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The technologies that are used mainly in the seawater desalination industry are reviewed and evaluated in this article. The utilization principles, applications, and problems of these processes are summarized and discussed. The desalination methods are compared with each other for performance ratio (PR), gain output ratio (GOR), unit energy consumption (kWh/m3), or unit operating cost ($/m3) and afterward the preferred method is identified. © 2014
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Desalination and Water Treatment
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A review on energy consumption of desalination
Younes Ghalavanda, Mohammad Sadegh Hatamipoura & Amir Rahimia
a Chemical Engineering Department, University of Isfahan, Isfahan, Iran, Tel./Fax: 0098 311
Published online: 04 Mar 2014.
To cite this article: Younes Ghalavand, Mohammad Sadegh Hatamipour & Amir Rahimi (2014): A review on energy
consumption of desalination processes, Desalination and Water Treatment, DOI: 10.1080/19443994.2014.892837
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A review on energy consumption of desalination processes
Younes Ghalavand, Mohammad Sadegh Hatamipour*, Amir Rahimi
Chemical Engineering Department, University of Isfahan, Isfahan, Iran, Tel./Fax: 0098 311 7934031; email:
Received 7 July 2013; Accepted 24 January 2014
The technologies that are used mainly in the seawater desalination industry are reviewed
and evaluated in this article. The utilization principles, applications, and problems of these
processes are summarized and discussed. The desalination methods are compared with
each other for performance ratio (PR), gain output ratio (GOR), unit energy consumption
), or unit operating cost ($/m
) and afterward the preferred method is identified.
Keywords: Desalination processes; Gain output ratio; Performance ratio; Energy consumption
1. Introduction
The increase in world population, accompaniment
with increase in industrial and agricultural activities
in the recent decade, has led to excessive exploitation
of available water resources and freshwater resources
pollution. Therefore, adopting various methods for
converting polluted water or salty water into potable
water is necessary.
In general, water is divided into five main
Freshwater (0.5 g/L and less salinity)
Brackish water (0.5–30 g/L salinity)
Saline water (30–50 g/L salinity)
Sea water (35 g/L salinity)
Brine water (50 g/L and more salinity)
One of the most popular methods to produce pota-
ble water is “Desalination”, in which the salty water is
converted into potable water by the removal of salt
content. All desalination methods can be classified
into four categories:
(1) Thermal
(2) Crystallization
(3) Membrane
(4) Other
Fig. 1illustrates an overview on desalination
In this article, the above methods are described
with respect to their subsets, features, applications,
and problems.
1.1. Thermal desalination methods
In this category, the required energy for desalina-
tion is supplied by a heating source such as natural
gas, steam, electricity, renewable energy, etc. In these
systems, gain output ratio (GOR) or performance ratio
(PR) is defined as efficiency. GOR is defined as: the
ratio of the mass of water produced through a
desalination process over a fixed quantity of energy
consumed. In many practical cases, steam may not be
the medium of heat transfer, so the PR is most
commonly defined as the mass, in pounds, of water
produced by desalination per 1,000 BTU of heat
*Corresponding author.
1944-3994/1944-3986 Ó2014 Balaban Desalination Publications. All rights reserved.
Desalination and Water Treatment (2014) 1–16
doi: 10.1080/19443994.2014.892837
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provided to the process. The SI equivalent of this
formulation is the number of kg of water produced
per 2,326 kJ of heat [1].
1.2. Simple boiling
Boiling is the rapid vaporization of liquid occur-
ring when it is heated to its boiling point (100˚C in
atmospheric pressure), the temperature at which the
vapor pressure of the liquid is equal to the pressure
exerted on the liquid by the surrounding atmosphere
(below the boiling point liquid evaporates from its
surface). Boiling process can be used as a method of
water disinfection and desalination but is only advo-
cated as an emergency water treatment method
because this method consumes a high amount of
energy (since there is no internal energy recovery,
GOR for this process is always less than one). Today,
this method is mostly applied in producing steam
with the least application in desalination. Fig. 2
illustrates a scheme for this method.
1.3. Multi-stage flash
Multi-stage flash (MSF) is the main process for
the desalination industry with a market share close
to 60% of the total world production capacity until
the late twentieth century. MSF still has a sizeable
market share in the beginning of twenty-first
century [2]. This method contains 90% of the
thermal desalination methods [3]. There are many
new articles on this method in the field of
Fig. 1. Desalination methods tree.
Fig. 2. A simple boiling evaporator.
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modeling, simulation, energy analysis, optimization,
thermodynamic, etc [410]. Fig. 3shows a schematic
diagram of the MSF system.
This system consist of several flashing stages
(increasing the flashing stages can increase internal
energy recovery), a brine heater, pumping units, vent-
ing system, and a cooling water control loop. Incoming
sea water passes through the heat exchanger where its
temperature increases. Next, it is passed to the brine
heater where the steam from an external source sup-
plies the energy for the process and heats the sea water
in the heat exchanger to the maximum process temper-
ature (80–90˚C). Then it is released into the first vacuum
chamber, the water vapor condenses into freshwater
product by the cooling water control loop and this
operation is repeated for other stages. These are the
special and distinguishing features of the MSF process.
A small number of connection tubes are installed in the
MSF process construction which restricts leakage prob-
lems and simplifies the maintenance work. Evaporation
and condensation could be performed in several stages,
hence an increase in efficiency. Despite the develop-
ment and progress in the MSF process, the performance
ratio has shown a value of 8 [2], while in the latest stud-
ies, the reported value is 14 [12].
Some important features of MSF desalination
method are as follows:
Suitable for the region with cold salty water
such as Middle East
Ability for combination with renewable energy
sources such as solar
Simple design and construction
Process reliability
Extensive experience for operation and mainte-
Suitable for normal and high desalination capaci-
GOR: 8–14
1.4. Multiple effect distillation
This method is similar to MSF. In multi-effect dis-
tillation plant, the column pressures are adjusted such
that the cooling (energy removal) in one column func-
tions as the heating source (energy input) in another
column. To accomplish this, each column must be
operated at a different pressure. In the conventional
multiple effect distillation (MED) plant, the sea water
enters the first effect and is raised to the boiling point.
