Nanofiltration (NF) is a pressure-driven membrane process between ultrafiltration and reverse osmosis. Its molecular weight cut-off is typically in the range of several hundred to one thousand daltons. It maintains high rejection of divalent and multivalent ions while allowing some monovalent ions to pass, so it is often used for softening, decolorization, and separation and concentration of materials.
Separation Principle
- The separation mechanism combines sieving effects and charge repulsion (Donnan effect), with significantly higher rejection of divalent ions than monovalent ions.
- Operating pressure is lower than that of reverse osmosis, and energy consumption is usually lower than that of reverse osmosis when treating the same volume of water.
- It enables desalination without complete salt removal and is suitable for material separation scenarios where some monovalent salts need to be retained.
Product Features
- It has high rejection of divalent ions such as sulfate, calcium, and magnesium, and can be used for water softening and hardness control.
- It effectively removes macromolecular organics, pigments, and some COD, significantly improving product water color.
- Operating pressure and operating energy consumption are lower than those of reverse osmosis, and system configuration and operating costs are relatively moderate.
- It can be combined with ultrafiltration and reverse osmosis to form a staged membrane process, balancing recovery rate and effluent quality.
Application Industries
- Salt fractionation in high-salinity wastewater and separation and enrichment of monovalent/divalent ions.
- Decolorization, COD removal, and concentration and recovery of printing and dyeing, dye, and fine chemical mother liquors.
- Softening, nitrate removal, and removal of trace organics in drinking water and industrial water.
- Separation, purification, and concentration of functional materials in the food and pharmaceutical industries.
Specifications and Models
| Parameter | Unit | Typical value |
|---|---|---|
| Molecular weight cutoff | Da | 200–1000 (typical) |
| Divalent ion rejection | % | 90–98 (typical) |
| Operating pressure | MPa | 0.5–2.0 (typical) |
| Operating temperature | ℃ | 5–45 (typical) |
| Applicable pH range | — | 3–10 (typical, depending on material) |
| Feed water SDI₁₅ requirement | — | ≤ 5 (typical) |
The data in the table are common ranges for similar equipment and are for selection reference only; specific specifications, models, materials, connections, and control methods must be confirmed during the selection stage based on water quality, treatment scale, and site conditions.