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Experimental Study of a Brackish Water Desalination Plant
Estudio experimental de una planta de desalinización de agua salobre
Estudo experimental de uma planta de dessalinização de água salobra
Ifrah Asif
1
, Mirza Hammad Baig
2
,(*), Sohail Hasnain
3
, Sadia Ahmed
4
Recibido: 15/05/2024 Aceptado: 12/10/2024
Summary. - Water desalination is crucial for addressing global water scarcity affecting over 2 billion people. By
2050, water demand could rise by 20-30% due to population growth and urbanization. Currently, over 40% of the
global population lacks access to clean water due to overexploitation of conventional sources like rivers and
groundwater. This report focuses on experimental analysis of brackish water desalination, primarily using reverse
osmosis (RO). Desalination plays a vital role in converting seawater or brackish water into drinkable water, especially
in coastal areas. The study explores various desalination methods such as ion exchange, membrane distillation, and
vapor compression distillation. Technological advancements, particularly in RO distillation process has enhanced
efficiency and sustainability. In this report, pre-treatment processes, including filtration, chemical dosing, antiscalant
injection, water softening, are also employed to remove contaminants before desalination. The performance of RO is
evaluated based on factors like pressure drop, feed flow rate, and recovery ratio, analyzing water flux, salt rejection
rate, energy consumption, and system efficiency. The results provide insights into optimizing brackish water
desalination and the discussions are carried out for improvement of the ways such as post treatment, membrane
cleaning and advancement in membrane materials for sustainable freshwater production.
Keywords: Water desalination, brackish water, reverse osmosis, multistage, ion exchange, recovery ratio, flux, salt
rejection rate.
(*) Corresponding Author
1
Lecturer, Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan,
ifrahasif@neduet.edu.pk, ORCID iD: https://orcid.org/0000-0001-7551-2199
2
Lecturer, Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan
hammadbaig@neduet.edu.pk, ORCID iD: https://orcid.org/0000-0001-7544-8297
3
Lecturer, Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan
sohail@cloud.neduet.edu.pk, ORCID iD: https://orcid.org/0009-0005-2970-2908
4
Undergraduate Student, Department of Mechanical Engineering, NED University of Engineering and Technology, Karachi, Pakistan
ahmed4406016@cloud.neduet.edu.pk, ORCID iD: https://orcid.org/0009-0007-6072-3437
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Resumen. - La desalinización del agua es crucial para abordar la escasez global del agua que afecta a más de 2
mil millones de personas. Para 2050, la demanda de agua podría aumentar en un 20-30% debido al crecimiento de
la población y la urbanización. Actualmente, más del 40% de la población mundial carece de acceso al agua limpia
debido a la sobreexplotación de fuentes convencionales como ríos y agua subterránea. Este informe se centra en el
análisis experimental de la desalinización de agua salobre, utilizando principalmente la ósmosis inversa (RO). La
desalinización juega un papel vital en la conversión de agua de mar o agua salobre en agua potable, especialmente
en las zonas costeras. El estudio explora varios métodos de desalinización, como el intercambio de iones, la destilación
de membrana y la destilación de compresión de vapor. Los avances tecnológicos, particularmente en el proceso de
destilación de RO, han mejorado la eficiencia y la sostenibilidad. En este informe, también se emplean procesos de
pretratamiento, incluida la filtración, la dosificación química, la inyección antiscal de inyección, el ablandamiento
del agua, para eliminar los contaminantes antes de la desalinización. El rendimiento de RO se evalúa en función de
factores como la caída de presión, la velocidad de flujo de alimentación y la relación de recuperación, el análisis del
flujo de agua, la tasa de rechazo de la sal, el consumo de energía y la eficiencia del sistema. Los resultados
proporcionan información sobre la optimización de la desalinización de agua salobre y las discusiones se llevan a
cabo para mejorar las formas en que el tratamiento posterior, la limpieza de membranas y el avance en los materiales
de membrana para la producción sostenible de agua dulce.
Palabras clave: Desalinización del agua, agua salobre, ósmosis inversa, etapas múltiples, intercambio de iones,
relación de recuperación, flujo, tasa de rechazo de la sal.
