Water quality assessment downstream of oil and gas produced water discharges intended for beneficial reuse in arid regions

Utica/Point Pleasant brine isotopic compositions (δ7Li, δ11B, δ138Ba) elucidate mechanisms of lithium enrichment in the Appalachian Basin

Global Li production will require a ∼500 % increase to meet 2050 projected energy storage demands. One potential source is oil and gas wastewater (i.e., produced water or brine), which naturally has high total dissolved solids (TDS) concentrations, that can also be enriched in Li (>100 mg/L). Understanding the sources and mechanisms responsible for high naturally-occurring Li concentrations can aid in efficient targeting of these brines. The isotopic composition (δ7Li, δ11B, δ138Ba) of produced water and core samples from the Utica Shale and Point Pleasant Formation (UPP) in the Appalachian Basin, USA indicates that depth-dependent thermal maturity and water-rock interaction, including diagenetic clay mineral transformations, likely control Li concentrations. A survey of Li content in produced waters throughout the USA indicates that Appalachian Basin brines from the Marcellus Shale to the UPP have the potential for economic resource recovery.

Prioritizing Organic Pollutants for Shale Gas Exploitation: Life Cycle Environmental Risk Assessments in China and the US

Environmental impacts associated with shale gas exploitation have been historically underestimated due to neglecting to account for the production or the release of end-of-pipe organic pollutants. Here, we assessed the environmental impacts of shale gas production in China and the United States using life cycle assessment. Through data mining, we compiled literature information on organic pollutants in flowback and produced water (FPW), followed by assessments using USEtox to evaluate end-of-pipe risks. Results were incorporated to reveal the life cycle risks associated with shale gas exploitation in both countries. China exhibited higher environmental impacts than the US during the production phase. Substantially different types of organic compounds were observed in the FPW between two countries. Human carcinogenic and ecological toxicity attributed to organics in FPW was 3 orders of magnitude higher than that during the production phase in the US. Conversely, in China, end-of-pipe organics accounted for approximately 52%, 1%, and 47% of the overall human carcinogenic, noncarcinogenic, and ecological impacts, respectively. This may be partially limited by the quantitative data available. While uncertainties exist associated with data availability, our study highlights the significance of integrating impacts from shale gas production to end-of-pipe pollution for comprehensive environmental risk assessments.

Oil and gas produced waters fail to meet beneficial reuse recommendations for use as dust suppressants

Produced water from conventional oil and gas wells (O&G PW) is beneficially reused as an inexpensive alternative to commercial dust suppressants which minimize inhalable particulate matter (PM10) from unpaved roads. The efficacy and environmental impacts of using O&G PW instead of commercial products have not been extensively investigated, although O&G PW has been used for dust suppression for decades and often has elevated concentrations of environmental pollutants. In this study, the effectiveness of O&G PW is compared to commercial products under variable humidity conditions by measuring total generated PM10 emissions from treated road aggregate discs. To measure environmental impacts, model roadbeds were treated with six O&G PW and commercial products then subjected to a simulated two-year, 24-h storm event. Generated runoff water was collected and characterized. In efficacy studies, O&G PW offered variable dust reduction (10-85 %) compared to rainwater controls under high humidity (50 %) conditions but performed similarly or worse than controls when humidity was low (20 %). Conversely, all but two commercial products reduced dust emissions by over 90 % regardless of humidity. In rainfall-runoff experiments, roads treated with O&G PWs and CaCl2 Brine generated runoff that was hypersaline, indicating that mobilization of soluble salts could contribute to freshwater salinization. Though most runoff concentrations were highest from roadbeds treated with CaCl2 Brine, runoff from roadbeds treated with O&G PW had the highest concentrations of combined radium (83.6 pCi/L), sodium (3560 mg/L), and suspended solids (5330 mg/L). High sodium concentrations likely dispersed clay particles, which increased road mass loss by 47.2 kg solids/km/storm event compared to rainwater controls. Roadbeds treated with CaCl2 Brine, which had low sodium concentrations, reduced solid road mass loss by 98.1 kg solids/km/storm event. Based on this study, O&G PW do not perform as well as commercial products and pose unique risks to environmental health.

Effects of oilfield-produced water discharge on the spatial patterns of microbial communities in arid soils

Recently intensified oil exploitation has resulted in the discharge of large amounts of wastewater containing high concentrations of organic matter and nutrients into the receiving aquatic and soil environments; however, the effects of oilfield-produced water on the soil microbiota are poorly understood. In this study, we conducted a comprehensive analysis to reveal the composition and diversity of the microbial community at horizontal and vertical scales in a typical arid soil receiving oilfield-produced water in Northwest China. Oilfield-produced water caused an increase in microbial diversity at the horizontal scale, and the communities in the topsoil were more variable than those in the subsoil. Additionally, the microbial taxonomic composition differed significantly between the near- and far-producing water soils, with Proteobacteria and Halobacterota dominating the water-affected and reference soil communities, respectively. Soil property analysis revealed that pH, salt, and total organic content influenced the bacterial communities. Furthermore, the oil-produced water promoted the complexity and modularity of distance-associated microbial networks, indicating positive interactions for soil ecosystem function, but not for irrigation or livestock watering. This is the first detailed examination of the microbial communities in soil receiving oilfield-produced water, providing new insights for understanding the microbial spatial distributions in receiving arid soils.

