185
bumping (Ginzburg et al. 2008; Kazi 2012). The following techniques are available
as far as off-line fouling control strategy is concerned: (a) manual cleaning, (b) liquid jet, (c) steam, (d) air jet, and (e) chemical and physical cleaning (Kazi 2012).
This information will help other researchers to mitigate fouling propensity particularly in membrane distillation.
Over the past decade, a lot of attention was focused toward the mitigation and
prevention of membrane fouling. As mentioned in the previous section, plenty of
conventional methods can be used to mitigate the concern of fouling, but very
recently, nonconventional methods for the pre-treatment are being used to promote
the concept of reusability and minimize the energy requirement. Some of the nonconventional methods are mentioned below.
Corresponding to Gryta et al. and Yang et al., magnetic water treatment (MWT)
proves very responsive for wastewater treatment from heat exchangers of power
plants (Gryta 2011; Yang 2005). According to Hsu et al., the magnetic field decelerates the nucleation and enhances the crystal growth rate (Hsu et al. 2002). This
modifies the crystal morphology and forms deposition layers that can be simply
washed off. Another mitigation technique is to treat the membrane used and alter the
surface morphology and consequently the surface properties of the membrane. In
recent years, studies have highlighted the importance of making a membrane superhydrophobic. Due to superhydrophobicity of the membrane, very less nutrient
retention is possible on the membrane surface. Correspondingly, diminished microbial growth was very evident according to recent studies. Generally, it can be understood from literature that hydrophobicity tackles problems related to biofouling.
Most of the method mentioned above are done at both industrial and laboratory
scale but are still not commercially available. Chemical cleaning is the most implied
commercially available method to counter fouling. Acids, alkaline solutions, surfactants, and chelating metals are few agents used for chemical treatment. Use of acids
(weak and strong) in membrane distillation is very significant to clean the scales
over the membrane surface. Though this method cannot be used to tackle the problem of pore blocking as it might cause serious damage to the membrane internally,
cleansing with alkaline solution could be used to reduce organic fouling. Generally,
rinsing or wash-off method can only be used when the scales are deposited on the
surface of the membrane. However, this method might have an adverse effect on
pore blocking and could result in membrane wetting if rinsed continuously; therefore, complete recovery is quite impossible in this case. Rinsing utilizing both acid
and base solutions leads to the removal of most of the deposition, recovering the
hydrophobic characteristic of the membrane (Gryta 2008b).
6.5 Conclusion
In this present chapter, the versatility of membrane distillation for producing reusable water has been described thoroughly. The unique beneficial features of membrane distillation, viz., higher recovery and higher rejection of nonvolatile solutes,
6 Fouling and Wetting: A Major Challenge for Membrane Distillation
bumping (Ginzburg et al. 2008; Kazi 2012). The following techniques are available
as far as off-line fouling control strategy is concerned: (a) manual cleaning, (b) liquid jet, (c) steam, (d) air jet, and (e) chemical and physical cleaning (Kazi 2012).
This information will help other researchers to mitigate fouling propensity particularly in membrane distillation.
Over the past decade, a lot of attention was focused toward the mitigation and
prevention of membrane fouling. As mentioned in the previous section, plenty of
conventional methods can be used to mitigate the concern of fouling, but very
recently, nonconventional methods for the pre-treatment are being used to promote
the concept of reusability and minimize the energy requirement. Some of the nonconventional methods are mentioned below.
Corresponding to Gryta et al. and Yang et al., magnetic water treatment (MWT)
proves very responsive for wastewater treatment from heat exchangers of power
plants (Gryta 2011; Yang 2005). According to Hsu et al., the magnetic field decelerates the nucleation and enhances the crystal growth rate (Hsu et al. 2002). This
modifies the crystal morphology and forms deposition layers that can be simply
washed off. Another mitigation technique is to treat the membrane used and alter the
surface morphology and consequently the surface properties of the membrane. In
recent years, studies have highlighted the importance of making a membrane superhydrophobic. Due to superhydrophobicity of the membrane, very less nutrient
retention is possible on the membrane surface. Correspondingly, diminished microbial growth was very evident according to recent studies. Generally, it can be understood from literature that hydrophobicity tackles problems related to biofouling.
Most of the method mentioned above are done at both industrial and laboratory
scale but are still not commercially available. Chemical cleaning is the most implied
commercially available method to counter fouling. Acids, alkaline solutions, surfactants, and chelating metals are few agents used for chemical treatment. Use of acids
(weak and strong) in membrane distillation is very significant to clean the scales
over the membrane surface. Though this method cannot be used to tackle the problem of pore blocking as it might cause serious damage to the membrane internally,
cleansing with alkaline solution could be used to reduce organic fouling. Generally,
rinsing or wash-off method can only be used when the scales are deposited on the
surface of the membrane. However, this method might have an adverse effect on
pore blocking and could result in membrane wetting if rinsed continuously; therefore, complete recovery is quite impossible in this case. Rinsing utilizing both acid
and base solutions leads to the removal of most of the deposition, recovering the
hydrophobic characteristic of the membrane (Gryta 2008b).
6.5 Conclusion
In this present chapter, the versatility of membrane distillation for producing reusable water has been described thoroughly. The unique beneficial features of membrane distillation, viz., higher recovery and higher rejection of nonvolatile solutes,
6 Fouling and Wetting: A Major Challenge for Membrane Distillation