Evaluation of several white-rot fungi for the decolorization of a binary mixture of anionic dyes and characterization of the residual biomass as potential organic soil amendment

Abstract

Industrial pollution is a great concern for modern society and developing cyclic processes is one of the major challenges. As far as we know, this work is the first to report the use of multiple white-rot fungi species for degrading a binary mixture of anionic dyes under solid state fermentation (SSF) conditions and a further physicochemical characterization of the residual biomass. First, eight white-rot fungi decolorized the dye mixture of brilliant blue FCF and allura red AC adsorbed onto corncob, reaching decolorizations between 11.47% and 87.64%. Then, I. lacteus, B. adusta and T. versicolor, based on the decolorization yield, were selected to evaluate the effect of carbon:nitrogen ratio, moisture content and inoculum quantity on the decolorization percentage. The factorial designs showed that C:N ratio had a negative effect while moisture and inoculum quantity a positive effect. In terms of the kinetics, the three white-rot fungi achieved their maximum decolorization level, around 80.11–86.04%, after 10-12 days. I. lacteus exhibited the highest decolorization percentage, even though only the enzyme manganese peroxidase was detected, with a maximum activity of 6.62 U gds−1 at day 14. Besides, T. versicolor was the only species with laccase activity, with a maximum of 15.94 U gds−1 at day 6 of fermentation. The physicochemical characterization of the biomass allowed to conclude that these aggregates represent a potential organic amendment, as for their significant oxidizable organic carbon (more than 9.5% on wet basis) and essential nutrients content, as well as for their low ash content (less than 1% on wet basis). Finally, for outlining an efficient bioremediation cycle, a cheap and effective methodology for drying the biomass at the end of the SSF process is required.