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Application of forward osmosis in reusing the brackish concentrate produced in reverse osmosis plants with secondary treated wastewater as feed solution: A case study


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This study aimed to investigate the variation of aluminum species in a drinking water distribution system in a city in northeastern China. The aluminum species were determined by fluorometric methods. Results showed that suspended aluminum (Sus-Al) was the major species in the drinking water supplied by plant B and accounted for about 42% of the total aluminum (Tol-Al). The concentrations of Sus-Al and Tol-Al could be controlled effectively by introducing reservoir water. In the water source switching process, the water quality variation led to the suddenly release of Sus-Al, especially in a cast iron pipeline that had been in service for more than 30 years, but the soluble aluminum varied little. In the plant A service areas, the average concentrations of the inorganic monomeric aluminum (IM-Al), monomeric aluminum (Mon-Al), and soluble aluminum (Sol-Al) were 0.008 mg L −1 , 0.03 mg L −1 , and 0.04 mg L −1 , respectively, and their concentrations in the plant B service areas were higher. The pH and fluoride were the major parameters affecting the soluble aluminum speciation. With a solution pH of 6.5-7.5 and fluoride below 0.3 mg L −1 , the Sol-Al could be controlled within 0.1 mg L −1. Water quality regulation and terminal filtration were suggested for residual aluminum control.
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Application of forward osmosis in reusing the brackish
concentrate produced in reverse osmosis plants with
secondary treated wastewater as feed solution: a case
W. D. Wang, M. Esparra, H. Liu and Y. F. Xie
This study evaluated the feasibility of forward osmosis (FO) in diluting and reusing the concentrate
produced in a reverse osmosis (RO) plant in James City County, VA. Secondary treated wastewater
(STW) was used as the feed solution. Findings indicated that pH had slight effects on the water ux of
the FO membrane. As the concentration of total dissolved solids (TDS) in the concentrate was diluted
from 12.5 to 1.0 g/L or the temperature in the STW decreased from 23 to 10 WC, the membrane ux
decreased from 2.2 to 0.59 and 0.81 L/(m
h), respectively. The FO membrane showed a good
performance in the rejection of organic pollutants, with only a small part of the protein-like
substances and disinfection byproducts permeating to the diluted concentrate. During an 89-hour
continuous operation, water ux decline due to membrane fouling was not observed. Controlling the
TDS in the second-stage FO efuent at 1.5 g/L, approximately 8.3% of the pump energy input could
be saved. The consumption of groundwater was reduced from 22.7 ×10
to 10.6 ×10
/d. FO was
proved to be an effective method in both diluting the discharged concentrate and reducing the
energy consumption of RO.
W. D. Wang
M. Esparra
Y. F. Xie (corresponding author)
Department of Civil and Environmental
The Pennsylvania State University,
PA 17057,
W. D. Wang
H. Liu
Department of Environmental and Municipal
Xian University of Architecture and Technology,
Xian 710055,
Y. F. Xie
Department of Environment,
Tsinghua University,
Beijing 100084,
Key words |brackish water, drinking water, forward osmosis, secondary treated wastewater
With the increase in water demand, many utilities are turn-
ing to non-traditional water, such as brackish water,
seawater, and even wastewater, as a possible water source
in many countries and areas of the world (National
Research Council (US) ). Accordingly, reverse osmosis
(RO) is becoming more and more common as a technique
to produce drinking water because of its high efciency in
pollutant removal (Herzberg et al. ). This is the case
for James City County in Virginia, USA, where groundwater
with a high salt content (brackish water) is the main water
source. The raw water is desalinated by a RO system. One
of the major issues that the actual process presents is dispo-
sal of the concentrate. Due to the environmental impacts of
high salinity water, the discharge of desalination
concentrated solutions is highly controlled by the regulatory
agencies. Strict regulations have been created over the last
decade, making it more difcult to build a new facility or ret-
rot/expand existing ones.
