Flowback Wastewater Research Articles

Long-term and efficient treatment of shale gas flowback wastewater by the novel double SEP@Fe-Mn/RGO composite membranes method

The long-term and efficient treatment of shale gas wastewater is an inevitable tendency. This study employed the SEP@Fe-Mn/RGO composite membrane series for the membrane separation treatment of shale gas wastewater. Different proportions and different function of SEP@Fe-Mn/RGO composite membranes were obtained through the method of electrostatic self-assembly. This study researched the “Trade-off” issue of membranes separation through the analysis，resulting in membranes that best meets the separation requirements for shale gas wastewater. After two membrane separation, The oil-water separation efficiency (COD 2040 mg/L and TOC 487.14 mg/L) of shale gas wastewater was >99.3 %. The removal rate of the main salt component (Na2SO4) reached 83.56 %, and the removal rate of major heavy metal ions (Fe3+, Cr3+, Ba2+) was above 60 %. Because of the continuous generation of in-situ bubbles by the reaction of MnO2 with H2O2, and Fenton reactions on the membrane, which further accelerated the separation of pollutants. In a variety of harsh water environments, this membrane series remained stable within 12 h. Simple to prepare, cost-effective, low in energy consumption, and environmentally friendly, which makes it promising for wide applications in the field of petroleum water treatment.

Molecular comparison of organic matter removal from shale gas flowback wastewater: Ozonation versus Fenton process

Shale gas extraction process generates a large amount of shale gas flowback wastewater (SGFW) containing refractory organic compounds, which can pose serious environmental threats if not properly treated. However, the extremely complex compositions of organics in SGFW are still unknown and their transformation pathways in O3- and •OH-dominated systems are not well recognized, which restrain the selection of treatment technology and optimization of operational parameters. The removal characteristics and reaction mechanism of dissolved organic matter (DOM) in SGFW treated by ozonation and Fenton processes were comparatively investigated using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The results showed that both processes could degrade low-oxygen highly unsaturated and phenolic organics, polyphenolics and polycyclic aromatics, and transform them into aliphatic organics and high-oxygen highly unsaturated and phenolic organics. With increasing action of reactive oxygen species (O3 for ozonation and •OH for Fenton process), the degradation products (mainly aliphatic organics) increased during ozonation. However, in Fenton process, a wider range of DOM was removed without aliphatic organics accumulation. The degradation mechanisms of DOM during ozonation and Fenton processes included oxygen addition reactions (+3O, +H2O2, and +2O) as dominant pathways. However, ozonation showed more violent oxygenation, hydroxylation, and carboxylation, while Fenton process presented more violent chain-breaking reactions. These results revealed the selective oxidation of ozone and nonselective oxidation of •OH during SGFW treatment, and provided theoretical support for selecting SGFW treatment approaches.

Heterogeneous Fenton treatment of shale gas fracturing flow-back wastewater by spherical Fe/Al2O3 catalyst.

In this work, efficient Fenton strategy have been proposed for degradation of shale gas fracturing flow-back wastewater using the spherical Fe/Al2O3 supported catalyst. Prior to actual fracturing fluid treatment, the typical model wastewaters such as p-nitrophenol and polyacrylamide were employed to evaluate the catalytic properties of prepared catalyst, and then Fenton treatment of the shale gas fracturing flow-back wastewater was performed on the self-assembled catalytic degradation reactor for continuous flow purification. Results showed that under the conditions of 0.25 mol L-1 impregnating concentration, pH 4, 50 g L-1 catalyst and 0.75 mL L-1 30% H2O2, the removal efficiency of p-nitrophenol and polyacrylamide reached 74% and 61%, respectively, while the COD removal of fracturing flow-back fluid was approximately 48% with the residual 88 mg L-1 COD, meeting the emission standards of the integrated wastewater discharge standard (GB 8978-1996, COD < 100 mg L-1). This work offers new alternatives for Fenton treatment of real wastewater by efficient and low-cost supported catalysts.

