Toxicity change patterns and its mechanism during the degradation of nitrogen-heterocyclic compounds by O(3)/UV

Many nitrogen-heterocyclic compounds (NHCs) are toxic and recalcitrant contaminants that need to be degraded by advanced oxidation processes. In this study, quinoline, isoquinoline and indole were selected to investigate their toxicity patterns during the degradation by O(3)/UV. It was found that for all the three NHCs there was some H(2)O(2) formed in the degradation process, which caused the sharp increase of toxicity to Photobacterium phosphoreum. The toxicity decreasing patterns after H(2)O(2) elimination were different for quinoline (or isoquinoline) and indole. After H(2)O(2) elimination, for quinoline or isoquinoline the toxicity decreased concurrently with the decrease of its concentration, while for indole the toxicity lagged behind its removal rate. The rate constant of the NHC with O(3) (k(D)) was the decisive parameter of its toxicity pattern because of its critical role in determining the degradation rate of the NHC. Two quantitative structure-activity relationship equations for the k(D) values of simple NHCs and homocyclic aromatics were successfully established, which would be useful to predict their toxicity patterns.     

Electrochemical oxidation of nitrogen-heterocyclic compounds at boron-doped diamond electrode

Nitrogen-heterocyclic compounds (NHCs) are toxic and bio-refractory contaminants widely spread in environment. This study investigated electrochemical degradation of NHCs at boron-doped diamond (BDD) anode with particular attention to the effect of different number and position of nitrogen atoms in molecular structure. Five classical NHCs with similar structures including indole (ID), quinoline (QL), isoquinoline (IQL), benzotriazole (BT) and benzimidazole (BM) were selected as the target compounds. Results of bulk electrolysis showed that degradation of all NHCs was fit to a pseudo first-order equation. The five compounds were degraded with the following sequence: ID > QL > IQL > BT > BM in terms of their rates of oxidation. Quantum chemical calculation was combined with experimental results to describe the degradation character of NHCs at BDD anode. A linear relationship between degradation rate and delocalization energy was observed, which demonstrated that electronic charge was redistributed through the conjugation system and accumulated at the active sites under the attack of hydroxyl radicals produced at BDD anode. Moreover, atom charge was calculated by semi empirical PM3 method and active sites of NHCs were identified respectively. Analysis of intermediates by GC-MS showed agreement with calculation results.     

Electro-Fenton pretreatment for the improvement of tylosin biodegradability

The feasibility of an electro-Fenton process to treat tylosin (TYL), a non-biodegradable antibiotic, was examined in a discontinuous electrochemical cell with divided cathodic and anodic compartments. Only 15 min electrolysis was needed for total tylosin degradation using a carbon felt cathode and a platinum anode; while 6 h electrolysis was needed to achieve high oxidation and mineralization yields, 96 and 88 % respectively. Biodegradability improvement was shown since BOD₅/COD increased from 0 initially to 0.6 after 6 h electrolysis (for 100 mg L^?1 initial TYL). With the aim of combining electro-Fenton with a biological treatment, an oxidation time in the range 2 to 4 h has been however considered. Results of AOS (average oxidation state) and COD/TOC suggested that the pretreatment could be stopped after 2 h rather than 4 h; while in the same time, the increase of biodegradability between 2 and 4 h suggested that this latter duration seemed more appropriate. In order to conclude, biological cultures have been therefore carried out for various electrolysis times. TYL solutions electrolyzed during 2 and 4 h were then treated with activated sludge during 25 days, showing 57 and 67 % total organic carbon (TOC) removal, respectively, namely 77 and 88 % overall TOC removal if both processes were considered. Activated sludge cultures appeared, therefore, in agreement with the assessment made from the analysis of physico-chemical parameters (AOS and COD/TOC), since the gain in terms of mineralization expected from increasing electrolysis duration appeared too low to balance the additional energy consumption.     