Both the water feed and heating vapor to the evapora-
tors flow in the same direction. The remaining water
is pumped to the second effect, where it is once more
applied to a tube bundle. This process continues for
several effects, about 4–21 effects in a typical big plant
[13,14] (an increase in flashing stages can increase the
internal energy recovery). In the new designed plants,
which are shown in Fig. 4, the sea water (feed) is
divided into several parts before entering the flash
drums. The produced vapor from the salty water is
Fig. 3. A scheme for MSF desalination [11].
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sent to the next stage for heating the next stage feed
where it is condensed through the next stage and
freshwater is obtained. Finally, the residue water is
discharged from the system and returned to the sea.
Some important features about MED desalination
method are mentioned in previous works [1422]as
Suitable for the region with hot salty water
Combination with renewable energy
Simple design and construction
Process reliability
Extensive experience for operation and mainte-
Suitable for normal and high desalination capaci-
GOR: 9–18
1.5. Vapor compression
In the vapor compression (VC) process, the heat
for evaporating the sea water is generated through VC
[23]. Two methods are used to condense the water
vapor and to produce the amount of sufficient heat to
evaporate the incoming sea water: a mechanical
compressor and a steam jet. In this method, sea water
is evaporated and the vapor is passed through a
compressor. Here, the vapor is compressed, which
leads to an increase in vapor dew point (in this
condition the compressed vapor dew point is higher
than sea water boiling point), so vapor can be
condensed by sea water indirect contact (it can save a
lot of energy) and cause to evaporate sea water. In
order to reduce the energy consumption of the
compressor, compression ratio should be selected
close to one. In this process, the sea water temperature
is held at 100˚C.
VC units are built in a variety of configurations in
order to promote sea water evaporation. The compres-
sor creates a vacuum in the evaporator and then com-
presses the vapor taken from the evaporator and
condenses it in a tube bundle. A simple scheme for
VC method is illustrated in Fig. 5.
The power consumption of this method is high
(because of compressor usage) but it becomes econom-
ically feasible when energized by solar cell [24].
Some features about this method are as follows:
High energy consumption
Low occupied space in comparison with MSF
and MED
Fig. 4. A scheme for MED desalination [11].
Fig. 5. A scheme for VC desalination.
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Suitable for low desalination capacity
Less popular in comparison with other thermal
GOR: 12–14
1.6. Membrane distillation
Here, the hot saline solution flows in direct contact
with hydrophobic micro-porous membranes, and the
cold solution flows on the cold side of the membrane.
The temperature difference between the hot and cold
faces of the membrane causes the vapor pressure of
the concentrated solution to be higher than that of the
cold fluid; as a result, water starts to evaporate at the
hot side of the membrane, penetrates through the
membrane pores, and then is transferred and con-
densed on the cold fluid or condensed in a film on a
cooling plate [25]. A scheme of membrane distillation
(MD) desalination is illustrated in Fig. 6.
MD systems can be classified into four configura-
tions, according to the nature of the cold side of the
(1) The direct contact membrane distillation,
where the membrane is only in direct contact
only with liquid phases [2729]. In this config-
uration, a thin membrane is located between
hot brackish water and cold freshwater; in the
hot side, water is evaporated and passed
through the membrane and finally condensed
in the cold side of the membrane.
(2) The vacuum membrane distillation (VMD),
where the vapor phase is evacuated from the
liquid through the membrane and condensed
in a separate device, if needed [30,31]. In this
configuration, the membrane is installed
between the hot brackish water and a vacuum
chamber in order to increase the chemical
potential between two sides of the membrane.
After water vaporization, water is evacuated
to another membrane side and moved to con-
densation section.
(3) The air gap membrane distillation, where an
air gap is interposed between the membrane
and the condensation surface [32]. In this con-
figuration, vapor is penetrated through the
membrane and an air gap; finally, it is cooled
by a cold plate and freshwater is produced.
(4) The sweeping gas membrane distillation,
where a stripping gas is used for carrying of
the produced vapor, instead of vacuum as in
VMD [3337]. When it is needed to condense
vapor in another place, this configuration can
be useful. In this condition, after the water is
vaporized and passed through the membrane,
vapor is carried by sweeping gas (air or nitro-
gen). Through this method, the freshwater is
produced in condensation place.
Some features of the MD method are as follows:
No pressure is necessary to operate the system
It could be combined with renewable energy
Operable at low and high temperatures (45–
Suitable for low and normal desalination
1.7. Humidification de-humidification
The humidification de-humidification (HDH)
process is based on the fact that air can carry big
quantities of water vapor. The vapor-carrying capa-
bility of air increases with temperature: 1 kg of dry
air can carry 0.5 kg of vapor and about 670 kcal
when its temperature rises from 30 to 80˚C. When
the salt water is exposed to the flowing air, a
Fig. 6. A scheme for membrane distillation [26].
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certain quantity of vapor is extracted by air, which
provokes cooling. Distilled water, on the other hand,
may be recovered by bringing the humid air in con-
tact with a cold surface, which causes the condensa-
tion of part of the vapor in the air [38]. Generally,
the condensation occurs in a heat exchanger where
the salt water is preheated by the latent heat of con-
densation. An external heat source is therefore nec-
essary to compensate heat loss. A scheme for HDH
system is illustrated in Fig. 7.
The HDH technique is especially suited for sea
water desalination in arid region when the demand
for water is decentralized [40,41]. Solar desalination
based on the HDH cycle presents the best method of
solar desalination due to overall high energy efficiency
[42]. The advantages of this technique are:
Flexibility in capacity (low, normal and high)
Flexibility in arrangement
Moderate insulation
Moderate operating cost
Using low-grade thermal energy such as solar
and geothermal
High performance ratio (GOR up to 16.7) [43]
Low corrosion of the facilities
High ability for combination with other methods
Ability for operation in one or several stages
The HDH systems are classified under three main
broad categories [4449] (Fig. 8). Operating conditions
relate to the category of the system while the operat-
ing temperature is usually between 50 and 90˚C.
