Master of Science (MSc)
Faculty of Science
Dr. Robin Slawson
Improved techniques for remediating groundwater systems are required for the more than 500,000 contaminated sites in North America. Many of these sites are the legacy of historical industrial operations, inappropriate disposal practices and accidental releases. The most widely observed contaminant at many of these sites is petroleum hydrocarbons (PHCs). Recently, remediation efforts that involve the sequential application of treatment technologies have gained widespread interest. One specific sequential technology application or treatment train employs the aggressive nature of a chemical oxidation followed by bioremediation for polishing. When persulfate is used as the chemical oxidant its natural degradation by-product is sulfate, an electron acceptor for sulfate-reducing bacteria. Hence in this thesis, the focus is on ways to optimize the mass removal behaviour of a treatment train that involves the use of PHC biodegrading sulfate-reducing bacteria as a bioremediation tool for the ‘polishing’ of a contaminated site. Persulfate was predicted to have a multitude of effects on microbial communities, both positive and negative. It was hypothesized that the production of sulfate would enhance the sulfate-reducing community and subsequently increase biodegradation potential following a persulfate treatment. However, the use of a strong oxidant like persulfate may also have detrimental effects on microbial communities. In order to test this hypothesis, a bench-scale system was implemented to gather data for the analyses of this remediation technique. Microbiological methods and chemical analyses of geochemical parameters were used to examine diversity, richness and abundance of sulfate-reducing communities following persulfate treatments. Initially, the successful generation of anaerobic bioreactors containing an indigenous sulfate-reducing microbial community from a freshwater aquifer was completed and confirmed using colony-PCR. Approximately 3 ppm total PHC was then introduced into the reactors and the microbial community was then allowed to acclimate to the conditions. PHC biodegradation was confirmed (~ 5.7 µg/L/hr). The community was then exposed to two types of oxidants, unactivated and alkaline-activated persulfate. Immediately following exposure, culture-based methods revealed almost complete reduction of the microbial community (≤101 CFU/mL and SRB cells/mL). qPCR on a gene conserved within the sulfate-reducing phylogeny confirmed this reduction. However, by the fourth week of the recovery phase, bacterial counts and target genes rose above pre-treatment levels, indicating enhancement of the sulfate-reducing community following the oxidant exposure(s). However, the recovered community displayed differences in structure and function, as revealed by microbial community fingerprint profiles and a lowered biodegradation potential (~2.7 µg/L/hr). Overall this research illustrated the successful application of a remediation treatment train at a bench-scale level.
Bartlett, Christopher K., "Sulfate-Reducing Bacteria Community Analysis: ISCO/ISB Coupled Remediation" (2016). Theses and Dissertations (Comprehensive). 1810.