Recent updates on electrochemical degradation of bio-refractory organic pollutants using BDD anode: a mini review

Boron-doped diamond (BDD) is playing an important role in environmental electrochemistry and has been successfully applied to the degradation of various bio-refractory organic pollutants. However, the review concerning recent progress in this research area is still very limited. This mini-review updated recent advances on the removal of three kinds of bio-refractory wastewaters including pharmaceuticals, pesticides, and dyes using BDD electrode. It summarized the important parameters in three electrochemical oxidation processes, i.e., anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) and compared their different degradation mechanisms and behaviors. As an attractive improvement of PEF, solar photoelectro-Fenton using sunlight as UV/vis source presented cost-effectiveness, in which the energy consumption for enrofloxacin removal was 0.246 kWh/(g TOC), which was much lower than that of 0.743 and 0.467 kWh/(g TOC) by AO and EF under similar conditions. Finally the existing problems and future prospects in research were suggested.     

Efficient removal of insecticide “imidacloprid” from water by electrochemical advanced oxidation processes

The oxidative degradation of imidacloprid (ICP) has been carried out by electrochemical advanced oxidation processes (EAOPs), anodic oxidation, and electro-Fenton, in which hydroxyl radicals are generated electrocatalytically. Carbon-felt cathode and platinum or boron-doped diamond (BDD) anodes were used in electrolysis cell. To determine optimum operating conditions, the effects of applied current and catalyst concentration were investigated. The decay of ICP during the oxidative degradation was well fitted to pseudo-first-order reaction kinetics and absolute rate constant of the oxidation of ICP by hydroxyl radicals was found to be k _abs(ICP)?=?1.23?×?10⁹ L mol^?1 s^?1. The results showed that both anodic oxidation and electro-Fenton process with BDD anode exhibited high mineralization efficiency reaching 91 and 94 % total organic carbon (TOC) removal at 2 h, respectively. For Pt-EF process, mineralization efficiency was also obtained as 71 %. The degradation products of ICP were identified and a plausible general oxidation mechanism was proposed. Some of the main reaction intermediates such as 6-chloronicotinic acid, 6-chloronicotinaldehyde, and 6-hydroxynicotinic acid were determined by GC-MS analysis. Before complete mineralization, formic, acetic, oxalic, and glyoxylic acids were identified as end-products. The initial chlorine and organic nitrogen present in ICP were found to be converted to inorganic anions Cl^?, NO₃ ^?, and NH₄ ⁺.     

Oxidative and energetic efficiency of different electrochemical oxidation processes for chloroanilines abatement in aqueous medium

The oxidative efficiency and energy consumption, in the degradation of chloroanilines by anodic oxidation, indirect oxidation with electrogenerated hydrogen peroxide and electro-Fenton have been compared, using a laboratory system driven by a LabVIEW virtual controller. Solutions were oxidized in an undivided cell, where H(2)O(2) was generated electrochemically by reduction of atmospheric oxygen bubbled at a carbon cloth cathode. The electro-Fenton process showed the best degradation power, in terms of efficiency of removal and energy consumption. This process was applied to the purification of a solution obtained by washing a polluted soil. Under laboratory conditions, electro-Fenton removed 75% COD of this wastewater with a specific energy consumption of 0.3kWh per gram of COD, corresponding to 41.8kWhm(-3).     

共基质体系下漆酶介体系统降解氮杂环化合物的研究

采用2,2-连氮-双-(3-乙基苯并噻吡咯啉-6-磺酸)(ABTS)作为介体,与纯漆酶组成漆酶介体系统(LMS),分别研究了单基质和共基质体系下LMS对氮杂环化合物的降解。结果表明:(1)LMS对单基质和共基质体系中的吲哚的降解反应很快达到平衡,约为1h。(2)共基质体系中吡啶的引入,对吲哚的降解没有明显的促进或抑制作用;共基质体系中喹啉的引入,对吲哚的降解有较小的促进作用,而同时引入吡啶和喹啉,一定程度上也促进了吲哚的降解。(3)喹啉不能被LMS所降解。共基质体系中吲哚的引入,对吡啶的降解有一定的抑制作用;对喹啉的降解有一定的促进作用。(4)在LMS的作用下,推断吲哚生成的中间产物是氧化吲哚和靛红;吡啶生成的产物是戊二醛和戊二酸;喹啉最先生成2-羟基喹啉。     

