distillation, forward osmosis, and nanofiltration which are impacting desalination,
wastewater treatment, and other separation processes. Development of ultrafiltration
initially as a pretreatment for reverse osmosis systems has found more utility as
membrane bioreactors for the secondary treatment of wastewater and many other
applications in the production of safe drinking water and sterile water. These
membranes can be used as membrane contactors for carrying out conventional unit
operations such as membrane solvent extraction, gas separation, and crystallization.
Charged membranes have been demonstrated for processes such as electrodeionization and electrodialysis with bipolar membrane besides electrodialysis
which are more environment-friendly and are capable of not only treating wastewater but also recovering value. The membranes available today separate either water
or a few solutes from its solution. Consequently, all these processes have a role to
play in the water treatment.
8.4.1 Pressure-Driven Processes
Applications of Reverse Osmosis
Desalination Reverse osmosis application for seawater desalination has recorded a
tremendous growth with the developments of membranes (Yang et al. 2018), energy
recovery devices (Kadai and Bosleman 2018), and rugged pretreatment systems. A
state-of-the-art review published (Qasim et al. 2019) recently recounts the various
developments taken place over the last few decades. The present specific energy
consumption for seawater desalination is reported to be around 2.5–4 kWh/m
3
(Voutchkov 2018; Karabelas et al. 2018). The advent of ultrafiltration membranes
as a pretreatment system has contributed to the improved design with higher specific
recoveries for the membrane element. Even though desalination systems can be
designed using any of the four configurations, spiral configuration is extensively
used in large-scale installations. Hollow fiber configuration was used in the initial
period but later discontinued due to practical problems with reference to maintenance. Even though the first demonstrated reverse osmosis plant was in tubular
configuration, it is not the preferred configuration in many applications being the
least compact configuration. Plate and frame modules are used for small-capacity
desalination systems particularly for seawater desalination in ships where constraints
of space, head room, and inventory-carrying capacity exist.
A membrane element is the basic unit which can be assembled in series. A
number of spiral membrane elements (not more than seven) assembled in a pressure
vessel is called a module. When feedwater flows through the module, two streams
emerge: one concentrated stream and the other permeate stream normally designated
as “product.” The performance parameters are solute rejection, recovery, product
water (permeate) flux, and module pressure drop. Solute rejection is defined as the
fraction of the solutes, which is retained in the feed side (concentrate) and is
mathematically represented as follows:
262
A. Kapoor et al.
wastewater treatment, and other separation processes. Development of ultrafiltration
initially as a pretreatment for reverse osmosis systems has found more utility as
membrane bioreactors for the secondary treatment of wastewater and many other
applications in the production of safe drinking water and sterile water. These
membranes can be used as membrane contactors for carrying out conventional unit
operations such as membrane solvent extraction, gas separation, and crystallization.
Charged membranes have been demonstrated for processes such as electrodeionization and electrodialysis with bipolar membrane besides electrodialysis
which are more environment-friendly and are capable of not only treating wastewater but also recovering value. The membranes available today separate either water
or a few solutes from its solution. Consequently, all these processes have a role to
play in the water treatment.
8.4.1 Pressure-Driven Processes
Applications of Reverse Osmosis
Desalination Reverse osmosis application for seawater desalination has recorded a
tremendous growth with the developments of membranes (Yang et al. 2018), energy
recovery devices (Kadai and Bosleman 2018), and rugged pretreatment systems. A
state-of-the-art review published (Qasim et al. 2019) recently recounts the various
developments taken place over the last few decades. The present specific energy
consumption for seawater desalination is reported to be around 2.5–4 kWh/m
3
(Voutchkov 2018; Karabelas et al. 2018). The advent of ultrafiltration membranes
as a pretreatment system has contributed to the improved design with higher specific
recoveries for the membrane element. Even though desalination systems can be
designed using any of the four configurations, spiral configuration is extensively
used in large-scale installations. Hollow fiber configuration was used in the initial
period but later discontinued due to practical problems with reference to maintenance. Even though the first demonstrated reverse osmosis plant was in tubular
configuration, it is not the preferred configuration in many applications being the
least compact configuration. Plate and frame modules are used for small-capacity
desalination systems particularly for seawater desalination in ships where constraints
of space, head room, and inventory-carrying capacity exist.
A membrane element is the basic unit which can be assembled in series. A
number of spiral membrane elements (not more than seven) assembled in a pressure
vessel is called a module. When feedwater flows through the module, two streams
emerge: one concentrated stream and the other permeate stream normally designated
as “product.” The performance parameters are solute rejection, recovery, product
water (permeate) flux, and module pressure drop. Solute rejection is defined as the
fraction of the solutes, which is retained in the feed side (concentrate) and is
mathematically represented as follows:
262
A. Kapoor et al.