The influence of salinity on the chronic toxicity of shale gas flowback wastewater to freshwater organisms

The potential environmental risk associated with flowback waters generated during hydraulic fracturing of target shale gas formations needs to be assessed to enable management decisions and actions that prevent adverse impacts on aquatic ecosystems. Using direct toxicity assessment (DTA), we determined that the shale gas flowback wastewater (FWW) from two exploration wells (Tanumbirini-1 and Kyalla 117 N2) in the Beetaloo Sub-basin, Northern Territory, Australia were chronically toxic to eight freshwater biota. Salinity in the respective FWWs contributed 16% and 55% of the chronic toxicity at the 50% effect level. The remaining toxicity was attributed to unidentified chemicals and interactive effects from the mixture of identified organics, inorganics and radionuclides. The most sensitive chronic endpoints were the snail (Physa acuta) embryo development (0.08–1.1% EC10), microalga (Chlorella sp. 12) growth rate inhibition (0.23–3.7% EC10) and water flea (Ceriodaphnia cf. dubia) reproduction (0.38–4.9% EC10). No effect and 10% effect concentrations from the DTA were used in a species sensitivity distribution to derive “safe” dilutions of 1 in 300 and 1 in 1140 for the two FWWs. These dilutions would provide site-specific long-term protection to 95% of aquatic biota in the unlikely event of an accidental spill or seepage.

Integration of coagulation and ozonation with flat-sheet ceramic membrane filtration for shale gas hydraulic fracturing wastewater treatment: A laboratory study.

The performance of the integrated process of coagulation and ozonation with ceramic membrane filtration was evaluated for the treatment of shale gas hydraulic fracturing flowback wastewater (HFFW). The removal efficiencies of carbon oxygen demand (CODCr ), dissolved organic carbon (DOC), petroleum oils, and turbidity in effluent by the combined process were 87.1%, 72.2%, 94.3%, and 99.6%, respectively. Compared with sole membrane filtration, the transmembrane pressure (TMP) of ceramic membrane filtration was reduced by >99% with the integrated process. The coagulation and ozonation can effectively remove the organics with high molecular weights in the cake layer of ceramic membrane. To the best of our knowledge, this work proposed the combined process of coagulation, ozonation, and flat-sheet ceramic membrane filtration for the treatment of HFFW for the first time. The water quality of the effluent met the discharge standard (Comprehensive Wastewater Discharge Standard GB8978-1996). The findings can provide an important technical foundation for the innovation of integrated equipment for HFFW treatment. PRACTITIONER POINTS: An integrated process combining coagulation and ozonation with flat-sheet ceramic membrane ultrafiltration for the treatment of shale gas wastewater. The water quality of this integrated process met the discharge standard. Coagulation and ozonation effectively alleviated the membrane fouling related to organics with high molecular weights. A new avenue for on-site treatment of shale gas wastewater and an alternative of the current centralized wastewater management.

Heterogeneous electro-Fenton catalysis with self-supporting CFP@MnO2-Fe3O4/C cathode for shale gas fracturing flowback wastewater

Self-supporting electrodes have triggered great interests in improving electro-Fenton (EF) system for degradation of refractory organic pollutants. In this work, a novel self-supporting carbon fiber paper (CFP) electrode modified by transition metals, e.g. Fe and Mn, was fabricated and employed as a heterogeneous EF cathode. The prepared electrode exhibited excellent degradation for a number of typical organic pollutants along with superior stability. Remarkably, a high removal efficiency was achieved in the EF treatment of shale gas fracturing flowback wastewater. Results indicated that 65.2% TOC and 74.8% COD were eliminated after 4 h degradation. The residual COD value of the real wastewater was 80 mg L−1, meeting the emission requirement of the integrated wastewater discharge standard (COD＜100 mg L−1) with a low specific energy consumption of 6.9kWhkg−1COD−1. This work demonstrates a competing alternative for efficient decontamination of real wastewater using an electro-Fenton strategy with a low-cost electrode.

