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The Effectiveness of Sand Filters for the Removal of Colloidal Manganese Oxides from Water Using Selected Cations as Filter Aids


A mathematical-chemical relationship derived to predict the most effective concentrations of Ca2+ for coagulation of manganese oxide particles and deposition on a rotating disc type silica surface, was shown to predict the effective concentration of Ca2+ for removal of manganese oxide by model rapid sand filters. The concentration of calcium necessary to cause effective removal of manganese oxide was shown to be stoichiometric with the oxide concentration.

The relationship derived was acceptable in predicting the removal efficiency of both 1-inch ID - 4-inch deep and 4-inch ID - 3-foot deep sand filters. Differences in pH had little effect on the maximum effectiveness concentration of Ca2+. However, precoating of the sand with Ca2+, and rate of filtration were shown to greatly effect the concentration of Ca2+ for effective manganese oxide removal.

The cost of treating naturally occurring waters of Wyoming was shown to be small if rapid sand filtration plants were available. For example, most Wyoming waters contained enough Ca2+ that further additions of this cation would not have to be made. Consequently, the only cost would be the cost of oxidizing the manganese. If MnO-4 was used as an oxidant the cost was shown to be about 0.19 cents/cap/day. In rare cases where lime would have to be added to increase the Ca2+ concentration, the cost would rise to only 0.34 cents/cap/day. Unfortunately, most Wyoming communities do not have existing sand filtration plants making the removal of manganese by this method uneconomical. The benefit gained by removing the manganese is usually not worth building a filter plant solely for that purpose.

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