Reverse osmosis is a filtration membrane separation technology.
The filtration membrane is a semi permeable membrane with a pore size of up to 0.0001um, which filters minerals and microorganisms from water. Impurities in water such as soluble solids, organic matter, colloidal substances, and bacteria are intercepted by reverse osmosis membranes, concentrated and removed in the interception solution. First level reverse osmosis can remove over 97% of dissolved solids in raw water. The working principle is to separate pure water from a solution containing solutes using a semi permeable membrane that can only pass through water. At this point, the water on the pure water side spontaneously passes through the semi permeable membrane and enters the solution side, causing the water level on the solution side to rise. This phenomenon is called permeation. When the liquid level rises to a certain height, the pressure on both sides of the membrane reaches equilibrium, and the liquid level on the solution side no longer rises. At this point, there is a pressure difference on both sides of the membrane, called osmotic pressure. If a pressure greater than the osmotic pressure is applied to the solution side, the water molecules in the solution will be squeezed to the pure water side, which is exactly the opposite of osmosis, known as reverse osmosis. Due to the pressure, water molecules in the solution enter pure water, increasing the amount of pure water while the solution itself is concentrated. The principle of reverse osmosis desalination is to apply a pressure greater than natural osmotic pressure, causing the permeation to proceed in the opposite direction, pressing the water molecules in the raw water to the other side of the membrane, thereby achieving the goal of removing salt from water.Reverse osmosis (RO) is an efficient water treatment technology that selectively separates impurities in water under pressure through a semi permeable membrane. It is widely used in fields such as drinking water purification, industrial pure water preparation, and seawater desalination.
The filtration function of reverse osmosis.Reverse osmosis membrane (pore size approximately 0.0001 μ m) can remove the following pollutants:
|Pollutant Type | Removal Rate | Typical Substances |
|———————-|————|————–|
|Dissolved salts (TDS) | 90-99% | NaCl, Ca ² ⁺, Mg²⁺, SO₄²⁻ |
| Heavy metals | 95-99% | Lead (Pb), arsenic (As), mercury (Hg), cadmium (Cd)|
|Bacteria&Viruses |>99.9% | Escherichia coli, Cryptosporidium, Norovirus|
|Organic matter | 90~98% | Pesticide, drug residue, humic acid|
|Colloids&Particles |>99% | Sediments, rust, colloidal silica|
|Radioactive material | 90-95% | Uranium (U), Radium (Ra)|
Filtering mechanism :
Screening effect: extremely small pore size, physically blocking large molecular pollutants.
Charge repulsion: The membrane surface is negatively charged and repels anions (such as Cl ⁻, SO ₄² ⁻).
Dissolution diffusion: Water molecules preferentially pass through the membrane, while soluble impurities are intercepted.
2. Types of water produced by reverse osmosis
According to the inlet water quality and RO system configuration, the produced water can be divided into the following categories:
(1) Drinking water (household/commercial RO)
Features : TDS < 50 ppm， The taste is refreshing, but it may require post mineralization (such as adding calcium and magnesium).
Application : Direct drinking machine, bottled water production.
(2) Industrial pure water&high-purity water
Characteristics: Conductivity<10 μ S/cm (even<1 μ S/cm), requiring combination with EDI (Electrodeionization) or mixed bed polishing.
Application : Semiconductor, pharmaceutical, boiler feedwater.
(3) Desalinated seawater (SWRO)
Characteristics : Inlet TDS 35000 ppm (seawater) → Produced TDS<500 ppm.
Challenge: Requires high pressure (800~1200 psi), anti fouling film, and energy recovery device.
(4) Wastewater reuse water
Features: Treat industrial wastewater (such as electroplating, printing and dyeing) or municipal reclaimed water, with a recovery rate of 50-75%.
Key : Strengthen pre-treatment (UF+RO) to prevent membrane fouling.
Post time: Apr-12-2025