Water close loop or air close loop can increase the
internal energy recovery and decrease the total energy
1.8. Dew-vaporation
This method is similar to HDH process but in this
process, the evaporator and condenser are the same.
Here, a flat plate gets energy from produced vapor
and transfers it to the sea water in order to vaporize
part of the water. An increase in the plate condensa-
tion can increase the internal energy recovery. The
mechanism in this process is same as that of the HDH
process [50]. A scheme for this process is illustrated in
Fig. 9.
Some of the important features of this process are:
Usable for low desalination capacity
Moderate insulation
Moderate operating cost
Using low-grade thermal energy such as solar
and geothermal
Less mass transfer surface in comparison with
Less space occupation in comparison with HDH
GOR: up to 11 (in multi-stage systems) [52]
The thermal desalination methods are summarized
in Table 1.
Fig. 7. A HDH desalination apparatus [39].
Fig. 8. HDH classification.
Fig. 9. A scheme for Dew-vaporation desalination [51].
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2. Crystallization desalination methods
When water molecules become crystallized, the ice
crystals formed are salt free. During this process,
dissolved salt is excluded. This concept is applied in
desalination process to remove salt from water and
make it freshwater. There are two main desalination
processes based on crystallization: freezing and
2.1. Freezing
During the process of freezing, the dissolved salt is
excluded during the formation of ice crystals. Under
controlled conditions, the sea water can be desalinated
by freezing to form the ice crystals. Before the entire
mass of water is frozen, the mixture is washed and
rinsed to remove the salts in the remaining water or
adhering to the ice. The ice is then melted down to
produce freshwater. Therefore, the freezing process con-
sists of cooling the sea water feed, partial crystallization
of ice, separation of ice from sea water, melting of ice,
refrigeration, and heat rejection [14]. There are two main
processes for freezing desalination: vacuum freezing
desalination (VFD) and secondary refrigerant fluid
2.1.1. Vacuum freezing desalination
In this method, cooled saline water is sprayed into
a vacuum chamber (4 mbara); some of the water
flashes off as vapor removing more heat from water
and causing ice to form. The ice floats on the brine
and is washed with freshwater, melted and the
freshwater which is less dense than the brine flows
out of the washer-melter (Fig. 10). Theoretically, freez-
ing desalination has a lower energy requirement than
other thermal processes but a few small freezing
plants were built in the last 40 years and this process
is not commercially developed [53].
2.1.2. Secondary refrigerant fluid
In this type of freezing desalination, a liquid
hydrocarbon refrigerant such as propane or butane
is vaporized in direct contact with the saline water
(refrigerant temperature is related to the type of
Table 1
Thermal desalination summary
Method GOR Capacity Operating temperature
Boiling < 1 Not applicable About 100˚C
MSF 8–14 Normal & high 40–90˚C
MED 9–18 Normal & high 40–90˚C
VC 12–14 Low About 100˚C
MD Low & normal 45–90˚C
HDH Up to 16.7 Low & normal 50–90˚C
Dew-vaporation Up to 11 Low 50–90˚C
Fig. 10. A scheme for VFD desalination.
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refrigerant); thus, slurry of ice is produced in brine.
The vaporized refrigerant is compressed and after
cooling is recycled to the freezer chamber. The
slurry of ice is taken off, washed, and transferred to
the melter where freshwater is produced. The
advantage of SRF method is its low susceptibility to
scaling and corrosion. A scheme for this method is
shown in Fig. 11.
Some important features of the freezing desalina-
tion process are mentioned as follows:
Lower theoretical energy consumption
Minimal potential corrosion
Little scaling or precipitation
Hardship for producing vacuum (for VFD)
Handling the ice and water mixtures which are
mechanically complicated to move and process
2.2. Hydration
In this process, the saline water is mixed with a
hydrocarbon which forms hydrates or clathrates. In
a hydrate, a hydrocarbon molecule is enclosed in a
molecular cage of water molecules forming a solid
ice-like phase as shown in Fig. 12. The cage or
hydrate forms ice-like crystals which contain none
of the salts present in the sea water in which the
hydrate forms; in the next stage, the hydrocarbon
shall be removed from water and freshwater is
produced [54].
This technology is still under development but
when applicable at larger scale, it could be a cheap
alternative to the traditional thermal and membrane
desalination processes. A scheme for hydration
desalination process which is proposed by Javanmardi
and Moshfeghian is shown in Fig. 13. They showed
that the investment and operating cost for this process
are more than other conventional methods such as
MSF and RO [55].
There are some methods for water deionization in
crystallization category such as fluidized bed crystalli-
zation [56]; but these methods are widely used for
removing of water hardness not for salt (specially Na
and Cl
) removal.
3. Membrane desalination methods
In this category, the main element for salt
separation from water is membrane. There are four
Fig. 11. SRF desalination.
Fig. 12. A hydrate crystal [54].
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methods for membrane desalination: RO, FO, ED, and
microbial cell.
3.1. Reverse osmosis
Reverse osmosis (RO) is the main technology
applied in membrane desalination. The RO process is
based on separation rather than distillation, although
MD can be performed. This method contains 80% of
membrane desalination methods [3].
In this process, the osmotic pressure is overcome
by applying an external pressure higher than the
osmotic pressure on the sea water; thus, water flows
in the reverse direction to the natural flow across
the membrane, leaving the dissolved salts behind
the membrane with an increase in salt concentration.
No heating or phase separation change is necessary.
The major part of energy required for desalting is
for pressurizing the sea water feed. In this process,
a great amount of energy is consumed for pumping
(because of high pressure gradient). The typical
operation cost in a RO process is illustrated in
Fig. 14.
