Oxidation of manganese in drinking water systems using potassium permanganate

Abstract

South Gippsland Region Water Authority experience manganese problems in most of their surface water reservoirs. Manganese is present in the form of manganese(II) ions and manganic dioxide solids. At low dissolved oxygen levels, the manganic dioxide is reduced to the manganese(II) ion. If not oxidised, the manganese(II) ion escapes through water treatment facilities and enters the supply system. Once in the system, the manganese ions are gradually oxidised to insoluble manganic dioxide causing dirty water problems which can stain clothes and bathing equipment. As part of the water treatment process, manganese(II) can be oxidised to insoluble manganic oxide and then removed by clarification and filtration. Generally, oxidation can be achieved by aeration or chemical oxidation by addition of an oxidising agent such as potassium permanganate (KMnO4) or chlorine. However, due to fluctuations of manganese levels in raw water, treatment techniques are often very difficult. This paper shares the experiences of South Gippsland Water in using potassium permanganate as part of the water treatment process to remove manganese in its surface water reservoirs. Whilst consideration is given to the advantages and disadvantages of alternative oxidation methods, this paper primarily focuses on the use of KMnO4 to remove manganese and the resulting analytical problems associated with monitoring manganese levels.