Biological process calculator

Nitrogen Removal Calculator

Estimate ammonia nitrification, nitrate denitrification, oxygen demand, alkalinity effects, carbon demand, and preliminary anoxic-zone volume for an MBR or activated-sludge nitrogen-removal system.

Preliminary nitrogen balance: This tool is for screening and assumes the ammonia removed is nitrified and the nitrate above the selected target is denitrified. It excludes nitrogen assimilation, sidestream loads, recycle hydraulics, temperature and DO corrections, inhibition, and process-specific solids effects.

Input parameters

Enter average nitrogen concentrations and process assumptions.

Average Influent Flow

m³/day

Nitrification targets

Influent Ammonia-N

mg/L as NH₄-N

Target Effluent Ammonia-N

mg/L as NH₄-N

Denitrification targets and carbon

Influent Nitrate-N

mg/L as NO₃-N

Target Effluent Nitrate-N

mg/L as NO₃-N

Available Readily Biodegradable COD

mg/L COD available to denitrification

COD Required per Nitrate-N Denitrified

kg COD per kg NO₃-N; theoretical methanol-equivalent basis

Preliminary anoxic-zone sizing

Anoxic-Zone MLVSS

mg/L MLVSS

Specific Denitrification Rate (SDNR)

g NO₃-N/(g MLVSS·day); select from site-specific conditions

Integrated alkalinity and chemical screen

Influent Alkalinity

mg/L as CaCO₃

Target Effluent Alkalinity

mg/L as CaCO₃; residual pH buffer target

Supplementary Alkalinity Chemical

Chemical Strength

fraction; 1.00 for dry chemical, 0.50 for a 50% solution

Chemical Solution Density

kg/L; use 1.00 for dry chemical output

Calculated results

All nitrogen quantities are reported as elemental N unless otherwise stated.

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

Equations used

The calculator applies stoichiometric nitrification factors of 4.57 kg O₂/kg NH₄-N and 7.14 kg as CaCO₃/kg NH₄-N. It applies denitrification credits of 2.86 kg O₂/kg NO₃-N and 3.57 kg as CaCO₃/kg NO₃-N. [1]

NH₄-N nitrified = Q × (NH_4,in − NH_4,target) ÷ 1,000

NO₃-N available = NO_3,in + NH₄-N nitrified concentration

NO₃-N denitrified = Q × (NO_3,available − NO_3,target) ÷ 1,000

Nitrification O₂ = NH₄-N nitrified × 4.57

Nitrification alkalinity = NH₄-N nitrified × 7.14

Denitrification COD demand = NO₃-N denitrified × selected COD/N ratio

Anoxic volume = NO₃-N denitrified × 1,000 ÷ (SDNR × MLVSS)

Scope and interpretation

Nitrogen removal depends on sufficient aerobic solids retention time, alkalinity, oxygen, anoxic conditions, available carbon, mixing, temperature, and inhibition control. The design calculations here do not replace a process model or pilot/plant data. NYS DEC nitrogen-removal training [1] EPA Nitrogen Control design manual [2]

Nitrogen-removal stoichiometric 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 estimates ammonia nitrification, nitrate available for denitrification, oxygen and alkalinity effects, COD demand, SDNR-based anoxic volume, and optional chemical alkalinity dosing. The fixed coefficients are theoretical stoichiometric equivalents, not complete kinetic or aeration models.

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, Nutrient Control Design Manual (2010)
U.S. EPA, Process Design Manual for Nitrogen Control
New York State DEC, Long Island Sound Nitrogen Removal Training Program, Module 2

Assumptions, limitations, and review actions

The simplified balance assumes ammonia removed is nitrified to nitrate and omits organic nitrogen, assimilation, nitrite, sidestreams, RAS/internal recycle, peak/seasonal conditions, temperature, pH, DO, inhibition, carbon bioavailability, mixing, and SRT effects.
2.86 COD/N is a theoretical baseline; actual carbon demand depends on substrate, yield, endogenous demand, residual COD, and configuration. SDNR and the editable chemical factors require site/product evidence.
Oxygen demand is not blower capacity, and alkalinity dose is not a chemical-feed approval. Check product assay, density, pH, alkalinity species, supplier data, controls, safety, and permit requirements.

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.