very high, 11,000–12,000 mg/L (Tables 8.10 and 8.11). The reason for this is due to
that during vegetable oil refining effluents at neutralization stage of soap-stock are
decomposed with sulfuric acid for the production of acid oil. The chemical equation
for this reaction is given in Eq. 8.2. Phosphorus content of the wastewater is also
high which is due to that crude oil has phosphorus compounds in its structures and
due to the use of phosphoric acid at the degumming stage. It can be seen that
wastewaters resulted during sunflower oil as well as corn oil refining are highly
colored due to the extraction of oil from vegetables together with color pigments and
the presence of natural organics. Vegetable oil refining wastewater has high color
content because it contains a lot of dissolved organic matter. However, the color
content of such wastewater has not been given much attention in the literature. It is
observed that corn oil refining wastewaters have more polluting load and more acidic
character when compared to sunflower oil refining wastewater.
When the results of are examined, it can be seen that BOD 5 values are quite low
when compared to corresponding COD values. This result indicates that there might
be some hidden BOD which cannot be completely determined in 5 days and needs
longer period for accurate measurement, and therefore, BOD 5 is inadequate in
characterization of this kind of wastewaters.
The BOD 5 /COD ratios of the factory wastewaters are 0.15 and 0.2 for corn oil
and sunflower oil refining wastewaters [20]. Aslan et al. [53] investigated the
biodegradability of vegetable oil refinery wastewaters and concluded that they
have a low BOD 5 /COD ratio and that these wastewaters cannot be treated only by
biological treatment. Furthermore, their transport presents high risk of clogging in
pumps and piping. In addition, COD/N/P (C/N/P) ratios of corn oil and sunflower oil
refining effluents calculated from the average values of the total COD, TKN, and
total phosphorus ratio were found as 52/3/1 and 22/3/1, respectively. These ratios
indicate that there is no nutrient deficiency for wastewater microorganisms in terms
of N and P. However, very low BOD 5 /COD ratios suggest that only biological
treatment is not enough for treatment of the factory wastewaters.
4.4.1 Caustic Neutralization and Physical Treatment
In soap-stock unit, wastewaters produced during soap-stock chopping in the reaction
tanks, containing a strong acid (pH ¼ 0–1), are taken into reaction tank 4 as shown in
Fig. 8.8a. This tank is dosed with caustic soda from the top and the air is provided
from the bottom of the tank for the reaction of caustic soda with wastewater to adjust
desired pH. The wastewater is then sent to the pumping pit.
During the production at oil refining stage, wash water coming from separators
reaches to the soap-stock unit after leaving the system. The pH of these waters is
around 9–11. As shown in Fig. 8.8b, these waters are taken into tank 3 and sulfuric
acid is added and heated by steam in order to facilitate the separation of oil and soap
residues from water. The effluent of this tank is then directed to another tank,
upgrade pit, and here, pH of the water is automatically adjusted to pH range of
3–5 by the addition of caustic soda. This operation is performed during the
8 Vegetable Oil Refining Wastes
363
that during vegetable oil refining effluents at neutralization stage of soap-stock are
decomposed with sulfuric acid for the production of acid oil. The chemical equation
for this reaction is given in Eq. 8.2. Phosphorus content of the wastewater is also
high which is due to that crude oil has phosphorus compounds in its structures and
due to the use of phosphoric acid at the degumming stage. It can be seen that
wastewaters resulted during sunflower oil as well as corn oil refining are highly
colored due to the extraction of oil from vegetables together with color pigments and
the presence of natural organics. Vegetable oil refining wastewater has high color
content because it contains a lot of dissolved organic matter. However, the color
content of such wastewater has not been given much attention in the literature. It is
observed that corn oil refining wastewaters have more polluting load and more acidic
character when compared to sunflower oil refining wastewater.
When the results of are examined, it can be seen that BOD 5 values are quite low
when compared to corresponding COD values. This result indicates that there might
be some hidden BOD which cannot be completely determined in 5 days and needs
longer period for accurate measurement, and therefore, BOD 5 is inadequate in
characterization of this kind of wastewaters.
The BOD 5 /COD ratios of the factory wastewaters are 0.15 and 0.2 for corn oil
and sunflower oil refining wastewaters [20]. Aslan et al. [53] investigated the
biodegradability of vegetable oil refinery wastewaters and concluded that they
have a low BOD 5 /COD ratio and that these wastewaters cannot be treated only by
biological treatment. Furthermore, their transport presents high risk of clogging in
pumps and piping. In addition, COD/N/P (C/N/P) ratios of corn oil and sunflower oil
refining effluents calculated from the average values of the total COD, TKN, and
total phosphorus ratio were found as 52/3/1 and 22/3/1, respectively. These ratios
indicate that there is no nutrient deficiency for wastewater microorganisms in terms
of N and P. However, very low BOD 5 /COD ratios suggest that only biological
treatment is not enough for treatment of the factory wastewaters.
4.4.1 Caustic Neutralization and Physical Treatment
In soap-stock unit, wastewaters produced during soap-stock chopping in the reaction
tanks, containing a strong acid (pH ¼ 0–1), are taken into reaction tank 4 as shown in
Fig. 8.8a. This tank is dosed with caustic soda from the top and the air is provided
from the bottom of the tank for the reaction of caustic soda with wastewater to adjust
desired pH. The wastewater is then sent to the pumping pit.
During the production at oil refining stage, wash water coming from separators
reaches to the soap-stock unit after leaving the system. The pH of these waters is
around 9–11. As shown in Fig. 8.8b, these waters are taken into tank 3 and sulfuric
acid is added and heated by steam in order to facilitate the separation of oil and soap
residues from water. The effluent of this tank is then directed to another tank,
upgrade pit, and here, pH of the water is automatically adjusted to pH range of
3–5 by the addition of caustic soda. This operation is performed during the
8 Vegetable Oil Refining Wastes
363