Influence of pH and concentration on the decolorization and degradation of BR red azo dye by ozonization/Influencia do pH e concentracao na descoloracao e degradacao do azo corante vermelho BR por ozonizacao

Ozone application has been generally reported based only on the oxidation of textile dyes. In this study, a central composite design and surface response methodology were applied to optimize operational parameters pH and concentration of the dye in the decolorization process. The oxidation of Corafix BR Red Azo dye in aqueous solutions was carried out in a semi-batch bubble column reactor with ozone production at 0.702 g [hour.sup.-1]. Tests were performed at pH 4, 7 e 10 and initial dye concentration of 50, 100 and 150 mg [L.sup.-1]. The maximum removal efficiency was 98% for pH 10 and initial dye concentration of 50 mg [L.sup.-1] with pseudo-first order constant rate ([k.sub.1]) of 0.0595 [min.sup.-1]. Statistical analysis determined the influence of pH and dye concentration in the decolorization process. The pH presented a positive effect on the decolorization while the variation in dye concentration had a negative effect on the same variable, indicating the higher the pH and the lower the initial concentration of dye, the higher the efficiency. Toxicity tests performed before and after ozonization showed acute toxicity for the test organism Daphnia similis with higher percentage of mortality after ozonization. Keywords: dye removal; AOP; ozone; textile effluent. A aplicacao do ozonio tem sido, geralmente, reportada com base apenas na oxidacao de corantes texteis. Neste estudo o delineamento composto central rotacional e a metodologia de superficie de resposta foram aplicados para otimizar os parametros operacionais pH e concentracao do corante no processo de descoloracao. A oxidacao do corante Azo Corafix Red BR em solucao aquosa foi realizada em uma coluna de ozonizacao semibatelada com producao de ozonio de 0,702 g [h.sup.- 1]. Os testes foram realizados em pH 4, 7 e 10 e concentracao inicial do corante de 50, 100 e 150 mg [L.sup.- 1]. A eficiencia de remocao maxima alcancada foi de 98% para pH 10 e concentracao inicial de corante de 50 mg [L.sup.-1] com constante cinetica de pseudo-primeira ordem ([k.sub.1]) de 0,0595 [h.sup.-1]. Analises estatisticas determinaram a influencia do pH e concentracao do corante no processo de descoloracao. O pH apresentou efeito positivo na descoloracao, enquanto a variacao do corante apresentou efeito negativo na mesma variavel, indicando que quanto maior o pH e menor a concentracao inicial de corante maior a eficiencia. Os testes de toxicidade, realizados antes e apos a ozonizacao, mostraram toxicidade aguda para o o