Pumps Used in Seawater Reverse Osmosis Systems
- Usable Water Resources in the World
Factors such as population growth, urbanisation, global warming and industrialisation are placing increasing pressure on existing water resources. This is causing significant problems, particularly in the supply of drinking and domestic water. The depletion of water resources has made their sustainable management and protection a necessity. Current projections show that water scarcity will deepen further in the coming years. In this context, developing alternative water production methods is as critically important as managing water resources sustainably.
Innovative methods such as seawater desalination, rainwater harvesting and wastewater recovery are among the effective strategies for combating water scarcity. Although a large part of the Earth’s surface is covered by water, freshwater resources suitable for drinking and use are quite limited. Only 2.5% of the total water reserve on Earth is freshwater, and only 0.3% of this is accessible for the natural environment and human use. This reality clearly demonstrates the importance of protecting water resources and managing them sustainably.
1.1 Depletion of Freshwater Resources
Freshwater resources are rapidly declining under the influence of various environmental and human-induced factors. This is linked to some of the main causes threatening water security on a global scale:
- Drought and Climate Change: Global climate change has negative effects on the hydrological cycle, increasing the frequency and severity of droughts. It also raises the likelihood of extreme weather events.
- Industrialisation and Pollution: Chemicals used intensively in industrial activities and agricultural production adversely affect the quality of freshwater resources and cause serious degradation in aquatic ecosystems.
- Population Growth and Urbanisation: Rapid population growth and unplanned urbanisation significantly increase demand for freshwater resources and further intensify the pressure on them.
- Seawater Desalination and Reverse Osmosis Technology
Seawater desalination stands out as an effective solution to water scarcity in regions with insufficient water resources. In this context, reverse osmosis technology is regarded as one of the most widely used methods for obtaining drinking and domestic water from seawater. In the reverse osmosis process, seawater is passed through a semi-permeable membrane filter under high pressure to remove salt and other impurities.
The physical properties of seawater, which makes up around 97% of the water on the Earth’s surface, vary depending on environmental factors such as temperature, salinity and atmospheric pressure. The characteristic properties of seawater are directly related to hydrostatic pressure, which changes particularly with increasing depth. Temperature is a fundamental parameter that determines the dissolving capacity of seawater, and this directly affects the dissolution rates and quantities of minerals and other dissolved elements.
The salinity of seawater results from the dissolution of minerals under the influence of temperature differences in rocks, chemical processes and other physical factors. In the open seas, salinity generally ranges between 3.3% and 3.7%, although depending on depth and climatic and regional conditions it can vary between 2.8% and 4.0%. In general, the average salinity of seawater is taken as 3.5%.
2.1 Salt Minerals in Seawater
The chemical composition and salinity of seawater depend on the presence of various dissolved salt minerals. These minerals include:
- Chloride (Cl⁻)
- Sulphate (SO₄²⁻)
- Bicarbonate (HCO₃⁻)
- Bromide (Br⁻)
- Borate (H₂BO₃⁻)
- Fluoride (F⁻)
- Sodium (Na⁺)
- Magnesium (Mg²⁺)
- Calcium (Ca²⁺)
- Potassium (K⁺)
- Strontium (Sr²⁺)
These minerals determine the chemical properties of seawater and contribute to its salinity. The effect of each mineral on salinity may vary depending on regional and environmental factors.
2.2 Osmosis
Osmosis is the process in which a low-concentration liquid moves through a semi-permeable membrane towards a higher-concentration liquid, reducing the concentration difference. This process continues naturally until the osmotic pressure between the two liquids is balanced. Osmosis functions as a fundamental mechanism for maintaining water balance in biological systems.
2.2.A Reverse Osmosis
Reverse osmosis is achieved by reversing the natural osmosis process. In this method, an external pressure exceeding the osmotic pressure is applied to the high-concentration liquid. This pressure causes water to move in the opposite direction and be purified through the membrane. Minerals, salts and other dissolved substances are retained on one side of the membrane, while low-concentration purified water is obtained on the other side.
Reverse osmosis is an effective technology widely used in treating seawater for drinking or domestic use. This method offers a sustainable solution, particularly in regions where water scarcity has reached serious levels.
- Grundfos Seawater Pumps and SWRO Recovery Systems
Pumps used in seawater treatment systems are made from special materials resistant to the corrosive effects of seawater. Pumps developed by Grundfos are widely used in seawater reverse osmosis (SWRO) systems and deliver superior performance in these systems.
