Soil amendment with olive mill wastes: impact on groundwater

Area of Science:

• Environmental Science
• Soil Science
• Agricultural Chemistry

Background:

• Olive mill waste (OMW) is a significant byproduct of olive oil production, posing disposal challenges.
• Sustainable management of OMW is crucial to prevent potential environmental pollution, particularly groundwater contamination.
• Assessing the impact of OMW application on soil and water quality is essential for its safe utilization.

Purpose of the Study:

• To evaluate the potential groundwater contamination from soil application of olive mill wastes.
• To compare the effects of liquid olive mill wastewater (OMW) and solid composted olive pomace on leachate composition.
• To determine the necessity of pre-treatment for OMW before soil application.

Main Methods:

• Soil lysimeters were treated with OMW at two rates (80 and 320 m³/ha), pre-treated OMW, composted olive pomace, and freshwater (control).
• Leachate was analyzed for electric conductivity, pH, potassium, total polyphenols, and nitrates.
• Parameters were monitored to assess potential groundwater contamination.

Main Results:

• All tested amendments, including OMW at four times the Italian legal rate, showed minimal impact on groundwater quality.
• Pre-treatment of OMW by catalytical digestion with MnO2 did not significantly reduce its already low impact on groundwater.
• Composted olive pomace application was found to be equally safe, with no significant adverse effects observed.

Conclusions:

• Olive mill wastes, including OMW and composted pomace, can be safely applied to soil without significant risk of groundwater contamination.
• Current Italian regulations for OMW application rates are conservative, with higher rates potentially being safe.
• Pre-treatment of OMW is not required to mitigate groundwater contamination risks when applied to soil under the tested conditions.