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 and the regulators are letting you know about it.
A few years ago, we shared an article with you, Got Manganese, discussing what Mn is, the problems it can cause within water systems, and how it’s treated. With a recent resurgence in regulatory activity on this common groundwater constituent, we thought it would be a valuable time to reiterate many of our sentiments from that first article with updated, relevant information for 2018.
What is Manganese?
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 and is naturally occurring in many surface water sources. It is also common to find iron (Fe) when Mn is present.
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 elevated temperatures (hot water heaters, dishwashers, etc.).
Manganese can have an adverse impact on everyday items, over time. This photo shows a typical manganese coating on the sink of a raw water pump station.
Exposure to Mn
Mn is an essential nutrient that is important for normal processes in the body and can even be found in many multivitamins. However, adverse health effects can be caused by inadequate consumption or over exposure. In 2004 the EPA issued a report titled Drinking Water Health Advisory for Manganese with information suggesting that children and infants should not consume water with Mn concentrations above 0.3 mg/L for sustained periods of time. High concentrations of Mn have been found to effect nervous systems. Younger children and babies are more susceptible than adults because manganese-supplemented baby formula and foods may contain an excess of Mn when mixed with water high in Mn. The detailed report can be found here: EPA Magnese Drinking Water Report.
Is it Regulated?
The U.S. Environmental Protection Agency (EPA) has set a Secondary Maximum Contaminant Level (SMCL) of 0.05 mg/L, which is a recommended concentration but not an enforceable limit. This was set for aesthetic concerns to avoid stains on plumbing and laundered clothes and believed to be more than adequate to protect human health. Each state however can choose to adopt the standard or set a more stringent one. On November 17, 2016 the EPA announced its final Drinking Water Contaminant Candidate List 4 that included Mn.
Regulatory Pressure on Massachusetts
One state that has put a stronger regulatory focus on Mn is Massachusetts. In 2015, the Massachusetts Department of Environmental Protection (MassDEP) issued guidance on control of manganese concentrations in water supplies. The guidance states that in Massachusetts, if the Mn concentration in a raw water exceeds 0.05 mg/L but is less than or equal to 0.30 mg/L, an assessment by MassDEP’s Office of Research and Standards is necessary to determine if treatment shall be required. If the Mn concentration in raw water exceeds 0.30 mg/L, removal is required. Many municipalities required removal at the onset of this new regulation and initial testing in 2015; now additional communities are being required to prepare a Corrective Action Plan (CAP) for the treatment of Mn due to increasing levels found during subsequent quarterly sampling.
How is it Treated?
Depending on the raw water concentration, manganese can be treated in two ways: (1) sequestration or (2) removal.
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 but are not limited to: filtration with a variety of oxide coatings 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.
The water engineers at Wright-Pierce have extensive experience with water chemistry and water treatment. In fact, we are currently working with several utilities to develop Mn management strategies. If your source water(s) contain detectable concentrations of manganese and/or if you have any questions on this topic, please don’t hesitate to contact us today.