Chlorine Dose to Oxidize Iron and Manganese
The free-chlorine dose to oxidize dissolved iron and manganese ahead of a filter.
Example
You enter
- Iron Fe (mg/L) 3
- Manganese Mn (mg/L) 0.5
- Other chlorine demand (mg/L) 0.5
- Target free residual (mg/L) 0.3
- Flow (MGD) 0.05
You get
- Chlorine dose 3.31 mg/L
- Chlorine feed 1.38 lb/day
Details, formula, and sources
0.62 mg Cl2 per mg of ferrous iron, 1.30 mg Cl2 per mg of manganese, plus any other chlorine demand and the free residual to carry; lb/day = dose x flow (MGD) x 8.34. Fe 3.0, Mn 0.5, 0.5 demand, 0.3 residual is a 3.31 mg/L dose, 1.38 lb/day at 0.05 MGD. Iron oxidizes in minutes, but manganese is slow at low pH and usually needs a pH near 8 or a catalytic (greensand / pyrolusite) filter to finish; permanganate or air are alternatives. A dosing estimate; jar tests, the pH, the contact time, and the state primacy agency govern the actual feed.
dose_mgl = 0.62 x fe_mgl + 1.30 x mn_mgl + extra_demand_mgl + target_residual_mgl; dose_lb_day = dose_mgl x flow_mgd x 8.34.
AWWA / Ten States Standards iron-and-manganese oxidation stoichiometry (0.62 mg Cl2/mg Fe, 1.30 mg Cl2/mg Mn), by name; jar tests and the state primacy agency govern.
The oxidation stoichiometry (0.62 and 1.30) and the 8.34 pounds formula are public water-treatment relations; the raw Fe/Mn, the demand, the residual, and the flow come from the water quality and the plant.
Estimate. Operator of record and primacy agency govern.
Field names used by the API: fe_mgl, mn_mgl, extra_demand_mgl, target_residual_mgl, flow_mgd, dose_mgl, dose_lb_day
- Oxidation stoichiometry 0.62 mg Cl2 per mg Fe(II); 1.30 mg Cl2 per mg Mn(II); plus demand and residualAWWA / Ten States
- Manganese kinetics Mn(II) is slow below pH ~8; often needs a catalytic (greensand / pyrolusite) filter or permanganatewater-treatment practice