Olive Wastewater

Olive oil extraction processes are usually grouped into press extraction and centrifugation extraction systems (two-phase and three-phase centrifugal olive oil extraction). The extraction of olive oil generates huge quantities of wastes having a great impact on land and water environments because of their high phytotoxicity. Pressure and three-phase centrifugation systems produce a liquid effluent called olive mill wastewater (OMW) or vegetation water. Typically, 0.5-1.5 m3 of OMWs per 1,000 kg of olives are produced depending on the process used. OMWs appear like violet-dark brown liquids with acid reaction (pH from 3 to 6) containing great quantity of suspended matter, high degree of organic pollution (COD, 40-220 g/L; BOD, 35-110 g/L), high electrical conductivity, reducing sugars up to 60 % of the dry substance and polyphenols (0.5-24 g/L) (Takac and Karakaya 2009). The organic content is mainly represented by polyphenols, carbohydrates, polysaccharides, sugars, nitro compounds, polyalcohols, and oil. Ultrafiltration (UF) membranes allow to separate macromolecules and colloids having molecular weight between 500 and 250,000 Da; they can be used to remove most parts of COD from pretreated OMWs producing a permeate stream which can be submitted to a biological treatment to comply with law limits relevant to BOD and COD (Borsani and Ferrando 1996). A scheme of OMW treatment including a concentration step via UF is depicted in Fig. 1.