For those who live and work In northern Minnesota, environmental quality— especially water quality— is a daily concern. Many livelihoods and cultural practices are at stake in this region rich in water and minerals, and sulfate pollution is a high-profile issue.

Sulfate is a problem elsewhere in the state, too, at some municipal wastewater treatment plants and food and ethanol industrial sites. But by far the most critical sulfate pollution is in northern Minnesota’s Iron Range, where taconite mines and processing plants discharge large volumes of high-sulfate waters into a boggy landscape where three continental watersheds meet. Raising the stakes even further, some of those discharged waters flow into traditional wild ricing areas— and wild rice is highly sensitive to sulfate, as described in a study by the Minnesota Pollution Control Agency. The sulfate issue truly dramatizes the varied interests found in this region.

Balancing multiple needs

To make use of northern Minnesota’s natural resources, its people have pursued a variety of livelihoods and traditions over time. Here, wild rice has been harvested by generations of indigenous peoples, an ongoing practice with deep cultural significance as well as economic value to many tribal communities. The Arrowhead region is an outdoor destination bordering on the Boundary Waters Canoe Area, offering boating, fishing, hiking, winter sports— and jobs related to those activities. And for over a century, the Iron Range has provided over half of the nation’s iron and taconite, shipped across the Great Lakes for steelmaking. These mining jobs are crucial to the economy of the region, the state, and the nation. Steel is crucial to our country’s infrastructure, even as we transition to a greener economy.

How can Minnesota protect the waters of this region in ways that balance all these needs? For decades that question has puzzled decision-makers and environmental regulators, especially regarding sulfate levels in surface water and groundwater impacted by mining operations. Do we protect the environment, or do we protect the mining operations? At Clearwater BioLogic, we see that as a false choice. We can protect both— with the right water treatment process in place.

Designated Wild Rice Waters in Minnesota’s Arrowhead Region

ClearWater Wild rice waters (blue dots) share the same watersheds with the Biwabik Iron Formation (red line), along which mining operations are clustered.

ClearWater Hand-harvested by canoe, wild rice is a nutritious food essential to the traditional diet and a source of pride for all Minnesotans.

The challenge: Excess sulfate

On the Iron Range, many of the lakes visible on a map are actually mine pit lakes, formed in abandoned iron ore pits, taconite pits and from their tailings ponds. Rainwater runs over the rock walls of the old dig sites to collect at the bottom and form lakes. That rock contains sulfide ores such as pyrite that react with water and oxygen, forming dissolved sulfate that accumulates in the water. Over time this concentration increases, often reaching 1000 milligrams per liter (mg/L) and higher. This water seeps into the surrounding lands and eventually reaches creeks that flow into the three watersheds of the region: the Lake Superior, Mississippi River, and the Hudson Bay Watersheds.

Sulfate (SO4) is a naturally occurring substance in water bodies, and at low concentrations it causes few problems. But at higher levels it can damage ecosystems and cause health problems like diarrhea and dehydration in wildlife, livestock, and even in humans, particularly infants, per the Environmental Protection Agency.

That’s why federal and state environmental agencies have set specific sulfate limits— and continue to adjust those limits— for various classes of water, depending on its intended use. Those uses range from domestic consumption to aquatic life to industrial or agricultural consumption.

Some relevant standards in northern Minnesota:
  • For industrial use (which includes mining), the Minnesota Pollution Control Agency is now setting a sulfate standard of 600 mg/L. (Compare that to the 1000 mg/L levels often found in mine-pit lakes.)
  • For drinking water, the EPA sets a secondary standard of 250 ml/liter of sulfate.
  • For wild rice production areas, the MPCA has set a very stringent standard of 10 mg/L.


The sulfate problem has thus been widely studied, documented and addressed in regulatory standards, but over the years those standards have not been enforced. One key obstacle: the current method to adequately treat sulfate, reverse osmosis, has been deemed prohibitively expensive by many mining operations. What Minnesota needs is a cost-effective way for mining operations to clean up these waters: a sustainable method that protects the environment and the livelihoods that depend on it. That’s where Clearwater BioLogic comes in.

A cost-effective solution

We at Clearwater BioLogic have developed a scalable, modular system that uses natural means to take sulfate out of water, even from concentrations of more than 1000 mg/L. The system can be set to meet the wild rice standard of 10 mg/L or even a goal of zero sulfate if needed. It’s a three-stage process: reducing sulfate biologically to sulfide, chemically converting sulfide to sulfur, and removing the sulfur from the system. Because it operates under water, it works effectively in all seasons.

Using natural, cost-effective methods, we can help ensure that water discharged from mining lands does not harm wild rice, while also providing a more economical method for mining companies to meet Minnesota’s sulfate standards. The Clearwater BioLogic bioreactor system is patented under US 10,597,318 B2 patent. (See “System details” for more details.)

It’s a triple win for Minnesota:
  • Good for the environment
  • Good for jobs and culture
  • Good for business
ClearWater Pilot-scale field test of a solar-powered Clearwater BioLogic system in a mining application.