In the RO process, hydraulic pressure is used to oppose
and exceed the osmotic pressure of a saline aqueous feed
solution. The applied pressure is the driving force for the
mass transport through a semi-permeable membrane
(Greenlee et al. ;Malaeb & Ayoub ). The membrane
allows the passage of clean water, while the salt and other
contaminants are held back (National Research Council
(US) ). Accordingly, both the energy consumed in the
RO unit and the salt content in the discharged concentrate
are high (Stoughton & Lietzke ;Lattemann & Höpner
533 © IWA Publishing 2016 Journal of Water Reuse and Desalination |06.4 |2016
doi: 10.2166/wrd.2016.097
;Semiat ;Elimelech & Phillip ). Although great
gains have been made over the last decade in the RO tech-
nology to increase its energy efciency, energy costs still
contribute as much as 75% of the operation cost of desalina-
tion plants (Semiat ). Innovations that help to reduce
energy consumption and the amount of concentrate dis-
charged will strengthen the suitability of RO in drinking
water purication.
The amount of energy used in RO mainly depends on
the salt concentration of the feed solution, and can range
from 3.0 to 7.0 kWh/m
for seawater desalination (National
Research Council (US) ). For brackish water desalina-
tion, however, where the concentration of salt (110 g/L)
is notably lower than that of the seawater (1030 g/L), the
energy consumption is approximately 0.53.0 kWh/m
(National Research Council (US) ). For a feed solution
with low salt content, a notable decrease in the osmotic
pressure that must be overcome with applied hydraulic
pressure can be achieved (Semiat ;Subramani et al.
). Accordingly, the RO process would require less
energy to desalinate diluted brackish water than it does for
the raw brackish water, which is the upgrading plan pro-
posed by the authors for the upgrading of the existing RO
system in James City County. The secondary treated waste-
water (STW) was used as the dilution water.
Compared with direct dilution, forward osmosis (FO)
can enable the use of impaired water to dilute the water
entering the RO plant with high pollutant rejection ef-
ciency (Cath et al. ,). In the FO unit, a low salt
concentration water source, acting as the feed solution, is
separated by a selective FO membrane from water with a
high salt concentration, which acts as the draw solution.
The two solutions are placed on opposite sides of the mem-
brane. Fresh water will move from the feed solution towards
the draw solution, leaving contaminants retained in the
membrane (McCutcheon & Elimelech ;Qin et al.
). Accordingly, FO is probably a competitive technique
in diluting the inuent of the RO system.
However, the quality of the STW differs from traditional
water sources and has limited usages because of the pres-
ence of toxic organic materials (Carrara et al. ), which
pose a proven or potentially high health risk to humans. Pre-
vious studies have mainly focused on the rejection
performance of FO for a few parts of specic hazardous
materials, such as pharmaceuticals, personal care products,
and ame-retardants (Hancock et al. ;Kong et al. ,
). The application of STW as an indirect source water
in the hybrid FO/RO system and the organic rejection per-
formance of FO have not yet been studied in depth. The
objective of this work, therefore, is to investigate (i) the
water ux variation law with the dilution of the concentrate
and the variation in temperature and pH of the STW, (ii) the
organic rejection performance of the FO membrane, and
(iii) the feasibility of FO in diluting and reusing the concen-
trate produced in the RO unit using STW as the source
Existing RO desalination process in James City County,
James City County is a 144-square mile municipality located
at the head end of the Virginia Peninsula, between the James
and York Rivers in Virginia. The James City Service Auth-
ority operates the largest solely dependent groundwater
based water system in the Commonwealth of Virginia. The
majority of its groundwater supply system is derived from
the Potomac and Chickahominy-Piney Point Aquifers. The
water treatment facility consists of ve wells drawing brack-
ish groundwater from the Middle Potomac and Lower
Potomac aquifers. To obtain potable water, RO is used to
remove salts and other pollutants (Figure 1). The removed
salts, also known as concentrate, is discharged into the
James River. For every 18.9 ×10
/d of potable water pro-
duced, approximately 3.8 ×10
/d of concentrate is
Four RO skids are installed in the treatment facility for
the desalination of the raw water extracted from the
Lower Potomac Wells. The RO skids consist of a two-stage
membrane system. The rst stage consists of 20 vessels,
and the second stage consists of 10 additional vessels. The
vessels contain six membranes each. Groundwater is
pumped into the rst stage membranes of the RO skid.
The permeate is discharged to the permeate line. The con-
centrate from the rst stage RO becomes the feed water
for the second stage RO. The permeate from the second
stage combines with the permeate from the rst stage. The
concentrate from the second stage RO is piped to the con-
centrate line.
