Repository for Oil and Gas Energy Research (ROGER)

Abstract:
Produced water is the largest volume of waste product generated during oil and natural gas exploration and production. The traditional method to dispose of produced water involves deep well injection, but this option is becoming more challenging due to high operational cost, limited disposal capacity, and more stringent regulations. Meanwhile, large volumes of freshwater are used for hydraulic fracturing. The goal of this study is to develop cost-effective technologies, and optimize system design and operation to treat highly saline produced water (120–140 g/L total dissolved solids) for hydraulic fracturing. Produced water was collected from a salt water disposal facility in the Permian Basin, New Mexico. Chemical coagulation (CC) using ferric chloride and aluminum sulfate as coagulants was compared with electrocoagulation (EC) with aluminum electrodes for removal of suspended contaminants. The effects of coagulant dose, current density, and hydraulic retention time during EC on turbidity removal were investigated. Experimental results showed that aluminum sulfate was more efficient and cost-effective than ferric chloride for removing turbidity from produced water. The optimal aluminum dose was achieved at operating current density of 6.60 mA/cm2 and 12 min contact time during EC treatment, which resulted in 74% removal of suspended solids and 53%–78% removal of total organic carbon (TOC). The energy requirement of EC was calculated 0.36 kWh/m3 of water treated. The total operating cost of EC was estimated $0.44/m3 of treated water, which is 1.7 or 1.2 times higher than CC using alum or ferric chloride as the coagulant, respectively. The EC operating cost was primarily associated with the consumption of aluminum electrode materials due to faradaic reactions and electrodes corrosions. EC has the advantage of shorter retention time, in situ production of coagulants, less sludge generation, and high mobility for onsite produced water treatment. The fine particles and other contaminants after coagulation were further treated in continuous-flow columns packed with different filter media, including agricultural waste products (pecan shell, walnut shell, and biochar), and new and spent granular activated carbon (GAC). Turbidity, TOC, metals, and electrical conductivity were monitored to evaluate the performance of the treatment system and the adsorption capacities of different media. Biochar and GAC showed the greatest removal of turbidity and TOC in produced water. These treatment technologies were demonstrated to be effective for the removal of suspended constituents and iron, and to produce a clean brine for onsite reuse, such as hydraulic fracturing.

Abstract:
This work addresses three significant issues associated with hydraulic fracturing in US shale fields: flaring/venting of excess natural gas, disposal of flowback water and freshwater procurement. Flaring/venting of excess gas is a significant contributor to global emissions. This work presents a novel utilization concept, wherein excess gas is used onsite to power reverse osmosis (RO)-based treatment of flowback water to supply freshwater for oilfield operations. This study details technical and techno-economic analyses of the above concept. An analytical model is extended and improved to quantify RO-based freshwater production for flowback water of different salinities. The technical performance of RO systems is analyzed and compared with two competing gas utilization technologies (thermal desalination, atmospheric water harvesting). The use of these technologies in the top eight US shale fields is analyzed, and a techno-economic analysis of RO-based water treatment is conducted. Results indicate that this concept will significantly benefit the Eagle Ford and Niobrara shales. It can meet 200% of water requirements and reduce wastewater disposal by 60% in the Eagle Ford. Furthermore, such RO-based projects can have favorable payback periods of as low as one year. Importantly, this waste-to-value concept has worldwide relevance since the underlying issues are present globally.

Abstract:
Hydraulic fracturing of shale gas extraction generates numerous flowback and produced water (FPW), which will cause huge pollution if not properly treated. Gravity-driven membrane with economic advantages was applied as a pretreatment for desalinating this wastewater. The effects of membrane materials (polyvinylidene fluoride (PVDF) and polyvinylchloride (PVC)) with different mean pore sizes, porosities, contact angles, and pure water permeabilities and hydrostatic pressures (40 and 120 mbar) were investigated. The setups were operated for 90 days and the fluxes stabilized at about 0.87–1.00 L/(m2 h). PVDF membranes with higher price, had 6 % higher stable fluxes than PVC membranes, and the extracellular polymeric substances (EPS) contents in fouling layer of PVDF membranes were 10 %–20 % lower than those of PVC membranes. At higher pressures, the stable fluxes increased by only 8 %, but the total resistances increased by nearly 180 %, and there were more EPS, dissolved organic carbon, Na+, Ca2+, Mg2+, Cl− and NO3− on the fouling layer at 120 mbar. A denser cake layer was formed at a higher hydrostatic pressure, as observed by a scanning electron microscope and energy dispersive spectroscopy. Membrane properties and pressures had no significant effect on permeate quality (p > 0.05).

Abstract:
Salinization of global freshwater resources is a concerning health and economic issue of the 21st century and requires serious management and study to understand how, and by what mechanism, Total Dissolved Solids (TDS) is changing in major watersheds. Oil and gas (O&G) produced water is a complex and saline (10–300 g/L TDS) wastewater often disposed to surface waters post-treatment. However, in western U.S. states, beneficial use of minimally treated O&G produced water discharged to ephemeral streams is permitted through the EPA National Pollutant Discharge Elimination System (NPDES) for agriculture and wildlife propagation. In a remote Wyoming study region, beneficial use of O&G NPDES effluents annually contributes 13 billion L of water to surface water resources. The primary O&G TDS constituents are sulfate and sodium followed by chloride and calcium. Significant TDS increases from 2013 to 2016 in a large perennial river (River C) impacted by O&G effluent disposal, slight TDS increases in a perennial river (River B) and chronically elevated TDS (upwards of 2500 mg/L) in a smaller tributary (Tributary A) comprised mainly of O&G effluents led to an investigation of O&G impacts to surface waters in the region. Chloride-normalized metal ratios such as Br/Cl and δ2H and δ18O distinguished evaporation as the mechanism for increasing TDS derived from O&G on Tributary A, which is causing O&G effluents that meet NPDES regulations to not only exceed outfall regulations downstream where it is beneficially used mainly for irrigation and drinking water but also exceed aquatic life and livestock recommended limits. 87Sr/86Sr and δ34SSO4 suggested minor impacts from O&G TDS loading on River C but also support an additional salinity source, such as streambed geological controls, the cause of significantly increasing TDS. While lithium isotopes provided insight into the O&G effluent origin (δ7Li ranged 9–10‰) and water-sediment interactions along O&G effluent streams, they did not function as distinct salinity tracers in the larger downstream rivers. This study suggests a multi-isotope (87Sr/86Sr and δ34SSO4) approach is often necessary for fingerprinting salinization sources and determining best management practices because multiple salinity sources and environmental mechanisms may need to be identified to protect water quality.

Abstract:
Hydraulic fracturing (HF), or “fracking,” is the driving force behind the “shale gas revolution,” completely transforming the United States energy industry over the last two decades. HF requires that 4–6 million gallons per well (15,000–24,000 m3/well) of water be pumped underground to stimulate the release of entrapped hydrocarbons from unconventional (i.e., shale or carbonate) formations. Estimated U.S. production volumes exceed 150 billion gallons/year across the industry from unconventional wells alone and are projected to grow for at least another two decades. Concerns over the environmental impact from accidental or incidental release of produced water from HF wells (“U-PW”), along with evolving regulatory and economic drivers, has spurred great interest in technological innovation to enhance U-PW recycling and reuse. In this review, we analyze U-PW quantity and composition based on the latest U.S. Geographical Survey data, identify key contamination metrics useful in tracking water quality improvement in the context of HF operations, and suggest “fit-for-purpose treatment” to enhance cost-effective regulatory compliance, water recovery/reuse, and resource valorization. Drawing on industrial practice and technoeconomic constraints, we further assess the challenges associated with U-PW treatment for onshore U.S. operations. Presented are opportunities for targeted end-uses of treated U-PW. We highlight emerging technologies that may enhance cost-effective U-PW management as HF activities grow and evolve in the coming decades.

