Estudo do processo Sonoeletroquímico Fotoassistido para degradação dos pesticidas Ametrina, Diuron e Hexazinona

Abstract

Contamination of water by pesticides present in effluents from industrial and agricultural activities causes major environmental impacts, and the development of treatment technologies for these effluents is essential. In this study, a combination of three techniques we applied: electrochemical, photochemical and sonochemical - denominated photoassisted sonoelectrochemical degradation, for the degradation of the pesticides ametrine, diuron and hexazinone. For this purpose, the system was assembled using a bench scale electrochemical cell with continuous flow, the working electrode was Ti/Ru0,3Ti0,7O2, plate the counter electrode a Ti plate and the supporting electrolyte NaCl. The variables were defined, electric current and NaCl concentration, and was applied the experimental design in terms of concentration of free chlorine species. The electrochemical system was chosen for implementation of this design, because it was necessary to quantify the free chlorine species in this study. Thus, were determined the optimum process conditions to carry out the degradation assays. In photochemical degradation, the irradiation was applied by an ultraviolet light source. For sonochemical treatment, the ultrasonic energy was provided by means of a ultrasound bath. The degradation experiments were monitored by UV-vis spectroscopy, TOC, HPLC and phytotoxicity, and the energy efficiency of the process was evaluated. From the experimental design, the optimum process conditions obtained were 0.88 mol L-1, for NaCl concentration, and 0.78 A, for electric current. The photoassisted sonoelectrochemical degradation process promoted satisfactory generation of highly oxidizing species, allowing for efficient degradation of the studied pesticides, achieving a COT removal of 91%, 94% and 77%, for ametrine, diuron and hexazinone, respectively. By the HPLC analysis it can be inferred that this same process resulted in a removal of approximately 100% for ametrine and diuron, and 80.7% for hexazinone. Besides that, the combination of the three techniques showed a higher current efficiency, lower energy consumption and good energy efficiency of the system. The results indicated that the photoassisted sonoelectrochemical process can be applied to the degradation of pesticides ametrine, diuron and hexazinone, as a effective, appropriate and promising treatment.