Soil spreading of liquid olive mill processing wastes impacts leaching of adsorbed terbuthylazine

• OMWW is frequently spread on agricultural land for disposal.
• OMWW effect on leaching of adsorbed terbuthylazine was tested in four soils.
• Terbuthylazine solubility in OMWW is significantly higher than in water.
• Terbuthylazine leaching from OMWW-treated soils is lower than control treatment.
• Low soil organic carbon and clay contribute to reduced terbuthylazine leaching.

Olive mill waste water (OMWW) is a major byproduct of the three phase olive oil production process. OMWW has high acidity (pH ∼ 4–5), high salt content (EC ∼ 5–10 mS cm−1), extremely high biological and chemical oxygen demand (BOD and COD up to 100,000 and 220,000 mg L−1, respectively), and also high concentrations of organic compounds such as phenols and polyphenols. As a result, OMWW cannot be freely discharged into domestic wastewater treatment plants, but on-site treatment is very expensive and not sufficiently effective. Uses for OMWW such as agricultural recycling and co-composting were found to be impractical or expensive. Thus, OMWW is frequently spread on agricultural land for disposal. However, excessive or uncontrolled spreading of such organic-rich and saline wastewater could have many deleterious effects on soil quality, including salinization, phytotoxicity, or contaminant movement. The impact of OMWW on the leaching of adsorbed terbuthylazine, a soil-applied herbicide, was tested in four soils of varying physical and chemical properties. Although terbuthylazine solubility in OMWW is significantly higher than in water, leaching of adsorbed terbuthylazine from OMWW-treated soils was less than from control treatments. Low soil organic carbon and clay contents were major factors that contributed to reduced terbuthylazine leaching after soil treatment with OMWW.