Applications of Celite-adsorbed white radish (Raphanus sativus) peroxidase in batch process and continuous reactor for the degradation of reactive dyes

White radish peroxidase immobilized on Celite has been employed for the treatment of reactive dyes: Reactive Red 120 and Reactive Blue 171. A comparative study of decolorization of these dyes by soluble and immobilized white radish peroxidase was made. Effect of different redox mediators: 1-hydroxybenzotriazole, syringaldehyde, verataryl alcohol and violuric acid on the decolorization of reactive dyes by white radish peroxidase was tested. The investigated dyes were decolorized to different extents in the presence of these mediators. However, 1-hydroxybenzotriazole was found to be the most effective mediator for decolorization of Reactive Red 120 and Reactive Blue 171 by white radish peroxidase. Maximum decolorization of the dyes was observed at pH 5.0 and 40 °C in 1 h. Comparative operational stability performance of soluble and immobilized white radish peroxidase for the treatment of dyes was checked in the presence of various denaturing and inhibiting agents such as sodium azide, organic solvents and mercuric chloride. Among the studied dyes, white radish peroxidase exhibited significantly higher affinity for Reactive Red 120. Toxicity of the dyes was tested by Allium cepa test. Immobilized peroxidase decolorized dyes more effectively in batch process. Absorption spectra of treated and untreated dye solutions were found to show a marked difference. Efficiency of immobilized peroxidase was checked in a continuous reactor where the immobilized enzyme exhibited 73% decolorization of Reactive Red 120 even after 1 month of operation of the reactor.