16 mA/cm
2 . Meanwhile, the chemical oxygen demand was reduced for 90% after
20 min of electrolysis at the current density of 12 mA/cm
2 . In addition, 80% of oil
and grease was removed after 10 min of electrolysis at all tested current densities.
Giwa et al. (2012) studied the effects of current density, sodium chloride concentration, and electrolysis time on the treatment of the oily wastewater produced from a
petrochemical plant. The results showed that 97.43% of the most extreme turbidity
was removed at the optimum current density of 21.6 mA/cm
2 , salt concentration of
2 g/L and 30 min of electrolysis. Yang (2007) treated a high-turbidity (1800 FAU)
oily wastewater via electrocoagulation with the electrodes containing ferrous ions
and 100 mg/L sodium chloride. The turbidity of the oily wastewater was significantly reduced to 14 FAU after 4 min of treatment with a current of 2A and the
addition of 165.8 mg/L of iron. Xu and Zhu (2004) reported that the treatment of
refectory oily wastewater required the optimum current density of 10–14 A/m
2 ,
electrode distance of 10 mm, and pH of 3–10 for a cycle time of 30 min. In addition,
the ideal separation distance of the electrodes was found to be 10 mm, which resulted
in the efficient removal of 95% oil and chemical oxygen demand.
11.5 Hybrid Technologies for Oily Wastewater Treatment
The combination of various technologies has become an interest of studies for the
improvement of the oily wastewater treatment. Earlier in 2004, Mostefa and Tir
(2004) coupled electro-flotation with flocculation to improve oily wastewater treatment performance. The authors investigated the competency of three different
flocculants, which included iron sulfate, polyacrylamide, and aluminum sulfate. In
addition, the concentration of cutting oil also varied between 1 and 4%. Maximum
removals of turbidity (99%) and chemical oxygen demand (97%) were achieved at
the current density of 11.15 mA/cm
2 . 99% of oil was also removed when the iron
sulfate and aluminum sulfate flocculants were applied. Yan et al. (2010) employed
catalytic vacuum distillation with various promoters, such as iron (III) chloride,
kaolin, sulfuric acid, and sodium hydroxide for the treatment of petroleum refinery
wastewater with high chemical oxygen demand. The results showed that the catalytic vacuum distillation with sodium hydroxide promoter had higher purification
efficiency than the systems with other types of promoters. The system successfully
removed 99% of the chemical oxygen demand and lowered the effluent salinity.
Santo et al. (2012) applied the coagulation-flocculation and flotation methods to
reduce the organic matter, oil, and grease contents in the wastewater. PAX-18 (17%
alumina), aluminum sulfate, and ferric sulfate were chosen for the primary treatment
of coagulation-flocculation, whereas the flocculant used was NALCO 71408. The
combination of these materials could eliminate up to 95% of total petroleum
hydrocarbons from the oily wastewater. Santander et al. (2011) introduced the
combination techniques of flocculation and flotation in a modified jet (Jameson)
cell. The removal rates of the oily wastewater of the conventional and modified jet
cells were compared. The study outcomes demonstrated that the modified jet
11 Oily Wastewater Treatment
373
2 . Meanwhile, the chemical oxygen demand was reduced for 90% after
20 min of electrolysis at the current density of 12 mA/cm
2 . In addition, 80% of oil
and grease was removed after 10 min of electrolysis at all tested current densities.
Giwa et al. (2012) studied the effects of current density, sodium chloride concentration, and electrolysis time on the treatment of the oily wastewater produced from a
petrochemical plant. The results showed that 97.43% of the most extreme turbidity
was removed at the optimum current density of 21.6 mA/cm
2 , salt concentration of
2 g/L and 30 min of electrolysis. Yang (2007) treated a high-turbidity (1800 FAU)
oily wastewater via electrocoagulation with the electrodes containing ferrous ions
and 100 mg/L sodium chloride. The turbidity of the oily wastewater was significantly reduced to 14 FAU after 4 min of treatment with a current of 2A and the
addition of 165.8 mg/L of iron. Xu and Zhu (2004) reported that the treatment of
refectory oily wastewater required the optimum current density of 10–14 A/m
2 ,
electrode distance of 10 mm, and pH of 3–10 for a cycle time of 30 min. In addition,
the ideal separation distance of the electrodes was found to be 10 mm, which resulted
in the efficient removal of 95% oil and chemical oxygen demand.
11.5 Hybrid Technologies for Oily Wastewater Treatment
The combination of various technologies has become an interest of studies for the
improvement of the oily wastewater treatment. Earlier in 2004, Mostefa and Tir
(2004) coupled electro-flotation with flocculation to improve oily wastewater treatment performance. The authors investigated the competency of three different
flocculants, which included iron sulfate, polyacrylamide, and aluminum sulfate. In
addition, the concentration of cutting oil also varied between 1 and 4%. Maximum
removals of turbidity (99%) and chemical oxygen demand (97%) were achieved at
the current density of 11.15 mA/cm
2 . 99% of oil was also removed when the iron
sulfate and aluminum sulfate flocculants were applied. Yan et al. (2010) employed
catalytic vacuum distillation with various promoters, such as iron (III) chloride,
kaolin, sulfuric acid, and sodium hydroxide for the treatment of petroleum refinery
wastewater with high chemical oxygen demand. The results showed that the catalytic vacuum distillation with sodium hydroxide promoter had higher purification
efficiency than the systems with other types of promoters. The system successfully
removed 99% of the chemical oxygen demand and lowered the effluent salinity.
Santo et al. (2012) applied the coagulation-flocculation and flotation methods to
reduce the organic matter, oil, and grease contents in the wastewater. PAX-18 (17%
alumina), aluminum sulfate, and ferric sulfate were chosen for the primary treatment
of coagulation-flocculation, whereas the flocculant used was NALCO 71408. The
combination of these materials could eliminate up to 95% of total petroleum
hydrocarbons from the oily wastewater. Santander et al. (2011) introduced the
combination techniques of flocculation and flotation in a modified jet (Jameson)
cell. The removal rates of the oily wastewater of the conventional and modified jet
cells were compared. The study outcomes demonstrated that the modified jet
11 Oily Wastewater Treatment
373