Poly dosing and pump Selection calculator

Design Philosophy

Polyelectrolytes (polymers) are high-molecular-weight organic chemicals used as conditioning agents in sludge dewatering processes. They act by neutralizing the surface charge of sludge particles (for cationic polymers) or by bridging particles together, promoting the formation of larger, denser flocs that release water more readily under mechanical pressure or centrifugal force. The correct polymer dose is critical: under-dosing results in poor dewatering performance, while over-dosing is wasteful and can lead to sticky cake that blinds filter media.

Polymer is typically prepared as a dilute working solution (0.1–0.5% w/v) from a concentrated stock solution or neat emulsion polymer, and is dosed inline into the sludge feed pipe just upstream of the dewatering equipment. The dosing rate is expressed in grams of active polymer per kilogram of dry solids (g/kg DS), which is the standard basis recommended by Metcalf & Eddy and BWWT (TU Delft).

Polymer Dosing Rate

The volume of working polymer solution required per hour is:

Dosing Pump Selection

Dosing pumps for polymer service are typically progressive cavity or diaphragm metering pumps. The pump capacity is selected to match the maximum calculated dosing rate with a 10% margin, and is sized for a discharge pressure of 1.5 to 3.0 bar depending on the inline static pressure and pipe friction losses to the injection point.

Dilution Water Requirement

Where emulsion or dry polymer is used, a dilution water supply must be provided to prepare the working solution. The dilution water flow rate is the difference between the total working solution volume and the neat polymer volume dosed.

Solution Preparation Tank

The capacity of the polymer preparation and aging tank is sized to provide a minimum of 4 to 8 hours of storage at the design dosing rate, as recommended by Metcalf & Eddy. This ensures continuity of operation during polymer batch preparation and allows sufficient aging time for the polymer to fully hydrate.

(Source: Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th Ed.; BWWT Course — TU Delft)

Calculator

(Note – all Yellow are user defined value, all white are fixed values, all green are calculated value, all orange is calculated not to be shown)

Instructions

Enter values highlighted in the Yellow

Green highlights are the results

In case of any invalid result of non-functioning of the calculator, please write to us at design@swaenviro.com. We will try and help you with your sizing and calculation

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