Removal of methyl parathion from water by electrochemically generated Fenton's reagent

The electro-Fenton process was used to assess the degradation of methyl parathion (MP) in aqueous solutions. This oxidation process allows the production of hydroxyls radicals which react on the organic compounds, leading to their mineralization. Degradation experiments were performed either in perchloric, sulphuric, hydrochloric and nitric acid media under current controlled electrolysis conditions at different pH. The pH effect as well as the nature of the medium (i.e., the nature of the ions present in medium) on the degradation and mineralization efficiency were studied. The mineralization of the initial pollutant was investigated by total organic carbon measurements which show a complete mineralization at pH 3 in perchloric medium. The absolute rate constant of MP hydroxylation reaction was determined as (4.20+/-0.11)x10(9)M(-1)s(-1). Complete degradation of MP and its metabolites occur in less than 45min. Degradation reaction intermediates such as aromatic compounds, carboxylic acids and inorganic ions were identified and a mineralization pathway is proposed.     

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.     

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.     

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.     

Effects of operating parameters on advanced oxidation of diuron by the Fenton's reagent: a statistical design approach

Advanced oxidation of diuron in aqueous solution by Fenton's reagent using FeSO(4) as source of Fe(II) was investigated in the absence of light. Effects of operating parameters namely the concentrations of pesticide (diuron), H(2)O(2) and Fe(II) on oxidation of diuron was investigated by using Box-Behnken statistical experiment design and the surface response analysis. Diuron oxidation by the Fenton reagent was evaluated by determining the total organic carbon (TOC), diuron, and adsorbable organic halogen (AOX) removals. Concentration ranges of the reagents resulting in the highest level of diuron oxidation were determined. Diuron removal increased with increasing H(2)O(2) and Fe(II) concentrations up to a certain level. Diuron concentration had a more profound effect than H(2)O(2) and Fe(II) in removal of diuron, TOC and AOX from the aqueous solution. Nearly complete (98.5%) disappearance of diuron was achieved after 15min reaction period. However, only 58% of diuron was mineralized after 240min under optimal operating conditions indicating formation of some intermediate products. Optimal H(2)O(2)/Fe(II)/diuron ratio resulting in the maximum diuron removal (98.5%) was found to be 302/38/20 (mgl(-1)).     

Diuron mobility through vineyard soils contaminated with copper

The herbicide diuron is frequently applied to vineyard soils in Burgundy, along with repeated treatments with Bordeaux mixture (a blend of copper sulfate and calcium hydroxide) that result in elevated copper concentrations. Cu could in principle affect the fate and transport of diuron or its metabolites in the soil either directly by complexation or indirectly by altering the populations or activity of microbes involved in their degradation. To assess the effect of high Cu concentrations on diuron transport, an experiment was designed with ten undisturbed columns of calcareous and acidic soils contaminated with 17--509 mg kg(-1) total Cu (field-applied). Grass was planted on three columns. Diuron was applied to the soils in early May and in-ground lysimeters were exposed to outdoor conditions until November. Less than 1.2% of the diuron applied was found in the leachates as diuron or its metabolites. Higher concentrations were found in the effluents from the grass-covered columns (0.1--0.45%) than from the bare-soil columns (0.02--0.14%), and they were correlated with increases in dissolved organic carbon. The highest amounts of herbicide were measured in acidic-soil column leachates (0.98--1.14%) due to the low clay and organic matter contents of these soils. Cu also leached more readily through the acidic soils (32.8--1042 microg) than in the calcareous soils (9.5--63.4 microg). Unlike in the leachates, the amount of diuron remaining in the soils at the end of the experiment was weakly related to the Cu concentrations in the soils.     

