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

Use of Pt and boron-doped diamond anodes in the electrochemical advanced oxidation of Ponceau SS diazo dye in acidic sulfate medium

The electrochemical degradation of 2.5 L of solutions of Ponceau SS diazo dye in acidic sulfate medium has been studied in a pre-pilot flow plant with a BDD/air-diffusion or Pt/air-diffusion cell connected to an annular photoreactor. The decolorization and mineralization was enhanced in the order: electrochemical oxidation with electrogenerated H2O2 < electro-Fenton < photoelectro-Fenton. The two former methods performed better with the BDD anode, whereas the latter one yielded similar results for both anodes. From this, the use of less expensive active anodes like Ti|Pt instead of non-active BDD for photo-assisted Fenton-based electrochemical processes is recommended. In all methods, increasing current density led to greater degradation rate, but with lower mineralization current efficiency and higher energy consumption. Five primary aromatic products and four final carboxylic acids were detected, along with recalcitrant products poorly removed by hydroxyl radicals and UVA radiation

A ceramic electrode of ZrO2-Y2O3 for the generation of oxidant species in anodic oxidation. Assessment of the treatment of Acid Blue 29 dye in sulfate and chloride media

A micron-sized powder of 7% mol Y2O3 stabilized ZrO2 (YSZ) was used to deposit a ceramic coating onto Ti substrate by atmospheric plasma spray. The novel YSZ ceramic presented a dense structure with cubic crystalline structure. The as-synthesized YSZ ceramic as stable anode, coupled to a stainless-steel cathode, was assessed for the anodic oxidation of Acid Blue 29 diazo dye solutions in sulfate and chloride media. The decolorization of these solutions in acidic conditions was clearly faster with chloride as electrolyte, since the generated active chlorine HClO from anodic oxidation of Clwas more powerful oxidant than ¿OH formed from water discharge at the 7YSZ surface in sulfate medium. In alkaline conditions, the loss of color was drastically reduced because of the conversion of HClO into the weaker oxidant ClO, as well as the loss of oxidation power of ¿OH, partially compensated by the increasing oxidation ability of SO4¿formed from anodic oxidation of SO42ion. The effect of other experimental variables such as current density, as well as the concentration of each electrolyte and the dye, was examined. The best experimental conditions at pH 7.0 were found for 0.050 M of electrolyte at 20 and 10 mA cm-2 using sulfate and chloride media, respectively. In contrast, lower mineralization was achieved in chloride medium because of the formation of very recalcitrant and persistent chloro-derivatives that decelerated the mineralization process. In sulfate medium, NH4+, NO3and, to much lesser extent, NO2ions were released during mineralization, whereas tartaric, maleic, acetic and oxalic acids remained in the final solution

Photoelectro-Fenton treatment of pesticide triclopyr at neutral pH using Fe(III)-EDDS under UVA light or sunlight

One of the main challenges of electrochemical Fenton-based processes is the treatment of organic pollutants at near-neutral pH. As a potential approach to this problem, this work addresses the use of a low content of soluble chelated metal catalyst, formed between Fe(III) and ethylenediamine-N,N'-disuccinic (EDDS) acid (1:1), to degrade the herbicide triclopyr in 0.050 M Na2SO4 solutions at pH 7.0 by photoelectro-Fenton with UVA light or sunlight (PEF and SPEF, respectively). Comparison with electro-Fenton treatments revealed the crucial role of the photo-Fenton-like reaction, since this promoted the production of soluble Fe(II) that enhanced the pesticide removal. Hydroxyl radicals formed at the anode surface and in the bulk were the main oxidants. A boron-doped diamond (BDD) anode yielded a greater mineralization than an IrO2-based one, at the expense of reduced costeffectiveness. The effect of catalyst concentration and current density on the performance of PEF with BDD was examined. The PEF trials in 0.25 mMNa2SO4 + 0.35mMNaCl medium showed a large influence of generated active chlorine as oxidant, being IrO2 more suitable than RuO2 and BDD. In SPEF with BDD, the higher light intensity from solar photons accelerated the removal of the catalyst and triclopyr, with small effect on mineralization. A plausible route for the herbicide degradation by Fe(III)-EDDS-catalyzed PEF and SPEF is finally proposed based on detected byproducts: three heteroaromatic and four linear Naliphatic compounds, formamide, and tartronic and oxamic acids

