At the end of 2020, the Wisconsin Department of Natural Resources (WDNR) directed the public works director of Grantsburg, Wisconsin, a small village near the Wisconsin-Minnesota border, to post a “Do Not Drink the Water” public notice about high levels of manganese in the village’s drinking water.
Today, the village, which uses three wells to distribute water, is considering next steps that may include the installation of a new water filtration system. As it turns out, Grantsburg is just one of several communities in the western region of the state—as well as communities across the country—that have been warned about dangerous manganese levels in their water systems.
Currently, the U.S. Environmental Protection Agency (EPA) recommends that manganese levels be below 1 mg/L for adults and 0.3 mg/L for infants younger than six months. Since 2019, when the EPA launched an initiative focused on collecting data to determine whether manganese in drinking water should be regulated, the agency has adopted a new focus on manganese in drinking water and is requiring larger systems for testing across the nation.
Water Treatment Methods for Manganese Removal
Manganese in water supplies is often in a dissolved state. Traditional manganese treatment and removal technologies, which are designed to convert the metal in its dissolved state to a particulate form that can be clarified and filtered, are often simple operations that do not require the use of proprietary technologies.
Following are five of the most common methods for manganese removal.1
- Sequestration. Sequestering agents are phosphate blends used to surround and “sequester” high levels of minerals like iron and manganese in the water, so that they cannot react with oxygen and create issues.
- Oxidation + clarification + filtration. Most manganese treatment and removal processes incorporate oxidation for converting the metal in its dissolved state to a solid, followed by the use of a filtration process. A clarification step, which reduces the amount of solid to be removed by filters, is often required when there is a concentration of iron and manganese in the source water of 8 mg/L.
- Ion exchange. Traditionally used in home water softening systems, resins remove iron and manganese from water that has not been exposed to oxygen. This method is not recommended for water treatment at the municipal level.
- Filtration with manganese dioxide-coated media. There are many types of filtration systems that use manganese dioxide-coated media like greensand to filter iron and manganese. Water passes through a greensand filter to extract soluble manganese, which later forms insoluble manganese that can be removed by backwashing.
- Biological filtration. Raw water is pumped through a pressure vessel in which the growth of bacteria has been fostered. The bacteria oxidize the manganese and iron in the water, which gather in the filter in the form of dense precipitates. When the water contains both iron and manganese, two filtration stages are required.
When choosing a manganese treatment method, consideration should be given to the amount of manganese concentrations in the source water, as well as other water parameters that could impact the treatment. The screening process should include an examination of the technical and financial feasibility of the method, its sustainability, maintenance requirements and ease of integration into your existing facility.
1 Iron and Manganese Removal Handbook, Second Edition, American Water Works Association: https://www.awwa.org/Store/Product-Details/productId/28344
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