Greensand filters are designed primarily for the removal of iron from water supplies but they can also be effective in dealing with sulphur problems. Water flowing through such a filter is exposed to greensand media which iron and sulphur are oxidized. The oxidized forms of iron and sulphur are not water soluble. They therefore drop out of solution and collect on the filter media. Periodically, the greensand filter is flushed with a solution of potassium permanganate. This regenerates the media and washes the collected iron and sulphur down the drain.
Even with regeneration, under normal conditions the media in a greensand filter will have to be replaced every five years or so. A standard container of potassium permanganate ordinarily lasts about eight months.