Ozonização e oxidação com persulfato de sódio do corante azo reactive black 5: cinética, formação de subprodutos e metodologia de superfície de resposta

Abstract

Industrial textile effluent is generally characterized by high pH, intense color and extremely high salinity. Due to the complex characteristics of this effluent, more studies are being developed for its treatment. This study sought to evaluate the removal efficiency of Reactive Black 5 dye by ozonation and oxidation with sodium persulfate. For the ozonation a factorial design 22 was made with the variables pH (2, 3.5, 7, 10.5 and 12) and O3 flowrate (5, 6.5, 10, 13.5 and 15 L min-1), and to the oxidation with sodium persulfate, a a factorial design 23 prepared with the variables pH (2, 4, 7, 10 and 12), temperature (20, 28, 40, 52 and 60 °C) and sodium persulfate concentration (500, 905, 1500, 2095, 2500 mg L-1). The oxidation time of both processes was 60 minutes and the dye removal efficiencies over time were analyzed. The ozone production used in this study was 1.265 gO3 h-1 corresponding to air flowrate of 15 L min-1 and maximum O3 transfer to the solution of 60% in alkaline conditions (pH 12). By applying the central compound design (CCRD) the optimal condition of pH (11.30) and O3 flow (14.31 L min-1) for 6 min of ozonation was determined. At the end of 60 min the removal efficiency was above 90% to the evaluated conditions. For the oxidation with sodium persulfate, the maximum removal efficiency was 100% in the profiles with temperature above 40 oC, and in the optimum range of pH of 7.50, temperature of 52 °C, and concentration of SP of 1,731 mg L-1 after 60 minutes of treatment. The kinetics for both treatment processes resulted in pseudo-first order with kinetic constant to the sodium persulfate oxidation of k = 0,1798 min-1 and to the ozonation of k = 0,1358 min-1. Sulphate concentration increased over the treatment in 298 mg L-1 at the end of 60 minutes of treatment. No presence of metals was verified in the evaluated samples, indicating no influence of the resistance on the sodium persulfate activation. According to the chromatographic analysis to the determination of byproducts, ethenyl sulfonyl benzene was determined as an intermediate product of ozonization and sodium persulfate oxidation and in both treatments it was observed that the peak of this byproduct decreased over the time. Both ozone and sodium persulphate oxidation showed efficient results in the oxidation of textile dye RB 5.