Low-pressure membrane barrier that removes colloids, bacteria and suspended solids ahead of RO or NF, quantified by membrane area, TMP and flux condition.
- Active
- Available
Nanofiltration NF
Loose-rejection membrane separation between UF and RO, used for hardness reduction and partial demineralisation before an RO stage.
Overview
Loose-rejection membrane separation between UF and RO, used for hardness reduction and partial demineralisation before an RO stage.
How it works
Separation mechanism and feed window. Operates between UF and RO in rejection. It removes divalent ions preferentially but passes much of the monovalent load, so it is not a desalination step on its own.
What the process produces. A partially demineralised permeate. NF concentrates hardness, so the concentrate stream carries most of the removed load.
Energy. Low to moderate pressure — intermediate between UF and RO.
Process sequence
Where this technology normally sits in a treatment train. The steps either side of it are documented in the Library as separate entries.
- Pretreatment
- Nanofiltration (NF)
- Primary separation (RO)
Typical applications
- Partial demineralisation of brackish or hard water
- Hardness reduction ahead of RO to lower carbonate scaling load
- Chloride and sulphate reduction where full desalination is unnecessary
Main equipment
- NF membrane element or module
- NF feed pump
- Concentrate recirculation or reject handling
- Control and instrumentation
Key design parameters
The parameters an engineer actually sets, and why each one drives the design. EngiMetric does not assume any of them.
| Parameter | Why it matters |
|---|---|
| Recovery | Sets permeate and concentrate split. |
| Solute rejection | Sets how much of each species passes; NF is selective, not neutral. |
| Permeate flux | With recovery, sets required membrane area. |
Advantages
- Targets the ions that dominate scaling load.
- Lower pressure than RO for the same recovery on suitable water.
- Can replace part of an RO train where softening alone would be used.
Limitations
- Not a substitute for RO where full desalination is required.
- Selectivity is species- and pH-dependent, so generic rejection figures mislead.
- NF concentrates hardness into a smaller stream.
Engineering considerations
- Enter measured feed and product TDS; the balance is only meaningful when both are known.
- Concentrate TDS is derived by salt conservation and must be checked for saturation.
Status and EngiMetric support
Industry maturity and commercial status describe the technology itself. EngiMetric support and quantitative modeling describe what this platform does with it — and those two are read from the engineering registry at build time, so they cannot drift from the code.
- Engineering maturity
- Established How established the technology is in the industry. Not an EngiMetric claim.
- Commercial status
- Commercial Where the technology sits in the market. Not an EngiMetric claim.
- EngiMetric support
- Active Derived from the execution registry: nf is registered as supported.
- Design engine
- Planned Whether the Plant Designer can carry this as a configured process step.
- Quantitative modeling
- Available Derived: 2 of 2 registered capabilities run a deterministic engine.
What EngiMetric computes
These capabilities are registered in the EngiMetric execution registry. Each one runs a deterministic engine, so every result is reproducible from the inputs you supply.
- NF water and solute balance calculateNfBalance
- NF membrane area calculateNfMembraneArea
Related tools
Every tool below exists and is live. EngiMetric does not duplicate a formula here — the calculation lives in the tool, and this page links to it.
- Nanofiltration (NF) Membrane Engineering NF water and solute balance from recovery and rejection, then membrane area from the permeate flux.
- RO Scaling Risk & Pretreatment Analysis Saturation screening on the NF concentrate and the following RO feed.
- Water Analysis & Treatment Selection Feed chemistry and hardness that drive NF selectivity and scaling load.
Sources and references
- Rejection — Measured or manufacturer value; never assumed by EngiMetric.
EngiMetric does not publish a bibliography of external literature for catalogued technologies. Where a figure is required, it is entered by the engineer from a datasheet or a published reference, and it is labelled as an input.