The development of microfiltration membranes for oily wastewater treatment has
been widely reported. In 1997, Mueller et al. (1997) studied about the crossflow
microfiltration of oily water using two α-alumina membranes with the pore sizes of
0.2–0.8 μm and a surface modified polyacrylonitrile membrane with a pore size of
0.1 μm. All the microfiltration membranes showed the oil removal efficiencies of
above 98%. The membranes were cleaned using strong acid, base, and detergent
after the microfiltration process. However, none of these chemicals were effective in
removing the membrane foulants. Moreover, the fouling mechanism modeling
showed that internal and external fouling occurred in both α-alumina membranes.
Zhong et al. (2003) developed a zirconia microfiltration membrane for the oily
wastewater treatment. The membrane successfully reduced the oil concentration of
the wastewater from 200 to 8.7 mg/L, which satisfied the wastewater discharge
standard of Chinese national. Ebrahimi et al. (2010) studied the performance of
alumina microfiltration membrane in the oily wastewater treatment. Prior to the
microfiltration process, the wastewater was pretreated via ultrafiltration. The
microfiltration membrane demonstrated the oil and total organic carbon removals
of 61.4–38.6%, respectively. Furthermore, the microfiltration membrane also
showed a permeability of 715 L/m
2 h bar with an oil recovery of 61%.
11.3.2 Ultrafiltration
The membranes employed in the ultrafiltration process exhibit the pore sizes ranging
from 1 to 500 nm and can retain solutes with the molecular weight of
300–500,000 Da at the operating pressure of 100–700 kPa. The rejection properties
of the ultrafiltration membrane are determined by the molecular weight cutoff.
Molecular weight cutoff refers to the lowest molecular weight of solute in which
90% of the solutes is retained by the membrane. The molecular weight cutoff leads to
a clear understanding regarding the real efficiency of the rejection phenomenon of
the membrane. Ultrafiltration membranes can reject various types of proteins,
trypsins, and bovine serum albumin. Some of the other molecules that can be
separated via the ultrafiltration processes are polymers, sugar, colloidal particles,
biomolecules, colors, odor, and viruses (Winston and Sirkar 1992; Scott 1995).
Ultrafiltration has the same modes of operation as those in the microfiltration,
which include dead-end and crossflow filtration channels (Fig. 11.3a, b).
Various types of ultrafiltration membranes have been studied for the oily wastewater treatment. For instance, Li et al. (2006) modified the polyvinylidene fluoride
ultrafiltration membrane with nano-sized alumina particles for the purification of the
oily wastewater. The modified membrane showed a higher performance rate in the
elimination of the organic pollutants with the total organic carbon, oil and total
suspended solids removals of 98.0%, 98.0% and 98.7%, respectively. The incorporation of nano-sized alumina particles significantly improved the permeate flux and
anti-fouling performances, as well as achieved complete flux recovery after the
backwash cleaning process using 1 wt% OP-10 surfactant at pH 10. The results
11 Oily Wastewater Treatment
367
been widely reported. In 1997, Mueller et al. (1997) studied about the crossflow
microfiltration of oily water using two α-alumina membranes with the pore sizes of
0.2–0.8 μm and a surface modified polyacrylonitrile membrane with a pore size of
0.1 μm. All the microfiltration membranes showed the oil removal efficiencies of
above 98%. The membranes were cleaned using strong acid, base, and detergent
after the microfiltration process. However, none of these chemicals were effective in
removing the membrane foulants. Moreover, the fouling mechanism modeling
showed that internal and external fouling occurred in both α-alumina membranes.
Zhong et al. (2003) developed a zirconia microfiltration membrane for the oily
wastewater treatment. The membrane successfully reduced the oil concentration of
the wastewater from 200 to 8.7 mg/L, which satisfied the wastewater discharge
standard of Chinese national. Ebrahimi et al. (2010) studied the performance of
alumina microfiltration membrane in the oily wastewater treatment. Prior to the
microfiltration process, the wastewater was pretreated via ultrafiltration. The
microfiltration membrane demonstrated the oil and total organic carbon removals
of 61.4–38.6%, respectively. Furthermore, the microfiltration membrane also
showed a permeability of 715 L/m
2 h bar with an oil recovery of 61%.
11.3.2 Ultrafiltration
The membranes employed in the ultrafiltration process exhibit the pore sizes ranging
from 1 to 500 nm and can retain solutes with the molecular weight of
300–500,000 Da at the operating pressure of 100–700 kPa. The rejection properties
of the ultrafiltration membrane are determined by the molecular weight cutoff.
Molecular weight cutoff refers to the lowest molecular weight of solute in which
90% of the solutes is retained by the membrane. The molecular weight cutoff leads to
a clear understanding regarding the real efficiency of the rejection phenomenon of
the membrane. Ultrafiltration membranes can reject various types of proteins,
trypsins, and bovine serum albumin. Some of the other molecules that can be
separated via the ultrafiltration processes are polymers, sugar, colloidal particles,
biomolecules, colors, odor, and viruses (Winston and Sirkar 1992; Scott 1995).
Ultrafiltration has the same modes of operation as those in the microfiltration,
which include dead-end and crossflow filtration channels (Fig. 11.3a, b).
Various types of ultrafiltration membranes have been studied for the oily wastewater treatment. For instance, Li et al. (2006) modified the polyvinylidene fluoride
ultrafiltration membrane with nano-sized alumina particles for the purification of the
oily wastewater. The modified membrane showed a higher performance rate in the
elimination of the organic pollutants with the total organic carbon, oil and total
suspended solids removals of 98.0%, 98.0% and 98.7%, respectively. The incorporation of nano-sized alumina particles significantly improved the permeate flux and
anti-fouling performances, as well as achieved complete flux recovery after the
backwash cleaning process using 1 wt% OP-10 surfactant at pH 10. The results
11 Oily Wastewater Treatment
367