An Electroanalytical Solution for the Determination of Pb2+ in Progressive Hair Dyes Using the Cork–Graphite Sensor

open7Lead is one of the most toxic metals for living organisms: once absorbed by soft tissues, it is capable of triggering various pathologies, subsequently bioaccumulating in the bones. In consideration of this, its detection and quantification in products for human consumption and use is of great interest, especially if the procedure can be carried out in an easy, reproducible and economical way. This work presents the results of the electroanalytical determination of lead in three different commercial products used as progressive hair dyes. Analyses were performed by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV) using a composite cork–graphite sensor in 0.5M H2SO4 solution or 0.1M acetate buffer (pH 4.5), in the presence and absence of hair dye samples. The H2SO4 solution gave better results in terms of analyte sensitivity than the acetate buffer electrolyte. In both cases, well-defined signals for lead were obtained by DPSV analyses, enabling the calibration curve and figures of merit to be determined. The limits of detection (LOD) were found to be approximately 1.06 µM and 1.26 µM in H2SO4 and acetate buffer, respectively. The DPSV standard addition method was successfully applied to quantify the lead in hair dye samples, yielding values below 0.45% in Pb. All three analyzed samples were shown to comply with the limit set by the Brazilian Health Regulatory Agency, i.e., 0.6% lead in this type of product. The comparison of the electroanalytical results with those obtained by the reference method, based on the use of inductively coupled plasma optical emission spectrometry (ICP–OES), confirmed that the electroanalytical detection approach is potentially applicable as a strategy for quality control.openBarros, Thalita Medeiros; Medeiros de Araújo, Danyelle Medeiros de; Lemos de Melo, Alana Tamires Lemos de; Martínez-Huitle, Carlos Alberto; Vocciante, Marco; Ferro, Sergio; Vieira dos Santos, Elisama Vieira dosBarros, Thalita Medeiros; Medeiros de Araújo, Danyelle Medeiros de; Lemos de Melo, Alana Tamires Lemos de; Martínez-Huitle, Carlos Alberto; Vocciante, Marco; Ferro, Sergio; Vieira dos Santos, Elisama Vieira do

Improving biotreatability of hazardous effluents combining ZVI, electrolysis and photolysis

In this work, nine types of combination advanced oxidation processes/zero-valent iron (AOP-ZVI) were tested, in order to determine if any of these combinations demonstrate good chances as pretreatment for the biological degradation processes of organochlorinated pollutants. To do this, the changes undergone in the respirometric behavior, toxicity and short-term biodegradability were compared. The three AOPs studied were anodic oxidation with mixed metal oxides anodes (AO-MMO), with boron doped diamond anodes (AO-BDD) and photolysis and they were evaluated in three different modes: without any addition of ZVI, with ZVI-dehalogenation as pre-treatment and with ZVI-dehalogenation simultaneous to the AOP treatment. Clopyralid has been used as a model of chlorinated hydrocarbon pollutant. Results show that technologies proposed can successfully treat wastes polluted with clopyralid and the biological characteristics of the waste are significantly modified by dehalogenating the waste with ZVI, either previously to the treatment or simultaneously to the treatment, being the information provided by the three techniques very important in order to evaluate later combinations of the advanced oxidation technologies with biological treatments

Clopyralid degradation by AOPs enhanced with zero valent iron

Four different technologies have been compared (photolysis, ZVI + photolysis, electrolysis and ZVI + electrolysis) regarding the: (1) degradation of clopyralid, (2) extent of its mineralization, (3) formation of by-products and main reaction pathways. Results show that photolysis is the less efficient treatment and it only attains 5 % removal of the pollutant, much less than ZVI, which reaches 45 % removal and that electrolysis, which attains complete removal and 78 % mineralization within 4 h. When ZVI is used as pre-treatment of electrolysis, it was obtained the most efficient technology. The identification of transformation products was carried out for each treatment by LCsingle bondMS. In total, ten products were identified. Tentative pathways for preferential clopyralid degradation for all processes were proposed. This work draws attention of the synergisms caused by the coupling of techniques involving the treatment of chlorinated compound and sheds light on how the preferential mechanisms of each treatment evaluated occurred

Cobalt mediated electro-scrubbers for the degradation of gaseous perchloroethylene