Resumo. - A dessalinização da água é crucial para abordar a escassez global de água que afeta mais de 2 bilhões de
pessoas. Até 2050, a demanda da água poderá aumentar de 20 a 30% devido ao crescimento e urbanização da
população. Atualmente, mais de 40% da população global carece de acesso à água limpa devido à superexploração
de fontes convencionais como rios e águas subterrâneas. Este relatório se concentra na análise experimental da
dessalinização da água salobra, usando principalmente osmose reversa (RO). A dessalinização desempenha um papel
vital na conversão de água do mar ou água salobra em água potável, especialmente em áreas costeiras. O estudo
explora vários métodos de dessalinização, como troca de íons, destilação da membrana e destilação de compressão
de vapor. Os avanços tecnológicos, particularmente no processo de destilação de RO, aumentaram a eficiência e a
sustentabilidade. Neste relatório, os processos de pré-tratamento, incluindo filtração, dosagem química, injeção
antiscalante, amolecimento da água, também são empregados para remover contaminantes antes da dessalinização.
O desempenho do RO é avaliado com base em fatores como queda de pressão, taxa de fluxo de alimentação e taxa de
recuperação, análise de fluxo de água, taxa de rejeição de sal, consumo de energia e eficiência do sistema. Os
resultados fornecem informações sobre a otimização da dessalinização da água salobra e as discussões são realizadas
para melhorar as maneiras como pós -tratamento, limpeza de membranas e avanço em materiais de membrana para
produção sustentável de água doce.
Palavras-chave: Desalinização da água, água salobra, osmose reversa, vários estágios, troca de íons, taxa de
recuperação, fluxo, taxa de rejeição de sal.
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1. Introduction. - In water-stressed nations where desalinated water greatly outweighs freshwater source supplies,
desalination has come up as a critical component in helping to fulfill rising water demands.(Darre & Toor, 2018). In
the commercial distillation process, fresh water that is almost completely devoid of salt is separated from salt water,
with the salts concentrated in the rejected brine stream.(El-Dessouky & Ettouney, 2002). About 71% of the surface of
the Earth is made up of primarily saline water. According to estimates from the World Health Organization (WHO),
159 million people who depend on the oceans are among the 844 million individuals who lack access to safe potable
water globally.(Hoslett et al., 2018). Almost 99 % is seawater, which can be purified through desalination processes
for various potable and drinking usage purposes.(Kabir et al., 2024).
Salinity levels in brackish water are lower than in seawater due to a decrease in total dissolved solids (TDS). The low
salinity of brackish water (between 1000 and 10,000 mg/L TDS) makes it a good substitute. (Honarparvar et al., 2019).
Various techniques have been used to make saline/brackish water potable. Filtration, precipitation, sterilization,
chemical treatment, etc. are some processes that remove macro impurities from impure water.(Thimmaraju et al.,
2018).
There are two variety of desalination systems: thermal systems, which are powered by heat, and membrane-based
systems, which are powered by electricity. There are two primary varieties of the former: pressure-driven reverse
osmosis facilities and direct current electrical dialysis units that function under an electrical potential
difference.(Elbassoussi et al., 2024)
Membrane processes like RO have been widely adopted for water treatment and reuse. The global market for RO
continues to grow and is predicted to reach $8.1 billion by 2018.(Joo & Tansel, 2015). Over the last forty years, reverse
osmosis membrane technology has advanced to account for 44% of global desalting output capacity and 80% of all
desalination plants deployed globally.(Greenlee et al., 2009). Finding the ideal polymeric membrane materials was the
main focus of research from the late 1950s to the 1980s (Lee et al., 2011). However, membrane fouling is an inevitable
issue. Membrane fouling leads to higher operating pressure, flux decline, frequent chemical cleaning and shorter
membrane life. (Jiang et al., 2017). Based on the weight, substance, and energy balances and considering concentration
polarization a mathematical simulation model was created. The simulation results are over 96% near ROSA and over
80% close to the experimental data, according to comparison of this model and ROSA. (Hadadian et al., 2021)
Owing to its drawbacks, including the requirement for chemical input online, the conventional coagulation,
flocculation, and sedimentation chains are not seen to be an option in small water treatment systems. Many studies
have proposed membrane filtration (MF/UF) procedures in gravity-driven mode (GDM) that do not require pre-
treatment.(Rasouli et al., 2024). Gravity-driven membrane (GDM) filtration is a popular choice for long-term passive
filtration due to its high particle removal efficiency, low energy consumption and capacity to obtain a stabilized
flux.(Rasouli et al., 2024)
In many situations, tunable methods like membrane capacitive deionization (MCDI), capacitive deionization (CDI),
