Indirect Electrochemical Oxidation of Phenol in the Presence of Chloride for Wastewater Treatment

Electrochemical oxidation of phenol using a Ti/TiO₂‐RuO₂‐IrO₂ anode in the presence of chloride as the supporting electrolyte was investigated. The experiments were performed in an undivided batch reactor. Preliminary investigations showed that only a small fraction of phenol was oxidized by direct electrolysis, while complete degradation of phenol was achieved by indirect electrochemical oxidation using chloride as a supporting electrolyte. The effect of operating parameters such as initial pH, supporting electrolyte concentration, phenol concentration, and charge input was studied using Box‐Behnken second order composite experimental design. The effect of current density on COD removal was studied separately. TOC removal and AOX formation were studied for selected conditions. It was found that the formation of chlorinated organic compounds was pronounced at the beginning of electrolysis, but it was reduced to lower levels by extended electrolysis.     

Arsenic Removal from Industrial Effluent through Electrocoagulation

In the present investigation, it is attempted to remove arsenic from smelter industrial wastewater through electrocoagulation. Experiments covering a wide range of operating conditions for removal of the arsenic present in the smelter wastewater are carried out in a batch electrochemical reactor. Mild Steel and Stainless Steel plates have been used as the anode and cathode respectively. It has been observed from the present work that arsenic can be removed effectively through electrocoagulation.     

电化学工艺在废水处理中的应用

综述了电化学过程原理及电化学工艺在废水处理中的应用,讨论了电化学工艺的特点与改进方向。     

Removal of Nickel and Boron from Plating Rinse Effluent by Electrochemical and Chemical Techniques

In this work, electrotreatment of nickel and boron containing plating rinse effluents was studied with mild steel and aluminum electrodes. Industrial effluent treatment directly by an electrochemical technique is capable of removing 80–85 % nickel. The residual nickel interfered with boron determination by curcumin method. The pH fall during electrotreatment in industrial effluent is due to electrodeposition of nickel at the cathode surface, evidenced by simulated effluent treatment. Nickel concentration can be reduced below the discharge limit from the industrial plating effluent by chemical precipitation and coagulation at pH above 8. Chemical precipitation showed maximum boron removal of about 50 %. Boron removal was 29.3–41.9 % and 20.6–33.1 % with ferric chloride and aluminum sulfate, respectively. A combination of chemical precipitation at pH 8.7 followed by electrotreatment reduces nickel to the discharge limit and also maximizes boron removal up to 59 %.     

Combined Physicochemical Treatment of Textile and Mixed Industrial Wastewater

Wastewaters derived from a textile factory and an industrial park were subjected to treatment with ferric chloride coagulation; ozonation; ferric chloride pre-coagulation/Fenton-based process/lime post-coagulation; Fenton-based process/lime post-coagulation; and ferric chloride pre-coagulation/ozonation. Schemes with the Fenton-based process proved the most efficient for treatment of both wastewater samples. The characteristics of wastewater samples treated by a Fenton-based process at H₂O₂/COD weight ratio 0.5:1 complied with the discharge limits stated by regulations for wastewater directed to local sewerage. The Fenton-based process/lime post-coagulation scheme proved more efficient than ferric chloride pre-coagulation/Fenton-based process/lime post-coagulation system. The increase of H₂O₂/COD weight ratio to 2:1 resulted in 5 and 10% of residual COD and DOC, respectively. All studied processes and combined physicochemical treatment schemes, except single ozonation, resulted in toxicity reduction and biodegradability improvement in both wastewater samples. The operational costs of applied treatment schemes were calculated and indicated the Fenton-based process schemes as the most feasible and cost-effective.     

Electrochemical incineration of 1,2-dichloroethane: Effect of the electrode material

The electrochemical incineration of 1,2-dichloroethane (EDC) at Pt, Au, boron-doped diamond (BDD), Ebonex, stainless steel, Ti/IrO₂-Ta₂O₅ and PbO₂ has been studied in acid media by cyclic voltammetry and bulk electrolysis. It has been shown that the performances of the process dramatically depend on the anodic material. Higher current efficiencies were obtained at BDD. In particular, at proper values of applied current density, it is possible to obtain the almost complete conversion of EDC to CO₂ at BDD with current efficiencies higher than 40%.     