In Grundfos’ BMSX series pumps used in seawater reverse osmosis systems, materials such as 904L stainless steel and super duplex stainless steel, with a PREN (Pitting Resistance Equivalent Number) value of 34-40 providing high resistance to seawater, are preferred. These materials increase system reliability by offering high corrosion resistance and a long service life.
Grundfos pumps used in SWRO systems stand out with the following key advantages:
- High Efficiency: Saves energy and reduces the system’s operating costs.
- Corrosion Resistance: Offers long-term durability against the corrosive seawater environment.
- Elegant Design: Saves space with its compact and optimised design.
- Low Noise Level: Reduces the environmental impact of systems.
- Easy Maintenance: Provides ease of operation thanks to low maintenance requirements.
The Grundfos pumps used in SWRO systems vary according to system capacity. These pumps include:
- High-Pressure Pumps (BMhs): Provide the high pressure required for the reverse osmosis process.
- Booster Pumps (BMhp): Support increasing and stabilising flow in the system.
- Pressure Exchangers (PX): Work in integration with energy recovery systems to deliver energy savings of 50% and above.
Grundfos’ BMSX series pumps work in full compatibility with pressure exchanger systems, delivering optimised performance in seawater reverse osmosis systems with recovery. With these features, the BMSX series stands out as an innovative and highly efficient solution for sustainable water management.
3.1. Features of the BMS hs High-Pressure Pump and BM hp Booster Pump
High-pressure pumps used in seawater treatment systems are a critical component that delivers seawater under high pressure to the reverse osmosis (RO) membranes, enabling the water to be treated. By providing the necessary pressure, these pumps allow water molecules to pass through the semi-permeable membranes while salt and other impurities are retained by the membrane.
Grundfos’ BMS hs series high-pressure pumps are designed to optimise system performance. These pumps work with different motor options that offer high efficiency and durability. While they are fitted as standard with Siemens AC motors, permanent magnet (PM) motors with IE5 efficiency class can also be used on request.
IE5-class PM motors meet the highest energy efficiency standards in the industry, reducing energy consumption and lowering operating costs. In addition, these motors make an important contribution to sustainable water management by offering lower energy losses and higher performance.
BMS hs series pumps offer an innovative solution that meets the core requirements of seawater treatment systems and increase system reliability with their high performance.
3.3. Booster Pump (BMS hp) and Motors
Booster pumps are critical components in seawater treatment systems that support the high-pressure pumps by increasing water pressure. These pumps allow water to be delivered to the reverse osmosis (RO) membranes at sufficient pressure, reducing the load on the high-pressure pumps. This increases the overall energy efficiency of the system while also extending the life of the high-pressure pumps.
Grundfos’ BMS hp series booster pumps are equipped with three motor alternatives to suit different application requirements:
- Grundfos permanent magnet (PM) motors (IE5) and MGE motors with integrated drive: These motors offer high energy efficiency, optimising the system’s energy consumption. The integrated drive simplifies system control and performance optimisation.
- Grundfos fixed-speed MG motors (IE3): Providing high reliability and energy efficiency, these motors are a suitable solution for standard applications.
- Siemens AC motors (IE3): Used as a durable and efficient alternative for seawater treatment systems.
These motor options are designed to meet a range of needs in terms of energy efficiency, performance and durability. BMS hp series pumps offer an effective solution for optimising energy consumption in the system while lowering operating costs and increasing the sustainability of water treatment processes.
3.4. Pressure Exchanger (PX)
Pressure exchangers are devices that provide energy recovery by transferring the pressure energy of a high-pressure fluid to a low-pressure fluid. Many industrial processes operate at high pressures, and such processes have high-pressure waste streams. In handling high-pressure liquids, this pressure energy needs to be transferred to low-pressure fluids so that the waste pressure can be used efficiently.
In SWRO (Seawater Reverse Osmosis) seawater recovery systems, the use of a pressure exchanger (PX) is highly effective for increasing feed water pressure by making use of the pressure energy of high-pressure waste fluids. The PX provides energy recovery using fluids containing brine wastewater, typically at high pressures of 60-70 bar and with salinity of 80,000-90,000 ppm. This process allows the pressure energy of the waste fluid to be transferred to the low-pressure feed fluid, thereby increasing the pressure of the feed water.
This method allows booster pumps to be selected with lower capacities in terms of both hydraulics and motor power. As a result, the use of PX delivers energy savings of 50% to 60% and increases the overall efficiency of the system.
