MTM is granular manganese dioxide filter media used to reduce iron, manganese and hydrogen sulfide from water. Its active surface coating oxidizes and precipitates soluble iron and manganese. Hydrogen sulfide is oxidized to a sulfur. The precipitates are filtered out in the granular bed and removed by backwashing. At the point of exhaustion, the filter bed must be regenerated with a solution of potassium permanganate ( KMnO4 ), by which the oxidation power of the medium is re-established.