Electrochemical technologies for treating petroleum industry wastewater

This review focuses on recent developments in electrochemical technology (with special emphasis on electrocoagulation, electro-oxidation, and electro-Fenton) to treat petroleum industry effluents (offshore and hydraulic fracturing extraction, as well as refinery effluents). In addition, an overview is given of what these processes face to position themselves as consolidated technologies.     

Sensitively electrochemical detection of the DNA damage in situ by electro-Fenton reaction based on Fe@Fe2O3 core-shell nanonecklace and multi-walled carbon nanotube composite

An electrochemical biosensor for mimicking the metal-mediated DNA damage pathway in situ was presented. The Fenton reagents (H₂O₂ and iron ion) for the DNA damage were generated in situ with a constant rate from the sensing film. H₂O₂ and iron ion reacted further together to yield hydroxyl radical, which attacked DNA in the film. These courses of DNA damage were just like those happened in organism. The DNA damage was detected by monitoring the differential pulse voltammetric response of an electrochemical indicator, Co(phen)₃³⁺. Another electrochemical indicator, Ru(NH₃)₆³⁺, was also used for monitoring the DNA damage as a complementary means and the minimal detectable amount of DNA damage was 0.16 μg. The biosensor had good reproducibility. After this biosensor was used for 11 times, 90% of the first detection signal was obtained.     

Atomically Dispersed Iron Regulating Electronic Structure of Iron Atom Clusters for Electrocatalytic H2O2 Production and Biomass Upgrading

The integration of highly active single atoms (SAs) and atom clusters (ACs) into an electrocatalyst is critically important for high-efficiency two-electron oxygen reduction reaction (2e⁻ ORR) to hydrogen peroxide (H₂O₂). Here we report a tandem impregnation-pyrolysis-etching strategy to fabricate the oxygen-coordinated Fe SAs and ACs anchored on bacterial cellulose-derived carbon (BCC) (FeSAs/ACs-BCC). As the electrocatalyst, FeSAs/ACs-BCC exhibits superior electrocatalytic activity and selectivity toward 2e⁻ ORR, affording an onset potential of 0.78 V (vs. RHE) and a high H₂O₂ selectivity of 96.5 % in 0.1 M KOH. In a flow cell reactor, the FeSAs/ACs-BCC also achieves high-efficiency H₂O₂ production with a yield rate of 12.51±0.18 mol g_cat⁻¹ h⁻¹ and a faradaic efficiency of 89.4 %±1.3 % at 150 mA cm⁻². Additionally, the feasibility of coupling the produced H₂O₂ and electro-Fenton process for the valorization of ethylene glycol was explored in detail. The theoretical calculations uncover that the oxygen-coordinated Fe SAs effectively regulate the electronic structure of Fe ACs which are the 2e⁻ ORR active sites, resulting in the optimal binding strength of *OOH intermediate for high-efficiency H₂O₂ production.     

Catalytic treatment of petrochemical wastewater by electroassisted Fenton technologies

The electro-Fenton process, in which ferrous ions are produced on the anode and used as catalyst, was applied for treating the bioeffluent of petrochemical manufacturing wastewater.     

The efficacy of sono-electro-Fenton process for removal of Cefixime antibiotic from aqueous solutions by response surface methodology (RSM) and evaluation of toxicity of effluent by microorganisms

