Modern strategies for olive oil mill residues exploitation: environmental and energetical opportunities

SUMMARY: In the last ten years many investigation on olive oil mill residues composting were carried out. Olive husks (OH) and olive mill wastewaters (OMWW) from three or two phase extraction system and other agricultural residues were composted in pilot or industrial scale plants located in central and northern Italy. Composting tests were carried out using various technological solutions such as static/dynamic piles, aeration through mechanical turnover or inoculum addition. Processes were monitored through the assessment of microbiological, physico-chemical, biochemical-enzymatic, impedometric and phytotoxicity parameters. Cured compost were characterized and assayed for agronomic properties and suppressive activity against fungal plant pathogens. Some of these composts consistently reduced the growth in vitro of Verticillium dahliae and other fungal pathogens of important vegetal crops. The inhibitory activity decreased or disappeared when cured composts were autoclaved before their use; therefore the suppressive activity is mainly due to the beneficial residual microbial population selected during the composting process. In experiments performed with young olive plants and eggplants grown on soil artificially contaminated by V. dahliae microsclerotia (MC), the incorporation of 15% (w/w) of a selected cured compost or the antagonistic fungus Trichoderma viride as well as 15% (w/w) of cured compost and T. viride applied together significantly reduced the density of V. dahliae MC in the soil. The results of these investigations indicate that composted olive by-products show very promising fertilizer and amender effects and could be successfully used for biological control of fungal pathogens of vegetal crops in organic and integrated agriculture systems.