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.