Electro-oxidative abatement of low-salinity reverse osmosis membrane concentrates

The present study encompasses the application of electrolysis as novel treatment technique for the abatement of low-salinity concentrates generated from the filtrative treatment of water and wastewater. Four different materials have been tested as anode for a number of brine samples in a one-compartment electrolytic cell in galvanostatic mode. It was found that PbO(2) and SnO(2) anodes initiated electrochemical precipitation through an increase of the pH. Boron-doped diamond (BDD) and RuO(2) anodes successfully oxidised the pollutants in the brine and a linear removal of total ammonia nitrogen (TAN) and chemical oxygen demand (COD) was observed during the first phase of oxidation. Oxidation was predominantly achieved through indirect hypochlorite bulk oxidation; the higher oxidation rate and extent for the BDD anode was attributed to the higher selectivity and activity of the latter. Overall performance of the BDD electrode was higher than for RuO(2): higher rates for TAN (17.9 vs. 13.5mg/Ah) and COD (74.5 vs. 20.0mg/Ah) removal as well as higher overall current efficiencies (35.2% vs. 14.5%). Extensive colour removal was observed for both anodes (>90% decrease in absorbency at 455 nm).     

Electrochemical process combined with UV light irradiation for synergistic degradation of ammonia in chloride-containing solutions

An electrochemical process combined with ultraviolet light irradiation (UPE) using nonphotoactive dimensionally stable anodes (DSAs) like RuO₂/Ti and IrO₂/Ti in the presence of chlorides was investigated for ammonia degradation. In this process, the in situ electrogenerated active chlorine and in situ photogenerated chlorine radicals were responsible for the high efficiency of ammonia degradation. More than 97% of ammonia was converted to nitrogen and a significantly synergistic effect was confirmed. Compared with the single electrochemical (E) and photochemical (P) process, the degradation rates of ammonia and the average current efficiencies (ACEs) of the UPE process increased by 1.5 and 1.7 times using RuO₂/Ti and IrO₂/Ti electrodes, respectively. On the basis of the linear voltammograms, Electrochemical Impedance Spectra (EIS), UV-vis spectra, Electron Spin Resonance (ESR) analysis and a series of experiments designed, the synergistic mechanism was investigated. In addition, this unique process succeeded in transferring the reaction from the electrode surface to the bulk of the solution compared with the conventional photoelectrocatalytic (PEC) process. The loss of chloride decreased from 21.0% to 7.2% and the recycle of chloride was accelerated in the UPE process. Finally the effects of initial pH, current density and ammonia-nitrogen concentration were discussed. Results indicated that pH and ammonia concentration exerted little influences on the degradation rates and current density was the “rate-determining” factor.     

Reaction pathways and mechanisms of the electrochemical degradation of phenol on different electrodes

Laboratory experiments were carried out on the kinetics and pathways of the electrochemical (EC) degradation of phenol at three different types of anodes, Ti/SnO2-Sb, Ti/RuO2, and Pt. Although phenol was oxidised by all of the anodes at a current density of 20 mA/cm2 or a cell voltage of 4.6 V, there was a considerable difference between the three anode types in the effectiveness and performance of EC organic degradation. Phenol was readily mineralized at the Ti/SnO2-Sb anode, but its degradation was much slower at the Ti/RuO2 and Pt anodes. The analytical results of high-performance liquid chromatography (HPLC) and gas chromatography coupled with mass spectrometry (GC/MS) indicated that the intermediate products of EC phenol degradation, including benzoquinone and organic acids, were subsequently oxidised rapidly by the Ti/SnO2-Sb anode, but accumulated in the cells of Ti/RuO2 and Pt. There was also a formation of dark-coloured polymeric compounds and precipitates in the solutions electrolyzed by the Ti/RuO2 and Pt anodes, which was not observed for the Ti/SnO2-Sb cells. It is argued that anodic property not only affects the reaction kinetics of various steps of EC organic oxidation, but also alters the pathway of phenol electrolysis. Favourable surface treatment, such as the SnO2-Sb coating, provides the anode with an apparent catalytic function for rapid organic oxidation that is probably brought about by hydroxyl radicals generated from anodic water electrolysis.     

