Degradation and ecotoxicity of dye Reactive Black 5 after reductive-oxidative process : Environmental Science and Pollution Research

This research paper describes the study of a reduction-oxidation system using commercial steel wool (Fe0) and H2O2 for degradation of the dye Reactive Black 5 and aromatic compounds in water. The reductive process alone allowed the almost complete removal of color (97 ± 1 %) after 60 min of reaction. The decrease in spectral area (λ = 599 nm) associated with the chromophore group indicates breakage of the azo bonds. Moreover, the significant change in UV spectra can be associated with the formation of aromatic amines. Regarding the transformation products, a spectrophotometric method based on the diazotization reaction was employed to identify aromatic amines after reductive process, using sulfanilic acid as a model of aromatic amines. In addition, association with Fenton reagents improved the efficiency in the system with 93 ± 1 % degradation of intermediates formed during the reductive process. Ecotoxicological analysis revealed that the dye solution, after the reductive and oxidative processes, was not toxic to Lactuca sativa seeds. For Daphnia magna, the EC50 (%) values observed revealed that dye solution has an EC50(%) = 74.1 and after reductive process, the toxicity increased (EC50(%) = 63.5), which might be related to the formation of aromatic amines. However, after the Fenton process, the EC50 (%) was >100. These results demonstrated that the Fenton reaction using steel wool as an iron source was very efficient to decrease color, aromatic transformation products, and the ecotoxicity of Reactive Black 5 in solution.