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The discharge of effluents from the textile industry into water bodies has a severe impact on water quality. The photocatalytic degradation of two typical azo dyes used in the textile industry (Acid Brown 83 and Direct Blue 1) was studied using the catalysts titanium dioxide (TiO

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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 %).

Most dyes used in the textile industry are chemically stable and poorly biodegradable, therefore, they are persistent in the environment and difficult to degrade by conventional methods. An alternative treatment for this kind of substance is heterogeneous photocatalysis using TiO2, so, in this work, it is proposed to degrade Direct Blue 1 (DB1) using microparticulate TiO2 irradiated with e-beam at three different doses: 5, 10 and 20 kGy (J/kg). The DB1 degradation was implemented in a batch reactor (DB1 initial concentration = 50 mg L−1, pH 2.5, TiO2 concentration = 200 mg L−1). We have demonstrated that the photocatalytic power of TiO2, when irradiated with e-beam (5, 10, 20 kGy), varies slightly, with minor effects on photodegradation performance. However, the dose of 10 kGy showed a slightly better result, according to the DB1 photodegradation rate constant. Adsorption process was not affected by irradiation; its isotherm was fitted to Freundlich’s mathematical model. The DB1 photodegradation rate constants, after one hour of treatment, were: 0.0661 and 0.0742 min−1 for irradiated (10 kGy) and nonirradiated TiO2, respectively. The degradation rate constant has an increase of 12.3% for irradiated TiO2. Finally, there was no evidence of mineralization in the degradation process after 60 min of treatment. According to the results, the irradiation of microparticulate TiO2 with e-beam (10 kGy) slightly improves the photodegradation rate constant of DB1.