Ann T. Lemley

Oxidation of diazinon by anodic Fenton treatment

Anodic Fenton treatment (AFT) is a new technology that has several advantages over classic Fenton treatment and electrochemical Fenton treatment. The oxidation of diazinon by AFT using different electrolytes has been investigated. NaCl, KCl and Na2SO4 show similar effects on the extent and rate of oxidation, and the data can be fitted quite well by the AFT kinetics model. Use of NaNO3 as the electrolyte causes low-efficiency electrolysis and a subsequent low oxidation rate for diazinon. The NaCl concentration level in the anodic half-cell and the concentration ratio between the two half-cells is optimized at 0.04M and 4:1 (cathodic/anodic), respectively. The activation energy of diazinon oxidation by anodic Fenton treatment is estimated to be 12.6 +/- 0.6 kJ mol(-1), which is less than half of that for aqueous chlorine treatment. Diazoxon is the intermediary oxidation product. The oxidation of diazinon as a formulated product has also been investigated. Its dissipation kinetics can also be fitted quite well by the AFT model. Compared with the oxidation of pure diazinon, the oxidation rate of formulated diazinon is much lower, an indication that many formulation ingredients compete with diazinon for reaction with the hydroxyl radical.

Oxidative degradation and detoxification of aqueous carbofuran by membrane anodic Fenton treatment.

Anodic Fenton treatment (AFT), a new Fenton technology for the treatment of pesticide wastewater, has been reported previously. The substitution of an ion exchange membrane for the salt-bridge, an improvement to the practicality of the AFT without sacrificing treatment efficiency, has also been reported. The oxidative degradation by membrane AFT of carbofuran, a heavily used and toxic carbamate insecticide, was investigated in this study. The results show that the degradation kinetics of carbofuran with different initial concentrations obeys the AFT model, and the treatment efficiency increases with increasing initial concentration. Raising the treatment temperature can result in enhanced degradation of carbofuran in solution. The pseudo-activation energy of carbofuran by membrane AFT was estimated to be 7.66 kJ mol(-1). The results also show that AFT treatment can effectively remove COD and dramatically improve the biodegradability of carbofuran in solution. GC/MS analysis found four degradation products, revealing that the carbamate branch and 3-C in the furan ring are the first and second attack targets of hydroxyl radicals. As shown by the toxicity assay, the fatal toxicity of carbofuran to earthworms can be totally removed. The degradation of carbofuran by AFT is also a detoxification process.

Kinetics and mechanism of carbamazepine degradation by a modified Fenton-like reaction with ferric-nitrilotriacetate complexes

This study investigated the kinetics and mechanism of carbamazepine (CBZ) degradation over an initial pH range of 5.0-9.0 by a modified Fenton-like reaction using ferric-nitrilotriacetate (Fe(III)-NTA) complexes. The results indicate that CBZ degradation by Fe(III)-NTA/H2O2 can be described by pseudo first-order kinetics and mainly attributed to hydroxyl radical (OH) attack. Ten intermediates were identified during the degradation process, including hydroxy-CBZs, 10,11-epoxy-CBZ, quinonid CBZ derivatives, dihydroxy-CBZs, and hydroxy-CBZ-10,11-diols. The steady-state concentration of OH, ranging from 3.8 × 10(-16) to 2.1 × 10(-13)M, was strongly dependent on the concentration of Fe(III), the initial pH, and H2O2:Fe(III) and NTA:Fe(III) molar ratios. Optimal conditions of [Fe(III)]=1 × 10(-4)M, [H2O2:Fe(III)]=155:1 and [NTA:Fe(III)]=3:1 were obtained for the degradation of CBZ at neutral pH (7.0) and ambient temperature (25 °C); the corresponding degradation rate constant of CBZ, kapp, was 0.0419 (± 0.002) min(-1). The value of kapp increased with increasing pH from 5.0 to 9.0 due to the strong pH-dependence of Fe(III)-NTA complexes; Fe(III)(NTA)(OH)2(2-) was the most likely active iron species to activate H2O2 to produce OH. The temperature dependence of CBZ degradation by Fe(III)-NTA/H2O2 was characterized by an activation energy of 76.16 kJ mol(-1). A potential mechanism for the formation of OH by Fe(III)-NTA/H2O2 and possible degradation pathways of CBZ are proposed.