Removal of propham from water by using electro-Fenton technology: kinetics and mechanism

The removal of a carbamate herbicide, propham, from aqueous solution has been carried out by the electro-Fenton process. Hydroxyl radical, a strong oxidizing agent, was generated catalytically and used for the oxidation of propham aqueous solutions. The degradation kinetics of propham evidenced a pseudo-first order degradation. The absolute rate constant of second order reaction kinetics between propham and ()OH was determined as (2.2+/-0.10)x10(9)m(-1)s(-1). The mineralization of propham was followed by the organic carbon (TOC) removal. The optimal Fe(3+) concentration was found as 0.5mM at 300mA. The 94% of initial TOC of 0.25mM propham solution was removed in 8h at the optimal conditions by using the cathode area to solution volume ratio of 3.33dm(-1). The maximum mineralization current efficiency values were obtained at 60mA in the presence of 0.5mM Fe(3+). During the electro-Fenton treatment, several degradation products were formed. These intermediates were identified by using high performance liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry and ion chromatography analysis. The identified by-products allowed proposing a pathway for the propham mineralization.     

光电芬顿氧化法深度处理垃圾渗滤液研究

采用光电芬顿氧化法对北京市某垃圾填埋场已经生化处理后的垃圾渗滤液进行深度处理，分别考察了电流强度和铁的不同价态等因素对渗滤液总有机碳（TOC）、化学需氧量（COD）以及色度去除效果的影响，并对阳极氧化、电芬顿和光电芬顿不同反应过程进行了对比。通过分析渗滤液UV-Vis光谱(200～500 nm)变化和渗滤液中有机污染物的分子量变化，发现光电芬顿反应可以明显改善渗滤液生化性。深入研究了反应过程中铁价态的变化规律。试验结果发现，以高比表面积的活性炭纤维(ACF)为阴极的光电芬顿反应可以有效降解垃圾渗滤液，在pH为3，Fe²⁺ 浓度为1 mmol/L，电流为0.5 A，O₂通入量为250 mL/min条件下降解360 min，垃圾渗滤液TOC和COD去除率分别达到78.9%和62.8%，色度完全去除。     

Electro-oxidation of the dye azure B: kinetics,mechanism, and by-products

In this work, the electrochemical degradation of the dye azure B in aqueous solutions was studied by electrochemical advanced oxidation processes (EAOPs), electro-Fenton, and anodic oxidation processes, using Pt/carbon-felt and boron-doped diamond (BDD)/carbon-felt cells with H₂O₂ electrogeneration. The higher oxidation power of the electro-Fenton (EF) process using BDD anode was demonstrated. The oxidative degradation of azure B by the electrochemically generated hydroxyl radicals (^?OH) follows a pseudo-first-order kinetics. The apparent rate constants of the oxidation of azure B by ^?OH were measured according to pseudo-first-order kinetic model. The absolute rate constant of azure B hydroxylation reaction was determined by competition kinetics method and found to be 1.19?×?10⁹ M^?1 s^?1. It was found that the electrochemical degradation of the dye leads to the formation of aromatic by-products which are then oxidized to aliphatic carboxylic acids before their almost mineralization to CO₂ and inorganic ions (sulfate, nitrate, and ammonium). The evolution of the TOC removal and time course of short-chain carboxylic acids during treatment were also investigated.     

