J
Flux (molar)
p
Pressure (externally applied)
q
Flow rate (volumetric)
R
Water recovery
SR Solute rejection
SP Salt passage
Greek Letters
p Osmotic pressure (natural)
% Percent
Subscripts
F Feed
P Permeate
s
Salt
w Water
Superscript
° Degree
1 Introduction
Every living creature on the globe essentially requires water
for its survival and nurturing. Ample water is available on
Earth as seawater (94%), brackish water (2%), and freshwater (4%). Main sources of freshwater are underground
water (72%) and large masses of glacier ice (27%). Based on
its salinity level, water is mainly classified into high-salinity
seawater, medium-salinity brackish water, and low-salinity
freshwater (El-Manharawy and Hafez 2001). High-salinity
levels of brackish water limit its direct use as drinking water
according to World Health Organization (WHO) guidelines;
brackish water needs to be desalinated before it can be
consumed as drinking water. Desalination is a technique
used to obtain hygienic water appropriate for drinking,
domestic, and industrial consumption by eliminating salts,
minerals, and other contaminating agents from brackish
water or seawater (Shenvi et al. 2015). Clean water finds
vital applications in domestic, industrial, and farming sectors
(Aquastat 2013). Inappropriate handling of clean water,
exploitation of water resources, contamination of water
reservoirs, disproportionate population boom, and changing
meteorological conditions are the main reasons of water
shortage. The situation of water scarceness is even more
aggravated in distant localities.
Water desalination is believed to be the leading process to
obtain freshwater from various brackish water sources (Prihasto et al. 2009). Legislative policies of some countries to
maintain good quality of drinkable water require improvements in the efficiency of water desalination processes (Xia
et al. 2007). Conventional thermal desalination processes to
produce portable water are based on the principle of phase
change. These expensive energy-intensive methods include
multi-effect evaporation (MEE), multistage flash distillation
(MSFD), thermal vapor compression distillation (TVCD),
and mechanical vapor compression distillation (MVCD)
processes (Ali et al. 2018; Youssef et al. 2014). Recent
developments in membrane science and technology have
resulted in the adoption of more economical and high-tech
membrane-based desalination processes like reverse osmosis
(RO), ultrafiltration (UF), nanofiltration (NF), electrodialysis
(ED), and membrane distillation (MD) on account of their
low energy requirements, high process efficiency, compact
design, low space requirement, simple operation, and easy
process control (Altaee et al. 2014; Cay-Durgun and Lind
2018; Werber et al. 2016a, b; Qasim et al. 2018).
Among the contemporary membrane-based water desalination processes, reverse osmosis is the most economical,
mature, reliable, and state-of-the-minute technique to purify
brackish water and seawater (Atab et al. 2016; Goh 2018).
Depending upon salt concentration of raw feed water,
reverse osmosis processes are broadly characterized as seawater reverse osmosis (SWRO) plants processing seawater
having salinity of about 30,000 mg/L, and brackish water
reverse osmosis (BWRO) plants operating on brackish water
having salinity in the range of 500–10,000 mg/L. BWRO
processes are further categorized as high-salinity BRWO
process purifying feed water possessing salinity level in the
range of 2500–10,000 mg/L and low-salinity BRWO process desalting feed water having salinity in the range of 500–
2500 mg/L. Development of high-performance membrane
materials, reduced energy requirements, and optimized process conditions have helped the reverse osmosis-based
desalination technology to steadily capture the market
place. At present, more than half of the desalted water
accessible worldwide is being processed via reverse osmosis
technology to produce portable water at competitively low
price (Goh 2018). Desalination performance of BWRO
process depends on permeation properties of semipermeable
membrane, quality of feed water being processed, and
working conditions of the process.
