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Natural Attenuation of Nonionic Surfactants Used in Hydraulic Fracturing Fluids: Degradation Rates, Pathways, and Mechanisms Katie M. Heyob, Jens Blotevogel, Michael Brooker, Morgan Volker Evans, John J. Lenhart, Justin Wright, Regina Lamendella, Thomas Borch, and Paula J Mouser Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b01539 • Publication Date (Web): 06 Nov 2017 Downloaded from http://pubs.acs.org on November 8, 2017
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Natural Attenuation of Nonionic Surfactants Used in Hydraulic Fracturing Fluids: Degradation
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Rates, Pathways, and Mechanisms
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Katie M. Heyob†, Jens Blotevogel‡, Michael Brooker†, Morgan Volker†, John J. Lenhart†, Justin
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Wright , Regina Lamendella , Thomas Borch‡,||,§, and Paula J. Mouser*,†, ξ
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†
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Department of Civil, Environmental, and Geodetic Engineering, Ohio State University,
Columbus, Ohio 43210, United States ξ
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Department of Civil and Environmental Engineering, University of New Hampshire, Durham,
NH 03824, United States ‡
Department of Civil and Environmental Engineering, ||Department of Soil and Crop Science,
§
Department of Chemistry; Colorado State University, Fort Collins, CO 80523, United States
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Department of Biology, Juniata College, Huntingdon, PA 16652, United States
Keywords: alkyl ethoxylates, polyglycols, shale, Marcellus, nonylphenol, bacteria, diol dehydratase TOC ART
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ABSTRACT
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Hydraulic fracturing fluids are injected into shales to extend fracture networks that
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enhance oil and natural gas production from unconventional reservoirs. Here we evaluated the
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biodegradability of three widely used nonionic polyglycol ether surfactants (alkyl ethoxylates
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(AEOs), nonylphenol ethoxylates (NPEOs), and polypropylene glycols (PPGs)) that function as
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weatherizers, emulsifiers, wetting agents, and corrosion inhibitors in injected fluids. Under
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anaerobic conditions, we observed complete removal of AEOs and NPEOs from solution within
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three weeks regardless of whether surfactants were part of a chemical mixture or amended as
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individual additives. Microbial enzymatic chain shortening was responsible for a shift in
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ethoxymer molecular weight distributions and the accumulation of the metabolite acetate. PPGs
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bioattenuated the slowest, producing sizeable concentrations of acetone, an isomer of
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propionaldehyde. Surfactant chain shortening was coupled to an increased abundance of the diol
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dehydratase gene cluster (pduCDE) in Firmicutes metagenomes predicted from the 16S rRNA
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gene. The pduCDE enzymes are responsible for cleaving ethoxylate chain units into aldehydes
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before their fermentation into alcohols and carboxylic acids. This data provides new mechanistic
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insight into the environmental fate of hydraulic fracturing surfactants after accidental release
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through chain shortening and biotransformation, emphasizing the importance of compound
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structure disclosure for predicting biodegradation products.
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Environmental Science & Technology
INTRODUCTION
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High volume hydraulic fracturing (HVHF) well completion methods involve the delivery
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of 10-15 million liters of hydraulic fracturing fluid (HFF), composed of water and proppants
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(approximately 99% by mass) along with chemical additives (1%), at high pressures into shale
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formations to create fractures that enhance the extraction of oil and natural gas resources.1-3
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Recent studies have informed our understanding of organic compounds present in injected fluids
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and produced brines,4-7 including their inherent biodegradability and treatability.8-12 Much of the
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dissolved organic carbon (DOC) that constitutes additive pollutants within a typical HFF is
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quickly biodegraded (59% within 250 mg/L DOC) and mixed overnight (Table S1). Similarly, each of the four
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amendments (corrosion inhibitor, stimulation surfactant, polypropylene glycol (average
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molecular weight 425, Sigma Aldrich, St. Louis, MO) or propylene glycol (Thermo Fisher
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Scientific (Waltham, MA))) were combined with groundwater to a concentration of 350 mg/L
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total DOC and used in experiments within 24 hours.
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Anaerobic microcosm studies were conducted using Bennington silty loam collected as
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2-foot cores into sterile mason jars from soils adjacent to the airplane deicing pad at the Port
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Columbus International Airport in Franklin County, Ohio (GPS coordinates: 40.02 N 83.01 W).
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This location was specifically chosen to target microbial communities in former agricultural soils
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that were pre-acclimated to polyglycol compounds in order to diminish potential toxicity issues
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and reduce acclimation times to these compounds (i.e., best-case biodegradation scenario). The
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total organic carbon content of the sieved soil was 19 g/kg, the electrical conductivity was 299
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µS, and the pH was 7.4 based on a 1:1 Milli-Q water dilution41 and Orion probe measurements
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calculated prior to use. Particle size analysis of homogenized, sieved (2 mm mesh opening) soil
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cores showed the soil was 4% sand, 60% silt and 36% clay. A total of 20 g sieved soil and 100
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mL of amendment solution (SFF, stimulation surfactant, corrosion inhibitor, polypropylene
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glycol, propylene glycol, and/or raw groundwater) was added to bottles for a final 1:5 solid-to-
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liquid ratio. To achieve anaerobic conditions, liquids and solids were gassed with a 80:20 gas
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mixture containing N2 and CO2 for fifteen minutes. Bottles were then capped with rubber septa
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and crimp sealed, and headspace was gassed an additional fifteen minutes. Anaerobic conditions
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were confirmed through measurements of dissolved oxygen and other reduced chemical species
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(e.g. Fe(II)). Abiotic controls were autoclaved three times over a period of one week to de-
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activate cells and spores. All bottles were placed on a Thermo Scientific MaxQ 3000 shaker
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table at 75 rpm in the dark and held at 15 °C until sampling.
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Analysis of Dissolved Oxygen, pH, Chloride, Fe, Organic Carbon, and Organic Acids
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Solution pH and dissolved oxygen (DO) were measured on unfiltered samples using
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Orion Star probes (Thermo Fisher Scientific, Waltham, MA) calibrated prior to use. Changes in
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iron were monitored on unfiltered samples with a HACH DR/890 colorimeter (Loveland, CO)
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using method 8008.42 Filtered samples (PES 0.22 µm pore size, EMD Millipore, Billerica, MA)
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were used for analysis of chloride and organic constituents. Chloride, acetate, and propionate
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were analyzed by Ion Chromatography using a Dionex ICS 2100 and IonPac AS11-HC column
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at 35 °C at a flow rate of 1.5 mL/min and cell temperature of 30 °C. After acidification (pH
