Effect of olive‐processing technology on the utilization of olive mill pomace as a soil amendment

• Published in: Journal of environmental quality Vol. 52; no. 3; pp. 610 - 629
• Main Authors: Černe, Marko, Palčić, Igor, Major, Nikola, Pasković, Igor, Perković, Josipa, Užila, Zoran, Lukić, Marina, Romić, Marija, Zubin Ferri, Tea, Goreta Ban, Smiljana, Lapanje, Aleš, Hreščak, Jitka, Heath, David John, Ban, Dean
• Format: Journal Article
• Language: English
• Published: United States 01-05-2023
• Subjects: Copper; Industrial Waste - analysis; Olea - chemistry; Soil - chemistry; Spectroscopy, Fourier Transform Infrared; Technology
• ISSN: 0047-2425; 1537-2537
• DOI: 10.1002/jeq2.20464

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 analyzed for their total phenolic content (TPC), residual oil fraction, and elemental concentration. The samples were profiled using Fourier transform infrared spectroscopy (FT‐IR) and structurally characterized using scanning electron microscopy‐energy‐dispersive X‐ray spectroscopy (EDS). Compared to three‐phase samples, two‐phase OMP was more acidic (pH 4.5 vs. 5.0), with a higher TPC (3835 vs. 1576 mg/kg fresh weight), oil content (11.7% vs. 7.5% d.w., where d.w. is dry weight), electrical conductivity (EC, 5.1 vs. 3.0 mS/cm), and levels of calcium (Ca, 1.34 vs. 1.20 g/kg d.w.) and copper (Cu, 10.4 vs. 7.0 mg/kg d.w.). Similar values of carbon/nitrogen (C/N; 61 vs. 72), N (10 vs. 8.1 g/kg d.w.), phosphorus (1040 vs. 691 mg/kg d.w.), and potassium (K, 13.7 vs. 8.1 g/kg d.w.) were observed. The amounts of chromium, copper, nickel, and zinc 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.
Core ideas
The total phenols, residual oil, electrical conductivity , calcium and copper are higher in two‐phase than in three‐phase olive mill pomace (OMP).
The high potassium (K) abundance suggests the use of OMP as a fertilizer for K‐demanding crops.
Fourier transform infrared spectroscopy peaks ascribed to olive oil and lignin can discriminate between olive‐processing technologies.
Scanning electron microscopy revealed olive stone fragments and pulp in the OMP.
Calcium concentrates at the sharp edges of OMP particles, while K is evenly distributed.