and electrodialysis (ED) are superior to traditional reverse osmosis (RO) because of their lower energy requirements
and operating costs.(Honarparvar et al., 2019). Distillation is a thermal energy-based method that efficiently rids
polluted water of impurities. The basic idea behind this method is to boil the salt water, let it evaporate, and then collect
the condensed vapour to create pure water.(Thimmaraju et al., 2018)
Electrodialysis is a voltage driven process. This process uses electrical potential to remove salt using a membrane
leaving fresh water behind.(Thimmaraju et al., 2018). Because electrodialysis (ED) uses less energy than other methods
for treating industrial water, it is more practical. Anion exchange membranes (AEM) and cation exchange membranes
(CEM) are the two types of membranes utilized in electrodialysis.(Rathod et al., 2024). Seawater/brackish desalination
of water is a popular application for Multi Effect Desalination Systems (MED) driven by Mechanical Vapour
Compression (MVC). The energy utilized to power these devices can come from renewable sources, such as solar,
wind, or a mix of the two.(Shamet & Antar, 2023)
Membrane distillation (MD) presents a viable substitute for traditional saltwater desalination methods. Regrettably,
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the membrane production techniques often involve the use of hazardous solvents and non-biodegradable
polymers.(Gontarek-Castro & Castro-Muñoz, 2024). Membrane distillation (MD) is a crucial technique for achieving
nearly 0% discharge of hyper saline wastewater. However, it frequently faces problems due to the accumulation of
mineral scale on the membrane surface.(Zhu et al., 2024). Solar distillation is one of the solutions of getting potable
water using solar energy. Solar distillation unit coupled with thermal collectors, photovoltaic panels, and
concentrators.(Manchanda & Kumar, 2018)
2. Methodology. - Following are the foremost common methods that are utilized in the treatment and purification of
the water:
Boiling
Distillation
Water filters
Ultra violet light
Ion exchange
Microfiltration (MF)
Ultra-filtration (UF)
Nanofiltration (NF)
Reverse Osmosis (RO)
Vapor compression
Multistage flash
Electrodialysis
Boiling: Employed as a primary method during emergencies, boiling water effectively eliminates waterborne
pathogens, particularly when turbidity is present. It is recommended to maintain a vigorous boil for a minimum of 3
minutes (increasing to 5 minutes at higher elevations) to ensure thorough disinfection.
Distillation: This method involves heating water to produce steam, which is then condensed to remove impurities,
including volatile organic compounds (VOCs). Employing additional filtration mechanisms can augment the
purification process, ensuring a comprehensive removal of contaminants.
Water Filtration: Utilizing a variety of physical and adsorptive mechanisms, water filtration systems effectively
remove contaminants from water sources. Common types include sediment, ceramic, and activated carbon filters, each
offering unique advantages in purifying water.
UV Light: UV disinfection systems utilize ultraviolet light to eradicate bacteria and viruses by disrupting their genetic
material. This method provides a highly efficient and environmentally friendly approach to water treatment.
Ion Exchange: Ion exchange technology facilitates the removal of ions from water, resulting in demineralization.
While effective in purifying water, it is imperative to adhere to regular maintenance protocols to prevent microbial
contamination.
Microfiltration: Employing membranes with fine pores, microfiltration effectively removes particles, bacteria, and
other contaminants from water. This method finds extensive applications in various industries, including
pharmaceuticals and food processing.
Ultrafiltration: With smaller pore sizes compared to microfiltration, ultrafiltration systems can effectively concentrate
proteins and enzymes while removing larger molecules and particles. This process is integral in achieving high-purity
water for specialized applications.
Nanofiltration: Nanofiltration systems utilize advanced membrane technology to selectively remove small molecules
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and ions from water sources. This process is particularly useful in concentrating and purifying substances such as
sugars and dyes.
Reverse osmosis: Reverse Osmosis is a process that uses the membrane. It is abbreviated as RO. It has the smallest
pores size range from 0.0001-0.001 microns. The pressure requirement is 25-100 Bar which is the largest among all.
The RO process is used to remove water and concentrate very small molecular weight substances. Typical applications
include concentrating dairy or food products (lactose) , recovery/polishing of water from permeate , recovery/polishing
of evaporator condensate.
RO systems can be efficaciously pragmatic to saline groundwater, seawater and brackish water. It may also account
for confiscation of inorganic contaminants like, arsenic, nitrates, radio nuclides and other toxins such as pesticides.
