Elimination of pharmaceutical pollutants by solar photoelectro-Fenton process in a pilot plant.

In this study, the simultaneous degradation of antibiotics (ampicillin, sulfamethazine, and tetracycline; and non-steroidal anti-inflammatories (diclofenac and salicylic acid)) including the total organic carbon abatement by solar photoelectro-Fenton process was assessed. Eight liters of solution containing the mixture of the five pharmaceuticals in 1 mmol L-1 Fe2+, 0.05 mol L-1 Na2SO4 at pH 3 and 35 °C were electrolyzed applying different current densities (j = 10, 25, and 50 mA cm-2) in a solar-electrochemical pilot plant. The pilot plant was equipped with an electrochemical filter press cell with a dimensionally stable anode (DSA type) and an air-diffusion cathode coupled to a solar photoreactor exposed directly to sunlight radiation. All pharmaceuticals were degraded during the first 10 min. A TOC removal efficiency of 99.2% after 100 min of treatment with an energy consumption of 534.23 kW h (kgTOC)-1 and 7.15 kW h m-3 was achieved. The pharmaceutical concentration decay followed a pseudo-first-order kinetics. The specific energy per unit of mass of ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline was obtained at 11.73, 19.56, 35.2, 11.73, and 39.32 kW h (kgPD)-1 for ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline, respectively. With our results, we demonstrated that SPEF is an emerging technology for the treatment of this type of pollutants in short time.

Removal of Orange II (OII) dye by simulated solar photoelectro-Fenton and stability of WO2.72/Vulcan XC72 gas diffusion electrode.

The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm-2 and SSPEF at 150 mA cm-2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H2O2 had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H2O2 < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm-2) showed the best performance-mineralization current efficiency.

Influence of electrolysis conditions on the treatment of herbicide bentazon using artificial UVA radiation and sunlight. Identification of oxidation products.

The main objective of this work is to demonstrate the viability of solar photoelectro-Fenton (SPEF) process to degrade pesticides in urban wastewater matrix, selecting the herbicide bentazon as a model molecule. In order to provide a correct assessment of the role of the different oxidants and catalysts involved, bentazon was comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA-assisted EF (i.e., PEF) processes as well, either in sulfate or chloride media. Trials were made in a stirred tank reactor with an air-diffusion cathode and a boron-doped diamond (BDD), RuO2-based or Pt anode. In chlorinated matrices, the herbicide disappeared more rapidly using a RuO2-based anode because of the generated active chlorine. The best mineralization performance was always obtained using BDD due to its higher oxidation power, which allowed the complete destruction of refractory chloroderivatives. A concentration of 0.50 mM Fe2+ was found optimal to catalyze Fenton's reaction, largely enhancing the mineralization process under the action of OH. Among photo-assisted treatments, sunlight was proven superior to a UVA lamp to promote the photolysis of intermediates, owing to its greater UV irradiance and contribution of visible photons, although PEF also allowed achieving a large mineralization. In all cases, bentazon decay obeyed a pseudo-first-order kinetics. SPEF treatment in urban wastewater using BDD at only 16.6 mA cm-2 yielded 63.2% mineralization. A thorough, original reaction pathway for bentazon degradation is proposed, including seven non-chlorinated aromatics, sixteen chloroaromatics and two chloroaliphatics identified by GC-MS, most of them not previously reported in literature. Ion-exclusion HPLC allowed the detection of seven short-chain linear carboxylic acids.

Total mineralization of mixtures of Tartrazine, Ponceau SS and Direct Blue 71 azo dyes by solar photoelectro-Fenton in pre-pilot plant.

Mixtures of monoazo Tartrazine, diazo Ponceau SS and triazo Direct Blue 71 dyes with 105 mg L-1 of total organic carbon (TOC) in 0.050 M Na2SO4 at pH 3.0 have been treated by solar photoelectro-Fenton (SPEF). Experiments were carried out in a 2.5 L pre-pilot plant with a Pt/air-diffusion cell coupled to a solar planar photoreactor. Comparative trials were made by anodic oxidation with electrogenerated H2O2 (AO-H2O2) and electro-Fenton (EF) to better understand the role of oxidizing agents. AO-H2O2 gave poor degradation due to the low oxidation ability of OH formed at the Pt anode and H2O2 produced at the cathode. Similar color removal was achieved in EF and SPEF because the main oxidant was OH formed in the bulk from Fenton's reaction. EF yielded partial mineralization by formation of molecules with high stability against OH. In contrast, these by-products were rapidly photolyzed under sunlight irradiation in SPEF, which was the most powerful treatment. Up to 8 linear final carboxylic acids were detected, along with the release of sulfate and ammonium ions. The effect of Fe2+ and azo dye concentrations, and current density over the SPEF performance was assessed. Total mineralization of azo dyes mixtures occurred when operating up to 105 mg L-1 TOC with 0.50 mM Fe2+ at 100 mA cm-2.

Abatement of the antibiotic levofloxacin in a solar photoelectro-Fenton flow plant: Modeling the dissolved organic carbon concentration-time relationship.

The degradation of solutions of the antibiotic levofloxacin (LVN) in sulfate medium at pH 3.0 has been investigated at pre-pilot scale by solar photoelectro-Fenton (SPEF) process. The flow plant included an FM01-LC filter-press cell equipped with a Ti|Pt anode and a three-dimensional-like air-diffusion cathode, connected to a compound parabolic collector as photoreactor and a continuous stirred tank under recirculation batch mode. The effect of volumetric flow rate on H2O2 electrogeneration from O2 reduction was assessed. Then, the influence of initial LVN concentration and Fe2+ concentration as catalyst on dissolved organic carbon (DOC) removal was thoroughly investigated. LVN was gradually mineralized by SPEF process, with faster DOC abatement at 0.50 mM Fe2+, yielding 100% after 360 min at applied cathodic potential of -0.30 V|SHE. The high mineralization current efficiency (MCE) and low specific energy consumption (ECDOC) revealed the extraordinary role of homogeneous hydroxyl radicals and natural UV light, which allowed the degradation of the antibiotic and its by-products with MCE values greater than 100%. Five cyclic by-products, N,N-diethylformamide and three short-chain linear carboxylic acids were detected by GC-MS and HPLC analyses. A parametric model to simulate the DOC decay versus electrolysis time was implemented for the SPEF pre-pilot flow plant, showing good agreement with experimental data.

Electrochemical advanced oxidation processes as decentralized water treatment technologies to remediate domestic washing machine effluents.

Water scarcity is one of the major concerns worldwide. In order to secure this appreciated natural resource, management and development of water treatment technologies are mandatory. One feasible alternative is the consideration of water recycling/reuse at the household scale. Here, the treatment of actual washing machine effluent by electrochemical advanced oxidation processes was considered. Electrochemical oxidation and electro-Fenton technologies can be applied as decentralized small-scale water treatment devices. Therefore, efficient decolorization and total organic abatement have been followed. The results demonstrate the promising performance of solar photoelectro-Fenton process, where complete color and organic removal was attained after 240 min of treatment under optimum conditions by applying a current density of 66.6 mA cm-2. Thus, electrochemical technologies emerge as promising water-sustainable approaches.

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