Figure 1: Greensand filter regenerated with potassium permanganate
Credited to Wagenet, Mancl and Sailus- Northeast Regional Agricultural Services
Oxidizing filters are point-of-entry water treatment devices that combine oxidation and filtration processes to remove contaminants such as iron, manganese, and hydrogen sulfide from well water. In general, these filters are recommended for moderate levels of iron and manganese (combined concentration of 3 to 10 mg/L) and can remove up to 2-3 mg/L of hydrogen sulfide. (Higher concentrations require more frequent maintenance.)
How do oxidizing filters work?
A two-step process cleans the well water improving the water quality, taste, and smell:
Oxidation: First, they change contaminants like iron, manganese, and hydrogen sulfide, through a chemical reaction called oxidation, which often involves adding oxygen. This process changes the dissolved contaminants into a solid particle. Common chemical oxidants include chlorine, potassium permanganate, chlorine dioxide, and ozone.
Filtration: These larger solids become trapped in the media, removing them from the water. Backwashing, the process of reversing the flow of water to flush out accumlated debris and particles, is required to remove the trapped solids.
What media is used in an oxidizing filter?
These filters typically use a media that facilitates the oxidation.
Manganese Greensand Filters: Manganese greensand is the most common media used in oxidizing filters. Greensand is a naturally occurring marine sediment, primarily composed of the mineral glauconite, which is used as both a soil conditioner and a water filter. A chemical such as potassium permanganate is used to regenerate the filter media, which oxidizes iron and manganese. The oxidized particles are then trapped in the filter and removed through backwashing. Note: Potassium permanganate solution is toxic. It must be handled and stored carefully.
Bottle of potassium permanganate with warning labels/© Adobe Stock
Birm®: This media is a light silicon dioxide with a manganese dioxide coating. It does not require chemical regeneration but may be ineffective in the presence of organic matter, chlorine, hydrogen sulfide, tannins, or oil. Birm® requires a specific pH level for effective removal ((at least 6.8 for iron and 7.5 for manganese) and does require backwashing.
Others: Plastic resin beads, manufactured zeolite and Filox resin may also be used. Some media, such as Filox, require dissolved oxygen or another oxidant (like chlorine or hydrogen peroxide) to be effective. Regular backwashing is required.
What maintenance is required when using an oxidizing filter?
Oxidizing filters require a lot of maintenance. Key points to remember are:
Regular backwashing and regeneration (for manganese greensand) are necessary to maintain filter efficiency.
The frequency of maintenance increases with higher contaminant concentrations.
If chlorine is used as an oxidant, an activated carbon filter may be needed to remove residual taste and odor.
Additional Resources:
Drinking Water Treatment- Oxidizing Filters. National Cooperative Extension. 2025.
Iron and Manganese in Private Water Systems. PennState Extension. 2025.
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