Olive oil mill wastewaters (OOMW) generated in huge quantities over a short period every year (November - April) represent a significant environmental problem in Mediterranean countries. Their disposal may cause adverse effects on soils, surface- and groundwaters due to organic compounds content, such as organic acids, lipids, alcohols and polyphenols which are considered as phytotoxic (Paredes et al., 1986; Mekki et al., 2007; Zaharaki and Komnitsas, 2009).
One t of olives approximately produces 0.8 t of OOMW which are characterized as acidic (pH 4-5), with an average COD content of 80 g/L, high concentrations of suspended solids (7–15 g/L) and phenolic compounds (2–10 g/L). OOMW are also characterized by a variable brownish colour depending on the age and type of olives used (Riccardi et al., 2000; Ben Sassi et al., 2006; Khoufi et al., 2008).
For the treatment of OOMW, valorization and reuse, various management methods have been proposed (physical, physico-chemical, biological and thermal). However, no treatment method can be efficient when solely used, since high application cost considering the economic means of each individual olive-mill owner, is involved (Zaharaki and Komnitsas, 2009).
Evaporation in lagoons and disposal on agricultural soil is the most common management option in the Med region, due to low cost and dispersion of olive oil production units which are mostly small family businesses. This approach is followed to reduce volume by evaporation of water. On the other hand the properties of soil (e.g. texture, nutrient and organic matter content, seed germination and productivity) due to continuous direct application of OOMW or due to leakage from evaporation ponds may be altered to some degree (Kapellakis et al., 2006).
The usual treatment and disposal practice followed in Greece involves neutralization with lime and disposal in evaporation ponds/lagoons; OOMW are also disposed of in sea, river or soil. The construction of evaporation ponds rarely meets engineering criteria for stability and safe accommodation of liquid wastes, therefore OOMW often overflow and affect neighboring systems (agricultural soils, surface- and groundwater). The base of the ponds is in most cases permeable and thus the probability for groundwater and soil contamination is considered high (Paraskeva and Diamadopoulos, 2006; Oreopoulou and Russ, 2007; Kavvadias et al., 2010).
- Ben Sassi A., A. Boularbah, A. Jaouad, G. Walker and A. Boussaid (2006). A comparison of olive oil mill wastewaters (OWM) from three different processes in Morocco, Bioprocess Biochem 41, 74–78.
- Kapellakis I.E., K.P. Tsagarakis, Ch. Avramaki and A.N. Angelakis (2006). Olive mill wastewater management in river basins: A case study in Greece, Agr Water Manage 82, 354–370.
- Kavvadias V., M.K. Doula, K. Komnitsas and N. Liakopoulou (2010). Disposal of olive oil mill wastes in evaporation ponds: Effects on soil properties, J Hazard Mater 182, 144–155.
- Khoufi S., F. Aloui and S. Sayadi (2008). Extraction of antioxidants from olive mill wastewater and electro-coagulation of exhausted fraction to reduce its toxicity on anaerobic digestion, J Hazard Mater 151(2-3), 531–539.
- Mekki A., A. Dhouib and S. Sayadi (2007). Polyphenols dynamics and phytotoxicity in a soil amended by olive mill wastewaters, J Environ Manage 84, 134–140.
- Oreopoulou V. and W. Russ (2007). Utilization of By-Products and Treatment of Waste in the Food Industry, Series editor: Kristberg Kristbergsson, Springer.com.
- Paraskeva P. and E. Diamadopoulos (2006). Technologies for olive mill wastewater (OMW) treatment: a review, J Chem Technol Biotechnol 81, 1475–1485.
- Paredes M.J., M. Monteoliva-Sanochez, E. Moreno, J. Perez, A. Ramos-Cormenzana and J. Martinez (1986). Effect of waste waters from olive oil extraction plants on the bacterial population of soil, Chemosphere 15, 659–664.
- Riccardi C., M. Di Basilio, F. Savarese, L. Torrisi and M. Villarini (2000). Aging-related physical-chemical changes in olive oil mill effluent, J Environ Sci Health A 35, 349–356.
- Zaharaki D. and K., Komnitsas (2009). Existing and emerging technologies for the treatment of olive oil mill wastewaters, International Conference AMIREG 2009 “Towards sustainable development: Assessing the footprint of resource utilization and hazardous waste management” Athens, Greece, 7 - 9 September.