电化学法处理含酚模拟废水研究

实验以干电池中的碳棒作电极,用烧杯作电解池,在室温下通过改变电解时间的影响因素,对对苯二酚模拟废水进行电化学处理,利用高效液相色谱仪对其处理效果进行了分析研究,得到6V电压的电解条件下,140 min对苯二酚的出峰的最佳条件。     

Advanced Oxidation of Textile Wastewaters

Model dyeing and laundering wastewaters produced during two basic technological operations of the textile industry were subjected to treatment by advanced oxidation processes (AOPs). The following agents were used: ozone (O₃), hydrogen peroxide (H₂O₂) and UV radiation. They were applied separately and in all possible combinations: O₃ + UV, O₃ + H₂O₂, UV + H₂O₂, as well as all three at the same time: O₃ + UV + H₂O₂. Effluents before and after the treatment were analyzed according to requirements of the Polish Standards that included pH, color threshold, COD and concentration of anionic and non-ionic surfactants. Ozonation was carried out in a lab-scale bubble column reactor with a centrally located UV burner. The most effective version of AOPs proved to be the simultaneous use of all three agents. In the case of such treatment of dyeing wastewaters nearly complete discoloration and full decomposition of surface-active substances were obtained at 80% reduction of COD. A similar tendency was observed in the case of laundering wastewater, though in that case the results were slightly worse, which may be explained by much higher initial concentrations of the pollutants. Good treatment effects have also been obtained in combined treatment by simultaneous use of hydrogen peroxide and ozone.     

电生成活性氯的影响因素及其在有机废水处理中的应用

介绍了电生成活性氯的机理,通过间歇实验,考察了溶液中氯离子浓度、电流密度、pH值和阴离子对电生成活性氯的影响,并对比了有无氯离子时苯胺电化学氧化过程中的COD浓度变化.结果表明,氯离子浓度、电流密度和pH值对电生成活性氯的影响较大,当氯离子浓度为1.5 mol/L左右.pH为10时,电生成活性氯含量最高,电流密度超过40 mA/cm2后,电生成活性氯的量趋于恒定;CO-3和HCO-3对电生成活性氯影响不大,SO2-4和NO-3抑制活性氯生成,而具有还原性的阴离了则大量消耗活性氯.当体系中存在氯离子时,电化学直接氧化和间接氧化同时进行,有利于废水COD的去除.     

Use Of Ozone For The Treatment Of A Combined Urban And Industrial Effluent: A Case History

This paper describes the treatment of highly colored urban wastewater containing a high percentage of industrial effluents and a significant concentration of detergents. The kinetics of detergent ozonation were established through a series of pilot tests including variation of the ozone concentrations in the carrier gas. The results obtained concerning the optimum conditions of ozonation - treatment dose and contact time - have been used for the design of an industrial ozonation plant.     

Electrochemical treatment of aqueous solutions containing urea

Investigations on the anodic decomposition of urea using Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes were carried out. The kinetics of the process were examined in a periodic electrolyser. The effect of anodic current density, initial urea concentration, and sodium chloride concentration on the effectiveness of the basic process (average rate of urea decomposition, current efficiency, and unit power consumption) is discussed. When a Ti/Pt electrode is applied for urea removal from aqueous solution urea is not decomposed directly at the surface of the electrode, but rather in the bulk of the solution by hypochlorite formed during the process. When the Ti/(RuO₂–TiO₂)_40:60 electrode is used for the removal of urea from aqueous solutions, the reaction of urea with chlorine adsorbed at the electrode predominates. In both cases non-toxic products of urea decomposition (N₂, CO₂,) are formed. Comparison of the effectiveness of anodic decomposition of urea for the Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes in the periodic electrolyser at optimum process parameters has revealed that the former electrode is more favorable.     

Application of Response Surface Methodology for Coffee Effluent Treatment by Ozone and Combined Ozone/UV

This paper reports a study using ozone (O₃) and combined ozone/ultraviolet (O₃/UV) processes for color removal and caffeine degradation from synthetic coffee wastewater using a second-order response surface methodology (RSM) with a three-level central composite face-centered (CCF) design. The effects of O₃ concentration, initial pH, and reaction time were examined for both processes. The reaction time and pH were statistically significant for caffeine degradation and color removal. In the ozonation process, higher caffeine degradation and color removal were observed in alkaline pH, indicating that ozone attacks indirectly, consequently generating hydroxyl radicals. Regarding the ozone/UV process, it was observed that lower caffeine degradation and color removal occurred at neutral pH, indicating an adverse effect due to lower ozone dissolution and consequently the production of a smaller amount of free hydroxyl radicals. The achieved results showed that the techniques were efficient for color removal (85% and 99%, respectively) and caffeine degradation (88% and 98%, respectively).     

含氯漂白废水的电氧化处理

以二氧化铅为阳极,不锈钢网为阴极,用电化学氧化法处理多段漂白废水中的有害物质。其中二氧化铅电极是通过在碳棒上电镀而成的。研究发现,废水的电导率和pH值对于不同的废水在电化学氧化过程中的变化是不同的;而废水的COD和色度在整个过程中一直减少;氯化木质素的分子量和分子量分布发生了变化。     

An Electrochemical Model of a Solid Oxide Steam Electrolyzer for Hydrogen Production

An electrochemical model was developed to simulate the J–V characteristics of a solid oxide steam electrolyzer (SOSE) used for hydrogen production. Activation, concentration, and ohmic overpotentials were considered as the main factors for voltage loss. The Butler‐Volmer equation, Fick's model, and Ohm's law were applied to determine the overpotentials of a SOSE cell. The simulation results were compared with experimental data from the literature and good agreement was obtained. Additionally, parametric modeling analyses were conducted to study how the operating temperature and gas composition affected the electrical characteristics. It was found that the voltage loss could be reduced by increasing the operating temperature and steam molar fraction. It was also observed that an anode‐supported SOSE cell exhibited a higher hydrogen production efficiency than electrolyte‐supported and cathode‐supported cells. The electrochemical model can be used to perform further analysis in order to further understand the principles of SOSE hydrogen production, and to optimize SOSE cell and system designs.     

