Repository for Oil and Gas Energy Research (ROGER)

Abstract:
Substantial quantities of produced water generated during the extraction of oil and gas from unconventional reservoirs present significant environmental concern and increase the operating cost for this industry. Membrane Distillation (MD) can serve as a potential solution for beneficial reuse of produced water by generating high-quality permeate and reducing the volume of produced water requiring disposal. This study investigated treatment of produced water from Permian Basin in both laboratory and pilot-scale studies. Laboratory tests revealed the potential to successfully recover 50% of produced water although some increase in permeate conductivity was observed due to the passage of ammonia from the feed side. Initial pilot-scale test with filtration of raw produced water as the only pre-treatment step led to precipitation of SrSO4, NaCl, and Fe in the system once the solubility limits for these salts were exceeded. However, chemical pretreatment that included pH adjustment, aeration, and barite precipitation, allowed successful steady-state operation of the AGMD pilot system for 5 days where the produced water was concentrated from 127 g/L to 255 g/L (~50% water recovery) while recovering high quality permeate. Overall, greater than 99.7 % salt rejection was achieved with the average permeate flux of 1.86 LMH. Mass balance analysis suggested potential Ba and Ca precipitation in the system but there was no impact on AGMD performance and permeate quality during 5 days of continuous operation in the field.

Abstract:
Environmental concerns with unconventional oil and gas development are frequently centered on elevated water usage and the induction of seismic events during waste disposal. Reuse of produced water for subsequent production well stimulation can effectively address these concerns, but the variability among such samples must be well understood. Twenty-four samples of wastewater from unconventional oil and gas development were collected from south and west Texas to assess their variability and feasibility for direct reuse. Bulk metrics were collected, including total organic carbon, total nitrogen, as well as total dissolved and suspended solids. The profiles of pertinent inorganic constituents were also evaluated. Variations were not only seen between regions but also among samples collected from the same region. For example, the average total organic carbon for Eagle Ford samples collected was 700 ± 500 mg/L, while samples collected from the Per-mian Basin featured an average total organic carbon concentration of 600 ± 900 mg/L. The Permian Basin total organic carbon ranged from 38 to 2600 mg/L. The total dissolved solids levels had the same variability between regions, with an average value for Eagle Ford of 20,000 ± 10,000 mg/L and a Permian Basin value of 150,000 ± 40,000 mg/L. However, samples were more reproducible within a given region. Collectively, the data indicate that the direct reuse of raw produced water for subsequent production well development without treatment is not feasible based on the reported reuse thresholds. Unconventional development wastewater samples from the Permian Basin were also compared to produced water values from conventional oil and gas wells in the same region, as reported by the United States Geological Survey. Samples collected in the Permian Basin consistently demonstrated lower ionic strength compared to conventional produced water data.

Abstract:
Although shale gas has shown promising potential to alleviate energy crisis as a clean energy resource, more attention has been paid to the harmful environmental impacts during exploitation. It is a critical issue for the management of shale gas wastewater (SGW), especially the organic compounds. This review focuses on analytical methods and corresponding treatment technologies targeting organic matters in SGW. Firstly, detailed information about specific shale-derived organics and related organic compounds in SGW were overviewed. Secondly, the state-of-the art analytical methods for detecting organics in SGW were summarized. The gas chromatography paired with mass spectrometry was the most commonly used technique. Thirdly, relevant treatment technologies for SGW organic matters were systematically explored. Forward osmosis and membrane distillation ranked the top two most frequently used treatment processes. Moreover, quantitative analyses on the removal of general and single organic compounds by treatment technologies were conducted. Finally, challenges for the analytical methods and treatment technologies of organic matters in SGW were addressed. The lack of effective trace organic detection techniques and high cost of treatment technologies are the urgent problems to be solved. Advances in the extraction, detection, identification and disposal of trace organic matters are critical to address the issues.

Abstract:
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.

Abstract:
The expansion of oil and gas extraction from unconventional reservoirs has led to an increase in the amount of produced water that has to be managed by this industry. Direct contact membrane distillation (DCMD) is a promising technology for treatment of produced water to enable water recovery and reduce the environmental footprint of this industry. The feasibility of DCMD for the treatment of highly saline produced water from the Permian Basin in TX with commercially available polyethylene and polytetrafluoroethylene membranes was evaluated in this study. An increase in water recovery by a DCMD system operated in the batch (concentrating) mode led to an increase in permeate conductivity. Partial removal of organic compounds from the produced water by biodegradation, chemical oxidation, and/or activated carbon adsorption could not resolve deterioration in permeate quality, and none of the organics observed in the permeate contributed to its conductivity. The observed increase in permeate conductivity was attributed to the passage of ammonia vapor from the feed side followed by protonation on the permeate side. This study revealed that permeate conductivity may not always be a reliable indicator of membrane wetting and underscores the importance of understanding the interactions between specific solutes and membrane materials.

Abstract:
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.

Abstract:

Abstract:
Unconventional oil and gas (UOG) production requires a vast quantity of freshwater while generating substantial volumes of wastewater. Although numerous studies have focused on technology development, other aspects beyond treatment technology, including regulations, economics, system logistics, and public perception, play equally or more important roles collectively in the selection and deployment of UOG wastewater management practices. In this article, we begin with a critical analysis of the motivations that drive UOG wastewater management towards treatment and reuse. Then we examine four main barriers against such a paradigm shift, pertaining to treatment technology, regulatory compliance, economic feasibility, and social acceptance. Despite the need of further improving technology efficiency for UOG wastewater treatment, the lack of established regulatory framework, the uncertainties of economic viability, as well as public resistance, hinder practical implementation of treatment technologies. We highlight the importance of knowledge and collaborative efforts from engineers, regulators, policy makers, economists, and social scientists to address those barriers, and emphasize that future research efforts should be directed at domains well beyond treatment technology. A systems approach and broader collaboration across multiple disciplines is needed to translate technology innovation into solutions that truly improve water sustainability in the context of rising UOG production.