Electrochemical treatment of industrial wastewater containing 5-amino-6-methyl-2-benzimidazolone: toward an electrochemical-biological coupling

We studied the electrochemical oxidation, on Pt anodes, of industrial wastewaters containing 5-amino-6-methyl-2-benzimidazolone (AMBI). Electrolysis of this non-biodegradable effluent produces simultaneous oxidation of AMBI and chloride ions. Highly oxidative chlorine intermediate species further boost the degradation of AMBI. Solution temperature, pH and current density affect little the degradation of AMBI. At our best conditions, AMBI was 100% degraded in 45 min. However, because the reaction intermediates exhibited high toxicity and non-biodegradability, the electrolysis had to continue for 3 more hours in order to obtain a biocompatible solution. Then, complete mineralization of the outputs from the electrolytic cells was readily achieved in a fixed bed biological reactor.     

电极工作面积和孔隙液pH值对钢筋脱钝临界氯离子浓度的影响

基于模拟混凝土孔隙液中的钢筋脱钝试验,揭示了钢筋电极的工作面积和模拟混凝土孔隙液的pH值对钢筋脱钝过程中开路电位、极化电阻和腐蚀电流密度的影响规律,确定了不同钢筋电极工作面积和pH值条件下钢筋脱钝的临界氯离子浓度,分别建立了钢筋电极工作面积和模拟混凝土孔隙液pH值与钢筋脱钝临界氯离子浓度之间的定量关系.结果 表明:随着钢筋电极工作面积的增大,钢筋脱钝的临界氯离子浓度降低;随着模拟混凝土孔隙液pH值的增加,以自由氯离子浓度[Cl-]表征的临界氯离子浓度增加,而以[Cl-]/[OH-]表征的临界氯离子浓度降低;与开路电位和极化电阻相比,钢筋脱钝过程中腐蚀电流密度的突变点更加明显.     

Electro-catalytic oxidation of phenol on several metal-oxide electrodes in aqueous solution

Elecrtochemical degradation of phenol was evaluated at five typical anodes for mineralization to carbon dioxide or for being a pre-treatment method in toxic aromatic compounds. Three kinds of RuO(2)-base electrodes were prepared by thermal deposition, which were coated by the oxides of Ru or by Ru, Sn and Sb or by Ru, Sn, Sb and Gd on Ti metal surface, respectively. Another electrode Ti/ PbO(2) was prepared by electro-deposition method with PbO(2) coated on Ti. A Pt electrode was chosen for comparison. Characteristics of the typical five electrodes were investigated by cyclic voltammetry, SEM and its degradation ability for phenol. Performance for phenol degradation of the three RuO(2) electrodes lie in: Ti/Sb-Sn-RuO(2)-Gd> Ti/Sb-Sn-RuO(2)> Ti/RuO(2) and the electrode with beta-PbO(2) coating was superior to RuO(2)-based electrodes and Pt electrode. Aromatic ring opening take place at all researched electrodes and it is supposed that electrolysis run stop at different intermediates, such as benzoquinone, maleic acid, etc. Under the present experimental conditions, whole mineralization to CO(2) takes place only in the beta-PbO(2) anode. A pathway of electrochemical degradation of phenol was suggested based on the experimental analysis.     

Ti/SnO2,Ti/SnO2-Sb2O3阳极电催化氧化酸性品红的试验研究

采用热氧化法制备了Ti/SnO2和Ti/SnO2-Sb2 O3电极,以酸性品红为研究对象,对两种电极材料进行了性能比较,考察槽电压、电流密度、电解质浓度对电催化氧化处理系统的影响.结果表明:热氧化法制备出的Ti/SnO2-Sb2 O3电极,其电催化性能明显优于Ti/SnO2电极;以Ti/SnO2-Sb2 O3为阳极,在酸性品红初始浓度为100 mg/L、电极间距为2.5 cm、电流密度为75mA/cm2、电解质浓度取12 g Na2SO4/L时,60 min后酸性品红的去除率达到了95.41％.     

