Electrochemical treatment of wastewater containing phenolic compounds: oxidation at boron-doped diamond electrodes

This work investigates the performance of BDD electrodes during oxidation of aqueous solutions of phenol. The main reaction intermediates are identified, the effect of operating conditions on the faradic yield of the process, and the degree of mineralization achievable under different experimental conditions are evaluated. Due to the crucial role of mass transfer in the process, an impinging jet cell is used for the experiments. The results indicate that if a minimum value of current density is imposed, suitable initial conditions can be set at which the removal of the reactant is always under mass transfer control and the process is carried out at a faradic yield of about unity, up to the near-complete disappearance of total organic load. High current density and high mass transfer coefficient must be used in order to carry out the process with high space-time yield. The performance of BDD is compared to that obtained at Ti/RuO₂ anodes.     

Electrochemical oxidation of phenolic compounds using a flow-through electrolyser with porous solid electrodes

Organic compounds such as phenol and cresols may be found in industrial wastewater along with other organics and are difficult to be economically removed down to concentrations below environmentally permissible limits. By circulating a wastewater through an electrolytic reactor with a stack of porous solid anodes and cathodes, it has been demonstrated that it is feasible to electrochemically oxidize phenolic compounds in the presence of other organic molecules. A porous solid DSA^®-type titanium anode coated with several mixed oxide layers was used as the active material. At low applied current densities, phenol and cresol concentrations were reduced from 5000 ppb to below 20 ppb. The influence of the flow rate and electrodes number was also studied and it was demonstrated that the current density was the main factor to be considered. This work confirms the hypotheses of other authors on the reaction mechanisms involved during the electrochemical oxidation of cresol and phenol.     

The electrochemical oxidation of aqueous phenol at a glassy carbon electrode

The electrooxidation of phenol is of interest as a model compound for the treatment of aqueous organic wastes. The effect of voltage, concentration and temperature on the electrochemical oxidation of acidic dilute aqueous solutions of phenol was studied. Electrolysis was carried out by recirculating phenol solutions through a flow-by electrochemical reactor employing a reticulated glassy carbon anode. Concentrations of phenol and some breakdown products were monitored using HPLC analysis. Increased voltage was found to shift the product distribution to favour more oxidized products but also to increase electrode corrosion and decrease current efficiency. Higher phenol concentrations (over the range of 5-20 mmol/L) showed a shift in product distribution to favour less oxidized, mostly insoluble products. Elevated temperatures (about 50°C and higher) showed a marked ability to reduce electrode passivation and increase the phenol oxidation rate.     

Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Carbon felt is a potential material for electrochemical reduction of chromates. Very dilute solutions may be efficiently treated due to its large specific surface area and high porosity. In this work, the up-scaling of this technology is investigated using a new type of separated cell and once-through flow of industrial rinse water. A significant enhancement of the process is obtained due to copper deposition during long-term operation. The co-deposition and re-solution of copper occurs depending on the inlet chromate concentration. When previously deposited copper is present a current-free reduction of chromate takes place resulting in current efficiencies apparently above 100%. Very high space time yields are obtained even for effluents at low concentration and optimised conditions (high flow rates and pH 2). The economic feasibility of the technology is also considered. Continuous, single-pass operation results in lower energy requirements than batch processing. The economic potential of the process is also evaluated in comparison with chemical detoxification of chromate. The operating costs for the electrochemical treatment of very dilute effluents on a carbon felt electrode are 30% lower than for the chemical method.     

催化湿式氧化法处理含酚废水

进行了CuO/Al2O3、CuO MnO2/Al2O3、CuO K2O/Al2O3、CuO/CeO2催化剂在160℃和1.6MPa的氧气压力条件下,催化氧化法处理含酚废水的实验,结果表明催化剂CuO/CeO2具有最高的催化活性,COD为3000mg/L左右含酚废水,反应50min后降解97%。并测定了在135～165℃和1.6MPa氧气压力下,加入催化剂CuO/Al2O3氧化含酚废水的COD与时间的的关系,求取了反应的动力学方程。初步探讨了氧分压和溶液的pH对催化氧化反应速率的影响。     