A typical large sea water RO plant consists of four
major components: feed water pretreatment, high
pressure pumping, membrane separation, and
permeate post-treatment [58]. Major design consider-
ations for sea water RO plants are the flux, conversion
Fig. 13. A scheme for hydration desalination process [55].
Fig. 14. Operation cost in a RO desalination process [57].
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or recovery ratio, permeate salinity, membrane life,
power consumption, and feed water temperature.
Some of the RO process features are [5963]:
Recovery rate: up to 60%
2–5 kWh/m
power consumption
Need to high pretreatment area
High fixed capital investment (in Middle East)
May fouling or concentration polarization
Using high feed pressure for separation
Applicable for low salt concentration
High salt rejection
3.2. Forward osmosis
Forward osmosis (FO) is a membrane-based sepa-
ration process, like RO, which relies on the semi-per-
meable character of a membrane in salt removal.
However, unlike RO, the driving force here for separa-
tion is osmotic pressure, not hydraulic pressure. By
using a concentrated solution of high osmotic pressure
called the draw solution, water can be induced to flow
from saline water across the membrane, rejecting the
salt. The (now diluted) draw solution must be re-con-
centrated, yielding potable water and recycling the
draw solute [64]. The general process diagram is illus-
trated in Fig. 15.
Since the recovery or utility of the draw solute is
critical in successful implementation of the FO process,
depending on the intended use of the desalinated
water, various draw solutes may be used. Some current
versions of FO use an edible solute, such as concen-
trated glucose or ammonium salts. These salts (a mix-
ture of ammonium bicarbonate, ammonium carbonate,
and ammonium carbamate) are formed when ammonia
and carbon dioxide gasses are mixed in an aqueous
solution. The salt is rejected by the semi-permeable
membrane used in FO and is highly soluble, leading to
the reliable generation of high osmotic pressures.
Once the concentrated draw solution is applied in
separating water from the saline feed source, the sub-
sequent diluted draw solution may be treated ther-
mally to remove its ammonium salt solutes, producing
freshwater as the primary product of the FO process.
This thermal separation of draw solutes is based on
the useful characteristic of these salts to decompose
into ammonia and carbon dioxide gasses when the
solution is heated. The temperature at which this
occurs depends on the pressure of the solution [65].
FO has two main advantages in comparison with
RO: more desalination flux [64,66] and less pumping
energy consumption [67]. These advantages are pre-
sented in Figs. 16 and 17.
Some important features of FO desalination
process are:
Usable for low and moderate salt content
High desalination flux in comparison with RO
Fig. 15. A scheme for FO desalination process [64].
Fig. 16. Flux comparison between FO and RO [66].
Fig. 17. Energy consumption comparison between FO and
other process [67].
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Low energy consumption in comparison with
RO (less than 1 kWh/m
Using osmosis pressure, not hydraulic pressure
for separation
Higher fixed capital investment in comparison
with RO
May fouling or concentration polarization (lesser
than RO)
3.3. Electro-dialysis
In an electro-dialysis (ED) system, the anionic and
cationic membranes are formed into a multi-cell
arrangement built based on the plate-and-frame
principle to form up to 100 cell pairs in a stack. The
cation and anion exchange membranes are arranged
in an alternating pattern between the anode and cath-
ode. Each set of anion and cation membranes forms a
cell pair as shown in Fig. 18. Salt solution is pumped
through the cells while an electrical potential is main-
tained across the electrodes. The positively charged
cations in the solution migrate toward the cathode
and the negatively charged anions migrate toward the
anode. Cations pass through the negatively charged
cation exchange membrane but are retained by the
positively charged anion exchange membrane.
Similarly, anions pass through the anion exchange
membrane but are retained by the cation exchange
membrane. The outcome of this process is that one cell
of the pair becomes depleted of ions while the next
cell becomes enriched in ions [68]. This process is
widely used to remove dissolved ions from water spe-
cially Na
and Cl
Brackish water desalination is the vastest applica-
tion of ED. The competitive technologies apply ion
exchange for very dilute saline solutions, below 500
ppm [69]. In the 500–2000 ppm range, ED is often a
low-cost process. One advantage of ED applied to
brackish water desalination is that a big portion, about
80–95%, of the brackish feed is recovered as product
water. However, these high recoveries mean that the
concentration of brine stream is 5–20 times more than
the feed [70].
3.4. Microbial cell
Current water desalination techniques are energy
intensive and some of them operate at high pressures.
One of the newest desalination methods which oper-
ate without energy or high pressure is microbial cell.
A microbial fuel cell is modified by placing two mem-
branes between the anode and cathode, creating a
middle chamber. An anion exchange membrane
is placed next to the anode, and a cation exchange
Fig. 18. A scheme for ED desalination method [68].
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membrane is positioned next to the cathode as shown
in Fig. 19. When electrical current is produced by bac-
teria on the anode, ionic species in the middle cham-
ber are transferred into the two electrode chambers,
desalinating the water in the middle chamber [7175].
Some important features of microbial cell process
are mentioned as follows:
Usable as one to several pair of membrane
No need for electrical energy
Producing electrical energy during the process
Applicable for low-capacity plants
Having 90% salt rejection
This technology is still under development.
It should be mentioned that usually all membrane
desalination methods operate at ambient temperature.
4. Other desalination methods
Some processes are developed to desalinate sea
water which have not reached the level of commercial
success that MSF, MED, and RO have and they are
not included in the previous three categories. There
are three important methods which are not put in the
previous three categories: Air Dehydration, Ion
Exchange, and Hybrid.
4.1. Air dehydration
This method is usually used in humid area; in this
process, the humid air enters into the system and the
air moisture is extracted from the air as desalinated
water. These processors are machines that extract
water molecules from the atmospheric air, ultimately
causing a phase change from vapor to liquid. Three
classes of machines are proposed which cool a surface
below the dew point of the ambient air, concentrate
water vapor through use of solid or liquid desiccants,
or induce and control convection in a tower structure.
