turbines, reversible pumps, hydraulic turbo boosters, etc.
Energy recovery devices of latter type, capable of recovering
93–96% energy of the brine, comprise Dual Work Exchanger Energy Recovery System, Pressure exchanger, Sal Tec
device, etc.
Materials of construction to manufacture energy recovery
devices, piping and fittings, valves, and other associated
accessories should be mechanically strong as well as sustainable in chlorinated and corrosive environments (Olsson
2005; Olsson and Snis 2007). Commonly used materials to
manufacture BWRO plants include polyvinyl chloride
(PVC) and various grades of stainless steel like 316 L, 904
L, 254 SMO, and SAF 2507 (Voutchkov 2014).
6.4 Economic Aspects of BWRO Process
Owing to its lowest energy requirement, water purification
via reverse osmosis membrane technology is the most economical method among all the desalination processes (Wilf
and Bartels 2005). Overall water desalination cost of reverse
osmosis membrane process has heavily fallen over the last
few years on account of significant developments made in
membrane technology (Ghaffour et al. 2013). Notable
improvements in this area comprise increased water flux,
enhanced salt rejection, improved plant efficiency, better
energy recovery, reduced energy consumption, preparation
of high boron rejection membranes, and manufacturing of
fouling-resistant membranes (Lee et al. 2011; Amy et al.
2017; Zhao et al. 2013; Kang and Cao 2012).
6.5 Optimization of BWRO Process
Cost of producing drinking water through BWRO membrane
process can be further reduced by using larger pressure
vessels, employing high productivity and/or high rejection
membranes, utilizing membranes made from nanomaterials,
adopting hybrid membrane inter-stage design, and making
use of subsurface intakes instead of open intakes.
• Capital costs can be significantly reduced by shifting
from contemporary smaller 8 in. diameter to larger 16 in.
diameter pressure vessels to meet industrial standards as
per recommendations of membrane suppliers. Switching
to larger pressure vessels results in cost savings of fabrication and life cycle by 30% and 10%, respectively
(Bartels et al. 2005).
• High throughput and/or highly selective membranes can
also result in cost savings of BWRO membrane process
by optimizing water flux and salt rejection properties of
the membrane (Voutchkov 2018; Werber et al. 2016a, b).
• A tradeoff must be made between water recovery and
membrane area since they directly affect the working and
capital costs of membrane desalination process (Gordon
and Hui 2016; Elimelech and Phillip 2011; Zhu et al.
2009).
• Desalting performance of BWRO process can be considerably improved by employing high selectivity next
generation membranes made of nanomaterials such as
carbon nanotubes and graphene nanosheets (Werber et al.
2016a, b).
• Both the capital and operational costs of BWRO plant can
be reduced by using hybrid membrane inter-stage design
in which membrane elements of varying throughput and
rejection are mounted in a single pressure vessel to
achieve uniform flux distribution (Voutchkov 2018;
Peñate and García-Rodríguez 2011; Voutchkov 2014).
• Utilization of subsurface intakes in place of open intakes
decreases working cost, increases feed water quality, and
prolongs membrane life expectancy (Rachman et al.
2014). Good quality feed water does not require laborious
pre-treatment, thus reducing capital and operational costs
(Missimer et al. 2013).
7 Concluding Remarks
Salinity level and composition of regional brackish water
helps to determine appropriate process conditions, pretreatment specifications, best type of membrane material and
module, and economic aspects of a brackish water reverse
osmosis (BWRO) plant. Although originated few decades
earlier, membrane-based reverse osmosis desalination technology has now matured and surpassed conventional thermal
desalination processes. A well-designed BWRO purification
plant should safely and economically produce good quality
drinking water meeting the standards of the World Health
Organization (WHO). In spite of their high chlorine-resistant
properties, conventional cellulosic membranes now find a
little market space due to the availability of contemporary
high-performance thin-film composite and polymeric membranes. Commercial membranes available in flat sheet or
cylindrical shape are inserted in various modules to make the
BWRO desalination process more efficient and economical.
Owing to their low manufacturing cost, low fouling tendency, and low operating pressure, spiral wound modules
are the most commonly used types of BWRO membrane
modules setting aside other module types like plate and
frame, tubular, and hollow fiber. Main components of a
classic BWRO process system comprise pretreatment,
high-pressure
pumping,
membrane
module,
and
post-treatment units. Process parameters which need to be
Recent Trends in Membrane Processes for Water Purification …
53
Energy recovery devices of latter type, capable of recovering
93–96% energy of the brine, comprise Dual Work Exchanger Energy Recovery System, Pressure exchanger, Sal Tec
device, etc.
