Reverse osmosis membrane

Reverse osmosis membranes are artificial semipermeable membranes with specific properties that mimic biological semipermeable membranes. They are the core component of reverse osmosis technology. The principle of reverse osmosis technology is that, under the influence of an osmotic pressure exceeding that of the solution, substances cannot pass through the semipermeable membrane, thus separating these substances from water. The reverse osmosis membrane's very small pore size effectively removes dissolved salts, colloids, microorganisms, and organic matter from water. The system offers advantages such as high water quality, low energy consumption, zero pollution, simple process, and easy operation.

 Reverse osmosis membranes should have the following characteristics: (1) high desalination rate at high flow rate; (2) high mechanical strength and service life; (3) ability to function at low operating pressure; (4) ability to withstand the effects of chemical or biochemical reactions; (5) less affected by factors such as pH value and temperature; (6) easy to obtain raw materials for membrane production, simple processing, and low cost.

Performance Indicators

Desalination Rate

Desalination Rate = (1 – Product Water Salt Content / Influent Salt Content) × 100%

The salt rejection rate of a membrane element is determined during its manufacture. The salt rejection rate depends on the density of the ultra-thin desalination layer on the membrane element's surface. The denser the desalination layer, the higher the salt rejection rate, but also the lower the water yield. The salt rejection rate of reverse osmosis for different substances is primarily determined by the substance's structure and molecular weight. The salt rejection rate for high-valent ions and complex monovalent ions can exceed 99%. The salt rejection rate for monovalent ions such as sodium, potassium, and chloride is slightly lower, but can also exceed 98%. (The longer the membrane is used and the more chemical cleanings are performed, the lower the reverse osmosis membrane's salt rejection rate.) The salt rejection rate for organic compounds with a molecular weight greater than 100 can also reach 98%, but the removal rate for organic compounds with a molecular weight less than 100 is lower.

Permeation Rate

Water flux refers to the water production capacity of a reverse osmosis system, that is, the amount of water that passes through the membrane per unit time, usually expressed in tons/hour or gallons/day.

Salt permeation rate refers to the amount of salt that passes through a unit membrane area per unit time, also known as salt permeability or salt flux.

Recovery Rate

Recovery rate refers to the percentage of feed water converted into product water or permeate in a membrane system. It depends on the quality of the pretreated influent and water requirements. The recovery rate of a membrane system is determined during design.

Recovery rate = (product water flow rate / influent flow rate) × 100%