Organic matter evolution and partial detoxification in two-phase olive mill waste colonized by white-rot fungi

Dry olive mill residue (DOR) is a solid waste arising from the olive oil two-phase extraction system. The objective of the present study was to investigate the impact of an aerobic treatment of DOR with selected lignin-degrading fungi on both organic matter evolution and residual phytotoxicity of the waste. To this aim, several white-rot fungi, including Phlebia radiata, Coriolopsis rigida, Phanerochaete chrysosporium, Pycnoporus cinnabarinus, Poria subvermispora and Pleurotus pulmonarius were inoculated under axenic conditions for 2 and 20 weeks. The chemical composition and phytotoxicity of DOR were scarcely affected by fungi after 2 weeks incubation. By contrast, both a significant depletion of phenolic compounds and a partial removal of phytoxicity towards Lycopersicum esculentum plants were generally obtained after 20 weeks. The most effective fungus in degrading lignin, total phenols and in removing phytotoxicity was C. rigida. A high correlation was observed between phytotoxicity and phenols added to soil with the waste.