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ABSTRACT: The electrochemical incineration of omeprazole, a widely prescribed gastrointestinal drug which is detected in natural waters, has been studied in a phosphate buffer of pH 7.0 by anodic oxidation with electrogenerated H(2)O(2) (AO-H(2)O(2)) operating at constant current density (j). The experiments were carried out in a cell equipped with either a Pt or a boron-doped diamond (BDD) anode and an air-diffusion cathode to continuously produce H(2)O(2). In these systems, organics are mainly oxidized by hydroxyl radicals formed at the Pt or BDD surface from water oxidation. A partial total organic carbon (TOC) abatement close to 78% for omeprazole was achieved by AO-H(2)O(2) with a BDD anode after consumption of 18 Ah L(-1) at 100 mA cm(-2), whereas the alternative use of Pt did not allow mineralizing the drug. However, the drug was totally removed using both anodes, although it decayed more rapidly using BDD. In this latter system, increasing j accelerated the degradation process, but lowering the mineralization current efficiency. Greater drug content also enhanced the degradation rate with higher mineralization degree and current efficiency. The kinetics for omeprazole decay always followed a pseudo-first-order reaction and its rate constant increased with increasing j and with decreasing its concentration. Seven heteroaromatic intermediates and four hydroxylated derivatives were detected by LC-MS, while nine short-linear carboxylic acids were identified and quantified by ion-exclusion HPLC. These acids were largely accumulated using Pt and rapidly removed using BDD, thus explaining the partial mineralization of omeprazole achieved by AO-H(2)O(2) with the latter anode. The release of inorganic ions such as NO(3)(-), NH(4)(+) and SO(4)(2-) was followed by ionic chromatography. A plausible reaction sequence for omeprazole mineralization involving all intermediates detected is proposed.
Water Research 01/2013; · 4.86 Impact Factor
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ABSTRACT: The degradation of 100 mL of 244 mg L(-1) of the azo dye Acid Red 29 (AR29) has been studied by photoelectro-Fenton (PEF) using an undivided cell containing a boron-doped diamond (BDD) anode and an air-diffusion cathode under UVA irradiation. The effect of current density, concentration of catalytic Fe(2+) and pH on the process was examined. Quick decolorization and almost total mineralization were achieved due to the synergistic action of UVA light and oxidant hydroxyl radicals formed in the bulk from Fenton's reaction between electrogenerated H(2)O(2) at the cathode and added Fe(2+), as well as in the BDD surface from water oxidation. Optimum PEF conditions were found for 0.5-1.0 mM Fe(2+) and pH 3.0. Comparable electro-Fenton (EF) degradations in the dark yielded much poorer mineralization. The decay kinetics of AR29 followed a pseudo-first-order reaction with similar rate for EF and PEF. The azo dye disappeared much more rapidly than solution color, suggesting the formation of colored conjugated products with λ(max) similar to that of AR29. Ion-exclusion HPLC allowed the detection and quantification of tetrahydroxy-p-benzoquinone, oxalic, oxalacetic, tartronic, tartaric, oxamic, malonic and fumaric acids as intermediates in the PEF process. Oxalic acid, accumulated in large extent, was quickly destroyed by the efficient photolysis of Fe(III)-oxalate complexes with UVA light, whereas tartronic and oxamic acids were the most persistent byproducts because of the larger stability of their Fe(III) complexes. The mineralization of the initial N of the azo dye yielded NH(4)(+) ion and NO(3)(-) ion in smaller proportion.
Chemosphere 07/2012; 89(6):751-8. · 3.21 Impact Factor
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ABSTRACT: A central composite rotatable design and response surface methodology were used to optimize the experimental variables of the electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) degradations of 2.5L of sulfanilic acid solutions in 0.05M Na(2)SO(4). Electrolyses were performed with a pre-pilot flow plant containing a Pt/air diffusion reactor generating H(2)O(2). In SPEF, it was coupled with a solar photoreactor under an UV irradiation intensity of ca. 31Wm(-2). Optimum variables of 100mAcm(-2), 0.5mM Fe(2+) and pH 4.0 were determined after 240min of EF and 120min of SPEF. Under these conditions, EF gave 47% of mineralization, whereas SPEF was much more powerful yielding 76% mineralization with 275kWh kg(-1) total organic carbon (TOC) energy consumption and 52% current efficiency. Sulfanilic acid decayed at similar rate in both treatments following a pseudo-first-order kinetics. The final solution treated by EF contained a stable mixture of tartaric, acetic, oxalic and oxamic acids, which form Fe(III) complexes that are not attacked by hydroxyl radicals formed from H(2)O(2) and added Fe(2+). The quick photolysis of these complexes by UV light of sunlight explains the higher oxidation power of SPEF. NH(4)(+) was the main inorganic nitrogen ion released in both processes.
Journal of hazardous materials 04/2012; 221-222:288-97. · 4.14 Impact Factor
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ABSTRACT: The mineralization of flumequine, an antimicrobial agent belonging to the first generation of synthetic fluoroquinolones which is detected in natural waters, has been studied by electrochemical advanced oxidation processes (EAOPs) like electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. The experiments were performed in a cell containing a boron-doped diamond (BDD) anode and an air-diffusion cathode to generate H(2)O(2) at constant current. The Fe(2+) ion added to the medium increased the solubility of the drug by the formation of a complex of intense orange colour and also reacted with electrogenerated H(2)O(2) to form hydroxyl radical from Fenton reaction. Oxidant hydroxyl radicals at the BDD surface were produced from water oxidation. A partial mineralization of flumequine in a solution near to saturation with optimum 2.0mM Fe(2+) at pH 3.0 was achieved by EF. The PEF process was more powerful, giving an almost total mineralization with 94-96% total organic carbon removal. Increasing current accelerated both treatments, but with decreasing mineralization current efficiency. Comparative treatments using a real wastewater matrix led to similar degradation degrees. The kinetics for flumequine decay always followed a pseudo-first-order reaction and its rate constant, similar for both EAOPs, raised with increasing current. Generated carboxylic acids like malonic, formic, oxalic and oxamic acids were quantified by ion-exclusion HPLC. Fe(III)-oxalate and Fe(III)-oxamate complexes were the most persistent by-products under EF conditions and their quicker photolysis by UVA light explains the higher oxidation power of PEF. The release of inorganic ions such as F(-), NO(3)(-) and in lesser extent NH(4)(+) was followed by ionic chromatography.