紫外光助臭氧化处理活性艳红K-2BP废水研究

以 30 0W高压汞灯为光源 ,研究了紫外光联合臭氧化、单纯臭氧氧化及单纯紫外光照处理 4 0 0mg/L的活性艳红K 2BP废水的可行性。结果表明 :光催化臭氧化可加速有机物的矿化。在同样时间条件下 ,三者氧化能力由大至小为 :UV/O3 >单独O3 >单独UV。运用TOC、紫外 可见光谱 (UV Vis)、毛细管电泳 (CE)等分析技术初步探讨了紫外光催化臭氧化活性艳红K 2BP溶液的降解效果及降解机理。     

Degradation and mineralization of sulcotrione and mesotrione in aqueous medium by the electro-Fenton process: a kinetic study

Introduction

The degradation and mineralization of two triketone (TRK) herbicides, including sulcotrione and mesotrione, by the electro-Fenton process (electro-Fenton using Pt anode (EF-Pt), electro-Fenton with BDD anode (EF-BDD) and anodic oxidation with BDD anode) were investigated in acidic aqueous medium.

Methods

The reactivity of both herbicides toward hydroxyl radicals was found to depend on the electron-withdrawing effect of the aromatic chlorine or nitro substituents. The degradation of sulcotrione and mesotrione obeyed apparent first-order reaction kinetics, and their absolute rate constants with hydroxyl radicals at pH?3.0 were determined by the competitive kinetics method.

Results and discussion

The hydroxylation absolute rate constant (k _abs) values of both TRK herbicides ranged from 8.20?×?10⁸ (sulcotrione) to 1.01?×?10⁹ (mesotrione) L?mol^?1?s^?1, whereas those of the TRK main cyclic or aromatic by-products, namely cyclohexane 1,3-dione , (2-chloro-4-methylsulphonyl) benzoic acid and 4-(methylsulphonyl)-2-nitrobenzoic acid, comprised between 5.90?×?10⁸ and 3.29?×?10⁹?L?mol^?1?s^?1. The efficiency of mineralization of aqueous solutions of both TRK herbicides was evaluated in terms of total organic carbon removal. Mineralization yields of about 97?C98% were reached in optimal conditions for a 6-h electro-Fenton treatment time.

Conclusions

The mineralization process steps involved the oxidative opening of the aromatic or cyclic TRK by-products, leading to the formation of short-chain carboxylic acids, and, then, of carbon dioxide and inorganic ions.     

Enhanced degradation of azo dye alizarin yellow R in a combined process of iron–carbon microelectrolysis and aerobic bio-contact oxidation

Purpose

With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.

Materials and methods

The combined ABO (with effective volume of 2.4?l) and ICME (with effectively volume of 0.4?l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6?h.

Results

At the HRT of 6?h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4?h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.

Conclusion

The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.     

同分异构体喹啉和异喹啉的缺氧降解性能比较

研究了同分异构体的含氮杂环化合物喹啉和异喹啉在缺氧条件下的降解情况,发现两者表现出不同的缺氧降解特性。喹啉可以在缺氧条件下得到有效降解,其缺氧降解的最佳碳氮比为8。在最佳碳氮比条件下,喹啉的缺氧降解过程符合一级动力学规律,在其降解过程中首先以硝酸盐为电子受体,当硝酸盐氮浓度为零时,亚硝酸盐氮浓度达到最高,此后喹啉的降解主要以亚硝酸盐为电子受体,并和亚硝酸盐氮同时达到最低浓度。异喹啉对硝酸盐的利用甚微,其降解主要表现为厌氧降解特征,降解过程符合零级动力学规律。     

Degradation of Acid Orange 7 by electrochemically generated (*)OH radicals in acidic aqueous medium using a boron-doped diamond or platinum anode: a mechanistic study