534 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
The raw water used in the drinking water plant is
pumped from ve wells. One of them supplies approxi-
mately 3.8 ×10
/d groundwater with low salt
concentration (Middle Potomac Well). The other four
wells supply approximately 18.9 ×10
/d groundwater
with a higher salt concentration (Lower Potomac Well).
The water quality of both types of wells is presented in
Table 1. Treatment with RO removes nearly all of the salts
in the Lower Potomac Well water. To maintain a normal
range of salt contents in the potable water, the RO efuent
is blended with the groundwater pumped from the Middle
Potomac Well as shown in Figure 1. The concentration of
Figure 1 |Current drinking water treatment process and the proposed upgrading plan based on a two-stage FO system (dashed line) in James City County.
Table 1 |Water quality of the well waters, concentrate, and the STW used in the experiment
Water quality parameters Middle Potomac Well Lower Potomac Well Concentrate STW
pH 7.98.2 7.67.8 8.3 7.5
Temperature (WC) 13 13 13 1030
Conductivity (μS/cm) 1,500 4,500 25,430 9.1
TDS (mg/L) 1,000 2,300 12,500 280
(mg/L) 417 1,100 6,127.4
(mg/L) 6.1 20.3 105 18.0
(mg/L) 1.5 4.2 25 14.5
Iron (mg/L) 0.01 0.02 0.1 0.05
(mg/L) 41 29 164
(mg/L) 340 1,250 7,625
Alkalinity (mg/L) 320 340 1,910 52.0
Turbidity (NTU) <1.0 <1.0 <1.0 5.2
THMs (μg/L) ND ND ND 105.0
HAAs (μg/L) ND ND ND 15.5
TOC (mg/L) 0.06 0.05 0.19 11.2
, data not available; ND, under determination limit.
535 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
total dissolved solids (TDS) in the brackish water is approxi-
mately 2,500 mg/L, which increases to approximately
13,000 mg/L after being concentrated. To avoid the dis-
charge of this highly concentrated brackish water, a two-
stage FO is suggested for the upgrading of the RO system
in James City County.
Feed and draw solution of the FO system
The concentrate, which was used as the draw solution, was
obtained from the RO system in James City County, VA. The
STW, provided by a wastewater treatment plant in Middle-
town, PA, was used as the feed solution, as the plant is
conveniently located near the Harrisburg campus where
the experiments were conducted. This wastewater treatment
plant consists of a solids grinder and grit remover, primary
clarication, biological treatment with clarication, chlorine
addition for disinfection, and de-chlorination prior to dis-
charge. The quality of the concentrate and the STW are
listed in Table 1.
FO cross ow setup
A bench-scale FO system including a membrane permeation
unit, a water circuiting system, and a monitor and data
recording system (Figure 2) was constructed and operated
in the Environmental Engineering Laboratories at The
Pennsylvania State University Harrisburg campus. The
membrane permeation unit was made of acrylic plastic
and had channel dimensions of 10.5 cm long, 5.0 cm wide,
and 0.2 cm deep. The total effective membrane area was
52.5 cm
. The FO membrane was provided by Hydration
Technologies, Inc. (Albany, OR). The active layer made
from cellulose triacetate (CTA) is supported by an embedded
polyester screen to give the membrane asymmetry and
additional mechanical stability (McCutcheon & Elimelech
). The recommended working pH and temperature of
the FO membrane was in the ranges of 3.08.0 and
071 WC, respectively.
Feed and draw solutions were continuously circulated
between the storage tanks and the membrane cell. The
initial volumes of the feed and draw solutions were 350
mL and 1,000 mL, respectively. The cross-ow rate on
each side of the membrane was the same, and was
Figure 2 |FO setup used in the experiment.
536 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
controlled at 45 mL/min with a variable speed pump (Cole-
Parmer, Vernon Hills, IL). Changes in the weight of the
draw solution were recorded by a digital balance (TL2100,
Mettler Toledo, Germany) to determine the membrane
ux of the pure water. The active layer of the FO membrane
was facing the feed solution throughout the experiment.
To examine the effect of pH on the ux of water,
0.1 mol/L NaOH was added to the feed solution to increase
its pH from 7.5 to 8.5. The total running time was controlled
at approximately 15 min. To determine the effects of the
water temperature on the ux of the FO membrane, the
temperature of the feed solution was adjusted between 3
and 30 WC in a constant-temperature incubator. To assess
the effects of membrane fouling on water ux, the variation
of the water ux of the FO membrane was monitored in 89 h
of continuous running. The pH and temperature of the draw
solution were maintained at 8.0 and 23 WC, respectively.
