Waterworks that treat groundwater must almost always remove iron and manganese to prevent deposits in the pipelines. To this end, iron and manganese are oxidised with oxygen and retained as insoluble oxide particles in filters. Stoichiometrically, the oxidation of iron and manganese requires only small amounts of oxygen. This is therefore often carried out with air oxygen unless the ground water is already oversatured with nitrogen. If groundwater also contains ammonium, this can also be oxidised in the filters if sufficient oxygen is dissolved in the water. However, aeration rapidly reaches its limits here.