A β-cyclodextrin–chitosan complex as the immobilization matrix for horseradish peroxidase and its application for the removal of azo dyes from textile effluent

Abstract

The aim of this study was to develop a system based on the use of immobilized horseradish peroxidase (HRP) for the removal of color due to azo dyes from a textile effluent. The maximum binding of HRP on a β-cyclodextrin (CD)–chitosan complex was achieved at pH 8.0. Oxidative removal of azo dyes from effluent by water-soluble and β-CD–chitosan–HRP inclusion complexes was monitored by HPLC analysis. The crosslinked peroxidase preparation made with a β-CD–chitosan complex was more active, effective and stable than the un-crosslinked and the water-soluble enzyme preparations. The maximum dye oxidation from the diluted textile effluent was observed in the presence of 0.6 mM H2O2 and 0.2 U ml−1 at pH 8.0 and at 40 °C for 2 h. A batch process with HRP was also performed, whereby complete dye removal from the effluent was obtained with a crosslinked β-CD–chitosan complex within 120 min. On the other hand, a β-CD–chitosan–HRP-based continuous bed reactor was found to be efficient for complete removal of the dye from the effluent during 15 days of operation. The reuse of the crosslinked enzyme preparations proved to be more effective in the decolorization of textile effluent than the un-crosslinked enzyme preparations. Based on a comet assay the genotoxicity associated the colored effluent was completely lost after HRP oxidation of the dye, showing the dye metabolites are not toxic.