Patented devices vary in scale and potable water out-
put from small units suitable for one person’s daily
needs to structures as big as multi-story office build-
ings in coastal region and humid region [76]. This
process is not commercialized yet and is only used for
small capacity plants with a high operating cost.
4.2. Ion exchange
The ion exchange technologies are often used for
water softening among other applications. The ion
exchange system can best be described as the inter-
change of ions between a solid phase and a liquid
phase that surrounds the solid. Chemical resins (solid
phase) are designed to exchange their ions with liquid
phase (feed water) ions, which purify the water. Res-
ins can be made of naturally occurring inorganic
materials (such as zeolites) or synthetic materials.
Modern ion exchange materials are prepared from
synthetic polymers customized for different applica-
tions. Ion exchange technologies applied to desalina-
tion are rather complex. In brief, saltwater (feed
water) is passed through the resin beads where salt
ions from the saltwater are replaced for other ions. No
heat is required for this process, it operates at ambient
temperature. The process removes Na
and Cl
from feed water, thus producing potable water. Ion
exchange can be applied in combination with RO pro-
cess such as blending water treated by ion exchange
with RO product potable water to increase water pro-
duction [77].
Ion exchange technology demonstrates significant
advantages in removing boron in a desalination appli-
cation. Due to its high selectivity, ion exchange resin
performance is not influenced by operating conditions
Fig. 19. A scheme for microbial cell desalination [72].
Fig. 20. Solvent extraction desalination schematic [80].
12 Y. Ghalavand et al. / Desalination and Water Treatment
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such as temperature, pH, or salinity. Its high water
yield makes it an ideal technology when retrofitting
an existing plant for boron removal, with minimum
capacity loss [78].
4.3. Solvent extraction
In this method, a saline solution (e.g. sea water) is
brought into contact with a directional solvent (edible
oil). The saline solution and solvent are heated before
or after contact to enhance the directional dissolution
of water into the solvent, thereby producing distinct
phases; a first phase containing the solvent and water
from the saline solution and a second phase contain-
ing a highly concentrated residue of the saline
solution. The first phase is extracted from the second.
Alternatively, the second phase can be extracted from
the first phase. After extraction, the first phase is
cooled to precipitate the water from the solvent and
the precipitated water is removed from the solvent.
The extracted water can be in the form of substantially
pure water (e.g. suitable for industrial or agricultural
use or even meeting drinking water standards of
purity, such as 99.95% purity) [79]. A scheme of sol-
vent extraction desalination method is illustrated in
Fig. 20.
This method can use low-quality heat, generated
from terrestrial heat sources, the ocean, the sun, or as
waste heat from other processes. These desalination
methods can also be easily applied and can offer sig-
nificant energy and economic savings in comparison
with present desalination methods.
4.4. Hybrid systems
Desalination plants require significant amounts of
energy in the form of heat and/or electricity. So,
Fig. 21. A typical capital cost for desalination plants [88].
Table 2
Economic Parameters for MSF, MED, and RO [2,1214,43,52,67,88,89]
Capacity (m
/d) UPC (US$/m
) GOR (kg/kg) UPE (kWh/m
) Reference
SWRO 10,000 0.95 5.1–7.45 [88]
50,000 0.70 [88]
275,000 0.50 [88]
500,000 0.45 [88]
BWRO 10,000 0.38 2–5 [88]
50,000 0.25 [88]
275,000 0.16 [88]
500,000 0.14 [88]
MSF 10,000 1.97 8–14 5–6 [2,12,67,88]
50,000 1.23 [2,12,67,88]
275,000 0.74 [2,12,67,88]
500,000 0.62 [2,12,67,88]
MED 10,000 1.17 9–18 3–4 [13,14,67,88]
50,000 0.89 [13,14,67,88]
275,000 0.67 [13,14,67,88]
500,000 0.60 [13,14,67,88]
FO – <1 [67]
HDH 16.7 – [43]
Solar HDH 0.67 [43]
Dew-vaporation – 11 [52]
Solar dew-vaporation 0.34 [43]
VC 12–14 11–14.56 [89]
ED 2.6–5.5 [89]
Y. Ghalavand et al. / Desalination and Water Treatment 13
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hybrid systems which combine the thermal and mem-
brane processes or other utilities are being studied as
promising options for improving the economics aspect
of the issue [81]. The hybridization of RO and MSF
plants is being investigated by many researchers [82].
The hybrid RO-MSF plants have potential advantages
of a low power demand, improved water quality, and
lower running and maintenance costs compared to
stand-alone RO or MSF plants.
In industrial scale, ED-RO hybrid processes are
used for high recovery of product water from brackish
water without compromising on water quality. In this
hybrid process, ED unit is operated in high TDS
region (low system resistance and thus high
efficiency), and RO system is operated in low TDS
region, to reduce salinity load on membrane [83]. In
another industrial application for producing deminer-
alized (DM) water, RO and ion exchange methods are
combined as a hybrid system. In this system, a high
proportion of hardness is removed by RO and other
ions are removed by ion exchange system to reach
DM water with TDS < 1 [84].
Also hybrid system can include dual-purpose
plants. In these plants, two or three systems are usu-
ally combined with each other to increase energy effi-
ciency of the system as a whole, for example
combination of MSF or RO desalination system with
nuclear plant to absorb heat loss and increase energy
efficiency [85]. Combination of a HDH system and an
air conditioning unit or a HDH system and a cooling
tower can increase water production rate and decrease
energy consumption for the combined system [86]. A
combination of Ro and power plant can increase fuel
efficiency up to 70% [87].
5. Conclusion
In this article, the technologies mainly used in
sea water desalination industry are presented
together with a review of technologies applicable in
sea water desalination systems erected in various
parts of the world. The most important parameter in
the design of each plant is the energy consumption
or operating cost. In desalination system, this
parameter is mentioned as PR, GOR, unit energy
consumption (kWh/m
), or unit operating cost
). All of these parameters are applied to obtain
the performance of a desalination system; for exam-
ple, GOR or PR is usually applied in thermal meth-
ods and unit energy consumption is applied in
membrane methods.
