Electrochemical degradation of chlorophenoxy and chlorobenzoic herbicides in acidic aqueous medium by the peroxi-coagulation method

The degradation of 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as chlorophenoxy herbicides, as well as of 3,6-dichloro-2-methoxybenzoic acid (dicamba) as chlorobenzoic herbicide, has been studied by peroxi-coagulation. This electrochemical method yields a very effective depollution of all compounds in acidic aqueous medium of pH 3.0 working under pH regulation, since they are oxidized with hydroxyl radicals produced from Fenton's reaction between Fe(2+) and H(2)O(2) generated by the corresponding Fe anode and O(2)-diffusion cathode. Their products can then be removed by mineralization or coagulation with the Fe(OH)(3) precipitate formed. Both degradative paths compete at low currents, but coagulation predominates at high currents. The peroxi-coagulation process of dicamba at I>or=300 mA leads to more than 90% of coagulation, being much more efficient than its comparative electro-Fenton treatment with a Pt anode and 1 mM Fe(2+), where only mineralization takes place. For the chlorophenoxy compounds, electro-Fenton gives a slightly lower depollution than peroxi-coagulation, because more easily oxidable products are produced. Oxidation of chlorinated products during peroxi-coagulation is accompanied by the release of chloride ion to the solution. The efficiency of this method decreases with increasing electrolysis time and current. The decay of all herbicides follows a pseudo-first-order reaction, with a similar constant rate for 4-CPA, MCPA, 2,4-D and 2,4,5-T, and a higher value for dicamba.     

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.     

Mineralization of the biocide chloroxylenol by electrochemical advanced oxidation processes

Electrochemical advanced oxidation processes (EAOPs) are environmentally friendly methods based on the destruction of organic pollutants in wastewaters with in situ electrogenerated hydroxyl radical. This species is formed in anodic oxidation (AO) from water oxidation at the anode and in indirect electro-oxidation methods like electro-Fenton (EF) and photoelectro-Fenton (PEF) also from reaction between catalytic Fe2+ and H2O2 continuously produced at the O2-diffusion cathode. The PEF method involves the irradiation of the treated solution with UVA light to enhance the photolysis of organics including Fe(III) complexes. In this work, the oxidation power of such EAOPs to decontaminate synthetic wastewaters of the biocide chloroxylenol (4-chloro-3,5-dimethylphenol) at pH 3.0 is comparatively examined with an undivided electrolytic cell containing a Pt or boron-doped diamond (BDD) anode and a stainless steel or O2-diffusion cathode. The initial chlorine is released as Cl(-) ion, which remains stable in the medium using Pt or is oxidized to Cl2 on BDD. The biocide solutions can be completely decontaminated using AO with a BDD anode, as well as PEF with a Pt or BDD anode. The PEF procedure with a BDD anode is the most powerful method leading to total mineralization in about 300 min, practically independent of current density. When current density rises, the degradation rate of processes increases, but they become less efficient due to the larger enhancement of waste reactions of oxidants. Chloroxylenol is much more rapidly removed in EF and PEF than in AO. 2,6-dimethylhydroquinone, 2,6-dimethyl-p-benzoquinone and 3,5-dimethyl-2-hydroxy-p-benzoquinone are identified as aromatic by-products, and maleic, malonic, pyruvic, acetic and oxalic acids are found as generated carboxylic acids. A general pathway for chloroxylenol mineralization by all EAOPs including the above by-products is proposed.     

组合阳极联合气体扩散阴极电催化降解苯胺

采用气体扩散电极为阴极,钛基氧化物（Ti／SnO2-Sb2O5-IrO2）和金属铁构成组合阳极,构建了新型电化学氧化体系用于降解有机污染物。利用该氧化体系,在不同实验条件下考察了苯胺降解的效果与降解过程的相关规律。结果表明,阴极电位、铁阳极通电时间以及苯胺初始浓度均显著影响苯胺的降解效果。当阴极电位为-0．7V,pH3．0,铁阳极通电时间20min时,电化学处理200mg／L苯胺480min,TOC的去除效率达到80．4％,矿化电流效率（MCE）为8．6％,显示了该氧化体系具有良好的有机物降解能力。此外,苯胺降解过程中氨氮和硝态氮浓度的变化表明,苯胺分子中的氮主要转化为NH4和NO3^-。     

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.     

