RESUMEN
The aim of this study is to propose a continuous physicochemical model accounting for the active chlorine production used to degrade recalcitrant sulfamethoxazole (SMX) in an electrochemical flow reactor. The computational model describes the fluid mechanics and mass transfer occurring in the re/actor, along with the electrode kinetics of hydrogen evolution reaction arising on a stainless steel cathode, and the chloride oxidation on a DSA. Specifically, the anodic contributions assume the heterogeneous nature of the adsorbed chlorine species formed on this surface, which are a model requirement to correctly define the experimental reactor performance and degradation efficiency of the contaminant. The experimental validation conducted at different applied current densities, volumetric flows, and chloride concentrations is adequately explained by the model, thus evidencing some of the phenomena controlling the electrocatalytic chlorine production for environmental applications. The best conditions to eliminate the SMX are proposed based on the theoretical analysis of the current efficiency calculated with the model, and experimentally confirmed. The use of the Ti/RuO2-ZrO2-Sb2O3 anode at the bench scale improves the SMX removal by using electro-generated chlorine species adsorbed on its surface, which remarkably increases the oxidation potential of the system along with chlorine desorbed from the electrode. This is a technological innovation concerning other mediated oxidation methods entirely using oxidants in solution.
Asunto(s)
Sulfametoxazol , Contaminantes Químicos del Agua , Cloruros , Cloro/análisis , Electrodos , Oxidación-Reducción , Contaminantes Químicos del Agua/análisisRESUMEN
The elimination of cephalexin (CPX) using electro-generated Cl2-active on Ti/RuO2-IrO2 anode was assessed in different effluents: deionized water (DW), municipal wastewater (MWW) and urine. Single Ti/RuO2 and Ti/IrO2 catalysts were prepared to compare their morphologies and electrochemical behavior against the binary DSA. XRD and profile refinement suggest that Ti/RuO2-IrO2 forms a solid solution, where RuO2 and IrO2 growths are oriented by the TiO2 substrate through substitution of Ir by Ru atoms within its rutile-type structure. SEM reveals mud-cracked structures with flat areas for all catalysts, while EDS analysis indicates atomic ratios in the range of the oxide stoichiometries in the nominal concentrations used during synthesis. A considerably higher CPX degradation is achieved in the presence of NaCl than in Na2SO4 or Na3PO4 media due to the active chlorine generation. A faster CPX degradation is reached when the current density is increased or the pH value is lowered. This last behavior may be ascribed to an acid-catalyzed reaction between HClO and CPX. Degradation rates of 22.5, 3.96, and 0.576⯵molâ¯L-1â¯min-1 were observed for DW, MWW and urine, respectively. The lower efficiency measured in these last two effluents was related to the presence of organic matter and urea in the matrix. A degradation pathway is proposed based on HPLC-DAD and HPLC-MS analysis, indicating the fast formation (5â¯min) of CPX-(S)-sulfoxide and CPX-(R)-sulfoxide, generated due the Cl2-active attack at the CPX thioether. Furthermore, antimicrobial activity elimination of the treated solution is reached once CPX, and the initial by-products are considerably eliminated. Finally, even if only 16% of initial TOC is removed, BOD5 tests prove the ability of electro-generated Cl2-active to transform the antibiotic into biodegradable compounds. A similar strategy can be used for the abatement of other recalcitrant compounds contained in real water matrices such as urine and municipal wastewaters.
Asunto(s)
Cefalexina/análisis , Cloro/química , Iridio/química , Rutenio/química , Eliminación de Residuos Líquidos/métodos , Contaminantes Químicos del Agua/análisis , Antibacterianos/análisis , Electrodos , Aguas Residuales/análisisRESUMEN
Taking crystal violet (CV) dye as pollutant model, the electrode, electrolyte and current density (i) relationship for electro-degrading organic molecules is discussed. Boron-doped diamond (BDD) or Iridium dioxide (IrO2) used as anode materials were tested with Na2SO4 or NaCl as electrolytes. CV degradation and generated oxidants showed that degradation pathways and efficiency are strongly linked to the current density-electrode-electrolyte interaction. With BDD, the degradation pathway depends on i: If i
Asunto(s)
Boro/química , Cloruros/química , Diamante/química , Iridio/química , Sulfatos/química , Contaminantes Químicos del Agua/química , Colorantes/química , Electroquímica , Electrodos , Violeta de Genciana/química , Eliminación de Residuos Líquidos/métodosRESUMEN
This paper explores the applicability of electrochemical oxidation on a triphenylmethane dye compound model, hexamethylpararosaniline chloride (or crystal violet, CV), using BDD anodes. The effect of the important electrochemical parameters: current density (2.5-15 m A cm(-2)), dye concentration (33-600 mg L(-1)), sodium sulphate concentration (7.1-50.0 g L(-1)) and initial pH (3-11) on the efficiency of the electrochemical process was evaluated. The results indicated that while the current density was lower than the limiting current density, no side products (hydrogen peroxide, peroxodisulphate, ozone and chlorinated oxidizing compounds) were generated and the degradation, through OH radical attack, occurred with high efficiency. Analysis of intermediates using GC-MS investigation identified several products: N-methylaniline, N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-methyl-N-methylaniline, 4-dimethylaminophenol, 4-dimethylaminobenzoic acid, 4-(N,N-dimethylamino)-4'-(N',N'-dimethylamino) diphenylmethane, 4-(4-dimethylaminophenyl)-N,N-dimethylaniline, 4-(N,N-dimethylamino)-4'-(N',N'-dimethylamino) benzophenone. The presence of these aromatic structures showed that the main CV degradation pathway is related to the reaction of CV with the OH radical. Under optimal conditions, practically 100% of the initial substrate and COD were eliminated in approximately 35 min of electrolysis; indicating that the early CV by-products were completely degraded by the electrochemical system.