How Much Chlorine To Inject to Treat Iron & Manganese Before Iron Filters?
How much chlorine to inject?
How much chlorine to inject? A common question we often get is, how much chlorine do I need to inject before my iron filter to treat iron, manganese, and hydrogen sulfide (rotten egg odor)?
The short answer is:
- 0.62 mg/l of chlorine per mg/l of iron;
- 1.29 mg/l of chlorine per mg/l of manganese
- 8.33 mg/l of chlorine per mg/l of sulfide
Note that mg/L (milligram per liter) is the same as saying PPM (parts per million).
Pre-Treatment With Chlorine and Filtration with Pro-OX Manganese Dioxide Media
A rapid and efficient method for removing iron, manganese, and hydrogen sulfide is to chlorinate the raw water, allow a 30–60 second retention time, and filter with Pro-OX manganese dioxide filter media. This process is a common form of chlorine injection for iron removal.
To inhibit the growth of iron and sulfur bacteria, a level greater than 0.5 mg/l of oxidant (chlorine) should be injected into the storage tanks and distribution system.
Water is received from the well source and treated with chlorine to oxidize the iron, manganese, and sulfides present. The iron is oxidized to ferric iron, the manganese to the manganic form, and the sulfides to sulfate.
Sulfate is common in water supplies and does not contribute an objectionable taste or odor. A sufficient amount of chlorine is added to the water to meet the chemical demand and reach the chlorine breakpoint. The distribution system receives a minimum free chlorine residual of 0.5 mg/l. Depending on conditions, a higher residual may be injected.
How Much Chlorine To Inject?
Stoichiometry is used to determine the number of reactants (in this case, chlorine) needed in a given reaction. It describes the quantitative relationships among substances as they participate in chemical reactions.
The stoichiometric equivalent for chlorine needed to oxidize iron, manganese, and sulfide is:
- 0.62 mg/l of chlorine per mg/l of iron;
- 1.29 mg/l of chlorine per mg/l of manganese
- 8.33 mg/l of chlorine per mg/l of sulfide
- Plus, organic demands may be present, determined by jar testing or field pilot tests.
Plus, organic demands may be present, determined by jar testing or field pilot tests.
If your water contains both iron and manganese, chlorine injection for iron removal is generally more effective than hydrogen peroxide, which does not work well with manganese present.
For a more technical look at chlorine oxidation in iron and manganese removal, see this research article on ScienceDirect, which explores how chlorine interacts with various contaminants during water treatment.