Abstract:
Membrane-based processes are increasingly applied in shale gas flowback and produced water (SGFPW) reuse. However, severe membrane fouling remains a big challenge for maintaining long-term operation. The present paper investigates for the first time the performance of the integrated ozonation-ultrafiltration (UF)-reverse osmosis (RO) process to treat SGFPW for water reuse. Results showed that pre-ozonation could efficiently mitigate membrane fouling. The integrated process removed more than 98% of total dissolved solids (TDS), 96% of dissolved organic carbon (DOC), and 96% of all ionic constituents in SGFPW. Significantly, the effluent could meet the water quality standards of irrigation, livestock water, and surface discharge. Removal of targeted pollutants is negatively influenced by the high concentrations of chloride and bromide because of their high reactivity with ozone and hydroxyl radicals (HO·). Through pre-ozonation, the total fouling index and the hydraulically irreversible fouling index decreased by more than 85% and 47%, respectively. The variation of particle sizes in SGFPW by pre-ozonation manifested the mechanism of UF membrane fouling mitigation, i.e., the pre-ozonation decomposed macromolecular organics into low fractions. The optimal ozone flow rate is 0.4 L/min. Results demonstrated that a sustainable SGFPW reuse could be achieved by the current integrated process.

Abstract:
Reusing produced water for hydraulic fracturing simultaneously satisfies challenges of fresh water sourcing and the installation/operation of an extensive disposal well infrastructure. Herein, we systematically and rigorously investigate produced water treatment for reuse during hydraulic fracturing. Highly saline and turbid produced water from the Permian Basin was treated by adding chlorine as an oxidant, FeCl3 as the primary coagulant, and an anionic polymer to induce high rate sedimentation to generate “clean brine” by removing suspended solids and iron over a range of environmentally relevant temperatures. Mobile phone video capture, optical microscopy, and digital image/video analysis were employed to characterize floc morphology and measure its size and settling velocity. Conformational changes of the polymeric coagulant between 4 and 44 °C were inferred from viscosity and dynamic light scattering measurements providing clues to its performance characteristics. Floc settling velocities measured over the entire range of polymer dosages and temperatures were empirically modelled incorporating their fractal nature, average size, and the viscosity of the produced water using only a single fitting parameter. Juxtaposing the anionic polymer with the hydrolyzing metal-ion coagulant effectively destabilized the suspension and caused floc growth through a combination of enmeshment, adsorption and charge neutralization and inter-particle bridging as evidenced by Fourier transform infrared spectroscopy and thermogravimetric analysis. Very high turbidity (≥98%) and total iron (≥97%) removals were accomplished even with very short flocculation and sedimentation times of only 6 min each suggesting the feasibility of this approach to reuse produced water for hydraulic fracturing.

Abstract:
Membrane filtration is a technique that can be successfully applied to remove oil from stable oil-in-water emulsions. This is especially interesting for the re-use of produced water (PW), a water stream stemming from the petrochemical industry, which contains dispersed oil, surface-active components and often has a high ionic strength. Due to the complexity of this emulsion, membrane fouling by produced water is more severe and less understood than membrane fouling by more simple oil-in-water emulsions. In this work, we study the relation between surfactant type and the effect of the ionic strength on membrane filtration of an artificial produced water emulsion. As surfactants, we use anionic sodium dodecyl sulphate (SDS), cationic hexadecyltrimethylammonium bromide (CTAB), nonionic Triton TMX-100 (TX) and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), at various ionic strengths (1, 10, 100 mM NaCl). Filtration experiments on a regenerated cellulose ultrafiltration (UF) membrane showed a pronounced effect of the ionic strength for the charged surfactants SDS and CTAB, although the nature of the effect was quite different. For anionic SDS, an increasing ionic strength leads to less droplet-droplet repulsion, allowing a denser cake layer to form, resulting in a much more pronounced flux decline. CTAB, on the other hand leads to a lower interfacial tension than observed for SDS, and thus more deformable oil droplets. At high ionic strength, increased surfactant adsorption leads to such a low oil-water surface tension that the oil droplets can permeate through the much smaller membrane pores. For the nonionic surfactant TX, no clear effect of the ionic strength was observed, but the flux decline is very high compared to the other surfactants. For the zwitterionic surfactant DDAPS, the flux decline was found to be very low and even decreased with increasing ionic strength, suggesting that membrane fouling decreases with increasing ionic strength. Especially promising is that at lower surfactant concentration (0.1 CMC) and high ionic strength no flux decline was observed, while a high oil retention (85%) was obtained. From our results, it becomes clear that the type of the surfactant used is crucial for a successful application of membrane filtration for PW treatment, especially at high ionic strengths. In addition, they point out that the application of zwitterionic surfactants can be highly beneficial for PW treatment with membranes.

Abstract:
The shale gas flowback and produced water (FPW) from hydraulic fracturing in the Sichuan province of China has relatively low to moderate levels of total dissolved solids (<20 g/L) and organics (<50 mg/L of dissolved organic carbon). As such, a combined ultrafiltration (UF), reverse osmosis (RO) system can be successfully applied to desalinate this feed water with the goal of reuse. However, the concentration of influent organic matter and particulates in the UF and RO stage is high, and the overall ionic and organics composition is highly complex, so that the membrane processes do not perform well, also due to fouling. To ensure the long-term and efficient operation of the UF-RO stages, a combined pretreatment of the FPW with coagulation and adsorption was investigated. The effect of different parameters on the performance on the system was studied in detail. Overall, the coagulation-adsorption pre-treatment greatly reduced fouling of the membrane processes, thanks to the high removal rate of turbidity (98.8%) and dissolved organic carbon (86.3%). The adsorption of organic matter by powdered activated carbon was best described by the Freundlich equilibrium model, with a pseudo second-order model representing the adsorption kinetics. Also, the various ions had competitive removal rates during the adsorption step, a phenomenon reported for the first time for FPW treatment. Also, an optimal dose of activated carbon existed to maximize fouling reduction and effluent quality. The overall treatment system produced a high-quality water streams, suitable for reuse.

Abstract:
Oil and gas (O&G) production in the United States is expected to grow at a substantial rate over the coming decades. Environmental sustainability related to water consumption during O&G extraction can be addressed through treatment and reuse of water returning to the surface after well completion. Water quality is an important factor in reuse applications, and specific treatment technologies must be utilized to remove different contaminants. Among others, biological active filtration can remove dissolved organic matter as a pre-treatment for surface discharge or to facilitate reuse in such applications as hydraulic fracturing, dust suppression, road stabilization, and crop irrigation. Yet, the formation of byproducts during treatment of O&G wastewater remains a concern when evaluating reuse applications. In this study, we investigated the previously unnoticed biotic formation of iodinated organic compounds (IOCs) such as triiodomethane during biological treatment of O&G wastewater for beneficial reuse. Iodide and several IOCs were quantified in O&G produced water before and after treatment in biological active filters filled with different media types over 13 weeks of operation. While iodide and total IOCs were measured at concentrations <53 mg/L and 147 μg/L, respectively, before biological treatment, total IOCs were measured at concentrations close to 4 mg/L after biological treatment. Triiodomethane was the IOC that was predominantly present. IOC formation had a negative strong correlation (r = −0.7 to −0.8, p < 0.05, n = 9) with iodide concentration in the treated O&G wastewater, indicating that iodide introduced to the biological active filter system was utilized in various reactions, including biologically mediated halogenation of organic matter. Additionally, iodide-oxidizing bacteria augmented in the treated produced water pointed towards potential negative environmental implications when releasing biologically treated halide-rich wastewater effluents to the aquatic environment.

