CEE 155 Hydraulic fracturing wastewater: Treatment challenges,

options and innovations

Group 1 Adam Richardson, Annie Yu, Reilly Clewes and Scott Braithwaite

December 4, 2015

Abstract: The United States has in recent years seen a boom in its oil and natural gas industry, in part accelerated by the expansion of hydraulic fracturing, or “fracking.” Although fracking offers many benefits for natural gas production, it is highly controversial in terms of environmental effects. This is in no small part due to the uncertain nature of the wastewater generated via fracking procedures, which have been known to contain contaminants ranging from surfactants to biocides to radioactive components. As of now the database of known information is glaringly incomplete, highlighting the need for further collective research. Relevant to this is the development of sophisticated detection methods, which will facilitate study as well as assist in treatment technologies. Currently, fracking wastewater management options include underground injection, wastewater treatment, and wastewater recycling. Less conventional methods of treatment include more recent innovations such as mixing fracturing fluid with acid mine drainage, and reverse and forward osmosis. Keywords: hydraulic fracturing, wastewater treatment, wastewater recycling, underground injection, acid mine drainage

INTRODUCTION

Over the past decade the commercially unfeasible became feasible. Advances in directional drilling and high­pressure hydraulic fracturing, known together as “fracking,” have revolutionized natural gas production, positioning the United States to become the largest natural gas producer worldwide (Lutz et al., 2013). On its current trajectory, fracking will produce more than 75% of domestic natural gas by 2035 (Morrison, 2015). Yet as the vast production potential becomes increasingly realized, so do the environmental management challenges.

Wastewater management and disposal have emerged as central concerns and drivers of the controversy. Fracking, after all, involves injecting large volumes of fluid deep underground to break up tight rock formations to extract natural gas and other hydrocarbons. For every well drilled, 10 to 20 million liters (3 to 5 million gallons) of water are used, which includes sand and surfactants as “proppants” to open fissures and optimize the amount of gas and oil extracted (Arnaud, 2015) as well as assorted chemical additives that vary by the recovery method and underlying geology (Morrison, 2015). The returning early­stage water is called “flowback” and still contains the additives. Additional water continues to return throughout the life of the well and is called “produced water,” which is a mix of underground water and the fracking fluid. Together the flowback and produced water make up the wastewater from fracking, a complex mixture of organics, metals and radioactive material. According to the U.S. Environmental Protection Agency (USEPA, 2015), fracking wastewater management options include underground injection control (UIC) well disposal, wastewater treatment and reuse, and wastewater treatment and discharge at a centralized waste treatment (CWT) facility. See Figure 1 for an overview of water management for fracking.

As a major example, fracking of the Marcellus shale formation under Pennsylvania and the surrounding region increased the wastewater generated by nearly 6­fold since 2004 (Lutz et al., 2013), totaling over 6 million cubic meters by 2013 (Rahm et al., 2013). With only 9 UIC wells available (USEPA, 2015), existing disposal capacity is being quickly saturated (see Figure 2). Future development becomes limited by novel logistical or technological solutions for wastewater management. Treatment and reuse are becoming increasingly popular in this region, especially given that less than 1% of the Marcellus shale has been explored to date (Lutz et al., 2013). Fortunately, USEPA (2015) has not found evidence that fracking has led to widespread, systemic impacts on drinking water resources in the United States thus far.

In an effort to clarify the unique challenges of hydraulic fracturing wastewater management, this paper will first identify and analyze specific contaminants and water quality problems that are prevalent throughout the fracking industry. The next area of focus will be on methods of detection. Of particular interest are the advanced chemical techniques that prove essential in detecting the extensive range of contaminants associated with hydraulic fracturing fluid (HFF), as well as recently developed procedures and innovations. Lastly, various wastewater management options will be discussed at length, with an emphasis on their respective advantages and disadvantages with regard to efficacy and economy.

CONTAMINANT DESCRIPTION

Although a federal requirement to disclose the materials used in fracking fluids is lacking, over 30 states have taken or are in the process of taking up the slack by requiring disclosure (Morrison, 2015). To date, a number of analyses provide snapshots of parts of the fracking water process, although a more comprehensive picture is still lacking. A voluntary disclosure website (fracfocus.org) attempts to fill the gap.

