Chlorine Dose to Oxidize Iron and Manganese
The free-chlorine dose to oxidize dissolved iron and manganese ahead of a filter: 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.
Formula and source
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.
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