Why do desalination membranes require high pressure?

　　Desalination membranes require high pressure primarily because reverse osmosis technology must overcome the high osmotic pressure of seawater, forcing water molecules to pass through the membrane pores while retaining salt ions. The pressure generated by the weight of seawater itself is far from sufficient to meet this demand; therefore, a high-pressure pump must be used to provide adequate external pressure and flow rate.

　　The role of osmotic pressure

　　A desalination membrane is a semipermeable membrane that allows only water molecules to pass through while blocking impurities such as salts and colloids. Because seawater has a high concentration of dissolved solutes like salts, its natural osmotic pressure is relatively high. To produce freshwater, an external pressure greater than this osmotic pressure must be applied; otherwise, water molecules will not be able to cross the membrane pores against their concentration gradient.

　　Function of the high-pressure pump

　　Provide sufficient pressure: The high-pressure pump overcomes osmotic pressure through mechanical boosting, ensuring that water molecules continuously pass through the membrane pores into the freshwater side, while salts remain on the high-pressure side.

　　Regulating flow: The high-pressure pump maintains a stable flow rate through frequency conversion control, ensuring desalination efficiency. If the flow rate is insufficient, it may lead to overload of the membrane elements or a decrease in water production.

　　Technical limitation: The pressure generated by the weight of seawater itself is extremely low—around 0.1 MPa—far below the pressure required by reverse osmosis membranes (which typically need more than 0.3 MPa). Therefore, it is essential to rely on external pressurization equipment.