Comparative study of the degradation of real textile effluents by photocatalytic reactions involving UV/TiO2/H2O2 and UV/Fe2+/H2O2 systems

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Abstract

This work investigated the treatability of real textile effluents using several systems involving advanced oxidation processes (AOPs) such as UV/H2O2, UV/TiO2, UV/TiO2/H2O2, and UV/Fe2+/H2O2. The efficiency of each technique was evaluated according to the reduction levels observed in the UV absorbance of the effluents, COD, and organic nitrogen reduction, as well as mineralization as indicated by the formation of ammonium, nitrate, and sulfate ions. The results indicate the association of TiO2 and H2O2 as the most efficient treatment for removing organic pollutants from textile effluents. In spite of their efficiency, Fenton reactions based treatment proved to be slower and exhibited more complicated kinetics than the ones using TiO2, which are pseudo-first-order reactions. Decolorization was fast and effective in all the experiments despite the fact that only H2O2 was used.

Introduction

The color of a water sample is related to the decrease in light intensity as it passes through the sample, mainly due to the presence of organic and inorganic material in the colloidal form. Industrial effluents such as textile industry ones are characterized by the gradual coloring of natural waters. Besides the negative effects on water appearance, which makes it repulsive to consumers, the presence of organic matter in the natural waters is directly associated with toxicity and carcinogenicity caused by dyes, surfactants, suspended solids, organochlorinated compounds, etc. that can be present in the effluent [1].

From an environmental point of view, decolorizing the washing bath is one of the greatest problems of the textile industry. It is estimated that more than 15% of the world dye production is released into the environment during synthesis, processing, and use. This is alarming since it means ca. 400 tonnes a day. This loss is due mainly to incomplete dye fixing (10–20%) during the textile fiber dyeing step (Fig. 1) [2].

Several techniques such as membrane filtration, adsorption [3], coagulation [4], and biodegradation [5] have been used to solve the problems caused by the toxic substances contained in industrial effluents. However, all of these treatments result in secondary pollution, since they transfer the toxic substances from the liquid phase to other phases such as the sludge, used membranes, and saturated adsorbents, which cause another environmental problem. Therefore, there has been an increased interest in advanced oxidation processes (AOPs) that is an alternative destructive treatment in which chemical species are reduced into smaller fragments and even to the point of mineralization. AOPs are processes involving UV or visible radiation associated with substances such as H2O2 [6], semiconductors such as TiO2 [7], and ZnO [8], Fe2+ or Fe3+ [9], O3 [10], and/or their variations and associations.

In this way, the aim of the present work is to compare the degradation behavior of real textile effluents using the following oxidation processes: UV/H2O2, UV/TiO2, UV/TiO2/H2O2, and UV/Fe2+/H2O2.

Section snippets

Materials

The textile effluent samples (EFA, EFB, and EFC) presenting colorants (Yellow Procion, Red Procion, and Remazol Brilliant Blue R), sodium chloride, and surfactant agents as main the composition were kindly provided by a fabric manufacturer from the northwest region of Paraná State (PR), Brazil. TiO2 (P-25, 80% anatase, 20% rutile with a specific surface of 50 m2 g−1) was kindly provided by Degussa and used without previous purification. H2O2 (30%, analytical grade) was purchased from Sinth. All

Results and discussion

Because of the evidences indicating that the degradation of organic substrates occurs on the surface of the catalyst, adsorption was considered a very important step in the photocatalytic process [13]. Therefore, previous adsorption tests were carried out and the results showed that acid pH (3–3.5) is the most indicated for standard dye adsorption on TiO2 surface. Thus, the degradation of the real textile effluent samples composed mostly of dyes, sodium chloride, and surfactant agents were

Conclusion

The obtained results prove that the treatment of textile effluents using advanced oxidation processes with UV radiation is effective for decolorization, COD reduction, and mineralization in short irradiation time. The fact that these treatment processes do not generate residues justifies the use of any of the techniques. The general efficiency presented by the techniques decreased as following: UV/TiO2/H2O2 > UV/Fe2+/H2O2 > UV/TiO2 > UV/H2O2. More detailed studies would be necessary in order to

Acknowledgement

CNPq, Capes, Fundação Araucária, MR Malharia.

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