Materials of construction to manufacture energy recovery
devices, piping and fittings, valves, and other associated
accessories should be mechanically strong as well as sustainable in chlorinated and corrosive environments (Olsson
2005; Olsson and Snis 2007). Commonly used materials to
manufacture BWRO plants include polyvinyl chloride
(PVC) and various grades of stainless steel like 316 L, 904
L, 254 SMO, and SAF 2507 (Voutchkov 2014).
6.4 Economic Aspects of BWRO Process
Owing to its lowest energy requirement, water purification
via reverse osmosis membrane technology is the most economical method among all the desalination processes (Wilf
and Bartels 2005). Overall water desalination cost of reverse
osmosis membrane process has heavily fallen over the last
few years on account of significant developments made in
membrane technology (Ghaffour et al. 2013). Notable
improvements in this area comprise increased water flux,
enhanced salt rejection, improved plant efficiency, better
energy recovery, reduced energy consumption, preparation
of high boron rejection membranes, and manufacturing of
fouling-resistant membranes (Lee et al. 2011; Amy et al.
2017; Zhao et al. 2013; Kang and Cao 2012).
6.5 Optimization of BWRO Process
Cost of producing drinking water through BWRO membrane
process can be further reduced by using larger pressure
vessels, employing high productivity and/or high rejection
membranes, utilizing membranes made from nanomaterials,
adopting hybrid membrane inter-stage design, and making
use of subsurface intakes instead of open intakes.
• Capital costs can be significantly reduced by shifting
from contemporary smaller 8 in. diameter to larger 16 in.
diameter pressure vessels to meet industrial standards as
per recommendations of membrane suppliers. Switching
to larger pressure vessels results in cost savings of fabrication and life cycle by 30% and 10%, respectively
(Bartels et al. 2005).
• High throughput and/or highly selective membranes can
also result in cost savings of BWRO membrane process
by optimizing water flux and salt rejection properties of
the membrane (Voutchkov 2018; Werber et al. 2016a, b).
• A tradeoff must be made between water recovery and
membrane area since they directly affect the working and
capital costs of membrane desalination process (Gordon
and Hui 2016; Elimelech and Phillip 2011; Zhu et al.
2009).
• Desalting performance of BWRO process can be considerably improved by employing high selectivity next
generation membranes made of nanomaterials such as
carbon nanotubes and graphene nanosheets (Werber et al.
2016a, b).
• Both the capital and operational costs of BWRO plant can
be reduced by using hybrid membrane inter-stage design
in which membrane elements of varying throughput and
rejection are mounted in a single pressure vessel to
achieve uniform flux distribution (Voutchkov 2018;
Peñate and García-Rodríguez 2011; Voutchkov 2014).
• Utilization of subsurface intakes in place of open intakes
decreases working cost, increases feed water quality, and
prolongs membrane life expectancy (Rachman et al.
2014). Good quality feed water does not require laborious
pre-treatment, thus reducing capital and operational costs
(Missimer et al. 2013).
7 Concluding Remarks
Salinity level and composition of regional brackish water
helps to determine appropriate process conditions, pretreatment specifications, best type of membrane material and
module, and economic aspects of a brackish water reverse
osmosis (BWRO) plant. Although originated few decades
earlier, membrane-based reverse osmosis desalination technology has now matured and surpassed conventional thermal
desalination processes. A well-designed BWRO purification
plant should safely and economically produce good quality
drinking water meeting the standards of the World Health
Organization (WHO). In spite of their high chlorine-resistant
properties, conventional cellulosic membranes now find a
little market space due to the availability of contemporary
high-performance thin-film composite and polymeric membranes. Commercial membranes available in flat sheet or
cylindrical shape are inserted in various modules to make the
BWRO desalination process more efficient and economical.
Owing to their low manufacturing cost, low fouling tendency, and low operating pressure, spiral wound modules
are the most commonly used types of BWRO membrane
modules setting aside other module types like plate and
frame, tubular, and hollow fiber. Main components of a
classic BWRO process system comprise pretreatment,
high-pressure
pumping,
membrane
module,
and
post-treatment units. Process parameters which need to be
Recent Trends in Membrane Processes for Water Purification …
53