基于AC/SnO2-Sb粒子电极的苯酚电催化氧化

采用热分解法,以活性炭(AC)颗粒为基体,利用Sn-Sb固溶特性制备具有催化活性的AC/SnO₂-Sb粒子电极,并通过N₂吸附法、扫描电镜(SEM)、X射线衍射(XRD)及电化学测试对其微孔结构、微观形貌、物相组成和电催化活性进行表征.结果表明,SnO₂-Sb活性组分减少了AC介孔但未破坏高孔隙结构,且以固溶体形式广泛分布于AC孔道表面,不仅增强了AC孔隙内部降解有机物的活性,还增加了电催化活性位点,有助于提升催生羟基自由基的能力;同时只有AC/SnO₂-Sb粒子电极的循环伏安曲线(CV)在1.10V存在明显的苯酚氧化峰,说明SnO₂-Sb固溶体在电催化氧化的作用下,可直接参与苯酚的催化降解.以模拟苯酚废水考察粒子电极的电催化活性以及稳定性,结果表明,在电流密度12.0mA/cm² 和反应时间3h条件下,AC/SnO₂-Sb粒子电极的COD和苯酚去除率分别为78.43%和79.52%,均高于AC粒子电极的去除率.此外,AC/SnO₂-Sb在30天连续水处理中表现出较好的电化学稳定性.     

含油废水吸附饱和活性炭纤维的电化学再生

为了对有机物吸附饱和的活性炭纤维(ACF)进行电化学再生研究,以含油废水为模拟有机物,通过测量再生前后ACF对含油废水的吸附效果,考察了电流密度、再生时间、pH值、电解质的电化学再生的影响因素,并研究了电化学再生过程对ACF结构的影响以及ACF电化学再生的机理。结果表明,在电流密度为30 mA·cm^-2,pH值为4,15 g·L^-1 NaCl的溶液中再生120 min,再生率可达到90%,5次电化学再生循环后,ACF保持较高的吸附容量。再生后ACF的表面没有明显损伤,比表面积也没有明显减小,微孔孔径分布于0.5～1.0 nm。由紫外光谱分析可知,ACF的电化学再生机理主要包括电脱附及电化学氧化过程。     

Oxidation of carboxylic acids at boron-doped diamond electrodes for wastewater treatment

Thin boron-doped diamond films have been prepared by HF CVD (hot filament chemical vapour deposition technique) on conductive p-Si substrate (Si/Diamond). The morphology of these Si/diamond electrodes has been investigated by SEM and Raman spectroscopy. The electrochemical behaviour of the Si/diamond electrodes in 1 M H₂SO₄ and in 1 M H₂SO₄ + carboxylic acids has been investigated by cyclic voltammetry. Finally, the electrochemical oxidation of some simple carboxylic acids (acetic, formic, oxalic) has been investigated by bulk electrolysis. These acids can be oxidized at Si/diamond anodes to CO₂, in the potential region of water and/or the supporting electrolyte decomposition, with high current efficiency.     

含酚废水的氧化法处理

含酚废水是一种危害极大的工业废水，经济而有效地处理含酚废水极为重要。氧化法是一类极具发展前途的含酚废水处理技术。本文综述了氧化法处理含酚废水的研究进展。     

Mn-Sn-Sb/γ-Al2O3粒子电极对苯酚的降解特性

研制了复合氧化物负载型Mn-Sn-Sb/γ-Al₂O₃粒子电极并填充于主阴阳极之间,实现了三维电催化氧化反应,并采用XRD、SEM对粒子电极进行了表征.结果表明,该粒子电极对目标污染物苯酚显示了良好的电催化活性和稳定性,在相同反应条件下,不加粒子电极的二维电解时苯酚的降解率为55.6%,而三维电催化氧化过程中降解率为90.8%,大大提高了苯酚去除效果.研究苯酚降解的动力学规律表明,苯酚降解符合表观一级反应动力学规律.利用GC-MS分析了苯酚降解主要中间产物为异丁酸、丙二酸、对苯醌、丁烯酸、乙二酸、顺丁烯二酸、丁二酸、邻苯二酚、对苯二酚及间苯二酚等,并据此推测了苯酚电催化氧化的可能反应途径.     