Abstract:
Produced water (PW) is the largest by-product of the oil and gas industry. Its management is both economically and environmentally costly. PW reuse for irrigation offers an alternative to current disposal practices while providing water to irrigators in drylands. The aim of this investigation was to evaluate the environmental effects of irrigation with PW. The SALTIRSOIL_M model was used to simulate the irrigation of sugar beet with 15 PWs of a wide range of qualities in four climates of different aridity and on four contrasting soil types. The impacts on soil salinity, sodicity and pH as well as on crop yield and drainage water salinity were estimated. Well-drained soils with low water content at field capacity (Arenosol) are less sensitive to salinisation while a relatively high gypsum content (Gypsisol) makes the soil less vulnerable to both sodification and salinisation. On the contrary, clayey soils with higher water content at field capacity and lower gypsum content must be avoided as the soil structural stability as well as a tolerable soil electrical conductivity for the crop cannot be maintained on the long-term. Soil pH was not found to be sensitive to PW quality. Drainage water quality was found to be closely linked to PW quality although it is also influenced by the soil type. The impact of drainage water on the aquifer must be considered and reuse or disposal implemented accordingly for achieving sustainable irrigation. Finally, increasing aridity intensifies soil and drainage water salinity and sodicity. This investigation highlights the importance of adapting the existing irrigation water quality guidelines through the use of models to include relevant parameters related to soil type and aridity. Indeed, it will support the petroleum industry and irrigators, to estimate the risks due to watering crops with PW and will encourage its sustainable reuse in water-scarce areas.

Abstract:
Unconventional oil and gas extraction is on the rise across the United States and comprises an integral component in meeting the nation’s energy needs. The primary by-product of this industrious process is produced water, which is a challenging matrix to remediate because of its complex physical and chemical composition. Forward osmosis is a viable option to treat high-salinity produced water; however, fouling has been an issue. This study aimed to treat produced water before using forward osmosis as a remediation option. Trials consisted of a series of five experiments in order to evaluate the performance of the membrane. Samples were treated by centrifugation, activated carbon, filtration, ferric chloride, as well as coagulants and a polymer. It can be concluded that forward osmosis can be used to extract water from high-salinity oil field brines and produced water, and that pretreating the produced water decreased the tendency for fouling. The pretreatment with the overall best performance was activated carbon, which also yielded the lowest total organic carbon concentrations of 1.9 mg/L. During remediation trials using produced water pretreated with activated carbon as the feed solution, there was a 14% decrease in flux over the course of the 7 h trials. The membrane performance was restored after washing.

Abstract:
Shale oil and gas exploitation not only consumes substantial amounts of freshwater but also generates large quantities of hazardous wastewater. Tremendous research efforts have been invested in developing membrane-based technologies for the treatment of shale oil and gas wastewater. Despite their success at the laboratory scale, membrane processes have not been implemented at full scale in the oil and gas fields. In this article, we analyze the growing demands of wastewater treatment in shale oil and gas production, and then critically review the current stage of membrane technologies applied to the treatment of shale oil and gas wastewater. We focus on the unique niche of those technologies due to their advantages and limitations, and use mechanical vapor compression as the benchmark for comparison. We also highlight the importance of pretreatment as a key component of integrated treatment trains, in order to improve the performance of downstream membrane processes and water product quality. We emphasize the lack of sufficient efforts to scale up existing membrane technologies, and suggest that a stronger collaboration between academia and industry is of paramount importance to translate membrane technologies developed in the laboratory to the practical applications by the shale oil and gas industry.Open image in new window

Abstract:
Shale gas fracturing flowback water (SGFFW) contained high concentration of colloids and organics which can cause severe fouling for membrane distillation (MD). It is desirable to identify the key foulants for MD fouling for real SGWWFs treatment. In this study, coagulation and membrane filtrations with different molecular weight cut-off (MWCO) were applied to try to separate the different fractions and identify the key fouling/wetting component and evaluate the efficacy in alleviating MD fouling for real SGWWFs treatment. The organics with molecular weight of 20 kDa, which also belongs to humic acid-like components, protein-like components and fulvic acid-like components removed by coagulation can effectively mitigated MD fouling. However, the rest fraction of high molecular weight components of 20 kDa and low molecular weight components (i.e., 200 Da) removed by UF membrane, has less significant effect on the water flux of MD. Despite the further removal of small MW compounds, and even the removal of Ca2+ and Mg2+by NF slightly affect the water flux, indicating that the aromatic protein (21.2%) could cause severe wetting of the MD membrane. However, SEM-EDS demonstrated that the combination of organic fouling and crystallization of Ca and Ba contribute to the fouling of MD membrane. These studies demonstrated the removal of high molecular weight colloids by coagulation and aromatic protein with the molecular weight of 200Da might be vital for MD fouling and wetting, respectively.

Abstract:
The significant development of oil and gas from the Marcellus Shale and other geological formations in Pennsylvania over the last decade has generated large volumes of liquid and solid waste. In this paper we use data reported to the Pennsylvania Department of Environmental Protection (PADEP) to examine temporal and spatial trends in generation and management of liquid and solid waste from both conventional and unconventional oil and gas activities in Pennsylvania between 1991 and 2017. While previous assessments have examined this waste inventory in part, no complete assessment of waste quantity, waste types, waste handling practices, and spatial waste tracking has been undertaken using all currently available full years of Pennsylvania oil and gas waste data. In 2017 more than half of oil and gas wastewater by volume was reused at well pads to facilitate more hydrocarbon production while the majority of solid waste by volume was disposed of at in-state landfills. The spatial resolution of reporting of wastewater generation and handling from unconventional operations has improved substantially with recent regulations and reporting requirements; however, conventional oil and gas development was exempt from the more stringent reporting requirements and thus spatially-explicit data on wastewater generation and handling from conventional oil and gas development is still lacking. In addition, a third of the liquid waste across all years in the database lack a reported final destination. Spatially explicit cradle-to-grave reporting for waste handling from both conventional and unconventional oil and gas development is important to assess a number of environmental and human health hazards and risks of oil and gas development and associated operations and practices.

Abstract:
Recovery of natural gas and oil from unconventional (shale) reservoirs relies on horizontal drilling and hydraulic fracturing to make it economical. Hydraulic fracturing generates vast quantities of flowback and produced water (FPW) and its composition exhibits huge spatial and temporal variations among shale plays. This review focuses on the characteristics and management of wastewaters originating for oil and gas extraction. Wastewater characteristics, including the quantity and chemical composition of the FPW, are discussed. The future of unconventional oil and gas industry hinges on effective management of FPW. Membrane technologies have the potential to offer solutions to sustainable reuse of this water resource. The performance of a range of membrane processes is evaluated and compared. Emerging membrane-based technologies employed in similar fields are also discussed. The results in peer-reviewed publications could offer a guide for the selection of appropriate technologies based on the desired application. Membrane fouling, lack of pilot- and full-scale experience and high energy consumption are primary challenges for membrane applications in FPW. Then challenges and future research needs are addressed, advances in membrane materials, systematic analyses of organics and electric generation from salinity gradient are promising approaches to address the issues.

