8.4.6 Forward Osmosis
Forward osmosis is gaining importance as a technology for desalination, concentration of solutions, and energy recovery. Its advantage emanates from being a passive
process in nature (not requiring any external source of energy) as the separation is
driven osmotic pressure differential between the draw solution and the feed. The
challenges to realize the potential require a membrane with good water flux, a less
reverse solute transport, and above all a convenient and cost-effective means of
recovering pure water from the diluted osmotic sink. No doubt, the literature is
replete with novel membranes such as cellulose triacetate (Ong et al. 2015), thin film
composite (Ren and McCutcheon 2014), thin film nanofiltration (Ma et al. 2013),
biomimetic (Fane and Tang 2012), and draw solute ranging from inorganic solutes,
phase change material, low-molecular-weight organic solutes, and volatile solute or
dissolved gas solutions (Lutchmiah et al. 2014). Since forward osmosis desalination
is a two-step process, many combinations are being investigated using thermal and
mechanical energy. Basically, the present methods adopted for forward osmosis
desalination includes the combination of forward osmosis and reverse osmosis (Cath
et al. 2010), forward osmosis–nanofiltration (Kim et al. 2018), forward osmosis–
distillation (McCutcheon et al. 2006), and forward osmosis–phase change material
(Kim et al. 2016). Apart from these, aquaporin-incorporated vesicles exhibit excellent water permeability and high salt rejection, owing to the superior intrinsic
characteristics of the aquaporin’s as water channels (Li et al. 2017). Double-skinned
forward osmosis membranes have also been proposed (Song et al. 2015a).
Forward osmosis as a standalone desalination option is not practical because of
the nonavailability suitable draw solute which can be easily regenerated to recover
the product water. Forward osmosis has more potential in wastewater treatment
(Lutchmiah et al. 2014) as it can be used for the concentration of the waste. Besides,
the water that is removed can be recovered by secondary processes such as reverse
osmosis/nanofiltration. Alternately, fertilizers can be used as draw solute so that the
resulting dilute solution can be directly used in the field. Similarly, if pretreated
seawater is used as a draw solution for wastewater, the seawater would get diluted,
thereby savings in energy cost for seawater desalination (Akther et al. 2015).
8.4.7 Diffusion Dialysis
Because of the low flux, the applications of diffusion dialysis have been limited to
the recovery of acids and alkalis from the discharges from steel production, metalrefining, electroplating, cation exchange resin regeneration, nonferrous metal
smelting, aluminum etching, and tungsten ore smelting (Jeong et al. 2005). An
excellent review by Luo et al. (2011) indicate that many acid recovery systems
installed in different industries have made profits suggesting diffusion dialysis is
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A. Kapoor et al.
Forward osmosis is gaining importance as a technology for desalination, concentration of solutions, and energy recovery. Its advantage emanates from being a passive
process in nature (not requiring any external source of energy) as the separation is
driven osmotic pressure differential between the draw solution and the feed. The
challenges to realize the potential require a membrane with good water flux, a less
reverse solute transport, and above all a convenient and cost-effective means of
recovering pure water from the diluted osmotic sink. No doubt, the literature is
replete with novel membranes such as cellulose triacetate (Ong et al. 2015), thin film
composite (Ren and McCutcheon 2014), thin film nanofiltration (Ma et al. 2013),
biomimetic (Fane and Tang 2012), and draw solute ranging from inorganic solutes,
phase change material, low-molecular-weight organic solutes, and volatile solute or
dissolved gas solutions (Lutchmiah et al. 2014). Since forward osmosis desalination
is a two-step process, many combinations are being investigated using thermal and
mechanical energy. Basically, the present methods adopted for forward osmosis
desalination includes the combination of forward osmosis and reverse osmosis (Cath
et al. 2010), forward osmosis–nanofiltration (Kim et al. 2018), forward osmosis–
distillation (McCutcheon et al. 2006), and forward osmosis–phase change material
(Kim et al. 2016). Apart from these, aquaporin-incorporated vesicles exhibit excellent water permeability and high salt rejection, owing to the superior intrinsic
characteristics of the aquaporin’s as water channels (Li et al. 2017). Double-skinned
forward osmosis membranes have also been proposed (Song et al. 2015a).
Forward osmosis as a standalone desalination option is not practical because of
the nonavailability suitable draw solute which can be easily regenerated to recover
the product water. Forward osmosis has more potential in wastewater treatment
(Lutchmiah et al. 2014) as it can be used for the concentration of the waste. Besides,
the water that is removed can be recovered by secondary processes such as reverse
osmosis/nanofiltration. Alternately, fertilizers can be used as draw solute so that the
resulting dilute solution can be directly used in the field. Similarly, if pretreated
seawater is used as a draw solution for wastewater, the seawater would get diluted,
thereby savings in energy cost for seawater desalination (Akther et al. 2015).
8.4.7 Diffusion Dialysis
Because of the low flux, the applications of diffusion dialysis have been limited to
the recovery of acids and alkalis from the discharges from steel production, metalrefining, electroplating, cation exchange resin regeneration, nonferrous metal
smelting, aluminum etching, and tungsten ore smelting (Jeong et al. 2005). An
excellent review by Luo et al. (2011) indicate that many acid recovery systems
installed in different industries have made profits suggesting diffusion dialysis is
272
A. Kapoor et al.