Both the flowback and produced water can contain the original additives plus contaminants acquired deep underground, including the following:

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Fine sand to prop open fractures so natural gas can escape

Surfactants to reduce surface tension and friction, improve recovery of oil and inhibit scale

Antimicrobial compounds (e.g., glutaraldehyde) to kill microbes that produce corrosive acid or form well­clogging biofilms

Brine salts (e.g., iodide, bromide) because hydrocarbons formed in ancient oceans

High total dissolved solids (TDS) from underground minerals

Radionuclides (e.g., radium­226) found naturally underground

Natural gas and petroleum

Chemical reaction byproducts are also possible, with some reactions facilitated by the

fractured shale surfaces, and polymerization byproducts are possible due to the high temperature and pressure used (Arnaud, 2015). The fate and degradation of the antimicrobial compounds, known for their toxicity, have been reviewed by a group of Colorado researchers (Kahrilas et al., 2015).

Several studies provide snapshots of the variety of compounds found in fracking wastewater. From a Colorado well, Linden et al. (2015) identified 180 volatile organics, including xylenes, acetone and 2­butanone. Looking for inorganic compounds, Harkness et al. (2015) found elevated iodide, bromide and ammonium. The ammonium was at toxic levels (420 mg/L) and bromide and iodide are especially difficult to remove from drinking water, not to mention they can lead to the formation of carcinogenic disinfection byproducts. Finally, technologically enhanced naturally occurring radioactive material is brought to the surface in particles from the fractured underground rock formations, which may be filtered out, end up in landfills and subsequently leach out. Worker exposures can be worrisome because for radium­226 the total radioactivity goes up by a factor of about 6 within 15 days in a closed system due to the production of radon and other short­lived decay products (Arnaud, 2015).

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DETECTION METHODS

While measurement of some of the characteristics of fracking wastewater is straightforward (such as temperature, pH and TDS), the wide variety of organic compounds, their degradation products, inorganics and radionuclides require modern analytical chemistry techniques that are often quite expensive. Researchers at the University of Maryland have identified over 2,500 organic chemicals in fracking wastewater using Fourier transform ion cyclotron resonance mass spectrometry, and a group at Rice University used gas chromatography with mass spectrometry to identify remnants of fuel in the wastewater (Arnaud, 2015). Ethoxylated surfactants, including polyethylene glycols and linear alkyl ethoxylates, are major components of flowback and have been detected by both ultrahigh pressure liquid chromatography with Kendrick mass­defect quadrupole time­of­flight mass spectrometry (Thurman et al., 2014) and more­standard high performance liquid chromatography with tandem mass spectrometry (USEPA, 2014). The identification of bromide as an indicator of fracking contamination has led to an innovative technique: a microfluidic paper­based analytical device that uses quantitative colorimetric detection via a smartphone (Loh et al., 2015). Radionuclides, particularly radium­226, have been detected using the more cost­effective technique of inductively coupled plasma with mass spectrometry with results equivalent to the more­expensive standard method of high­purity germanium gamma spectroscopy (Zhang et al., 2015). Once the fracking wastewater has been well characterized, treatment options can be tailored to the specific contaminants, as outlined by Lester et al. (2015).

STANDARD TREATMENT METHODS

Most fracking wastewater in the United States is disposed of through underground injection. This is usually the least expensive management method, barring high transportation costs (USEPA, 2015). According to the USEPA, more than 98% of produced water generated by the oil and gas industry (including fracking operations) in the United States is injected underground. While this is not a treatment method that actually removes contaminants, underground injection protects the drinking water supply by placing the wastewater at depths well below aquifers.

Specifically, Class II Underground Injection Control Wells, in accordance with EPA regulations pursuant to the Safe Drinking Water Act, dispose of wastewater at depths of approximately 2,000 to 8,000 feet (Marcellus Shale Coalition, 2015). These wells inject water beneath confining geological layers such as shale. Around 40% of oil and gas industry wastewater is injected into Class II wells. Although the proportion specifically for fracking is hard to determine, the available data indicate that Class II wells are the main fracking wastewater management method (USEPA, 2015).

The primary limitation to the use of injection into Class II wells is the geographic distribution of the wells. Their location is limited by geology, and most are found in Texas,

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Oklahoma and Kansas (USEPA, 2015). Moving forward, seismic concerns may also affect the viability of underground injection (USEPA, 2015).