Abstract:
We developed an integrated treatment train that enables effective treatment of shale oil and gas produced water generated from the Wattenberg field in northeast Colorado. Membrane distillation (MD) was performed in tandem with simple and inexpensive pretreatment steps, namely precipitative softening (PS) and walnut shell filtration (WSF). PS removed various particulate, organic, and inorganic foulants, thereby mitigating fouling and scaling potential of the produced water. WSF displayed exceptional efficiencies (≥95%) in eliminating volatile toxic compounds including benzene, ethylbenzene, toluene, and xylenes (BTEX) along with additional gasoline and diesel range organic compounds. With pretreatment, the water vapor flux of MD decreased by only 10% at a total water recovery of 82.5%, with boron and total BTEX concentrations in the MD distillate meeting the regulatory requirements for irrigation and typical discharge limits, respectively. The use of pretreatment also led to robust membrane reusability within three consecutive treatment cycles, with MD water flux fully restored after physical membrane cleaning. Our results highlight the necessity of pretreatment prior to MD treatment of produced water and demonstrate the potential of our treatment train to achieve a cost-effective and on-site wastewater treatment system that improves the sustainability of the shale oil and gas industry.

Abstract:
Forward osmosis (FO) and membrane distillation (MD) are emerging technologies of interest for the treatment of high salinity brines. In this study, we aim to demonstrate the feasibility of an integrated FO-MD system for water recovery from high salinity produced waters obtained from shale gas extraction facilities. In the proposed hybrid system, FO draws water from high salinity feed, while MD regenerates the diluted FO draw solution. We show that this process integration can combine the advantages of both processes; low fouling tendency, possibility of using low-grade waste heat as the main energy source and high quality permeate. We further integrate the FO-MD system with an electrocoagulation (EC) system as pretreatment and show stable performance with minimal fouling. EC removed total organic carbon and total suspended solids by up to 78% and 96%, respectively. We studied the impact of experimental conditions (temperature, flow velocity and draw solution concentration) on performance of the integrated system in short-term experiments. In addition, we conducted long-term experiments using two different produced waters. We show that to achieve continuous high recovery with maximized water flux, a combination of two MD membranes can provide a viable solution.

Abstract:
Colloids and organics in shale gas fracturing flowback water (SGFFW) during shale gas extraction are of primary concerns. Coagulation combined with oxidation might be a promising process for SGFFW treatment. In this study, a novel electrocoagulation-peroxone (ECP) process was developed for SGFFW treatment by simultaneous coagulation and oxidation process with a Al plate as the anode and a carbon-PTFE gas diffusion electrode as the cathode, realizing the simultaneous processes of coagulation, H2O2 generation and activation by O3 at the cathode. Compared with electrocoagulation (EC) and peroxi-electrocoagulation (PEC), COD removal efficiency mainly followed the declining order of ECP, PEC and EC under the optimal current density of 50 mA cm−2. The appearance of medium MW fraction (1919 Da) during ozonation and PEC but disappearance in ECP indicated that these intermediate products couldn't be degraded by ozonation and PEC but could be further oxidized and mineralized by the hydroxyl radical produced by the cathode in ECP, demonstrating the hydroxyl radical might be responsible for the significant enhancement of COD removal. The pseudo-first order kinetic model can well fit ozonation and EC process but not the PEC and ECP process due to the synthetic effect of coagulation and oxidation. However, the proposed mechanism based model can generally fit ECP satisfactorily. The average current efficiency for PEC was 35.4% and 12% higher than that of ozonation and EC, respectively. This study demonstrated the feasibility of establishing a high efficiency and space-saving electrochemical system with integrated anodic coagulation and cathodic electro-peroxone for SGFFW treatment.

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The selection of an appropriate draw solution is crucial to the successful implementation of desalination for the treatment of highly saline fracking wastewaters via the forward osmosis (FO) process. In this report, four organic compounds (potassium acetate, potassium formate, sodium glycolate, and sodium propionate) were identified as candidate draw solutes for the first time for desalination of fracking wastewater by FO. Higher average FO water fluxes were achieved for the identified organic draw solutions (10.50–13.26 LMH for synthetic fracking wastewater and 19.05–24.05 LMH for real fracking wastewater) compared to commonly used draw solution, NaCl (average FO water flux: 8.25 LMH for synthetic fracking wastewater and 14.44 LMH for real fracking wastewater). Higher average FO water fluxes were obtained due to likely lower reverse salt fluxes for the organic draw solutions compared to NaCl. Higher FO water fluxes were achieved for the real fracking wastewater, as compared to the synthetic wastewater, due to higher osmotic pressure differences between feed and draw solutions. Membrane distillation could be used as a downstream separation technique in the FO process for recycling of the identified draw solutes.

Abstract:
Water generated by hydraulic fracturing for the production of oil and gas, commonly termed ‘produced water’, may contain residual organic compounds from the fracturing process or the subsurface formation. Biological treatment is a potential technology to remove residual organic compounds in produced water. Biocides are often added to both fracturing fluids and produced water to limit undesirable microbiological activity, and glutaraldehyde is the most commonly used biocide in hydraulic fracturing. Residual biocides in produced water can limit biological treatment efficiency. We evaluated the effect of glutaraldehyde on the biodegradation of five of the most commonly reported organic compounds in hydraulic fracturing fluids in an engineered biofilm treatment. Our results demonstrated that glutaraldehyde delays biological organic compound removal by introducing a biodegradation lag phase. In addition, the effects of glutaraldehyde were more pronounced for more rapidly degraded compounds. Finally, the presence of glutaraldehyde did not decrease microbial abundance nor drive microbial community structure, suggesting that observed effects were due to altered microbial activity. These results highlight the necessity to consider co-contaminant interactions during treatment of complex waste streams where residual biocide may be present.

Abstract:
Two traditional pretreatment methods were adopted for the pretreatment of shale gas produced water in view of facilitation for subsequent treatment processes. The research was focused on alkali precipitation due to its better performance on shale gas produced water pretreatment compared with flocculation. Agitating time, settling time, stirring speed, dosage of coagulant aids were determined by optimal configuration. The results showed that adding together with 1.0 g/L NaOH and 2.0 g/L Na2CO3 under 200 rpm stirring for 5 min and after 30 min settling, suspended solids (SS) in the effluent could drop below 20 mg/L and concentration of hardness ion could be less than 150 mg/L, which was well met the water quality to facilitate the following single or multiple-effect evaporation. The optimized alkaline pretreatment method towards produced water had excellent adaptability and practicability with economic cost and easy operation. It had significant potential and could be widely used in the shale gas produced water pretreatment process.

