The Clearwater BioLogic sulfate remediation system was developed and tested in northern Minnesota, where a century of iron and taconite mining has left excess sulfide in abandoned mine-pit lakes. In the mid-1960s, area lakes and rivers were found to contain rising sulfate levels, and at times acidic runoff and dissolved metals. These substances were harming ecosystems, including the wild rice that grows in some of those waters. In 1973 Minnesota established a strict sulfate standard (10 milligrams per liter) to protect wild rice, but it was rarely enforced for lack of a cost-effective remediation method. Over time, reverse osmosis systems were developed to remediate sulfate, but they were deemed prohibitively expensive by the mining companies. The stalemate persisted for decades.
The idea for a new, affordable, nature-based sulfate remediation system came from environmental engineer Jeffrey Hanson, an Iron Range native. Through a globe-spanning career, Hanson had addressed a variety of mining-related environmental issues and founded his own company, Clearwater Layline. When he returned to Minnesota in 2005, he brought a fresh eye to the sulfate problem. Over the next decade, Hanson conceived of a sulfate remediation process with three steps: biological reduction, chemical conversion, and removal. Along the way, other partners helped develop each part of the system.
A key idea for the biological phase arose through Hanson’s work on another project: floating islands for placement in polluted water bodies. These islands were designed to host naturally occurring water-purifying microbes on their undersides, where recycled plastic fibers offered high surface area while allowing for ease of waterflow; the islands also offered habitat for aquatic plants and wildlife. That success led Hanson to consider designing a floating bioreactor— again with both high surface area and high void volume— specifically to host sulfate-reducing bacteria (SRB) in an underwater containment vessel. These bacteria occur naturally in bogs and swamps, where they reduce sulfate to hydrogen sulfide. Perhaps that nature-mimicking process could be applied in mine pit lakes. Bioremediation engineer Mark Riensell aided Hanson in that insight.
Hanson’s concept for a scalable raft of bioreactor modules hosting sulfate-reducing bacteria. Shown here: 2 rafts, each with 8 modules. Patented US 10,597,318 B2.
Exploring sulfate removal now became the focus of Hanson’s own company, Clearwater Layline,
aided by associate Rob Scarlett. In 2011, bench scale tests confirmed that SRB could be
encouraged to proliferate in a controlled system and that they would convert sulfate to
hydrogen sulfide, which could then be treated with iron to form an insoluble precipitate for
removal from the system.
For full-scale field testing, Clearwater Layline developed a series of floating bioreactor modules, each one a drumlike 4000-gallon containment vessel. Linked in rafts of eight around a central settling tank, the submerged modules would host sulfate-reducing bacteria that would attach to recycled fibers (each module’s fibers offering 100,000 square meters of surface area). Solar-powered pumps would keep water moving through each module, and controlled nutrients for the bacteria would be added through an inlet port. Through an outlet port, the sulfate-reduced water would flow to the central settling tank.
Compared to attachment media of other bio-carriers, the Clearwater BioLogic module’s surface area offers a huge advantage.
Field testing, summer 2014.
In early spring of 2013, the first four bioreactor modules were launched into the mine pit lake, which had a sulfate concentration of about 1,100 mg per liter. By July the units had proven their success.
In 2014 fourteen new bioreactor modules were deployed for year-round operation as Phase 2 of the field tests, again funded by IRRRB and NRRI. The data quickly confirmed effective wintertime operation and excellent sulfate reduction. NRRI and the University of Minnesota recognized that Clearwater Layline’s project could be a platform for gaining a better understanding of the sulfate-reduction process.
The system operates reliably year-round.
In early 2018, Clearwater Layline worked with RNAS Remediation Products to define new electron
donor and nutrient feed possibilities that will significantly reduce the operating costs of the
biological part of the sulfate reduction system. This biological system is patented under US
The chemical phase of the system incorporates USP Technologies’ proven PRI-SC method of converting hydrogen sulfide to elemental sulfur and ferric hydroxide. The technology produces a sludge that can be totally removed from the water to avoid any possible recreation of sulfate or sulfide further downstream. The USP Technologies PRI-SC system is patented under US 6,775,604 and US 7,147,783 (See “System details” for more details.).
A new company, Clearwater BioLogic, LLC, was then formed between Jeffrey Hanson of Clearwater Layline, LLC and Bill Newman of RNAS Remediation Products Inc. to install and operate sulfate reduction systems based on this combined technology. In 2018, Clearwater BioLogic was chosen for the University of Minnesota’s MN Cup Challenge, a competition for new enterprises. Showcasing its sulfate-reduction system, the company was a division semifinalist and the winner in the “Best Startup in Greater Minnesota” category. Media attention includes an interview with Jeffey Hanson by Minnesota Public Radio’s Elizabeth Dunbar, “Can science settle the dispute over wild rice? Babbitt native says yes, by imitating nature” (May 15, 2018)
Clearwater BioLogic provides Sulfate Solutions: Following Nature’s Lead.