Abstract:
This paper presents a mathematical programming approach for the strategic planning of managing wastewater generated by hydraulic fracturing operations in shale gas production. The proposed approach aims to achieve optimal selection of treatment, storage, and reuse activities. The approach also accounts for the variability of wastewater characteristics including the short-term flowback and transition water as well as the longer-term produced water. Because of the different compositions of the pollutants in the various types of wastewater, stream segregation is considered as an option. Furthermore, the model accounts for seasonal variabilities in freshwater availability. Economic and environmental objectives are considered. The economic objective function aims to determine the minimum total cost, which is composed of freshwater, treatment, storage, and transport costs. Credit is given for reused water. The environmental objective focuses on the reduction of freshwater requirements needed for the fracturing step. The proposed model determines trade-offs between cost and water consumption. A case study is presented, and the results show that it is possible to reduce up to 32.43% of freshwater consumed and to reuse up to 12.26% of the total wastewater from wells for fracturing needs.

Abstract:
The high management cost of wastewater generated during oil and gas production using hydraulic fracturing technology necessitates economically viable alternative technologies for remediation and reuse. In this study, an Oklahoma native microalgae strain, Komvophoron sp., was grown in four different flowback and produced water samples generated during hydraulic fracturing. Biomass production profile and pollutant removal efficiency of the strain were evaluated. The experimental data demonstrated that this strain was able to grow in all wastewater samples examined when suitable light intensity and CO2 flow rate were provided. Biomass productivity of the strain varied from 5.5 to 12 g m−3 day−1 depending on the wastewater sample used in the cultivation experiments. Very high nitrogen and phosphorus removal from the growth medium, up to 99 and 63%, respectively, could be achieved by growing and harvesting algal biomass in the wastewater samples. A mathematical model developed based on pH, light intensity and CO2 enriched air flow rate as system variables well described the experimental biomass productivity and pollutant removal efficiency data. The proposed mathematical model was successfully used to identify sets of operating conditions which would maximize biomass productivity and macronutrient removal efficiencies. Hence, the model developed in this study is a useful tool to assess technical viability and design of an efficient algal wastewater remediation process to reduce the impact of hydraulic fracturing on environment while producing biomass that can be converted to industrial bio-products including biofuels.

Abstract:
Advances in water treatment technologies paired with potential restrictions on oil and gas (O the sole major breakthrough has been in the development of salt-tolerant fracturing chemicals that allow for reuse of produced water for fracking operations. Guided research should assist in the development of fit-for-purpose solutions to maximize the reuse of treated produced water. This is exemplified by the case studies presented here that detail currently operating treatment facilities for reclamation and reuse of produced water.

Abstract:
The effects of salinity shock on the anaerobic treatment of fracturing wastewater regarding chemical oxygen demand (COD) removal performance, sludge characteristics and microbial community were investigated. Results showed COD removal efficiency decreased from 76.0% to 69.1%, 65.6%, 33.7% and 21.9% with the increase of salinity from 2.5 g/L to 10, 15, 25 and 45 g/L, respectively. The cumulative biogas production decreased by 13.8%–81.1% when salinity increased to 15–85 g/L. The increase of salinity led to the decline in particle size of granular sludge, and the activity of granular sludge, including SMA, coenzyme F420 and dehydrogenase, was inhibited significantly. Flow cytometry indicated the percentage of damaged cells in granular sludge gradually increased with the increase of salinity. Sequence analysis illustrated that microbial community structure in anaerobic digestion reactor was influenced by the salinity, high salinity reduced the diversity of archaea and decreased the abundance of methanogens, especially Methanosaeta.

Abstract:
The effectiveness of oil and gas produced water (OGPW) applied to unpaved roads to reduce particulate matter (PM10) generation has not been well-characterized. Here we quantify the efficacy of OGPW compared to commercial and alternative byproducts as dust suppressants applied to unpaved roads and estimate efficacy of a dust suppressant extrapolated from both lab experiments and published data for OGPW across U.S. states. Both treated and untreated OGPW, simulated brines, and commercial dust suppressants were characterized by major and trace element composition and then applied to road aggregate in the laboratory. PM10 generation after treatment was quantified, both before and after simulated rain events to assess the need for multiple applications. We found the dust suppression efficacy of all OGPW to be less than commercial products and alternative byproducts such as waste soybean oil. In addition, OGPW lost efficacy following simulated rain events, which would require repeated applications of OGPW to maintain dust suppression. The dust suppression efficacy of OGPW can be estimated based on two chemical measurements, the sodium absorption ratio (SAR) and the total dissolved solids (TDS). OGPW with the lowest SAR and highest TDS performed best as dust suppressants while high SAR and lower TDS led to greater dust generation.

Abstract:
Low-cost gravity-driven membrane (GDM) filtration has the potential to efficiently manage highly decentralized shale gas wastewater (SGW). In this work, the feasibility of combining low dosage pre-ozonation with the GDM process was evaluated in the treatment of SGW. The results showed that pre-ozonation significantly increased the stable flux (372%) of GDM filtration, while slightly deteriorating the quality of the effluent water in terms of organic content (−14%). These results were mainly attributed to the conversion of macromolecular organics to low-molecular weight fractions by pre-ozonation. Interestingly, pre-ozonation markedly increased the flux (198%) in the first month of operation also for a GDM process added with granular activated carbon (GGDM). Nevertheless, the flux of O3-GGDM systems dropped sharply around the 25th day of operation, which might be due to the rapid accumulation of pollutants in the high flux stage and the formation of a dense fouling layer. Pre-ozonation remarkably influenced the microbial community structure. And O3-GDM systems were characterized by distinct core microorganisms, which might degrade specific organics in SGW. Furthermore, O3-GDM outperformed simple GDM as a pretreatment for RO. These findings can provide valuable references for combining oxidation technologies with the GDM process in treating refractory wastewater.

