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Biostimulation and Petroleum Hydrocarbon Remediation: Effects on Microbial Communities and Geochemistry

Posted on 2017-10-18 in Events
Oct 20, 2017

Please join us for a Graduate Student Seminar this Friday October 20 at 3:30 pm in rm 155 Geology presented by Scott Colville, MSc candidate:

Biostimulation and Petroleum Hydrocarbon Remediation:

Effects on Microbial Communities and Geochemistry

Scott Colville

University of Saskatchewan

Groundwater at a petroleum hydrocarbon (PHC) contaminated site in Saskatoon, SK was amended with a solution of sodium tripolyphosphate, nitrate, and ferric ammonium citrate to enhance PHC-remediation. The amended groundwater was circulated and re-amended approximately every two weeks from July 2016 to October 2016. Groundwater samples were collected for geochemical and microbiological analyses prior to biostimulation (June 2016), during biostimulation (August 2016 and October 2016), and after one field season of biostimulation (June 2017). Sediment samples were collected from boreholes to characterize mineralogy before and after biostimulation.

The objectives of this study were to: 1) examine the effects of the biostimulation solution on site microbiology and geochemistry over time, and 2) develop a conceptual model of the microbiological and geochemical effects of biostimulation at the site. The hypotheses of this study are that the biostimulation solution would: 1) enrich genera of bacteria known to couple Fe(III) reduction to PHC-oxidation, 2) lead to increased levels of dissolved and mineralized anaerobic respiration products (e.g. Fe2+ and magnetite), and 3) enhance PHC-remediation at the site.

We extracted DNA from filtered groundwater samples and used high-throughput 16S rRNA gene sequencing to complete a microbial census. Sequence results were processed using the mothur software package. Groundwater samples were also analyzed for general chemistry (e.g. major ions, alkalinity, and pH), dissolved metals, and PHCs (BTEX and F1-F2 PHCs). Filtered groundwater samples were also analyzed for metabolites from PHC-biodegradation. Increased metabolite concentrations would indicate enhanced PHC-remediation. Sediment mineralogy was characterized using synchrotron techniques (PXRD, S XANES, and Fe XANES) at the Canadian Light Source.

Sediment mineralogy and groundwater geochemistry suggest that Fe(III)-reduction and SO4-reduction are important biogeochemical reactions occurring at the site. Sequencing results from groundwater samples show that relatives of Fe(III)-reducers (Geobacter and unclassified Comamonadaceae) and SO4-reducers (Desulfosporosinus) were the most common bacteria in the contaminated region of the site, and that during biostimulation Fe(III)-reducers (unclassified Comamonadaceae) were enriched at the expense of SO4-reducers (Desulfosporosinus). These unclassified Comamonadaceae were likely enriched due to increasing nitrogen concentrations, and outcompeted the Desulfosporosinus for carbon and nutrients. However, sequencing results from June 2017 (after biostimulation) show the Desulfosporosinus community increasing. PHC concentrations and metabolite data suggest that biostimulation has enhanced PHC-remediation at the site. Overall, these results show that the biostimulation enhanced PHC-remediation through Fe(III)-reduction, but SO4-reduction could be an important biogeochemical reaction in future remediation at the site.

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