Land Application of Olive Oil Mill Waste Water in a Poplar Plantation: Initial Site Characterization

Olive (Olea europaea L.) cultivation covers roughly 4% of the agricultural area in the EU. It is widespread throughout the Mediterranean region, especially Spain (48%) and Italy (22.5%), where this crop is important for the rural economy, local heritage and the environment. Oil extraction procedures produce an aqueous effluent ("vegetation water") and a solid residue, mainly containing the olive skin and stone ("olive husk"). Vegetation waters, known as olive mill waste waters (OMWW), are becoming a major environmental problem because of the large amount produced and the toxicity of the phenolic compounds present. About 2.5 litres of OMWW are released per litre of oil produced, yielding an annual amount of 1.36 Mm3 just in Italy (based on 2007/2008 data). In addition to polyphenols, the effluent contains high levels of plant nutrients, organic compounds, and inorganic salts. Excess amounts of these constituents can adversely impact soil and water quality. On the other hand, OMWW can be a valuable water source, fertilizer and soil amendment to improve soil conditions for plant growth. Yet, since biological purification of OMWW is particularly difficult due to its chemical and biological composition, managing its disposal back to the environment is extremely important. Land application of OMWW on soils cultivated with high evaporative demand and tolerant plants such as poplar could enhance the biological and chemical degradation of the effluent and solve the disposal problem. Therefore, we initiated a project in an olive farm near Pisa, Tuscany, for studying the fate of the OMWW constituents in a poplar short rotation forestry plantation. In this work we present the experimental design and preliminary results, discussing the initial characterization of the site's soil.