A comparative study of the degradation of Acid Orange 7 (AO 7) aqueous solutions in acidic medium of pH 3.0 by electro-Fenton process using Pt or boron-doped diamond (BDD) anode was reported. The oxidative degradation of AO 7 by electrochemically generated hydroxyl radicals follows a pseudo-first order kinetic with a similar rate constant with BDD or Pt anode. The absolute rate constant of the AO 7 hydroxylation reaction was determined as (1.10+/-0.04)x10(10)M(-1)s(-1) by using the competition kinetic method. The comparative study of TOC measurements during electro-Fenton treatment showed a higher mineralization rate with BDD than Pt anode at the first hours of electrolysis because of the higher oxidizing power of this anode. The electro-Fenton degradation of AO 7 was followed by monitoring the formation and evolution of aromatic intermediates which are oxidized to aliphatic carboxylic acids before mineralization (transformation to CO(2) and inorganic ions, i.e. sulphate, nitrate and ammonium). The follow-up of the solution toxicity evolution shows the formation of intermediates more toxic than AO 7 and the connection between toxicity and aromaticity. A mineralization reaction pathway of AO 7 by electro-Fenton degradation involving all the intermediates identified was proposed.     

Decomposition of nitrotoluenes from trinitrotoluene manufacturing process by Electro-Fenton oxidation

Oxidative degradation of dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid was conducted by Electro-Fenton's reagents. The electrolytic experiments were carried out to elucidate the influence of various operating parameters on the performance of mineralization of total organic compounds (TOC) in spent acid, including reaction temperature, dosage of oxygen, sulfuric acid concentration and dosage of ferrous ions. It deserves to note that organic compounds could be completely destructed by Electro-Fenton's reagent with in situ electrogenerated hydrogen peroxide obtained from cathodic reduction of oxygen, which was mainly supplied by anodic oxidation of water. Based on the spectra analyzed by gas chromatograph/mass spectrometer, it is proposed that initial denitration of 2,4,6-TNT gives rise to formation of 2,4-DNT and/or 2,6-DNT, which undergo the cleavage of nitro group into o-mononitrotoluene, followed by denitration to toluene and subsequent oxidation of the methyl group. Owing to the removal of both TOC and partial amounts of water simultaneously, the electrolytic method established is potentially applied to regenerate spent acid from toluene nitration processes in practice.     

NaNO(2)/FeCl(3) catalyzed wet oxidation of the azo dye Acid Orange 7

A combination of ferric chloride and sodium nitrite significantly improved the wet oxidation of the azo dye Acid Orange 7 (AO7) in acid aqueous media (pH 2.6) under moderate conditions (T=150 degrees C; oxygen pressure=0.5 MPa). To evaluate the catalytic system, wet oxidation of AO7 was carried out at temperatures between 90 and 150 degrees C and oxygen pressures ranging from 0.1 to 0.5 MPa. The effect of initial solution pH from 2.6 to 11.4 and the amount of catalyst on the degradation of AO7 were also investigated. AO7 initial concentration was kept 200 mg L(-1). The degradation process was monitored by UV-visible spectroscopy, HPLC, IC (ion chromatography), GC-MS and TOC analysis. At 150 degrees C and 0.5 MPa oxygen pressure, 56% TOC was removed after 4h of treatment, while no obvious TOC removal were achieved without catalyst at the same experimental condition. The main degradation products were some small organic acids: formic acid, acetic acid, pyruvic acid, oxalic acid, succinic acid (identified and quantified by IC) and phthalic acid (identified by GC-MS).     

