiO2-SiO2/GAC particles for enhanced electrocatalytic removal of acid orange 7 (AO7) dyeing wastewater in a three-dimensional electrochemical reactor

Abstract In this work, granular activated carbon (GAC) supported TiO2-SiO2 oxide (TiO2-SiO2/GAC) was prepared and packed in a three-dimensional electrochemical reactor (3DER) for the removal of acid orange 7 (AO7) dyeing wastewater. The characteristics and the electrocatalytic performance of the prepared TiO2-SiO2/GAC were investigated to verify the feasibility of TiO2-SiO2/GAC application as particle electrodes. Results show that the TiO2-SiO2/GAC could significantly improve the AO7 removal efficiency, extend service life of particle electrodes, and enhance the stability of 3DER system. Orthogonal array was designed to optimize the operation parameters of 3DER, which was determined as electric field intensity 1 V/cm, filling amount of TiO2-SiO2/GAC particles 200 g/L, electrolytic concentration (Na2SO4) 0.07 mol/L, pH 3, treatment time 120 min. Under the optimal condition, the AO7 decolorization rate and COD removal efficiency are 83.20% and 48.95% respectively. The possible intermediates generated in 3DER during AO7 decomposition were identified and the biodegradability of the effluent was also estimated. Results suggest that the 3DER with TiO2-SiO2/GAC particle electrodes could be an alternative for the pretreatment of dyeing wastewater before biological treatment.

Enhanced Electroreductive Removal of Bromate by a Supported Pd-In Bimetallic Catalyst: Kinetics and Mechanism Investigation.

In this work, the electroreductive removal of bromate by a Pd1-In4/Al2O3 catalyst in a three-dimensional electrochemical reactor was investigated. A total of 96.4% of bromate could be efficiently reduced and completely converted into bromide within 30 min under optimized conditions. On the basis of the characterization results and kinetics analysis, a synergistic effect of Pd and In was observed, and Pd1-In4/Al2O3 had the highest reaction rate constant of 0.1275 min-1 (vs 0.0413, 0.0328, and 0.0253 min-1 for In/Al2O3, Pd/Al2O3, and Al2O3). The results of electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the bromate removal process, while the direct reduction played a more important role. Moreover, the introduction of In could increase the zeta potential of Pd1-In4/Al2O3, facilitating bromate adsorption and its subsequent reduction on the catalyst. Finally, a reaction mechanism for bromate reduction by Pd1-In4/Al2O3 was proposed based on all the experimental results.

Electrochemical degradation of 2-diethylamino-6-methyl-4-hydroxypyrimidine using three-dimensional electrodes reactor with ceramic particle electrodes

Abstract The removal of 2-diethylamino-6-methyl-4-hydroxypyrimidine (DTMHP) in simulated wastewater was investigated using a three-dimensional electrodes reactor with ceramic particles serving as packed bed particle electrodes, lead alloy as anode, and stainless steel as cathode. The particle electrodes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). It was showed that the particle electrodes have porous structure. Comparable experiments indicated the high catalytic activity and current efficiency of three-dimensional electrochemical reactor with ceramic particle electrodes. The effects of initial pH, cell voltage on the degradation efficiency were also studied. A removal of 83.45% pyrimidine ring and 35.17% COD were obtained within 150 min under initial pH of 3 and cell voltage of 15 V. Special attention was paid to the target pollutant degradation pathway in this system. It was found that the organic carbon of the pollutant could be degraded effectively, but the mineralization of organic nitrogen was relatively inefficient. The mineralization process could be dramatically promoted by the presence of NaCl, which might be transformed into active chlorine under electrochemical conditions resulting in indirect oxidation. A possible catalytic mechanism of the three-dimensional reactor was also proposed. Overall, the three dimensional electrode method could be considered as a viable alternative for the treatment of pesticide wastewater.

Design of a neutral three-dimensional electro-Fenton system with various bentonite-based Fe particle electrodes: A comparative study

Three-dimensional electrochemical reactor coupling electro-Fenton degradation of phenol with three kinds of bentonite-based various iron species (Fe-Bent): Fe3O4-Bent, Fe2O3-Bent and Fe0-Bent, as particle electrodes at original pH (6·24) was investigated. At the optimal reaction conditions, a maximum of 92·48% phenol removal and 67·48% chemical oxygen demand removal were achieved in the presence of Fe0-Bent. By evaluating Fe leaching behaviours from the particle electrodes during the degradation of phenol, it was found that both homogeneous and heterogeneous electro-Fenton reactions were all involved in the phenol degradation. Moreover, the evolution of ·OH was evaluated and its relationship with Fe leaching and phenol removal was also discussed. The results show that Fe0-Bent can act as the most efficient catalyst in this system at natural conditions, and the feasibility of the proposed combined system of electro-Fenton and three-dimensional electrochemical reactor in the removal of pollutant from wastewater.