LAUSR

In the Mediterranean basin, the treatment and disposal of olive mill pomace (OMP) remain a salient environmental issue for the olive oil-producing industry. This study assesses the effects of olive-processing technology (three-phase and two-phase systems) on the potential use of OMP as a soil amendment. Samples from 12 Croatian olive mills were analysed for their total phenolic content (TPC), residual oil fraction, and elemental concentration. The samples were profiled using FT-IR spectroscopy and structurally characterised using SEM-EDS. Compared to three-phase samples, two-phase OMP was more acidic (pH 4.5 vs pH 5.0), with a higher TPC (3835 vs 1576 mg/kg f.w.), oil content (11.7 vs 7.5% d.w.), EC (5.1 vs 3.0 mS/cm), and levels of Ca (1.34 vs 1.20 g/kg d.w.) and Cu (10.4 vs 7.0 mg/kg d.w.). Similar values of C/N (61 vs 72), N (10 vs 8.1 g/kg d.w.), P (1040 vs 691 mg/kg d.w.), and K (13.7 vs 8.1 g/kg d.w.) were observed. The amounts of Cr, Cu, Ni, and Zn were below EC limits in both cases. The EDS mapping revealed that Ca was concentrated at sharp-edged OMP particles while K was evenly distributed, suggesting that pelletized OMP compost is preferable for amending soil to obtain a homogeneous distribution of nutrients. It was also possible to distinguish between OMPs based on oil and lignin absorption bands in their FT-IR spectra. According to the obtained results, composting is recommended for both types of OMP to produce a safe product for amendment purposes. This article is protected by copyright. All rights reserved.