The increasing use of antibiotics by humans and their persistence in the environment leads to the development of drug resistance, which is nowadays considered as an environmental problem. The aim of this study was to determine the efficacy of sono-electro-Fenton process for removal of Cefixime antibiotic from aqueous solutions by Response Surface Methodology (RSM) and to evaluate the toxicity of effluent by microorganisms. In the present study, the degradation of synthetic wastewater containing Cefixime was investigated in a reactor (with a useful volume of 1 L) located in the chamber of the ultrasonic device. The effects of pH, hydrogen peroxide concentration, voltage, initial antibiotic concentration, and electrolysis time were investigated using the Box-Behnken model, and the optimal conditions for elimination were obtained by analyzing the variance. The performance of the electro-Fenton and ultrasonic process was evaluated separately and in combination under optimal conditions. Toxicity of inlet and outlet was tested by Escherichia coli and Staphylococcus aureus, and growth inhibition percentage was calculated. The intermediates were determined by LC-MS with the lowest molecular mass. The results showed that the sono-electro-Fenton process under optimum conditions, including pH of 3.07, hydrogen peroxide concentration of 0.85 mL/L, voltage 15 V, initial antibiotic concentration 10.4 mg/L and electrolysis time of 81.5 min has a percentage of removal of 97.5%. Under optimum conditions, the percentage of removal by electro-Fenton and ultrasonic separately were 81.7% and 9%, respectively, and in the hybrid process of sono-electro-Fenton, the percentage of removal increased to 97.5%. The results also showed that the biological toxicity of the outlet effluent from the sono-electro-Fenton process, compared to the inlet solution, was significantly reduced. So, we conclude that the Sono-electro-Fenton process has a significant effect on the removal of Cefixime from aqueous solutions and can also significantly reduce the biological toxicity of the effluent.     

W元素掺杂CeO2非均相电芬顿催化剂高效处理含油污水

制备了W元素掺杂的CeO₂复合材料, 通过扫描电子显微镜、 透射电子显微镜、 X射线衍射和X射线光电子能谱等对W-CeO₂-0.4催化材料进行表征. 结果表明, 具有不规则片状形貌的W元素掺杂CeO₂复合材料提高了单一CeO₂的类芬顿催化效果; 将其作为非均相电芬顿催化剂对含油污水的处理效果明显优于电吸附和物理吸附过程. 进一步的参数优化处理实验发现, 在电压为4 V, pH=3时, 采用W-CeO₂-0.4作为催化剂的条件下, 对含油污水的净化能力在90 min内达到了99.8%, 总有机碳(TOC)去除率达到了约90%, 化学需氧量(COD)去除率达到了76%.     

电聚合制备聚苯胺@石墨毡复合电极及其在电芬顿过程中的高效电催化性能

作为一种高级氧化技术(AOPs),芬顿氧化法(Fenton)因其操作简单、绿色高效而备受关注.其基本原理是Fe2+催化H2O2产生的羟基自由基(?OH)进攻有机物使之降解为无机小分子或盐.电芬顿法(Electro-Fenton,E-Fenton)是利用电化学方法原位生成H2O2的Fenton衍生法,其优点在于不需要从外界加入H2O2、高效节能、无选择性、并且易于和其他处理技术耦合,是一种非常有价值和应用前景的新型水处理技术.电芬顿技术的理论探究和工艺优化,是当今高级氧化技术的理论和实践研究的重要内容.E-Fenton过程的关键步骤是阴极材料上氧还原反应(Oxygen reduction reaction,ORR)持续生成H2O2.由于析氢过电位高、稳定性好、性能优异,碳材料成为ORR反应最常用的电催化阴极材料.石墨毡作为一种三维多孔立体材料,具有电化学活性面积大、传质好、导电性强、价格低等优点,是ORR的理想阴极材料.聚苯胺材料作为一种导电高分子材料,价格便宜、加工性好、且含有丰富的N原子,在基础研究和实际应用领域都十分活跃.我们创新性地采用电聚合的方法合成了聚苯胺@石墨毡(PANI@GF)复合电极,并通过降解邻苯二甲酸二甲酯(dimethyl phthalate,DMP)研究了其在电芬顿过程中的电催化性能.通过扫描电镜、X射线光电子能谱分析对电极表面结构和杂原子掺杂性进行了物化表征.结果显示PANI@GF复合电极同时具有宏观和微观的三维多孔结构,这种结构蓬松的多孔结构为氧气提供了合适的传递通道和足够的反应面积.所制备复合电极中N原子含量约为1.9%,且吡啶N和吡咯N的含量相对较高.这些N原子来自聚苯胺分子中含有的大量N原子,并能够促进ORR反应.石墨毡和聚苯胺两种材料的在结构和组分上的特点,使得PANI@GF复合电极具有优异的电芬顿降解DMP的性能.在DMP浓度为50 mg/L、电位0.5 V(vs.SCE)、氧气流速为0.4 L/min的条件下,其DMP降解反应表观动力学常数达0.0753 min-1,是石墨毡电极表观动力学常数(0.0151 min-1)的5倍.PANI@GF复合电极制备的最优聚合时间和碳化温度分别为1 h和900℃.这是因为聚合时间太长,可能导致聚苯胺层厚度大,微孔结构被堵塞,进而降低了反应活性面积和影响氧气传质效果,使得电极性能下降;而聚合时间太短,可能导致电极复合不充分.高温碳化可以使石墨毡表面聚苯胺层形成更多的孔结构,从而有利于ORR过程.DMP降解过程中氧气流速、Fe2+用量以及pH值等工艺条件对电极性能有一定的影响,结果表明其相应的优化值分别为0.4 L/min、1.0 mmol/L和3.0.当氧气流速过低时,溶液中低浓度的溶解氧使ORR过程受传质过程限制,导致电极不能充分反应;当氧气流速过大时,并不会增加已经达到饱和的溶液中的氧气浓度,而过大的氧气速率会冲击电极表面,降低电极稳定性而影响其催化性能.对Fe2+.用量而言,E-Fenton过程有多种Fe循环途径,不同的铁含量对于电极性能影响不明显.因此,1.0 mmol/L的Fe含量足够满足实验需要.pH值对E-Fenton过程至关重要,pH较高时,铁离子会形成配合物,阻碍铁循环,并且会导致H2O2的分解,从而降低电极DMP降解性能;而当pH太低时,较多的酸增加成本,且需要后续处理过程以消除酸的影响.实验结果表明3.0是最优pH值,与传统Fenton方法的最适pH相符.PANI@GF复合电极具有高效催化降解DMP的能力,在电芬顿技术处理有机废水中有潜在应用.     