Pressure exchangers play a critical role in maximising energy efficiency, reducing operating costs and contributing to sustainable water treatment processes. The integration of this technology offers an important solution for water recovery and energy optimisation.
3.5. SWRO: An Example Project Without Energy Recovery
As shown in Figure 3.5, the system in question has no recovery mechanism. For this reason, wastewater at a pressure of 68 bar is discharged directly. Because the pressure energy in the wastewater cannot be utilised, the high-pressure pump had to be selected with a larger capacity. This adversely affects the energy efficiency of the system and leads to an increase in specific energy consumption.
In this system without energy recovery, 6.45 kW of energy is required to produce 1 m³ of water. The annual energy consumption cost is around EUR 118,000. This is an example of a system that could be made more efficient through improvements aimed at increasing energy efficiency.
The use of energy recovery technologies significantly reduces energy consumption, lowering operating costs and increasing environmental sustainability. In this context, innovative solutions that deliver energy efficiency in SWRO systems play an important role in water treatment processes.
3.6. SWRO: An Example Project With Energy Recovery
As shown in Figure 3.5, while specific energy consumption in systems without a recovery mechanism is around 6.45 kWh per cubic metre, in applications with energy recovery systems this value can fall to around 3 kWh/m³. This makes it possible to achieve savings of more than 50% in energy consumption.
Recovering the pressure energy of the waste brine stream reduces the payback period of the investment in recovery systems to under one year, significantly increasing the economic efficiency of the system. Thanks to this mechanism, as the amount of energy used in the system decreases, the annual energy consumption cost also falls to around EUR 55,000.
Energy recovery technologies not only increase energy efficiency but also reduce operating costs, offering a more sustainable water treatment process. Such systems offer economically attractive solutions with high-efficiency operations and low operating expenses.
- Advantages of Seawater Reverse Osmosis (SWRO) Systems
4.1. A Solution to Water Scarcity
Reliable Water Source: SWRO systems provide a reliable water source in water-scarce regions by converting seawater into clean water of drinking quality. These systems play a critical role where water resources are insufficient, offering sustainable solutions especially for drinking water supply.
Industrial and Agricultural Use: SWRO systems provide clean water suitable not only for drinking but also for various applications such as industrial processes and agricultural irrigation. This eases the challenges faced in water supply in the agricultural and industrial sectors.
4.2. Environmental and Economic Advantages
Sustainability: Seawater is an almost inexhaustible resource. SWRO systems enable sustainable water supply by reducing dependence on freshwater resources. This preserves environmental balance in terms of renewable and long-term water use.
Energy Efficiency: Modern SWRO systems are equipped with energy recovery technologies, which reduce energy costs. These technologies increase energy efficiency and improve the operational efficiency of the system.
4.3. Technological Developments
High-Efficiency Membranes: New-generation membranes provide higher efficiency and lower energy consumption, significantly increasing the performance of SWRO systems. These developments in membrane technology increase the speed and efficiency of water treatment processes.
Energy Recovery Systems: Energy recovery systems are one of the most important innovations used in SWRO applications. These systems significantly reduce energy consumption, lowering operating costs and minimising environmental impact.
4.4. Quality and Safety
High-Quality Water: SWRO systems produce safe drinking water by treating water to high quality standards. This provides a major advantage, especially in terms of health and safety. By producing water free of salt and contaminants, the systems guarantee drinking water quality.
Flexibility: SWRO systems can be customised to different scales and needs. This flexibility increases the usability of the systems in various applications and helps them adapt to different geographical and industrial conditions.
REFERENCES:
- Demir, A. (Trans.) (2023). Grundfos Pumps in Water Treatment
- Copilot AI.
- Grundfos. (2004). Grundfos Industry Pump Handbook.
- Grundfos. (2024). GPC (Grundfos Product Center) Pump Selection. Available at: https://www.grundfos.com/tr
- Bıyıklı, Y. E. (2017). Ters Osmoz Yöntemi ile Deniz Suyundan İçme-Kullanma Suyu Teminin Teknik ve Ekonomik Olarak Değerlendirilmesi: Avşa Örneği [Technical and Economic Evaluation of Drinking and Domestic Water Supply from Seawater by Reverse Osmosis: The Case of Avşa].
Author
Ahmet Demir
Pump Valve and Systems MagazinePompa Vana · September-October 2026Read the latest issue free →
