Peroxidase from waste cabbage (Brassica oleracea capitata L.) exhibits the potential to biodegrade phenol and synthetic dyes from wastewater

Abstract

Peroxidases are well known for their ability to biodegrade some recalcitrant organic pollutants like phenol and their derivatives resulting in a reduction in their toxicity. The present study was designed to extract, characterize, and evaluate the potential of partially purified peroxidase from discarded and decaying waste cabbage leaves in the biodegradation of phenol and some common synthetic azo dyes. This was done by first partially purifying the crude extract of waste cabbage peroxidase (WCP) using ammonium sulfate precipitation, dialysis, and gel filtration chromatography. Thereafter, the experimental determination of protein concentration, peroxidase activity, and biodegradation of phenol and azo dyes was done spectrophotometrically. The results showed a purification fold of 87.65 with a 34.92% yield. The partially purified peroxidase had its optimum activity at temperature 30 °C, pH 5.5 while showing broad substrate preference with ABTS been the substrate. The stability studies also showed that WCP was stable over a wide range of pH (4.0–7.0) and 41% of its original activity was retained at 80 °C indicating that it is a thermostable enzyme. The kinetic data of WCP showed Km values of 1.24, 17.89, and 19.24 mM and Vmax values of 1111.11, 909.09, and 588.24 mM /minutes for ABTS, guaiacol, and o-dianisidine respectively. Three metal ions, Hg2+, Cu2+, Ni2+, organic solvent (acetone), EDTA, and urea inhibited peroxidase activity; whereas Mn2+ and Zn2+ showed slight activation. The partially purified WCP exhibited high efficiency for the biodegradation of synthetic azo dyes and phenol at the lab-scale. After 48 h incubation, the waste cabbage peroxidase efficiently catalyzed the decolorization of tested azo dyes at varying degrees; azo blue 5, azo purple, azo yellow 6, and citrus red 2, with a percentage decolorization of 85.1, 69.1, 46.2 and 42.9%, respectively. The waste cabbage peroxidase also shows up to 91.1% efficiency for degradation of phenol in aqueous solution after 60 min. Findings from this study provide promising evidence on the possibility of utilizing/recycling a readily abundant waste cabbage to useful bioproducts like peroxidase enzyme with the ability to biodegrade azo dyes and phenol at a small scale in the laboratory. Moreover, the findings from this study increase the prospect of waste cabbage peroxidase for the treatment of industrial effluents containing dyes and phenolic pollutants. The approach of transforming waste from one source into a useful biocatalyst that can potentially be exploited to treat waste pollutants from a different source offers a chain of green technology.