How it works
- the selective membrane — NF sits between UF and RO. Its pores and surface charge reject divalent ions strongly — calcium, magnesium, sulphate — while letting a good share of sodium and chloride through. That selectivity is the entire point.
- 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.
- 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.
- 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.
Design parameters
The panel opposite runs the same correlations as the NF-590 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Feed flow — m³/h
- Feed hardness — mg/L CaCO₃
- Feed chloride — mg/L
- Recovery — %
- Divalent rejection — %
- Monovalent rejection — %
Open the full NF-590 design sheet for the governing equations, the accepted design envelopes and the worked calculation.