掺硼金刚石薄膜电极电化学氧化对铜绿微囊藻的生长抑制

阳极材料采用掺硼金刚石薄膜板状电极,研究了电化学氧化中电流密度、电解时间、pH、氯离子浓度、硫酸根离子浓度对铜绿微囊藻生长抑制的影响,以及电解前后藻细胞形态的变化。结果表明,4个影响因素对铜绿微囊藻生长抑制效果显著。抑藻效果随电流密度、电解时间的增加而增加,电流密度为17mA/cm2时藻细胞出现破裂、细胞内物质流出的现象,抑藻效果较好;当电解时间为20min时,可完全抑制藻细胞生长;再增大电解时间,对抑藻效果无明显促进作用,初始pH在中性及酸性条件下可完全抑制藻细胞生长。抑藻效果与溶液中氯离子、硫酸根离子浓度成正相关,当溶液中氯离子浓度为6mg/L时,可完全抑制藻细胞生长;无氯离子时,藻细胞在4d后出现继续增长现象。     

Influence of operating conditions on the ammonia electro-oxidation rate in wastewaters from power plants (ELONITA technique)

Power plants, like many other industries, are confronted with the need to reduce the nitrogen content of their wastewaters. Indirect electro-oxidation, through hypochlorite formation, is a possible answer to an ammonia-nitrogen problem, through converting it into gaseous nitrogen. Several parameters affect the ammonia oxidation rate: current density, chloride concentration and the presence of oxygen-containing anions, mainly SO(4)(2-), CO(3)(2-) and PO(4)(3-). pH values between 5.5 and 10 have been found to have no effect on the ammonia oxidation rate. However, at higher pH values (above 11), the oxidation slows down and chlorate ions appear. A model can be fitted from the experiments to predict the ammonia oxidation rate based on four main parameters: pH, current density, sulfate concentration and chloride concentration. The average difference between the predicted oxidation rates and the experimental measures is only 6.5%. This model confirms that the optimal operating conditions are a high chloride concentration (7 gl(-1)), no sulfate and a high current density (1200 Am(-2)).     

Electrolytic oxygen generation for subsurface delivery: effects of precipitation at the cathode and an assessment of side reactions

This research investigated the oxygen-generating characteristics and side reactions of an electrolytic cell assembly that could be used to remediate sites with contaminants that are amenable to aerobic biodegradation. The oxygen-generating capabilities of new electrolytic cells and cells with light and heavy calcium carbonate precipitates on the cathode were evaluated in the laboratory under current densities ranging from 0.5 to 5.0 mA/cm2. Higher current densities resulted in higher mass transfer coefficients (K(L)a) and greater saturation oxygen concentrations (Csat). As the cathodic deposits increased, the K(L)a tended to decrease and the Csat tended to increase. The oxygen transfer efficiency (OTE) did not vary as a function of current density or cathode coating, while the average OTE for all the tests was 67%. Laboratory column tests showed that chlorine production increased with current density and depended on chloride levels in the water. Hydrogen peroxide was generated at low concentrations (< 1 mg/L) and at higher levels when chloride was absent in the feed solution. Calcium removal from solution increased with current density and resulted in a decrease in solution pH. Tests at a field monitoring well showed average Csat levels of 16.9 mg/L after 14 days of operation, no chlorine production because of low chloride levels in the well, artificially elevated hydrogen peroxide levels because of background interferences, and a pH decrease of 2.4 units. With passive venting, the average hydrogen gas levels at the headspace of the well were less than 1%.     

Design parameters for an electrochemical cell with porous electrode to treat metal-ion solution

An electrochemical reactor was designed and operated to treat the solution containing copper ions. Design parameters for the electrochemical reactor using the porous cathode and RuO2/IrO2/Ti anode were investigated. The porous cathode was prepared by the electroless nickel deposition on polyurethane. The apparent current, the gap between cathode and anode, and hydraulic retention time (HRT) were selected as design parameters. The copper removal rate increased with an increase in apparent current. It was not affected by the gap between the cathode and the anode. A reduction in hydraulic retention time stimulated the mass transfer toward the electrode and increased the cathodic current efficiency. Dimensional analysis was conducted to obtain the design equation for scale-up of the electrochemical reactor. The dependence of Sh on Re, Sc, and characteristic lengths, DC/A/L and DW/C/L, was described in the form of a power series. The coefficients were obtained from experimental data.     

Electrochemical oxidation of phenol on metaloxide electrodes

We investigated the process of electrochemical oxidation of phenol on titanium-oxide-manganese and oxide-cobalt anodes. The data on the impact of current density and phenol concentration in the solution on the degree of decomposition and energy costs were presented.     