光电催化氧化法降解藻毒素MCLR

使用DSA阳极,对光电催化氧化降解藻毒素MCLR的效能及其影响因素进行了研究。结果表明,电极表面的TiO2在光催化氧化降解MCLR的过程中发挥了明显的光催化作用。在光降解、电催化氧化、光催化氧化和光电催化氧化4个过程中,光电催化氧化对MCLR和TOC的去除率最高,分别可达100%和13%,并且光电催化氧化的去除率大于光催化氧化和电催化氧化之和,表明后两者的耦合过程产生了一定的协同作用。辐照光源和电流密度存在最佳匹配条件,分别为UVC辐照、电流密度10 mA/cm2和UVA辐照、电流密度1.0 mA/cm2,此条件下光电协同作用最显著。在光电催化氧化过程中,随极板间距增大而出现的去除率下降取决于电催化过程,而不是光催化过程;光电催化氧化MCLR的去除率随其初始浓度增加而减小。     

Degradation of the herbicide 2,4-DP by anodic oxidation, electro-Fenton and photoelectro-Fenton using platinum and boron-doped diamond anodes

This paper reports the degradation of 2,4-DP (2-(2,4-dichlorophenoxy)-propionic acid) solutions of pH 3.0 by environmentally friendly electrochemical methods such as anodic oxidation, electro-Fenton and photoelectro-Fenton with a Pt or boron-doped diamond (BDD) anode. In the two latter techniques an O(2)-diffusion cathode was used and 1.0mM Fe(2+) was added to the solution to give hydroxyl radical (*OH) from Fenton's reaction between Fe(2+) and H(2)O(2) generated at the cathode. All treatments with BDD are viable to decontaminate acidic wastewaters containing 2,4-DP since they give complete mineralization, with loss of chloride ion, at high current due to the great production of oxidant *OH at the BDD surface favoring the destruction of final carboxylic acids. *OH formed from Fenton's reaction destroys more rapidly aromatic products, making the electro-Fenton and photoelectro-Fenton processes much more efficient than anodic oxidation. UVA light in photoelectro-Fenton with BDD has little effect on the degradation rate of pollutants. The comparative procedures with Pt lead to slower decontamination because of the lower oxidizing power of this anode. The effect of current on the degradation rate and efficiency of all methods is studied. The 2,4-DP decay always follows a pseudo-first-order kinetics. Chlorohydroquinone, chloro-p-benzoquinone and maleic, fumaric, malic, lactic, pyruvic, acetic, formic and oxalic acids are detected as products by chromatographic techniques. A general sequence accounting for by the reaction of all these intermediates with the different oxidizing agents is proposed.     

Degradation of clofibric acid in acidic aqueous medium by electro-Fenton and photoelectro-Fenton

Acidic aqueous solutions of clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid), the bioactive metabolite of various lipid-regulating drugs, have been degraded by indirect electrooxidation methods such as electro-Fenton and photoelectro-Fenton with Fe(2+) as catalyst using an undivided electrolytic cell with a Pt anode and an O(2)-diffusion cathode able to electrogenerate H(2)O(2). At pH 3.0 about 80% of mineralization is achieved with the electro-Fenton method due to the efficient production of oxidant hydroxyl radical from Fenton's reaction between Fe(2+) and H(2)O(2), but stable Fe(3+) complexes are formed. The photoelectro-Fenton method favors the photodecomposition of these species under UVA irradiation, reaching more than 96% of decontamination. The mineralization current efficiency increases with rising metabolite concentration up to saturation and with decreasing current density. The photoelectro-Fenton method is then viable for treating acidic wastewaters containing this pollutant. Comparative degradation by anodic oxidation (without Fe(2+)) yields poor decontamination. Chloride ion is released during all degradation processes. The decay kinetics of clofibric acid always follows a pseudo-first-order reaction, with a similar rate constant in electro-Fenton and photoelectro-Fenton that increases with rising current density, but decreases at greater metabolite concentration. 4-Chlorophenol, 4-chlorocatechol, 4-chlororesorcinol, hydroquinone, p-benzoquinone and 1,2,4-benzenetriol, along with carboxylic acids such as 2-hydroxyisobutyric, tartronic, maleic, fumaric, formic and oxalic, are detected as intermediates. The ultimate product is oxalic acid, which forms very stable Fe(3+)-oxalato complexes under electro-Fenton conditions. These complexes are efficiently photodecarboxylated in photoelectro-Fenton under the action of UVA light.