Nutrient Addition (N and P) Calculator

Industrial wastewaters are often short on nitrogen and phosphorus for healthy biological growth. Enter your BOD load and available nutrients to find the deficit and the urea and phosphoric acid feed rates.

Flow

Flow unit

BOD₅ load (lb/day)Influent BOD applied to the biological process.

Available nitrogen (mg/L as N)Influent TKN or ammonia-N. Default 0.

Available phosphorus (mg/L as P)Influent total P. Default 0.

Nitrogen source

Phosphorus source

Nutrient Balance

Item	Value

How the calculation works

Formulas (100:5:1 BOD:N:P by weight)
Nitrogen required (lb/day) = 0.05 x BOD load (lb/day)
Phosphorus required (lb/day) = 0.01 x BOD load (lb/day)
Available nutrient (lb/day) = 8.34 x flow (MGD) x concentration (mg/L)
Deficit (lb/day) = max(0, required – available)
Urea (lb/day) = nitrogen deficit / 0.46
Phosphoric acid 75% (lb/day) = phosphorus deficit / 0.237

Supplement	Nutrient fraction
Urea (46-0-0)	0.46 N
Phosphoric acid, 75% H₃PO₄	0.237 P

Notes & limitations

The 100:5:1 BOD:N:P ratio is the classic rule of thumb for aerobic biological treatment (Metcalf & Eddy). It is based on BOD₅; nutrient-limited industrial wastes (food processing, pulp and paper, chemical plants) are the usual candidates for supplementation.

Use soluble or biodegradable BOD for a tighter estimate — the 100:5:1 ratio assumes the BOD is actually available to the biomass.
Excess nitrogen or phosphorus passes through to the effluent and can cause permit violations; feed to the deficit only and verify with effluent nutrient data.
Urea hydrolyzes to ammonia and consumes some alkalinity; phosphoric acid lowers pH. Watch effluent pH and alkalinity when feeding either.
If your plant nitrifies, part of the supplemented ammonia becomes nitrate — coordinate with your nitrogen removal targets.

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