电化学法去除SO2/NOX的研究进展

本文对采用电化学方法去除SO2/NOx废气这一新的研究方法进行了综述.在用酞花青钴(CoPc)修饰的碳气体扩散电极上,SO2在空气中的体积百分数在20%以下时可以完全被氧化为硫酸,以连二硫酸盐(S2O2-4)作还原剂,Fe2+-EDTA作络合剂时,NO以90%以上的程度还原为NH+4与NH2(SO3H)等低价含氮化合物,产物中未见N2、N2O与NO2等气体,氧化产物SO2-3(或HSO-3)在Pb阴极上还原再生为S2O2-4.用Ce4+作氧化剂可将SO2/NO2氧化为相应的酸,还原产物Ce3+经电解氧化后循环使用.     

电催化氧化法处理染料废水的影响因素及动力学

以钛涂膜极板为阳极、石墨极板为阴极、Fe2O3/γ-Al2O3为多相催化剂,构建电-多相催化氧化体系,研究了该体系对酸性大红模拟染料废水中COD的去除效果及其影响因素,优化了实验条件,并初步探讨了COD的降解机理。结果表明,在槽电压20 V,pH 4,曝气量0.24 m3/h,极板间距3 cm的条件下,COD的去除率最高,达到64.5%;COD的降解近似符合一级动力学方程:ln(C0/C)=0.0034t+0.719。在电-多相催化氧化体系中,废水中的有机物被直接矿化或降解为小分子有机物。     

Electrochemical degradation of bromopyrogallol red in presence of cobalt ions

This paper summarizes the results of a degradation test of bromopyrogallol red (BPR) and textile dye wastewater (TDW) with a conventional three-electrode potentiostatic system in the presence of cobalt ions (electro Co(2+)-H2O2 system). H2O2, produced by the two-electron reduction of O2 at the cathode, would react with Co2+ ions, leading to the generation of hydroxyl radicals (*OH), which caused the degradation of the organic pollutants. With BPR degradation process as the reference point, the optimal conditions (pH=4.0 and the concentration of Co2+ is 0.1 mM) and the treating capacity of the system were both studied and compared with electro-Fenton's reagent. Many benefits were shown by the electro Co(2+)-H2O2 system, such as less metal ions consumption, more moderate conditions and faster reaction process. Treated with the system for 0.5 h, chemical oxygen demand and biological oxygen demand of TDW (pH=5.2), without pH adjustment, were reduced by 95.7% and 92.7%, respectively. These characteristics make the method another appropriate solution for wastewater treatment, especially for those contaminated by organic pollutants.     

Degradation of 2,7-dichlorodibenzo-p-dioxin by Fe(3+)-H(2)O(2) mixed reagent

Fe(3+)-H(2)O(2) mixed reagent, but not Fe(2+)-H(2)O(2), was found to be capable of degrading 2,7-dichlorodibenzo-p-dioxin (DCDD). A reaction mixture of FeCl(3) (8 mM) and H(2)O(2) (1%) caused approximately 50% degradation within 6 h and >90% degradation within 24 h at 27 degrees C. Increasing the temperature remarkably stimulated degradation: at 70 degrees C, approximately 100% degradation was achieved within 15 min. When DCDD-treated model soil (5 micrograms/g) was conducted, approximately 100% of the DCDD was degraded within 30 min at 70 degrees C (both reagents were added every 10 min). These results suggest that Fe(3+)-H(2)O(2) mixed reagent may be a new tool for combating persistent environmental pollutants such as dioxins and polychlorinated biphenyls.     

Electrochemical combustion of herbicide mecoprop in aqueous medium using a flow reactor with a boron-doped diamond anode