BiVO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;/MnO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Composite Photocatalytic Material for the Shale Gas Flowback Wastewater Treatment

The management and disposal of the shale gas flowback wastewater is one of the greatest challenges associated with the exploration and extraction of unconventional natural gas resources. High salinity and complex chemical composition of fracturing fluids are the main limiting factors for beneficial reuse of the shale gas flowback wastewater, which has become a tough problem in the global environmental field. In this study, a composite photocatalytic oxidant of MnO2 modified BiVO4 was successfully synthesized with one-step hydrothermal method, and used to treat the shale gas flowback wastewater. The synergistic effect of photocatalysis and oxidation has made a great contribution to the removal of COD value in wastewater. When catalyst dosage was 0.6 g, the pH value was controlled to 3, and visible light exposure was 4 h, the prepared BiVO4/MnO2 exhibited the optimum photocatalytic oxidation activity, and the removal efficiency of COD could reach 65.5%, which is better than that of pure BiVO4 or MnO2. Furthermore, in this case, the COD value could be decreased from 188 mg/L to 64.9 mg/L, complying with the first-level standard limit requirements in the integrated wastewater discharge standard (GB8978-1996). Moreover, in the viewpoint of dynamics, Langmuir isothermal-like equation can better describe the relationship between COD removal efficiency and illumination time.

Biosurfactant-facilitated biodegradation of hydrophobic organic compounds in hydraulic fracturing flowback wastewater: A dose–effect analysis

Abstract This work investigated the effects of biosurfactant at varied dose on the bioremediation of hydraulic fracturing flowback wastewater (HFFW) and explored the associated mechanism. Initially, a biosurfactant-producing strain Pseudomonas sp. CH1 was isolated from oily sludge. The glycolipid biosurfactant produced by CH1 have a critical micelle concentration (CMC) of 80 mg/L, and showed high stability over a wide range of temperature (0–120 °C), pH (4–12), and salinity (0%–16%, w/v). Addition of sub-CMC dose of biosurfactant to HFFW greatly enhanced the microbial growth and activity, upregulated the expression levels of degradation-related genes, and effectively promoted the biodegradation of n-alkanes (reduction from 272.21 to 56.93 mg/L) and PAHs (reduction from 61.6 to 16.36 μ g/L) in 7 days. The results suggested the feasibility of applying biosurfactant with sub-CMC dose to remediate HFFW and contribute significantly to the optimization of surfactant-facilitated bioremediation strategies.

Optimal Design of a UF-RO Treatment System for Shale Gas Fracturing Flowback Wastewater

A 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 minimizing storage tank capacity. Three nonlinear programming optimization models are developed for an optimal design of the 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 of 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 the UF-RO desalination system.

The roles of suspended solids in persulfate/Fe2+ treatment of hydraulic fracturing wastewater: Synergistic interplay of inherent wastewater components

The high content and low removal efficiency of suspended solids (SS) in wastewater derived from shale gas development via hydraulic fracturing has raised advanced treatment problems (e.g., organics removal) and environmental concerns. In this study, two kinds of suspended solids were separated from synthetic flowback wastewater (FWW) after 1 or 14 days of sedimentation. The physicochemical properties, porous structures, surface chemistry, and particle stability of the obtained 1-/14-day solids were characterized. To illustrate the specific roles of SS during radical-based FWW treatment, the removal of di-(2-ethylhexyl) phthalate (DEHP, a typical recalcitrant organic that has been identified in FWW) by a ferrous iron/peroxysulphate (Fe2+/PS) system was examined as a representative case. Results showed that DEHP was simultaneously adsorbed onto the solids and degraded by Fe2+/PS. The removal processes were governed by the phase distribution of DEHP and Fe2+, and the distribution was influenced by interactions between the 1-/14-day solids, Fe2+/PS, and various FWW components. Polyacrylamide (PAM), an anionic surfactant commonly detected in FWW, can attach to the solids and aid in maintaining the structural and compositional integrity of the solids. Due to stronger adsorption with PAM, the 14-day solids retained less DEHP and Fe2+, contributing to enhanced DEHP degradation in the solution phase as compared to the 1-day solids. Thus, sufficient sedimentation is advantageous for the degradation of recalcitrant organic contaminants (e.g., DEHP) in FWW treatment. Moreover, certain FWW components (i.e., PAM and ethylene glycol) can interact with FWW solids, creating a positive synergistic effect on organic removal efficiency.