Abstract:
The 2017 Texas Water Development Board's State Water Plan predicts a 41% gap between water demand and existing supply by 2070. This reflects an overall projection, but the challenge will affect various regions of the state differently. Texas has 16 regional water planning zones characterized by distinct populations, water demands, and existing water supplies. Each is expected to face variations of pressures, such as increased agricultural and energy development (particularly hydraulic fracturing) and urban growth that do not necessarily follow the region's water plan. Great variability in resource distribution and competing resource demands across Texas will result in the emergence of distinct hotspots, each with unique characteristics that require multiple, localized, interventions to bridge the statewide water gap. This study explores three such hotspots: 1) water-food competition in Lubbock and the potential of producing 3 billion gallons of treated municipal waste water and encouraging dryland agriculture; 2) implementing Low Impact Developments (LIDs) for agriculture in the City of San Antonio, potentially adding 47 billion gallons of water supply, but carrying a potentially high financial cost; and 3) water-energy interrelations in the Eagle Ford Shale in light of well counts, climate dynamics, and population growth. The growing water gap is a state wide problem that requires holistic assessments that capture the impact on the tightly interconnected water, energy, and food systems. Better understanding the trade-offs associated with each ‘solution’ and enabling informed dialogue between stakeholders, offers a basis for formulating localized policy recommendations specific to each hotspot.

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Abstract:
Hydraulic fracturing wastewaters (HFWWs) contain synthetic organic components and metal ions derived from the formation waters. The risk of spills of HFWW that could impact soil quality and water resources is of great concern. The ability of synthetic components, such as surfactants, in HFWW to be transported through soil and to mobilize metals in soil was examined using column experiments. A spill of HFWW was simulated in bench scale soil column experiments that used an agricultural soil and simulated seven 10-year rain events representing a total of one year's worth of precipitation for Weld County, Colorado. Although no surfactants or their transformation products were found in leachate samples, copper, lead, and iron were mobilized at environmentally relevant concentrations. In general, after the initial spill event, metal concentrations increased until the fourth rain event before decreasing. Results from this study suggest that transport of metals was caused by the high concentrations of salts present in HFWW. This is the first study utilizing authentic HFWWs to investigate the transport of surfactants and their effect on metal mobilization. Importantly, a significant decrease in the water infiltration rate of the soil was observed, leading to the point where water was unable to percolate through due to increasing salinity, potentially having a severe impact on crop production.

Abstract:
Unconventional oil and gas development is achieved through a series of sub-processes, which utilize large amounts of water, proppant, and chemical additives to retrieve sequestered hydrocarbons from low permeability petroliferous strata. As a result, a large amount of wastewater is produced, which is traditionally disposed of via subsurface injection into non-productive stratum throughout the country. However, this method of waste management has been linked to the induction of seismic events in a number of regions across North America, calling into question the environmental stewardship and sustainability of subsurface waste disposal. Advancements in water treatment technologies have improved the efficacy and financial viability of produced water recycling for beneficial reuse in the oil and gas sector. This review will cover the various treatment options that are currently being utilized in shale energy basins to remove organic, inorganic, and biological constituents, as well as some emerging technologies that are designed to remove pertinent contaminants that would otherwise preclude the reuse of produced water for production well stimulation.

Abstract:
In the western U.S., produced water from oil and gas wells discharged to surface water augments downstream supplies used for irrigation and livestock watering. Here we investigate six permitted discharges on three neighboring tributary systems in Wyoming. During 2013–16, we evaluated radium activities of the permitted discharges and the potential for radium accumulation in associated stream sediments. Radium activities of the sediments at the points of discharge ranged from approximately 200–3600 Bq kg−1 with elevated activities above the background of 74 Bq kg−1 over 30 km downstream of one permitted discharge. Sediment as deep as 30 cm near the point of discharge had radium activities elevated above background. X-ray diffraction and targeted sequential extraction of radium in sediments indicate that radium is likely coprecipitated with carbonate and, to a lesser extent, sulfate minerals. PHREEQC modeling predicts radium coprecipitation with aragonite and barite, but over-estimates the latter compared to observations of downstream sediment, where carbonate predominates. Mass-balance calculations indicate over 3 billion Bq of radium activity (226Ra + 228Ra) is discharged each year from five of the discharges, combined, with only 5 percent of the annual load retained in stream sediments within 100 m of the effluent discharges; the remaining 95 percent of the radium is transported farther downstream as sediment-associated and aqueous species.

Abstract:
Hydraulic fracturing generates large volumes of produced water, and treatment of produced water may be necessary for disposal or reuse. Biological treatment of produced water is a potential approach to remove organic constituents and reduce fouling, in conjunction with other treatment processes. This study investigates the biological treatability of produced water samples from the Utica and Bakken Shales using engineered biofilms. Observed total dissolved organic carbon (DOC) removal varied between 1-87% at normalized total dissolved solids concentrations, suggesting that the composition of produced water, including organic constituents and trace elements such as nutrients and metals, is an important driver of biological treatment performance. Mass spectrometric analyses of the DOC composition revealed various alkanes in all samples, but differences in non-ionic surfactant, halogenated, and acidic compound content. Statistical data reduction approaches suggest that the latter two groups are correlated with reduced biodegradation kinetics. These results demonstrate that the combination of biodegradation performance and organic speciation can guide the assessment of the biological treatment of produced water.

Abstract:
Unconventional oil and gas extraction (UOG) has expanded rapidly across the United States, as it has become an established technique for oil and gas extraction from low permeability shales. There are more than 900,000 active oil and gas wells in the United States, and more than 130,000 have been drilled since 2010.1 The U.S. Energy Information Administration (EIA) estimates that in 2017, about 16.76 trillion cubic feet (Tcf) of dry natural gas was produced from shale resources in the United States, including the Bakken (North Dakota and Montana), Niobrara (Colorado), Marcellus and Utica (Pennsylvania, Ohio, and West Virginia), Haynesville (Louisiana and East Texas), Eagle Ford (South Texas), and Permian Basin (West Texas and Southeast New Mexico) shale plays.

Abstract:
The Colorado Water Plan estimates as much as 0.8 million irrigated acres may dry up statewide from agricultural to municipal and industrial transfers. To help mitigate this loss, new sources of water are being explored in Colorado. One such source may be produced water. Oil and gas production in 2016 alone produced over 300 million barrels of produced water. Currently, the most common method of disposal of produced water is deep well injection, which is costly and has been shown to cause induced seismicity. Treating this water to agricultural standards eliminates the need to dispose of this water and provides a new source of water. This research explores which counties in Colorado may be best suited to reusing produced water for agriculture based on a combined index of need, quality of produced water, and quantity of produced water. The volumetric impact of using produced water for agricultural needs is determined for the top six counties. Irrigation demand is obtained using evapotranspiration estimates from a range of methods, including remote sensing products and ground-based observations. The economic feasibility of treating produced water to irrigation standards is also determined using an integrated decision selection tool (iDST). We find that produced water can make a substantial volumetric impact on irrigation demand in some counties. Results from the iDST indicate that while costs of treating produced water are higher than the cost of injection into private disposal wells, the costs are much less than disposal into commercial wells. The results of this research may aid in the transition between viewing produced water as a waste product and using it as a tool to help secure water for the arid west.

