Laboratory Composting Assays of the Solid Residue Resulting from the Flocculation of Oil Mill Wastewater With Different Lignocellulosic Residues

Abstract

The manufacturing process of olive oil yields a highly contaminating residue whose elimination supposes a serious environmental problem still unresolved in the principal olive oil-producing countries. Nonetheless, this residue is rich in organic matter and minerals, which makes its use as a fertilizer or organic amendment significant to the poor soils that abound so much in the countries where it originates. In accordance with its peculiar characteristics, its direct applications could lead to more adverse than beneficial effects, for which reason it would be necessary to carry out a previous composting process in order to utilize it. The principal objective of the present study is to evaluate the quality of different products obtained through the composting of the solid residue that results from the flocculation of the oil mill wastewater. To facilitate composting, the residue of flocculation (FOMW) was mixed with different lignocellulosic residues (straw, vine shoots, olive branches and olive husk). The composting was carried out in a climatic chamber in PVC containers having a capacity of 5 litres. Samples were periodically taken which were characterized and analyzed. Except for the mixture of FOMW with olive husk, in the rest of the mixtures assayed, an important degradation of organic matter as well as cellulose was observed. In addition, a decline of phytotoxicity which the initial product presented was observed. The results obtained show that the composting of this residue, when mixed with others of lignocellulosic character, is an effective manner of resolving the problem, while generating quality products from the point of view of its agricultural utilization.