Managing Manganese with Microbes

UMN researchers bring back microbes from Japan for water treatment in Minnesota

by Deirdre Manion-Fischer

Manganese is an essential micronutrient present in Minnesota’s groundwater, but in some areas, especially the southwestern part of the state, manganese levels are high enough to raise health concerns. Over time, at high concentrations, the metal can accumulate in the brain and result in neurological conditions among older adults. “There’s no cost-effective technology for removing manganese and other pollutants such as sulfate from our waterways,” says Satoshi Ishii, an associate professor in the Department of Soil, Water, and Climate and a member of the University’s BioTechnology Institute (BTI). Instead, Ishii and fellow BTI member Cara Santelli, a geomicrobiologist and assistant professor in the Department of Earth Sciences turned to bioremediation to solve the problem.

Bioremediation uses microorganisms to break down harmful chemicals in water and soils. Ishii identified the microbe capable of removing manganese from water in Onneto Yu-no- taki falls, a waterfall in his native Japan. The falls contained high levels of manganese and sulfate, and as Ishii suspected, high levels of manganese-oxidizing microorganisms.

Emily Anderson, a graduate student in Ishii’s lab recently built a lab-scale bioreactor to house the manganese-oxidizing microorganisms. “I’m really interested in using living systems to clean water, especially when we don’t have the resources to do it in other ways.”

The bioreactor mimics the environment in the Onneto Yu-no- taki falls waterfall where a biofilm made up of microorganisms coats the streambed, and rocks covered in manganese oxides appear to have turned black. In the bioreactor, water flows through three consecutive rectangular compartments made of transparent plastic. In each compartment, microorganisms oxidize manganese and remove it from the solution. The bacteria, fungi, and algae form mats coating the sides of the compartments and algae serve as a food source for the manganese-oxidizing microorganisms. Over time, you can see tanks turn from green to black as the manganese oxides build.

Anderson tracks manganese oxidation by sampling the water and how much dissolved manganese was removed by the biological activity. She was surprised by how fast the oxidation occurred. The bioreactor removed all the dissolved manganese in a couple of hours.

Santelli and Ishii plan to optimize the process and refine the bioreactor’s design to determine which organisms are most efficient at oxidizing manganese. So far, Anderson has identified 60 different manganese-oxidizing microorganisms in the sediment samples Ishii brought back, and with the manganese oxidation working, the plan is to incorporate sulfate removal as well. Where
manganese is found in high amounts, sulfate is often present as well. It’s a particular concern in Northern Minnesota where bacteria in the subsoil transform sulfate into sulfide, which can inhibit the growth of wild rice.

The MnDRIVE team partnered with Barr Engineering, an environmental consulting company with headquarters in Minneapolis. Barr helped design a bioreactor that could be easily scaled up and will also help the team identify manganese and sulfate contaminated sites in Minnesota. Eventually, industrial-scale bioreactors could be used in water treatment facilities, and provide a cost-effective, sustainable solution to one of the state’s enduring environmental challenges.