Multivariate analysis of photo-Fenton degradation of the herbicides tebuthiuron, diuron and 2,4-D

The degradation of herbicides in aqueous solution by photo-Fenton process using ferrioxalate complex (FeOx) as source of Fe2+ was evaluated under blacklight irradiation. The commercial products of the herbicides tebuthiuron, diuron and 2,4-D were used. The multivariate analysis, more precisely, the response surface methodology was applied to evaluate the role of FeOx and hydrogen peroxide concentrations as variables in the degradation process, and in particular, to define the concentration ranges that result in the most efficient degradation of the herbicides. The degradation process was evaluated by the determination of the remaining total organic carbon content (TOC), by monitoring the decrease of the concentrations of the original compounds using HPLC and by the chloride ion release in the case of diuron and 2,4-D. Under optimized conditions, 20 min were sufficient to mineralize 93% of TOC from 2,4-D and 90% of diuron, including oxalate. Complete dechlorination of these compounds was achieved after 10 min reaction. It was found that the most recalcitrant herbicide is tebuthiuron, while diuron shows the highest degradability. However, under optimized conditions the initial concentration of tebuthiuron was reduced to less than 15%, while diuron and 2,4-D were reduced to around 2% after only 1 min reaction. Furthermore, it was observed that the ferrioxalate complex plays a more important role than H2O2 in the photodegradation of these herbicides in the ranges of concentrations investigated.     

Influence of UV irradiation on the toxicity of phenylurea herbicides using Microtox test

Halogenated phenylurea herbicides are not very toxic by themselves to animals, but their exposure to UV light may significantly increase the toxicity of their solutions. Absorption of light may indeed induce a phototransformation of the herbicide with a possible formation of more toxic intermediate photoproducts. Fortunately in environmental conditions photolysis is usually slow and photoproducts do not accumulate appreciably. Microtox was used for the evaluation of the toxicity of the crude irradiated solutions of some phenylurea herbicides. The sharp initial increase of toxicity shown by metobromuron solutions is mainly due to intermediate photoproducts which rapidly disappear. In the case of diuron and metoxuron toxicity is due to minor photoproducts and it does not disappear so rapidly. Hence the decrease of herbicide concentration is not necessarily associated to a lower toxicity of the solution.     

Degradation of diuron in aqueous solution by ozonation

Degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in aqueous solution and the proposed degradation mechanism of diuron by ozonation were investigated. The factors that affect the degradation efficiency of diuron were examined. The generated inorganic ions and organic acids during the ozonation process were detected. Total organic carbon removal rate and the amount of the released Cl(-) increased with increasing ozonation time, but only 80.0% of the maximum theoretical concentration of Cl(-) at total mineralization was detected when initial diuron concentration was 13.8 mg L(-1). For N species, the final concentrations of NO3(-) and NH4+ after 60 min of reaction time were 0.28 and 0.19 mg L(-1), respectively. The generated acetic acid, formic acid and oxalic acid were detected during the reaction process. The main degradation pathway of diuron by ozonation involved a series of dechlorination-hydroxylation, dealkylation and oxidative opening of the aromatic ring processes, leading to small organic species and inorganic species. The degradation efficiency of diuron increased with decreasing initial diuron concentration. Higher pH value, more ozone dosage, additive Na2CO3, additive NaHCO3 and additive H2O2 were all advantageous to improve the degradation efficiency of diuron.     

Leaching of oryzalin and diuron through undisturbed vineyard soil columns under outdoor conditions

Field studies monitoring herbicide pollution in the vineyards of Burgundy (France) have revealed that drinking water reservoirs are contaminated with several pre-emergence herbicides. An assessment of the leaching of two such herbicides, diuron and oryzalin, was therefore performed using lysimeters, under outdoor conditions, from May 2001 to May 2002. Four vineyard soils from Vosne-Romanée (Burgundy) were chosen along a topolithosequence: a rendosol and three calcosols. After 673 mm of rainfall, greater amounts of diuron than oryzalin were measured in percolates: respectively 0.10-0.84% and 0.02-0.43% of applied herbicide, depending on soils. Measurements for diuron metabolites detected greater amounts of DCPMU than DCPU in the percolates: respectively 0.05-0.13% and 0-0.04% of the applied diuron. At the end of the monitoring period, more residues of diuron than oryzalin were recovered in the soil profiles: respectively 4.6-9% and 1.4-4.4%. The oryzalin residues were found mainly in the upper 10 cm of soil columns, whereas diuron residues were present in the whole core. The mobility of both oryzalin and diuron seems fairly well-related to soil organic carbon content; the mobility of diuron is also related to soil texture (sand and coarse material contents). Under such experimental conditions, this study confirms that diuron leaching, and therefore potential groundwater contamination, is greater than that of oryzalin.     

