NF-590Nanofiltration — Selective Rejection and Softening

How it works

1. The selective membrane — NF sits between UF and RO. Its pores and surface charge reject divalent ions strongly — calcium, magnesium, sulfate — while letting a good share of sodium and chloride through. That selectivity is the entire point.
2. Why that matters — Hardness is what scales your heat exchangers and ruins your boilers. Chloride mostly does not. Rejecting only what you need to reject means far less osmotic pressure to overcome, so NF runs at 4–10 bar where RO would need 15–25.
3. Along the element — Same concentration effect as RO, but the two species diverge. Divalent concentration climbs steeply toward the tail while monovalent barely moves. The scaling limit arrives before the osmotic limit — which is why antiscalant, not pressure, sets the recovery.
4. What governs it — Recovery against concentrate hardness is the binding pair. Drag recovery up and watch concentrate hardness run away while permeate quality barely improves — you are buying scaling risk for nothing. Antiscalant dose and recovery are one decision.
5. The 8-inch spiral element — The industry standard: 37 m² a piece, six or seven to a vessel, and every supplier makes one that fits. Feed spacer channels are under a millimetre, so the feed must arrive clarified with an SDI below 5 — there is no backwash to recover from a mistake.

Design parameters

The panel opposite runs the same correlations as the NF-590 design sheet, so the animation and the calculator cannot disagree. Every parameter below is live — drag one and the picture responds.

Open the full NF-590 design sheet for the other seven inputs, all thirty-three results with their envelopes, the six equations printed beside the numbers they produce, and a calculation record you can export and put in a design file.