Olive Mill Wastewater Powers Greener Breakthrough in Moroccan Shale Oil Extraction

A recent study published in the journal Fuel reported how olive mill wastewater (OMW) can be used for environmentally friendly shale oil recovery (1). This study, which was conducted by a team of researchers at Hassan II University of Casablanca, focuses on the Timahdit Y-layer oil shale deposit and achieves oil recovery yields that exceed those of conventional extraction methods.

Morocco is an oil-rich country in northwest Africa that borders Algeria to the east and the disputed territory of Western Sahara in the south. As a result, it has extensive oil shale reserves, which account for approximately 15% of the entire world’s reserves (2). Most of the oil shale deposits are found in the Tangier, Tarfaya, and Timahdit regions of the country (2).

These deposits represent an untapped energy source for the country. Extracting shale oil, however, comes with certain challenges. For one, the process is dependent on high temperatures. Second, it is an energy-intensive process, and, finally, these processes require environmentally hazard solvents (1).

Because of the need to extract oil shale, scientists have been investigating more sustainable methods for doing so. In this study, the research team explored sub-critical water extraction using OMW as a low-cost, non-toxic solvent capable of enhancing shale oil recovery while simultaneously addressing the environmental burden associated with olive oil production (1).

OMW is generated in large quantities across the Mediterranean countries and is known for its high organic load and phytotoxic properties, making disposal a persistent environmental challenge (1). The study reframes this waste stream as a valuable resource, aligning energy production with waste valorization and environmental protection goals.

The team examined several operational parameters, including OMW quantity, temperature, pressure, extraction time, and pH, and tested them to see how each affects the oil yield from carbonate-free Timahdit Y-layer shale. Through systematic optimization, they identified a set of conditions that delivered exceptional performance. Under optimal parameters, 25 g of shale was combined with 25 g of OMW adjusted to a pH of 11.5, then processed at 325 °C and 10.0 MPa for 120 minutes with continuous mixing (1).

Under these conditions, the team achieved a shale oil recovery yield of approximately 94.5 wt%, surpassing yields obtained using conventional high-temperature autoclave methods (1). According to the authors of this study, this represents one of the highest recovery efficiencies reported for Moroccan oil shale under sub-critical extraction conditions (1). “This setup,” the authors wrote in their study (1), “ensures an efficient interaction between the shale and the extraction medium, leveraging the properties of OMW to enhance the process.”

Beyond yield, oil quality was a central focus of the study. Spectroscopic characterization using Fourier transform infrared (FT-IR) spectroscopy and hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy revealed that the extracted oils are rich in aromatic hydrocarbons and relatively low in paraffinic compounds (1). This compositional profile is significant, as aromatic-rich oils can be advantageous for certain downstream refining and chemical applications.

The FT-IR spectra were recorded across the 400–4000 cm⁻¹ range using a Bruker Tensor 27 spectrometer, while ¹H NMR analyses were conducted on a Bruker JNM-ECZ500R/S1 system operating at 500 MHz. These analyses confirmed the successful maturation and solubilization of organic matter within the shale matrix under sub-critical conditions, supported by the chemical properties of OMW (1).

The authors emphasized that pH played a particularly important role in the extraction mechanism (1). Adjusting OMW to a strongly alkaline pH enhanced interactions between the solvent and the shale’s organic matter, improving solubilization and oil release. Temperature and pressure were also critical, with the chosen sub-critical conditions striking a balance between efficiency and environmental impact (1).

This project forms part of a broader research initiative at Hassan II University of Casablanca focused on the sustainable use of natural resources, with particular emphasis on Morocco’s oil shale reserves (1). By combining sub-critical water extraction with an agricultural waste-derived solvent, the study offers a dual environmental benefit: reducing reliance on toxic extraction chemicals and mitigating the harmful effects of olive mill effluents on ecosystems and human health.

References

1. Chham, A.-i.; Hannache, H.; Saoiabi, A.; et al. Sustainable and Eco-environmental Green Sub-critical Water Extraction of Moroccan Shale Oil Using Oleic Discharges Waste. Fuel 2026, 403, 136030. DOI: 10.1016/j.fuel.2025.136030
2. El Idrissi, H. S.; Samaouali, A.; El Rhaffari, Y.; et al. Characterization of the Petrophysical Properties of the Timahdit Oil Shale Layers in Morocco. Geosciences 2020, 10 (9), 337. DOI: 10.3390/geosciences10090337