Degradation of some biorecalcitrant pesticides by homogeneous and heterogeneous photocatalytic ozonation

Photo-Fenton/ozone (PhFO) and TiO2-photocatalysis/ozone (PhCO) coupled systems are used as advanced oxidation processes for the degradation of the following biorecalcitrant pesticides: alachlor, atrazine, chlorfenvinfos, diuron, isoproturon and pentachlorophenol. These organic compounds are considered Priority Hazardous Substances by the Water Framework Directive of the European Commission. The degradation process of the different pesticides, that occurs through oxidation of the organic molecules by means of their reaction with generated OH radical, follows a first and zero-order kinetics, when PhFO and PhCO are applied, respectively. These two Advanced Oxidation Processes, together with the traditional ozone+UV, have been used to investigate TOC reduction of the different pesticide aqueous solutions. The best results of pesticide mineralization are obtained when PhFO is applied; with the use of this advanced oxidation process the aqueous pesticide solutions become detoxyfied except in the case of atrazine and alachlor aqueous solutions for which no detoxification is achieved at the experimental conditions used in the work, at least after 2 and 3 h of treatment, respectively.     

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 diuron in aqueous solution by ozonation

Degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in aqueous solution and the proposed degradation mechanism of diuron by ozonation were investigated. The factors that affect the degradation efficiency of diuron were examined. The generated inorganic ions and organic acids during the ozonation process were detected. Total organic carbon removal rate and the amount of the released Cl^? increased with increasing ozonation time, but only 80.0% of the maximum theoretical concentration of Cl^? at total mineralization was detected when initial diuron concentration was 13.8 mg L^?1. For N species, the final concentrations of NO₃ ^? and NH₄ ⁺ after 60 min of reaction time were 0.28 and 0.19 mg L^?1, respectively. The generated acetic acid, formic acid and oxalic acid were detected during the reaction process. The main degradation pathway of diuron by ozonation involved a series of dechlorination-hydroxylation, dealkylation and oxidative opening of the aromatic ring processes, leading to small organic species and inorganic species. The degradation efficiency of diuron increased with decreasing initial diuron concentration. Higher pH value, more ozone dosage, additive Na₂CO₃, additive NaHCO₃ and additive H₂O₂ were all advantageous to improve the degradation efficiency of diuron.     

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.     

Using iron-loaded sepiolite obtained by adsorption as a catalyst in the electro-Fenton oxidation of Reactive Black 5

This study explores the possibility of using iron-loaded sepiolite, obtained by recovering iron from polluted water, as a catalyst in the electro-Fenton oxidation of organic pollutants in textile effluents. The removal of iron ions from aqueous solution by adsorption on sepiolite was studied in batch tests at iron concentrations between 100 and 1,000 ppm. Electro-Fenton experiments were carried out in an electrochemical cell with a working volume of 0.15 L, an air flow of 1 L/min, and 3 g of iron-loaded sepiolite. An electric field was applied using a boron-doped diamond anode and a graphite sheet cathode connected to a direct current power supply with a constant potential drop. Reactive Black 5 (100 mg/L) was selected as the model dye. The adsorption isotherms proved the ability of the used adsorbent. The removal of the iron ion by adsorption on sepiolite was in the range of 80–100 % for the studied concentration range. The Langmuir and Freundlich isotherms were found to be applicable in terms of the relatively high regression values. Iron-loaded sepiolite could be used as an effective heterogeneous catalyst for the degradation of organic dyes in the electro-Fenton process. Successive batch processes were performed at optimal working conditions (5 V and pH 2). The results indicate the suitability of the proposed combined process, adsorption to iron remediation followed by the application of the obtained iron-loaded sepiolite to the electro-Fenton technique, to oxidize polluted effluents.     

