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Nanofiltration
NF Membranes — Nanofiltration Modules
NF membranes separate at roughly 200 to 1,000 daltons, rejecting divalent ions such as calcium, magnesium and sulphate at 90 to 98 percent while passing 20 to 80 percent of monovalent salt. They suit softening, colour and COD reduction where full desalination is not wanted.
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Answer first
What NF Membranes Are, and How They Are Specified
NF membranes separate at roughly 200 to 1,000 daltons, rejecting divalent ions such as calcium, magnesium and sulphate at 90 to 98 percent while passing 20 to 80 percent of monovalent salt. They suit softening, colour and COD reduction where full desalination is not wanted.
Nanofiltration occupies the gap between ultrafiltration and reverse osmosis, and its defining characteristic is selectivity rather than rejection. It discriminates strongly between divalent and monovalent ions, which is what makes it useful for softening and colour removal while leaving a mineral profile intact.
That selectivity is also the trap. NF is frequently specified as a lower-pressure reverse osmosis, and on a feed whose problem is sodium chloride it simply passes most of it.
Specification
NF module specification
| Parameter | Typical value or range | Notes |
|---|---|---|
| Molecular weight cut-off | Roughly 200–1,000 Da | Between UF and RO |
| Divalent ion rejection | 90–98 % | Ca²⁺, Mg²⁺, SO₄²⁻ |
| Monovalent salt rejection | 20–80 % retained | Much of the NaCl passes |
| Operating pressure | 5–15 bar | Lower than RO for comparable flux |
| Colour and larger organics | Substantially removed | A common driver in textile and surface water duty |
| Module format | Spiral wound, standard element sizes | Fits standard pressure vessels |
| Free chlorine tolerance | Effectively nil on polyamide | Same protection as RO is required |
Molecular weight cut-off
- Typical value or range
- Roughly 200–1,000 Da
- Notes
- Between UF and RO
Divalent ion rejection
- Typical value or range
- 90–98 %
- Notes
- Ca²⁺, Mg²⁺, SO₄²⁻
Monovalent salt rejection
- Typical value or range
- 20–80 % retained
- Notes
- Much of the NaCl passes
Operating pressure
- Typical value or range
- 5–15 bar
- Notes
- Lower than RO for comparable flux
Colour and larger organics
- Typical value or range
- Substantially removed
- Notes
- A common driver in textile and surface water duty
Module format
- Typical value or range
- Spiral wound, standard element sizes
- Notes
- Fits standard pressure vessels
Free chlorine tolerance
- Typical value or range
- Effectively nil on polyamide
- Notes
- Same protection as RO is required
Typical ranges across the membrane class. Final values follow the datasheet of the element quoted.
Selection guidance
Specify NF against an ion breakdown, never against TDS
TDS is a single number that hides the composition NF actually acts on. A feed at 1,500 ppm TDS that is mostly calcium and sulphate is an excellent NF candidate; the same 1,500 ppm as sodium chloride is a poor one, because most of it will pass.
Ask the laboratory for the ionic breakdown — calcium, magnesium, sodium, sulphate, chloride and bicarbonate — before deciding between NF and RO. The split between divalent and monovalent species is the whole decision.
Application mapping
Where NF Membranes Are Used
Softening without desalination
- Typical requirement
- Hardness reduced, mineral character retained
- Indicated configuration
- NF sized against the divalent fraction of the feed
Textile and dye effluent
- Typical requirement
- Colour and COD reduction
- Indicated configuration
- NF behind UF, with recovery set from sulphate saturation
Surface water with colour
- Typical requirement
- Organic colour removal at moderate pressure
- Indicated configuration
- NF after clarification and UF
Commercial terms
How This Category Is Quoted
Water treatment does not have a list price, and any supplier quoting one before seeing a feed analysis is quoting a different plant from the one you need.
Pricing basis
On request, and capacity-dependent. Plant pricing moves with capacity, feed water analysis and the recovery target; membranes, cartridges and resins are quoted per element, per lot or per litre of media.
Order quantity
From a single replacement element or a case of cartridges through to full plant scope. Consumable lines are quoted per box or per lot, and the lot size is stated on the quotation.
Lead time
Confirmed per line item at quotation stage. Stocked consumable lines and made-to-order plant differ substantially, so a single blanket lead time for the category would be misleading — the quotation carries the figure for each line.
Invoicing
GST invoice against company or institutional purchase order. Proforma issued where advance payment or internal approval requires it.
Delivery coverage
Despatch from Delhi NCR across India, including plant, project and institutional sites. Delivery city and site access are asked for at enquiry because both affect despatch mode.
Documentation
Technical datasheet for the item quoted, and a test certificate where the principal supplies one with that product. Tender and institutional documentation formats are prepared on request — send the format with the enquiry so the quotation is issued in a form you can submit without rework.
Request for quotation
Request a Quote — NF Membranes
Fields marked with an asterisk are required. The technical fields are what usually decide whether you get a quotation on the first pass or three emails of clarification.
Frequently asked
NF Membranes — Common Questions
What is the difference between NF and RO?
Selectivity. NF rejects divalent ions at 90 to 98 percent but passes 20 to 80 percent of monovalent salts. RO rejects both at 96 to 99.8 percent.
NF runs at lower pressure — 5 to 15 bar against 10 to 17 bar for brackish RO — which is why it looks attractive. The saving is only real if passing monovalent salt is acceptable in your product water.
Can nanofiltration replace a softener?
It can, and it does so without salt regeneration or the associated effluent. NF removes calcium and magnesium at 90 to 98 percent along with sulphate.
The comparison should include membrane replacement and cleaning against salt and regeneration cost over the plant life, and whether the monovalent passage is acceptable downstream.
Does NF need the same chlorine protection as RO?
Yes, where the membrane is polyamide, which most spiral NF elements are. Free chlorine oxidises the film and the damage is not reversible by cleaning.
Carbon or SMBS dosing ahead of the module, plus a downstream free-chlorine check, applies exactly as it does for RO.
Related Products and Categories
Specified alongside nf membranes, and the category this page sits in.
UF membranes upstreamBrackish water RO membranes for full desalinationIon exchange resins as an alternative to softeningBack to Membrane Filtration
- Delhi NCR base with pan-India supply, including plant and project sites.