Illegal dumping of oil and gas wastewater alters arid soil microbial communities

The Permian Basin, underlying southeast New Mexico and west Texas, is one of the most productive oil and gas (OG) provinces in the United States. Oil and gas production yields large volumes of wastewater with complex chemistries, and the environmental health risks posed by these OG wastewaters on sensitive desert ecosystems are poorly understood. Starting in November 2017, 39 illegal dumps, as defined by federal and state regulations, of OG wastewater were identified in southeastern New Mexico, releasing ~600,000 L of fluid onto dryland soils. To evaluate the impacts of these releases, we analyzed changes in soil geochemistry and microbial community composition by comparing soils from within OG wastewater dump-affected samples to unaffected zones. We observed significant changes in soil geochemistry for all dump-affected compared with control samples, reflecting the residual salts and hydrocarbons from the OG-wastewater release (e.g., enriched in sodium, chloride, and bromide). Microbial community structure significantly (P < 0.01) differed between dump and control zones, with soils from dump areas having significantly (P < 0.01) lower alpha diversity and differences in phylogenetic composition. Dump-affected soil samples showed an increase in halophilic and halotolerant taxa, including members of the Marinobacteraceae, Halomonadaceae, and Halobacteroidaceae, suggesting that the high salinity of the dumped OG wastewater was exerting a strong selective pressure on microbial community structure. Taxa with high similarity to known hydrocarbon-degrading organisms were also detected in the dump-affected soil samples. Overall, this study demonstrates the potential for OG wastewater exposure to change the geochemistry and microbial community dynamics of arid soils.IMPORTANCEThe long-term environmental health impacts resulting from releases of oil and gas (OG) wastewater, typically brines with varying compositions of ions, hydrocarbons, and other constituents, are understudied. This is especially true for sensitive desert ecosystems, where soil microbes are key primary producers and drivers of nutrient cycling. We found that releases of OG wastewater can lead to shifts in microbial community composition and function toward salt- and hydrocarbon-tolerant taxa that are not typically found in desert soils, thus altering the impacted dryland soil ecosystem. Loss of key microbial taxa, such as those that catalyze organic carbon cycling, increase arid soil fertility, promote plant health, and affect soil moisture retention, could result in cascading effects across the sensitive desert ecosystem. By characterizing environmental changes due to releases of OG wastewater to soils overlying the Permian Basin, we gain further insights into how OG wastewater may alter dryland soil microbial functions and ecosystems.

Toxicity and chemical characterization of shale gas wastewater discharged to the receiving water: Evidence from toxicity identification evaluation

Flowback and produced water (FPW) generated from shale gas extraction is a complex mixture consisting of injected drilling fluid, deep formation water, and byproducts of downhole reactions. Limited knowledge is available regarding the impact of discharged FPW on surface water in China. With the development of shale gas exploitation, this emphasizes an urgent need for comprehensive assessments and stringent regulations to ensure the safe disposal of shale gas extraction-related wastewater. Herein, we explored potential impacts of treated shale gas wastewater discharged into a local river in southwest China through toxicity identification evaluation (TIE). Results revealed that organics and particulates significantly contributed to the overall toxicity of the treated FPW wastewater. Through target and suspect chemical analyses, various categories of organic contaminants were detected, including alkanes, aromatic hydrocarbons, biocides, phenols, and phthalates. Furthermore, non-target analysis uncovered the presence of surfactant-related contaminants in tissues of exposed organisms, but their contribution to the observed toxicity was unclear due to the lack of effect data for these compounds. Higher toxicity was found at the discharge point compared with upstream sites; however, the toxicity was rapidly mitigated due to dilution in the receiving river, posing little impact on downstream areas. Our study highlighted the importance of monitoring toxicity and water quality of FPW effluent even though dilution could be a viable approach when the water volume in the discharge was small.

Increases in trade secret designations in hydraulic fracturing fluids and their potential implications for environmental health and water quality

Hydraulic fracturing is an increasingly common method of oil and gas extraction across the United States. Many of the chemicals used in hydraulic fracturing processes have been proven detrimental to human and environmental health. While disclosure frameworks have advanced significantly in the last 20 years, the practice of withholding chemical identities as "trade secrets" or "proprietary claims" continues to represent a major absence in the data available on hydraulic fracturing. Here, we analyze rates of trade secret claims using FracFocus, a nationwide database of hydraulic fracturing data, from January 1, 2014 to December 31, 2022. We use the open-source tool Open-FF, which collates FracFocus data, makes it accessible for systematic analysis, and performs several quality-control measures. We found that the use by mass of chemicals designated as trade secrets has increased over the study time period, from 728 million pounds in 2014 to 2.96 billion pounds in 2022 (or a 43.7% average yearly increase). A total of 10.4 billion pounds of chemicals were withheld as trade secrets in this time period. The water volume used (and therefore total mass of fracturing fluid) per fracturing job has shown a large increase from 2014 to 2022, which partly explains the increase in mass of chemicals withheld as trade secrets over this time period, even as total fracturing jobs and individual counts of proprietary records have decreased. Our analysis also shows increasing rates of claiming proppants (which can include small grains of sand, ceramic, or other mineral substances used to prop open fractures) as proprietary. However, the mean and median masses of non-proppant constituents designated as trade secrets have also increased over the study period. We also find that the total proportion of all disclosures including proprietary designations has increased by 1.1% per year, from 79.3% in 2014 to 87.5% in 2022. In addition, most disclosures designate more than one chemical record as proprietary: trade secret withholding is most likely to apply to 10-25% of all records in an individual disclosure. We also show the top ten reported purposes that most commonly include proprietary designations, after removing vague or multiple entries, the first three of which are corrosion inhibitors, friction reducers, and surfactants. Finally, we report the top ten operators and suppliers using and supplying proprietary chemicals, ranked by mass used or supplied, over our study period. These results suggest the importance of revisiting the role of proprietary designations within state and federal disclosure mechanisms.