Water Research 02/2012; 46(7):2067-76. · 4.86 Impact Factor
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ABSTRACT: A central composite rotatable design and response surface methodology (RSM) were used to optimize the experimental variables of the solar photoelectro-Fenton (SPEF) treatment of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA). The experiments were made with a flow plant containing a Pt/air-diffusion reactor coupled to a solar compound parabolic collector (CPC) under recirculation of 10 L of 186 mg L(-1) MCPA solutions in 0.05 M Na(2)SO(4) at a liquid flow rate of 180 L h(-1) with an average UV irradiation intensity of about 32 Wm(-2). The optimum variables found for the SPEF process were 5.0 A, 1.0mM Fe(2+) and pH 3.0 after 120 min of electrolysis. Under these conditions, 75% of mineralization with 71% of current efficiency and 87.7 k Wh kg(-1) TOC of energy consumption were obtained. MCPA decayed under the attack of generated hydroxyl radicals following a pseudo-first-order kinetics. Hydroxyl radicals also destroyed 4-chloro-2-methylphenol, methylhydroquinone and methyl-p-benzoquinone detected as aromatic by-products. Glycolic, maleic, fumaric, malic, succinic, tartronic, oxalic and formic acids were identified as generated carboxylic acids, which form Fe(III) complexes that are quickly photodecarboxylated by the UV irradiation of sunlight at the CPC photoreactor. A reaction sequence for the SPEF degradation of MCPA was proposed.
Journal of hazardous materials 08/2011; 194:109-18. · 4.14 Impact Factor
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ABSTRACT: Oxalic and oxamic acids are the ultimate and more persistent by-products of the degradation of N-aromatics by electrochemical advanced oxidation processes (EAOPs). In this paper, the kinetics and oxidative paths of these acids have been studied for several EAOPs using a boron-doped diamond (BDD) anode and a stainless steel or an air-diffusion cathode. Anodic oxidation (AO-BDD) in the presence of Fe(2+) (AO-BDD-Fe(2+)) and under UVA irradiation (AO-BDD-Fe(2+)-UVA), along with electro-Fenton (EF-BDD), was tested. The oxidation of both acids and their iron complexes on BDD was clarified by cyclic voltammetry. AO-BDD allowed the overall mineralization of oxalic acid, but oxamic acid was removed much more slowly. Each acid underwent a similar decay in AO-BDD-Fe(2+) and EF-BDD, as expected if its iron complexes were not attacked by hydroxyl radicals in the bulk. The faster and total mineralization of both acids was achieved in AO-BDD-Fe(2+)-UVA due to the high photoactivity of their Fe(III) complexes that were continuously regenerated by oxidation of their Fe(II) complexes. Oxamic acid always released a larger proportion of NH(4)(+) than NO(3)(-) ion, as well as volatile NO(x) species. Both acids were independently oxidized at the anode in AO-BDD, but in AO-BDD-Fe(2+)-UVA oxamic acid was more slowly degraded as its content decreased, without significant effect on oxalic acid decay. The increase in current density enhanced the oxidation power of the latter method, with loss of efficiency. High Fe(2+) contents inhibited the oxidation of Fe(II) complexes by the competitive oxidation of Fe(2+) to Fe(3+). Low current densities and Fe(2+) contents are preferable to remove more efficiently these acids by the most potent AO-BDD-Fe(2+)-UVA method.
Water Research 04/2011; 45(9):2975-84. · 4.86 Impact Factor
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ABSTRACT: The degradation of diclofenac, a common non-steroidal anti-inflammatory drug, in aqueous medium has been studied by anodic oxidation (AO) using an undivided cell with a Pt or boron-doped diamond (BDD) anode. Operating without pH regulation, AO with Pt acidifies the solution with precipitation of its protonated form, whereas using BDD, the solution becomes alkaline and only attains partial mineralization. Total incineration of low contents of the drug is feasible by AO with BDD in a neutral buffer medium of pH 6.5. Comparative treatment with Pt gives poor decontamination. The diclofenac decay always follows a pseudo first-order reaction. The increase in current for AO with BDD accelerates the degradative process, but decreases its efficiency. 2-Hydroxyphenylacetic acid, 2,5-dihydroxyphenylacetic acid, 2,6-dichloroaniline and 2,6-dichlorohydroquinone have been identified as aromatic intermediates. For AO with Pt, high amounts of malic, succinic, tartaric and oxalic acids are accumulated in the bulk and the N-derivatives produced are rapidly destroyed with loss of NH4+. When BDD is employed, some carboxylic acids are also accumulated in small extent, with a larger persistence of oxalic and oxamic acids. The process involves the formation of different N-derivatives that slowly release NH4+ and NO3(-) ions. Chloride ion is lost in all cases.
Chemosphere 03/2010; 79(6):605-12. · 3.21 Impact Factor