The mechanism of RO systems works on such track where the pressure is applied to a greater concentration solution
to go through semipermeable plastic membrane and producing a more strenuous solution. Pressurization of the feed
water is the basic energy need for RO. Within the membrane module containing compactly arranged passages, the feed
water must be acquiesced and other pollutants causing the turbidity must be eradicated.
In RO systems, membrane washing via backwashing is crucial to maintain performance and extend membrane life.
However, particles that accumulate cannot be completely removed, leading to reduced efficiency. Scaling, primarily
due to calcium carbonate, decreases membrane permeability and irreversibly damages membranes. Fouling, the
accumulation of solids on membrane surfaces, further diminishes system performance, causing pressure and flux
losses. Proper waste disposal is essential due to the high concentration of brine produced, typically exceeding that of
seawater. Discharging brine into sewerage lines can impact underground water levels and ecological balance over time.
Throughout the world there are many of the municipal water treatment facilities that utilizes RO membrane. Although
it looks similar and is fabricated in a different way to RO membranes for dairy and other highly specific sanitary
applications.
3. Experimental analysis of reverse osmosis. - For the experimental analysis of reverse osmosis, the brackish water
was first pre-treated to remove any large particles or organic matter that could damage the semipermeable membrane.
3.1. Pre-treatment. - The pre-treatment processes involved were sediment filtration, carbon filtration, water softening,
antiscalant injection and micro filtration.
Sediment filtration: Firstly, water passes through sediment filters to remove larger particles like sand or dirt.
Carbon filtration: Then, the carbon filtration was done to remove chlorine and organic compounds present in
water.
Water softening: Then, water softening was done to remove the calcium and magnesium ions.
Antiscalant solution: Then, antiscalant solution was injected to prevent the scale formation in the RO
membrane.
Micro-filtration: Then, the micro-filtration was done to remove the micro-organisms and bacteria that could
foul the RO membrane.
Figure I. Pre-treatment of brackish water.
3.2. Methodology for Experimental analysis of reverse osmosis. - In the experimental analysis of reverse osmosis
(RO), meticulous pre-treatment of brackish water was paramount to safeguard the integrity of the semipermeable
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membrane. This pre-treatment regimen encompassed a series of sophisticated processes tailored to remove various
contaminants that could compromise membrane performance.
Initially, the brackish water underwent sediment filtration, a crucial step aimed at eliminating larger particles such as
sand and dirt. Subsequently, carbon filtration was employed to effectively remove chlorine and organic compounds
present in the water, ensuring optimal membrane function. Following carbon filtration, water softening procedures
were implemented to tackle the removal of calcium and magnesium ions, which are notorious for causing scale
formation on the RO membrane. To further fortify membrane protection, an antiscalant solution was judiciously
injected to mitigate the risk of scale deposition, thereby prolonging membrane longevity and efficacy. Moreover,
microfiltration was meticulously conducted to target the removal of microorganisms and bacteria that could potentially
foul the RO membrane, ensuring the highest standards of water purity and safety.
The equations involved to calculate these factors are as,

(Halliday et al., 2013)

(Wang & Zhou, 2013)


(Baker, 2023)

(Davis, 2010)

(Moran et al., 2010)
In the given context: Q represents flow rate, A represents area, Qp represents permeate flow rate, Qf represents feed
flow rate, TMP represents trans-membrane pressure, Cp represents concentration of solute in permeate, Cf represents
concentration of solute in the feed, P represents power consumption and t represents time.
Figure II. Reverse Osmosis process.
4. Experimental analysis of ion exchange distillation. - In the ion exchange process for treating brackish water, the
resin bed undergoes meticulous preparation through regeneration with a brine solution to enhance its exchange
capacity. Once ready, the brackish water is introduced into the system, initiating the ion exchange phenomenon. As
water flows through the resin bed, unwanted ions are removed, and desirable ions are released, facilitating purification.
Throughout the process, careful monitoring of parameters such as water flow rate, resin exchange capacity, and contact
time ensures optimal performance. After treatment, the exhausted resin is regenerated using a brine solution,
maintaining the system’s effectiveness in producing high-quality water.
