Assessment of photo electro-Fenton and solar photo electro-Fenton processes for the efficient degradation of asulam herbicide.

The degradation of asulam herbicide by photo electro-Fenton (PEF) and solar photo electro-Fenton (SPEF) processes was studied using an undivided electrochemical BDD/carbon-felt cell to generate H2O2 continuously. A central composite design combined with response surface methodology was applied to determine the optimal operating conditions of current intensity = 0.30 A, [Fe2+] = 0.3 mM, and [Na2SO4] = 0.11 M at pH 3 to achieve the complete degradation of asulam by electro-Fenton. Subsequently, the SPEF process was more efficient treatment compared to PEF, achieving a complete degradation of asulam and 98% of mineralization in 180 min. Moreover, 4-aminobenzenesulfonamide, 4-aminophenol, and 4-benzoquinone were detected as aromatic intermediates, whereas acetic acid, oxalic acid, and NO3- ions were identified as final degradation by-products. Thus, the SPEF process is an efficient alternative for the complete degradation and mineralization of herbicide asulam in an aqueous solution under natural sunlight.

Degradation of anti-inflammatory drugs in municipal wastewater by heterogeneous photocatalysis and electro-Fenton process.

Non-steroidal anti-inflammatory drugs (NSAID) are compounds frequently found in municipal wastewater and their degradation by conventional wastewater treatment plants (WWTP) is generally incomplete. This study compared the efficiency of two advanced oxidation processes (AOP), namely heterogeneous photocatalysis (HP) and electro-Fenton (EF), in the degradation of a mixture of common NSAID (diclofenac, ibuprofen and naproxen) dissolved in either deionized water or effluent from a WWTP. Both processes were effective in degrading the NSAID mixture and the trend of degradation was as follows, diclofenac > naproxen > ibuprofen. EF with a current density of 40 mA cm-2 and 0.3 mmol Fe2+ L-1 was the most efficient process to mineralize the organic compounds, achieving up to 92% TOC removal in deionized water and 90% in the WWTP effluent after 3 h of reaction. HP with 1.4 g TiO2 L-1 at pH 7 under sunlight, produced 85% TOC removal in deionized water and 39% in WWTP effluent also after 3 h treatment. The lower TOC removal efficiency shown by HP with the WWTP effluent was attributed mainly to the scavenging of reactive species by background organic matter in the wastewater. On the contrary, inorganic ions in the wastewater may produce oxidazing species during the EF process, which contributes to a higher degradation efficiency. EF is a promising option for the treatment of anti-inflammatory pharmaceuticals in municipal WWTP at competitive electrical energy efficiencies.

Optimization of solid-phase extraction of parabens and benzophenones in water samples using a combination of Plakett-Burman and Box-Behnken designs.

An automated method for the analysis of methylparaben, propylparaben, benzophenone-3, and benzophenone-4 in water effluents via on-line solid-phase extraction coupled with high-performance liquid chromatography/ultraviolet detection was proposed. The preconcentration parameters were studied using Plackett-Burman and Box-Behnken experimental designs using a C18 sorbent material. The results demonstrated that the eluent volume, composition, and sorbent amount were statistically significant. Optimal conditions for these variables were an eluent volume of 1.55 mL, eluent composition of acetonitrile 100% v/v, and sorbent amount of 100 mg. The eluted sample was analyzed on-line using high-performance liquid chromatography equipped with a reversed-phase C18 column and ultraviolet detection. Separation of the analytes was achieved in 15 min using gradient elution with acetonitrile/water. A simple, sensitive, and rapid analytical method was proposed for personal care compounds without sophisticated or expensive equipment. The limits of detection were 1.20, 1.73, 2.51, and 4.67 µg/L for propylparaben, methylparaben, benzophenone-3, and benzophenone-4, respectively. The analysis time was 48 min, consuming only 1.59 mL of eluent acetonitrile for the solid phase extraction step, with minimal sample handling. The method was applied to the analysis of spiked swimming pool and wastewater, with recoveries between 65-107%. These results indicate the reliability of the flow-based procedure.