Efficient removal of triphenylmethane dyes from aqueous medium by in situ electrogenerated Fenton's reagent at carbon-felt cathode

Fenton's reagent (Fe2+ +H2O2) has been electrogenerated in situ in an undivided electrolytic cell from the effective reduction of Fe3+ and O2 at carbon-felt cathode for the treatment of aqueous solutions of four triphenylmethane dyes (TPMs), namely malachite green (MG), crystal violet (CV), methyl green (MeG) and fast green FCF (FCF), at pH 3.0 and room temperature. MG has been used as a model among them to study the influence of some experimental parameters on the decay kinetics, COD removal and current efficiency. The results in such electro-Fenton system are explained in terms of the many parasitic reactions involving .OH. Higher efficiency values are obtained with rising organic content and decreasing applied current. The first stage of the mineralization process, involving aromatic by-products, leads to fast decoloration as well as quick initial COD removal that fit well to a pseudo-first-order kinetics. At prolonged electrolysis time, the mineralization rate and efficiency decrease due to the formation of hardly oxidizable compounds and the enhancement of wasting reactions. Solutions of all four TPMs are quickly degraded following a pseudo-first-order decay kinetics. The absolute rate constant (kTPM) for their reaction with .OH increases in the order MeG相似文献   

Assessment of metolachlor and diuron leaching in a tropical soil using undisturbed soil columns under laboratory conditions

In the present study, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-metoxi-1-methylethyl)acetamide] leaching was studied in undisturbed soil columns collected in a cotton crop area in Mato Grosso State, Brazil. The pesticides were applied to the soil surface in dosages similar to those used in a cotton plantation. To assess the leaching process, soil columns were submitted to simulated rain under laboratory conditions at 25 ± 3°C, in the absence of wind and direct solar radiation. During the rain simulations, leachate solutions were collected and herbicide concentrations were determined. At the end of the experiment, the soil columns were cut into 10 cm sections to determine the remaining herbicide concentrations through the soil profile. Metolachlor was detected in all soil sections, and approximately 4% of the applied mass was leached. Diuron was detected only in the upper two soil sections and was not detected in the leachate. A linear correlation (r > 0.94) between the metolachlor soil concentrations and the organic contents of the soil sections was observed. Mass balance suggests that around 56% of diuron and 40% of metolachlor were degraded during the experiments. Measurements of the water table depth in the area where the samples were collected showed that it varied from 2 to 6 m and is therefore vulnerable to contamination by the studied herbicides, particularly metolachlor, which demonstrated a higher leaching potential.     

Treatment of Basic Red 29 dye solution using iron-aluminum electrode pairs by electrocoagulation and electro-Fenton methods

The aim of this study is the treatment of Basic Red 29 (BR29) dye solution using hybrid iron-aluminum electrodes by electrocoagulation and electro-Fenton methods. The effect of current density, initial pH, supporting electrolyte, H₂O₂, and initial dye concentration on dye removal efficiency was investigated, and the best experimental conditions were obtained. Time-coarse variation of UV-Vis spectra and toxicity and chemical oxygen demand (COD) removal were also examined at the best experimental conditions. Both systems were found very successful for the removal of BR29 dye. The removal efficiency of >95 % for BR29 dye solution was reached easily in a short time. At the best experimental conditions, for the initial BR29 concentration of 100 mg/L, >95 % BR29 dye and 71.43 % COD removal were obtained after 20 and 40 min of electrolysis, respectively. Additionally, toxicity results for electro-Fenton treatment of 100 mg/L BR29 were also very promising. According to the results obtained, although electro-Fenton is more effective, both systems can be used successfully to treat textile wastewater including dyes.     

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 ⁺.     

Sodium dodecyl sulphate-enhanced desorption of atrazine: effect of surfactant concentration and of organic matter content of soils

A study was made of the adsorption-desorption of atrazine in aqueous medium in five soils with organic matter (OM) contents in the range 1.4-10.3% and also of the desorption of the herbicide in aqueous solutions of the anionic surfactant sodium dodecyl sulphate (SDS) at critical micelle concentrations (cmc) of 0.75, 1.50, 5 and 10. The adsorption and desorption isotherms in water together with the desorption isotherms in SDS solutions with concentrations of 0.75 and 1.50 cmc fit the Freundlich adsorption equation. All the desorption isotherms displayed hysteresis. The increase or reduction in hysteresis of the desorption isotherms in SDS solutions with respect to those of desorption in water depend on the SDS concentration and on the OM content of the soils. Below the cmc, SDS only increases the desorption of atrazine in the soil with the highest OM content (10.3%). However, above the cmc (5 and 10 cmc) the desorption of atrazine increases in all soils, the efficiency of desorption increasing with the OM content of the soils.