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Figure III. Ion exchange process
4.1. Experimental analysis of vapor compression distillation. - For the experimental analysis of vapor compression
distillation, the equipment and setup were prepared, including the vapor compression distillation unit, heat source,
condenser, and collection vessels. Then, a specific brackish water sample was selected for testing. The distillation
process was initiated by applying heat to the brackish water, causing evaporation. The vapor was then compressed
using a compressor, increasing its temperature and pressure. Next, the compressed vapor was cooled in the condenser,
causing it to condense back into liquid form. The resulting distilled water was collected in the vessels, while the
remaining concentrated brine was disposed of. Throughout the experiment, various parameters such as temperature,
pressure, and flow rate were measured and recorded. The collected data was then analyzed to evaluate the performance
of the vapor compression distillation process and determine its efficiency in producing fresh water from brackish water.
4.2. Experimental analysis of electrodialysis distillation. - For the experimental analysis of electrodialysis
distillation, firstly, the experimental setup was prepared, including the electrodialysis cell, electrodes, and brackish
water feed solution. The cell was filled with the feed solution, and the electrodes were positioned accordingly. Then,
an electric field was applied across the cell, causing the migration of ions through ion-exchange membranes. This
process helped separate the ions and remove impurities from the brackish water. The purified water and concentrated
brine were collected separately. Throughout the experiment, parameters such as voltage, current, and conductivity
were measured and recorded. The collected data was then analyzed to evaluate the performance of the electrodialysis
distillation process and assess its efficiency in desalinating brackish water.
4.3. Experimental analysis of multi-stage flash distillation. - For the experimental analysis of multi-stage flash
distillation, firstly, the experimental setup was prepared, including the flash chamber, heat source, and brackish water
feed. The brackish water was heated using the heat source, causing it to evaporate. The resulting vapor was then
condensed in a series of flash chambers, each operating at a lower pressure than the previous one. This process allowed
for the separation of fresh water vapor from the concentrated brine. The fresh water vapor was collected and condensed
into liquid form, while the concentrated brine was removed. Throughout the experiment, parameters such as
temperature, pressure, and flow rate were carefully monitored and recorded. The collected data was then analyzed to
evaluate the efficiency and performance of the multi-stage flash distillation process.
Figure IV. Multi-stage flash distillation.
5. Results and Discussions. - The specifications of the membrane used in reverse osmosis are shown in Table I. In
Table II, the dimensions of the membrane are shown and the operating limits and maximum pressure, temperature
conditions and the pH range for both short term and continuous cleaning are listed in Table III. In Table IV, the system
details of the ROSA software are shown including the feed pressure, temperature, TDS, flow factor, avg NDP. Number
of elements is taken to be 1 and in Table V, for 1 element the stage details are shown. The re-circulation flow, permeate
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pressure and boost pressure are found to be zero in this case. The raw water test report before the reverse osmosis is
shown in Table VI and the results of the reverse osmosis are shown in the final test report after the process of reverse
osmosis in Table VII. The total dissolved solids (TDS) was 3230 ppm initially but after the RO process it became 15
ppm. The total hardness initially was 710 ppm and after the RO process it became 150 ppm and the total suspended
solids were found to be nil. From all of these results, it is clearly shown that the brackish water is converted into pure
and drinkable water and all the impurities including the dissolved and suspended solids, organic compounds, bacteria,
chlorine, micro-organisms, chloramines are removed by virtue of reverse osmosis. For further purification and
advanced cleaning and to make the process more, there are various ways including the advancement in membrane
cleaning, membrane technology, more effective monitoring and post-treatment. Advancement in membrane materials
and design can enhance permeability, selectivity, and durability, improving overall efficiency. Implementing regular
membrane cleaning protocols using appropriate chemicals and techniques to remove fouling and maintain
performance. All of these factors and other factors as effective pump designs, pressure recovery devices, and
optimization of operating conditions such as accurate pressure drop and flow rate through the membrane can improve
RO plant’s efficiency.
Product
Part
number
Active area
ft²(m²)
Applied pressure
psig(bar)
Permeate flow rate
gpd(m³/d)
Stabilized salt
rejection %
BW30-
4040
80783
82(7.6)
225(15.5)
2400(9.1)
99.5
Table I. Membrane specifications.
A
B
C
D
40.0(1,016)
1.05(26.7)
0.75(19)
3.9(99)
Table II. Membrane dimensions.
Table III. Operating limits.