电解法深度处理生活垃圾焚烧厂渗滤液研究

采用三元电极对垃圾焚烧厂渗滤液的生化-混凝出水进行电解处理，研究了其处理效果及影响因素。结果表明，在电解反应过程中COD的降解符合三级反应动力学，其t时刻的出水浓度为：Ct=（2kt＋C0^-2）^-0.5；电流、pH值、电解时间、氯离子浓度、进水COD浓度对有机物去除率的影响较大，而极间距、温度和极水比则影响较小。此外，考察了该电极对氮化合物的去除效果。结果表明，在电解过程中亚硝态氮很快被氧化成硝态氮，之后氨氮转化为氮气，总氮基本以硝态氮的形式存在。     

用丝束电极模拟研究混凝土中钢筋的锈蚀

用丝束电极模拟混凝土中钢筋表面的不同位置,研究了浸于pH=12,浓度为10％的NaCl溶液中直至9d的混凝土中钢筋的锈蚀状况．通过测量丝束电极的自然腐蚀电位、极化电阻、腐蚀电流,以及在丝束电极探头附近混凝土的密实性、孔溶液的pH值和Cl^-含量的取样分析,研究了由于混凝土的不均匀性造成Cl^-在其中扩散的不均匀性所致的钢筋锈蚀状况．结果表明：混凝土保护层越厚,则电极自然腐蚀电位越高,钢筋实际锈蚀状况也越轻;在混凝土密实性较高区域的孔溶液PH值相对较高,Cl^-含量较低,由于该区域电极的自然腐蚀电位较高,因而电极的实际腐蚀状况较轻,而在混凝土密实性较低的区域,情况则刚好相反．     

Application of electrooxidation process for treating concentrated wastewater from distillery industry with a voluminous electrode

Experiments in a laboratory scale were carried out to reduce color and chemical oxygen demand (COD) in distillery wastewater by using electrooxidation processes. A cylindrical electrochemical reactor constructed in an axial configuration with 0.2m diameter and 0.35 m height was employed in this study. Two materials including graphite particles and titanium sponge were used as the voluminous anodes. A cathode made from Ti/RuO(2) was placed 0.04-0.05 m above the upper level of anode particles. Effect of parameters including initial pH of wastewater (1-5), time of dilution, current intensity (1-10A), type of additive (H(2)O(2) and NaCl), and additive concentration were investigated. The results indicated that the anode made from titanium sponge showed a higher potential to treat wastewater than the another one. The treatment in acidic condition (pH=1) provided the maximum oxidation of organic pollutants in wastewater. The presence of additives can promote the reduction of COD and color in wastewater approximately 89.62% and 92.24%, respectively. The maximum current efficiency was reached at the first 30 min and decreased slightly as electrolysis time proceeded due to the formation of passivation on the electrode surface. The energy consumption was obtained in the range of 2.82-4.83 kWh/kgCOD or 24.08-28.07 kWh/m(3) wastewater depending upon the concentration of additive. The kinetics of COD reduction was the pseudo first-order reaction with a fast rate constant of 6.78 min(-1).     

电极对加速氯离子透过水泥石性能的影响

本文研究了加速氯离子渗透过水泥石试验中铜电极和不锈钢对试验结果的影响;研究表明：铜电极在试验过程中腐蚀严重,产生大量沉淀物,导致阳极溶液中氯离子浓度和通过试件电流值的测量结果偏小;不锈钢电极在试验过程中表面有轻微点蚀,底部腐蚀较严重,同时也产生沉淀物,致使测量结果偏小,但效果好于铜电极.     

Electroprecipitation treatment of acid mine wastewater

The utilization of electroprecipitation for the treatment of acid solutions associated with the non-ferrous mining industry on a laboratory scale is explored. The electrolytic couple involved in the active process includes a consumable metal anode and an inert cathode. Mechanistically, oxidation of the anode is matched by the reduction of dissolved hydrogen ion to H₂ gas resulting in a pH increase in solution. Heavy metal removal is accomplished by either precipitation of hydrous oxides or by adsorption. Reduction of the solution metal content of from 100% for Al³⁺ to 25% for Mn²⁻ is accomplished using a stainless steel rod anode; final solution pH stabilizes at a value of 4.9. Stabilization of solution pH reflects the attainment of kinetic equilibrium with respect to the rates of oxidation at the anode and diffusion of the oxidized products to the cathode where they precipitate as the hydroxide. Zinc and lead sacrificial anodes are also studied.     