The typical capital cost and energy comparison
between the most applicable desalination methods
(MSF, MED, RO, etc.) are illustrated in Fig. 21 and
Table 2.
Here, it could be suggested that the FO desalina-
tion method [especially because of high flux and low
power consumption (according to Figs. 16 and 17)] is
the best choice in this category and could be
developed in future years.
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... The membrane is kept between the hot feed flow stream and a vacuum space, while vapor is selected in an external condenser, outside of the membrane module [5]. The vacuum on the permeate flow stream permits a higher partial pressure gradient, leading to an additional driving force for the process, and thus a higher permeate production rate compared to other membrane distillation (MD) configurations [6,7]. Another benefit of the use of VMD is the fact that a vacuum leads to negligible heat loss by conduction. ...
... The vapor is then driven to the heat pump's evaporator, which extracts the heat from the vapor that condensates (4i-5). The recovered freshwater is finally collected in a tank (5)(6). The heat pump is used to supply heat to the brine, but also to condensate the vapor as it exits the flash tank. ...
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Conference Paper
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Bubble column humidifiers (BCHs) are frequently used for the humidification of air in various water treatment applications. A potential but not yet profoundly investigated application of such devices is the treatment of oily wastewater. To evaluate this application, the accumulation of an oil-water emulsion using a BCH is experimentally analyzed. The amount of evaporating water vapor can be evaluated by measuring the humidity ratio of the outlet air. However, humidity measurements are difficult in close to saturated conditions, as the formation of liquid droplets on the sensor impacts the measurement accuracy. We use a heating section after the humidifier, such that no liquid droplets are formed on the sensor. This enables us a more accurate humidity measurement. Two batch measurement runs are conducted with (1) tap water and (2) an oil-water emulsion as the respective liquid phase. The humidity measurement in high humidity conditions is highly accurate with an error margin of below 3 % and can be used to predict the oil concentration of the remaining liquid during operation. The measured humidity ratio corresponds with the removed amount of water vapor for both tap water and the accumulation of an oil-water emulsion. Our measurements show that the residual water content in the oil-water emulsion is below 4 %.
... Despite the consumption of energy in pumping water alongside the membrane in RO process, the energy use in MSF and MED processes is for converting water to steam [81,82]. The amount of salt in feed water may significantly influence energy consumption in desalination process [83,84]. The presence of greater amount of salt in feed water eventuates in higher osmotic pressure, which means that more transmembrane pressure must be used. ...
Over the last decades, sustainable supplement of freshwater has been a global challenge for growing population all over the world. Abundance of brackish/seawater on the surface of the earth has motivated the scientists to apply novel desalination technologies to meet the increasing demand of water in various industrial/non-industrial applications. The main objective of this paper is to analytically evaluate the efficiency of membrane-based desalination techniques such as reverse osmosis, ultrafiltration, microfiltration and nanofiltration and discuss the advantages and disadvantages of each of them in water treatment. Moreover, a techno-economic comparison between commonly employed desalination technologies is aimed to present to assess the cost-effectiveness and true cost of conventional technologies. Discussion about the application of novel nanomaterials for decreasing the energy demand following with disparate approaches to control the fouling phenomenon is another important purpose of this review paper.
... Water is categorized into five principal classes-(a) freshwater (0.05 wt% and less salinity); (b) brackish water (0.05-3 wt% salinity); (c) saline water (3-5 wt% salinity); (d) seawater (3.5 wt% salinity), (e) brine water (5 wt% and more salinity). Freshwater paucity is on the rise in many countries of the world because of the rapid depletion of ground and surface water 1 . The apparent answer to the worldwide water shortfall is the desalination since 97.5% of water available on Earth's surface is salty. ...
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Freeze desalination (FD) has several benefits compared to vaporization-based and membrane-based desalination methods. The FD process needs approximately 1/7th of the latent heat required by the vaporization-based desalination processes. The involvement of sub-zero temperature in FD reduces the risk of corrosion and scaling. This paper reviews the advances in FD methods involving stand-alone and hybrid methods that operate with and without utilizing the energy released during the re-gasification of liquefied natural gas. Moreover, the paper discusses the future focus areas for research and development to make FD a commercially feasible technology. Potable water was produced from brackish water and seawater by FD wherein the nucleation was achieved by ice seeding, the mixing of rejected salt from ice into the liquid phase was controlled appropriately, growth of ice crystals was slow, and liquid subcooling was maintained at approximately 4 K. The post-treatment of obtained ice is needed to produce potable water if the process is instigated without ice seeding. The plant capacity of stand-alone progressive FD was higher than the stand-alone suspension FD of seawater. The integration of the falling-film, fractional thawing, and block FD method showed significantly improved plant capacity than the stand-alone suspension FD method. The energy consumption of stand-alone PFC and SFC-based desalination with latent heat recovery was reported close to the reverse osmosis (RO) method. The hybrid (integration of the suspension FD method with membrane distillation) FD method utilizing LNG cold energy consumed less energy than the conventional RO method.
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This is the 9th Heat Powered Cycles Conference. The first edition of the conference was held at Nottingham in 1997. This time the event was co-organized by the University of the Basque Country, (Bilbao, Spain), The University of Applied Sciences, Vorarlberg, (Austria), and GamaTech Thermal Solutions, (Brazil). The conference took place at the University of the Basque Country and hosted by the Department of Energy Engineering at the University of the Basque Country by Prof. Jesús María Blanco Ilzarbe. In addition to formal presentations of technical papers, including invited Keynote papers, the event includes poster sessions and two Special Sessions, being one related to Intelligent Thermal Energy Systems and The Energy in the Post-Covid Scenario, along with a full social program. The conference is concerned with scientific and technological innovations relating to the efficient and economic use of heat, derived from all its sources, for the production of cooling, heating, and mechanical power either independently or co-generatively. Subject areas of particular interest include; hybrid cycles, ORCs, Stirling cycle machines, thermo-acoustic engines and coolers, sorption cycle refrigerators and heat pumps, jet-pump (ejector) machines, temperature amplifiers (heat transformers), chemical heat pumps, new working fluids, mass and heat transfer phenomena, desalination of brackish water and seawater, compact heat exchanger research (including foams and other micro-channel research), thermo-economics, process optimisation and modelling, process, and cycle thermodynamics.
