RO antiscalant is dosed upstream of the membranes to reduce precipitation of sparingly soluble salts as feedwater becomes concentrated in the reject stream. The correct product and dose depend on feedwater analysis, recovery, pH, temperature and membrane-system design.
Do not choose dose from a generic rule
A typical-looking ppm value does not mean it is correct for every water. Antiscalant selection should be supported by a projection or scaling calculation using the actual feed analysis and planned recovery.
Converting dose to consumption
Once an approved dose is known, the active/product calculation follows the same method as other chemicals:
Product kg/hr = Flow (m³/hr) × Dose (mg/L) ÷ 1000 ÷ Product fraction
For a liquid product, divide kg/hr by density to obtain L/hr.
Injection point
Antiscalant should be thoroughly mixed before the membrane array and generally upstream of final cartridge filtration according to the system design. Poor mixing or intermittent feed can create periods of inadequate protection.
What to monitor
- Dosing pump output and calibration.
- Chemical tank consumption versus expected usage.
- Feed pH and conductivity/TDS.
- RO recovery and concentrate chemistry.
- Normalized permeate flow and differential pressure.
Overfeed is not a universal solution
Excessive antiscalant adds cost and may interact with other treatment chemicals. If scaling continues, investigate feed analysis, pH, recovery, pretreatment performance and actual dosing before simply increasing the setpoint.