The Clearwater BioLogic sulfate remediation system was developed and tested in northern Minnesota, where a century of iron and taconite mining has left excess sulfate 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 concept
The idea for a new, affordable, nature-based sulfate remediation system came from environmental engineer Jeffrey Hanson, an Iron Range native. 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, conversion with iron, 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: two linked rafts, each with eight modules around a central tank. Patented US-10.597.318-B2 and US-11.104.596.
The latest development is to use reactive, reduced, iron to react with the hydrogen sulfide produced in the first biological step. This reaction forms iron sulfide that can be trapped on the surface of the iron or precipitated out as a fine-grained iron sulfide slurry. The precipitant can then be removed from the system effectively ellkiminate the sulfur and avoiding any regeneration of sulfate downstream. Patent Pending on this second phase.
The work begins: Field testing, phase 1
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 (SRB) 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.
With this design concept in hand, Clearwater Layline made plans for Phase I field tests of the modular Floating Sulfate-Reducing Bioreactor. Funding was provided in 2012 by the Laurentian Partnership of the Iron Range Resource and Rehabilitation Board (IRRRB) and the Natural Resource Research Institute (NRRI) of the University of Minnesota. Cliffs Natural Resources and PolyMet Mining agreed to let the company use a mine pit lake at the former Erie/LTV mine site near Babbitt.
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.
Field testing, phase 2
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.
Progress was boosted further in 2015 by a grant from MnDRIVE, a partnership between the University of Minnesota and the State of Minnesota that aligns research with industry needs to address “grand challenges.” The grant enabled NRRI and Clearwater Layline to build an additional bioreactor raft of seven modules, along with the previous fourteen, and provide research data for NRRI, UMD, and the University of Minnesota through late fall 2016. In July 2017, the results and conclusions were published as The MnDRIVE Interdisciplinary Project Implementation of Smart Remediation Technologies to Reduce Sulfate in Northeast Minnesota Watersheds.
The report confirms that
- The modular system successfully operated year-round for over 4 years.
- From beginning sulfate concentrations of about 1,100 mg per liter, the system regularly achieved 90% + sulfate reduction to hydrogen sulfide.
- The system provided up to 100% sulfate removal, even in winter.
- Sulfur was removed as FeS and elemental S precipitates.
Even after the publication of the MnDRIVE report, Clearwater Layline continued analyzing the data and reviewing operational records. The company found ways to improve the system throughput, stabilize performance, and significantly reduce capital costs.
Formation of Clearwater BioLogic
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-10.597.318-B2 and US-11.104.596.
The second step of the system incorporates reactive, metalic iron. This iron has been reduced from iron oxide by removing the oxygen to create a reactive iron that bonds with the hydrogen sulfide produced biologically in the first step. See System Details for more information.
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 included a May 2018 interview with Jeffrey Hanson by Minnesota Public Radio’s Elizabeth Dunbar: Can science settle the dispute over wild rice? Babbitt native says yes, by imitating nature.
Clearwater BioLogic provides Sulfate Solutions: Following Nature’s Lead.