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Olive fruit processing produces large amounts of by-products, including liquid and solid wastes arising from olive oil extraction and the production of table olives. The disposal without any treatment of the wastewaters, arising mainly from the olive-mill (OMWW) and to a lesser degree from the table olive industries, is known to cause serious environmental problems. A wide range of technological processes are available nowadays for reducing the pollutant effects of OMWW and for its transformation into valuable products, the most suitable procedures being found to involve recycling rather than detoxification of this waste. Moreover, antipollution legislation has been forcing the utilization of OMWW as an alternative to disposal. Thus, in view of the current need for upgrading by-products at all stages of the olive oil industry (Demichelli M. and Bontoux L., 1996), increasing attention has been paid to discovering a use for OMWW.

OMWW is composed of vegetation water, soft tissues of the olive fruit, and water used at the different stages of oil production. The vegetation water in the olive fruit represents 45-50% of the weight of the fruit and a volume of up to 7 million m3 is produced each year, in addition to the water added during the olive oil extraction process. The organic matter content is 15-18%, which implies an annual production of 1-1.2 million tons of substance that may be used as raw material either to recover valuable natural constituents/by-products or as a culture from which to develop microorganisms for new products (Fiestas Ros de Ursinos J.A. et al., 1996). Since the early 1970s, the pressure of pollution has promoted studies on conversion of OMWW to useful products like fertilizer, animal feed, a medium of fermentation for single cell protein (SCP) and enzymes, production of alcohol (ethanol, butanol, mannitol), biogas, etc. Lately, several techniques have been developed for the efficient and economic extraction of antioxidants27. Fig. 10.1 shows schematically some fields for the end products of treated OMWW.

27The applications of OMWW have been reviewed by Ramos-Cormenzana (1986) and widely discussed at the Granada Olive Oil Conference held in 1995, in Granada, Spain.

The use of olive-mill liquid wastes is known since antiquity. A predecessor of OMWW is amurca. Amurca or olive oil lees, the watery bitter-tasting liquid residue obtained when the oil is drained from compressed olives, had many uses in agriculture. Amurca has been described by several ancient authors as having a universal remedy against insects, weeds, and plant diseases (Columella, Pliny the Elder, Cato, and others). Amurca has also been used for smoothing out plaster floors, oiling leather, etc.; however, many of these uses are not exactly applicable for the modern day28.

Solid olive-mill wastes have been traditionally used as fuel, both domestic and industrial, and animal feed — see Fig. 10.2. Other uses include use as fertilizer and construction material.

The use of the two-phase processing technique generated a new by-product that is a combination of liquid and solid wastes (2POMW). In Spain, a massive change from the traditional three-phase to the new two-phase process has taken place, and large volumes of this waste (~4.5 million tons per year) are already produced (Junta de Andalucía, 2002; Alburquerque J.A. et al., 2004). The massive production of this by-product intensified the efforts to find possible uses and diminish its environmental impact (EU project: FAIR CT96-1420 "IMPROLIVE").

Fig. 10.2. Piles of olive residue in a warehouse at the excavation site of Karanis in the Fayoum region of Egypt. This olive residue, which was once thought to be bread, was used for animal feed and fuel. (http://www.umich.edu/~kelseydb/Exhibits/Food/text/farm2.html#oil).

Fig. 10.2. Piles of olive residue in a warehouse at the excavation site of Karanis in the Fayoum region of Egypt. This olive residue, which was once thought to be bread, was used for animal feed and fuel. (http://www.umich.edu/~kelseydb/Exhibits/Food/text/farm2.html#oil).

28http://www.oliveoilsource.com.

Olive tree culture by-products include unpicked fruit, pruning, and harvest residues. Historically pruning brush was used for energy on small landholdings, but with availability of alternate energy sources and higher labor costs, only larger wood is still used for burning. Smaller wood and foliage can be chopped and incorporated into the soil or burned. Ashes can be spread on the fields to release potassium and trace elements. Increased production of olives has not been shown to justify expenses involved with such procedures (Amirante P. and Pipitone F., 2002). Using pruning brush for fuel or animal feed seems more promising.

It is also worth mentioning the wastes generated from olive oil use. The main by-product of olive oil use is waste cooking oil. Used cooking olive oil constitutes a waste which is included in the group of urban and municipal wastes. Its main use at present is in animal feed (although controversial) and, in a much smaller proportion, in the manufacture of soaps, biodegradable lubricants (although not recyclable), combustion (recovery of energy in industrial plants), or even fuel for engines (Dorado M.P. et al., 2004). An unusual by-product of the cosmetic use of olive oil in the antiquity was gloios — see Fig. 10.3.

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