Fenton process combined with precipitation for the removal of Direct Blue 1 dye: A new approach

Abstract

Azo dyes are recalcitrant pollutants present in effluents of several industries. Due to their chemical stability, their degradation efficiency is not satisfactory by conventional technologies. Advanced oxidation processes, such as Fenton, can be applied for the removal of recalcitrant compounds. However, these methods are still costly. In this work, Fenton and precipitation treatments were combined for the removal (i.e., decolorization) of direct blue 1 (DB1), as an option to decrease operational costs. The individual treatments were studied separately using DB1 solutions 0.04 mmol L-1 to determine the effects of the parameters involved in each process. For the Fenton treatment, the c(Fe2+):c(H2O2) ratio that allowed the highest DB1 decolorization was 1:40. Regarding precipitation, the highest dye decolorization was achieved at a pH value of 6.0. Moreover, it was determined that a minimum c(DB1):c(Fe2+) ratio of 1:7.7 is needed to allow the decolorization of the dye by precipitation. Fenton assisted with precipitation tests were performed with DB1 solutions 0.09 mmol L-1 and using a c(DB1):c(Fe2+) ratio of 1:7.3 (which allows only partial precipitation of DB1). The results suggested that the dye can be treated by a Fenton process for 5 min and then precipitated to achieve the almost total decolorization of the dye (97.79 %). Azo dyes are recalcitrant pollutants present in effluents of several industries. Due to their chemical stability, their degradation efficiency is not satisfactory by conventional technologies. Advanced oxidation processes, such as Fenton, can be applied for the removal of recalcitrant compounds. However, these methods are still costly. In this work, Fenton and precipitation treatments were combined for the removal (i.e., decolorization) of direct blue 1 (DB1), as an option to decrease operational costs. The individual treatments were studied separately using DB1 solutions 0.04 mmol L-1 to determine the effects of the parameters involved in each process. For the Fenton treatment, the c(Fe2+):c(H2O2) ratio that allowed the highest DB1 decolorization was 1:40. Regarding precipitation, the highest dye decolorization was achieved at a pH value of 6.0. Moreover, it was determined that a minimum c(DB1):c(Fe2+) ratio of 1:7.7 is needed to allow the decolorization of the dye by precipitation. Fenton assisted with precipitation tests were performed with DB1 solutions 0.09 mmol L-1 and using a c(DB1):c(Fe2+) ratio of 1:7.3 (which allows only partial precipitation of DB1). The results suggested that the dye can be treated by a Fenton process for 5 min and then precipitated to achieve the almost total decolorization of the dye (97.79 %).