Controlled injection of antiscalants, scale inhibitors and acid keeps reverse-osmosis membranes, cooling circuits and boilers free of carbonate, sulphate and silica scale. Get the dose wrong and you either foul the membrane or waste expensive chemical — so antiscalant dosing is a precision, continuous duty that rewards good pump selection and tight control.
Antiscalants are threshold inhibitors — they work at doses far below the stoichiometric scaling load, distorting crystal growth so sparingly-soluble salts stay in solution past their saturation point. Typical RO doses sit at 2–5 mg/L on the feed, dosed continuously and flow-paced. Under-dose and scale builds on the last membrane elements where concentration is highest; over-dose and you waste chemical, risk biofouling on the phosphonate, and can even nucleate the very scale you are trying to prevent. The dose is set from a projection of the feed-water saturation indices and confirmed against the membrane supplier's antiscalant model — then held precisely on the live plant. See how this sits inside RO protection and RO optimisation.
| Inhibitor type | Targets | Notes |
|---|---|---|
| Phosphonates | CaCO₃, CaSO₄, BaSO₄ | Workhorse RO antiscalant; broad scale coverage |
| Polyacrylates / polymers | CaCO₃, metal oxides, particulates | Dispersant action; good for colloidal fouling |
| Polymaleic / co-polymers | Silica, calcium phosphate | For high-silica and phosphate-laden feeds |
| Acid (H₂SO₄ / HCl) | Carbonate scale (via LSI) | Lowers pH to depress carbonate saturation |
| Scale/corrosion inhibitor blends | Scale + corrosion (cooling) | Cooling-water duty; combined programmes |
Check wetted-material compatibility → · Storage & containment
Dose is proportioned to feed flow so concentration stays constant through turndown — the basis of reliable inhibition.
Clean, neat inhibitor suits a motor-driven diaphragm pump with calibration column — high accuracy at low flow.
Injected upstream of the cartridge filter with a quill for instant dispersion — never into a dead leg.
Loss-of-dose alarm and RO high-pressure-pump interlock prevent running membranes unprotected.
Most antiscalant is dosed neat for stability; dilution only where very low flows need pump turndown headroom.
Periodic drawdown checks against the calibration column confirm actual dose — see calibration & verification.
Dosing equations · System sizing · Overdosing troubleshooting
Send us the feed-water analysis and recovery target — we will project the saturation indices, set the antiscalant dose and build the dosing skid to hold it.
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