Abstract:
Pressure-retarded osmosis (PRO) is a promising membrane technology for harnessing the osmotic energy of saline solutions. PRO is typically considered with seawater/river water pairings however greater energy can be recovered from hypersaline solutions including produced water (PW) from the petroleum industry. One of the major challenges facing the utilization of hypersaline PW is its high fouling propensity on membranes. In this unique experimental evaluation, real PW from different sites was pretreated to varying degrees: i) minimal, ii) intermediate, and iii) extensive. The treated effluent was subsequently used for PRO testing and fouling rates were assessed for different membrane configurations over multiple cycles. Commercial grade flat sheet (FLS) coupons and novel hollow fiber (HF) modules were compared to validate the lower fouling propensity of HF membranes in PRO application. When minimally pretreated PW (10-micron cartridge filtration (CF)) was tested in FLS mode, severe membrane fouling occurred and the PRO flux decreased by 60%. In contrast, HF modules showed <1% flux decrease under both minimal and intermediate pretreatment schemes. Extensive pretreatment (1-micron CF, dissolved air flotation (DAF), powdered activated carbon, and microfiltration) reduced FLS PRO flux decline to <1%. These results confirm that PW can be treated to suitable levels for PRO application to avoid membrane fouling. Further validation of these pretreatment methods requires long term pilot testing and techno-economic assessment.

Abstract:
Hydraulic fracturing wastewater (HFW), a byproduct of hydraulic fracturing oil extraction, contains a complex mixture of oil, aldehydes, and benzene compounds. Efficient and eco-friendly HFW treatment means are critical for the oil extraction industry, particularly in developing countries. In this study, two biological processes namely an anaerobic/anoxic/moving bed biofilm reactor (A2-MBBR) and an A2-MBBR with a microfiltration membrane (A2-MFMBBR) were established, and assessed for the real HFW treatment. Removal efficiencies of chemical oxygen demand (COD) and NH4+-N were over 92% and 95%, respectively, in both processes with a hydraulic retention time of 72 h. The majority of organic compounds in both systems identified by GC–MS were degraded in the anaerobic units. In comparison, A2-MFMBBR demonstrated higher removal efficiencies for oil, total suspended solids, and complex compounds. The average relative abundances of refractory compound degrading bacteria were 43.4% and 51.6% in the A2-MBBR and A2-MFMBBR, respectively, which was consistent with the COD and oil removal, and suggested that the MBR could maintain a high diversity of microorganisms and contribute to deep recalcitrant organics degradation. This study sheds light on the potential of using a compact biological process for the real HFW treatment.

Abstract:
Abstract The resurgence of oil and gas extraction in the Appalachian Basin has resulted in an excess of oil and gas brines in Pennsylvania, West Virginia, and Ohio. Primarily driven by unconventional development, this expansion has also impacted conventional wells and consequently, created economic pressure to develop effective and cheap disposal options. Using brine as a road treatment, directly or as a processed deicer, however, creates substantial concern that naturally occurring radioactive material in the brines can contaminate roads and road-side areas. Current decision making is based on risk exposure scenarios developed by regulatory agencies based on recreational users in rural areas and exposures to drivers during a typical commute. These scenarios are not appropriate for evaluating exposures to residential deicer users or people living near treated streets. More appropriate exposure scenarios were developed in this work and exposures predicted with these models based on laboratory measurements and literature data. Exposure scenarios currently used for regulatory assessment of brine road treatment result in predicted exposures of 0.4-0.6 mrem/year. Residential exposures predicted by the scenarios developed in this work are 4.6 mrem/year. If the maximum range of near-road soil radium concentrations observed in the region is used in this residential scenario (60 pCi/g 226 Ra, 50 pCi/g 228 Ra), residents living near these roads would be exposed to an estimated 296 mrems/year, above regulatory exposure thresholds used in nuclear facility siting assessments. These results underline the urgent need to clarify exposure risks from the use of oil and gas brines as a road treatment, particularly given the existing disparities in the distribution of road impacts across socioeconomic status.

Abstract:
As hydraulic fracturing (HF) practices keep expanding in China, a comparative understanding of biological characteristics of flowback and produced waters (FPW) and sludge in impoundments for FPW reserve will help propose appropriate treatment strategies. Therefore, in this study, the microbial communities and functions in impoundments that collected wastewaters from dozens of wells were characterized. The results showed that microbial richness and diversity were significantly increased in sludge compared with those in FPW. The vast majority of microorganisms found in FPW and sludge are organic degraders, providing the possibility of using these indigenous microorganisms to biodegrade organic compounds. Our laboratory findings first show that wastewater pretreatment using these microorganisms was effective, and organic compounds in FPW from different shale formations were removed by 35–68% within 72 h in a wide temperature range (8 – 30 ℃). Meanwhile, highly toxic compounds such as phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), and petroleum hydrocarbons were effectively eliminated in reactors. The main microorganisms, key functional genes, and putative pathways for alkanes, PAHs, and PAEs degradation were also identified.

