Nitrification Alkalinity Requirement Calculator

Nitrifying wastewater plants consume alkalinity as they oxidize ammonia. Enter your ammonia load and influent alkalinity to see whether you’ll run short — and how much supplemental chemical to feed.

Flow

Flow unit

Influent NH₄-N (mg/L)

Effluent NH₄-N (mg/L)Target ammonia remaining after nitrification.

Influent alkalinity (mg/L as CaCO₃)

NO₃-N denitrified (mg/L)Nitrate removed by denitrification; gives an alkalinity credit. Default 0.

Target effluent residual alkalinity (mg/L as CaCO₃)Keep 60–100 to protect pH.

Supplemental chemical

Alkalinity Balance

Item	Value

How the calculation works

Formulas (all alkalinity as CaCO₃)
NH₄-N oxidized = max(0, influent NH₄-N − effluent NH₄-N)
Alkalinity consumed = 7.14 × NH₄-N oxidized
Denitrification credit = 3.57 × NO₃-N denitrified
Net consumption = consumed − credit
Projected remaining = influent alkalinity − net consumption
Shortfall = net consumption + target residual − influent alkalinity
Chemical dose (mg/L) = shortfall × conversion factor (only when shortfall > 0)
Feed rate (lb/day) = 8.34 × flow (MGD) × dose (mg/L)

Supplemental chemical	mg chemical per mg/L as CaCO₃
Soda ash (Na₂CO₃)	1.06
Hydrated lime (Ca(OH)₂)	0.74
Caustic soda (NaOH)	0.80
Sodium bicarbonate (NaHCO₃)	1.68

Notes & limitations

The 7.14 mg CaCO₃ per mg NH₄-N oxidized is the theoretical nitrification demand (Metcalf & Eddy / EPA wastewater treatment references). Actual consumption varies with biomass synthesis and wastewater characteristics — verify with lab data.

Keep a 60–100 mg/L residual alkalinity to protect pH and keep nitrifiers active; low pH slows nitrification and can stall it.
Chemical choice has side effects: lime adds hardness and sludge, caustic adds sodium, soda ash and bicarbonate add neither hardness nor sodium load. Choose per plant needs and discharge constraints.
The denitrification credit assumes the listed NO₃-N is actually reduced to nitrogen gas; partial denitrification recovers less alkalinity.
This tool is for operational guidance. Confirm feed changes against lab alkalinity/pH profiling and plant SOPs.

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