Olive mill wastewater treatment

Abstract

The cultivation of olive trees and the production and use of olive oil has been a well-known and established practice in the Mediterranean region for more than 7000 years. The consumption of olive oil is rapidly increasing worldwide, due to its high dietetic and nutritional value. According to the IOOC (2004), the production of olive oil increased from 1.85 million tons in 1984 to 3.17 million tons in 2003 (70% increase) (Table 8.1). There are approximately 750 million productive olive trees worldwide, 98% of them located in the Mediterranean region, where more than 97% of olive oil is produced. The three major olive oil producers worldwide are Spain, Italy, and Greece, followed by Turkey, Tunisia, and to a lesser extent Portugal, Morocco, and Algeria. The data presented in Figure 8.1 reflect the importance of the olive oil sector in the Mediterranean area and consequently the magnitude of the problems related with the disposal of large amounts of wastes produced during olive oil production. The traditional press extraction method as well as the continuous three-phase decanter process, which is most widely used for the production of olive oil, generate three products: olive oil (20%) and two streams of waste: a wet solid waste (30%) called "crude olive cake" or "olive husk" and an aqueous waste called "olive mill wastewater" or "olive mill effluent" or "alpechin" (50%). The solid waste (crude olive cake) is the residue that remains after the first pressing of the olives and is a mixture of olive pulp and olive stones. At present, olive husk is processed in seed oil factories in order to extract the small amount of oil remaining in the waste. Both crude and exhausted olive cake can be used as solid fuels (due to their high heating value), for animal feed supplement, or return to the olive grove as mulch. While economic concerns regarding the profitability of seed oil production now are being questioned, the problem of disposal of olive husk is adequately solved by one of these three alternatives. On the other hand, as far as olive mill wastewater (OMWW) treatment and disposal is concerned, the situation is much more complicated in practice. Attempts to alleviate the problem, especially in the major olive oil-producing countries, are more than 50 years old; yet, there has been little success in finding an environmentally friendly and economically viable solution to be generally adopted. © 2007 Springer Science+Business Media, LLC.