Abstract:
Water scarcity is one of the main challenges worldwide that might propose various engineering and economic issues. Petroleum industries have encountered these issues seriously, which required pretreatment facilities before reinjecting the produced water into the production wells. To assure that the treated water has no side effect on the environment, the treatment processes would perform three times by the photo-Fenton flotation method. This paper, it is aimed to calculate the treated water, required water, and saving water for chemically enhanced oil recovery methods (CEOR), hydraulic fracturing (HF), and other service facilities for completion and drilling performances. According to the results of this study, oil-well#3 has the highest water savings among all the wells with the 89% of daily water-saving, and oil-well#4 has the highest water savings among oil wells with the 75% of daily water saving. Consequently, in Sirri oilfield, the water-saving percentage is about 82% and 72%, which indicated that it is required 18%, 28% of the total water volume for implantation of HF process and CEOR methods, respectively. The total annual required water for this oilfield is 4131 MM m3/Day.

Abstract:
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.

Abstract:
This study investigated the removal of organic compounds from shale gas fracturing flowback water (FFW) by an integrated electro-coagulation and electro-peroxone (EC-EP) process in a divided electrochemical reactor. During the EC-EP process, electricity was efficiently utilized to produce both aluminum ion (Al3+) from electrochemical oxidation of an aluminum anode in the anodic compartment and hydrogen peroxide (H2O2) from oxygen reduction at a carbon-based cathode in the cathodic compartment. The in-situ generated H2O2 then reacted with ozone (O3) sparged in the cathodic compartment to produce hydroxyl radicals (•OH) for pollutant oxidation. The results showed that by sequentially treating the selected FFW by the EC and EP process in the anodic and cathodic compartment for 30 min, respectively, the EC-EP process effectively removed ~95% of total organic carbon (TOC) from the FFW, meeting the wastewater discharge standard for TOC (≤30 mg/L) with a low specific energy consumption of 0.11–0.21 kWh/g TOC removed. In contrast, individual EC and EP process, as well as the previously investigated ECP process that combined the EC and EP process in an undivided reactor, removed only ~76%, 32%, and 80% TOC from the FFW under similar reaction conditions, and thus could not meet the wastewater discharge standard. These results demonstrate that the EC-EP process successfully integrates the merit of the EC and EP process and may thus provide a cost-effective way to remove organic compounds for FFW disposal and reuses.

Abstract:
Understanding the speciation and fate of radium during operational discharge from the offshore oil and gas industry into the marine environment is important in assessing its long term environmental impact. In the current work, 226Ra concentrations in marine sediments contaminated by produced water discharge from a site in the UK were analysed using gamma spectroscopy. Radium was present in field samples (0.1–0.3 Bq g−1) within International Atomic Energy Agency activity thresholds and was found to be primarily associated with micron sized radiobarite particles (≤2 μm). Experimental studies of synthetic/field produced water and seawater mixing under laboratory conditions showed that a significant proportion of radium (up to 97%) co-precipitated with barite confirming the radiobarite fate pathway. The results showed that produced water discharge into the marine environment results in the formation of radiobarite particles which incorporate a significant portion of radium and can be deposited in marine sediments.

Abstract:
The oilfield produced water is a major waste stream in places where shale-gas production is growing rapidly. The reuse of produced water merits consideration because this practice helps reduce freshwater demand for fracking and moderates water pollution. Knowledge about the chemistry of produced water is needed to develop sustainable treatment/reuse strategies and set standards for acceptable levels of treatment of produced water. Thus, the author performed the first comprehensive analysis of oilfield produced water collected from the Bakken shale play in the U.S. state of North Dakota that represents the nation's third-largest net increase in proven crude oil reserves. The concentrations of a total of 36 elements in 13 IUPAC groups were determined. Among them, a few metals that are critical to the economy of the United States were detected at elevated concentrations (median, mg/L): K (7,620), Mg (2780), Sr (1610), Li (69), and Mn (33). Heavy metals essential for plants and animals, including Cu, Zn, and Mn, were detected at ppm levels. Measurable concentrations of highly toxic metal ions such as Cd and Pb were not detected. Concentrations of rare earth elements and platinum group metals were below respective detection limits. The produced water samples had very high total dissolved solids (237,680 ± 73,828 mg/L) and total hardness (>31,000 mg/L as CaCO3) but an extremely low alkalinity (152.4 ± 184.9 mg/L as CaCO3); therefore, softening by lime and soda was ineffective. Softening by caustic soda removed 99.5% hardness ions (Ca and Mg) under alkaline conditions. This study provides vital insight into the chemistry and treatability of produced water containing various metals.

Abstract:
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.

Abstract:
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.

Abstract:
The large-scale extraction of unconventional resources from shale reservoirs utilizing horizontal hydraulic fracturing has significantly improved economic development in U.S. However, the increased well production has been accompanied by rising concerns about potential impact resulting from excessive freshwater usage and wastewater generation. Currently, water issues have become increasingly challenging with the development of shale reservoirs. In this paper, technical, economic, and environmental challenges encountered during energy production are reviewed with a focus on water issues due to hydraulic fracturing in the U.S. Moreover, the detailed discussion of characteristics and contaminant sources of wastewater indicates the wastewater composition is complicated and varies over time and location. Understanding these factors contributed to high contaminant levels of wastewaters is important to grow awareness of the impacts of hydraulic fracturing on water quality for both operators and the public. Furthermore, pertinent wastewater management strategies for different purposes are highlighted. Although there is no one-size-fits-all solution, understanding the advantages and limitations of different treatment methods is critical for decision-makers to develop appropriate management system. The aim behind this review is to provide a reference for selecting better and practical solutions for current wastewater issues and identifying key issues for future research.

