production. SBE contains 20–40% by weight of oil, fat, and colored pigments
[78]. This means that the bleaching earths, especially those containing polyunsaturated fats, have self-flammable properties [79]. Therefore, spent bleaching
earths are listed as hazardous wastes and their disposal or treatment is difficult in the
environment. Also, spent bleaching earths include color pigments like carotene and
chlorophyll and oxidation products which are present in the vegetable oil [9]. In
order to reduce their fat/oil contents, spent bleaching earth can be extracted with
hexane and the oil present in them can be recovered and used as second-quality oil
for different purposes. By this way, the oil content of spent bleaching earth can be
reduced to below 1%. Thus, bleaching earth becomes a solid waste consisting of
inorganic chemicals. This still might be reused as bleaching earth at the secondquality oil production facilities [63].
Soap-stock is accepted as a by-product, which is generated from the alkalirefining of the vegetable oil, otherwise treated as waste. The soap-stock contains
50% total fatty matter and, therefore, it has a commercial value [8]. But it also
contains significant amount of phosphatides, pigments, and other contaminants.
Therefore, soap-stock cannot be used in good-quality soap production. They chemically break down into acid oil. The breakdown can be accomplished by using a
strong concentrated acid. This produced acid oil can be assessed by selling it to soap
production factories [9].
Lecithin is formed at the degumming stage of the oil refining. Basically, it is a
mixture of phosphatides and small amounts of water-soluble components like
glycolipids and oligosaccharides. The gums from the centrifuge are processed by
treating with H 2 O 2 and then dried. After reduction of moisture, the product is cooled.
Thus, lecithin is obtained and used in foods and in cosmetic and pharmaceutical
industries. The best-quality lecithin can be produced from fresh oil [8, 9].
Spent nickel catalyst is generated from hydrogenation process of refined vegetable oil during the production of Vanaspati (hard oil). The continuous use of nickel
catalyst leads to high content of fat adherence to it [8].
Deodorizer distillate is the volatile organic material which is steam distilled in the
deodorization of vegetable oil and hydrogenated vegetable oil. The distillate produced in the industry contains tocopherols and sterols, which are valuable raw
materials for production of vitamin E and steroid drugs [8].
Wastewater treatment sludge consists of all chemical or biological sludges
gathered from the bottom of sedimentation tanks of physicochemical and/or biological treatment. Biological sludge production is clearly located in the aeration basin
and sludge is composed of minerals (10–30%), biomass (20–50%), and non-biomass
organics (20–40%). A portion of the sludge is returned to the biological treatment
processes while the excess sludge is sold as a fertilizer or stored in landfills.
Chemical sludge or lime sludge generated during the process after dewatering of
produced wastewater has beneficial reuses [8]. Although its contents vary depending
on the chemicals used during the refining of oil, waste sludge from physicochemical
treatment contains low-molecular-weight oils produced during refining of oils at the
deodorization stage, esters, alcohols, and other semi-volatile organic compounds
found in oil, which are organic substances produced during chemical adsorption of
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D. Kaya and Y.-T. Hung
[78]. This means that the bleaching earths, especially those containing polyunsaturated fats, have self-flammable properties [79]. Therefore, spent bleaching
earths are listed as hazardous wastes and their disposal or treatment is difficult in the
environment. Also, spent bleaching earths include color pigments like carotene and
chlorophyll and oxidation products which are present in the vegetable oil [9]. In
order to reduce their fat/oil contents, spent bleaching earth can be extracted with
hexane and the oil present in them can be recovered and used as second-quality oil
for different purposes. By this way, the oil content of spent bleaching earth can be
reduced to below 1%. Thus, bleaching earth becomes a solid waste consisting of
inorganic chemicals. This still might be reused as bleaching earth at the secondquality oil production facilities [63].
Soap-stock is accepted as a by-product, which is generated from the alkalirefining of the vegetable oil, otherwise treated as waste. The soap-stock contains
50% total fatty matter and, therefore, it has a commercial value [8]. But it also
contains significant amount of phosphatides, pigments, and other contaminants.
Therefore, soap-stock cannot be used in good-quality soap production. They chemically break down into acid oil. The breakdown can be accomplished by using a
strong concentrated acid. This produced acid oil can be assessed by selling it to soap
production factories [9].
Lecithin is formed at the degumming stage of the oil refining. Basically, it is a
mixture of phosphatides and small amounts of water-soluble components like
glycolipids and oligosaccharides. The gums from the centrifuge are processed by
treating with H 2 O 2 and then dried. After reduction of moisture, the product is cooled.
Thus, lecithin is obtained and used in foods and in cosmetic and pharmaceutical
industries. The best-quality lecithin can be produced from fresh oil [8, 9].
Spent nickel catalyst is generated from hydrogenation process of refined vegetable oil during the production of Vanaspati (hard oil). The continuous use of nickel
catalyst leads to high content of fat adherence to it [8].
Deodorizer distillate is the volatile organic material which is steam distilled in the
deodorization of vegetable oil and hydrogenated vegetable oil. The distillate produced in the industry contains tocopherols and sterols, which are valuable raw
materials for production of vitamin E and steroid drugs [8].
Wastewater treatment sludge consists of all chemical or biological sludges
gathered from the bottom of sedimentation tanks of physicochemical and/or biological treatment. Biological sludge production is clearly located in the aeration basin
and sludge is composed of minerals (10–30%), biomass (20–50%), and non-biomass
organics (20–40%). A portion of the sludge is returned to the biological treatment
processes while the excess sludge is sold as a fertilizer or stored in landfills.
Chemical sludge or lime sludge generated during the process after dewatering of
produced wastewater has beneficial reuses [8]. Although its contents vary depending
on the chemicals used during the refining of oil, waste sludge from physicochemical
treatment contains low-molecular-weight oils produced during refining of oils at the
deodorization stage, esters, alcohols, and other semi-volatile organic compounds
found in oil, which are organic substances produced during chemical adsorption of
354
D. Kaya and Y.-T. Hung