RESUMO
The aim of the present study was to investigate the electrochemical formation of free chlorine species (HOCl/ClO-) and their subsequent use for the degradation of the pesticide atrazine. Initially, the process of electrochemical-free chlorine production was investigated using a bench-scale electrochemical flow-cell. The most significant variables (electrolyte concentration ([NaCl]) and inter-electrode gap) of the process were obtained using a 23 factorial design and the optimum process conditions (1.73â molâ L-1 and 0.56â cm) were determined by a central composite design. Following optimization of free chlorine production, three degradation techniques were investigated, individually and in combination, for atrazine degradation: electrochemical, photochemical and sonochemical. The method using the techniques in combination was denominated sono-photo-assisted electrochemical degradation. Constant current assays were performed and the sono-photo-assisted electrochemical process promoted more efficient removal of atrazine, achieving total organic carbon removal of â¼98% and removal of atrazine to levels below the detection limit (>99%) in under 30â min of treatment. Furthermore, the combination of three techniques displayed lower energy consumption, and phytotoxicity tests (Lactuca sativa) showed that there was no increase in toxicity.
Assuntos
Atrazina , Poluentes Químicos da Água , Purificação da Água , Cloro , Técnicas Eletroquímicas , Oxirredução , Raios UltravioletaRESUMO
The present paper presents the study of (1) the optimization of electrochemical-free chlorine production using an experimental design approach, and (2) the application of the optimum conditions obtained for the application in photo-assisted electrochemical degradation of simulated textile effluent. In the experimental design the influence of inter-electrode gap, pH, NaCl concentration and current was considered. It was observed that the four variables studied are significant for the process, with NaCl concentration and current being the most significant variables for free chlorine production. The maximum free chlorine production was obtained at a current of 2.33â A and NaCl concentrations in 0.96â molâ dm-3. The application of the optimized conditions with simultaneous UV irradiation resulted in up to 83.1% Total Organic Carbon removal and 100% of colour removal over 180â min of electrolysis. The results indicate that a systematic (statistical) approach to the electrochemical treatment of pollutants can save time and reagents.
Assuntos
Poluentes Ambientais , Poluentes Químicos da Água , Cloro , Eletrólise , Oxirredução , Projetos de Pesquisa , Indústria TêxtilRESUMO
The influence of chloride ion concentration during the photo-assisted electrochemical degradation of simulated textile effluent, using a commercial Ti/Ru0.3Ti0.7O2 anode, was evaluated. Initially, the effect of applied current and supporting electrolyte concentration on the conversion of chloride ions to form reactive chlorine species in 90 min of experiment was analyzed in order to determine the maximum production of reactive chlorine species. The optimum conditions encountered (1.5 A and 0.3 mol dm(-3) NaCl) were subsequently employed for the degradation of simulated textile effluent. The efficiency of the process was determined through the analysis of chemical oxygen demand (COD), total organic carbon (TOC), of the presence of organochlorine products and phytotoxicity. Photo-assisted electrochemical degradation was more efficient for COD and TOC removal than the electrochemical technique alone. With simultaneous UV irradiation, a reduced quantity of reactive chlorine was produced, indicating that photolysis of the chlorine species led to the formation of hydroxyl radicals. This fact turns a simple electrochemical process into an advanced oxidation process.