Electrochemical treatment of 2,4-dinitrophenol aqueous wastes using boron-doped diamond anodes

The electrochemical oxidation of 2,4-dinitrophenol (2,4-DNP) aqueous wastes has been studied using both, bulk electrolysis and voltammetric techniques. To carry out the bulk electrolysis, a bench-scale plant with a single compartment electrochemical flow cell was used. Boron-doped diamond (BDD) materials were used as the anode and stainless steel (AISI 304) as the cathode. According to the obtained results, a simple mechanistic model has been proposed. The oxidation of 2,4-DNP leads to the appearance of phenol and quinonic compounds and to the release of the nitro groups from the aromatic ring, in a first step. In a second step, these organics are transformed into carboxylic acids (mainly maleic and oxalic acid). The process ends with the formation of carbon dioxide (CO₂). The effects of the waste characteristics (composition and pH) and of the operation parameters of the process (temperature and current density) have also been studied in this work. The complete removal of the organic compounds contained in the waste has been obtained in all essays.     

Electrochemical removal of antibiotics from wastewaters

Electro-oxidation tests with different anodes (Ti/Pt, DSA^® type, graphite and three-dimensional (3D) electrode made of a fixed bed of activated carbon pellets) were performed on aqueous solutions containing the antibiotics Ofloxacin and Lincomycin. The effectiveness of the treatment of wastewater containing pharmaceuticals was assessed, as well as the electro-oxidation mechanism.

The use of high electrode potentials (>2.8 V versus NHE) ensured either significant anodic surface activation or minimization of fouling by in situ generated polymeric material. The use of a membrane-divided cell showed positive aspects in terms of molecule demolition, and average power consumption. The electro-oxidation was found to occur with first order kinetics mainly at anode surface when using Na₂SO₄ at low concentration (0.02N). Under these conditions, Ofloxacin is efficiently oxidized over all tested anodes (e.g. 50 mgcm⁻² A⁻¹ h⁻¹ for the bi-dimensional Ti/Pt electrode), whereas Lincomycin is oxidized with slow overall kinetics mainly due to difficult deprotonation, a step that precedes the primary electron transfer stage of the oxidation process. The three-dimensional electrode would be the most appropriate for continuous industrial-scale process. However, at the used potential, unacceptable corrosion of the carbon based electrode was noticed.     

Oxidation of Emerging Contaminants during Pilot-Scale Ozonation of Secondary Treated Municipal Effluent

The transformation of 41 target emerging contaminants in secondary treated municipal wastewater effluent in Canada was examined at pilot-scale, at transferred ozone doses of 2.8 mg/L (0.46 O₃/mg DOC) and 4.4 mg/L (0.72 mg O₃/mg DOC). In general, transformation efficiencies of CECs either increased or were retained at the higher ozone dose. The higher ozone dose of 0.72 mg O₃/mg DOC (Z_spec = 0.6 mg O₃/mg DOC) was sufficient to transform 21 of the 31 detected CECs by over 80% as well as achieving the disinfection target of < 200 MPN E. coli per 100 mL.     

Electrochemically Assisted Photocatalytic Oxidation of Nitrite over Cr‐Doped TiO2 under Visible Light

To investigate the photocatalytic oxidation (PCO) of nitrite ions under visible light, Cr‐doped TiO₂ supported on a titanium plate was used as a photoelectrode operated under anodic bias potential. The results showed that applying bias potential (E_appl) played an important role in the PCO of NO₂^–. Without bias potential the PCO reaction could not be initiated due to the rapid recombination rate of the photogenerated carriers, but when the potential was larger than 1.2 V (vs. saturated calomel electrode, SCE) the removal efficiency of NO₂^– increased up to 90 % within 3 h for an initial concentration of 8 mg L^–1. Zero‐order kinetics were observed at E_appl = 0.4 V (vs. SCE), while pseudo first order kinetics were found at E_appl ≥ 0.8 V (vs. SCE). The effects of the initial concentration of NO₂^–, initial solution pH, the gas atmosphere, and cathodic reaction on the PCO of NO₂^– were studied as well. Furthermore, the PCO mechanism of NO₂^– was investigated by using tert‐butyl alcohol or benzoic acid as a diagnostic probe. It showed that the PCO of NO₂^– under visible light most probably proceeded indirectly via OH radicals, not directly via the valence‐band holes.