Low-pressure reverse osmosis membranes are reverse osmosis membrane elements operating at relatively low pressures. Their operating pressure range is typically between 1-10 bar (approximately 0.1-1 MPa), with ultra-low-pressure models capable of operating at 0.3-0.7 MPa. These membrane elements are composed of cross-linked aromatic polyamide, polysulfone, and polyester nonwoven fabric. Their working principle involves applying pressure to drive water molecules to permeate in the reverse direction, thereby removing contaminants such as calcium, magnesium, heavy metal ions, and organic fluoride compounds from the water. This membrane has desalination capabilities for brackish water, surface water, and groundwater with a salinity below 10,000 ppm, achieving a desalination rate of up to 99.5%. Industrially, low-pressure reverse osmosis membranes are mainly used for producing high-purity water, boiler feedwater, and packaged drinking water, with applications spanning the electronics and power industries, as well as wastewater reuse.
The operating pressure of the reverse osmosis process is determined by the osmotic pressure of the aqueous solution and the performance of the reverse osmosis membrane. When a reverse osmosis membrane performs well, it can achieve a permeation rate close to the theoretical calculation and a high desalination rate as long as the operating pressure is slightly higher than the osmotic pressure. This is considered an ideal low-pressure reverse osmosis membrane. Another type, ultra-low-pressure reverse osmosis membranes, are used for aqueous solutions with very low salt content. Because their osmotic pressure is already very low, the operating pressure is also low. Currently, industrial low-pressure reverse osmosis membranes are used for desalination of aqueous solutions with a salt content of approximately 1×10⁻³, with an operating pressure range of 1-10 bar (approximately 0.1-1 MPa). As the operating pressure decreases, the permeation rate decreases exponentially, and the desalination rate decreases by percentage points. According to GB/T 32373-2025 standard, the test conditions for low-pressure reverse osmosis membranes are: sodium chloride concentration 1500±20 mg/L, test pressure 1.03±0.02 MPa, applicable water flux 20~25 L/(m²·h), and application field is general industrial water.