Another strategy is transporting the wastewater to a municipal treatment facility or a central waste treatment (CWT) facility. A CWT facility accepts industrial waste from off­site, treats it and discharges it to surface water or to a municipal facility for further treatment. Treated wastewater can also be reused in fracking operations, which is a common strategy in areas where access to Class II wells is limited, such as Pennsylvania (USEPA, 2015). According to the USEPA, there are 73 CWT facilities currently treating or planning to treat fracking wastewater, 39 of which are in Pennsylvania.

The treatment processes at CWT facilities differ depending on the fate of the effluent. So called “zero­discharge facilities” do not discharge either directly or indirectly to surface water, and therefore do not require TDS removal (USEPA, 2015). Instead, their effluent is destined primarily for reuse in fracking wells, as well as some disposal by evaporation or use for irrigation. These facilities employ basic treatment processes effective for the removal of suspended solids, oil and grease, scale­forming compounds, and metals (USEPA, 2015). The treatment technologies are similar to those found at a municipal facilities: granular media filtration, coagulation and sedimentation, chemical precipitation and dissolved air flotation (USEPA, 2015).

During the early years of the fracking boom, a large proportion of the wastewater transported for treatment was sent to municipal facilities. In Pennsylvania, the amount received by municipal facilities increased from less than 30 million liters per year from 2001­2004, to 460 million liters in 2008 (Lutz et al., 2013). Most of these facilities, however, were not equipped to treat TDS, resulting in a shift to treatment at CWTs (Ferrar et al., 2013; Lutz et al., 2013). Most new CWT facilities have TDS removal capabilities (USEPA, 2015). These advanced treatment technologies are more energy­ and labor­intensive because they include membrane filtration, thermal distillation, ion exchange and adsorption (USEPA, 2015). A promising new technology emerging is filtration with nano­structured membranes. The oily compounds in fracking wastewater will degrade a traditional membrane, but nano­structured ones have the potential to effectively repel oils as well as removing heavy metal ions (Stebe, 2015).

The recycling of fracking wastewater for use in new well development has increased in recent years, rising from 13% before 2011 to 56% in that year (Lutz et al., 2013). Reuse has the advantage of requiring much less treatment than for water destined for discharge to surface water bodies; however, scaling from high ion concentrations and corrosion from anaerobic bacteria byproducts must be addressed (Lutz et al., 2013). High transportation costs make on­site treatment for reuse economically desirable and also avoid potential for spills or leaks during transport (USEPA, 2014).

INNOVATIVE TREATMENT METHODS One of the more creative treatment methods being developed is the mixing of HFF with

the runoff from mine tailings and works, called acid mine drainage (AMD). This is done to remove the heavy metals and radioactive isotopes through binding, precipitation, and adsorption

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with chemicals and particles that are found in the AMD (Kondash et al., 2014). This technique, which is currently being studied by a team working from Duke University, has seen radioactive isotope removal rates of 60­100% within 48 hours of mixing (Kondash et al., 2014). The resulting mixed solution contains lower levels of TDS, heavy metals, and radioactive isotopes than those of the original HFF and AMD. Needless to say, this method is attractive because it takes two contaminated wastewaters and combines them into a far cleaner product, reducing the need for further treatment as well as the amount of fresh water necessary to process either the ADM or HFF alone (Kondash et al., 2014). Because this method requires the capture and transport of AMD, it can be labor­intensive. It can also be moderately costly, because the wastewater requires further processing after mixing. Laboratory tests are being scaled to real­world situations to determine whether this method is cost­effective (Kondash et al., 2014).

Although reverse osmosis is a common treatment method, innovations are required to apply it to HFF. Under reverse osmosis, a contaminated fluid is forced through a membrane that has pores only large enough to allow water molecules through. Since the fluid is being driven against its concentration gradient, high pressures must be applied to overcome osmotic pressure (hence, “reverse” osmosis). Because larger pressures—and thus larger energy costs—are necessary to treat water with high TDS levels (Younos and Tulou, 2005), reverse osmosis is currently limited to treating TDS concentrations of under approximately 40,000 mg/L (USEPA, 2015), which poses a challenge to TDS­laden HFF. Fortunately, a team from the University of Pennsylvania is developing a membrane that can process wastewater with high contamination efficiently, and even remove a wider range of contaminants.