Water quality and membrane structure analysis
The trihalomethanes (THMs) and haloacetic acids (HAAs)
were analyzed by gas chromatography with an electron cap-
ture detector (Agilent 7890A, Santa Clara, USA) after liquid-
liquid extraction and methylation (for HAAs only) accord-
ing to the standard method of EPA551.1 and EPA552.3,
respectively. Standard solutions of four THMs, including
, bromodichlorobromomethane (CHCl
Br), chlorodi-
bromomethane (CHBr
Cl), and bromoform (CHBr
), and
six HAAs, including monochloroacetic acid, monobromoa-
cetic acid, dichloroacetic acid (DCAA), bromochloroacetic
acid (BCAA), dibromoacetic acid, and trichloroacetic acid
(TCAA), were purchased from Sigma-Aldrich (Germany).
pH and temperature were monitored on-line using a
Logger Pro 3.8.6 with corresponding sensors. Before
measuring, all sensors were calibrated with standard sol-
utions. TDS was measured according to standard method
2540c (APHA et al. ). The concentration of organic mat-
ters was measured by a total organic carbon (TOC) analyzer
(TOC-VCPH, Shimadzu, Japan) and a spectrometer (T6,
Puxi, China) at 254 nm.
Fluorescence measurements were conducted using a
spectrouorometer (FP-6500, Jasco, Japan) equipped with
a 150 W xenon lamp at 23 WC. A 1.0 cm quartz cuvette
with four optical windows was used for the analyses. An
emission scan was conducted from 250 to 600 nm at a wave-
length step of 5 nm and excitation wavelengths from 220 to
450 nm at a 5 nm interval. The detector was set to high sen-
sitivity, and the scanning speed was maintained at
2,000 nm/min. To observe the surface characteristics of
the FO membrane, scanning electron microscopy (SEM)
(JSM-6490LV, JEOL Ltd, Japan) was applied. The SEM
samples were sputter-coated with gold before conducting
Effects of TDS in the concentrate on the water ux of
the FO membrane
The experiments were conducted for 15 min to avoid the
effects of membrane fouling. As shown in Figure 3, the aver-
age water ux of the FO membrane was approximately
2.2 L/(m
h) when the TDS concentration in the concen-
trate (draw solution) was 12.5 g/L. This would benet the
application of FO in the dilution and reuse of the concen-
trate. Without membrane fouling, the water ux could be
maintained above 2.0 L/(m
·h). Decreasing the concen-
tration of TDS in the draw solution to 6.0 g/L, the water
ux of the FO membrane decreased notably to 1.3 L/(m
Figure 3 |Variation of water ux with the concentration of TDS in the draw solution.
537 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
Unlike the draw solutions with high TDS, for the draw sol-
utions with TDS below 2.0 g/L, the variation of TDS
showed fewer effects on the membrane ux (Figure 3).
Decreasing the concentration of TDS in the draw solution
further to 2.0 g/L and 1.0 g/L, the membrane uxes were
similar, at 0.72 L/(m
·h) and 0.59 L/(m
·h), respectively.
The water ux of the FO membrane is positively pro-
portional to the content of TDS in the draw solution. To
obtain a high water ux,alargedifferenceinTDSbetween
the feed and draw solution is desired. As described in Equation
(1) (Cath et al. ),thegreaterthedifferenceinosmotic
potential, the faster water moves through the membrane. Mean-
keeps decreasing with the permeation of pure water through
lower, the water ux decreased with operation time:
Jw¼A(σΔπΔP) (1)
where J
is the water ux, A is the water permeability con-
stant of the membrane, σis the reection coefcient, and
ΔPis the applied pressure (Cath et al. ). For FO, ΔPis
zero, making the water ux directly proportional to the
difference in osmotic pressure.
Effects of pH and temperature in the STW on the water
ux of the FO membrane
The water ux of the FO membrane increased gradually as
the solution pH increased. The highest value of approxi-
mately 2.45 L/(m
·h) was obtained at pH 8.5 (Figure 4(a)).