This work focuses on the treatment of gaseous perchloroethylene (PCE) using electro-scrubbing with diamond electrodes and cobalt mediators. PCE was obtained by direct desorption from an aqueous solution containing 150 mg L−1, trying to a real pollution case. The electro-scrubber consisted of a packed absorption column connected with an undivided electrochemical cell. Diamond anodes supported on two different substrates (tantalum and silicon) were used and the results indicated that Ta/BDD was more successful in the production of Co (III) species and in the degradation of PCE. Three experimental systems were studied for comparison purposes: absorbent free of Co (III) precursors, absorbent containing Co (III) precursors, and absorbent containing Co (III) precursors undergoing previous electrolysis to the electro-scrubbing to facilitate the accumulation of oxidants. The most successful option was the last, confirming the important role of mediated electrochemical processes in the degradation of PCE. Trichloroacetic acid (TCA) and carbon tetrachloride (CCl4) were found as the primary reaction products and ethyl chloroacetate esters were also identified. A comprehensive mechanism of the processes happening inside electro-scrubber is proposed.Este trabajo se centra en el tratamiento del percloroetileno gaseoso (PCE) mediante electro-fregado con electrodos de diamante y mediadores de cobalto. El PCE se obtuvo por desorción directa de una solución acuosa que contenía 150 mg L -1 , tratando de un caso de contaminación real. El electrodepurador constaba de una columna de absorción empaquetada conectada con una celda electroquímica no dividida. Se utilizaron ánodos de diamante soportados sobre dos sustratos diferentes (tantalio y silicio) y los resultados indicaron que Ta / BDD tuvo más éxito en la producción de especies de Co (III) y en la degradación de PCE. Se estudiaron tres sistemas experimentales con fines comparativos: absorbente libre de precursores de Co (III), absorbente que contiene precursores de Co (III) y absorbente que contiene precursores de Co (III) sometidos a electrólisis previa.al electro-fregado para facilitar la acumulación de oxidantes. La opción más exitosa fue la última, lo que confirma el importante papel de los procesos electroquímicos mediados en la degradación del PCE. Se encontraron ácido tricloroacético (TCA) y tetracloruro de carbono (CCl 4 ) como productos de reacción primarios y también se identificaron ésteres de cloroacetato de etilo. Se propone un mecanismo integral de los procesos que ocurren dentro del electrodepurador

Treatment of toluene gaseous streams using packed column electro-scrubbers and cobalt mediators

An absorption system has been combined with an electrochemical cell to treat a gaseous stream polluted with toluene. Toluene retention in 3 h operation tests was higher than 87.0% in the case of treating the gaseous stream with single scrubbing, 97.0% in the case of using electro-scrubbing and over 99.0% in using cobalt-mediated electro-scrubbing. It was found that the amount of toluene that escapes from the electro-scrubber does not only depend on the flow rate but also on the current density and the presence of the metallic mediator. The higher the current densities are, the higher the amount of electrochemically degraded toluene is. In addition to the mediating effect of the metal catalyst, the results also suggest an important participation of the redox sulfate/persulfate pair in the degradation of toluene. Only methyl-cyclohexane (at very low concentrations) is observed as intermediate, despite carboxylic acids were also initially expected. The formation of this compound can be explained in terms of the hydrogenation of toluene. The very low concentrations absorbed, and the very high current densities, support the occurrence of an electrochemical cold combustion in the electro-scrubber.Se ha combinado un sistema de absorción con una celda electroquímica para tratar una corriente gaseosa contaminada con tolueno. La retención de tolueno en las pruebas de funcionamiento de 3 h fue superior al 87,0% en el caso del tratamiento de la corriente gaseosa con lavado simple, al 97,0% en el caso de electro-fregado y superior al 99,0% con electro-fregado con cobalto. Se encontró que la cantidad de tolueno que escapa del electrodepurador no solo depende del caudal sino también de la densidad de la corriente y de la presencia del mediador metálico. Cuanto mayores sean las densidades de corriente, mayor será la cantidad de tolueno degradado electroquímicamente. Además del efecto mediador del catalizador metálico, los resultados también sugieren una participación importante del par redox sulfato / persulfato en la degradación del tolueno. Sólo metilciclohexano (a concentraciones muy bajas) se observa como intermedio, a pesar de que inicialmente también se esperaban ácidos carboxílicos. La formación de este compuesto se puede explicar en términos de hidrogenación de tolueno. Las muy bajas concentraciones absorbidas y las altísimas densidades de corriente favorecen la aparición de una combustión electroquímica en frío en el electrodepurador