Azo Dye Decolourisation using Crude Peroxidase from Armoracia rusticana Hairy Roots

Abstract

Aim: The objective of the present work was to assess the ability of crude peroxidase from hairy roots of Armoracia rusticana (horseradish) to decolourise two model azo dyes: The mono-azo dye Methyl Orange (MO) and the di-azo dye Bismarck Brown (BB). Study Design: The enzymatic decolourisation of aqueous solutions of the model dyes was performed by varying reaction parameters like pH of reaction mixture, crude enzyme concentration, dye concentration and hydrogen peroxide concentration; at ambient temperature (25±2ºC). The emphasis was on using a crude extract that showed high enzyme activity, despite being obtained by minimum processing, and virtually no purification. Methodology: Hairy root cultures of A. rusticana were used as the source of crude peroxidase. The hairy root tissue was macerated using phosphate buffer (pH 5.8) and centrifuged. The clear supernatant was used as crude enzyme. The decolourisation of the dyes was assessed using spectrophotometric method. Appropriate controls to account for bleaching due to hydrogen peroxide were maintained. Decolourisation of MO and BB by the Fenton reaction was used as a positive control for decolourisation. Results: The crude peroxidase extract can bring about up to 73% and 32% decolourisation of MO and BB respectively within a reaction time of two hours (2h). Conclusion: The outcome of the present work can find application in the enzymatic treatment of wastewater containing azo dyes. This oxidative decolourisation method appears to be better suited to the decolourisation of mono-azo dyes.