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Enhanced Petroleum Hydrocarbon Remediation by Biostimulation: Effects on Groundwater Microbial Communities, Geochemistry, and Mineralogy



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Groundwater at a petroleum hydrocarbon (PHC) contaminated site in Saskatoon, SK was amended with a solution of nitrate as nitric acid, sodium tripolyphosphate, and ferric-ammonium-citrate to enhance PHC remediation. Groundwater was collected for geochemical and microbiological analyses before, during, and after biostimulation amendments. Sediment samples were also collected to characterize mineralogy before and after biostimulation. I hypothesized that the biostimulation solution would enrich taxa that couple Fe(III) reduction to PHC oxidation, increase levels of dissolved and mineralized Fe(III) reduction products, and enhance PHC remediation. I performed high-throughput amplicon sequencing of the 16S rRNA gene of genomic DNA extracted from filtered groundwater samples and performed a microbial community analysis on the data. Groundwater samples were also analyzed for general chemistry (e.g., pH, alkalinity, cations, and anions), PHCs (e.g., BTEX), and metabolites of PHC biodegradation. Sediment mineralogy was characterized using synchrotron techniques (e.g., Fe XANES). This was a novel approach provided unique insights into the biogeochemistry of PHC biodegradation. Metabolite results provided strong evidence that the biodegradation is occurring at this site and multiple lines of evidence suggest that Fe(III) and sulfate reduction were the key biogeochemical processes occurring at the site. Relatives of Fe(III) reducers (Geobacter and unclassified Comamonadaceae) and sulfate reducers (Desulfosporosinus) dominated the microbial community profiles of the contaminated monitoring wells. During biostimulation, proportions of unclassified Comamonadaceae increased relative to other bacteria in some monitoring wells because of the availability of fixed nitrogen (e.g., ammonia). In other areas of the site this did not occur; in these cases, PHC concentrations decreased less. Multiple lines of evidence also suggest that nitrate in the biostimulation solution caused FeS oxidation. This nitrate-dependent FeS oxidation possibly decreased PHC biodegradation potential either by decreasing nutrient availability and/or shifting the microbial community profile. Overall, these results suggest that the biostimulation solution stimulated Fe(III) reduction.



bioremediation, biostimulation, petroleum hydrocarbons, BTEX, biogeochemistry



Master of Science (M.Sc.)


Geological Sciences




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