Applications of Nanofiltration
Nanofiltration is slowly emerging as an alternative to reverse osmosis in some
applications and as supplementary technology in some other cases. The
nanofiltration membrane elements are available in many average pore sizes designated as NF40, NF90, etc., indicating the approximate solute rejection of sodium
chloride. Minor charge on the surface of the membrane coupled with higher pore
sizes relative to reverse osmosis enables the separation of monovalent species
resulting in the concentration of macromolecules. Because of the passage of some
solutes, the effective operating pressure is less due to the net osmotic pressure being
lower. Consequently, larger molecules and multivalent ionic species can be separated through nanofiltration, like dyes, as well as uranyl species from the solution.
Nanofiltration has potential applications (Astro chemicals and Bio Technologies
2019) in many areas including water softening and removal of natural organic
materials. Experimental investigations on using reverse osmosis and nanofiltration
(Abid et al. 2012) for the dye removal indicated that nanofiltration system can
provide permeate water, meeting the environmental standards by a big margin at
50% electric power relative to reverse osmosis membranes due to reduction in
operating pressure. A number of studies have also confirmed the utility of separation
of dyes and intermediates (Kelewou et al. 2015; Zhu et al. 2013) using nanofiltration.
Review of existing processes for dye removal found that membrane processes have
high potential (Ahmad et al. 2015) and require some of the challenges like fouling
and sludge production that need to be addressed. Nanofiltration finds use in the
separation of low-molecular-weight species from the bulk solution as indicated by
studies, where the separation of ammonium nitrate could be achieved from uranyl
nitrate (Prabhakar et al. 1996; Zhongwei et al. 2017).
8.4.2 Electro-membrane Process Applications
Electrodialysis process was used for desalination particularly for brackish water
desalination in the late 1980s and early 1990s. The following are the limitations of
electrodialysis:
1. It is difficult to produce high purity water because of the inherent electrical
resistance of water.
2. Polarization near the membrane surface decreases the efficiency of the system
leading to increase in power consumption. In addition, power consumption also
increases with the concentration of the feed, as more ions have to be transported
through the membrane.
3. The efficiency of electrodialysis decreases in the presence of bivalent salts such as
calcium, sulfate, magnesium, etc.
4. As on date, no practical energy recovery system is available even though some
attempts are made to recover energy using the concept of reverse electrodialysis.
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A. Kapoor et al.
Nanofiltration is slowly emerging as an alternative to reverse osmosis in some
applications and as supplementary technology in some other cases. The
nanofiltration membrane elements are available in many average pore sizes designated as NF40, NF90, etc., indicating the approximate solute rejection of sodium
chloride. Minor charge on the surface of the membrane coupled with higher pore
sizes relative to reverse osmosis enables the separation of monovalent species
resulting in the concentration of macromolecules. Because of the passage of some
solutes, the effective operating pressure is less due to the net osmotic pressure being
lower. Consequently, larger molecules and multivalent ionic species can be separated through nanofiltration, like dyes, as well as uranyl species from the solution.
Nanofiltration has potential applications (Astro chemicals and Bio Technologies
2019) in many areas including water softening and removal of natural organic
materials. Experimental investigations on using reverse osmosis and nanofiltration
(Abid et al. 2012) for the dye removal indicated that nanofiltration system can
provide permeate water, meeting the environmental standards by a big margin at
50% electric power relative to reverse osmosis membranes due to reduction in
operating pressure. A number of studies have also confirmed the utility of separation
of dyes and intermediates (Kelewou et al. 2015; Zhu et al. 2013) using nanofiltration.
Review of existing processes for dye removal found that membrane processes have
high potential (Ahmad et al. 2015) and require some of the challenges like fouling
and sludge production that need to be addressed. Nanofiltration finds use in the
separation of low-molecular-weight species from the bulk solution as indicated by
studies, where the separation of ammonium nitrate could be achieved from uranyl
nitrate (Prabhakar et al. 1996; Zhongwei et al. 2017).
8.4.2 Electro-membrane Process Applications
Electrodialysis process was used for desalination particularly for brackish water
desalination in the late 1980s and early 1990s. The following are the limitations of
electrodialysis:
1. It is difficult to produce high purity water because of the inherent electrical
resistance of water.
2. Polarization near the membrane surface decreases the efficiency of the system
leading to increase in power consumption. In addition, power consumption also
increases with the concentration of the feed, as more ions have to be transported
through the membrane.
3. The efficiency of electrodialysis decreases in the presence of bivalent salts such as
calcium, sulfate, magnesium, etc.
4. As on date, no practical energy recovery system is available even though some
attempts are made to recover energy using the concept of reverse electrodialysis.
266
A. Kapoor et al.