Biodegradation of olive mill solid waste by Anthracophyllum discolor and Stereum hirsutum: effect of copper and manganese supplementation

Abstract

Anthracophyllum hirsutum and Stereum hirsutum produce manganese peroxidase (MnP) and laccase to break down lignin, a potential biological pretreatment for lignocellulosic biomass. This work aimed to evaluate the effect of copper (Cu) and manganese (Mn) added to olive mill solid waste (OMSW) inoculated with A. discolor and S. hirsutum on ligninolytic enzyme activity, lignin degradation, and phenolic compound removal. Different optimal metal dosages were determined for each fungal strain. For S. hirsutum, the addition of 6.1 mg Cu kg⁻1 and 7.3 mg Mn kg⁻1 resulted in 173 ± 5 U·L⁻1 MnP activity (an 863% increase compared to no metal addition) and 42 ± 3% lignin degradation (183% higher than with no metal addition, 15 ± 3%). These conditions also led to 65–75% phenol removal efficiencies in OMSW at 25 days and 80–95% in leachates between 20 and 30 days. For A. discolor, 14.6 mg Mn kg⁻1 yielded 37 ± 7 U·L⁻1 MnP activity (a 142% increase compared to no metal addition) and 38 ± 7% lignin degradation (150% higher than with no metal addition, 15 ± 3%). Under these conditions, A. discolor achieved 80–90% phenol removal in leachates at 20 days. These results demonstrate the positive effect of optimised metal supplementation, highlighting the potential of S. hirsutum and A. discolor for effective lignocellulosic biomass pretreatment and future mycoremediation processes.