The anodic oxidation of 1.8l of solutions with mecoprop (2-(4-chloro-2-methylphenoxy)-propionic acid or MCPP) up to 0.64 g l(-1) in Na2SO4 as background electrolyte within the pH range 2.0-12.0 has been studied using a flow plant containing a one-compartment filter-press electrolytic reactor with a boron-doped diamond (BDD) anode and a stainless steel cathode, both of 20-cm2 area. Electrolyses carried out in batch under steady conditions and operating at constant current density between 50 and 150 mA cm(-2) always yield complete mineralization due to the great concentration of hydroxyl radical generated at the BDD anode. The degradation rate is practically independent of pH and Na2SO4 concentration, but it becomes faster with increasing MCPP concentration, current density, temperature and liquid flow rate. The effect of these parameters on current efficiency and energy cost has also been investigated. Generated weak oxidants such as H2O2 and peroxodisulfate ion have little influence on the mineralization process. The kinetics for the herbicide decay follows a pseudo first-order reaction with a higher rate constant when current density increases. Aromatic products such as 4-chloro-o-cresol, 2-methylhydroquinone and 2-methyl-p-benzoquinone, and generated carboxylic acids such as maleic, fumaric, lactic, pyruvic, tartronic, acetic and oxalic, have been identified as intermediates by chromatographic techniques. The initial chlorine is completely released in the form of chloride ion, which is slowly oxidized to Cl2 at the BDD anode. A reaction pathway for MCPP mineralization involving all products detected is proposed.     

可渗透反应复合电极法对土壤重金属的电动去除

将零价铁(Fe0)、沸石等活性材料附着在电极上形成可渗透反应层并构成可渗透反应复合电极,采用不同的复合电极对Cd2+、Ni 2+、Pb2+和Cu2+等4种阳离子型重金属污染土壤进行了电动力学修复。研究了不同可渗透反应复合电极对土壤pH的控制效果以及对重金属的去除作用,分析了迁移到复合电极中的重金属形态变化。结果表明,复合电极中添加酸、碱性沸石并适时更换,可有效中和、截留阴阳极电解产生的OH-和H+,避免或减缓土壤酸碱迁移带的形成,防止重金属离子的过早沉淀及土壤过度酸化,极大提高了重金属的去除率。复合电极中Fe0可将迁移进来的重金属离子进行还原稳定,实现重金属污染物的捕获与固定,与迁移到沸石复合电极中的4种重金属不稳定态相比,"Fe0+沸石"复合电极中重金属不稳定态分别下降了61.4、60.5、61.4、57.1百分点。结果还显示,阴极采用"Fe0+沸石"复合电极并适时进行更换,施加1.5V/cm的直流电压修复10d后,土壤中Cd、Ni、Pb、Cu的总去除率分别为44.5%、41.5%、33.5%和36.7%,且进一步延长修复时间和持续更换电极可获得更为理想的修复效果。     

Chemical oxidative degradation of methyl tert-butyl ether in aqueous solution by Fenton's reagent

Degradation of methyl tert-butyl ether (MTBE) in aqueous solution by Fenton's reagent (Fe2+ and H2O2) was investigated. Effects of reaction conditions on the oxidation efficiency of MTBE by Fenton's reagent were examined in batch experiments. Under optimum conditions, 15 mM H2O2, 2 mM Fe2+, pH 2.8 and room temperature, the initial 1 mM MTBE solution was reduced by 99% within 120 min. Results showed that MTBE was decomposed in a two-stage reaction. MTBE was first decomposed swiftly based on a Fe2+/H2O2 reaction and then decomposed somewhat less rapidly based on a Fe3+/H2O2 reaction. The detection of Fe2+ also supported the theory of the two-stage reaction for the oxidation of MTBE by Fenton's reagent. The dissolved oxygen in the solution decreased rapidly in the first stage reaction, but it showed a slow increase in the second stage with a zero-order kinetics. A reaction mechanism involving two different pathways for the decomposition of MTBE by Fenton's reagent was also proposed. Chemicals including tert-butyl formate, tert-butyl alcohol, methyl acetate and acetone were identified to be the primary intermediates and by-products of the degradation processes.     