Abstract:
Unconventional oil and gas residual solid wastes are generally disposed in municipal waste landfills (RCRA Subtitle D), but they contain valuable raw materials such as proppant sands. A novel process for recovering raw materials from hydraulic fracturing residual waste is presented. Specifically, a novel hydroacoustic cavitation system, combined with physical separation devices, can create a distinct stream of highly concentrated sand, and another distinct stream of clay from the residual solid waste by the dispersive energy of cavitation conjoined with ultrasonics, ozone and hydrogen peroxide. This combination cleaned the sand grains, by removing previously aggregated clays and residues from the sand surfaces. When these unit operations were followed by a hydrocyclone and spiral, the solids could be separated by particle size, yielding primarily cleaned sand in one flow stream; clays and fine particles in another; and silts in yet a third stream. Consequently, the separation of particle sizes also affected radium distribution – the sand grains had low radium activities, as lows as 0.207 Bq g−1 (5.6 pCi g−1). In contrast, the clays had elevated radium activities, as high as 1.85–3.7 Bq g−1 (50–100 pCi g−1) – and much of this radium was affiliated with organics and salts that could be separated from the clays. We propose that the reclaimed sand could be reused as hydraulic fracturing proppant. The separation of sand from silt and clay could reduce the volume and radium masses of wastes that are disposed in landfills. This could represent a significant savings to facilities handling oil and gas waste, as much as $100 000–300 000 per year. Disposing the radium-enriched salts and organics downhole will mitigate radium release to the surface. Additionally, the reclaimed sand could have market value, and this could represent as much as a third of the cost savings. Tests that employed the toxicity characteristic leaching protocol (TCLP) on these separated solids streams determined that this novel treatment diminished the risk of radium mobility for the reclaimed sand, clays or disposed material, rendering them better suited for landfilling.

Abstract:
Unconventional oil and gas operations are on the rise and an integral component to meeting the nation's energy needs. Produced water is the primary by-product of oil and gas operations, and it has proven challenging to treat to date. The aim of this study was to evaluate the feasibility of using forward osmosis with thin-film composite hollow fiber membranes as a remediation option for produced water with high total dissolved solids levels from the Permian Basin. Trials consisted of a series of 5 experiments in order to evaluate the performance of the membrane. Three PW samples, each from different locations, were used to conduct the series of experiments and compare the performance of the membranes with TDS levels ranging from 16,000 to 210,000 mg/L. It can be concluded that forward osmosis can be used to extract water from high salinity oil field brines and PW. Flux decreased over the course of the trials due to a combination of membrane fouling, concentration polarization, and temperature fluctuations. The flux of the PW was similar to the flux measured for the PW mimic with small difference due to the influence of activity on the osmotic pressure. The flux was also influenced by temperature and the linear velocity of the feed solution and draw solution.

Abstract:
The high volume of flowback water (FW) generated during shale gas exploitation is highly saline, and contains complex organics, iron, heavy metals, and sulfate, thereby posing a significant challenge for the environmental management of the unconventional natural gas industry. Herein, the treatment of FW in a sulfur-cycle-mediated microbial fuel cell (MFC) is reported. Simultaneous removal efficiency for chemical oxygen demand (COD) and total iron from a synthetic FW was achieved, at 72±7% and 90.6±8.7%, respectively, with power generation of 2667±529 mW/m3 in a closed-circuit MFC (CC-MFC). However, much lower iron removal (38.5±4.5%) occurred in the open-circuit MFC (OC-MFC), where the generated FeS fine did not precipitate because of sulfide supersaturation. Enrichment of both sulfur-oxidizing bacteria (SOB), namely Helicobacteraceae in the anolyte and the electricity-producing bacteria, namely Desulfuromonadales on the anode likely accelerated the sulfur cycle through the biological and bioelectrochemical oxidation of sulfide in the anodic chamber, and effectively increased the molar ratio of total iron to sulfide, thus alleviating sulfide supersaturation in the closed circuitry. Enrichment of SOB in the anolyte might be attributed to the formation of FeS electricity wire and likely contributed to the stable high power generation. Bacteroidetes, Firmicutes, Proteobacteria, and Chloroflexi enriched in the anodic chamber were responsible for degrading complex organics in the FW. The treatment of real FW in the sulfur-cycle-mediated MFC also achieved high efficiency. This research provides a promising approach for the treatment of wastewater containing organic matters, heavy metals, and sulfate by using a sulfur-cycle-mediated MFC.

Abstract:
Development of unconventional gas resources is currently one of the most rapidly growing trends in the oil and natural gas industry. Exploration of shale gas requires significant quantities of water for hydraulic fracturing. Meanwhile, large volumes of produced water are generated during gas production. Treatment and beneficial use of hydraulic fracturing flowback and produced water provides opportunities for sustainable unconventional gas operations while minimizing impacts to environment, local water resources, and public health. Considering the broad variety of treatment technologies and the wide spectrum of flowback and produced water qualities, selecting appropriate treatment and management options involves a complex decision-making process that requires understanding of treatment technologies, water quality, reuse requirements, and consideration of multiple criteria, constraints, and objectives. This study presents an integrated decision support tool (iDST) to assist in selection of treatment technologies and evaluation of the feasibility of potential water reuse options. The Marcellus Shale in Pennsylvania and the Barnett Shale in Texas were selected as case studies to demonstrate produced water treatment technologies and beneficial reuse options considering realistic site-specific conditions, assumptions, and future projections such as well numbers and locations, water demands, flowback and produced water quality and quantity, disposal availability, and costs. The iDST provides an interactive user interface to select suitable technologies for produced water treatment and reuse based on user preference, target water quality, and current disposal options.

Abstract:
Hydraulic fracturing of the Marcellus Shale produces wastewaters that are hypersaline and highly enriched in isotopes of radium. Radium is understood to derive from the Marcellus Shale itself, but its source phases and their contributions to wastewater production have not been described. Using sequential extractions and experimental leachates, we characterize two distinct end-members that could contribute Ra to wastewaters, (1) a mineral phase, which hosts labile228Ra and has 226Ra/228Ra atom ratios ~250, and (2) an organic phase, which hosts exchangeable226Ra and has 226Ra/228Ra ~10,000. In leaching experiments we observed rapid extraction of Ra from these phases, with high ionic strength solutions leaching up to 14% of Ra from the shale in just hours. Radium concentrations and 226Ra/228Ra ratios increase with [Ca2+] of the leaching solution, and solutions approaching 1 M Ca2+ produce 226Ra/228Ra ratios compatible with Marcellus wastewaters. In contrast, pure water removes <0.5% of Ra from the shale with low 226Ra/228Ra ratios incompatible with wastewaters. Experimental results and wastewater data together provide a coherent picture, that the distinctive Ra isotopic signature of Marcellus wastewaters results from contemporaneous water-rock interactions that promote desorption of 226Ra from organics during hydraulic fracturing.

Abstract:
Effective and affordable treatment of hydraulic fracturing flowback and produced water (FPW) is a major challenge for the sustainability of unconventional shale-gas exploration and development. We investigated the effectiveness of different combinations of activated sludge (AS), three microbial preparations, and ten plants (ryegrass, water dropwort, typha, reed, iris, canna, water caltrop, rape, water spinach, and Alternanthera philoxeroides) on the treatment performance of FPW. Water quality parameters (NH4-N, NO3-N, NO2-N, CODcr, and BOD) and the algal toxicity of the treated FPW were used as metrics to assess the treatment efficiency. The results showed that AS had higher treatment efficiency than the prepared microorganisms, and water dropwort was the best plant candidate for boosting performance of AS treatment of FPW. The treated FPW showed improved water quality and microbial diversity. The Shannon-Wiener index increased from 4.76 to 7.98 with FPW treatment. The relative abundance of microbes with a greater resistance to high salt conditions, such as Bacteroidetes, Firmicutes, Chloroflexi, increased substantially in the treated FPW. The combination of water dropwort and AS showed the greatest improvement in water quality, the highest algal density and microbial diversity, thus indicating good potential for this candidate in the treatment of FPW.

