Denitrification Methanol Dose Calculator
Post-anoxic denitrification usually needs an external carbon source. Enter your nitrate load and anoxic-zone dissolved oxygen to size the methanol dose and daily feed rate.
Methanol Requirement
| Item | Value |
|---|
How the calculation works
Formulas
Theoretical methanol demand = 2.47 x NO3-N removed (McCarty stoichiometry, includes biomass synthesis)
DO correction = 1.0 x dissolved oxygen in the anoxic zone (practical factor; stoichiometric 0.67 rises with biomass yield)
Methanol dose (mg/L as pure CH3OH) = (2.47 x NO3-N + 1.0 x DO) x safety factor
Methanol (lb/day) = 8.34 x flow (MGD) x dose (mg/L)
Product (lb/day) = methanol (lb/day) / (strength / 100)
Product (gal/day) = product (lb/day) / 6.63
Theoretical methanol demand = 2.47 x NO3-N removed (McCarty stoichiometry, includes biomass synthesis)
DO correction = 1.0 x dissolved oxygen in the anoxic zone (practical factor; stoichiometric 0.67 rises with biomass yield)
Methanol dose (mg/L as pure CH3OH) = (2.47 x NO3-N + 1.0 x DO) x safety factor
Methanol (lb/day) = 8.34 x flow (MGD) x dose (mg/L)
Product (lb/day) = methanol (lb/day) / (strength / 100)
Product (gal/day) = product (lb/day) / 6.63
| Constant | Value |
|---|---|
| Theoretical methanol per NO3-N (mg/mg) | 2.47 |
| Practical rule-of-thumb ratio (mg/mg) | 3.0 |
| DO correction factor (mg CH3OH per mg DO) | 1.0 |
| Methanol density (lb/gal) | 6.63 |
Notes & limitations
The 2.47 mg methanol per mg NO3-N is the theoretical McCarty stoichiometry (Metcalf & Eddy, Wastewater Engineering). In practice most plants feed at about 3:1 to cover DO intrusion, mixing inefficiency, and influent variability — confirm with nitrate profiling across the anoxic zone.
- Dissolved oxygen entering the anoxic zone is consumed before denitrification starts. Keep anoxic-zone DO near zero with proper mixing and internal recycle control; every 1 mg/L of DO costs roughly 1 mg/L of extra methanol.
- Overdosing methanol raises effluent BOD and wastes chemical; underdosing leaves nitrate in the effluent. Pace the feed to the nitrate load (flow-paced or nitrate-analyzer-paced).
- Methanol is flammable and regulated for storage (fire code, OSHA). This tool sizes the dose only — follow your facility’s hazardous-material procedures for handling and storage.
- Alternative carbon sources (glycerol, acetate, proprietary products) have different stoichiometric ratios; do not apply the 2.47 factor to them.
← All water treatment calculators · Related: Nitrification Alkalinity Calculator