The membrane used in this study was made from CTA
with embedded polyester screen support. Under basic con-
ditions, the number of deprotonated hydroxyl groups (with
negative charge) in the membrane matrix increased notably,
which probably forced adjacent polymers apart, thus
increasing water permeability (Braghetta et al. ;You
et al. ). However, because osmotic pressure is the driving
force in FO, and this pressure was relatively stable under
different pH conditions, the overall variation of membrane
ux with pH was slight.
Compared with pH, temperature showed a more signi-
cant effect on the water ux through the FO membrane. As
shown in Figure 4(b), the average water ux was
approximately 2.75 L/(m
·h) when the temperature of the
draw solution was 30 WC, corresponding to the STW temp-
erature in summer, and decreased notably to
approximately 0.81 L/(m
·h) at 10 WC, corresponding to the
STW temperature in winter. A linear relationship was
found between the membrane ux and the solution tempera-
ture. The slope and intercept of the best t line were
calculated to be 0.102 and 0.372 respectively, which was
close to the values (0.064 and 0.227) obtained by Wang
et al. ()using rainwater and cooling water as the feed
and draw solutions, respectively.
However, based on the vant Hoff equation (You et al.
), the osmotic pressure of the feed solution decreases
with the decrease of its temperature, which will increase
the net osmotic pressure for driving the water in the FO
Figure 4 |Effects of pH (a) and temperature (b) in the STW on the water ux of the FO
538 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
process. Besides net osmotic pressure, both the absolute and
kinematic viscosities of the feed solution increased notably
with the decrease of feed solution temperature (Phuntsho
et al. ). Kim et al. ()determined that as the solution
temperature decreased from 50 WCto20
WC, osmotic coef-
cients and diffusivity decreased by 6.6% and 48.3%
respectively, which increased the internal concentration
polarization (ICP). The increased ICP and solution viscosity
was probably the major reason that inhibited the permeation
of pure water at low temperatures.
Organic rejection performance of the FO membrane
One of the challenges in using the STW as a potable water
source is whether the FO membrane could effectively
remove the organic matter existing in the STW. The
amount of organic matter transported to the diluted concen-
trate was evaluated using both UV
and TOC. The UV
of the draw solution increased slightly from 0.195 to 0.211,
corresponding to an increase in TOC from 0.44 to 0.65 mg/L
in 8 h of operation (Figure 5(a)). This indicated that the
membrane used in this study provided a good organic
matter rejection performance. The amount of organic
pollutants entering the inuent of the RO unit from the
STW was few.
Besides UV
and TOC, a 3D excitationemission
matrix uorescence spectrum was used to investigate the
type of organic matter that passed through the FO membrane.
The organic matter contained in the STW (feed solution) was
rich in humic acid-like substances (Figure 5(b)), associated
with the peak of Ex/Em ¼420440/235245 nm in the uor-
escence spectrum (Henderson et al. ). Compared with
the STW, the concentrate (draw solution) was low in organic
pollutants, and no peak associated with organic matter was
observed (Figure 5(c)). After 8 h of operation, only one peak
(Ex/Em ¼375/350 nm) contributed by protein-like
Figure 5 |Variations of UV
and TOC in the draw solution (concentrate) with operation time (a), and the 3D excitationemission matrix of the feed solution (STW) (b) and draw solution
before (c) and after (d) 8 h of operation.
539 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
substances (Reynolds ;Liu et al. ) relating to the
activity of bacteria was observed. This further proved that
the FO membrane used in this study had a high capacity to
remove organic matter (Figure 5(d)).
Besides the protein-like substances, part of the disinfec-
tion byproducts (DBPs) corresponding to the killing of
bacteria might also permeate to the draw solution. Maintain-
ing water temperature at approximately 23 WC, the system
was run for 8 h at pH 6.5, 7.5, and 8.5, respectively. The con-
centration of THMs in the STW was 105 μg/L (Figure 6(a)),
which was much higher than that of HAAs (15.5 μg/L).
However, the total amounts of THMs and HAAs permeating
through the FO membrane was similar under different pH
conditions. The concentrations of both THMs and HAAs
that permeated into the draw solution were in the range of
5.28.4 μg/L, indicating that the FO membrane was effective
in DBP removal.
