Decolorization of Reactive Black 5 by suspended growing yeasts and ca-alginate beads immobilized yeasts

Abstract

An eco-friendly treatment of industrial dyes and effluents is the biggest environmental challenge for textile industries. Numerous bio-decolorization processes have been studied, but their industrial application is still marginal due to practical and economic obstacles. In this survey, we analyzed the immobilization of T. Akiyoshidainum HP-2023 in Ca-alginate beads to improve its practical effectiveness. The effects of different parameters on the decolorization of Reactive Black 5 by immobilized cells of T. akiyoshidainum HP-2023 were investigated under aerobic conditions. The analyzed factors included alginate concentration (1, 2 and 2.75%), initial dye concentration (200, 400, 600 and 800 mg/L) and rotation speed (150, 200 and 250 r/min). Under optimal conditions, (2% sodium alginate, 200mg/l, and 200 r/min), the immobilized yeast caused to 95% decolorization in 6 h, while free, suspended cells, achieved only 50% decolorization in the same period. In addition, immobilized yeast decolorizes a wider range of initial dyes. Immobilized cells could completely decolorize 600mg/l of Reactive Black 5 within 24 h, and caused 75% decolorization of 800 mg/L of the dye in 24 h. Furthermore, results of successive cycles of decolorization showed that insolubilized beads were reusable for at least four repeated cycles keeping a high efficiency in color removal. Results of decolorization tests suggested that Ca-alginate immobilized yeast may effectively be used for decolorization of dyes present in industrial effluents.