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The Stainers: Iron & Manganese

Removal: Chlorination & Carbon Filtration
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Neither water softeners nor the iron filters will be effective if the iron or manganese is bound into organic matter, if iron or manganese bacteria are present, or if the iron or manganese concentrations are really high. Iron or manganese bound into organic compounds is not available for removal by ion exchange, and the oxidizing power of the iron filter media is not strong enough to break these materials down. Thus, organic iron or manganese compounds often pass through softeners and filters with no significant removal. Similarly, iron or manganese bacteria can foul softeners and filters rapidly, and even when removal is good part of the time, high flow rates may cause "slugs" of dirty water to appear in the treated water.

In such cases, a chemical feed pump can be used to introduce a solution of household hypochlorite bleach into the water system ahead of the pressure tank. The chemical feed pump can be wired to operate with the well pump, thus giving good proportioning of the bleach to the water. This produces disinfection of the water with oxidation of the iron and organic matter.

Just as in disinfection, the feed rate of the chlorine is usually adjusted to produce a chlorine residual of 3 to 5 ppm at the outlet of the pressure tank. This will cause the oxidation of the iron, manganese, and organic matter usually in the time it takes for the water to flow through the pressure tank. In a few cases, additional contact time is necessary to obtain complete destruction of the organic matter present. An activated carbon filter in the water line from the pressure tank may then be used to remove the precipitated matter and excess chlorine from the water. This filter must be backwashed periodically to flush the accumulated solids to a drain, and small amounts of activated carbon added from time to time to replace that consumed by the chlorine. Since the chlorine solutions tend to lose strength, they should be made up fresh each week.

An additional advantage of this process is that it can be used to neutralize acid waters. When the pH of the water is low, it can be very corrosive. Complete removal of iron and manganese will not always be obtained if the pH is below about 7.5. Where such conditions exist, common soda ash solution may be used to neutralize the acidity present and to increase the pH to 7.5 to 8.0. Thus, the water will be made less corrosive, and good iron and manganese removal will be achieved.

Further, the plumbing in the home can be arranged to provide hard, iron-free water for sprinkling and toilets where the hardness is not important, and a softener installed to provide softened water for other water lines in the home.

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