Electro-Fenton degradation of the antibiotic sulfanilamide with Pt/carbon-felt and BDD/carbon-felt cells. Kinetics,reaction intermediates,and toxicity assessment

The degradation of 230 mL of a 0.6-mM sulfanilamide solution in 0.05 M Na₂SO₄ of pH 3.0 has been studied by electro-Fenton process. The electrolytic cell contained either a Pt or boron-doped diamond (BDD) anode and a carbon-felt cathode. Under these conditions, organics are oxidized by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton’s reaction between initially added (and then electrochemically regenerated) Fe²⁺ and cathodically generated H₂O₂. From the decay of sulfanilamide concentration determined by reversed-phase liquid chromatography, an optimum Fe²⁺ concentration of 0.20 mM in both cells was found. The drug disappeared more rapidly using BDD than Pt, and, in both cases, it was more quickly removed with raising applied current. Almost total mineralization was achieved using the BDD/carbon-felt cell, whereas the alternative use of Pt anode led to a slightly lower mineralization degree. In both cells, the degradation rate was accelerated at higher current but with the concomitant fall of mineralization current efficiency due to the greater increase in rate of the parasitic reactions of hydroxyl radicals. Reversed-phase liquid chromatography allowed the identification of catechol, resorcinol, hydroquinone, p-benzoquinone, and 1,2,4-trihydroxybenzene as aromatic intermediates, whereas ion exclusion chromatography revealed the formation of malic, maleic, fumaric, acetic, oxalic, formic, and oxamic acids. NH₄ ⁺, NO₃ ^?, and SO₄ ^2? ions were released during the electro-Fenton process. A plausible reaction sequence for sulfanilamide mineralization involving all detected intermediates has been proposed. The toxicity of the solution was assessed from the Vibrio fischeri bacteria luminescence inhibition. Although it acquired its maximum value at short electrolysis time, the solution was completely detoxified at the end of the electro-Fenton treatment, regardless of the anode used.     

Comparison of advanced oxidation processes and identification of monuron photodegradation products in aqueous solution

The photodegradation of monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in aqueous solutions under simulated solar irradiation has been conducted by different advanced oxidation processes (UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/H(2)O(2)/TiO(2), UV/TiO(2), dark H(2)O(2)/Fe(3+)). The degradation rates were always higher for the homogeneous catalysis in photo-Fenton reactions (UV/H(2)O(2)/Fe(2+)) compared to the heterogeneous photocatalytic systems (TiO(2)/UV and UV/H(2)O(2)/TiO(2)). Optimal concentrations of Fe(2+) and H(2)O(2) for the abatement of the herbicide in the photo-Fenton system were found to be 1 mM Fe(II) and 10 mM H(2)O(2). Several intermediary products were identified using large volume injection micro-liquid chromatography with UV detection (mu-LC-UV), mu-LC-MS and GC-MS techniques and a degradation mechanism has been proposed.     

Persulfate oxidation for in situ remediation of TCE. I. Activated by ferrous ion with and without a persulfate-thiosulfate redox couple

The objective of the laboratory study is to examine the conditions under which transition metal ions (e.g., ferrous ion, Fe2+) could activate the persulfate anion (S2O8(2)-) to produce a powerful oxidant known as the sulfate free radical (SO4-*) with a standard redox potential of 2.6 V. The SO4-* is capable of destroying groundwater contaminants in situ such as trichloroethylene (TCE). Experiments using Fe2+ as an activator under various molar ratios of S2O8(2)-/Fe2+/TCE in an aqueous system indicated that partial TCE degradation occurred almost instantaneously and then the reaction stalled. Either destruction of SO4-* in the presence of excess Fe2+ or the rapid conversion of all Fe2+ to Fe3+ limited the ultimate oxidizing capability of the system. Sequential addition of Fe2+ in small increments resulted in an increased TCE removal efficiency. Therefore, it appeared that Fe2+ played an important role in generating SO4-*. An observation of oxidation-reduction potential (ORP) variations revealed that the addition of sodium thiosulfate (Na2S2O3) to the ferrous ion activated persulfate system could significantly decrease the strong oxidizing conditions. It was hypothesized that the thiosulfate induced reducing conditions might convert Fe3+ to a lower valence state of Fe2+, making the Fe2+ available to activate persulfate decomposition. The sequential addition of thiosulfate (S2O3(2)-), after the initial stalling of ferrous ion activated persulfate oxidation of TCE, resulted in an improvement in TCE removal. The ferrous ion activated persulfate-thiosulfate redox couple resulted in fairly complete TCE degradation in aqueous systems in a short time frame. In soil slurry systems, TCE degradation was slower in comparison to aqueous systems.     