Developments in electrode materials for wastewater treatment

This review provides a current opinion about the most recent advances in the development of novel materials (i.e., anodes and cathodes), as well as new synthesis methodologies, which have been used in water and wastewater treatment by electrochemically driven oxidation technologies. The first section focuses on the advances to produce novel anodic materials comprising the active anodes — which play a key role in direct and indirect oxidation and the nonactive materials — which attract attention due to their high capacity to generate hydroxyl radicals. The second section describes recent progress on the novel emerging cathodic materials that are directly related to in situ electrogeneration of oxidants and are commonly applied in the electro-Fenton technology. Finally, the perspectives and prospects of these novel electrode materials for environmental applications are given.     

A comparative study for treatment of white liquor by different applications of Fenton process

In this paper, the treatability of white liquor by conventional (CFP), modified (MFP) and electro-Fenton oxidation processes (EFP) was investigated depending on the COD parameter. Based on the experimental results, up to 62.4%, 58.4% and 54.9% COD removals by the CFP, MFP and EFP were achieved, respectively. It was observed that adjustment of initial pH to acidic values is not required in the CFP. The optimal operational conditions were found to be [Fe²⁺] = 500 mg/L, [H₂O₂] = 1000 mg/L at pH 7.3 (original pH) in the CFP, [Fe⁰] = 1250 mg/L, [H₂O₂] = 1000 mg/L at pH 3 in the MFP, and I = 1.0 A, [H₂O₂] = 1500 mg/L at pH 3 in the EFP, respectively. As a result, the CFP has been determined as a more efficient alternative treatment method.     

Upgrading and expanding the electro-Fenton and related processes

The Fenton-based electrochemical advanced oxidation processes are currently recognized as the most effective technologies to achieve fast and complete degradation of target organic contaminants in water. Electro-Fenton was the pioneering process, but a larger mineralization is attained via UV and solar photoelectro-Fenton processes due to the occurrence of key photoreduction reactions. In practice, the decontamination effectiveness turns out to be limited as solution pH increases and the two-electron oxygen reduction reaction occurring at the cathode becomes inefficient or insufficient. Here, we focus on the current opinion in two crucial features of the reviewed processes: (i) trends in cathodic H₂O₂ electrogeneration, showing the oxygen reduction reaction upgrading upon use of new and/or more sustainable electrocatalysts, cathode configurations and reactor designs; and (ii) advances in iron-based catalysts, with the main purpose of expanding the application to a much wider pH range, eventually surpassing the classical acidic limitation associated to conventional Fenton's reaction.