Degradação de corante azo Acid black 210 Na por meio de eletro-oxidação com eletrodos de grafite

Abstract

The presence of refractory compounds, like synthetic dyes, in the environment implies in a risk due to the toxic characteristics of some compounds and by­products originated by the incomplete degradation of them. The azo dye class is one of the most used in the textile industry and tannery, nonetheless, these dyes have a toxic potential and they are resistant to the conventional treatment degradation methods. Therefore, the efficiency of electrooxidation using graphite electrodes in the sodium chloride presence was analyzed for the azo dye Acid Black 210 Na degradation. The tests were performed following a completely randomized design, being tested 4 treatments (A, B, C and D) with 4 repetitions in each treatment, with different electric current densities (4, 12, 20 and 30 mA.cm­2). The treatment with the best performance, evidenced by the statistical analysis (ANOVA and mean comparison test) was used for the degradation kinetic modeling. The degradation efficiency was evaluated by molecular absorbance spectroscopy in the wavelengths of 459 and 609 nm and the kinetic degradation was adjusted for the wavelength of 319 nm. Through the statistical analysis, the treatment C proved to be the best option, with percentage degradation of 79.69% and 91.90% in the wavelengths of 459 and 609 nm, respectively, with free chlorine residual of 5,03 ppm and pH of 5,33, the treatment was done using 20 mA.cm2. The treatment C operational cost was 20.80 USD.m­3, around 52% lower than treatment D. The degradation kinetic was adjusted according to a second­order model, with R2 of 0,978 and a rate constant of 0,561 L.g­1min­1. The toxicity analysis indicated that toxicity for Daphnia magna and Lactuca sativa increases after electrooxidation, due to the presence of free chlorine concentration and the presence of chlorate compounds demonstrate by the infrared spectrum. The formation of aromatics by products wasn’t observed, so concludes that electrooxidation is efficient in the azo dye Acid Black 210 Na degradation, however, operational adjust is necessary for inhibiting chlorate compounds formation that increases the toxicity.