Comparative study using ion exchange resins to separate and reduce NORM from oil and gas flowback wastewater

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

Simultaneous Energy and Water Optimisation in Shale Exploration

This work presents a mathematical model for the simultaneous optimisation of water and energy usage in hydraulic fracturing using a continuous time scheduling formulation. The recycling/reuse of fracturing water is achieved through the purification of flowback wastewater using thermally driven membrane distillation (MD). A detailed design model for this technology is incorporated within the water network superstructure in order to allow for the simultaneous optimisation of water, operation, capital cost, and energy used. The study also examines the feasibility of utilising the co-produced gas that is traditionally flared as a potential source of energy for MD. The application of the model results in a 22.42% reduction in freshwater consumption and 23.24% savings in the total cost of freshwater. The membrane thermal energy consumption is in the order of 244 × 103 kJ/m3 of water, which is found to be less than the range of thermal consumption values reported for membrane distillation in the literature. Although the obtained results are not generally applicable to all shale gas plays, the proposed framework and supporting models aid in understanding the potential impact of using scheduling and optimisation techniques to address flowback wastewater management.

Formation of Particulate Matter from the Oxidation of Evaporated Hydraulic Fracturing Wastewater

The use of hydraulic fracturing for production of petroleum and natural gas has increased dramatically in the past decade, but the environmental impacts of this technology remain unclear. Experiments were conducted to quantify airborne emissions from 12 samples of hydraulic fracturing flowback wastewater collected in the Permian Basin, as well as the photochemical processing of these emissions leading to the formation of particulate matter (PM). The concentration of total volatile carbon (hydrocarbons evaporating at room temperature) averaged 29 mg of carbon per liter. After photochemical oxidation under high NO x conditions, the amount of organic PM formed per milliliter of wastewater evaporated averaged 24 μg; the amount of ammonium nitrate formed averaged 262 μg. Based on the mean PM formation observed in these experiments, the estimated formation of PM from evaporated flowback wastewater in the state of Texas is in the range of estimated PM emissions from diesel engines used in oil rigs. Evaporation of flowback wastewater, a hitherto unrecognized source of secondary pollutants, could significantly contribute to ambient PM concentrations.

Hybrid membrane bio-systems for sustainable treatment of oil and gas produced water and fracturing flowback water

Abstract Development of unconventional oil and gas (O&G) resources through hydraulic fracturing has surged in recent years. While declines in oil prices have temporarily reduced spending towards research and development of innovative water management techniques, regulations and expected increase in freshwater demand and cost are intensifying competition among treatment providers to develop sustainable and efficient strategies for wastewater treatment and reuse. In this study, biologically active filtration, ultrafiltration, and nanofiltration were tested for the treatment of O&G produced water (PW) and fracturing flowback wastewater. Results indicate that with seeding of microorganisms naturally present in PW, a resilient biofilm can develop that effectively removes organic matter from O&G waste streams. This serves as a pretreatment step for subsequent membrane desalination, mitigating membrane fouling. With thorough pretreatment, more than 99% of organic constituents and more than 94% of total dissolved solids can be removed, producing high quality permeate suitable for advanced reuse applications.

Optimal reuse of flowback wastewater in hydraulic fracturing including seasonal and environmental constraints

This article presents a mathematical programing formulation for the optimal management of flowback water in shale gas wells. The formulation accounts for the time‐based generation of the flowback water, the options for treatment, storage, reuse, and disposal. The economic and environmental objectives are considered. The economic objective function is aimed at determining the minimum cost for the fresh water, treatment, storage, disposals, and transportation. The environmental objectives account for the fresh water usage and wastewater discharge. To carry out the water integration, a reuse network including treatment is proposed. Additionally, the model considers seasonal fluctuations in the fresh water availability. A given scheduling for the completion phases of the wells is required to implement the methodology. Finally, an example problem is presented to show the applicability of the proposed methodology. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1634–1645, 2016

Simplifying Treatment for Complex Waste Streams: Oil and Gas Produced Water and Fracturing Flowback Wastewater

Simplifying Treatment for Complex Waste Streams: Oil and Gas Produced Water and Fracturing Flowback Wastewater