Toxicity and chemical composition of commercial road palliatives versus oil and gas produced waters

Across the United States, road palliatives are applied to roads for maintenance operations that improve road safety. In the winter, solid rock salts and brine solutions are used to reduce the accumulation of snow and ice, while in the summer, dust suppressants are used to minimize fugitive dust emissions. Many of these products are chloride-based salts that have been linked to freshwater salinization, toxicity to aquatic organisms, and damage to infrastructure. To minimize these impacts, organic products have been gaining attention, though their widespread adoption has been limited due to their higher cost. In some states, using produced water from conventionally drilled oil and gas wells (OGPWs) on roads is permitted as a cost-effective alternative to commercial products, despite its typically elevated concentrations of heavy metals, radioactivity, and organic micropollutants. In this study, 17 road palliatives used for winter and summer road maintenance were collected and their chemical composition and potential human toxicity were characterized. Results from this study demonstrated that liquid brine solutions had elevated levels of trace metals (Zn, Cu, Sr, Li) that could pose risks to human and environmental health. The radium activity of liquid calcium chloride products was comparable to the activity of OGPWs and could be a significant source of radium to the environment. The organic fractions of evaluated OGPWs and chloride-based products posed little risk to human health. However, organic-based dust suppressants regulated toxicity pathways related to xenobiotic metabolism, lipid metabolism, endocrine disruption, and oxidative stress, indicating their use could lead to environmental harm and health risks to operators handing these products and residents living near treated roads.

Outcomes of the Halliburton Loophole: Chemicals regulated by the Safe Drinking Water Act in US fracking disclosures, 2014-2021

Hydraulic fracturing (fracking) has enabled the United States to lead the world in gas and oil production over the past decade; 17.6 million Americans now live within a mile of an oil or gas well (Czolowski et al., 2017). This major expansion in fossil fuel production is possible in part due to the 2005 Energy Policy Act and its "Halliburton Loophole," which exempts fracking activity from regulation under the Safe Drinking Water Act (SDWA). To begin quantifying the environmental and economic impacts of this loophole, this study undertakes an aggregate analysis of chemicals that would otherwise be regulated by SDWA within FracFocus, an industry-sponsored fracking disclosure database. This paper quantifies the total disclosures and total mass of these chemicals used between 2014 and 2021, examines trends in their use, and investigates which companies most use and supply them. We find that 28 SDWA-regulated chemicals are reported in FracFocus, and 62-73% of all disclosures (depending on year) report at least one SDWA-regulated chemical. Of these, 19,700 disclosures report using SDWA-regulated chemicals in masses that exceed their reportable quantities as defined under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Finally, while the most common direct-supplier category is "company name not reported," Halliburton is the second-most named direct supplier of SWDA regulated chemicals. Halliburton is also the supplier most frequently associated with fracks that use SDWA regulated chemicals. These results show the necessity of a more robust and federally mandated disclosure system and suggest the importance of revisiting exemptions such as the Halliburton Loophole.

Water footprint of shale gas development in China in the carbon neutral era

The production of shale gas in China has repercussions for the global energy landscape and carbon neutrality. However, limited and threatened water resources may hinder the expansion of shale-derived natural gas, one of China's most promising development prospects. Coupling historical trends with policy guidance, we project that baseline water stress will intensify in two-thirds of China's provinces in the next decade. By 2035, annual water use for shale gas hydraulic fracturing activities is likely to increase to 16-35 million m³, with 13.8-23.7 million m³ of wastewater produced annually to extract 38-48 billion m³ of gas from ∼4800 shale gas wells. Analysis suggests that this projection is based on previously underestimated geological constraints (e.g., deep continental facies) in shale gas development in China. Nevertheless, forecasts suggest that the water footprint of shale development will become impossible to ignore, particularly in drought-stricken areas, indicating the potential risk of competition for water among shale development, domestic use, food production, and ecological protection. Meanwhile, the annual wastewater management market will increase to $0.2 billion by 2035. Our study suggests a critical need to direct attention to the (shale) energy-water nexus and develop multi-pronged policies to facilitate China's transition to carbon neutrality.

Mixture Toxicity of Three Unconventional Gas Fracking Chemicals, Barium, O-Cresol, and Sodium Chloride, to the Freshwater Shrimp Paratya australiensis

The 96-h acute toxicity of barium (Ba²⁺ ), o-cresol, and sodium chloride (NaCl) to Paratya australiensis was assessed in single, binary, and ternary combinations in addition to three biochemical assays: glutathione S-transferase, acetylcholinesterase, and sodium-potassium adenosine triphosphatase. The 96-h lethal concentrations that expressed 50% mortality (LC50) in the single-toxicant exposures were Ba²⁺  = 23.4 mg/L, o-cresol = 12.2 mg/L, and NaCl = 4198 mg/L. Mortality from o-cresol exposure occurred between 11 and 22 mg/L, whereas Ba²⁺ was more gradual across 10-105 mg/L, and most of the NaCl mortality occurred between 2050 and 4100 mg/L. Toxic units were used to assess the binary and ternary interactions of the toxicants. A more than additive effect was observed for most combinations in the binary chemical exposures, with the ternary combinations yielding highly synergistic interactions. Greater synergism was observed with the 96-h LC50 of o-cresol in combination with the three concentrations of NaCl (1025, 2050, and 3075 mg/L) compared with Ba²⁺ , with toxic units of 0.38, 0.48, and 0.10 (o-cresol) and 0.71, 0.67, and 0.50 (Ba²⁺ ). No notable enzyme activity trends were observed in the enzyme biomarker responses from both individual and mixture exposures. Although acute single-species toxicity tests tend to underestimate the effects of Ba²⁺ , o-cresol, and NaCl on populations, communities, and ecosystems in seminatural (e.g., mesocosms) and natural systems, there are currently no published acute toxicity data available for P. australiensis and the three toxicants used in the present study. The present study shows that chemicals with different toxicity mechanisms can potentially lead to more synergistic responses. Environ Toxicol Chem 2023;42:481-494. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Dissolved organic matter within oil and gas associated wastewaters from U.S. unconventional petroleum plays: Comparisons and consequences for disposal and reuse

