Treatment process
Nanofiltration
A looser membrane than reverse osmosis that rejects divalent ions and larger organics while passing much of the monovalent salt — useful where the goal is softening and organics removal rather than desalination.
Key facts
- Scale
- Municipal
- Treatment stage
- Membrane separation
How it works
Operates at lower pressure than RO. Rejects calcium, magnesium, sulphate and organic molecules above roughly 200–1,000 daltons, while sodium and chloride pass more freely.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Hardness | Sodium and chloride, substantially |
| 2 | Colour and natural organic matter | Nitrate, only partially |
| 3 | Sulphate | — |
| 4 | Pesticides and many micropollutants | — |
| 5 | Most PFAS | — |
Trade-offs
- Lower energy than RO for the same softening duty
- Still produces a concentrate stream
- Product water needs stabilising before distribution
Related intelligence
Reverse osmosissame topicChlorinationsame topicGranular activated carbonsame topicCombined sewer overflowsame topicIon exchange softeningsame topicUltraviolet disinfectionsame topicCoagulation and flocculationsame topicActivated sludgesame topicRapid gravity filtrationsame topicChloraminationsame topicDistillationsame topicSlow sand filtrationsame topic
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted
- American Water Works Association — AWWA standards, water audits and utility benchmarking. Public but restricted · Publisher terms — public access, reuse not clearly granted