Out of the 2,500 olive mills spread out all over Greece 850 are located in the Peloponnese, where 25% of all Greek olive oil is produced. Along with this high amount of oil production comes a huge amount of waste. For a few months, from November to March every year, olive oil mills in Greece create a whopping 2,750,000 tons of wastewater known as olive oil mill wastewaters (OOMW).
Each year with the growing popularity for olive oil, the very basis of the healthy Mediterranean diet, the amount of wastewater containing pomace (olive pulp and skins) is growing. Before this increased demand for olive oil, wastewater was dumped at the side of the fields where it created better soil and plenty of water for crops. Now the amount of waste is so large because of increased olive oil production the land can no longer absorb it.
The disposal of wastewater is an ongoing environmental and financial headache. New ideas and methods are being tested constantly as wastewater containing acids, lipids, alcohols, and polyphenols, if not disposed of correctly, may be harmful to soil and to both above ground and underground water supplies. In Mediterranean countries this is a huge problem as most methods of disposal (manual, thermal, biological) are expensive and prove to be well out of the economic means of small family-run olive oil mills.
Up until 2011 there were no official regulations for the disposal of olive oil wastewaters. A new law created in 2011 regulates the reuse of treated wastewater as irrigation, for example, and dried pomace used as fuel. To obtain their licenses for running olive mills olive farmers are bound to adhere to the environmental regulations, disposing of OOMW in the correct way. Unfortunately, due to the high cost of the disposal techniques, less effective, cheaper methods are often used and many olive oil mills do not fulfil regulations.
The most usual form of wastewater disposal in Greece and the Mediterranean is the evaporation method. Special pools or ponds are constructed to hold wastewater where, ideally, it will safely evaporate. Not always the case as there is the fear of leakage and over spill causing contamination to the surrounding area. Another practice is to spread the OOMW over the land. Here exists the fear of soil damage. In Greece, lime is added to neutralize the OOMW before disposal in evaporation ponds, the sea, and rivers, or over the land, which minimizes the threat of soil and water contamination.
Methods tried using leftover pomace (olive residue), which contains a lot of oil as heating fuel have been quite successful. Greece hopes to turn olive waste into Euros by experimenting using the olive oil waste to produce electricity.