Analysis of methyl tert.-butyl ether and its degradation products by direct aqueous injection onto gas chromatography with mass spectrometry or flame ionization detection systems.

A method was developed to analyze methyl tert.-butyl ether (MTBE) and its degradation products by gas chromatography with mass spectrometry (GC-MS) or flame ionization detection (FID) with direct aqueous injection. The column had dimensions of 30 m x 0.25 mm with film thickness 0.25 microm and a stationary phase of FFAP (nitroterephthalic acid-modified polyethylene glycol). The optimized GC conditions for non-acid components were as follows: carrier gas flow-rate,l mL/min; oven temperature, 35 degrees C for 5.5 min, ramped to 90 degrees C at 25 degrees C/min, then ramped to 200 degrees C at 40 degrees C/min and held at 200 degrees C for 8 min. The conditions for the acid components were: carrier gas flow-rate, 1 mL/min; oven temperature, 110 degrees C for 2 min, ramped to 150 degrees C at 10 degrees C/min, then ramped to 200 degrees C at 40 degrees C/min. The injection port contained a silanized-glass reverse-cup liner filled with Carbofrit. The minimum concentrations for the linear range for the selective ion monitoring mode were 30 to 100 microg/L, depending on the analytes. The minimum detection limit was 1 mg/L for MTBE and tert.-butanol when using FID. More components could be analyzed with the FFAP-type column than with the cyanopropylphenyl-dimethyl polysiloxane-type column.

Degradation of sulfonamides in aqueous solution by membrane anodic fenton treatment.

Two agricultural antibiotics used heavily in agriculture, sulfamethazine and sulfadiazine, were degraded in an aqueous system by anodic Fenton treatment (AFT), an advanced oxidation technique that has been shown to be effective in degrading various pesticides but has not been applied to antibiotics. The effects of the H(2)O(2)/Fe(2+) ratio, Fe(2+) delivery rate, and initial contaminant concentration on the degradation of sulfamethazine by AFT were determined. The optimal H(2)O(2)/Fe(2+) ratio was determined to be 10:1, and the optimal Fe(2+) delivery rate was found to be between 38.9 and 54.4 microM min(-1). Under these conditions, sulfamethazine was completely degraded within 10 min at a range of concentrations (18-250 microM) commonly found in manure lagoons, contaminated rivers, and groundwater. Using the same optimal conditions, the effect of pH on the degradation of sulfadiazine by AFT was analyzed, and 100 microM sulfadiazine was degraded within 6-8 min of treatment at a range of pH values (3.1-7.1) that could potentially be found in aquatic environments. Degradation products and pathways were proposed for both compounds, and it was inferred that AFT degradation products of sulfadiazine and sulfamethazine are unlikely to retain the bacteriostatic properties of their parent compounds. An aquatic toxicity test employing Lemna gibba confirmed that AFT removes the bacteriostatic properties of sulfamethazine and sulfadiazine during degradation.

Atrazine degradation by anodic Fenton treatment

Anodic Fenton treatment (AFT), an hydroxyl radical oxidation process recently developed for the degradation of aqueous pesticide waste, was applied to the degradation of atrazine, seven degradation products, and a formulated atrazine product. Using AFT, degradation of the parent compound occurred in 3 min. The concentration profiles of seven degradation products formed during treatment were measured, and degradation pathways are proposed for the treatment. The primary termination product after 10 min was dechlorinated ammeline. Three different 14C labeled atrazine compounds (ethyl, isopropyl and U-triazine ring labeled atrazine) were also treated in an air-tight AFT apparatus and the mass balance was calculated. The triazine ring was not cleaved during this treatment process. Formulated atrazine was 70% degraded in 3 min. AFT holds promise as an effective pesticide-laden water treatment technology.