Advanced oxidation of real sulfamethoxazole + trimethoprim formulations using different anodes and electrolytes.

A commercial sulfamethoxazole + trimethoprim formulation has been degraded in 0.050 M Na2SO4 at pH 3.0 by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF), photoelectro-Fenton with a 6-W UVA lamp (PEF) and solar photoelectro-Fenton (SPEF). The tests were performed in an undivided cell with an IrO2-based, Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 electrogeneration. The anode material had little effect on the accumulated H2O2 concentration. Both drugs always obeyed a pseudo-first-order decay with low apparent rate constant in EO-H2O2. Much higher values were found in EF, PEF and SPEF, showing no difference because the main oxidant was always OH formed from Fenton's reaction between H2O2 and added Fe2+. The solution mineralization increased in the sequence EO-H2O2 < EF < PEF < SPEF regardless of the anode. The IrO2-based and Pt anodes behaved similarly but BDD was always more powerful. In SPEF, similar mineralization profiles were found for all anodes because of the rapid removal of photoactive intermediates by sunlight. About 87% mineralization was obtained as maximum for the powerful SPEF with BDD anode. Addition of Cl- enhanced the decay of both drugs due to their quicker reaction with generated active chlorine, but the formation of persistent chloroderivatives decelerated the mineralization process. Final carboxylic acids like oxalic and oxamic were detected, yielding Fe(III) complexes that remained stable in EF with BDD but were rapidly photolyzed in SPEF with BDD, explaining its superior mineralization ability.

Salicylic acid degradation by advanced oxidation processes. Coupling of solar photoelectro-Fenton and solar heterogeneous photocatalysis.

A 3.0 L solar flow plant with a Pt/air-diffusion (anode/cathode) cell, a solar photoreactor and a photocatalytic photoreactor filled with TiO2-coated glass spheres has been utilized to couple solar photoelectro-Fenton (SPEF) and solar heterogeneous photocatalysis (SPC) for treating a 165mgL(-1) salicylic acid solution of pH 3.0. Organics were destroyed by OH radicals formed on the TiO2 photocatalyst and at the Pt anode during water oxidation and in the bulk from Fenton's reaction between added Fe(2+) and cathodically generated H2O2, along with the photolytic action of sunlight. Poor salicylic acid removal and mineralization were attained using SPC, anodic oxidation with electrogenerated H2O2 (AO-H2O2) and coupled AO-H2O2-SPC. The electro-Fenton process accelerated the substrate decay, but with low mineralization by the formation of byproducts that are hardly destroyed by OH. The mineralization was strongly increased by SPEF due to the photolysis of products by sunlight, being enhanced by coupled SPEF-SPC due to the additional oxidation by OH at the TiO2 surface. The effect of current density on the performance of both processes was examined. The most potent SPEF-SPC process at 150mAcm(-2) yielded 87% mineralization and 13% current efficiency after consuming 6.0AhL(-1). Maleic, fumaric and oxalic acids detected as final carboxylic acids were completely removed by SPEF and SPEF-SPC.

Coupling of solar photoelectro-Fenton with a BDD anode and solar heterogeneous photocatalysis for the mineralization of the herbicide atrazine.

Here, the synergetic effect of coupling solar photoelectro-Fenton (SPEF) and solar heterogeneous photocatalysis (SPC) on the mineralization of 200mL of a 20mg L(-1) atrazine solution, prepared from the commercial herbicide Gesaprim, at pH 3.0 was studied. Uniform, homogeneous and adherent anatase-TiO2 films onto glass spheres of 5mm diameter were prepared by the sol-gel dip-coating method and used as catalyst for SPC. However, this procedure yielded a poor removal of the substrate because of the low oxidation ability of positive holes and OH formed at the catalyst surface to destroy it. Atrazine decay was improved using anodic oxidation (AO), electro-Fenton (EF), SPEF and coupled SPEF-SPC at 100mA. The electrolytic cell contained a boron-doped diamond (BDD) anode and H2O2 was generated at a BDD cathode fed with an air flow. The removal and mineralization of atrazine increased when more oxidizing agents were generated in the sequence AO