Alkalinity Requirement Calculator
Calculate alkalinity consumption from nitrification, recovery from denitrification, and supplemental chemical dosing requirements for pH stability in an MBR system.
Process stability: Maintaining a residual alkalinity of 50–100 mg/L as CaCO₃ in the effluent is recommended to provide a pH buffer for the nitrification process. Insufficient alkalinity can lead to pH drops, inhibiting biological activity and potentially damaging membrane performance.
Enter values and select Calculate to view the alkalinity requirement screen.
Equations used
The alkalinity balance accounts for the biological consumption of alkalinity during nitrification and the partial recovery during denitrification.
Stoichiometric factors
Standard engineering constants are used for the biological process:
- Nitrification: 7.14 g alkalinity (as CaCO₃) consumed per g NH₄-N oxidized.
- Denitrification: 3.57 g alkalinity (as CaCO₃) recovered per g NO₃-N reduced.
Chemical factors (kg chemical per kg CaCO₃ equivalent):
- Sodium Bicarbonate: 1.68
- Soda Ash: 1.06
- Caustic Soda (100%): 0.80
- Hydrated Lime: 0.74
- Magnesium Hydroxide: 0.58
Alkalinity requirement calculation 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 and nitrate denitrification from entered concentrations, applies 7.14 kg as CaCO3 per kg NH4-N consumed and 3.57 kg as CaCO3 per kg NO3-N recovered, then converts any deficit into the selected commercial chemical using factor, strength, and density inputs.
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/AWWA, Nitrification technical guidance
- Water Research Foundation, Tertiary Denitrification Processes for Low Nitrogen and Phosphorus
- WEF Manual of Practice No. 34, Nutrient Removal
- Metcalf & Eddy/AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.
Assumptions, limitations, and review actions
- This is a steady-state stoichiometric screen. It assumes ammonia removal is nitrified and calculated nitrate is denitrified; it does not model pH, temperature, alkalinity speciation, CO2 stripping, recycle/sidestreams, incomplete reactions, or process location.
- 7.14 and 3.57 are approximate factors on an as-CaCO3 basis. Residual-alkalinity guidance is context-dependent; do not treat generic 50–100 mg/L statements as universal limits.
- Commercial chemical factors, strength, assay, density, solubility, storage, mixing, compatibility, and controls must be checked against the actual supplier specification, SDS, plant data, and authority 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.