Make your RO unit more efficient

• Water Treatment Basics How to choose the right RO membrane

The selection and reasonable matching of RO membranes determine the core capabilities of RO devices, and there are many types of RO membranes on the market, and the prices are also very different. Except for a very small number of subdivisions of special membranes with certain technical added value (price overflow), the prices of RO films of conventional materials, models and application scenarios of most manufacturers have become transparent and stable. Generally speaking, the price of imported RO membrane is slightly more expensive than that of domestic RO membrane, but it has slight advantages in terms of stability, service life, core indicators (desalination rate, water yield, recovery rate) and so on.

Data reference vendor : HID, Times Huitong, Dow, Hydeneng, Shihan

• Product type (application scenario):

Ultra-low pressure membrane element: ultra-low pressure RO membrane element can be selected for inlet water TDS≤1000mg/L (ppm), which is suitable for salt concentration food production, municipal water, pure water preparation, irrigation water, second-stage water supply of two-stage membrane system and other industrial applications.

Ultra-low pressure membrane element: ultra-low pressure RO membrane element can be selected for inlet water TDS≤1500mg/L, which is suitable for desalination treatment with municipal tap water and groundwater as raw water.
   Low-pressure (brackish water) membrane element: brackish water RO membrane element can be selected for 2000≤TDS≤5000mg/L inlet water, which is suitable for desalination treatment of surface water, groundwater, reclaimed water as raw water, and desalination of brackish water.

Low (anti-) pollution membrane element: 2000≤ TDS≤8000mg/L inlet water can choose anti-pollution RO membrane element, suitable for electric power, steel, electroplating, petrochemical, coal chemical, printing and dyeing, papermaking, landfill leachate and other wastewater treatment and reclaimed water reuse projects.

Seawater membrane element: seawater desalination RO membrane element can be selected for influent TDS≥10000mg/L, which is suitable for water treatment industries such as high salt concentration solution or wastewater concentration, seawater desalination, (near) zero discharge, etc.

• Different series of use scenarios

XLP series: very low pressure membrane element, generally suitable for the treatment of low salt water sources with low salt content requirements for low desalination rate, such as surface water, groundwater, tap water and municipal water with a salt content of less than 1000ppm, especially suitable for the second stage desalination of two-stage reverse osmosis lure. It is mainly used in various fields such as purified water of various scales, boiler make-up water, food processing and pharmaceutical manufacturing industries.

ULP series: ultra-low pressure membrane element, generally suitable for desalination treatment of surface water, groundwater, tap water and municipal water with a salt content of about 2000ppm or less, mainly used in packaged water, drinking water, boiler supply water, food processing and pharmaceutical manufacturing industry and other fields.

LP series: low-pressure membrane element, generally suitable for brackish water with a salt content of less than 10,000ppm, surface water, groundwater, tap water and other water sources desalination, mainly used in various scales of packaged water, drinking water, industrial pure water, high purity water, boiler feed water preparation, can also be used for wastewater reuse, material concentration, purification and refining and other purposes.

AF series: anti-fouling membrane element, generally suitable for desalination treatment of complex feed water with a salt content of less than 10000 ppm, mainly used for desalination and pure water production of various lakes and rivers water, mine water, municipal reclaimed water, industrial wastewater, RO concentrated water, etc.

SW series: seawater membrane element, generally suitable for the treatment of seawater and high-concentration Kuwei water, can be used for seawater desalination, high-concentration Kuwei water desalination, power generation boiler feed water and other industrial water treatment, can also be used for wastewater reuse, food and drug and other high value-added substances concentration and recovery and other application fields.

• Basic data of reverse osmosis membrane

Salt rejection rate: The desalination rate of the RO membrane element has been determined at the time of its manufacturing, and the desalination rate depends on the density of the ultra-thin desalination layer on the surface of the RO membrane element, the denser the desalination layer, the higher the desalination rate, and the lower the water production. The desalination rate of RO membrane for different substances is mainly determined by the structure and molecular weight of the substance, the desalination rate of high-valent ions and complex monovalent ions can exceed 99%, and the desalination rate of monovalent ions such as sodium ions, potassium ions, and chloride ions is slightly lower, but it can also exceed 98% (the longer the RO membrane is used, the more times of chemical cleaning, the lower the desalination rate of RO membrane) The removal rate of organic matter with a molecular weight greater than 100 can also be over 98%, but the removal rate of organic matter with a molecular weight of less than 100 is lower.

Calculation method of salt rejection rate and salt permeability of RO membrane:

Salt permeability of RO membrane = RO membrane permeate concentration/influent water concentration ×100%

Desalination rate of RO membrane = (salt content of permeate water / salt content of influent water of 1-RO membrane) ×100%

Water Production: GPD = Gallons (US)/Day, GFD = Gallons (US)/per square foot/day

Water yield of RO membrane – refers to the water yield capacity of the RO system, i.e., the amount of water passing through the RO membrane per unit of time, usually expressed in tonnes per hour or gallons per day. 1 gallon (US) = 3.785 liters, 1 cubic meter = 264.2 gallons (US).

The permeability of the RO membrane is also an important indicator of the water yield of the RO membrane element. Refers to the flow rate of permeate per unit membrane area, usually expressed in gallons per square foot per day (GFD). Excessive osmotic flow rate will lead to an accelerated water flow rate perpendicular to the surface of the RO membrane, which will exacerbate membrane fouling.

Pressure (optimum working pressure): 1 kg pressure = 1 bar ≈ 14.5 psi = head 10m (pump)

PSI (Pounds per square inch) is a unit of measurement. P refers to pound, S refers to square, I refers to inches, and the United States is used to use psi as a unit, which means pound-force per square inch.

The operating pressure of RO membranes is usually between 2-20MPa, depending on factors such as the type, size, material, and water quality of the membrane element. In general, the higher the operating pressure of the RO membrane, the higher the desalination efficiency, but it also increases the risk of element wear and membrane fouling. Therefore, the working pressure of the RO membrane needs to be controlled within a reasonable range to ensure its stability and life

In practical applications, the operating pressure of RO membranes needs to be adjusted according to water quality and treatment requirements. For example, in seawater desalination, the working pressure of RO membranes is usually between 5-10MPa to achieve high desalination efficiency and long life. In industrial wastewater treatment, RO membranes can work at higher pressures to cope with complex water quality and higher concentrations of salt.

Recovery Rate: RO membrane recovery – refers to the percentage of feed water in the RO membrane system that is converted into permeate or permeate. It is determined according to the quality of the pretreated influent water and the water requirements of the RO system. The recovery rate of the RO membrane system is determined at the time of design.
Recovery rate of RO membrane = (permeate flow rate of RO membrane / influent flow) ×100%