Wastewater generated during petroleum extraction (produced water) may contain high concentrations of dissolved organics due to their intimate association with organic-rich source rocks, expelled petroleum, and organic additives to fluids used for hydraulic fracturing of unconventional (e.g., shale) reservoirs. Dissolved organic matter (DOM) within produced water represents a challenge for treatment prior to beneficial reuse. High salinities characteristic of produced water, often 10× greater than seawater, coupled to the complex DOM ensemble create analytical obstacles with typical methods. Excitation-emission matrix spectroscopy (EEMS) can rapidly characterize the fluorescent component of DOM with little impact from matrix effects. We applied EEMS to evaluate DOM composition in 18 produced water samples from six North American unconventional petroleum plays. Represented reservoirs include the Eagle Ford Shale (Gulf Coast Basin), Wolfcamp/Cline Shales (Permian Basin), Marcellus Shale and Utica/Point Pleasant (Appalachian Basin), Niobrara Chalk (Denver-Julesburg Basin), and the Bakken Formation (Williston Basin). Results indicate that the relative chromophoric DOM composition in unconventional produced water may distinguish different lithologies, thermal maturity of resource types (e.g., heavy oil vs. dry gas), and fracturing fluid compositions, but is generally insensitive to salinity and DOM concentration. These results are discussed with perspective toward DOM influence on geochemical processes and the potential for targeted organic compound treatment for the reuse of produced water.

Combining eDNA and morphological approaches to reveal the impacts of long-term discharges of shale gas wastewaters on receiving waters

The potential threats of shale gas wastewater discharges to receiving waters is of great concern. In this study, chemical analyses and biomonitoring were performed three times in a small river that received treated wastewater over a two-year period. The results of chemical analyses showed that the concentrations of chloride, conductivity, barium, and strontium increased at the discharge site, but their concentrations decreased considerably farther downstream (≥500 m). The concentrations of toxic organic compounds (16 US EPA priority polycyclic aromatic hydrocarbons and 6 priority phthalates), trace metals (strontium, arsenic, zinc, copper, chromium, lead, cadmium, nickel, and neodymium), and natural radionuclides (⁴⁰K, ²³⁸U, ²²⁶Ra, and ²³²Th) were comparable to the corresponding background values or did not exhibit obvious accumulation in sediments with continued discharge. Morphological and environmental DNA approaches were used to reveal the potential effects of wastewater discharges on aquatic ecosystems. The results showed that the community structure of benthic invertebrates was not altered by the long-term discharges of shale gas wastewaters. However, the biodiversity indices (richness and Shannon) from the two approaches showed inconsistencies, which were caused by multiple reasons, and that substrates had a strong influence on the morphological biodiversity indices. A multimetric index was proposed to further analyze morphological and environmental DNA data, and the results showed no significant difference between the upstream and downstream sites. Generally, the chemical and biological results both demonstrated that the discharges of shale gas wastewaters had limited impacts on river ecosystems within two years.

Produced Water Treatment and Valorization: A Techno-Economical Review

In recent years, environmental concerns have urged companies in the energy sector to modify their industrial activities to facilitate greater environmental stewardship. For example, the practice of unconventional oil and gas extraction has drawn the ire of regulators and various environmental groups due to its reliance on millions of barrels of fresh water—which is generally drawn from natural sources and public water supplies—for hydraulic fracturing well stimulation. Additionally, this process generates two substantial waste streams, which are collectively characterized as flowback and produced water. Whereas flowback water is comprised of various chemical additives that are used during hydraulic fracturing; produced water is a complex mixture of microbiota, inorganic and organic constituents derived from the petroliferous strata. This review will discuss the obstacles of managing and treating flowback and produced waters, concentrating on the hardest constituents to remove by current technologies and their effect on the environment if left untreated. Additionally, this work will address the opportunities associated with repurposing produced water for various applications as an alternative to subsurface injection, which has a number of environmental concerns. This review also uses lithium to evaluate the feasibility of extracting valuable metals from produced water using commercially available technologies.

Complex impacts of hydraulic fracturing return fluids on soil microbial community respiration, structure, and functional potentials

The consequences of soils exposed to hydraulic fracturing (HF) return fluid, often collectively termed flowback and produced water (FPW), are poorly understood, even though soils are a common receptor of FPW spills. Here, we investigate the impacts on soil microbiota exposed to FPW collected from the Montney Formation of western Canada. We measured soil respiration, microbial community structure, and functional potentials under FPW exposure across a range of concentrations, exposure time, and soil types (luvisol and chernozem). We find that soil type governs microbial community response upon FPW exposure. Within each soil, FPW exposure led to reduced biotic soil respiration, and shifted microbial community structure and functional potentials. We detect substantially higher species richness and more unique functional genes in FPW-exposed soils than in FPW-unexposed soils, with metagenome-assembled genomes (e.g., Marinobacter persicus) from luvisol soil exposed to concentrated FPW being most similar to genomes from HF/FPW sites. Our data demonstrate the complex impacts of microbial communities following FPW exposure, and highlight the site-specific effects in evaluation of spills and agricultural reuse of FPW on the normal soil functions. This article is protected by copyright. All rights reserved.

