If you have manganese (Mn) in your raw water source(s) and are not treating for it, there’s a good possibility that your consumers are letting you know about it. Whether it’s a call about dirty water, staining of bathroom fixtures, or laundry staining you’ve probably had to respond to one or all of these consumer complaints. In fact, you may be hearing more about manganese in the future as regulators take a closer look at it and how it relates to public health.
What is it?
Mn is a naturally occurring mineral found in rocks and soil that constitutes approximately 0.1% of the earth’s crust. It is a common natural constituent of groundwater that may exist in elevated concentrations. Mn is also naturally occurring in many surface water sources. It is also common to find iron (Fe) when manganese is present. The glacial aquifer system which underlies most of New England is a known contributor of these constituents.
When found in drinking water sources, Mn is typically in its reduced state (Mn+2). In this state, the Mn is dissolved and is essentially invisible to the naked eye. Once the Mn is oxidized it changes state (Mn+3) and forms particulates which can cause consumer complaints. Common drinking water processes that can oxidize or speed up the process include aeration, disinfection, elevated pH, and high temperatures (hot water heaters, dishwashers, etc.).
Manganese is an essential nutrient that is important for normal processes in the body and can be actually found in many multivitamins. However, adverse health effects can be caused by inadequate consumption or over exposure.
How is Mn treated?
Depending on the raw water concentration, manganese can be treated in two ways: it can either be sequestered or removed.
Mn Sequestration: For low levels of Mn, sequestration can be a cost effective strategy for mitigating the more traditional aesthetic concerns associated with Mn. Sequestration involves adding a sequestering agent (typically a polyphosphate) that temporarily binds with the dissolved manganese to prevent it from oxidizing and causing the undesirable aesthetic impacts.
Mn Removal: When manganese levels are too high for sequestration, treatment for its removal is the solution. There are a variety of treatment processes available for the removal of Mn that include filtration with a variety of oxide coated and other proprietary medias, ion exchange and membrane filtration. Each process has its advantages and disadvantages and the optimum strategy depends on the water chemistry and other water quality objectives/constraints. Occasionally Mn is bonded to naturally occurring organic compounds. This can dramatically alter the required treatment strategy. Other treatment objectives, such as for corrosion control and disinfection, can be adversely impacted by Mn control strategies, and it is important that Mn control strategies be selected with a global understanding of all the water quality goals and constraints
Wright-Pierce’s water engineers have significant expertise with water chemistry and water treatment. We are helping many utilities develop Mn management strategies. Be sure to contact us if your source water(s) contain detectable concentrations of manganese and/or if you have any questions on this topic.