This is the 9th Heat Powered Cycles Conference. The first edition of the conference was held at Nottingham in 1997. This time the event was co-organized by the University of the Basque Country, (Bilbao, Spain), The University of Applied Sciences, Vorarlberg, (Austria), and GamaTech Thermal Solutions, (Brazil). The conference took place at the University of the Basque Country and hosted by the Department of Energy Engineering at the University of the Basque Country by Prof. Jesús María Blanco Ilzarbe. In addition to formal presentations of technical papers, including invited Keynote papers, the event includes poster sessions and two Special Sessions, being one related to Intelligent Thermal Energy Systems and The Energy in the Post-Covid Scenario, along with a full social program. The conference is concerned with scientific and technological innovations relating to the efficient and economic use of heat, derived from all its sources, for the production of cooling, heating, and mechanical power either independently or co-generatively.
This project is the result of a volunteer program that took place in the Republic Guinea-Bissau (RGB) at the Paediatric Hospital. The Paediatric Hospital was working with the same technologic skills as Portugal in the 70’s years. There was no wired network between departments, no informatic system and all work was handmade. The physicians received incomplete clinical reports and, sometimes, with gross errors. There was no triage neither outpatient short list during the medical urgency period. The outpatients needed to wait for long time to get the analytical report and most time without meal or single bread. On the Clinical Analysis Laboratory, the biologic sample identification and the manual data report were lower changes to be credible and there was no final checklist. This paper describes the improvements made by the authors in the hospital logistical processes and in the development and implementation of an information system that was started in March 2018. These improvements were developed based on lean manufacturing principles, on methods and best practices for some referenced case studies fromAmerica, Saudi Arabia, Italy and England. As a result, the hospital reduced outpatient waiting time, improved Hospital, Laboratory and outpatient outcomes, increased confidence work for physicians and laboratory technics
Desalination processes are key to untangle the energy-water-environment nexus, to attain a green equitable world, and to address water scarcity on all continents. However, conventional desalination methods are energy-intensive, which stresses the balance of the nexus. Hydrate based desalination (HBD) is an innovative desalination process with the potential to desalinate both low- and high-salinity streams, including brackish water, seawater, and effluents. It recovers clean water in the form of ice-like structures, known as gas hydrates. Gas hydrates are crystalline nonstoichiometric solids composed of interlocking water molecules that physically encompass gaseous guest molecules. During the hydrate formation process, dissolved ions and salts are excluded from the hydrate crystals, resulting in high purity ice-like structures. This paper presents a comprehensive review on our fundamental understanding of gas hydrates and their applications in desalination. The effect of additives on the kinetics of HBD, which remains its Achilles' heel, is also studied. Finally, a comparative analysis between HBD and conventional desalination methods regarding their energy requirements indicates the strong potential of HBD as an energy efficient and selective desalination method, which could improve the overall sustainability of the energy-water-environment nexus.
Substantially pure water is produced via desalination using a directional solvent that directionally dissolves water but does not dissolve salt. The directional solvent is heated to dissolve water from the salt solution into the directional solvent. The remaining highly concentrated salt water is removed, and the solution of directional solvent and water is cooled to precipitate substantially pure water out of the solution.
Atmospheric water vapour processing (AWVP) technology is reviewed. These processors are machines which extract water molecules from the atmosphere, ultimately causing a phase change from vapour to liquid. Three classes of machines have been proposed. The machines either cool a surface below the dewpoint of the ambient air, concentrate water vapour through use of solid or liquid desiccants, or induce and control convection in a tower structure. Patented devices vary in scale and potable water output from small units suitable for one person's daily needs to structures as large as multi-story office buildings capable of supplying drinking water to an urban neighbourhood. Energy and mass cascades (flowcharts) are presented for the three types of water vapour processors. The flowcharts assist in classifying designs and discussing their strengths and limitations. Practicality and appropriateness of the various designs for contributing to water supplies are considered along with water cost estimates. Prototypes that have been tested successfully are highlighted. Absolute humidity (meteorological normals) ranges from 4.0 g of water vapour per cubic metre of surface air in the atmosphere (Las Vegas, Nevada, USA) to 21.2 g m-3 (Djibouti, Republic of Djibouti). Antofagasta, Chile has a normal absolute humidity of 10.9 g m-3. A 40% efficient machine in the vicinity of Antofagasta requires an airflow of 10 m3 s-1 to produce 3767 l of water per day. At a consumption of 50 l per person per day, 75 people could have basic water requirements for drinking, sanitation, bathing, and cooking met by a decentralized and simplified water supply infrastructure with attendant economic and societal benefits.
The Saline Water Conversion Corporation (SWCC), Saudi Arabia, began operating reverse osmosis (RO) desalination plants as early as in 1978 with small capacities and is now operating the largest seawater RO plants in the world. The rich experience gained by SWCC in more than 20 years of operation of these plants has been used to address some of the problems faced earlier and in improving the design of the new RO plants. One of the recent RO plants, which is due for commissioning, is the 91,000 m3/d plant at Al Jubail, on the coast of the Arabian Gulf. When placed in operation, it will be among the largest seawater RO desalination plants in the world. Considering the significance of a well designed pretreatment section for the successful operation of any RO plant, a pilot filtration plant was placed in operation during August 1993. The trials were carried out over a period of more than one year and the results were adapted in the plant design. This paper presents the salient design features of the plant and the improvements made.