Chemical and Reactive Transport Processes Associated with Hydraulic Fracturing of Unconventional Oil/Gas Shales

Hydraulic fracturing of unconventional oil/gas shales has changed the energy landscape of the U.S. Recovery of hydrocarbons from tight, hydraulically fractured shales is a highly inefficient process, with estimated recoveries of <25% for natural gas and <5% for oil. This review focuses on the complex chemical interactions of additives in hydraulic fracturing fluid (HFF) with minerals and organic matter in oil/gas shales. These interactions are intended to increase hydrocarbon recovery by increasing porosities and permeabilities of tight shales. However, fluid-shale interactions result in the dissolution of shale minerals and the release and transport of chemical components. They also result in mineral precipitation in the shale matrix, which can reduce permeability, porosity, and hydrocarbon recovery. Competition between mineral dissolution and mineral precipitation processes influences the amounts of oil and gas recovered. We review the temporal/spatial origins and distribution of unconventional oil/gas shales from mudstones and shales, followed by discussion of their global and U.S. distributions and compositional differences from different U.S. sedimentary basins. We discuss the major types of chemical additives in HFF with their intended purposes, including drilling muds. Fracture distribution, porosity, permeability, and the identity and molecular-level speciation of minerals and organic matter in oil/gas shales throughout the hydraulic fracturing process are discussed. Also discussed are analysis methods used in characterizing oil/gas shales before and after hydraulic fracturing, including permeametry and porosimetry measurements, X-ray diffraction/Rietveld refinement, X-ray computed tomography, scanning/transmission electron microscopy, and laboratory- and synchrotron-based imaging/spectroscopic methods. Reactive transport and spatial scaling are discussed in some detail in order to relate fundamental molecular-scale processes to fluid transport. Our review concludes with a discussion of potential environmental impacts of hydraulic fracturing and important knowledge gaps that must be bridged to achieve improved mechanistic understanding of fluid transport in oil/gas shales.

Risk assessment of pollutants in flowback and produced waters and sludge in impoundments

Due to the growing hydraulic fracturing (HF) practices in China, the environmental risks of pollutants in flowback and produced waters (FPW) and sludge in impoundments for FPW reserves have drawn increasing attention. In this context, we first characterized the comparative geochemical characteristics of the FPW and the sludge in impoundments that collected FPW from 75 shale gas wells, and then the risks associated with the pollutants were assessed. The results demonstrated that four organic compounds detected in the FPW, naphthalene, acenaphthene, dibutyl phthalate, and bis(2-ethylhexyl)phthalate, were potential threats to surface waters. The concentrations of trace metals (copper, cadmium, manganese, chromium, nickel, zinc, arsenic, and lead) in the FPW and sludge were low; however, those of iron, barium, and strontium were high. The accumulation of chromium, nickel, zinc, and lead in the sludge became more evident as the depth increased. The environmental risks from heavy metals in the one-year precipitated sludge were comparable to those reported in the environment. However, the radium equivalent activities were 10-41 times higher than the recommended value for human health safety, indicating potential radiation risks. Although hydrophobic organic compounds, such as high-molecular-weight polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), benzene, ethylbenzene, toluene, and xylene (BTEX), tended to accumulate in the sludge, their environmental risks were within tolerable ranges after proper treatment. Multiple antibiotic resistance genes (ARGs), such as those for macrolide, lincosamide, streptogramin (MLS), tetracycline, and multidrug resistances, were detected in the shale gas wastewaters and sludge. Therefore, the environmental risks of these emerging pollutants upon being discharged or leaked into surface waters require further attention.

A critical review of advanced nanotechnology and hybrid membrane based water recycling, reuse, and wastewater treatment processes

One of the modern challenges is to provide clean and affordable drinking water. Water scarcity is caused by the growing population in the world and pollutants contaminate all remaining water sources. Innovative water treatment solutions have been provided by nanotechnology. Microorganisms, organic suspensions, and inorganic heavy metal ions, among other things, are common water contaminants. Since antiquity, a wide range of water clean-up methods have been employed to address this issue. Breakthroughs in water purification procedures have occurred during the previous four decades, with the most significant one being the use of nanomaterials and nanomembranes. Nanoparticles and nanomembranes (polymeric membranes) have recently been used in engineered materials (TiO₂, ZnO, CuO, Ag, CNT's and mixed oxide nanoparticles, for example). Engineered nanomembranes, nanocomposites and nanoparticles have been used in this review article's discussion of water purification technologies. The review also discusses the risk and solutions of using nanoparticles and nanocomposites in the future.

Constructed wetlands for polishing oil and gas produced water releases

Produced water (PW) is the largest waste stream associated with oil and gas (O&G) operations and contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials and any remaining chemical additives. In some areas in Wyoming, constructed wetlands (CWs) are used to polish PW downstream of National Pollutant Discharge Elimination System (NPDES) PW release points. In recent years, there has been increased interest in finding lower cost options, such as CWs, for PW treatment. The goal of this study was to understand the efficacy of removal and environmental fate of O&G organic chemical additives in CW systems used to treat PW released for agricultural beneficial reuse. To achieve this goal, we analyzed water and sediment samples for organic O&G chemical additives and conducted 16S rRNA gene sequencing for microbial community characterization on three such systems in Wyoming, USA. Three surfactants (polyethylene glycols, polypropylene glycols, and nonylphenol ethoxylates) and one biocide (alkyldimethylammonium chloride) were detected in all three PW discharges and >94% removal of all species from PW was achieved after treatment in two CWs in series. These O&G extraction additives were detected in all sediment samples collected downstream of PW discharges. Chemical and microbial analyses indicated that sorption and biodegradation were the main attenuation mechanisms for these species. Additionally, all three discharges showed a trend of increasingly diverse, but similar, microbial communities with greater distance from NPDES PW discharge points. Results of this study can be used to inform design and management of constructed wetlands for produced water treatment.