Abstract:
This work proposes an optimization approach for designing efficient water networks for the shale gas production through the recycle and reuse of wastewater streams reducing the freshwater consumption and effluents considering economic and environmental goals. The economic objective function aims to minimize the total annual cost for the water network including the costs associated with storage, treatment and disposal (capital cost) as well as freshwater cost, treatment cost and transportation costs. The environmental objective is addressed to deal with the minimization of the environmental impact associated with the discharged concentration of total dissolved solids in the wastewater streams and the freshwater consumption through an environmental function that represents the benefit for removing pollutants using the eco-indicator 99 methodology. The methodology requires a given scheduling for the completion phases of the target wells to be properly implemented by the available hydraulic fracturing crews during a time horizon. The model formulation is configured to determine the optimal sizes for the equipment involved by the project, particularly the sizes for storage and treatment units are quantified by the optimization process. A case study is solved to evaluate the effectiveness of the proposed optimization approach.Graphical abstract Open image in new window

Abstract:
Recent advances in hydraulic fracturing, in conjunction with horizontal drilling, have enabled large-scale extraction of natural gas and oil from shale formations. Despite its advances and enormous economic benefits, opportunities remain to increase hydraulic fracturing efficiency and minimize potential environmental impacts. This review specifically examines three key themes associated with development and utilization of hydraulic fracturing fluids: 1) characteristics and behavior of fracturing fluids, 2) understanding and predicting migration and fate of fracturing fluids, 3) technologies to reduce environmental impact of fracturing fluids. The paper discusses key and new techniques and findings on rheology of hydrogel-based fluids, high fidelity simulation of propagation transport, potential environmental impacts, geosynthetics in mitigating contamination, and greener fracturing fluids. It is indicated that future development relies on advances in understanding of physical processes, modeling capabilities, and monitoring techniques.

Abstract:
Extensive efforts have been made to tailor membrane surface wettability in order to mitigate fouling and wetting in membrane distillation (MD), but the developed membranes have rarely been challenged with real industrial wastewater. This study compared three membranes − a hydrophobic PVDF membrane, a superhydrophobic PVDF membrane, and a composite PVDF membrane with hydrophilic coating − in MD desalination of shale oil and gas produced water from the Wattenberg field in northeast Colorado. Two produced water samples with varied chemical compositions were collected and used as the feedwater. In a single treatment cycle, the composite membrane showed the best fouling resistance for the first sample, while all the tested membranes experienced similar flux decline with the second sample. Thus, the relationship between membrane surface wettability and fouling propensity in MD treatment of real produced water was influenced by feedwater composition. This effect was reflected by distinct features of fouling layers resulting from the two produced water samples, revealed by detailed microscopic and spectroscopic characterization. In three treatment cycles with physical membrane cleaning, the hydrophobic and composite membranes suffered from accelerated membrane fouling after each cycle, whereas a decelerated flux decline was observed for the superhydrophobic membrane. The better reusability of the superhydrophobic membrane, however, was achieved at the expense of initial water vapor flux. Our study suggests that one should comprehensively consider fouling/wetting resistance, water productivity, and reusability in the design and selection of appropriate membranes for MD treatment, and that long-term testing with multiple treatment cycles should be performed to assess MD membrane performance more accurately.

Abstract:
Oil- and gas-produced water (PW) which contains various pollutants is an enormous threat to the environment. In this study, a novel low-cost bio-adsorbent was prepared from shrimp shell and acid-activated montmorillonite. The results of FT-IR spectroscopy, energy dispersive X-ray (EDX) analysis, and SEM-EDX technique indicated that the chitosan-activated montmorillonite (CTS-A-MMT) was prepared successfully. The synthesized CTS-A-MMT was applied to remove simultaneously five cationic and anionic metal species and crude oil from synthetic and real oilfield PW. The adsorption data indicated that crude oil and all studied metals (except As) were adsorbed to CTS-A-MMT in a monolayer model (best fitted by Langmuir model), while As adsorption fits well with Freundlich model. Kinetic models’ evaluation demonstrated that the adsorption kinetics of metals on CTS-A-MMT are initially controlled by the chemical reaction (film diffusion) followed by intra-particle diffusion. Application of the prepared CTS-A-MMT in real oilfield PW indicated removal efficiency of 65 to 93% for metals and 87% for crude oil in simultaneous removal experiments. Presence of additional ions in PW decreased the removal of studied metals and crude oil considerably; however, the concentration of the investigated pollutants in treated PW is less than the ocean discharge criteria. It is concluded that the prepared CTS-A-MMT composite is a low-cost and effective adsorbent for treating wastewater contaminated with crude oil and heavy metals (i.e., PW).

Abstract:
For several decades, high-salinity water brought to the surface during oil and gas (O&G) production has been treated and discharged to waterways under National Pollutant Discharge Elimination System (NPDES) permits. In Pennsylvania, USA, a portion of the treated O&G wastewater discharged to streams from 2008 to 2011 originated from unconventional (Marcellus) wells. We collected freshwater mussels, Elliptio dilatata and Elliptio complanata, both upstream and downstream of a NPDES-permitted facility, and for comparison, we also collected mussels from the Juniata and Delaware Rivers that have no reported O&G discharge. We observed changes in both the Sr/Cashell and 87Sr/86Srshell in shell samples collected downstream of the facility that corresponded to the time period of greatest Marcellus wastewater disposal (2009–2011). Importantly, the changes in Sr/Cashell and 87Sr/86Srshell shifted toward values characteristic of O&G wastewater produced from the Marcellus Formation. Conversely, shells collected upstream of the discharge and from waterways without treatment facilities showed lower variability and no trend in either Sr/Cashell or 87Sr/86Srshell with time (2008–2015). These findings suggest that (1) freshwater mussels may be used to monitor changes in water chemistry through time and help identify specific pollutant sources and (2) O&G contaminants likely bioaccumulated in areas of surface water disposal.

Abstract:
At the forefront of the discussions about climate change and energy independence has been the process of hydraulic fracturing, which utilizes large amounts of water, proppants, and chemical additives to stimulate sequestered hydrocarbons from impermeable subsurface strata. This process also produces large amounts of heterogeneous flowback and formation waters, the subsurface disposal of which has most recently been linked to the induction of anthropogenic earthquakes. As such, the management of these waste streams has provided a newfound impetus to explore recycling alternatives to reduce the reliance on subsurface disposal and fresh water resources. However, the biogeochemical characteristics of produced oilfield waste render its recycling and reutilization for production well stimulation a substantial challenge. Here we present a comprehensive analysis of produced waste from the Eagle Ford shale region before, during, and after treatment through adjustable separation, flocculation, and disinfection technologies. The collection of bulk measurements revealed significant reductions in suspended and dissolved constituents that could otherwise preclude untreated produced water from being utilized for production well stimulation. Additionally, a significant step-wise reduction in pertinent scaling and well-fouling elements was observed, in conjunction with notable fluctuations in the microbiomes of highly variable produced waters. Collectively, these data provide insight into the efficacies of available water treatment modalities within the shale energy sector, which is currently challenged with improving the environmental stewardship of produced water management.