Feed flow to stage 1
6.93 gpm
Feed pressure
200.6 psig
Flow factor
0.85
Total active area
78.00 ft²
Pass 1 permeate flow
1.04 gpm
Pass 1 recovery
15.00 %
Feed temperature
25°C
Feed TDS
3250.01mg/l
Average pass 1 flux
19.2 gfd
Number of elements
1
Average NDP
154.2 psig
Concentration
44.14 psig
Power
0.76 kW
Specific energy
12.13 kWh/kg
Table IV: System details.
Maximum
operating
temperature
°F(°C)
Maximum
operating
pressure
psi(bar)
Maximum
feed flow
rate
Gpm(m³/h)
Maximum
pressure
drop
Psig(bar)
pH range
(continuous
operation)
pH range
(short
term
cleaning)
Maximum
feed silt
density
index
Free
chlorine
tolerance
113°F(45°C)
600 psi(41
bar)
4040
elements
16gpm(3.6
m³/h)
15 psig(1
bar)
2-11
1-12
SDI 5
<0.1 ppm
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Stage
Element
#PV
#Ele
Feed flow
Feed pressure
Rrcirc flow
Conc flow
Conc pressure
Permeate flow
Avg flux
Permeate press
Boost press
Perm TDS
Table V. Stage details.
Parameters
Analysis Results
Units
Total dissolved solids
3230
ppm
Total suspended solids
2
ppm
Total hardness
710
ppm as CaCO3
pH
7.5
-
Calcium hardness
256
ppm as CaCO3
Magnesium hardness
454
ppm as CaCO3
Iron total
0.2
ppm as Fe2+
Table VI. Raw (brackish) water test report.
Parameters
Analysis results
Units
Total dissolved solids
15
ppm
Total suspended solids
Nil
ppm
Total hardness
150
ppm as CaCO3
pH
7.5
-
Calcium hardness
40
ppm as CaCO3
Magnesium hardness
53
ppm as CaCO3
Iron total
Nil
ppm as Fe2+
Table VII. Final report of water after RO process.
5. Comparative Analysis of Desalination Methods and Advantages of Reverse Osmosis (RO). -
5.1. Reverse Osmosis (RO). - RO is a membrane-based technology that forces saline water through a semipermeable
membrane under high pressure, selectively rejecting salts and other dissolved impurities. This process has gained
prominence as the leading desalination method globally.
Advantages: RO systems demonstrate high salt rejection rates (up to 99%) and are highly effective across a range of
salinity levels, from seawater to brackish sources. They also tend to consume less energy than thermal desalination
methods due to their non-reliance on heat, making RO more economically viable, particularly for high-volume
applications. Moreover, advancements in membrane materials and configurations have increased permeability and
selectivity while mitigating fouling, thus improving RO’s operational efficiency and lifespan.
Disadvantages: Despite its efficacy, RO membranes are susceptible to fouling from organic matter, scale, and
biofouling, necessitating regular maintenance and chemical cleaning protocols. High-pressure requirements for
seawater desalination also elevate energy costs and can increase system wear.
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5.2. Multi-Effect Distillation (MED). - MED is a thermal process that involves a series of evaporators (“effects”)
where steam from one effect heats the next stage at progressively lower temperatures.
Advantages: MED is robust and ideal for large-scale desalination applications, especially when renewable heat sources
are available. Its multi-stage design allows for efficient energy recycling, and it is less prone to biological fouling,
making it suitable for regions with high salinity or limited maintenance resources.
Disadvantages: The high capital costs and spatial requirements make MED less feasible for smaller facilities.
Additionally, MED’s reliance on thermal energy results in elevated operational costs and makes it susceptible to
fluctuations in energy prices.
5.3. Multi-Stage Flash (MSF). - MSF desalination rapidly heats seawater, which is then “flashed” to steam in multiple
stages under decreasing pressure levels.
Advantages: MSF systems are highly reliable and capable of long operational lifespans, making them suitable for
continuous, large-scale desalination. They are also effective for high-salinity seawater and can leverage waste heat,
contributing to energy efficiency in combined power and water production settings.
Disadvantages: MSF is one of the most energy-intensive desalination technologies, given its heavy reliance on thermal
energy. The high operational and maintenance costs, coupled with significant environmental concerns related to brine
discharge, restrict its widespread use.
5.4. Electrodialysis (ED). - ED utilizes an electric field to drive ions through selective membranes, effectively
separating salts from water.
Advantages: ED is particularly efficient for low-salinity water sources, such as brackish water, due to its low energy
consumption relative to salinity. It also has minimal chemical requirements for maintenance and can be more cost-
effective at smaller scales.