Characterization and Treatment Technologies Applied for Produced Water in Qatar

Qatar is one of the major natural gas (NG) producing countries, which has the world’s third-largest NG reserves besides the largest supplier of liquefied natural gas (LNG). Since the produced water (PW) generated in the oil and gas industry is considered as the largest waste stream, cost-effective PW management becomes fundamentally essential. The oil/gas industries in Qatar produce large amounts of PW daily, hence the key challenges facing these industries reducing the volume of PW injected in disposal wells by a level of 50% for ensuring the long-term sustainability of the reservoir. Moreover, it is important to study the characteristics of PW to determine the appropriate method to treat it and then use it for various applications such as irrigation, or dispose of it without harming the environment. This review paper targets to highlight the generation of PW in Qatar, as well as discuss the characteristics of chemical, physical, and biological treatment techniques in detail. These processes and methods discussed are not only applied by Qatari companies, but also by other companies associated or in collaboration with those in Qatar. Finally, case studies from different companies in Qatar and the challenges of treating the PW are discussed. From the different studies analyzed, various techniques as well as sequencing of different techniques were noted to be employed for the effective treatment of PW.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review

There is considerable debate about the sustainability of the hydraulic fracturing (HF) water cycle in North America. Recently, this debate has expanded to China, where HF activities continue to grow. Here, we provide a critical review of the HF water cycle in China, including water withdrawal practices and flowback and produced water (FPW) management and their environmental impacts, with a comprehensive comparison to the U.S. and Canada (North America). Water stress in arid regions, as well as water management challenges, FPW contamination of aquatic and soil systems, and induced seismicity are all impacts of the HF water cycle in China, the U.S., and Canada. In light of experience gained in North America, standardized practices for analyzing and reporting FPW chemistry and microbiology in China are needed to inform its efficient and safe treatment, discharge and reuse, and identification of potential contaminants. Additionally, conducting ecotoxicological studies is an essential next step to fully reveal the impacts of accidental FPW releases into aquatic and soil ecosystems in China. From a policy perspective, the development of China's unconventional resources lags behind North America's in terms of overall regulation, especially with regard to water withdrawal, FPW management, and routine monitoring. Our study suggests that common environmental risks exist within the world's two largest HF regions, and practices used in North America may help prevent or mitigate adverse effects in China.

Toxicity of hydraulic fracturing wastewater from black shale natural-gas wells influenced by well maturity and chemical additives

Hydraulic fracturing of deep shale formations generates large volumes of wastewater that must be managed through treatment, reuse, or disposal. Produced wastewater liberates formation-derived radionuclides and contains previously uncharacterized organohalides thought to be generated within the shale well, both posing unknown toxicity to human and ecological health. Here, we assess the toxicity of 42 input media and produced fluid samples collected from four wells in the Utica formation and Marcellus Shale using two distinct endpoint screening assays. Broad spectrum acute toxicity was assessed using a bioluminescence inhibition assay employing the halotolerant bacterium Aliivibrio fischeri, while predictive mammalian cytotoxicity was evaluated using a N-acetylcysteine (NAC) thiol reactivity assay. The acute toxicity and thiol reactivity of early-stage flowback was higher than later produced fluids, with levels diminishing through time as the natural gas wells matured. Acute toxicity of early stage flowback and drilling muds were on par with the positive control, 3,5-dichlorophenol (6.8 mg L-1). Differences in both acute toxicity and thiol reactivity between paired natural gas well samples were associated with specific chemical additives. Samples from wells containing a larger diversity and concentration of organic additives resulted in higher acute toxicity, while samples from a well applying a higher composition of ammonium persulfate, a strong oxidizer, showed greater thiol reactivity, predictive of higher mammalian toxicity. Both acute toxicity and thiol reactivity are consistently detected in produced waters, in some cases present up to nine months after hydraulic fracturing. These results support that specific chemical additives, the reactions generated by the additives, or the constituents liberated from the formation by the additives contribute to the toxicity of hydraulic fracturing produced waters and reinforces the need for careful consideration of early produced fluid management.

Thermal Desalination of Produced Water—An Analysis of the Partitioning of Constituents into Product Streams and Its Implications for Beneficial Use Outside the O&G Industry

To understand partitioning of produced water (PW) constituents using thermal desalination, PW from the Delaware Basin was desalinated using a crystallization process and modeled using OLI Systems, Inc. (OLI, Parsippany, NJ, USA) chemistry software. The incorporation of a pretreatment step, steam stripping, prior to desalination was predicted to be effective at removing hydrocarbons (across a range of volatilities). As expected, inorganics were almost completely retained in the residual brine which was confirmed by OLI. As evaporation progressed, sparingly soluble compounds such as gypsum and celestite precipitated first and overall solids production at this stage was low (<1% of total solids). Further evaporation resulted in saturation of the residual brine with respect to NaCl, which started to precipitate in bulk up to a practical desalination limit of approximately 68% by mass (approximately 80% by volume). Beyond this point, the residual brine and solids mixture became too viscous to be pumped. Gravimetrically determined total dissolved solids (TDS) for PW, distillate and residual brine was found to be much higher than prediction, potentially due to the presence of neutral species, unstripped gases and organic (likely hydrophilic) constituents. Although the distillate had low TDS, the presence of unknown constituents including organic compounds in the distillate will likely require polishing treatment to mitigate potential toxicity associated with such compounds or transformation products post-release if discharged to the environment. OLI predicted near-complete retention of acetate in the residual brine. In contrast, laboratory tests showed nearly 50% partitioning of acetate into the distillate. Although not modeled, propionate partitioning was even higher at 94%. The inclusion of ammonia as an input species in OLI greatly improved the match between test data and model prediction. Additionally, it was hypothesized that acetic acid/acetate could have formed a volatile adduct with ammonia that increased its volatility and partitioning into the distillate. The findings of this study inform beneficial use by describing the chemical composition of desalination-derived distillate, brine and salt products. This study also identified alternative approaches, both treatment and non-treatment, for managing PW from unconventional operations.

