Ligninase-catalysed decolorization of synthetic dyes

Many synthetic dyes in industrial wastewaters are resistant to degradation in conventional biological treatment process. Decolorization of eight synthetic dyes including azo, anthraquinone, metal complex and indigo were examined in white-rot fungal cultures and by fungal peroxidase-catalysed oxidation. The dyes were not decolorized by manganese-dependent peroxidase (MnP) while above 80% color was removed by ligninase-catalysed oxidation. Dye decolorization rate increased linearly with ligninase doses. Compared with fungal cultures in which ligninase was detected, partially purified ligninase showed a consistent and higher extent of dye decolorization with other essential components being provided such as veratryl alcohol, hydrogen peroxide and acidic pH (3.5–5). Veratryl alcohol had a critical concentration level above which no further effect on dye decolorization was observed. Depending on the influence of H2O2 on dye decolorization, the eight dyes can be divided into two groups; one had an optimum H2O2 concentration and the other showed increased decolorization with high H2O2 doses. Dye concentration had a negative effect on decolorization rate in general. The dye concentration above which the negative effect was observed varied from 10 to 125 mg/L, depending on individual dye structure. These results indicate that a highly efficient bioprocess using white-rot fungi to remove color from industrial effluents should produce ligninase, H2O2, veratryl alcohol continuously and coordinately under acidic condition and controlled back-mixing flow of wastewater.