Disadvantages: ED’s limited desalination capability for seawater restricts its applicability in high-salinity contexts.
Additionally, membrane fouling can still be an issue, especially in water sources with high organic content.
5.4. Membrane Distillation (MD). - MD is a thermally driven membrane process that utilizes a temperature gradient
to drive water vapor through a hydrophobic membrane, leaving salts behind.
Advantages: MD achieves high salt rejection and can utilize waste heat, making it suitable for niche applications,
including zero-liquid discharge systems. MD systems can operate at relatively low temperatures, which reduces
thermal energy demands.
Disadvantages: Scaling and fouling issues can impact membrane performance, and the technology remains cost-
intensive due to complex membrane requirements. Additionally, the reliance on non-biodegradable materials raises
environmental concerns, limiting MD’s sustainability profile.
RO’s superiority lies in its combination of high efficiency, flexibility, and scalability across various salinity levels and
operational scales. Unlike thermal processes, which require significant energy input and large physical footprints, RO
is compact and energy-efficient, especially when treating brackish or moderately saline water. Its adaptability to
different water sources and the continuous innovation in membrane technology make RO an optimal solution for
desalination. While fouling remains a challenge, advancements in fouling-resistant membranes and cleaning protocols
have made RO systems increasingly resilient, reducing maintenance frequency and prolonging membrane life. These
qualities position RO as the preferred choice for sustainable desalination, especially where operational flexibility and
cost-effectiveness are critical considerations.
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6. Factors Influencing the Performance of the Reverse Osmosis (RO) Process
6.1. Membrane Characteristics. - The efficiency of the RO process is closely linked to the properties of the membrane
used:
6.2. Material Composition. - Polyamide membranes are widely chosen for brackish water desalination due to their
high salt rejection capabilities and durability. In contrast, cellulose acetate membranes are less commonly used due to
their lower resistance to pH variations.
6.3. Pore Structure. - The size and structure of the membrane’s pores directly influence salt rejection. Smaller pores
typically enhance salt rejection but may reduce the flow rate. For brackish water, membranes are designed to balance
pore size, achieving effective salt removal while maintaining adequate water permeability.
6.4. Fouling Resistance. - RO membranes are prone to fouling from organic matter, salts, and biological growth,
which can reduce efficiency. To combat this, anti-fouling coatings are often applied, enhancing the membrane’s
operational life and sustaining process performance.
7. Operating Conditions. - The conditions under which RO operates significantly impact its effectiveness:
7.1. Pressure. - Brackish water desalination operates at a lower pressure range (10-20 bar) than seawater desalination,
due to its reduced salinity. The pressure must be sufficient to overcome the osmotic pressure, enabling permeate flow
while optimizing energy use.
7.2. Temperature. - Elevated temperatures generally increase water permeability but may compromise salt rejection.
As a result, RO systems for brackish water typically operate at moderate temperatures to balance water flux and salt
removal.
7.3. Recovery Rate. - The recovery rate, or the percentage of feed water converted into permeate, is optimized to
prevent excessive concentration of salts at the membrane surface. This concentration polarization can lead to fouling,
so maintaining an appropriate recovery rate is essential for system efficiency and durability.
8. Water Quality. - The initial quality of the feed water, including salinity and the presence of contaminants, also
affects RO performance.
8.1. Salinity. - Although brackish water is less saline than seawater, it still requires effective salt removal to achieve
the desired level of purification. Lower salinity allows for energy-efficient operation at reduced pressures.
8.2. Contaminants. - Brackish water may contain organic materials, suspended particles, and microorganisms that can
lead to membrane fouling. Pre-treatment, such as sedimentation or filtration, is typically applied to improve RO
performance by minimizing the risk of fouling.
9. Conclusion. - After undergoing reverse osmosis (RO), the water undergoes a significant transformation in its
composition. The total dissolved solids (TDS) decrease significantly from an initial 3230 ppm to just 15 ppm. Similarly,
the total hardness decreases from 710 ppm to 150 ppm after treatment, and there are no total suspended solids present.
These results demonstrate the effectiveness of reverse osmosis in removing various pollutants, such as dissolved and
suspended particles, organic compounds, bacteria, chlorine, microorganisms, and chloramines. As a result, the treated
water becomes pure and safe for consumption. The substantial reduction in TDS and hardness levels, along with the
absence of suspended solids, underscores the efficiency of the RO process in water purification.
