Electroflotation Applied to the Treatment of Wastewaters Containing Chlorimuron-Ethyl, a Sulfonylurea Herbicide

Abstract

Electroflotation (EF) is an electroanalytical technique commonly used for the separation of substances suspended in an aqueous phase. However, these studies are limited to the separation of wastes or contaminants, without destroying the contaminants. In this study, EF was applied as an advanced oxidation process, aiming to decontaminate wastewater containing sulfonylurea herbicides (chlorimuron-ethyl). Electroflotations were performed in an electroflotator reactor developed in the Laboratory of Environmental Chemistry, Institute of Chemistry of Sao Carlos, University of Sao Paulo, Brazil. The reactor was built in acrylic and was provided with aluminium electrodes. In addition, the anion electrode also was an agitation bar, that ensured the homogeneity of the solution during the process. Four assays were performed with varying salt concentrations (electrolyte-NaCl) and a direct electric current (I) was applied through the electrodes. Chemical monitoring was performed to determine the efficiency of the electrochemical process. Analysis of water samples by HPLC allowed the electrochemical reaction to be monitored, indicating a disturbance of the reaction medium (presence of byproducts of degradation). Gas chromatography coupled with mass spectrometry (GC-MS) was used to elucidate the mechanism of degradation and assist in the identification of the byproducts. According to the chromatograms obtained by HPLC-UV, the EF process changed the reaction medium, resulting in a displacement of the herbicide chromatographic peak and the appearance of bands without defined structure, related to the by-products generated. Based on the mass spectrum obtained, a mechanism of degradation was proposed, showing that EF does not totally destroy the chlorimuron-ethyl molecule, but it was successful in breaking important chemical bonds, responsible for the connection sulfonyl-urea. This study provides important information about the possibility of promoting the oxidation of toxic organic compounds by electroflotation, to generate less toxic and better environmentally adjusted effluents.