Abstract:
This research assessed the efficacy of UV and UV advanced oxidation processes (UV/AOPs) to reduce dissolved organic carbon (DOC), total petroleum hydrocarbons (TPH), and microorganisms in hydraulic fracturing produced water. To improve water quality conditions before UV treatment with and without added hydrogen peroxide (UV/H2O2), produced water was treated with coagulation, flocculation, and sedimentation (CFS) and biologically activated carbon filtration (BACF). BACF was more effective than CFS as a pre-UV and UV/AOP treatment strategy and reduced DOC, TPH, and absorbing species by over 70% which, subsequently, resulted in the highest hydroxyl radical steady-state concentrations during UV and UV/H2O2 experiments. UV alone minimally degraded DOC, while UV/H2O2 improved DOC and TPH degradation by 9% to 36%. Interestingly, UV without added H2O2 created an in situ AOP by generating hydroxyl radicals with similar steady-state concentrations to that of UV/H2O2. UV was found to be highly effective for the inactivation of microorganisms that were cultured in produced water by reducing microbial communities dominated by Citrobacter by 4 logs after only 30 mJ/cm2. Together, these results demonstrate UV/AOP as a potential strategy to not only improve the treatment and reuse of produced water but also reduce biocide use in fracturing fluids.

Abstract:
This review focuses on recent developments in electrochemical technology (with special emphasis on electrocoagulation, electro-oxidation, and electro-Fenton) to treat petroleum industry effluents (offshore and hydraulic fracturing extraction, as well as refinery effluents). In addition, an overview is given of what these processes face to position themselves as consolidated technologies.

Abstract:
Carboxymethyl cellulose (CMC) is a polymer used in many different industrial sectors. In the oil and gas industry, CMC is often used during hydraulic fracturing (fracking) operations as a thickening agent for effective proppant delivery. Accumulations of CMC at fracture faces (known as filter cakes) can impede oil and gas recovery. Although chemical oxidizers are added to disrupt these accumulations, there is industrial interest in developing alternative, enzyme-based treatments. Little is known about CMC biodegradation under fracking conditions. Here, we enriched a methanogenic CMC-degrading culture and demonstrated its ability to enzymatically utilize CMC under the conditions that typify oil fields. Using the extracellular enzyme fraction from the culture, significant CMC viscosity reduction was observed between 50 and 80˚C, at salinities up to 20% (w/v) and at pH 5-8 compared to controls. Similar levels of viscosity reduction by extracellular enzymes were observed under oxic and anoxic conditions. This proof-of-concept study demonstrates that enzyme biotechnology holds great promise as a viable approach to treating CMC filter cakes under oilfield conditions.

Abstract:
Arsenic (As) is a toxic trace element with many sources, including hydrocarbons such as oil, natural gas, oil sands, and oil- and gas-bearing shales. Arsenic from these hydrocarbon sources can be released to the environment through human activities of hydrocarbon production, storage, transportation and use. In addition, accidental release of hydrocarbons to aquifers with naturally occurring (geogenic) As can induce mobilization of As to groundwater through biogeochemical reactions triggered by hydrocarbon biodegradation. In this paper, we review the occurrence of As in different hydrocarbons and the release of As from these sources into the environment. We also examine the occurrence of As in wastes from hydrocarbon production, including produced water and sludge. Last, we discuss the potential for As release related to waste management, including accidental or intentional releases, and recycling and reuse of these wastes.

Abstract:
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.

Abstract:
The most massive waste stream generated by conventional and unconventional hydrocarbon exploration is the produced water (PW). The costs and environmental issues associated with the management and disposal of PW, which contains high concentrations of inorganic and organic pollutants, is one of the most challenging problems faced by the oil and gas industry. Many of the current strategies for the reuse and recycling of PW are inefficient because of varying water demand and the spatial and temporal variations in the chemical composition of PW. The chemical composition of PW is controlled by a multitude of factors and can vary significantly over time. This study aims to understand different parameters and processes that control the quality of PW generated from hydrocarbon-bearing Formations by analyzing relationships between their major ion concentrations, O, H, and Sr isotopic composition. We selected PW data sets from three conventional (Trenton, Edwards, and Wilcox Formations) and four unconventional (Lance, Marcellus, Bakken, and Mesaverde Formations) oil and gas Formations with varying lithology and depositional environment. Using comparative geochemical data analysis, we determined that the geochemical signature of PW is controlled by a complex interplay of several factors, including the original source of water (connate marine vs. non-marine), migration of the basinal fluids, the nature and degree of water-mineral-hydrocarbon interactions, water recharge, and processes such as evaporation and ultrafiltration processes, and production techniques (conventional vs. unconventional). The design of efficient PW recycle and reuse strategies requires a holistic understanding of the geological and hydrological history of each Formation and an account of temporal and spatial heterogeneities.

Abstract:
Leveraging waste heat has been considered to have significant potential for promoting the economic feasibility of wastewater treatment in unconventional oil and gas (UOG) production. However, its availability near well sites has not been fully understood and other energy sources may be also feasible. In this work, we quantitatively investigate the viability of using waste heat and well-pad natural gas to power on-site wastewater treatment by membrane distillation (MD) for twenty randomly selected wells located in the Denver-Julesburg (DJ) Basin, U.S. Results show that waste heat produced from on-site electrical loads is insufficient for MD treatment of all the wastewater generated during UOG production (2.2–24.3% of thermal energy required for MD treatment). Waste heat from hydraulic fracturing, which persists only for a short timeframe, is able to meet the full or partial energy requirement during the peak period of wastewater production (17–1005% of thermal energy required for MD treatment within the first two months of production), but this scenario varies among wells and is dependent on the energy efficiency of MD. Compared to waste heat, natural gas is a more consistent energy source. The treatment capacity of MD powered by natural gas at the well pad exceeds full wastewater treatment demands for all the twenty wells, with only two wells requiring short-term wastewater storage. Our work indicates that although waste heat has the potential to reduce the electricity consumption and cost of UOG wastewater treatment, it is unlikely to supply sufficient thermal energy required by MD for long-term treatment. Natural gas can serve as an alternative or complementary energy resource. Further investigations, in particular techno-economic analyses, are needed to identify the best suitable energy source or combination for on-site UOG wastewater treatment.

