The concept

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.

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.