Optimal Design of Thermal Membrane Distillation Systems for the Treatment of Shale Gas Flowback Water

Shale gas production is associated with the significant consumption of fresh water and discharge of wastewater. The flowback wastewater is tied to the hydraulic fracturing technology used for completing and stimulating the horizontal wells in the very tight formations characterizing the shale formation. Treatment and reuse of these large volumes of wastewater can lead to substantial savings in fresh water usage and reduction of the negative environmental impact thereby enhancing sustainability of the shale gas industry. Such treatment requires selective and cost-effective technology.Thermal membrane distillation (TMD) is an emerging technology that offers several advatanges such as high selectivity in separating water from inorganic solutes and modular nature that can accommodate a wide range of flows. It can also utilize low-level heats that are typically available from shale-gas production and processing.The objective of this work is to develop an optimization approach for the design of TMD systems to treat flowback water. A multi-period formulation is developed to account for the time-based variation in the flowrate and concentration of the flowback water. Modeling equations are used to relate design and operating variables to performance and cost. The optimization formulation also accounts for the period-based changes in the required design and operating variables and reconciles them over the selected periods. Other constraints include quality of the permeate and water-recovery ratio. The optimization formulation and design approach are applied to a case study for the treatment of flowback water for the Marcellus Shale Play. For 75% water recovery, the cost of the permeate is about $2.6/m3. As higher recoveries are sought, the cost per m3 of permeate increases due to capital productivity factors in dealing with the decreasing amount of flowback water over time. The results are reported using a Pareto chart that trades off recovery objectives with cost of treated water.

Matrix Complications in the Determination of Radium Levels in Hydraulic Fracturing Flowback Water from Marcellus Shale

The rapid proliferation of horizontal drilling and hydraulic fracturing for natural gas mining has raised concerns about the potential for adverse environmental impacts. One specific concern is the radioactivity content of associated “flowback” wastewater (FBW), which is enhanced with respect to naturally occurring radium (Ra) isotopes. Thus, development and validation of effective methods for analysis of Ra in FBW are critical to appropriate regulatory and safety decision making. Recent government documents have suggested the use of EPA method 903.0 for isotopic Ra determinations. This method has been used effectively to determine Ra levels in drinking water for decades. However, analysis of FBW by this method is questionable because of the remarkably high ionic strength and dissolved solid content observed, particularly in FBW from the Marcellus Shale region. These observations led us to investigate the utility of several common Ra analysis methods using a representative Marcellus Shale FBW sample. Methods examined included wet chemical approaches, such as EPA method 903.0, manganese dioxide (MnO2) preconcentration, and 3M Empore RAD radium disks, and direct measurement techniques such as radon (Rn) emanation and high-purity germanium (HPGe) gamma spectroscopy. Nondestructive HPGe and emanation techniques were effective in determining Ra levels, while wet chemical techniques recovered as little as 1% of 226Ra in the FBW sample studied. Our results question the reliability of wet chemical techniques for the determination of Ra content in Marcellus Shale FBW (because of the remarkably high ionic strength) and suggest that nondestructive approaches are most appropriate for these analyses. For FBW samples with a very high Ra content, large dilutions may allow the use of wet chemical techniques, but detection limit objectives must be considered.

Total arsenic and selenium analysis in Marcellus shale, high-salinity water, and hydrofracture flowback wastewater

Trace levels of arsenic and selenium can be toxic to living organisms yet their quantitation in high ionic strength or high salinity aqueous media is difficult due to the matrix interferences which can either suppress or enhance the analyte signal. A modified thiol cotton fiber (TCF) method employing lower flow rates and centrifugation has been used to remove the analyte from complex aqueous media and minimize the matrix interferences. This method has been tested using a USGS (SGR-1b) certified reference shale. It has been used to analyze Marcellus shale samples following microwave digestion as well as spiked samples of high salinity water (HSW) and flow back wastewater (WRF6) obtained from an actual gas well drilling operation. Quantitation of arsenic and selenium is carried out by graphite furnace atomic spectroscopy (GFAAS). Extraction of arsenic and selenium from Marcellus shale exposed to HSW and WRF6 for varying lengths of time is also reported.