Biodegradation in Waters from Hydraulic Fracturing: Chemistry, Microbiology, and Engineering

Abstract

Hydraulic fracturing is a method of oil and gas extraction from shale in which substantial volumes of water return to the surface containing chemicals and microorganisms. This paper begins to address the microbial composition and aqueous chemistry and the potential for intrinsic and enhanced bioremediation of these waters. The waters from a gas and oil shale in the Marcellus and Bakken regions, respectively, were analyzed for inorganic elements, organic chemicals, microbial taxonomic composition, and biodegradative capabilities. The waters were highly saline, reaching NaCl concentrations up to 3.5 N, but no significant levels of radioactive elements were detected. More than 1,000 organic compounds were separated and identified by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. The major classes of organic compounds, in order of decreasing abundance, were aliphatics, cycloaliphatics, single-ring aromatics, and polycyclic aromatic compounds. The bacterial genera found natively in the waters were identified by sequencing the 16S rRNA genes within the extracted DNA. The major genera identified included strains known to thrive under saline conditions (Halanaerobium, Marinobacter, Oceanimonas, Streptohalobacillus) and degrade petroleum hydrocarbons (Thauera, Pseudomonas, Marinobacterium, Williamsia, Colwellia). Microbial populations were extracted from the Bakken shale waters, encapsulated within silica gels, and then reintroduced into their waters of origin. Both intrinsic biodegradation from the free native microorganisms and enhanced biodegradation with the addition of encapsulated bacteria were observed. In total, this paper begins to better define the properties of waters derived from hydraulic fracturing and suggests a potential for the application of bioremediation to remove organic contaminants.