This chapter overviews the state-of-the-minute trends and
numerous aspects of reverse osmosis membrane processes
for water purification of brackish water. The fundamental
governing principle, theoretical background, and various
desalination performance measuring quantities associated
with reverse osmosis membrane desalination process
are comprehensively reviewed here. Recent advancements
made in the field of membrane material development to
prepare integrally skinned cellulose acetate membranes,
40
M. Sarfraz
Flux (molar)
p
Pressure (externally applied)
q
Flow rate (volumetric)
R
Water recovery
SR Solute rejection
SP Salt passage
Greek Letters
p Osmotic pressure (natural)
% Percent
Subscripts
F Feed
P Permeate
s
Salt
w Water
Superscript
° Degree
1 Introduction
Every living creature on the globe essentially requires water
for its survival and nurturing. Ample water is available on
Earth as seawater (94%), brackish water (2%), and freshwater (4%). Main sources of freshwater are underground
water (72%) and large masses of glacier ice (27%). Based on
its salinity level, water is mainly classified into high-salinity
seawater, medium-salinity brackish water, and low-salinity
freshwater (El-Manharawy and Hafez 2001). High-salinity
levels of brackish water limit its direct use as drinking water
according to World Health Organization (WHO) guidelines;
brackish water needs to be desalinated before it can be
consumed as drinking water. Desalination is a technique
used to obtain hygienic water appropriate for drinking,
domestic, and industrial consumption by eliminating salts,
minerals, and other contaminating agents from brackish
water or seawater (Shenvi et al. 2015). Clean water finds
vital applications in domestic, industrial, and farming sectors
(Aquastat 2013). Inappropriate handling of clean water,
exploitation of water resources, contamination of water
reservoirs, disproportionate population boom, and changing
meteorological conditions are the main reasons of water
shortage. The situation of water scarceness is even more
aggravated in distant localities.
Water desalination is believed to be the leading process to
obtain freshwater from various brackish water sources (Prihasto et al. 2009). Legislative policies of some countries to
maintain good quality of drinkable water require improvements in the efficiency of water desalination processes (Xia
et al. 2007). Conventional thermal desalination processes to
produce portable water are based on the principle of phase
change. These expensive energy-intensive methods include
multi-effect evaporation (MEE), multistage flash distillation
(MSFD), thermal vapor compression distillation (TVCD),
and mechanical vapor compression distillation (MVCD)
processes (Ali et al. 2018; Youssef et al. 2014). Recent
developments in membrane science and technology have
resulted in the adoption of more economical and high-tech
membrane-based desalination processes like reverse osmosis
(RO), ultrafiltration (UF), nanofiltration (NF), electrodialysis
(ED), and membrane distillation (MD) on account of their
low energy requirements, high process efficiency, compact
design, low space requirement, simple operation, and easy
process control (Altaee et al. 2014; Cay-Durgun and Lind
2018; Werber et al. 2016a, b; Qasim et al. 2018).
Among the contemporary membrane-based water desalination processes, reverse osmosis is the most economical,
mature, reliable, and state-of-the-minute technique to purify
brackish water and seawater (Atab et al. 2016; Goh 2018).
Depending upon salt concentration of raw feed water,
reverse osmosis processes are broadly characterized as seawater reverse osmosis (SWRO) plants processing seawater
having salinity of about 30,000 mg/L, and brackish water
reverse osmosis (BWRO) plants operating on brackish water
having salinity in the range of 500–10,000 mg/L. BWRO
processes are further categorized as high-salinity BRWO
process purifying feed water possessing salinity level in the
range of 2500–10,000 mg/L and low-salinity BRWO process desalting feed water having salinity in the range of 500–
2500 mg/L. Development of high-performance membrane
materials, reduced energy requirements, and optimized process conditions have helped the reverse osmosis-based
desalination technology to steadily capture the market
place. At present, more than half of the desalted water
accessible worldwide is being processed via reverse osmosis
technology to produce portable water at competitively low
price (Goh 2018). Desalination performance of BWRO
process depends on permeation properties of semipermeable
membrane, quality of feed water being processed, and
working conditions of the process.
This chapter overviews the state-of-the-minute trends and
numerous aspects of reverse osmosis membrane processes
for water purification of brackish water. The fundamental
governing principle, theoretical background, and various
desalination performance measuring quantities associated
with reverse osmosis membrane desalination process
are comprehensively reviewed here. Recent advancements
made in the field of membrane material development to
prepare integrally skinned cellulose acetate membranes,
40
M. Sarfraz