Industry Solutions
How to Size a Chemical Dosing System: Tank Volume, Pump Range, Concentration and Control
Size a chemical dosing system from dose, flow, concentration, pump range, storage time and control - not dosing tank volume alone.
A chemical dosing skid should connect the treatment requirement to the actual chemical feed rate.
The design should consider wastewater flow, required dose, product concentration, prepared solution strength, metering-pump range, storage time and control method.
Define the Chemical Duty
Typical applications include acid, caustic, coagulant, polymer, nutrient and disinfectant dosing.
Each chemical has different compatibility and preparation requirements.
Establish the Required Dose
Do not select a pump from a guessed mg/L value.
Convert Dose to Chemical Mass
A preliminary relationship is:
chemical mass per time = wastewater flow x required dose
Use consistent units.
This gives the actual chemical duty.
Account for Product Concentration
Commercial chemicals may be supplied as neat liquid, concentrated solution, powder or emulsion.
The metering flow depends on active concentration.
Select the Pump Range
The pump should cover minimum, normal and peak dose.
Check minimum stable flow, maximum flow, turndown, discharge pressure, material compatibility and control input.
An oversized pump may perform poorly at the low end.
Size the Tank
Tank volume should consider daily chemical consumption, delivery frequency, batch preparation, solution aging and operator workload.
Bigger is not always better.
Some prepared chemicals should not sit for excessive periods.
Check Mixing
Mixing may be required for dissolving powder, polymer preparation, maintaining suspension or homogenizing dilution.
Excessive shear can damage some polymers.
Check Materials
Review compatibility for the tank, pump head, tubing, valves, seals, mixer and instruments.
Use the actual chemical concentration and temperature.
Select the Control Method
Possible controls include fixed-rate dosing, flow-paced dosing, pH feedback, ORP feedback, residual analyzer and batch control.
The control signal should match the process objective.
Practical Checklist
Data Group | Information |
|---|---|
Wastewater | Minimum/normal/peak flow |
Chemical | Type and concentration |
Dose | Minimum/normal/peak |
Solution | Prepared concentration |
Pump | Flow, pressure, turndown |
Tank | Required storage/batch time |
Mixing | Preparation requirement |
Control | Flow, pH, ORP or analyzer |
Technical Basis
EPA chemical-feed references use metering pumps, storage tanks and adjustable controls as core components of chemical feed systems. For pH, coagulation and polymer applications, actual dose should be established from process testing.
The practical rule is:
calculate chemical mass first, then select solution strength, pump range, tank volume and control around the real operating range.
Need Help Sizing a Dosing System?
Send HydroNovus the wastewater flow, chemical type/concentration, dose range, operating hours, discharge pressure and preferred control method.