Catalyst filters (without regenerator)
Catalyst filters, with or without a regenerator, use a chemical reaction type of media to oxidize iron or manganese. As the water passes through the filtering bed, the minerals change from a soluble form (Fe 2+,Mn2+) to an insoluble form (Fe3+, Mn4+). This makes them easier to filter.
Certain water conditions are required to create the chemical reaction : the pH level, the iron to manganese ratio and the quantity of oxygen dissolved in the water.
Birm and Catalox: These products remove iron, manganese and sulphure if the pH is at a level that favours oxidation (7 to 7,5 for iron and 8 to 8,5 for Mn), just like the green sand.
However, if the pH levels in the water are not satisfactory, chlorine or air injections will be required for preoxidation. These products do not require a regenerating agent although they consume a great deal of water.
Birm : Sulphure is not present in the water and chlorine is not used as an oxidation media