In situ heterogeneous oxidative degradation of adsorbed cellulose-reactive anionic dye

Abstract

The release of industrial wastewater containing textile organic dyes without treatment affects human health and the environment. In this study, a two-step process to treat water contaminated with cellulose-reactive anionic dye is presented. First, the dye was adsorbed onto an inexpensive water hyacinth root powder (WHRP) bioadsorbent. Then, the dye-loaded WHRP was treated with Fenton reagents, allowing for in situ heterogeneous oxidation of the dye. The adsorption was performed from a solution containing between 100 and 300 mg dye/L, consistent with the effluent from textile processing plants. The corresponding loading on the WHRP was between 16.40 and 41.80 mg dye/g adsorbent. A short treatment time (less than 25 min) was achieved, which is more practical than previous reports that took several hours. To fully characterize the process, we studied the conditions affecting the in situ oxidation of adsorbed dye and developed a kinetic model for the reaction to find the optimal operating conditions necessary to achieve a high dye degradation percentage in a short timeframe. A first-order dependence between the reaction rate and the dye concentration was found, coupled with catalyst deactivation at a constant rate. However, increasing either the catalyst or the oxidant concentration above a certain threshold resulted in the inhibition of the dye degradation reaction. In this study, optimal dye degradation could be achieved using up to 31.60 mg dye/g adsorbent, with 0.9 M H2O2 and 3.6 mM Fe2+ at pH 3, resulting in more than 99 % dye degradation and nearly complete mineralization in less than 20 min. Thus, a relatively simple in situ dye oxidation process, well-suited for scale-up and continuous operation, was achieved.

Keywords

• Cellulose-reactive dye
• Adsorption
• In situ heterogenous dye oxidation
• Kinetic modeling
• Mineralization