Irrigation Systems for Land Spreading of Olive Oil Mill Wastewater

Mill wastewater has always created considerable environmental problems for countries producing olive oil. These problems, which are of increasing relevance in relation to the growing interest in protecting water resources, are of technical and economic nature and are mainly due to the quality of the wastewater (which contains a large amount of organic substances and solute or suspended minerals, and is highly fermentable), the seasonal nature of the production process, and the great territorial dislocation of the olive mills. In order to obtain wastewater which complies with current environmental legislation regarding discharge into water supply systems, it is necessary to use treatment plants with high running costs, which can be prohibitive in olive processing activities. Accumulation and subsequent distribution on the soil through irrigation plants may represent a sustainable solution to the various problems connected with olive mill wastewater (OMW) disposal. Besides allowing for a considerable saving in costs, the use of irrigation plants allows optimal distribution of wastewater. With gradual and uniform distribution, phytotoxic organic substances are held and broken down in the surface layer of the soil, far from the roots of the trees and from water tables. Several experiments highlight that the effects of OMW on crops, soils and the environment depend on the quantity of OMW distributed, but very little information on optimal systems and modalities used to spread OMW is available. A gradual, uniform distribution of OMW can be obtained through microirrigation systems. However, some system management problems may occur. In fact, the small orifices of the emitters and the filters used to protect them can be clogged by small particles or growths due to the suspended solid content of OMW, mainly of organic type. The paper dicusses both agronomic and operational aspects of OMW spreading. According to the analysis, some practical recommendations for agronomic OMW use by microirrigation systems are made.