油田污水的可生化性及生化反应动力学

以油田污水为研究对象,采用电化学氧化工艺来提高污水的可生化性,考察了不同因素对除污效果的影响。利用正交实验设计确定电化学氧化最佳工艺参数为:电解电压20 V,pH值5,极板间距2.0 cm,阳极为Ti/Ir形稳电极、双向脉冲电源,在此条件下电解30 min,油田污水COD去除率达到70%。利用BOD5/CODC r比值法和微生物呼吸速率法对污水的可生化性进行了研究,2种实验方法均表明处理前油田污水的可生化性较差,而经电化学氧化工艺处理后的污水可进行生化处理,同时在微生物呼吸速率法的基础上探讨了微生物的生化反应动力学,结果表明,实验条件下微生物的呼吸速率都严格遵循一级动力学关系式。     

Electrochemical synthesis of Cr(II) at carbon electrodes in acidic aqueous solutions

The electrochemical synthesis of Cr(II) has been investigated on a vitreous carbon rotating disc electrode and a graphite felt electrode using cyclic voltammetry, impedance spectroscopy and chronoamperometry. The results show that in 0.1 M Cr(III) + 0.5 M sulphuric acid and in 0.1 M Cr(III) + 1 M hydrochloric acid over an electrode potential range of –0.8 to 0.8 V vs SCE, the electrochemical reaction at carbon electrodes is essentially a surface process of proton adsorption and desorption, without significant hydrogen evolution and chromium(II) formation. At electrode potentials more negative than –0.8 V vs SCE, both hydrogen evolution and chromium(II) formation occurred simultaneously. At electrode potentials –0.8 to –1.2 V vs SCE, the electrochemical reduction of Cr(III) on carbon electrodes is controlled mainly by charge transfer rather than mass transport. Measurements on vitreous carbon and graphite felt electrodes in 1 M HCl, with and without 0.1 M CrCl₃, allowed the exchange current density and Tafel slope for hydrogen evolution, and for the reduction of Cr(III) to Cr(II), to be determined. The chromium(III) reduction on vitreous carbon and graphite electrodes can be predicted by the extended high field approximation of the Butler–Volmer equation, with a term reflecting the conversion rate of Cr(III) to Cr(II).     

三维电极方法降解L-亮氨酸的动力学及机理研究

以模拟L-亮氨酸废水为处理对象,用S-433D型氨基酸分析仪测定经三维电极处理不同时间后水样中L-亮氨酸含量,经拟合发现三维电极降解L-亮氨酸反应为一级反应,当废水中L-亮氨酸初始浓度较高时,反应动力学表现为零级反应.L-亮氨酸废水降解机理分析与实验结果相符合.     

活性炭纤维吸附石化废水中苯酚的吸附平衡及动力学

以活性炭纤维(ACF)为吸附剂,研究了ACF对石化废水中苯酚的吸附平衡及动力学。在25、40、55及65℃下测定了吸附平衡等温线,采用Langmuir、Freundlich和Redlich-Peterson等温方程对吸附平衡数据进行了拟合,结果表明吸附平衡数据更符合Langmuir与Redlich-Peterson方程。体系温度从25、40、55升高到65℃时,ACF对模拟废水中苯酚的吸附能力随温度升高而降低,而ACF对石化废水中苯酚的吸附能力并不完全随温度升高而降低。ACF对石化废水与模拟废水中苯酚的吸附过程均符合拟二级动力学方程。颗粒内扩散模型对吸附动力学实验数据的拟合结果表明,吸附初期吸附速率主要受颗粒内扩散控制且石化废水中苯酚吸附的k_id随温度升高而增大,吸附中后期吸附速率除了受颗粒内扩散控制外还受到外扩散的影响。热力学分析表明,石化废水中ACF吸附苯酚过程的ΔG<0,由于石油类物质对苯酚吸附的影响,温度升高ΔG的数值变化不大。     

