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

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.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat