Polyelectrolyte dosing calculation and calculator
Polyelectrolyte dosing calculation takes three numbers: your flow, the dose in mg/L and the strength of your polymer solution. Enter them below to get kilograms per day, the pump setting and the cost per litre treated.
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Mixing tank
Polymer cost per litre of water
How polyelectrolyte dosing calculation works
Every polyelectrolyte dosing calculation comes down to three formulas. The calculator above does them for you, but it helps to know what it is doing.
| You want | Formula |
|---|---|
| Polymer per day (kg/day) | Flow (m³/day) × dose (mg/L) ÷ 1,000 |
| Solution per day (litres/day) | Polymer (kg/day) × 1,000 ÷ solution strength (g/L) |
| Pump setting (litres/hour) | Solution per day ÷ hours the plant runs |
Worked example: a 500 m³/day ETP
A jar test shows 2 mg/L of Sunfloc Anionic HQ gives a clear clarifier. Polymer per day is 500 × 2 ÷ 1,000 = 1 kg/day. Made up at 0.1 percent (1 g/L), that is 1 × 1,000 ÷ 1 = 1,000 litres of solution a day. Over 24 hours the dosing pump runs at about 42 litres an hour. One 25 kg bag lasts about 25 days.
Quick reference: polymer use in kg/day
| Flow (m³/day) | 0.5 mg/L | 1 mg/L | 2 mg/L | 3 mg/L |
|---|---|---|---|---|
| 100 | 0.05 | 0.1 | 0.2 | 0.3 |
| 250 | 0.125 | 0.25 | 0.5 | 0.75 |
| 500 | 0.25 | 0.5 | 1 | 1.5 |
| 1,000 | 0.5 | 1 | 2 | 3 |
| 2,000 | 1 | 2 | 4 | 6 |
| 5,000 | 2.5 | 5 | 10 | 15 |
Sludge dewatering is calculated differently
For belt presses, centrifuges and filter presses, polymer is measured in kilograms per tonne of dry solids rather than mg/L of water. Multiply the dry solids you press each day (tonnes) by the dose (kg per tonne) to get kilograms per day. See sludge dewatering polymer and our dosing guide for typical ranges.
Polyelectrolyte dosing calculation: questions
How do you calculate polyelectrolyte dosing?
Multiply the flow in cubic metres per day by the dose in mg/L and divide by 1,000. The answer is the polymer you need in kilograms per day. For example, 500 m³/day at 2 mg/L needs 1 kg of polymer a day.
What dose of polyelectrolyte is typical?
For clarification after a coagulant, anionic grades usually start between 0.1 and 3 mg/L. For sludge dewatering, cationic grades are measured per tonne of dry solids instead. Always confirm the dose with a jar test on your own water.
What strength should the polymer solution be?
Most plants make up granular polyelectrolyte at 0.1 to 0.5 percent (1 to 5 g/L), below the grade's maximum use concentration. A weaker solution mixes into the water more easily; a stronger one needs a smaller tank.
How do I set the dosing pump?
Divide the kilograms per day by the solution strength in grams per litre to get litres of solution per day, then divide by the hours the plant runs. At 1 kg/day and 1 g/L, that is 1,000 litres a day, or about 42 litres an hour over 24 hours.
Are mg/L and ppm the same?
Yes. For water treatment, mg/L, ppm and grams per cubic metre are the same number.
Reading the results
The suggested doses are a place to start, not a final answer. Two plants with the same flow can need very different amounts of polymer, which is why the dose is settled by a jar test on your own water. Our lab will do that test for you at no cost.
Handy equivalents: mg/L, ppm and grams per cubic metre are the same number. A KLD is one cubic metre, or a thousand litres, a day. At 0.1% strength, every litre of solution carries one gram of polymer.
Not sure which grade suits your water?
Send us a one-litre sample or describe your process. We test it in our lab free of charge and recommend a grade and starting dose.