acetate/polyvinyl pyrrolidone blend (Fox 1980; Sekiguchi
et al. 1978; El-Gendi et al. 2017; Saljoughi and Mohammadi
2009). Desalination performance of important asymmetric
BWRO membranes is summarized in Table 2.
3.3 Thin-Film Interfacial Composite Membranes
Development of thin-film interfacial composite membranes
by Cadotte et al. via interfacial polymerization in 1981 was a
breakthrough in the field of water desalination technology
via reverse osmosis process (Cadotte 1981, 1985; Larson
et al. 1981). Intensive research carried out on thin-film
asymmetric membranes led to successful commercialization
and patenting of these membranes on industrial scale (Sasaki
et al. 1988, 1989; Hachisuka and Ikeda 2002). These
membranes consist of three layers: (1) woven polymer fabric
for membrane handling, (2) a porous polymer substratum
cast on the fabric to provide mechanical toughness, and (3) a
permselective dense layer of crosslinked polyamide deposited on the substrate via polymerization occurring at the
interface (Fig. 3). Commercial preparation technique of
interfacial composite membranes is almost same except that
the process is continuous and fast (Petersen 1993). Water
flux, salt elimination, fouling propensity, and operating
conditions of thin-film composite membranes can be optimized via separately choosing and modifying a proper
microporous substrate, barrier dense layer, reactive monomers, and suitable additives. Detailed description of some of
the commercially available polyamide-based thin-film composite membranes is enlisted in Table 3.
In contrast to cellulose acetate membranes, composite
membranes render substantially higher water fluxes along
with higher salt and silica rejections. Flux and selectivity of
these membranes are determined by the porosity of support
layer and crosslink density of selective layer, respectively.
Owing to their inherently thin selective layer deposited on a
microporous support layer, composite membranes can
function well under low operating pressure while withstanding relatively broader ranges of acidity scale (pH: 2–
12) and feed water temperature (up to 45 °C). These membranes, however, are susceptible to fouling and disinfectants
attack (Kucera 2010).
4 BWRO Membrane Modules
BWRO plants consist of membrane modules containing
efficient and economical packaging of huge surface areas
(thousands of square meters) of membranes to accomplish
desalination on large industrial scale. Effective module
designs guarantee process compactness, low capital cost,
easy installation, comfortable cleaning, and replacement of
membranes (Belfort 1984). Fabrication of inexpensive
membrane modules was a technological breakthrough to
launch membrane desalting process on a commercial scale in
1970s. Since membrane modules have been confidentially
fabricated inside private companies, lots of membranologists
are unacquainted about the issues of module design, fabrication, and operation.
Depending on their configuration, two basic types of
membrane module designs are flat and cylindrical (Mulder
1996). Flat shape membranes are implanted in plate and
frame and spiral wound modules, whereas membranes of
cylindrical profile are inserted in tubular, hollow fiber, and
capillary modules. In addition, some patents have reported
Table 1 Desalination properties
of commercially available
cellulosic membranes
Base polymer
Trade name
Permeate
flux (m
3
/
m
2 day)
Salt
rejection
(%)
Test conditions
References
Cellulose
triacetate
HOLLOSEP
®
HA 8130
0.52
94
1500 ppm NaCl,
29.4 bar, 25 °C,
75% recovery
Toyobo Co.
Ltd. (2006)
HOLLOSEP
®
HJ 9155
0.18
99.6
35,000 ppm NaCl,
53.9 bar, 25 °C,
30% recovery
M-C4040A
0.12
96.1
500 ppm tap water,
16.0 bar, 25 °C,
15% recovery, pH
7–8
Applied
Membranes
(2018)
Blend of
cellulose
diacetate and
cellulose
triacetate
CD series
0.37
98.5
2000 ppm NaCl,
29.3 bar, 25 °C,
pH 6.5, 15%
recovery
Suez Water
Technologies
(2018a)
CE series
0.40
97.5
Suez Water
Technologies
(2018b)
44
M. Sarfraz
et al. 1978; El-Gendi et al. 2017; Saljoughi and Mohammadi
2009). Desalination performance of important asymmetric
BWRO membranes is summarized in Table 2.
