Doctoral Dissertations

Date of Award

12-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Energy Science and Engineering

Major Professor

Terry C. Hazen

Committee Members

Kimberly E. Carter, Frank Loeffler, Gary S. Sayler, Amy K. Wolfe

Abstract

The goal of this dissertation was to better understand the environmental impacts of biocides used in unconventional oil and gas (UOG) practices. Specifically focusing on how industrial biocides may impact aquatic microbial communities, biocide degradation potential, and contribute to antimicrobial resistance propagation. Recently, the energy sector has seen a stark increase in biocide use, due to the dramatic growth in hydraulic fracturing (HF) operations. Biocides in HF are used to suppress microbial-induced corrosion, biofouling, and hydrogen sulfide production. The implications of biocide usage expansion, its impacts to antimicrobial resistance, and to environmental and public health risks are not fully understood.To understand these knowledge gaps, microcosm-based studies were used to investigate the effect of biocide addition to both HF-impacted and unimpacted streams. The two most common HF biocides, glutaraldehyde and 2-2-dibromo-3-nitrilopropionamide (DBNPA), were used in two otherwise identical experiments. Degradation of the biocides and microbial community changes were measured over time. Results suggest that glutaraldehyde is more persistent in stream waters previously impacted by HF. However, the microbial community was able to tolerate it as shown by higher microbial diversity and biomass. The DBNPA microcosms experiment showed that previous HF impact, associated with higher total organic carbon, favors a less toxic and persistent DBNPA degradation pathway. Many unidentified brominated species were detected in both HF-impacted and unimpacted conditions. Whole genome sequencing of strains belonging to environmentally relevant genera enriched during the biocide microcosm and isolated in biocide plates were investigated to find relevant genes correlated with DBNPA resistance. Thirteen orthologous genes with predicted functions such as mobile elements (recombinase and terminase), efflux pumps, and possible enzymatic deactivation of the biocide were found. Finally, the knowledge gaps that need to be addressed to perform a risk assessment of antimicrobial resistance caused by biocide usage in UOG production were identified and discussed. This work should help oil and gas operators, environmental response teams, and regulators reach convergence about the risks and aquatic microbial community response to biocides in UOG production and help with preventive strategies and better formulations to minimize the effect this practice has in the environment.

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