World water supply is struggling to meet demand. Production of fresh water from the oceans could supply this demand almost indefinitely. As global energy consumption continues to increase, water and energy resources are getting closely intertwined, especially with regards to the water consumption and contamination in the unconventional oil and gas industry. Development of effective, affordable desalination and water treatment technologies is thus vital to meeting future demand, maintaining economic development, enabling continued growth of energy resources, and preventing regional and international conflict. We have developed a new low temperature, membrane-free desalination technology using directional solvents capable of extracting pure water from a contaminated solution without themselves dissolving in the recovered water. This method dissolves the water into a directional solvent by increasing its temperature, rejects salts and other contaminants, then recovers pure water by cooling back to ambient temperature, and re-uses the solvent. The directional solvents used here include soybean oil, hexanoic acid, decanoic acid, and octanoic acid with the last two observed to be the most effective. These fatty acids exhibit the required characteristics by having a hydrophilic carboxylic acid end which bonds to water molecules but the hydrophobic chain prevents the dissolution of water soluble salts as well the dissolution of the solvent in water. Directional solvent extraction may be considered a molecular-level desalination approach. Directional Solvent Extraction circumvents the need for membranes, uses simple, inexpensive machinery, and by operating at low temperatures offers the potential for using waste heat. This technique also lends itself well to treatment of feed waters over a wide range of total dissolved solids (TDS) levels and is one of the very few known techniques to extract water from saturated brines. We demonstrate >95% salt rejection for seawater TDS concentrations (35,000 ppm) as well as for oilfield produced water TDS concentrations (>100,000 ppm) and saturated brines (300,000 ppm) through a benchtop batch process, and recovery ratios as high as 85% for feed TDS of 35,000 ppm through a multi-stage batch process. We have also designed, constructed, and demonstrated a semi-continuous process prototype. The energy and economic analysis suggests that this technique could become an effective, affordable method for seawater desalination and for treatment of produced water from unconventional oil and gas extraction.
Multistage flash (MSF) desalination plants are among the major sources of potable water in the world, in particular in the Arab Gulf area [1]. These are very large, complex and expensive plants, in which large amounts of seawater and energy are consumed. Accordingly, big quantities of concentrated brine are disposed of after the desalination treatment. These characteristics of MSF plants make issues such as optimization of the operation and minimization of the corresponding environmental impact of the greatest importance. To the aim of addressing all these aspects, mathematical models provide a very useful tool. This work describes a steady-state mathematical model developed to analyze the MSF desalination process. It is based on a detailed physicochemical representation of the process, including all the fundamental elementary phenomena. In particular, the model accounts for the geometry of the stages, the variation of the physical properties of water with temperature and salinity, the different non-idealities involved in the process, the mechanism of heat transfer and the role of fouling. The developed model allows to analyze the role of operating and design variables in determining the process performances in terms of steady-state behavior. These information are used not only for design purposes, but also to support the development of a dynamical model through which the time-dependent behavior of the plant can be studied.
The Saline Water Conversion Corporation (SWCC), Saudi Arabia, began operating reverse osmosis (RO) desalination plants as early as in 1978 with small capacities and is now operating the largest seawater RO plants in the world. The rich experience gained by SWCC in more than 20 years of operation of these plants has been used to address some of the problems faced earlier and in improving the design of the new RO plants. One of the recent RO plants, which is due for commissioning, is the 91,000 m3/d plant at Al Jubail, on the coast of the Arabian Gulf. When placed in operation, it will be among the largest seawater RO desalination plants in the world. Considering the significance of a well designed pretreatment section for the successful operation of any RO plant, a pilot filtration plant was placed in operation during August 1993. The trials were carried out over a period of more than one year and the results were adapted in the plant design. This paper presents the salient design features of the plant and the improvements made.
gPROMS software was used to study the dynamics of a multistage flash desalination brine circulation system (MSF-BR) as a function of major operating parameters. Most of the previous studies focused on MSF-BR dynamic model development however; it gave very little information on dynamic response of the system to the most significant process independent parameters. The present model was first validated against available industrial data of different plants. System dynamics were obtained upon increasing/decreasing several of the operating parameters over a range of ± 15%. Results show that increase/decrease of the cooling seawater flow rate have limited effect on the system dynamics. Increasing/decreasing the brine recycle flow had more sizeable effects on the system performance. Therefore, it was not possible to operate the system below 7% decrease of the design value. The most sensitive system response was obtained as function of the heating steam temperature. As a result, increase/decrease of this parameter was limited to 2% and 3%, respectively. The system seizes to operate because of the following: increase in the brine level above the design limits (approximately 0.5 m below the demister), decrease in brine level below gate height (blow through phenomena), decrease in the production capacity below the minimum design value.
This paper deals with the effects of equipment reliability consideration to thermoeconomic analysis of a combined power and multi stage flash water desalination plant. Exergy and thermoeconomic models of the considered process units are developed and presented in this work. An economic model of the system is developed according to the Total Revenue Requirement (TRR) method. This application can be very useful, either for the plant management in order to achieve a cost-effective operation, or for a better plant design. Equipment reliability using the state-space and the continuous Markov method is incorporated in thermoeconomic analysis to improve the cost values. The results show that the power and water costs with reliability consideration increased 4.1% and 6.4%, respectively. Additionally, the sensitivity analysis shows the relationship between the production cost and the system availability which can help the designer to decide how to improve the profit or competitiveness.
Desalination plants are increasingly regarded as a tool to preserve natural water resources and therefore as a means to protect the environment. Furthermore desalination plants are performing a public service which (for social reasons) take precedence over any other kind of industrial activity. Nevertheless few specific studies have been carried out so far in order to establish the environmental impact of a desalination plant compared with other technologies. Few studies have also been carried out in order to compare the environmental impact of each desalination technology and to describe means to further develop the design in order to smooth further the environmental impact. The environmental impact of power and desalination plant to intrinsically related to the efficiency of the system. This paper aims at describing these specific means and providing a tool and a guideline for the design of new desalination plants.