Wastewaters from the olive-oil extraction process: disposal or valorization? Otpadne vode iz procesa ekstrahiranja maslinovog ulja: uklanjanje ili valoriziranje?

Olive vegetation waters (OVW) represent a serious environmental problem for the solution of which several disposal methods have been proposed, such as, e.g., physicochemical treatments (decantation with lime and/or total oxidation; concen-tration, drying and incineration; ultrafiltration and reverse osmosys), agronomic (acquaculture; landspreading) and animal-breeding methods (direct utilization as animal feed or after protein enrichment by, e.g, yeast or fungal fermentation) and of the "biotechnological" type (fermentation; biological treatments). The OVW might also be a possible resource due to the presence of value products (e.g., antioxidants) and of simple and complex sugars which make the waste a possible basis medium for fermentation processes. This work presents a brief survey of studies conducted at the Departimento di Agrobiologia e Agrochimica, University of Tuscia, on the possible chemical and biotechnological valorization of the OVW. Technical feasibility of various fermentative processes either to obtain products of high added value (polysaccharides and enzymes such as lipase, laccase, Mn-peroxidase and pectinase) or to improve the waste’s agronomic use has been assessed. Main residues of the olive-oil extraction process are vegetation waters (OVW) and husks. Extraction system, pressure and centrifugation play an important role in the amount and characteristics of both olive oil and residues (Amirante et al., 1993). In the traditional centrifugation system, 50-100 l of water are added to 100kg of olive paste to reduce viscosity and to improve oil separation: as a consequence, large amounts of OVW are produced. During the last ten/twenty years, new centrifugation systems have been developed that require either less (10-20 l) or no water at all added during oil separation (Fig. 1). In either case, however, residues of the olive-oil extraction may represent a serious environmental problem. F. Federici: Wastewaters from the olive-oil extraction process: disposal or valorization? 16 After recovery of residual oil by solvent extraction, husks from traditional processes can find valid utilization as animal feed or as alternative fuel and in compost preparation. OVW, with washing waters, make the oil-mill waste waters (black waters) generally characterized by large volume and high polluting load. Moreover, compounds with biostatic activity (e.g., polyphenols) are largely present.