EFFECTIVE AGAINST: Oxidizing filters oxidize and filter iron, manganese, and hydrogen sulfide in one unit.
An oxidizing filter is an in-line, point-of-entry device (on the main incoming water line) that converts dissolved iron, manganese, and hydrogen sulfide to a solid form and then filters the particles out of the water.
How oxidizing filters work
The filter contains one of a variety of media, the most common being manganese-treated green sand. Other media used are manufactured zeolite, plastic resin beads, Birm, which is a light silicon dioxide with a manganese dioxide coating, and Filox, another manufactured resin. In many oxidizing filters, the media granules are prepared by washing them with a chemical – commonly potassium permanganate. This forms a black manganese oxide coating on the medium. The coating reacts with the iron, manganese, and hydrogen sulfide to form solid particles that are then trapped in the filter. Birm does not require a potassium permanganate wash. Instead, Birm adsorbs oxygen and iron present in the untreated water.
Most oxidizing filters remove up to 10 milligrams per liter iron or manganese every several weeks. Hydrogen sulfide, however, may exhaust a filter quickly and require regeneration every few days. Therefore, use oxidizing filters only for small amounts of hydrogen sulfide.
Most oxidizing filters remove 75 to 90 percent of the iron or manganese in the water. It may be necessary to follow the oxidizing filter with a water softener if the iron or manganese concentrations are not sufficiently reduced.
Regular backwashing is necessary to assure that the filter is working properly because particles can clog the filter within a few days to a few weeks. With certain oxidizing filters, the manganese oxide coating is used up, so regeneration may also be necessary. In many instances, the backwashing or regeneration chemical is potassium permanganate. Many vendors offer a backwashing or regeneration service for homes without the required backwash flow rate. They will supply a fresh filter and take the exhausted filter off-site for regeneration.
It is very important that the filter be kept clean. If the filter is not completely cleaned, a reddish-brown sludge will enter the distribution system. Do not use acid cleaners on zeolite because the acid degrades the zeolite. Use chlorine instead.
In its concentrated form potassium permanganate stains and irritates skin and is poisonous. Use caution when handling the chemical and store it in its original, labeled container out of reach of children and animals. Wear protective clothing, goggles, and gloves when handling potassium permanganate.
Birm, a type of filtering media, is variably effective in oxidizing manganese. Although it can also oxidize hydrogen sulfide, the sulfur particles that form can foul the Birm bed. Birm is not consumed in the oxidation process. It does not, therefore, need to be regenerated with a chemical such as potassium permanganate. It does require periodic backwashing, however, to remove the accumulated particles.
Questions to ask before you buy
Before purchasing a water treatment device, have your water tested at a state certified laboratory to determine the contaminants present. This will help you determine if oxidizing filters are an effective treatment method for your situation. See Questions to Ask Before You Buy A Water Treatment System for more information.
Adapted from: Wagenet,L., K. Mancl, and M. Sailus. (1995). Home Water Treatment. Northeast Regional Agricultural Engineering Service, Cooperative Extension. NRAES-48. Ithaca, NY.