The electrocatalytic reduction of nitrate in water on Pd/Sn-modified activated carbon fiber electrode

The Pd/Sn-modified activated carbon fiber (ACF) electrodes were successfully prepared by the impregnation of Pd2+ and Sn2+ ions onto ACF, and their electrocatalytic reduction capacity for nitrate ions in water was evaluated in a batch experiment. The electrode was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and temperature programmed reduction (TPR). The capacity for nitrate reduction depending on Sn content on the electrode and the pH of electrolyte was discussed at length. The results showed that at an applied current density of 1.11 mA cm(-2), nitrate ions in water (solution volume: 400 mL) were reduced from 110 to 3.4 mg L(-1) after 240 min with consecutive change of intermediate nitrite. Ammonium ions and nitrogen were formed as the main final products. The amount of other possible gaseous products (including NO and N2O) was trace. With the increase of Sn content on the Pd/Sn-modified ACF electrode, the activity for nitrate reduction went up to reach a maximum (at Pd/Sn = 4) and then decreased, while the selectivity to N2 was depressed. Higher pH value of electrolyte exhibited more suppression effect on the reduction of nitrite than that of nitrate. However, no significant influence on the final ammonia formation was observed. Additionally, Cu ion in water was found to cover the active sites of the electrode to make the electrode deactivated.     

Development of a continuous electrolytic system with discharging only one pH-controlled stream and its characteristics

In order to produce only a pH-controlled solution without discharging any unused solution, this work has developed a continuous electrolytic system with an ion exchange membrane-equipped electrolyzer and a tank, called as a pH-adjustment reservoir, placed just in front of the electrolyzer, where as a target solution was fed into the pH-adjustment reservoir, a portion of the solution in the pH-adjustment reservoir was circulated through the cathodic or anodic chamber of the electrolyzer depending on the type of the ion exchange membrane used, and another portion of the solution in the pH-adjustment reservoir was discharged from the electrolytic system through the opposite electrode chamber with its pH being controlled. The internal circulation of the pH-adjustment reservoir solution through the anodic chamber in the case of using a cation exchange membrane and that through the cathodic chamber in the case of using an anion exchange membrane could make the solution, discharged from the other counter chamber, effectively acidic and basic, respectively. The phenomena of the pH being controlled in the system could be explained by the electro-migration of the ion species in the solution through the ion exchange membrane under a cell potential difference between the anode and the cathode and its consequently-occurring non-charge equilibriums and the electrolytic water-split reactions in the anodic and cathodic chambers.     

Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2 anodes

Electrochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous solution was investigated over Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes. The degradation of PFOA followed pseudo-first-order kinetics. The degradation ratios on Ti/SnO₂-Sb, Ti/SnO₂-Sb/PbO₂, and Ti/SnO₂-Sb/MnO₂ anodes achieved 90.3%, 91.1%, and 31.7%, respectively, after 90 min electrolysis at an initial 100 mg/L PFOA concentration at a constant current density of 10 mA/cm² with a 10 mmol/L NaClO₄ supporting electrolyte solution. The defluorination rates of PFOA on these three anodes were 72.9%, 77.4%, 45.6%, respectively. The main influencing factors on electrochemical decomposition of PFOA over Ti/SnO₂-Sb anode were evaluated, including current density (5-40 mA/cm²), initial pH value (3-11), plate distance (0.5-2.0 cm), and initial concentration (5-500 mg/L). The results indicated that PFOA (100 mL of 100 mg/L) degradation ratio and defluorination ratio achieved 98.8% and 73.9%, respectively, at the optimal conditions after 90 min electrolysis. Under this optimal condition, the degradation rate constant and the degradation half-life were 0.064 min⁻¹ and 10.8 min, respectively. The intermediate products including short-chain perfluorinated carboxylic acids (PFCAs, C₂∼C₆) and perfluorocarbons (C₂∼C₇) were detected by electrospray ionization (ESI) mass spectrum. A possible electrochemical degradation mechanism of PFOA including electron transfer, Kolbe decarboxylation, radical reaction, decomposition, and hydrolysis was proposed. The electrochemical technique could be employed to degrade PFOA from contaminated wastewater as well as to reduce the toxicity of PFOA.