Electrodialysis system can be operated in batch mode for small-scale applications
or continuously for large industrial applications. Earliest applications of electrodialysis systems were in brackish desalination. Electrodialysis units have been deployed
for desalination up to 15,000 ppm salinity (Burn et al. 2015) with multiple stages.
For brackish water desalination up to 3000 ppm feed salinity, electrodialysis can
achieve about 80% recovery. Efforts to extend to seawater desalination could not be
successful because of very high specific power consumption. Improvements to
overcome the challenge through electrodialysis reversal also did not yield desired
results due to practical difficulties. Recent innovation of reverse electrodialysis (Mei
and Tang 2018) for recovering energy has shown positive results. Perhaps, in the
future with further developments, electrodialysis could become a viable alternative
for seawater desalination (Galama et al. 2014).
The major challenge of electrodialysis is the power consumption and concentration polarization, both of which increase with concentration of the feed. The
challenges were addressed by electrodialysis reversal to some extent, where the
polarity of the electrodes was frequently altered. Even though the issues were
addressed to some extent, the product water purity was affected due the frequent
change of “dilute” and “concentrate” compartments. Moreover, because of the
inherent poor conductivity of water, one has to contend with higher salinities of
product compared to reverse osmosis. In view of this, electrodialysis is not a
preferred alternative for desalination or water treatment applications. Electrodeionization is a minor modification of electrodialysis and is restricted to very low
salinity levels. Apart from desalination, electrodialysis has been studied extensively
for industrial wastewater treatment for the recovery of chromium (Nataraj et al.
2007), cadmium (Marder et al. 2003), and nickel (Scarazzato et al. 2018) from
plating industry effluents and acid mine drainage for recovering water (Cardoso et al.
2013) and to concentrate and recover nutrients from waste streams (Zhang et al.
2013).
8.4.3 Membrane Distillation
Membrane distillation has been demonstrated for its performance in desalination of
seawater (Camacho et al. 2013) in a number of studies. The process involves initially
the formation of vapor and subsequently its transfer through the membrane. The
transfer medium (membrane) and water vapor both are hydrophobic in nature, and
the product can be highly pure for an ideal membrane. Since the membrane has poresize distribution, some contamination is inevitable in condensed water. For largescale sustainable deployment, the challenges of low-flux and low liquid entry
pressure of the membranes have to be addressed.
Apart from desalination, direct contact membrane distillation has been utilized for
the recovery of water from pharmaceutical wastewater and radioactive wastewater
(Wang and Chung 2015). Studies were conducted to recover water in the crystallization process using membrane distillation crystallization (Chan et al. 2005; Ji et al.
8 Role of Membranes in Wastewater Treatment
267
or continuously for large industrial applications. Earliest applications of electrodialysis systems were in brackish desalination. Electrodialysis units have been deployed
for desalination up to 15,000 ppm salinity (Burn et al. 2015) with multiple stages.
For brackish water desalination up to 3000 ppm feed salinity, electrodialysis can
achieve about 80% recovery. Efforts to extend to seawater desalination could not be
successful because of very high specific power consumption. Improvements to
overcome the challenge through electrodialysis reversal also did not yield desired
results due to practical difficulties. Recent innovation of reverse electrodialysis (Mei
and Tang 2018) for recovering energy has shown positive results. Perhaps, in the
future with further developments, electrodialysis could become a viable alternative
for seawater desalination (Galama et al. 2014).
The major challenge of electrodialysis is the power consumption and concentration polarization, both of which increase with concentration of the feed. The
challenges were addressed by electrodialysis reversal to some extent, where the
polarity of the electrodes was frequently altered. Even though the issues were
addressed to some extent, the product water purity was affected due the frequent
change of “dilute” and “concentrate” compartments. Moreover, because of the
inherent poor conductivity of water, one has to contend with higher salinities of
product compared to reverse osmosis. In view of this, electrodialysis is not a
preferred alternative for desalination or water treatment applications. Electrodeionization is a minor modification of electrodialysis and is restricted to very low
salinity levels. Apart from desalination, electrodialysis has been studied extensively
for industrial wastewater treatment for the recovery of chromium (Nataraj et al.
2007), cadmium (Marder et al. 2003), and nickel (Scarazzato et al. 2018) from
plating industry effluents and acid mine drainage for recovering water (Cardoso et al.
2013) and to concentrate and recover nutrients from waste streams (Zhang et al.
2013).
8.4.3 Membrane Distillation
Membrane distillation has been demonstrated for its performance in desalination of
seawater (Camacho et al. 2013) in a number of studies. The process involves initially
the formation of vapor and subsequently its transfer through the membrane. The
transfer medium (membrane) and water vapor both are hydrophobic in nature, and
the product can be highly pure for an ideal membrane. Since the membrane has poresize distribution, some contamination is inevitable in condensed water. For largescale sustainable deployment, the challenges of low-flux and low liquid entry
pressure of the membranes have to be addressed.
Apart from desalination, direct contact membrane distillation has been utilized for
the recovery of water from pharmaceutical wastewater and radioactive wastewater
(Wang and Chung 2015). Studies were conducted to recover water in the crystallization process using membrane distillation crystallization (Chan et al. 2005; Ji et al.
8 Role of Membranes in Wastewater Treatment
267