The removal rates for THMs were above 95%, higher
than that of HAAs (5060%) under the selected pH con-
ditions (Figure 6(a)). The low rejection rate of HAAs was
probably related to its low initial concentration in the STW
used in our study (Xie ). These rejections are comparable
to the values reported for NF membranes (56100%) and RO
membranes (8694% for HAAs) (Agus & Sedlak ). We
speculate that the mechanisms underlying the removal of
THMs and HAAs might be size exclusion and charge repul-
sion, similar to the NF/RO membranes (Bellona et al. ;
Kong et al. ). Unlike HAAs, all of the THMs were
highly volatile organic materials (Lee et al. ). As the
hydraulic retention time of the STW in the feed solution
tank increased, part of the THMs might enter the air under
the effect of volatilization. Further study showed that the con-
centration of THMs mainly existing in the forms of CHCl
and CHCl
decreased notably from 101 to 6.7 μg/L after 4
days of retention (without stirring) in the feed solution tank
(Figure 6(b)). Compared with THMs, the concentration of
HAAs, mainly existing in the forms of DCAA, TCAA, and
BCAA, was relatively stable (Figure 6(c)).
Feasibility analysis of FO in brackish water desalination
system upgrading
Compared with RO, the water ux of FO was relatively
small, especially for the draw solution with low salt content.
To guarantee the average water ux, a two-stage FO in
which the TDS in the concentrate was diluted from 12.5
to 1.5 g/L in two series-connection draw solution tanks is
Figure 6 |Contents of DBPs permeating from the feed solution (STW) to the draw sol-
ution (concentrate) after running for 8 h (a), and the effects of hydraulic
retention time on the residual concentrations of THMs (b) and HAAs (c) in the
feed solution.
540 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
suggested for the upgrading of the existing RO system in
James City County, as shown in Figure 1. STW was used
as a feed solution. By controlling the retention time of the
concentrate in the draw solution tank, the TDS in the rst-
stage FO efuent was maintained at 6.0 g/L, corresponding
to an increase in the volume from 3.8×10
to 7.6 ×10
Sixty per cent of the rst-stage FO efuent was blended with
9.2 ×10
/d of the STW directly before it was discharged
to the James River. In the second-stage FO, 40% of the rst-
stage FO efuent was further diluted four times. The efu-
ent, with 1.5 g/L of TDS, was reused as the inuent of the
RO unit. The consumption of the groundwater could be
reduced from 22.7 ×10
to 10.6 ×10
Considering the concentration of organic matter perme-
ated into the diluted concentrate, part of which was reused
as the inuent for the RO, was limited based on accumulat-
ive values in 8 h, the effects of organic matter in the STW on
the quality of the treated drinking water could be ignored.
Before upgrading, the pump pressure needed in the RO
unit was approximately 0.6 MPa. Based on the water quality
shown in Table 1, NaCl and NaHCO
were assumed to be
contributing to the osmotic pressure generated by the brack-
ish water. Calculation results showed that after upgrading
the osmotic pressure existing between the two sides of the
RO membrane would decrease from 0.18 to 0.13 MPa so
as the salt content in the inuent decreased from 2.3 to
Figure 7 |Variation in water ux in an 89-hour operation (a), and the morphological characteristics of the FO membrane before (b) and after (c) running for 89 h.
541 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
1.78 g/L. Maintaining a water purication capacity of 22.7 ×
/d, the reduced pump pressure was determined to be
0.05 MPa, so approximately 8.3% of the input energy of the
pump station could be saved.
Besides, the fouling process of the FO membrane was
slow. As shown in Figure 7(a), as the operation time
increase, the water ux of the FO membrane decreased
from 2.3 to approximately 1.0 L/(m
·h). This decrease was
mainly caused by the dilution of the draw solution. Repla-
cing the diluted concentrate (draw solution) with the
concentrate taken from the pilot, the water ux of the FO
membrane returned to 2.3 L/(m
·h) even after running for
88 h. The above phenomenon indicated that the fouling pro-
cess of the FO membrane was slow or membrane fouling
showed little effect on the water ux. From the morphologi-
cal characteristics of the FO membrane (Figure 7(b) and
7(c)), the development of an obvious fouling layer, which
mainly contributed to the water ux decline (Lee et al.
), was not observed on the surface of the active side.
The low fouling rate of the FO membrane might be related
to the low osmotic pressure of the feed solution, which lim-
ited the transport of foulants to the surface of the membrane
(Tang et al. ).
