Oxidation can be achieved by aeration or by the use of oxidants such as chlorine, potassium permanganate, hypochlorite, chlorine dioxide, or ozone. An oxidation–filtration process is commonly used to remove Fe and Mn ions in a conventional water treatment plant. Ideally, oxidants are added first to transform Fe and Mn ions into oxides which can be removed by subsequent filtration. The efficiency of membrane filtration relies on the type and amount of the metal oxides formed in the oxidation stage.