Abstract:
On-site flowback treatment systems are typically rated and selected based on three fundamental categories: satisfying customer needs (e.g. meeting effluent quality, capacity, delivery time and time required to reach stable and steady effluent quality), common features comparison (e.g. treatment costs, stability of operation, scalability, logistics, and maintenance frequency) and through substantial product differentiation such as better service condition, overcoming current market limitations (e.g. fouling, salinity limit), and having lower environmental footprints and emissions. For treatment of flowback, multiple on-site treatment systems are available for primary separation (i.e. reducing TSS concentrations and particle size below 25 μm for disposal), secondary separation (i.e. removing TSS, iron and main scaling ions, and reducing particle size up to 5 μm for reuse), or tertiary treatment (i.e. reducing TDS concentration in the permeate/distillate to below 500 mg/L) for recycling or discharge. Depending on geographic features, frac-fluid characteristics, and regulatory aspects, operators may choose disposal or reuse of flowback water. Among these approaches, desalination is the least utilized option while in the majority of cases on-site basic separation is selected which can result in savings up to $306,800 per well. Compared to desalination systems, basic separation systems (e.g. electrocoagulation, dissolved air floatation) have higher treatment capacity (159–4133 m3/d) and specific water treatment production per occupied space (8.9–58.8 m3/m2), lower treatment costs ($2.90 to $13.30 per m3) and energy demand, and finally generate less waste owing to their high recovery of 98–99.5%, which reduces both operator costs and environmental burdens.

Abstract:
This work describes the discovery of amino-polyethylene-glycols, amino-polyethylene-glycol-carboxylates, and amino-polyethylene-glycol-amines in 20 produced water-samples from hydraulic fracturing in the western United States. These compounds, with masses in the range of m/z 120–986, were identified using solid phase extraction and liquid chromatography/quadrupole-time-of-flight mass spectrometry. The polymeric sorbent, Oasis HLB, gave the best recovery for all three ethoxylated surfactants and desalted the samples, which significantly reduced suppression of the mass spectral signal allowing detection and identification. The Kendrick mass defect, mass spectra, fragmentation pathways, and pure standards were used for confirmation. Finally, because these compounds are not explicitly listed in FracFocus reports, rather they are categorized as a proprietary surfactant blend; their identification is an important step in understanding the chemistry, treatment, and possible toxicity of hydraulic fracturing wastewater.

Abstract:
The application of horizontal drilling and hydraulic fracturing has enabled access to previously unrecoverable gas reservoirs. This method uses large quantities of water and the likely presence of NORM in the water that flows up to the wells have caused some concerns. In this study, a new cation resin, RSM-25HP, was compared to Dowex 50W-X8 resin for its ability to separate radium from produced water. Our results show that the RSM resin was able to retain barium and radium at higher acidities compared to the Dowex resin and could provide a higher degree of separation in the flowback water.

Abstract:
Membrane distillation (MD) has great potentials to treat produced water in energy industries. However, volatile organic compounds (VOCs) existing in the produced water added in the fracking process can hinder the treatment process regarding two aspects: permeate quality and MD flux performance. To address this challenge, this study aims to systematically study the effects of the VOCs on the MD permeation performance and permeate quality, and the mechanism of its penetration. Acetic acid, ethylene glycol, isopropyl alcohol (IPA), and 2-Butoxyethanol (2-BE), which are commonly found in the produced water, were extensively investigated and their impacts were reviewed and compared. Among all the VOCs, 2-BE had the highest mass transfer despite its low vapour pressure and large molecule weight. Some of the VOCs had surfactant properties, which meant they could penetrate the membrane pores easily during MD process. In long-term operation, pore wetting started to appear as the salt rejection was dropping in the MD process, and flux was also decreasing. Based on the results, this study suggested that the strength of surfactant properties and intra-molecular hydrogen bonds between water molecules and VOCs are as significant as vapour pressure for the VOCs in terms of mass transfer efficiency in MD system.

Abstract:
Sustainable wastewater management strategies are required to further minimize impacts of high-volume hydraulic fracturing (HVHF) as current practices such as reuse or direct disposal have long term limitations. Membranes can provide superior effluent quality in HVHF wastewater treatment, but the application of these systems is severely limited by membrane fouling. However, the key fouling components in HVHF wastewater have not yet been clearly identified and characterized. Here we demonstrate that fouling of microfiltration membranes by synthetic flowback water is mostly due to polyacrylamide (PAM), a major additive in slickwater fracturing fluids. A synthetic fracturing fluid was incubated with Marcellus Shale under HVHF conditions (80 degrees C, 83 bar, 24 h) to generate synthetic flowback water. Different HVHF conditions and fracturing fluid compositions generated a fouling index for flowback water ranging from 0.1 to 2000 m(-1), with these values well correlated with the peakmolecular weight (MW) (ranging from 10 to 1.5 x 10(4) kDa) and the concentration of high MW components in the water. The lowest fouling index was observed when PAM was further degraded by ammonium persulfate under HVHF conditions, although this is infrequently used with PAM in current fracturing operations. These results highlight the importance of PAM and its degradation products in fouling of subsequent membrane systems, providing insights that can help in the development of effective treatment processes for HVHF wastewater.

Abstract:
The extensive application of hydraulic fracturing technology has significantly promoted the large-scale development of shale gas. However, it is a great challenge for shale gas extraction to effectively manage large-volume flowback water (FW) with high salinity and complex organic substances. Here, we report an aerobic granular sludge (AGS) tolerable to high salinity, and suited to the treatment of FW. The performance of a sequencing batch reactor (SBR) with the AGS for the treatment of the synthetic FW and the microbial community structure at different salinity levels were investigated. The AGS fed with synthetic FW possessed a larger average particle size and a higher settling rate (50 m h−1). When NaCl concentration increased to 50.0 g L−1, the removal efficiency of total organic carbon (TOC) increased to 79 ± 1%, and the removal rate of polyacrylamide (PAM) raised up to 42.7 ± 0.7 g m−3 d−1. Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Sphingobacteriia dominated in the microbial community of AGS. Cellvibrionaceae, Rhodocyclaceae, Enterobacteriaceae, Moraxellaceae, Pseudomonadaceae, and Halomonadaceae belonging to Betaproteobacteria and Gammaproteobacteria played important role in degrading PAM, polycyclic aromatic hydrocarbons (PAH), and some other organics in FW at high salinity. These results suggest that an AGS-based SBR is a promising technology for the treatment of FW.

Abstract:
Radium in hydraulic fracturing wastewaters derives from two isotopically distinct end-members in the shale, labile 228Ra hosted by mineral surfaces (226Ra/228Ra atom ratio ~250) and exchangeable 226Ra hosted by organic surfaces (226Ra/228Ra ~10,000). Here we use mass balance and isotope mixing models to reconcile extraction of Ra from these phases with mechanisms of Marcellus wastewater production. Radium isotopic mass balance requires that the characteristic water-rock ratio between wastewater and shale is exceedingly low, on the order of 0.04, and that this ratio decreases with time during wastewater production. An evolving water-rock interaction drives increasing Ra concentrations (=[Ra]) and 226Ra/228Ra ratios during wastewater production, all mediated by increasing [Ca2+] that favors desorption of 226Ra from organics. Our observations and models of Ra isotope geochemistry are best reconciled with observations of water and salinity mass balance, δ18O, Na-Br-Cl, and 87Sr/86Sr if wastewater is produced by mixing of injected fluids with a limited volume of pore brine (on the order of 13% by volume), accompanied by contemporaneous extraction of excess alkaline earth elements by water-rock exchange. Validated using Ra isotope data, this model attributes the extreme salinity and [Ra] in wastewaters to the progressive, hydrologic enrichment of injected fluids during hydraulic fracturing.