Over the last decades, strict regulations have been estab-
lished to protect water bodies by limiting the amount of
TDS that are discharged into waterways. In this study,
the implementation of FO was considered to treat and
reuse the concentrate from the RO process. Solution pH
showed a slight effect on the ux of both pure water and
DBPs. With the decrease in water temperature, especially
in winter, the water ux of the FO membrane decreased
notably. Although part of the protein-like substances per-
meated into the draw solution, the FO membrane used in
this study showed a good performance in the rejection of
organic pollutants. More than 98% of TOC, 95% of
THMs, and 5060% of HAAs were removed from the
feed solution. Considering that these removals were
based on accumulative values in 8 h, the detrimental
effect of using STW as source water on the quality of the
produced drinking water could be ignored. Furthermore,
during an 89-hour operation, there was no observed ux
decline due to membrane fouling. By controlling the efu-
ent concentration of TDS in the second stage of FO at
1.5 g/L, the consumption of groundwater would decrease
to 10.6 ×10
/d. Approximately 8.3% of the pump
energy input was saved. Meanwhile, the environmental
impact caused by the discharge of concentrate into the
James River could be minimized.
This research was supported by the National Natural
Science Foundation of China (No. 21007050), the Science
and Technology Nova Program of Shaanxi (No.
2014KJXX-66), and the open funds of Zhejiang Provincial
Key Laboratory of Water Science and Technology.
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543 W. D. Wang et al. |Application of FO in reusing the brackish concentrate produced in RO plants Journal of Water Reuse and Desalination |06.4 |2016
... Generally, this potential of water reflect an increased risk of drought in some parts of the country, even in normal conditions, especially in the south and southeast, has created vast problems of water supply requirements. According to available statistics, indiscriminate withdrawal of groundwater sources leading to a further decline in groundwater levels and some plains, mostly in central and eastern of Iran, are facing serious saltwater [5,6]. The problem evaporative processes (MSF and MED), in addition to high energy consumption, is high deposition and corrosion which is controlled only by a skilled operator [7]. ...
Full-text available
Carbon aerogel its fabrication and characterization and its uses in this process were studied for desalinating of saline and brackish water. The carbon aerogel manufacturing process involves the polymerization and pyrolysis of the mixture of resorcinol and formaldehyde. Carbon aerogels were analyzed using BET, BJH, and T-plot after construction. The effect of various parameters (including the influent salt concentration, the intensity of electric current flow, the distance between the electrodes and pH) on salt adsorption were studied. Analysis of BET/BJH shown that the surface of aerogel was 677.8 m2/g. much of porosity in the samples of carbon aerogel were between 1-2 nm, namely micro-pour and a similar level 0f 456 m2/gr is dedicated to micro-pour, with a correlation coefficient (r) equal to 94.5. According to the results, it seems that carbon aerogel electrodes have a good structure in desalination of brackish and saline water.
Coal chemical industry (CCI) generally utilizes reverse osmosis (RO) for water reclamation, which generates a highly concentrated stream containing refractory organic substances and high-concentration total dissolved solids (TDS). To address this issue, the present work focuses on volume reduction of RO concentrate (ROC) produced from CCI by forward osmosis (FO). We investigated the effects of membrane orientation and draw solution (DS) concentration on FO performance. Foulant removal was tested by using chemical cleaning, physical cleaning and osmotic backwash (OB). AL-FS (active layer facing feed solution) mode outcompeted AL-DS (active layer facing draw solution) mode, achieving a flux of 26.4 LMH, 92.5% water reclamation and energy consumption of 0.050 kWh·m−3 with 4 M NaCl as DS. The FO process was able to reject >98% SO42−, Mg2+and Ca2+, 92–98% Si and 33–55% total organic carbon (TOC). Ten-cycle (10 × 20 h) accelerated fouling test demonstrated approximately 30% flux decline in association with Si-containing foulants which could be removed almost completely through OB with 97.1% flux recovery. This study provides a proof-of-concept demonstration of FO for volume reduction and water reclamation of ROC produced from CCI, making the treatment of ROC more efficient and more energy effective.
