Dealing With The Liquid By Products of Olive Oil Production
A resent study conducted by the Fraunhofer Institute for Interfacial Engineering and Biotechnolog focuses on the potential environmental hazards of olive oil production process. There are two major types of olive residue that are produced as a result of olive oil extraction: Olive Cake (Olive Pomace) and Vegetation Water. Olive Cake has immediate use in the bioenergy industry. However, the vegetation water, or black water as it is called among Turkish farmers pose an environmental conundrum. This waste product is rich in organic content yet not readily usable as liquid fertilizer. Olive vegetable water is rich in phenols which are potentially valuable due to their antioxidant qualities but liquid olive residue is an environmentally dangerous waste product. One liter of olive residue can contaminate several times more volume of water than regular household sewage and thus it is imperative that it should be prevented from leaking uncontrolled into ground water or open streams and rivers.
Olive Oil industry is an important part of the European Union agricultural sector with about 2.2 million metric tons produced every year. Now, it is important to note that for every one hundred kilograms of olives processed about 20-22 kg of olive oil is obtained. The actual amount varies depending on the production method, the olive breed, and time gap between picking and pressing. Again depending on the method between 85 and 175 kilograms of vegetable water is produced. Traditional olive presses that use only mechanical power to crush and press the olives produce the least amount of liquid residue. In contrast two phase and three phase production methods add water and heat to facilitate oil extraction and therefore produce a higher volume of contaminated liquid residue. Due to the high content of phenols, fatty acids and organic substances the discharge of liquid waste into rivers creates a phytotoxic effect in bodies of water. In some regions the residues are collected in storage ponds, which may also lead to damage to the environment.
From Olive Residue to Biogas
In an industry that is vital to several economies in the region drastic change does not come easily and actors involved in the sector need some convincing. Any proposal for changing practices needs to be backed up by research immaculately. Fraunhofer’s report is among such studies and it is an ongoing project. Over the recent decades use of olive biomass as a fuel source has been increasing. In fact locals have known and used olive cake as a substitute for firewood for millennia. Gradually the industry started to take notice of the economic potential of olive cake (alperujo, as it is called in Spanish). Today (i.e. 2010s) in many olive producing regions solid olive residue is not an environmental problem anymore. Especially Italian and Spanish olive related industries have integrated olive pomace relatively well in the agricultural and energy sectors. However, Turkey, the fourth largest producer of olives still wastes most of its olive cake (which is called pirina in Turkish, a Greek origin word if memory serves). Nevertheless, the real environmental problem is not the solid by products of the olive oil production. It is the liquid waste (alpechin in Spanish) that worries the environmentalists. Despite the fact that research into a cost-efficient, technically feasible and environmentally sound solution for the disposal of these residues has been going on for over 50 years, it has not yet been possible to find a satisfactory answer which can be comprehensively transferred to industrial applications. Together with nine European partners from research, industry and various associations the Fraunhofer IGB is developing a combined process during which organic substances present in high concentrations, such as polyphenols, are first extracted and reused as natural antioxidants. The residual biomass is then digested for the generation of bio gas.
Trial and Error
The major problem faced by researchers is the chemical composition of the liquid waste. Olive oil residues are characterized by a high concentration of potassium, organic and sulfur compounds and a low nitrogen concentration. Therefore, these residues constitute a special challenge for anaerobic microorganisms (for futher info check 1 or 2 ). Since digestion of biomass that comes from every different source needs a different optimal process experiments were carried out on a large number of solid and liquid waste batches which had been generated during olive oil production using different production methods in Spain, Italy and Greece. The results are generally encouraging. Organic content of both solid and liquid olive residues were successfully reduced to bio gas. In these experiments the methane content of the resulting gaseous by product was around 70 percent.
Where do we go from here?
Olive oil is a vital industry for many countries in the Mediterranean basin. Furthermore it involves millions of families, large and small scale producers and literally hundreds of millions of consumers. Olives and olive oil production will remain an important economic activity and total efficiency of the industries related to olives must be enhanced. Biogas production from liquid olive residue not only utilizes what is generally considered a waste product but also helps thwart an environmental threat.
New Perspectives on Olive Oil Residue
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