Composting of olive husks: Effect of process type and inoculation on the amount and quality of humic materials

Disposal of by-products from the olive oil industry has become an important environmental issue in the Mediterranean countries. The composting of husk s is a very difficult process because of their high content of polyphenolic compounds. We evaluated the efficiency of three different systems for comp osting: a) inoculated static pile, b) non-inoculated static pile, c) a larg e-scale pilot plant. The end-products taken from the inoculated and non-ino culated static piles showed a good increase in levels of aromatic structure s characterised by high molecular weights compared with the original materi al and with stored husks; inoculation enhanced the decomposition of the ali phatic moieties. The composting process was optimised by the use of the pil ot plant: analyses performed by Fourier-transformed infrared spectroscopy, isoelectrofocusing, high performance size-exclusion chromatography and capi llary electrophoresis agree in showing a more pronounced humification, test ified by qualitative and quantitative changes in humic and humic-like subst ances and by the concomitant decomposition of the original matrix.