Full-text available
Forward osmosis (FO) is an emerging technology for low energy desalination. Amongst the many other factors, temperature of the draw solution (DS) and feed solution (FS) plays an important role in influencing the performance of the FO process. In this study, the influence of the temperature and the temperature difference on the performance of FO process has been studied in terms of water and solute fluxes. Temperature difference was maintained by elevating only one of the solutions (either DS or FS). The results indicate that, water flux on average increases by up to 1.2% for every degree rise in temperature from 25 °C to 35 °C while this rise is 2.3% from 25 °C to 45 °C. Providing a temperature difference by elevating only the DS also enhanced the water flux significantly, although it was lower than FO process operated at isothermal conditions. However, elevating only the temperature of FS did not significantly improve the water flux although it was higher than the FO process operated at 25 °C. This has significant implications in FO process because the total mass of the DS requiring heat energy is significantly less than the total FS used. The influences of temperature in the FO process such as through changes in the thermodynamic properties of the solutions and the various concentration polarisation effects are also explained in details.
Forward osmosis (FO) represents a new membrane-based technology to desalinate seawater driven by osmotic pressure of solution spontaneously. Temperature is closely correlated to the solution physicochemical properties, and thus has a remarkable impact to transmembrane water flux of FO process. The primary goal of this study is to evaluate the dependence of FO performance on temperature. The water flux was predicted using steady-state models that incorporate temperature effect on osmotic pressure, hydrodynamics of boundary layer, transmembrane mass and heat flux processes. The experiments were performed in a FO module with sodium chloride serving as feed and draw solution. The results demonstrated a substantial positive correlation between water flux and bulk solution temperature in the range of 20–40 °C. As indicated by both theoretical prediction and experimental validation, the improvement of mass diffusion kinetics, rather than solution osmotic pressure, dominated the FO performance in terms of water transmembrane flux when temperature was increased. This should be preliminarily a result of decrease in solution viscosity, which was consistent with the decrease in polarization resistances of boundary layer, supporting layer as well as active layer. With the increased flow rate, water flux was increased at all temperatures due to the improvement of mass transfer at boundary layer. The magnitude of heat flux was observed to positively relate to the flow rate and transmembrane temperature difference. Toward more efficient and energy-effective operation, this study not only provides an insight into the effect of temperature on transmembrane water flux, but also suggests a strategic importance of regulating temperature in FO process.
This paper presents a review of recent advances in reverse osmosis technology as related to the major issues of concern in this rapidly growing desalination method. These issues include membrane fouling studies and control techniques, membrane characterization methods as well as applications to different water types and constituents present in the feed water. A summary of the major advances in RO performance and mechanism modeling is also presented and available transport models are introduced. Moreover, the two important issues of RO brine discharge and energy costs and recovery methods are discussed. Finally, future research trends and needs relevant to RO are highlighted.
Studies were conducted to examine the effect of solution chemistry, defined here as pH and ionic strength, on the permeability of negatively charged polymeric nanofiltration membranes. Water permeation through the membrane was demonstrated to decrease at conditions of low pH and high ionic strength in the absence of organic macromolecules. The reduction in membrane permeability was attributed to a compaction of the membrane matrix resulting from charge neutralization at the membrane surface and electric double layer compression. An uncharged model organic macromolecule (polyethylene glycol) was used to quantify the effects of solution chemistry on membrane compaction and solute rejection capabilities of the charged membrane. Studies of membrane permeability and rejection were then repeated with solutions containing natural organic matter (NOM), enabling concurrent evaluation of the effects of electric double layer compression as well as changes in both membrane structure and the apparent macromolecular size of charged NOM macromolecules.
Osmotically driven membrane processes use chemical potential difference between two aqueous solutions as a driving force for separation and concentration of feed streams or for recovery of energy. Forward osmosis was extensively studied in recent years and demonstrated that it can be successfully utilized in many applications of water treatment. In a new approach, the salinity difference between seawater and impaired water, such as reclaimed water, is used as a driving force for osmotic dilution of seawater before desalination. The osmotic dilution approach may provide at least four major benefits related to water and energy resources. These include lower energy desalination of seawater, multi-barrier protection of drinking water, reduction in reverse osmosis membrane fouling due to impurities in impaired water, and beneficial reuse of impaired water. The osmotic dilution process was investigated on both bench- and pilot-scales. Both secondary and tertiary treated effluents from a domestic wastewater treatment plant and impaired surface water were used as feed water to the process. Flux decline was minimal and under specific flow condition it was observed that membrane fouling was negligible. Additionally, the multiple membrane barriers provided high rejection of both organic and inorganic solutes and of trace organic chemicals.