Governing Formula & Concentration Basis
Antiscalants and coagulants are supplied as concentrated products that are diluted into the membrane feed. The active mass rate is set by the feed flow and the target dose, and the product pumping rate corrects for both product strength and density.
Qprod = Qf × Cd / (1000 × ρ × s) Where:
-
Qf= Feed flow rate dosed with the chemical [m³/h] -
Cd= Target dose concentration as product in the feed stream [mg/L] -
s= Product strength (fraction of active ingredient in the product) [%] -
ρ= Product density at pumping temperature [kg/L] -
Qprod= Required product dosing rate [L/h]
Derived Equations:
M = Qf × Cd / 1000 Qprod = M / (ρ × s) Vday = Qprod × 24 The dose is interpreted as product: the concentration delivered to the feed corresponds to the volume of product after dilution. When a strength is supplied, the true active dose delivered is Cd × s.
How to Use This Calculator
- Enter the feed flow being dosed (membrane feed from the high-pressure pump suction).
- Enter the target dose — typically 1.5–5 mg/L as product for antiscalant.
- Enter the product strength (100% for ready-to-use, 40–60% for dilute blends).
- Leave density at 1.0 for aqueous products, or adjust to 1.1–1.3 for concentrated blends.
Interpreting Results
The result is the chemical feed pump flow (L/h) plus daily consumption volume — the two values you need to size the dosing skid and the chemical inventory. The active-dose row confirms the true ppm delivered.
Accuracy Limits & Design Notes
- Assumes continuous steady dosing at constant feed flow; real plants use flow-paced pumps.
- Product density varies with temperature — use the datasheet value at operating temperature.
- Dose recommendations are membrane-manufacturer-specific; always confirm against the approved product program.
Frequently Asked Questions
What is a typical antiscalant dose?
Most phosphonate or polyacrylate antiscalants are dosed at 1.5–5 mg/L as product. The exact dose is set by the LSI of the brine and is confirmed by membrane manufacturers via their dosing programs.
Why does product strength matter?
A 40% strength product contains only 0.4 kg of active ingredient per liter, so you pump 2.5× more volume than a 100% product to deliver the same active mass.
Can this calculator size my dosing pump?
Yes — the product flow in L/h at full stroke, multiplied by a turndown safety factor (typically 150%), gives the pump rated capacity. Pair output with the concentrate flow at maximum recovery.
Engineering Disclaimer
Engineering Note: This calculator provides simplified engineering estimates for preliminary analysis and educational use. Actual RO system performance depends on membrane type, feedwater chemistry, temperature, pressure, recovery, concentration polarization, pretreatment, and operating conditions. Final system design should be verified using manufacturer data, validated design software, applicable standards, and qualified engineering review.
Technical References
- DuPont FilmTec™ Reverse Osmosis and Nanofiltration Technical Manual (Form No. 45-D01504-en).
- AWWA Manual M46: Reverse Osmosis and Nanofiltration, American Water Works Association.