Oil & gas produced water retention ponds as potential passive treatment for radium removal and beneficial reuse

Oil and gas (O&G) extraction generates large volumes of produced water (PW) in regions that are often water-stressed. In Wyoming, generators are permitted under the National Pollutant Discharge Elimination System (NPDES) program to discharge O&G PW for beneficial use. In one Wyoming study region, downstream of the NPDES facilities exist naturally occurring wetlands referred to herein as produced water retention ponds (PWRPs). Previously, it was found that dissolved radium (Ra) and organic contaminants are removed within 30 km of the discharges and higher-resolution sampling was required to understand contaminant attenuation mechanisms. In this study, we sampled three NPDES discharge facilities, five PWRPs, and a reference background wetland not impacted by O&G PW disposal. Water samples, grab sediments, sediment cores and vegetation were collected. No inorganic PW constituents were abated through the PWRP series but Ra was shown to accumulate within PWRP grab sediments, upwards of 2721 Bq kg^-1, compared to downstream sites. Ra mineral association with depth in the sediment profile is likely controlled by the S cycle under varying microbial communities and redox conditions. Under anoxic conditions, common in wetlands, Ra was available as an exchangeable ion, similar to Ca, Ba and Sr, and S was mostly water-soluble. ²²⁶Ra concentration ratios in vegetation samples, normalizing vegetation Ra to sediment Ra, indicated that ratios were highest in sediments containing less exchangeable ²²⁶Ra. Sequential leaching data paired with redox potentials suggest that oxic conditions are necessary to contain Ra in recalcitrant sediment minerals and prevent mobility and bioavailability.

Irrigation of wheat with select hydraulic fracturing chemicals: Evaluating plant uptake and growth impacts

Oilfield flowback and produced water (FPW) is a waste stream that may offer an alternative source of water for multiple beneficial uses. One practice gaining interest in several semi-arid states is the reuse of FPW for agricultural irrigation. However, it is unknown if the reuse of FPW on edible crops could increase health risks from ingestion of exposed food, or impact crop growth. A greenhouse experiment was conducted using wheat (Triticum aestivum) to investigate the uptake potential of select hydraulic fracturing additives known to be associated with health risks. The selected chemicals included acrylamide, didecyldimethylammonium chloride (DDAC), diethanolamine, and tetramethylammonium chloride (TMAC). Mature wheat grain was extracted and analyzed by liquid chromatography-triple quadrupole mass spectrometry (LC-QQQ) to quantify chemical uptake. Plant development observations were also documented to evaluate impacts of the chemicals on crop yield. Analytical results indicated that TMAC and diethanolamine had significantly higher uptake into both wheat grain and stems than control plants which were not exposed to the four chemicals under investigation. Acrylamide was measured in statistically higher concentrations in the stems only, while DDAC was not detected in grain or stems. Growth impacts included lodging in treated wheat plants due to increased stem height and grain weight, potentially resulting from increased nitrogen application. While analytical results show that uptake of select hydraulic fracturing chemicals in wheat grain and stems is measurable, reuse of FPW for irrigation in real world scenarios would likely result in less uptake because water would be subject to natural degradation, and often treatment and dilution practices. Nonetheless, based on the outstanding data gaps associated with this research topic, chemical specific treatment and regulatory safeguards are still recommended.

Endocrine disrupting activities and geochemistry of water resources associated with unconventional oil and gas activity

The rise of hydraulic fracturing and unconventional oil and gas (UOG) exploration in the United States has increased public concerns for water contamination induced from hydraulic fracturing fluids and associated wastewater spills. Herein, we collected surface and groundwater samples across Garfield County, Colorado, a drilling-dense region, and measured endocrine bioactivities, geochemical tracers of UOG wastewater, UOG-related organic contaminants in surface water, and evaluated UOG drilling production (weighted well scores, nearby well count, reported spills) surrounding sites. Elevated antagonist activities for the estrogen, androgen, progesterone, and glucocorticoid receptors were detected in surface water and associated with nearby shale gas well counts and density. The elevated endocrine activities were observed in surface water associated with medium and high UOG production (weighted UOG well score-based groups). These bioactivities were generally not associated with reported spills nearby, and often did not exhibit geochemical profiles associated with UOG wastewater from this region. Our results suggest the potential for releases of low-saline hydraulic fracturing fluids or chemicals used in other aspects of UOG production, similar to the chemistry of the local water, and dissimilar from defined spills of post-injection wastewater. Notably, water collected from certain medium and high UOG production sites exhibited bioactivities well above the levels known to impact the health of aquatic organisms, suggesting that further research to assess potential endocrine activities of UOG operations is warranted.

Forensic tracers of exposure to produced water in freshwater mussels: a preliminary assessment of Ba, Sr, and cyclic hydrocarbons

Hydraulic fracturing is often criticized due in part to the potential degradation of ground and surface water quality by high-salinity produced water generated during well stimulation and production. This preliminary study evaluated the response of the freshwater mussel, Elliptio complanata, after exposure to produced water. A limited number of adult mussels were grown over an 8-week period in tanks dosed with produced water collected from a hydraulically fractured well. The fatty tissue and carbonate shells were assessed for accumulation of both inorganic and organic pollutants. Ba, Sr, and cyclic hydrocarbons indicated the potential to accumulate in the soft tissue of freshwater mussels following exposure to diluted oil and gas produced water. Exposed mussels showed accumulation of Ba in the soft tissue several hundred times above background water concentrations and increased concentrations of Sr. Cyclic hydrocarbons were detected in dosed mussels and principle component analysis of gas chromatograph time-of-flight mass spectrometer results could be a novel tool to help identify areas where aquatic organisms are impacted by oil and gas produced water, but larger studies with greater replication are necessary to confirm these results.