10. Future recommendations. - There are various ways to enhance the purification process and achieve advanced
cleaning. This includes advancements in membrane technology, improved monitoring, and post-treatment. By
improving the permeability, selectivity, and durability of membranes through material and design enhancements,
overall efficiency can be increased. Implementing regular membrane cleaning procedures to prevent fouling and
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maintain performance using appropriate chemicals and methods is crucial. Efficiency can also be boosted by efficient
pump designs, pressure recovery equipment, and optimizing operating conditions like precise pressure drop and
membrane flow rate.
10.1. Membrane Cleaning Improvements. –
Tailored Chemical Cleaners: Use specific cleaning agents tailored to different types of fouling (e.g., acid cleaners
for scaling, alkaline cleaners for organic fouling). Customized chemical blends can target fouling more effectively and
minimize membrane damage.
Enzymatic Cleaning: For organic fouling, enzymatic cleaners can be employed to break down biofilm layers without
damaging the membrane material. This is especially useful in systems prone to biofouling.
Periodic Backwashing and Forward Osmosis: Integrate regular backwashing with air scouring to remove particles
from the membrane surface. In forward osmosis, alternating directions in flow help release deposited particles,
maintaining membrane permeability.
Electrically Enhanced Cleaning: Introducing an electric field across the membrane surface can help repel charged
foulants, reducing biofouling and scaling. This approach, called electrochemical cleaning, has shown potential in
maintaining flux and extending membrane lifespan.
10.2. Enhanced Monitoring Techniques. -
Real-time Fouling Detection Sensors: Install sensors that monitor pressure drop, permeate quality, and flow rates to
detect fouling or scaling as it develops. Optical or ultrasonic sensors can identify fouling layers in real time, enabling
proactive cleaning before significant flux reduction.
Automated Data Analytics: Use machine learning algorithms to analyze operational data (e.g., temperature, pressure,
and flux) and predict potential fouling events. This preemptive approach allows operators to adjust cleaning schedules
based on real-time data rather than fixed intervals.
pH and Conductivity Monitoring: Regularly monitor pH and conductivity levels, especially in feed and brine
streams, to detect changes indicating scaling or chemical imbalance. Conductivity monitoring, in particular, is useful
for tracking salinity changes that may require operational adjustments.
10.3. Post-Treatment Optimization. -
Advanced Oxidation Processes (AOPs): Implement AOPs, such as ozone or UV treatments, to degrade any
remaining organic contaminants and improve water quality. AOPs are highly effective in eliminating residual
micropollutants that may not be removed by membranes alone.
Activated Carbon Filtration: Use granular activated carbon (GAC) as a post-treatment step to adsorb dissolved
organic compounds (DOCs) and trace contaminants, improving taste and safety. GAC is effective for removing
substances that might otherwise compromise water quality.
Ion Exchange for Heavy Metals: In areas with potential heavy metal contamination, an ion exchange unit can
selectively remove ions like lead, copper, and mercury. This process is particularly beneficial when dealing with
brackish water sources with variable metal content.
Antiscalant Dosing in Post-Treatment: Apply controlled antiscalant dosing in the final stages to mitigate the
potential of scaling in downstream equipment, ensuring consistent quality and flow in distributed water.
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10.4. Operational Efficiency Enhancements. -
Energy Recovery Devices (ERDs): Incorporate ERDs, such as pressure exchangers or isobaric chambers, to capture
and reuse energy from the brine stream. This reduces overall energy costs and improves system efficiency.
Optimized Pressure and Flow Controls: Use variable-frequency drives (VFDs) on pumps to dynamically adjust
pressure and flow rates based on real-time demands and membrane conditions. Lower pressure settings during low
fouling can prolong membrane life.
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Author contribution:
1. Conception and design of the study
2. Data acquisition
3. Data analysis
4. Discussion of the results
5. Writing of the manuscript
6. Approval of the last version of the manuscript
IA has contributed to: 1, 2, 3, 4, 5 and 6.
MHB has contributed to: 1, 2, 3, 4, 5 and 6.
SH has contributed to: 1, 2, 3, 4, 5 and 6.
SA has contributed to: 1, 2, 3, 4, 5 and 6.
Acceptance Note: This article was approved by the journal editors Dr. Rafael Sotelo and Mag. Ing. Fernando A.
Hernández Gobertti.