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UBC Theses and Dissertations

Novel two-stage biochemical process for hybrid passive/active treatment of mine-influenced water Lundquist, Lauren

Abstract

The research goal was to develop and test a novel hybrid passive/active treatment system to remove metals from mine-influenced water that also contains sulfate. Current passive treatment systems for metal removal from sulfate-rich mine-influenced water include a type of biochemical reactor (BCR) called a permeable reactive barrier (PRB) which suffers from poor operational performance, such as metal sulfide retention and declining efficacy with time due to depletion of the solid organic materials. The lab-scale work of this thesis included proof-of-concept experiments in order to validate the proposed new design that decouples the metal removal and biological sulfate reduction steps into two stages and uses a liquid carbon source. The kinetic studies for sulfate reduction with leachates were done in batch bioreactors where a laboratory standard, lactate, achieved 66% sulfate removal and leachates from hay & wood chip mix and pulp & paper mill biosolids, achieved 66% and 34%, respectively. After proving that sulfate-reducing bacteria (SRB) could successfully utilize a leachate as a carbon source, the next step was to prove that the biologically produced (biogenic) sulfide in the bioreactors was effective at reacting with metal ions in the real mine-influenced water in order to create a metal precipitate. Zinc, cadmium and lead were removed at 90% and above. After the proof-of-concept experiments were completed in the lab, a continuous flow experiment was designed and implemented in the field at a mine site. The two-stage design decoupled the biological sulfate reduction reaction from the chemical metal precipitation reaction in a series of two packed-bed column reactors. Three different column systems were set up using a hay and wood chip mix leachate, molasses and a negative control. All three systems were tested for a duration of 96 days, showing that both tested liquid carbon sources could remove sulfate to extents greater than 73% and precipitate Zn, Cd and Pb to achieve greater than 85% removal. These results will inform further pilot testing on the mine site, and implementing the design improvements will help to avoid problems associated with passive treatment systems in the past.

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Attribution-NonCommercial-NoDerivatives 4.0 International