The impact of using low-saline oilfield produced water for irrigation on water and soil quality in California

The consecutive occurrence of drought and reduction in natural water availability over the past several decades requires searching for alternative water sources for the agriculture sector in California. One alternative source to supplement natural waters is oilfield produced water (OPW) generated from oilfields adjacent to agricultural areas. For over 25 years, OPW has been blended with surface water and used for irrigation in the Cawelo Water District of Kern County, as permitted by California Water Board policy. This study aims to evaluate the potential environmental impact, soil quality, and crop health risks of this policy. We examined a large spectrum of salts, metals, radionuclides (²²⁶Ra and ²²⁸Ra), and dissolved organic carbon (DOC) in OPW, blended OPW used for irrigation, groundwater, and soils irrigated by the three different water sources. We found that all studied water quality parameters in the blended OPW were below current California irrigation quality guidelines. Yet, soils irrigated by blended OPW showed higher salts and boron relative to soils irrigated by groundwater, implying long-term salts and boron accumulation. We did not, however, find systematic differences in ²²⁶Ra and ²²⁸Ra activities and DOC in soils irrigated by blended or unblended OPW relative to groundwater-irrigated soils. Based on a comparison of measured parameters, we conclude that the blended low-saline OPW used in the Cawelo Water District of California is of comparable quality to the local groundwater in the region. Nonetheless, the salt and boron soil accumulation can pose long-term risks to soil sodification, groundwater salinization, and plant health; as such, the use of low-saline OPW for irrigation use in California will require continual blending with fresh water and planting of boron-tolerant crops to avoid boron toxicity.

Reusing oil and gas produced water for agricultural irrigation: Effects on soil health and the soil microbiome

Produced water (PW) is a major waste-product of oil and gas production that some consider a viable agricultural irrigation water source. However, the presence of petroleum hydrocarbons, toxic metals and potentially high salinity of PW may be deleterious for soil health. Thus, we irrigated wheat with minimally treated PW to investigate effects on soil health, wheat growth, and the soil microbiome. Irrigation treatments included control irrigation water (IW), 1% and 5% PW dilutions (1% PW, 5% PW), and a saltwater solution with salinity equivalent to the 5% PW dilution (SW). Wheat was irrigated three times a week, for a total of 2.1 L per pot by harvest. During wheat growth, we measured plant physiological parameters, soil electrical conductivity, as well as profiled soil microbial diversity by performing 16S ribosomal ribonucleic acid (rRNA) gene analysis. Soil health parameters were measured after harvest, including chemical, biological, physical, and nutrient properties that were used to calculate an overall soil health index (SQI). SQI analysis revealed that the SW and 5% PW treatments had significantly reduced soil health as compared to the control. Furthermore, the 16S rRNA gene analysis showed that the microbial community membership and structure was significantly different between irrigation treatments, highlighting shifts in the soil microbiome which may impact soil biochemical cycling. Both the SW- and 5% PW-treated wheat had reduced yields as compared to the control. Our results indicate that irrigating wheat with minimally treated PW may result in yield decreases, as well as reducing both overall soil health and soil microbial community diversity. Future large-scale field studies are needed to determine the long-term soil health effects of PW on different soil types and crops.

Isotopic and element ratios fingerprint salinization impact from beneficial use of oil and gas produced water in the Western U.S

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 USEPA 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 for irrigation and drinking water but also exceed aquatic life and livestock recommended limits. ⁸⁷Sr/⁸⁶Sr and δ³⁴S_SO4 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 δ³⁴S_SO4) 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.

Mutagenicity assessment downstream of oil and gas produced water discharges intended for agricultural beneficial reuse

Produced water is the largest waste stream associated with oil and gas operations. This complex fluid contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials and any remaining chemical additives. In the United States, west of the 98th meridian, the federal National Pollutant Discharge Elimination System (NPDES) exemption allows release of produced water for agricultural beneficial reuse. The goal of this study was to quantify mutagenicity of a produced water NPDES release and discharge stream. We used four mutation assays in budding yeast cells that provide rate estimates for copy number variation (CNV) duplications and deletions, as well as forward and reversion point mutations. Higher mutation rates were observed at the discharge and decreased with distance downstream, which correlated with the concentrations of known carcinogens detected in the stream (e.g., benzene, radium), described in a companion study. Mutation rate increases were most prominent for CNV duplications and were higher than mutations observed in mixtures of known toxic compounds. Additionally, the samples were evaluated for acute toxicity in Daphnia magna and developmental toxicity in zebrafish. Acute toxicity was minimal, and no developmental toxicity was observed. This study illustrates that chemical analysis alone (McLaughlin et al., 2020) is insufficient for characterizing the risk of produced water NPDES releases and that a thorough evaluation of chronic toxicity is necessary to fully assess produced water for beneficial reuse.

Maximum Removal Efficiency of Barium, Strontium, Radium, and Sulfate with Optimum AMD-Marcellus Flowback Mixing Ratios for Beneficial Use in the Northern Appalachian Basin

Mixing of acid mine drainage (AMD) and hydraulic fracturing flowback fluids (HFFF) could represent an efficient management practice to simultaneously manage two complex energy wastewater streams while reducing freshwater resource consumption. AMD discharges offer generally high sulfate concentrations, especially from the bituminous coal region of Pennsylvania; unconventional Marcellus shale gas wells generally yield HFFF enriched in alkaline earth metals such as Sr and Ba, known to cause scaling issues in oil and gas (O&G) production. Mixing the two waters can precipitate HFFF-Ba and -Sr with AMD-SO₄, therefore removing them from solution. Four AMD discharges and HFFF from two unconventional Marcellus shale gas wells were characterized and mixed in batch reactors for 14 days. Ba could be completely removed from solution within 1 day of mixing in the form Ba_xSr_1-xSO₄ and no further significant precipitation occurred after 2 days. Total removal efficiencies of Ba + Sr + SO₄ and the proportion of Ba and Sr in Ba_xSr_1-xSO₄ depended upon the Ba/Sr ratio in the initial HFFF. A geochemical model was calibrated from batch reactor data and used to identify optimum AMD-HFFF mixing ratios that maximize total removal efficiencies (Ba + Sr + SO₄) for reuse in O&G development. Increasing Ba/Sr ratios can enhance total removal efficiency but decrease the efficiency of Ra removal. Thus, treatment objectives and intended beneficial reuse need to be identified prior to optimizing the treatment of HFFF with AMD.