Abstract:
Releases of oil and gas (OG) wastewaters can have complex effects on stream-water quality and downstream organisms, due to sediment-water interactions and groundwater/surface water exchange. Previously, elevated concentrations of sodium (Na), chloride (Cl), barium (Ba), strontium (Sr), and lithium (Li), and trace hydrocarbons were determined to be key markers of OG wastewater releases when combined with Sr and radium (Ra) isotopic compositions. Here, we assessed the persistence of an OG wastewater spill in a creek in North Dakota using a combination of geochemical measurements and modeling, hydrologic analysis, and geophysical investigations. OG wastewater comprised 0.1 to 0.3% of the stream-water compositions at downstream sites in February and June 2015, but could not be quantified in 2016 and 2017. However, OG-wastewater markers persisted in sediments and pore water for 2.5 years after the spill and up to 7.2-km downstream from the spill site. Concentrations of OG wastewater constituents were highly variable depending on the hydrologic conditions. Electromagnetic measurements indicated substantially higher electrical conductivity in groundwater seeps below the streambed 7.2 km downstream from the spill site. Geomorphic investigations revealed mobilization of sediment is an important contaminant transport process. Labile Ba, Ra, Sr, and ammonium (NH4) concentrations extracted from sediments indicated sediments are a long-term reservoir of these constituents, both in the creek and on the floodplain. Using the drivers of ecological effects identified at this intensively studied site we identified 41 watersheds across the North Dakota landscape that may be subject to similar episodic inputs from OG wastewater spills. Effects of contaminants released to the environment during OG waste management activities remain poorly understood; however, analyses of Ra and Sr isotopic compositions, as well trace inorganic and organic compound concentrations at these sites in pore-water provide insights into potentials for animal and human exposures well outside source remediation zones.

Abstract:
The Utica and Marcellus Shale Plays in the Appalachian Basin are the fourth and first largest natural gas producing plays in the United States, respectively. Hydrocarbon production generates large volumes of brine (“produced water”) that must be disposed of, treated, or reused. Though Marcellus brines have been studied extensively, there are few studies from the Utica Shale Play. This study presents new brine chemical analyses from 16 Utica Shale Play wells in Ohio and Pennsylvania. Results from Na–Cl–Br systematics and stable and radiogenic isotopes suggest that the Utica Shale Play brines are likely residual pore water concentrated beyond halite saturation during the formation of the Ordovician Beekmantown evaporative sequence. The narrow range of chemistry for the Utica Shale Play produced waters (e.g., total dissolved solids = 214–283 g/L) over both time and space implies a consistent composition for disposal and reuse planning. The amount of salt produced annually from the Utica Shale Play is equivalent to 3.4% of the annual U.S. halite production. Utica Shale Play brines have radium activities 580 times the EPA maximum contaminant level and are supersaturated with respect to barite, indicating the potential for surface and aqueous radium hazards if not properly disposed of.

Abstract:
Key technological breakthroughs, such as hydraulic fracturing (HF) and horizontal drilling, have facilitated the extraction of shale gas. The boost of the shale gas industry has changed global energy markets and led to a decline in natural gas and oil price. Endowed with massive shale gas resources, China is ambitious to develop its shale gas industry, driven by growing energy demand and critical environmental conditions. However, an increasing number of pollution problems coming along with extraction has threatened our environment with atmospheric pollution, water risk, induced seismicity, occupational health, safety, and so on. Because HF needs millions of tons of water and produces a large quantity of effluents, water management becomes one of the most threatened problems. Also, wastewater treatment has become a key factor restricting the development of China’s shale gas industry. In response, international and domestic enterprises have developed a variety of management processes, which are divided into three categories: reinjection, reuse in hydraulic fracturing, and discharge after treatment. In this paper we first summarize Chinese shale gas development, then analyze the production of shale gas wastewater through major extraction techniques. Finally, a review was conducted on current wastewater treatments utilized in China, and advice is offered for future treatment techniques.

Abstract:
Fertilizer drawn forward osmosis (FDFO) was proposed to extract fresh water from flowback and produced water (FPW) from shale gas extraction for irrigation, with fertilizer types and membrane orientations assessed. Draw solution (DS) with NH4H2PO4 displayed the best performance, while DS with (NH4)2HPO4 resulted in the most severe membrane fouling. DS with KCl and KNO3 led to substantial reverse solute fluxes. FDFO operation where the active layer of the membrane was facing the feed solution outperformed that when the active layer was facing the DS. Diluted DS and diluted FPW samples were used for irrigation of Cherry radish and Chinese cabbage. Compared to deionized water, irrigation with diluted DS (total dissolved solid (TDS) = 350 mg·L-1) promoted plant growth. In contrast, inhibited plant growth was observed when FPW with high salinity (TDS = 5000 mg·L-1) and low salinity (TDS = 1000 mg·L-1) was used for irrigation of long-term (8-week) plant cultures. Finally, upregulated genes were identified to illustrate the difference in plant growing. The results of this study provide a guide for efficient and safe use of FPW after FDFO treatment for agricultural application.

