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The Trail Biochemical Reactor and the Removal of Arsenic with a Focus on the Specific Role of Iron

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Title: The Trail Biochemical Reactor and the Removal of Arsenic with a Focus on the Specific Role of Iron
Author: Mattes, Allan
Department: School of Environmental Sciences
Program: Environmental Sciences
Advisor: Glasauer, Susan
Abstract: A bioremediation system was constructed in Trail British Columbia to treat high concentrations of Zn and sulphate through the formation of zinc sulphide (sphalerite). Arsenic concentrations were also high but it was unknown if arsenic would form similar sulphides and be removed. When it was, it was not clear what the mechanisms were. Therefore, a smaller pilot-scale sized system was constructed to specifically examine As removal to and delineate the removal mechanisms. It was noted that the concentration of Fe increased as seepage moved through the cells and it was hypothesized that this increase in Fe concentration could play a role in As removal. Analysis of the results of both the large system and the smaller system failed to fully explain As removal and it was decided to undertake a larger research program at the University of Guelph. Extensive analysis including As adsorption of the three substrate components (sand, limestone and pulp and paper biosolids) were completed. Most probable number bacteria studies of the small system were also completed. These results showed the expected bacteria as well as a previously unknown iron oxidizing bacteria. This IOB was isolated, characterized and identified. A second smaller system was constructed at Fleming College to further examine this bacteria. Anaerobic filtered samples of seepage were collected from horizontal sampling piezometers. These were analyzed by ICP-OES to measure the concentration of Fe and As on the filters. Correlation techniques were used to measure the association of these two elements on each filter. The same system was also used to study the changing internal dynamics of a BCR cell in operation. The final results provided information about the internal working of a BCR cell and showed that Fe was involved in some measure in these operations. Removal of arsenic in the Trail BCR was complex with multiple removal mechanisms. Formation of insoluble kottigite (Zn2(AsO4)3.7 H2O) initially takes place aerobically but it cannot form in the anaerobic regions of the cells. Arsenic can adsorb or co-precipitate on metal sulphides such as ZnS formed in the cells. In the most anaerobic regions orpiment (As2S3) can form.
Date: 2013-08

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