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Biological process calculator

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.

Input parameters
Enter average phosphorus loading, treatment target, and chemical product assumptions.
m³/day
Phosphorus mass balance
mg/L as P
mg/L as P
mg/L as P; use the estimate below or enter a site-specific value
Chemical product assumptions
The molar ratio refers to Fe:P or Al:P, respectively.
mol Fe or Al per mol P; adjust from jar tests and plant data
percent w/w active chemical in the supplied solution
kg/L of supplied solution
Calculated results
Phosphorus quantities are expressed as elemental P; chemical dose is preliminary.

Enter values and select Calculate to view the phosphorus-removal and dosing estimate.

Biomass-based 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.

Biological estimate inputs
Adjust assumptions to match conventional or enhanced biological phosphorus removal.
g VSS per g COD removed
fraction of decayed biomass retained as residue
day−1
days
g P/g VSS; typical 0.0267, up to 0.13 for designed EBPR
mg/L COD removed by biological treatment
Calculated biological phosphorus removal
The result is a concentration, not a percentage.

Select Estimate Biological P Removal to calculate the concentration.

Equation: Premoval = fp × Y × (1 + fd × kd × θx) × ΔCOD ÷ (1 + kd × θx). The default fp of 0.0267 represents a conventional biomass fraction; a value up to 0.13 can be screened for a system intentionally designed for enhanced biological phosphorus removal.

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.

Influent P load = Q × TPin ÷ 1,000
Target P load = Q × TPtarget ÷ 1,000
Biological P removal = Q × biological P removal concentration ÷ 1,000
Chemical P removal = max(Influent P load − Target P load − biological P removal, 0)
P molar load = Chemical P removal × 1,000 ÷ 30.974
Active FeCl3 = P molar load × Fe:P ratio × 162.20 ÷ 1,000
Active alum = P molar load × Al:P ratio × (594.0 ÷ 2) ÷ 1,000
Solution volume = Active chemical mass ÷ strength fraction ÷ density

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]