Abstract:
Wastewater discharges from cities and industries, especially megacities, and intensive livestock can be considered as main sources of pollution of our rivers and groundwater. Water pollution, therefore, constitutes a major threat to both aquatic ecosystems and human health. Here we address the influence of chemical pollution in waste- and drinking water, their associated potential toxicological effects, as well as, the available technologies for their removal. This opinion paper provides illustrative selected examples covering a broad range for both drinking water and wastewater treatment processes, for which a battery of toxicity tests is applied for their risk assessment. The examples are classified based on five hot topics: (i) Bioassays for toxicity evaluation, (ii) Toxicity of municipal wastewaters, (iii) Toxicity of pharmaceutical residues and hospital wastewaters, (iv) Toxicity of other non-urban effluent examples, and (v) Drinking water treatment processes and toxicity evaluation. 'Chemical analysis combined with batteries of bioassays covering a broad range of endpoints: cytotoxicity, endocrine disruption, genotoxicity, and other types seem to be good way to assess performance/efficiency of the water treatment processes when removing chemical contaminants.. Altogether, while recognizing that water treatment is a cornerstone for water pollution reduction, providing safe water for both human use and its return back to the aquatic environment will be undoubtedly enhanced with the use of ecotoxicity biomonitoring.

Abstract:
The increased water consumption for hydraulic fracturing and the volume of wastewater generated from shale gas and tight oil exploration are major environmental challenges associated with unconventional energy development. Recycling of the flowback and produced water for hydraulic fracturing is one of the solutions for reducing the water footprint of hydraulic fracturing and removing highly saline oil and gas wastewater. Here we investigated the implications of recycling saline wastewater for hydraulic fracturing by monitoring the natural gas production, flowback water volume, and the water quality of generated flowback water in shale gas wells from Changning gas field in Sichuan Basin, China. A comparison of two sets of shale gas wells, with six wells in each sub-group, from the same location in Changning gas field shows lower (~20%) natural gas production and higher flowback water volume (~18%) in wells that were fracked with recycled saline wastewater relative to wells that were fracked with fresh water after a year of production. Geochemical analysis suggests that hydraulic fracturing with saline wastewater increases the salinity of the wastewater and reduces the magnitude of water-shale rock interactions. In spite of the direct economic consequences in reduction in natural gas production from recycling of wastewater for hydraulic fracturing, in areas where water scarcity could become a limiting factor for future large-scale shale gas development, hydraulic fracturing with recycled flowback water can be more beneficial than utilization of limited freshwater resources, as long as the higher saline flowback water is fully recycled.

Abstract:
A linear programming (LP) model is presented to investigate optimal shale gas wastewater management strategies for Marcellus shale play in Pennsylvania (PA) focusing on membrane distillation (MD) as the treatment technology. The optimization framework established in this study incorporates (1) detailed treatment cost obtained from techno-economic assessment (TEA) of MD, (2) cost of wastewater transportation from shale gas sites to treatment or disposal facilities, and (3) cost of injection into salt water disposal (SWD) wells. The optimization model is applied to four case study areas with significant shale gas extraction: Greene and Washington counties in Southwest PA and Susquehanna and Bradford counties in Northeast PA. The results reveal that onsite treatment in combination with shale gas wastewater treatment at natural gas compressor stations (NG CS) where available waste heat can be utilized for the treatment process are the most economically advantageous management options. The optimal solution could result in over 60% benefit over direct disposal in SWD, which translates to over $16 million/year savings in the counties in Northeast PA. Furthermore, the results of sensitivity analysis indicate that transportation cost is a major contributor to the overall cost of shale gas wastewater management.

Abstract:
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.

Abstract:
This study models emissions quantities and neighboring exposure concentrations of six airborne pollutants, including PM10, PM2.5, crystalline silica, arsenic, uranium, and barium, that result from the disposal of Marcellus shale drill cuttings waste during the 2011-to-2017 period. Using these predicted exposures, this study evaluates current setback distances required in Pennsylvania from waste facilities. For potential residents living at the perimeter of the current setback distance, 274 m (900 ft), a waste disposal rate of 612.4 metric tons per day at landfills (the 99th percentile in record) does not result in exceedances of the exposure limits for any of the six investigated pollutants. However, the current setback distance can result in exceedance with respect to the 24-hr daily concentration standards for PM10 and PM2.5 established in the National Air Ambient Quality Standards (NAAQS), if daily waste disposal rate surpasses 900 metric tons per day. Dry depositions of barium-containing and uranium-containing particulate matter should not be a danger to public health based on these results. To investigate the air quality impacts of waste transportation and the potential for reductions, this paper describes an optimization of landfill locations in Pennsylvania indicating the potential benefits in reduced environmental health hazard level possible by decreasing the distance traveled by waste disposal trucks. This strategy could reduce annual emissions of PM10 and PM2.5 by a mean of 64% and reduce the expected number of annual fatal accidents by nearly half and should be considered a potential risk management goal in the long run. Therefore, policy to limit or encourage reduction of distances traveled by waste removal trucks and manage setback distances as a function of delivered waste quantities is merited. Implications This study shows the necessity of reviewing current setback distance required in Pennsylvania, which might not ensure 24-hr mean PM10 and PM2.5 levels below the values stated in National Ambient Air Quality Standards for the residents living at the perimeter. Furthermore, this study also reveals potential tremendous benefits from optimizing location of landfills accepting drill cuttings within Pennsylvania, with PM10 and PM2.5 emission, total distance traveled shrinking, and number of fatal accidents shrinking by nearly half.