电化学工艺在废水处理领域的应用

介绍了电化学处理废水的基本原理和影响电化学法处理废水效果的因素,同时指出了在电化学处理废水领域还需研究的问题。     

石墨毡作为粒子电极处理含酚废水的试验研究

采用石墨毡作为三维电极中的粒子电极,处理模拟苯酚废水,研究对比了不同阳极材料、粒子电极填充方式、初始pH值、槽电压、电极极性交替对苯酚降解效果的影响。电化学测试和电解试验结果表明,相比于304不锈钢和Ti/IrO_2-RuO_2电极,石墨毡在较高的电极电位下仍能对苯酚保持较高电催化活性。采用粒子串的填充方式能降低反应器内短路电流、提高电流效率,反应器的时空产率从2.27 g/(m3·h)提升至6.47 g/(m~3·h)。周期交替电极极性对苯酚最终去除率影响较低,通过SEM扫描发现苯酚聚合物及其他污染物在纤维表面的沉积得到抑制。在苯酚初始质量浓度为100 mg/L、p H值为8~10、槽电压为8 V、电极极性交替周期为5 min、粒子电极采用串填方式、HRT为120 min的条件下,苯酚去除率大于90.3%。     

Electrochemical treatment of olive mill wastewater

Background Olive mill wastewater (OMW) constitutes a very strong agro‐industrial wastewater posing severe environmental threats in olive oil producing countries. The main objective of this study was to treat olive mill wastewater by electrochemical oxidation. The variables studied included the type and concentration of electrolyte solutions, voltage and time applied. Results: The electrolyte type and concentration significantly affected the degradation efficiency of the electrochemical oxidation. Optimal conditions for NaCl concentration were 3% (w/v) and 16 V. At these conditions chemical oxygen demand (COD) removal reached 70.8% after 8 h of electrochemical treatment, while color and turbidity were completely removed after short periods of treatment. However, bio‐assays indicated that the ecotoxicity of the treated wastewater remained unchanged, possibly due to the formation of chlorinated by‐products. Na₂SO₄ did not demonstrate sufficient efficiency. The simultaneous use of FeCl₃ and NaCl contributed to electro‐coagulation of OMW. After settlement, two separate phases were formed: the supernatant phase and the settled solids. Under optimal conditions (2% Na₂SO₄ + 1% FeCl₃; 24 V), the removal efficiency of COD reached 85.5% at the supernatant phase. Conclusion: NaCl was an effective electrolyte for OMW treatment. The electro‐coagulation process was also a successful process, but as in the case of NaCl the remaining acute toxicity of treated OMW was high. Copyright © 2007 Society of Chemical Industry     

电化学氧化法处理海洋油田废水

在开采海洋油田时产生的废水，由于其含有苯系衍生物和多环芳烃化合物及氯离子，用生化降解法难以使其COD值达到我国有关法规规定的一级排放标准。用电化学氧化法处理某海洋油田废水，能使其COD值降至一级排放标准以下。用钛基钌铱锰锡钛多元氧化物涂层电极作阳极，钛作阴极，测定上述污水的电化学氧化指数（Electrochemical Oxidation Index）为0．228，电化学耗氧量（Electrochemical Oxygen Demand）为1．794g/g（以有机物计），其电化学氧化度75．3％，在电化学副反应产生的NaClO的协同作用下，电化学降解后产生的部分有机物可以进一步的进行化学降解，从而达到几乎完全消除废水中COD值的目的。     

碳气凝胶电极在双电层电容器中的研究进展

通过与无机气凝胶对比,引入碳气凝胶的导电特性。简述了双电层电容器的基本工作原理,综述了碳气凝胶在双电层电容器电极材料方面的研究进展。总结了碳气凝胶电极制备过程中关键因素,并提出了一些研究展望。     

Electrochemical oxidation of benzene at a glassy carbon electrode

Benzene oxidation in sulfuric acid at a glassy carbon electrode was investigated using voltammetric, chronoamperometric, and spectroscopic methods. The results are compared with those at a Pt electrode. Benzene was observed to be oxidized to benzoquinone presumably by active oxygen that was adsorbed on the GC electrode in the oxygen evolution region. It is concluded that oxidation at glassy carbon can produce benzoquinone or quinone-like compounds from an aqueous benzene solution. The applied potential for benzene oxidation should be less than 2.1 V vs RHE in order to prevent glassy carbon electrode damage by oxidation during long operation.