Forward osmosis, another innovative technology, uses a draw solution to draw water out of the HFF across a membrane gradient. This technique is used when it is easier to remove the draw solution from the water than it is to remove the original contaminants from the HFF (Coday et al., 2014). After dewatering, the draw solution concentrate is recycled, and the HFF brine is disposed of. The technologies used in these processes are well established and can be tailored to the specific wastestream. The downside, however, is that this process is very energy­intensive, requires costly machinery, and creates a large amount of byproducts; i.e., the HFF brine and spent membranes (Gregory et al., 2011). Typically, the cost is not attractive to fracking operators.

NATURAL TREATMENT METHODS

“Natural processes” is a broad, catch­all category that includes any treatment method involving nature to purify the water with little or no pre­treatment. These methods require little additional energy and are not labor­intensive, thus making them attractive if weather and physical space permit.

Common methods in dry climates are evaporation and percolation. For example, HFF can be spread across fields, placed in evaporation ponds, or sprayed on roads as an anti­dust agent (USEPA, 2015). There is great concern with these treatment methods, however, because the radioactive isotopes brought to the surface by the HFF are not adequately removed and end up leaching into groundwater (Brown, 2014).

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In colder climates, freeze­thaw is an option to improve the quality of the water with minimal effort (Gregory et al., 2011). The process works exactly as the name suggest: HFF is sprayed across “chilling sheets” during the cold months, where it freezes to form ice crystals. Due to the lower freezing point of salt solutions, the now­concentrated HFF brine sloughs off and can be disposed via other methods. When warm weather arrives, the ice thaws and is sent for further treatment. Although freeze­thaw requires labor it is fairly low­energy, albeit with a rather large time component.

As a final natural process, microbial organisms can be relied upon to remediate HFF. This approach involves surface discharges or discharging to artificially created wetlands or reed beds to bind/process the contaminants (USEPA, 2015). For surface discharges, a great deal of treatment is required prior to discharge. For artificially created wetlands and reed beds, the level of treatment before discharge is based on the tolerances and capture characteristics of the organisms present (USEPA, 2015). It is difficult to estimate the efficiencies of these treatment methods as a whole because pre­treatment is performed prior to discharge to the surface waters or artificial environments.

CONCLUSIONS

Fracking wastewater presents the oil and gas industry with familiar wastewater treatment challenges, although at larger quantities and with exotic additives. The most common form of wastewater management is underground injection, which is low­cost but limited by geographic distribution of injection wells. In the case where such wells are not available, wastewater can be rerouted to central waste treatment facilities. These facilities may discharge treated effluent to surface water or send it to a municipal facility for further treatment. Another option is to reuse the water for fracking operations, which removes the need to process the water through advanced treatment technologies that are energy­ and labor­intensive. On­site reuse also reduces associated transportation costs. The disadvantage of reuse methods, however, is that they often face problems with scaling and corrosion.

In addition to conventional methods, there are many innovative approaches to fracking wastewater management. One such technique is to combine hydraulic fracturing fluid with acid mine drainage, which effectively removes radioactive isotopes and heavy metals through precipitation and requires very little fresh water to do so. As a new technology, however, the costs are uncertain. Both reverse osmosis and forward osmosis use membrane technology to filter out contaminants. Although membrane technologies have improved, they remain very energy­intensive and result in a lot of byproduct. A less expensive treatment option is to exploit natural processes to treat wastewater. Such natural processes include evaporation and percolation (low energy and labor costs), freeze­thaw cycles (low energy but time­intensive), and biological processes facilitated through natural organisms (generally requires pre­treatment).

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REFERENCES Arnaud, C.H. (2015). Figuring out Fracking Wastewater. Chem. Eng. News, 93(7):8­12.

Brown, V.J. (2014). Radionuclides in Fracking Wastewater: Managing a Toxic Blend. Environmental Health Perspectives, 122(2), A50–A55.

Coday, B.D., Xu, P., Beaudry, E.G., Herron, J., Lampi, K., Hancock, N.T., Cath, T.Y. (2014). The sweet spot of forward osmosis: Treatment of produced water, drilling wastewater, and other complex and difficult liquid streams. Desalination, 333, 23­35.

