9, more than 90% of trace organics such as estrone can be rejected. Sulfamethoxazole and ibuprofen are also highly soluble at high pH (in the alkaline region) where
the compounds are negatively charged, but when the solution pH decreases, their
solubility decreases sharply [87]. Nghiem and Hawks reported an almost complete
rejection of sulfamethoxazole using the NF-270 membrane at a pH above 8.
Temperature is another parameter that can affect the water flux and rejection of
NSAIDs [83]. Increasing the feed temperature can lead to a change in the structure
and morphology of the polymer matrix, causing an increase in the mean pore radius
and MWCO [88]. An increase in the solubility of some NSAIDs can occur due to the
increase in the temperature of the surrounding solution [89].
Operating pressure and cross-flow velocity are important factors which can affect
the volume and quality of a product. An increase in the operating pressure can reduce
the shielding of negative charges on the surface of a membrane, which makes
repulsion more effective and enhances the rejection of negatively charged contaminants by NF/RO membranes [90]. Also, the permeate flux increases with cross-flow
velocity over a range of operating conditions because increasing the cross-flow
velocity increases the flux and rejection of NSAIDs due to a reduction in concentration polarization [90, 91].
The hydrophobicity of both contaminant and membrane can affect the rejection of
NSAIDs by NF/RO membranes. Contaminants such as steroid hormones with a high
hydrophobicity (log D > 3.2) can adsorb onto the surface of the membrane due to
hydrophobic–hydrophobic interactions [78, 92]. Nghiem et al. [82] reported that the
rejection of natural hormones by the NF-270 and NF-90 membranes was lower than
that expected based on steric hindrance. They explained this phenomenon by the
adsorption of these hydrophobic compounds onto the surface of the membrane
followed by diffusion through its polymeric matrix [83]. The membrane separation
processes (i.e., NF/RO) have demonstrated excellent capacity in removing NSAID
compounds; however, their inherent operation conditions (high pressure, membrane
fouling) require pretreatment process.
2.4 Integrated Process
Biological-based processes are the most pragmatic approach for wastewater treatment. However, the biological treatment alone is not effective for NSAID compounds (Sect. 2.1) for water reuse purposes. Because the biological treatment
processes can reduce large bulk of organic content, research reports a significant
synergy when it is integrated with other physical (i.e., membrane filtration and
adsorption)- and chemical (i.e., advanced oxidation)-based processes.
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
229
the compounds are negatively charged, but when the solution pH decreases, their
solubility decreases sharply [87]. Nghiem and Hawks reported an almost complete
rejection of sulfamethoxazole using the NF-270 membrane at a pH above 8.
Temperature is another parameter that can affect the water flux and rejection of
NSAIDs [83]. Increasing the feed temperature can lead to a change in the structure
and morphology of the polymer matrix, causing an increase in the mean pore radius
and MWCO [88]. An increase in the solubility of some NSAIDs can occur due to the
increase in the temperature of the surrounding solution [89].
Operating pressure and cross-flow velocity are important factors which can affect
the volume and quality of a product. An increase in the operating pressure can reduce
the shielding of negative charges on the surface of a membrane, which makes
repulsion more effective and enhances the rejection of negatively charged contaminants by NF/RO membranes [90]. Also, the permeate flux increases with cross-flow
velocity over a range of operating conditions because increasing the cross-flow
velocity increases the flux and rejection of NSAIDs due to a reduction in concentration polarization [90, 91].
The hydrophobicity of both contaminant and membrane can affect the rejection of
NSAIDs by NF/RO membranes. Contaminants such as steroid hormones with a high
hydrophobicity (log D > 3.2) can adsorb onto the surface of the membrane due to
hydrophobic–hydrophobic interactions [78, 92]. Nghiem et al. [82] reported that the
rejection of natural hormones by the NF-270 and NF-90 membranes was lower than
that expected based on steric hindrance. They explained this phenomenon by the
adsorption of these hydrophobic compounds onto the surface of the membrane
followed by diffusion through its polymeric matrix [83]. The membrane separation
processes (i.e., NF/RO) have demonstrated excellent capacity in removing NSAID
compounds; however, their inherent operation conditions (high pressure, membrane
fouling) require pretreatment process.
2.4 Integrated Process
Biological-based processes are the most pragmatic approach for wastewater treatment. However, the biological treatment alone is not effective for NSAID compounds (Sect. 2.1) for water reuse purposes. Because the biological treatment
processes can reduce large bulk of organic content, research reports a significant
synergy when it is integrated with other physical (i.e., membrane filtration and
adsorption)- and chemical (i.e., advanced oxidation)-based processes.
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
229