Phosphorus Removal & Chemical Dosing Calculator
Estimate a preliminary total-phosphorus mass balance and the product-dose range for ferric chloride or alum chemical precipitation following selected biological phosphorus removal.
Preliminary coagulant-dose screen: This tool converts the phosphorus removal remaining after selected biological uptake into a theoretical metal-salt requirement. Actual performance depends on orthophosphate availability, pH, alkalinity, mixing, flocculation, solids separation, competing reactions, and chemical-sludge handling.
Enter values and select Calculate to view the phosphorus-removal and dosing estimate.
Biological Phosphorus Removal Estimate
Estimate biological phosphorus removal as a concentration in the mixed influent using a biomass-yield relationship. The calculated value is expressed as mg/L as P and can be transferred to the chemical-dosing mass balance above.
Select Estimate Biological P Removal to calculate the concentration.
Equations used
The calculator first estimates phosphorus removal credited to biological uptake. The remaining phosphorus removal is converted to moles P, multiplied by the selected Fe:P or Al:P ratio, and converted to active coagulant mass. For alum, the formula mass is apportioned across its two aluminium ions.
Scope and interpretation
Metal salts precipitate phosphorus but require effective solids separation. The effective molar ratio is influenced by wastewater chemistry and the target residual, so jar testing or pilot data is essential before final design. Chemical phosphorus removal technical guidance [1] Coagulant-dose research [2]
Phosphorus-removal and chemical-dosing basis
Documentation revision: 2026-10-02. This page documents the calculation basis so an engineer can trace the inputs, units, assumptions, and review needs. Results are preliminary screening estimates; they are not a permit determination, OEM guarantee, or construction/procurement approval.
Method and source basis
The page subtracts the target and entered biological phosphorus credit from influent TP load, converts remaining phosphorus to molar load, applies user-entered Fe:P or Al:P ratio, and converts active chemical mass to commercial solution mass/volume using product strength and density.
The sources below provide technical context or analytical/design methodology. They do not endorse this calculator's defaults, and any jurisdiction-specific requirement applies only where that authority has jurisdiction.
- U.S. EPA, Design Manual: Phosphorus Removal (EPA 625/1-87/001)
- Government of Manitoba, Chemical Phosphorus Removal Alternatives
- Kim & Chung, Chemical precipitation as pretreatment for MBR municipal wastewater (2014), DOI 10.1007/s12205-014-0070-9
Assumptions, limitations, and review actions
- Theoretical stoichiometry is not actual dose. Demand depends on orthophosphate/TP fractions, pH, alkalinity, wastewater chemistry, competing reactions, dose point, mixing/flocculation, solids capture, polymer, and target residual.
- Biological removal is an entered credit, not a complete EBPR mass balance. Validate it and flag any credit that exceeds the available removal requirement; product strength, basis, density, and SDS must be confirmed.
- Jar, pilot, or comparable full-scale testing is required before chemical-feed, sludge-handling, safety, or permit design. Defaults are examples, not universal targets.
Professional review checkpoint
Before using the result for specification or operation, reconcile it with representative site data, the applicable permit and design standard, the selected equipment or membrane supplier's current data, and a qualified wastewater/process engineer. Record the input basis, date, units, and any pilot, bench-test, or comparable full-scale evidence used to select the assumptions.