电催化氧化处理除草剂异噁草酮废水的效能

为有效处理含异噁草酮除草剂废水,以Sb掺杂Ti／SnO2电极为阳极,不锈钢板为阴极,采用电催化氧化技术对异噁草酮废水进行降解,研究了不同影响因素对异噁草酮去除率的影响,并分析了异噁草酮的降解效果。结果表明,当异噁草酮初始浓度为100mg／L、电流密度为20mA／cm2、电解质投加量为0．10mol／L,反应120min后,异噁草酮去除率达到94％,此时TOC去除率为57．9％,能耗为25kWh／m2,且废水的可生化性能显著提高。     

Evaluation of different electrochemical methods on the oxidation and degradation of Reactive Blue 4 in aqueous solution

The oxidation of a reactive dye, Reactive Blue 4, RB4, (C.I. 61205), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode and reticulated vitreous carbon electrode occurs in only one step at 2.0 < pH < 12 involving a two-electron transfer to the amine group leading to the imide derivative. Dye solution was not decolorized effectively in this electrolysis process. Nevertheless, the oxidation of this dye on Ti/SnO2/SbO(x) (3% mol)/RuO2 (1% mol) electrode showed 100% of decolorization and 60% of total organic carbon removal in Na2SO4 0.2 M at pH 2.2 and potential of +2.4V. Experiments on degradation photoelectrocatalytic were also carried out for RB4 degradation in Na2SO4 0.1 M, pH 12, using a Ti/TiO2 photoanode biased at +1.0 V and UV light. After 1h of electrolysis the results indicated total color removal and 37% of mineralization.     

A comparative study of the effects of chloride, sulfate and nitrate ions on the rates of decomposition of H2O2 and organic compounds by Fe(II)/H2O2 and Fe(III)/H2O2

The effects of chloride, nitrate, perchlorate and sulfate ions on the rates of the decomposition of hydrogen peroxide and the oxidation of organic compounds by the Fenton's process have been investigated. Experiments were conducted in a batch reactor, in the dark at pH < or = 3.0 and at 25 degrees C. Data obtained from Fe(II)/H2O2 experiments with [Fe(II)]0/[H2O2]0 > or = 2 mol mol(-1), showed that the rates of reaction between Fe(II) and H2O2 followed the order SO4(2-) > ClO4(-) = NO3- = Cl-. For the Fe(III)/H2O2 process, identical rates were obtained in the presence of nitrate and perchlorate, whereas the presence of sulfate or chloride markedly decreased the rates of decomposition of H2O2 by Fe(III) and the rates of oxidation of atrazine ([atrazine]0 = 0.83 microM), 4-nitrophenol ([4-NP]0 = 1 mM) and acetic acid ([acetic acid]0 = 2 mM). These inhibitory effects have been attributed to a decrease of the rate of generation of hydroxyl radicals resulting from the formation of Fe(III) complexes and the formation of less reactive (SO4(*-)) or much less reactive (Cl2(*-)) inorganic radicals.     

Comparison of electrokinetic soil remediation methods using one fixed anode and approaching anodes

During the cation exchange membrane (CEM) enhanced electrokinetic (EK) soil remediation, the nearer to the anode, the higher are the H+ concentrations and the redox potentials. As both low pH and high redox potential are helpful to speed-up Cd electro-migration, soils near the anode can be quickly remedied. Usually EK process is operated with one fixed anode (FA). A novel CEM enhanced EK method with approaching anodes (AAs) is proposed to accelerate electro-migration effect. Several mesh Ti/Ru anodes were inserted as AAs in the treated soil. They were switched in turn from the anode towards the cathode. Thus high H+ ions concentrations and high redox potentials quickly migrate to the cathode. Consequently, soil remediation is accelerated and nearly 44% of energy and 40% of time can be saved. The mechanism of Cd electro-migration behavior in soils during CEM enhanced EK is described as the elution in an electrokinetically driven chromatogram.     

Degradation of the pharmaceutical metronidazole via UV, Fenton and photo-Fenton processes

Degradation rates and removal efficiencies of Metronidazole using UV, UV/H2O2, H2O2/Fe2+, and UV/H2O2/Fe2+ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H2O2 exhibited pseudo-first order reaction kinetics. By applying H2O2/Fe2+, and UV/H2O2/Fe2+ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200-400 nm, were 0.0033 and 0.0080 mol E(-1), respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H2O2. Adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV/H2O2/Fe2+ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.