Organic matter transformation and detoxification in dry olive mill residue by the saprophytic fungus Paecilomyces farinosus

Dry olive mill residue (DOR), the by-product of the two-phase extraction process, is very rich in organic matter and nutritionally relevant cations. For this reason, the agronomic use of this waste has been suggested although DOR exhibits significant phytotoxicity. The objective of this study was to investigate the impact of Paecilomyces farinosus on both organic mattermodification and detoxification of this waste. Humification ratio in DOR colonized by the fungus for 20 weeks was increased by about 65%with respect to the abiotic control and humification index reached 0.38, a value that characterizes well-humified materials. High performance size-exclusion chromatography of humic acids from fungal cultures showed a marked increase in both weight-averaged and number-averaged molecular weights with respect to abiotic controls. Water-soluble phenols were reduced by 45% in 20-week-old P. farinosus cultures on DOR andmass-balance ultra-filtration showed that the relative abundance of themolecular weight fraction of phenols above 30 kDa increased from 31 to 72% suggesting the occurrence of polymerization. Experiments performed with alfalfa grown on soils containing 2.5% (w/w) of abiotic controls and fungaltreated DOR showed that phytotoxicity was totally suppressed in the waste that underwent fungal treatment. 2008 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +39 0 761 357368; fax: +39 0 761 357242. E-mail address: [email protected] (A. D’Annibale). G Model PRBI-8531; No of Pages 10 Please cite this article in press as: Sampedro I, et al. Organic matter transformation and detoxification in dry olive mill residue by the saprophytic fungus Paecilomyces farinosus. Process Biochem (2008), doi:10.1016/j.procbio.2008.10.016