Abstract:
As global exploration of shale gas reserves increases, there is a need for accurate and efficient approach to proper water management, which is one of the vital problems related to shale gas production. This study looks at the effect of using multiple or hybrid treatment technologies in maximizing hydraulic fracturing wastewater reuse, whilst ensuring sustainability of the process in terms of energy and associated cost. The study considers ultrafiltration and membrane distillation processes as possible pre-treatment and desalination technologies for flowback water management. It also considers the possibility of supplying the electrical and thermal energy requirements of these regenerators using flared gas. Two different scenarios are considered based on flowback water composition in hydraulic fracturing in terms of salinity. Application of the proposed model to a case study leads to 24.13 % reduction in the quantity of water needed for fracturing. In terms of energy requirements, the approach yields 31.6 % reduction in the required thermal energy in membrane distillation and 8.62 % in energy requirement for ultrafiltration. For flowback water with moderate total dissolved solids concentration, 93.6 % of wastewater reuse comes from pre-treated water by ultrafiltration and 6.4 % from membrane distillation. However, as the flowback water salinity becomes higher, the percentage of pre-treated reusable water reduces to 81.1 % and the percentage supply through membrane distillation increases to 18.9 %. In all cases, the results indicate that the decision to allow the pre-treated water to pass through desalination technology strictly depends on the quantity of water required by a wellpad and the salinity of the wastewater.

Abstract:
Managing produced water from oil and gas wells constitutes a significant portion of the costs of operating a well. In this work, we have designed two different centralized water treatment facilities capable of managing produced water from oil and gas wells in Texas and Louisiana, both of which convert the produced water into the following valuable resources: ten-pound brine and fresh water. The two main designs each use commercially available technology with varying levels of establishment in treating produced water. Both treatment processes remove oil and grease and suspended solids, reduce the divalent ion concentrations, and concentrate the brines to a near-saturation state. The baseline design uses chemical precipitation to remove the divalent ions to meet the reuse specifications, whereas the advanced design uses nanofiltration (NF) membranes to separate divalent ions and uses reserve osmosis (RO) membranes to partially concentrate the brine. Both models use mechanical vapor recompression to concentrate the brine up to NaCl saturation. The baseline process is shown to be cost-effective for low-hardness brines. In the case of high hardness, the chemical precipitation step is cost-prohibitive. We find that NF membranes are a promising alternative to chemical precipitation as a means of separating monovalent and divalent ions.

Abstract:
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.

Abstract:
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 BaxSr1–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 BaxSr1–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.

Abstract:
Shale gas extraction processes generate a large amount of hypersaline wastewater, whose spills or discharges may significantly increase the bromide levels in downstream water supplies and result in the formation of brominated disinfection byproducts (DBPs) upon chlorination. Although a few studies have investigated selective bromide removal from produced water, the low removal efficiencies and complex system setups are not desirable. In this study, we examined a simple cost-effective approach for selective bromide removal from produced water relying on the oxidation by un-activated peroxymonosulfate (PMS). More than 95% of bromide was removed as Br2(g) in less than 10 min under weakly acidic conditions without significant formation of Cl2(g) even when the chloride concentration was more than two orders of magnitude higher. A kinetic model considering the involved reactions was then developed to describe the process well under various reaction conditions. The organic compounds in produced water neither noticeably lowered bromide removal efficiency nor reacted with the halogen species to form halogenated byproducts. The tests in batch and continuously-stirred tank reactor systems suggested that it was feasible to achieve both high bromide removal and neutral effluent pH such that further pH adjustment was not necessary before discharge. After the treatment, the effect of the produced water on DBP formation was largely eliminated.

Abstract:
The data in this report are associated with https://doi.org/10.1016/j.scitotenv.2020.137085 and include data on water volumes and water quality related to the major unconventional oil and gas plays in the U.S.. The data include volumes of water co-produced with oil and gas production, county-level estimates of annual water use volumes by various sectors, including hydraulic fracturing water use, and the quality of produced water. The data on volumes of produced water and hydraulic fracturing water volumes were obtained from the IHS Enerdeq and FracFocus databases. Water use in other sectors were obtained from the U.S. Geological Survey water use database. Data on produced water quality were obtained from the USGS produced waters database.

Abstract:
Membrane-based desalination system under consideration for shale gas fracturing flowback wastewater treatment involves ultrafiltration (UF), reverse osmosis (RO) and storage tanks. The membrane unit (UF, RO) consists of online washing, operation and offline chemical washing sub-units. These sub-units operate in semi-continuous mode and have the similar characteristics as batch water-using processes. Based on their semi-continuous behaviors, the models of UF and RO sub-units are developed. The objective is to maximize the total water production ratio and profit while minimize storage tank capacity. Three nonlinear programming optimization models are developed for optimal design of UF-RO treatment system for shale gas fracturing flowback wastewater. Two scenarios – fixed schedule and fixed operating period for UF/RO treatment sub-units are investigated. Results show that with the increasing the operation duration of treatment sub-units, the water production ratio and profit will increase. The schedule of treatment sub-units has significant impact on the water-storage profiles, without adversely affecting the water production ratio. The proposed approach can guide the design of UF-RO desalination system.

Abstract:
Unconventional shale gas exploitation presents complex problems in terms of radioactive waste disposal. Large volumes of saline produced water resulting from hydraulic fracturing are typically enriched in radium isotopes, up to several hundred Bq/dm3, orders of magnitude above national discharge limits. There is a need, therefore, to decontaminate the fluid prior to discharge, preferably by creating a less problematic radium-containing, solid waste form. Barite (barium sulphate) co-precipitation is a cost-effective method for achieving these objectives, provided the process can be controlled. In this work, radium recovery of ~90% has been achieved for simulant produced waters containing 100 Bq/dm3, using a single, optimised co-precipitation step. However, salinity has a significant effect on the efficiency of the process; higher salinity solutions requiring substantially more reagent to achieve the same recovery. If >90% radium removal is sought, multiple co-precipitation steps provide a much faster alternative than post-precipitation recrystallization of the barite solid phase, albeit at higher cost. The resulting solid waste has a relatively high specific radium activity but a much smaller volume, which presents a less intractable disposal problem for site operators than large volumes of radium-contaminated fluid.