Gas chromatographic–mass spectrometric determination of alachlor and its degradation products by direct aqueous injection

Abstract A GC–MS method, with direct aqueous injection, has been developed to determine alachlor and its degradation products in water. The method was optimized to give the following conditions: injection with splitless mode, injection port with silanized-glass reverse-cup liner filled with 0.5 cm Carbofrit above the cup; injection temperature of 250°C; and an analytical column with a stationary phase of 5% diphenyl and 95% dimethyl polysiloxane and dimensions of 60 m×0.25 mm×0.25 μm. The minimum detection limit is 0.05 to 1 mg/l in the GC–MS-SIM mode with variation of peak height less than 5% and 5 to 50 mg/l in the GC–MS-Scan mode for alachlor and its degradation products.

Treatment of two insecticides in an electrochemical Fenton system

The ability of an electrochemical Fenton system to degrade the organophosphorous insecticides malathion and methyl parathion was studied. A combination of hydrogen peroxide and electrochemically-generated iron was found to be successful in degrading the two insecticides, and optimization of the system was pursued. Augmentation with near UV light at an intensity of 1.67 x 10(17) quanta/sec and centered at a wavelength of 370 nm improved the degradation of malathion at low iron concentrations but did not affect other treatments. Adding the hydrogen peroxide slowly over the course of treatment rather than all at once at the beginning of each treatment did, however, greatly improve the system. Removal efficiencies of 98.0% or greater were achieved for both pesticides.

Species-Dependent Degradation of Ciprofloxacin in a Membrane Anodic Fenton System

The anodic Fenton treatment method (AFT) has been successfully applied to the removal of ciprofloxacin (CIP), a widely used fluoroquinolone antibiotic, from aqueous solution. Degradation kinetics were found to be species dependent. At initial pH 3.2, CIP remained in its cationic form and the kinetics followed a previously developed AFT model. At an initial near-neutral pH, CIP speciation changed during the degradation, due to pH changes over the process, and no obvious model fit the data. Density functional theory (DFT) calculations indicated a protonated species-dependent reaction affinity toward hydroxyl radicals. A new model based on the AFT model with the addition of species distribution during the degradation was derived, and it was shown to describe the degradation kinetics successfully. Degradation of reference compounds further confirmed that the free carboxylic acid group, which contributes to the species changes, plays a key role in the observed degradation pattern. Furthermore, degradation of reference CIP-metal complexes confirmed that the formation of these complexes does not have a major effect on the degradation pattern. Optimization of CIP degradation was carried out at pH 3.2 with an optimal H2O2/Fe2+ ratio found between 10:1 and 15:1. Three degradation pathways based on mass spectrometry data were also proposed: (1) hydroxylation and defluorination on the aromatic ring; (2) oxidative decarboxylation; and (3) oxidation on the piperazine ring and dealkylation. By the end of the AFT treatment, neither CIP nor its degradation products were detected, indicating successful removal of antibacterial properties.

Electrochemical treatment of acid dye systems: Sodium meta‐bisulfite addition to the andco system

Abstract Electrochemical treatment was shown to be successful in removing from solution two acid dyes used in the carpet industry. The Andco Environmental Processes laboratory scale iron electrode system was shown to decolorize solutions of Acid Red 337 (azo) and Acid Blue 40 (anthraquinone). High performance liquid chromatography (HPLC) with diode‐array detection was used to quantify dye removal and provide qualitative information about degradation products. Both degradation and adsorption contribute to removal of Acid Red 337; adsorption appears to be the primary mechanism responsible for removal of Acid Blue 40. Addition of sodium meta‐bisulfite to the Andco system was shown to enhance removal of both dyes. It is postulated that the dithionite and/or sulfoxylate radical anion that may be formed during the reduction of bisulfite is responsible for the more efficient cleavage of the azo linkage in Acid Red 337, causing further degradation. The mechanism for enhanced removal of Acid Blue 40 by addition of...