UMass researcher outlines treatment options and limits for manganese in drinking water

John Tobiasen, professional emeritus and part-time research professor in the Department of Civil and Environmental Engineering at UMass Amherst, described how manganese occurs in source waters and reviewed practical treatment approaches during an RCAP Solutions webinar on Sept. 16.

Tobiasen said manganese commonly appears in both groundwater and seasonally in surface waters and that its form — dissolved versus particulate — matters for treatment. He said aesthetic problems such as staining and turbidity often drive treatment needs, but manganese was put on the U.S. EPA contaminant candidate list and monitored under UCMR4 because of potential health concerns. "Manganese should be at 10 to 20 micrograms per liter," Tobiasen said, stating that levels below about 0.02 milligrams per liter help avoid chronic problems in distribution systems.

Why it matters: manganese interacts with other treatment concerns (iron, natural organic matter, PFAS) and can dominate treatment chemistry and costs. Tobiasen emphasized that treatment plans must account for chemical speciation, competing oxygen demand, and reaction kinetics rather than relying on simplified rules of thumb.

Key technical points Tobiasen presented: - Forms and occurrence: manganese occurs dissolved (Mn2+) under reducing conditions found in many wells and can be released from lake sediments seasonally; particulate forms dominate when turbidity is present. He noted manganese can co-occur with arsenic, hardness, natural organic matter and other contaminants. - Benchmarks cited: U.S. EPA lifetime health advisory 0.3 milligrams per liter (0.3 mg/L), WHO guideline ~0.08 mg/L, Health Canada guideline ~0.12 mg/L; EPA secondary (aesthetic) level is 0.05 mg/L. Tobiasen and other practitioners use a practical treatment goal near 0.02 mg/L (10–20 µg/L) to avoid chronic distribution issues. - Removal strategies: dissolved manganese must be converted to particles or removed by sorption/surface oxidation. Strong oxidants (permanganate, ozone, chlorine dioxide) are generally required to form particles quickly; free chlorine typically oxidizes manganese too slowly in the time frame of a treatment plant unless special conditions apply. Once manganese oxide coatings form on media, surface oxidation plus adsorption can effectively remove dissolved manganese when a suitable oxidant residual is provided across the media. - Media and process notes: traditional "greensand" approaches and manganese-oxide–coated media can work but have tradeoffs. Continuous free-chlorine across coated filters often regenerates media and removes manganese but may increase disinfection byproduct formation if natural organic matter is present on the surface. Permanganate dosing ahead of filters produces particles that must be removed and can pink the treated water if permanganate persists. - Contactors: Tobiasen highlighted manganese contactors — larger-grain, lower-density media beds placed after particle removal with a free-chlorine residual across the media — as an effective option used in examples including Winter and Hill (an Aquarian Water Company design), a groundwater plant in Brunswick, Maine, and a surface water plant in Groton, Connecticut. These contactors have been reported to remove dissolved manganese to below about 0.02 mg/L when operated with appropriate backwash intervals and oxidant dosing.

Tobiasen cautioned against long-term reliance on sequestration (chemical addition that keeps manganese in a sequestered dissolved form) because deposited metals can create legacy problems in distribution systems that show up during flushing or other events. He also described operational considerations such as the need to determine stoichiometric oxidant demand (including competing demands from natural organic matter, sulfide, ammonia) by jar testing and pilot trials.

UMass role and resources: Tobiasen said the UMass team supports technical assistance, bench/pilot testing and a mobile water innovation lab to help small systems evaluate options. He noted UMass has partnered with MassDEP and RCAP Solutions to provide implementation support for the ECSDC program and related work.

The webinar included audience polling and a question-and-answer period in which a chat question about permanganate use and its tendency to form particles was addressed. Tobiasen reiterated that permanganate must be consumed or removed before finished water delivery to avoid aesthetic issues and that permanganate-generated particles need effective particle removal ahead of any media contactor.

Tobiasen's presentation concluded with case-study data showing manganese oxide coatings on filters and the operating performance of contactors and intermittently regenerated filters; he and the webinar hosts encouraged systems to pursue site-specific bench or pilot work before adopting a full-scale treatment approach.

For systems considering options, Tobiasen and webinar hosts recommended documenting baseline forms (dissolved vs. particulate), running jar tests and pilots to define oxidant doses and kinetics, and coordinating design with particle-removal steps to avoid downstream water-quality problems.