Ferrar, K.J., Michanowicz, D.R., Christen, C.L., Mulcahy, N., Malone, S.L., Sharma, R.K. (2013). Assessment of Effluent Contaminants from Three Facilities Discharging Marcellus Shale Wastewater to Surface Waters in Pennsylvania. Environ. Sci. Technol., 47, 3472−3481.

Gregory, K.B., Vidic, R.D., Dzombak, D.A. (2011). Global Water Sustainability: Water Management Challenges Associated with the Production of Shale Gas by Hydraulic Fracturing. Elements, 7(3), 181­186.

Harkness, J.S., Dwyer, G.S., Warner, N.R., Parker, K.M., Mitch, W.A., Vengosh, A. (2015). Iodide, Bromide, and Ammonium in Hydraulic Fracturing and Oil and Gas Wastewaters: Environmental Implications. Environ. Sci. Technol., 49(3), 1955­1963.

Kahrilas, G.A., Blotevogel, J., Stewart, P.S., Borch, T. (2014). Biocides in hydraulic fracturing fluids: A critical review of their usage, mobility, degradation, and toxicity. Environ. Sci. Technol., 49(1), 16­32.

Kondash, A.J., Warner, N.R., Lahav, O., Vengosh, A. (2014). Radium and Barium Removal through Blending Hydraulic Fracturing Fluids with Acid Mine Drainage. Environ. Sci. Technol., 48, 1334−1342.

Lester, Y., Ferrer, I., Thurman, E.M., Sitterley, K.A., Korak, J.A., Aiken, G., Linden, K.G. (2015). Characterization of hydraulic fracturing flowback water in Colorado: Implications for water treatment. Science of The Total Environment, 512­513, 637–644.

Loh, L.J., Bandara, G.C., Weber, G.L., Remcho, V. T. (2015). Detection of water contamination from hydraulic fracturing wastewater: a μPAD for bromide analysis in natural waters. Analyst, 140(16), 5501­5507.

Lutz, B.D., Lewis, A.N., Doyle, M.W. (2013). Generation, transport, and disposal of wastewater associated with Marcellus Shale gas development. Water Resources Research, 49, 647–656.

Marcellus Shale Coalition (2015). Class IID Underground Injection Control (UIC) Wells: What should Pennsylvanians know? Fact sheet.

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Morrison, J. (2015). Disclosure Debate. Chem. Eng. News, 93(7), 13­14.

Rahm, B.G., Bates, J.T., Bertoia, L.R., Galford, A.E., Yoxtheimer, D.A., & Riha, S.J. (2013). Wastewater management and Marcellus Shale gas development: Trends, drivers, and planning implications. Journal of Environmental Management, 120, 105­113.

Stebe, K. (2015). Nano­structured membranes developed to filter wastewater produced by fracking. Membrane Technology, 2015(3), 9.

Thurman, E.M., Imma Ferrer, I., Blotevogel, J., Borch, T. (2014). Analysis of Hydraulic Fracturing Flowback and Produced Waters Using Accurate Mass: Identification of Ethoxylated Surfactants. Anal. Chem., 86, 9653­9661.

USEPA. (2014). The Verification of a Method for Detecting and Quantifying Diethylene Glycol, Triethylene Glycol, Tetraethylene Glycol, 2­Butoxyethanol and 2­Methoxyethanol in Ground and Surface Waters. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. EPA/600/R­14/008. January.

USEPA. (2015). Assessment of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources. External Review Draft. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. EPA/600/R­15/047. June.

Younos, T., Tulou, K. (2005). Overview of desalination techniques. Journal of Contemporary Water Research & Education, 132(1), 3­10.

Zhang, T., Bain, D., Hammack, R., Vidic, R.D. (2015). Analysis of Radium­226 in High Salinity Wastewater from Unconventional Gas Extraction by Inductively Coupled Plasma­Mass Spectrometry. Environ. Sci. Technol., 49, 2969­2976.

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TABLES None.

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FIGURES

Figure 1. Fracking operation water loop (Arnaud, 2015)

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Figure 2. Conventional and Marcellus shale wastewater volumes by year for each management method

(Lutz et al., 2013)

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