indicated that the modified polyvinylidene fluoride membrane could be a costeffective option for the treatment of oily wastewater. Salahi et al. (2010) employed
a hydrophilic 20 kDa polyacrylonitrile ultrafiltration membrane for the separation of
oily wastewater. The membrane achieved the high total suspended solids and oil
removals of 99%, but with low total dissolved solids removal of only 30%. The
membrane demonstrated the highest steady flux at the temperature of 50
C and pH
of 10 with the transmembrane pressure and crossflow velocity of 3 bar and 1 m/s,
respectively.
In addition, Ebrahimi et al. (2010) investigated the performance of the ceramic
ultrafiltration membrane composed of titania and alumina for the treatment of oily
wastewater with an oil concentration of 32.2 mg/L. The result showed a high organic
content removal of 78.2% at the applied pressure of 2 bar. Moreover, the membrane
could also remove the salt content at a lower pressure of 0.5 bar. In a bid to
understand the performance of the ultrafiltration membrane, Teodosiu et al. (1999)
used an ultrafiltration membrane system consisting of polyvinylpyrrolidone and
polyethersulfone membranes as a pretreatment of oily wastewater for the subsequent
reverse osmosis process. The authors also studied the effects of backflushing and
chemical cleaning on the rate of fouling and process efficiency. The results revealed
the high total suspended solids removal efficiency of 98% with low turbidity of
12.5–14.2 mg/L. However, the membrane system showed a low chemical oxygen
demand and total organic carbon. The results suggested that the ultrafiltration
membrane could be a feasible option for the pretreatment of the oily wastewater
prior to the reverse osmosis process.
11.3.3 Nanofiltration
Nanofiltration is a pressure-driven membrane process that utilizes membranes with
nano-sized pores to reject ionic and molecular species. Typically, nanofiltration
membranes exhibit pore sizes ranging from 1 to 10 nm, which are much smaller
than those of microfiltration and ultrafiltration membrane, but slightly larger than
that of the reverse osmosis membrane. Generally, nanofiltration membranes tend to
reject multivalent ions and larger particles without selective to the monovalent ions.
The passage of the solution (wastewater) through the membrane and the retainment
of the solute (oil particles and other pollutant ions) on the membrane is achieved
based on the structure of the membrane layer and the type of membrane material.
Several investigations have reported on the application of the nanofiltration
membranes for treating the oily wastewater in petroleum plants. Seland et al.
(1992) applied the nanofiltration technique to reduce the sulphate concentration in
the seawater for the oil reservoir injection. The technique demonstrated an excellent
overall salt rejection of 93%. Mondal and Wickramasinghe (2008) utilized two
different types of nanofiltration membranes for the treatment of produced water.
The investigation revealed that the semi aromatic nanofiltration membrane was able
to reduce the total dissolved solids and total organic carbon concentration from 2090
368
M. H. D. Othman et al.
a hydrophilic 20 kDa polyacrylonitrile ultrafiltration membrane for the separation of
oily wastewater. The membrane achieved the high total suspended solids and oil
removals of 99%, but with low total dissolved solids removal of only 30%. The
membrane demonstrated the highest steady flux at the temperature of 50
C and pH
of 10 with the transmembrane pressure and crossflow velocity of 3 bar and 1 m/s,
respectively.
In addition, Ebrahimi et al. (2010) investigated the performance of the ceramic
ultrafiltration membrane composed of titania and alumina for the treatment of oily
wastewater with an oil concentration of 32.2 mg/L. The result showed a high organic
content removal of 78.2% at the applied pressure of 2 bar. Moreover, the membrane
could also remove the salt content at a lower pressure of 0.5 bar. In a bid to
understand the performance of the ultrafiltration membrane, Teodosiu et al. (1999)
used an ultrafiltration membrane system consisting of polyvinylpyrrolidone and
polyethersulfone membranes as a pretreatment of oily wastewater for the subsequent
reverse osmosis process. The authors also studied the effects of backflushing and
chemical cleaning on the rate of fouling and process efficiency. The results revealed
the high total suspended solids removal efficiency of 98% with low turbidity of
12.5–14.2 mg/L. However, the membrane system showed a low chemical oxygen
demand and total organic carbon. The results suggested that the ultrafiltration
membrane could be a feasible option for the pretreatment of the oily wastewater
prior to the reverse osmosis process.
11.3.3 Nanofiltration
Nanofiltration is a pressure-driven membrane process that utilizes membranes with
nano-sized pores to reject ionic and molecular species. Typically, nanofiltration
membranes exhibit pore sizes ranging from 1 to 10 nm, which are much smaller
than those of microfiltration and ultrafiltration membrane, but slightly larger than
that of the reverse osmosis membrane. Generally, nanofiltration membranes tend to
reject multivalent ions and larger particles without selective to the monovalent ions.
The passage of the solution (wastewater) through the membrane and the retainment
of the solute (oil particles and other pollutant ions) on the membrane is achieved
based on the structure of the membrane layer and the type of membrane material.
Several investigations have reported on the application of the nanofiltration
membranes for treating the oily wastewater in petroleum plants. Seland et al.
(1992) applied the nanofiltration technique to reduce the sulphate concentration in
the seawater for the oil reservoir injection. The technique demonstrated an excellent
overall salt rejection of 93%. Mondal and Wickramasinghe (2008) utilized two
different types of nanofiltration membranes for the treatment of produced water.
The investigation revealed that the semi aromatic nanofiltration membrane was able
to reduce the total dissolved solids and total organic carbon concentration from 2090
368
M. H. D. Othman et al.