Land treatment of olive oil mill wastewater

Experiments carried out in lysimeters filled with two calcareous clayey soils (ca 40% CaCO₃; ca 40% clay), showed that a 2m layer of soil almost completely removed the organic and inorganic components of olive oil mill wastewater (OMW) when it was applied in doses of 5000–10000m³ha⁻¹year⁻¹. This efficiency was maintained for at least 2 years. In field experiments, the application of OMW to one of these soils during three successive years at an annual rate of up to 6000m³ha⁻¹ caused changes in some chemical properties of the soil, especially in the upper layer (0–50cm). Concentrations of soil organic matter, Kjeldahl N, soluble NO₃ and available P increased enhancing soil fertility. On the other hand, soil electrical conductivity and sodium adsorption ratio also increased but below the levels representing salinization or sodification hazard for the soil. Furthermore, leaching of Na⁺ and NO₃⁻ below the 1 m layer were detected.