3.3 Thin-Film Interfacial Composite Membranes
Development of thin-film interfacial composite membranes
by Cadotte et al. via interfacial polymerization in 1981 was a
breakthrough in the field of water desalination technology
via reverse osmosis process (Cadotte 1981, 1985; Larson
et al. 1981). Intensive research carried out on thin-film
asymmetric membranes led to successful commercialization
and patenting of these membranes on industrial scale (Sasaki
et al. 1988, 1989; Hachisuka and Ikeda 2002). These
membranes consist of three layers: (1) woven polymer fabric
for membrane handling, (2) a porous polymer substratum
cast on the fabric to provide mechanical toughness, and (3) a
permselective dense layer of crosslinked polyamide deposited on the substrate via polymerization occurring at the
interface (Fig. 3). Commercial preparation technique of
interfacial composite membranes is almost same except that
the process is continuous and fast (Petersen 1993). Water
flux, salt elimination, fouling propensity, and operating
conditions of thin-film composite membranes can be optimized via separately choosing and modifying a proper
microporous substrate, barrier dense layer, reactive monomers, and suitable additives. Detailed description of some of
the commercially available polyamide-based thin-film composite membranes is enlisted in Table 3.
In contrast to cellulose acetate membranes, composite
membranes render substantially higher water fluxes along
with higher salt and silica rejections. Flux and selectivity of
these membranes are determined by the porosity of support
layer and crosslink density of selective layer, respectively.
Owing to their inherently thin selective layer deposited on a
microporous support layer, composite membranes can
function well under low operating pressure while withstanding relatively broader ranges of acidity scale (pH: 2–
12) and feed water temperature (up to 45 °C). These membranes, however, are susceptible to fouling and disinfectants
attack (Kucera 2010).
4 BWRO Membrane Modules
BWRO plants consist of membrane modules containing
efficient and economical packaging of huge surface areas
(thousands of square meters) of membranes to accomplish
desalination on large industrial scale. Effective module
designs guarantee process compactness, low capital cost,
easy installation, comfortable cleaning, and replacement of
membranes (Belfort 1984). Fabrication of inexpensive
membrane modules was a technological breakthrough to
launch membrane desalting process on a commercial scale in
1970s. Since membrane modules have been confidentially
fabricated inside private companies, lots of membranologists
are unacquainted about the issues of module design, fabrication, and operation.
Depending on their configuration, two basic types of
membrane module designs are flat and cylindrical (Mulder
1996). Flat shape membranes are implanted in plate and
frame and spiral wound modules, whereas membranes of
cylindrical profile are inserted in tubular, hollow fiber, and
capillary modules. In addition, some patents have reported
Table 1 Desalination properties
of commercially available
cellulosic membranes
Base polymer
Trade name
Permeate
flux (m
3
/
m
2 day)
Salt
rejection
(%)
Test conditions
References
Cellulose
triacetate
HOLLOSEP
®
HA 8130
0.52
94
1500 ppm NaCl,
29.4 bar, 25 °C,
75% recovery
Toyobo Co.
Ltd. (2006)
HOLLOSEP
®
HJ 9155
0.18
99.6
35,000 ppm NaCl,
53.9 bar, 25 °C,
30% recovery
M-C4040A
0.12
96.1
500 ppm tap water,
16.0 bar, 25 °C,
15% recovery, pH
7–8
Applied
Membranes
(2018)
Blend of
cellulose
diacetate and
cellulose
triacetate
CD series
0.37
98.5
2000 ppm NaCl,
29.3 bar, 25 °C,
pH 6.5, 15%
recovery
Suez Water
Technologies
(2018a)
CE series
0.40
97.5
Suez Water
Technologies
(2018b)
44
M. Sarfraz