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The treatment and disposal of hypersaline produced water remains a challenge, particularly for oil and gas producers in the Permian basin where production wells generate significant amounts of wastewater, and the traditional method of injecting wastewater into disposal wells is coming under increasing scrutiny. Here we investigate the viability of using solar energy to power a multi-stage, surface heated, vacuum membrane distillation (SHVMD) with energy recovery to treat hypersaline produced wastewater from Midland, Texas. Membrane distillation is a process that can desalinate waters with high total dissolved solids concentration, and when incorporated into a system with surface heating and energy recovery can achieve high water recovery rates. Model results show that a 6-stage SHVMD system with a 54.4 % water recovery rate and a gained output ratio (GOR) of 3.28 has the potential to be economically viable when used to treat hypersaline produced water in the Permian basin. Assuming energy costs of $0.03/kWh thermal and $0.12kWh electric , we estimate a project net present value (NPV) of $225,525 and an internal rate of return (IRR) of 13.5 % when an air cooled condensor is used to cool the distillate and a NPV of $570,791 and IRR of 24.52 % when a liquid coooling source is available. This work presents a comprehensive economic assessment of utilizing a surface-heated membrane distillation system with heat recovery to treat hypersaline produced well water. • An economic analysis of surface-heated membrane distillation process for the treatment of hypersaline brine was performed • Under certain conditions, the process is economically viable compared to deep-well injection • Process economics are sensitive to the availability of liquid cooling, sunlight, and the cost of solar-thermal energy [ABSTRACT FROM AUTHOR]

Produced water from unconventional oil and gas reservoirs often contains non-ionic surfactants that are added to the hydraulic fracturing fluid to facilitate water release and enhance gas production. This study investigates the impact of currently used surfactants (i.e., nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs)) and proposed alternative surfactants on the performance of membrane distillation (MD) for produced water treatment. The impact of NPEOs and OPEOs on wetting of PTFE membranes was studied as a function of their concentrations and ethoxylate (EO) chain length in a lab-scale DCMD system. Additionally, alternative surfactants, including linear alcohol ethoxylates (LAEs), branched secondary alcohol ethoxylates (BAEs), and alkyl polyglycosides (APGs), were evaluated for their potential to replace NPEOs and OPEOs. Experimental results indicate that the increase in the number of EO units in NPEOs decreased their tendency to cause membrane wetting by reducing their interaction with hydrophobic surfaces. It was also observed that LAEs and APGs that are environmentally friendly alternatives did not cause membrane wetting. This study provides valuable insights into the underlying mechanisms of surfactant-membrane interactions and offers guidelines for surfactant alternatives that can potentially improve hydraulic fracturing and lower environmental concerns while facilitating the use of MD for produced water treatment and recovery. • Studied legacy and alternative hydraulic fracturing non-ionic surfactants with MD • Wetting tendency decreases with EO chain length in nonylphenol ethoxylates. • LAEs and APGs are environmentally friendly alternatives that prevent membrane wetting. • Contact angle and LEP were found to be the primary indicators of the wetting behavior. [ABSTRACT FROM AUTHOR]

Increasing disposal costs and environmental concerns have encouraged desalination projects in the Permian basin to cut down produced water (PW) volumes and improve the handling. This study aims to demonstrate performance of membrane-distillation (MD) for desalinating high-salinity PW. Prior to MD, electrocoagulation (EC) and microfiltration (MF) are used as primary and secondary pretreatments, respectively. These pretreatment steps are necessary to remove constituents such as suspended solids, oil, and grease. The integrated EC-MF process was followed by vacuum MD (VMD) to recover water and concentrate the brine stream. To improve latent heat recovery, vapor compression is integrated into the vacuum membrane distillation (VMD). Our EC-MF-VMD PW treatment process can treat 1000 L of PW per day, with water recoveries in the range of 30–70 %. Suspended solids and turbidity removal of 90 % and total organic carbon (TOC) removal of 60 % were achieved with EC-MF pretreatments, which effectively mitigated PW fouling potential. A custom-designed plate-and-frame VMD module was established which enabled unparalleled service flexibility to change membrane replacement and active area. Results from our systematic evaluation revealed that the flux of the commercial membranes in our VMD module varied from 5 to 66 Lm−2 h−1. The intensified VMD performance achieved by vapor compression led to remarkable improvement in energy efficiency in terms of gained output ratio (GOR = 2.7) and energy consumption per unit of water production (248 kWh m−3). This study demonstrates the capability of the MD process for PW treatment, revealing the reasonable potential for PW reuse and recycling. Although this process might be of interest for unique applications that justifies the cost, further improvements in energy consumption are required to make this technology feasible for commercialized desalination of oilfield produced waters. • MD prototype demonstrated for treating hypersaline produced water. • Hybridizing EC and MF resulted in superior pretreatment performance. • Custom-designed plate-and-frame MD module exhibited fluxes up to 66 Lm−2 h−1. • Long-term operation demonstrated excellent water recovery and GOR > 2.7. [ABSTRACT FROM AUTHOR]

Proper management and treatment of produced water has emerged as a big challenge for oil and gas industry. Increasingly stringent environmental regulations and economic constraints are compelling the use of more advanced treatment methods. Membrane operations are gaining significant interest for this application due to their broad range of separation capabilities, high efficiency and low operational cost. Commercially less-adopted membrane operations, such as membrane distillation (MD) and membrane crystallization (MCr) are gaining significant interest for produced water treatment due to their almost concentration-independent performance and less fouling potential. The current study analyzes the performance of an integrated microfiltration (MF) and direct contact membrane distillation (DCMD)/membrane crystallization (MCr) system for freshwater and minerals recovery from produced water. Based on the experimental data, thermodynamic/exergetic/quantitative analyses have been performed. Performance of the integrated processes has been compared with the conventional multi-stage flash (MSF) in terms of process intensification metrics . [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a promising technique for desalinating hypersaline brine, such as produced water (PW). To date, fouling and scaling have remained as major challenges for MD implementation. In this study, chlorine dioxide combined with induced air floatation (ClO 2 -IAF) was systematically investigated as a pretreatment prior to MD. First, the ClO 2 generation based on sodium chlorite and hydrochloric acid was optimized to maximize the on-demand ClO 2 production. The maximum production yield of 18.4% was obtained with 4 wt.% NaClO 2 and 20 wt.% HCl solutions, with a molar ratio of 1:1.25. Then, two real PW samples were pretreated, and removal efficiencies for total suspended solids (TSS), turbidity, iron, and total organic carbon (TOC) were comprehensively studied by varying the ClO 2 dosage between 6 and 91 mg/L. The ClO 2 -IAF pretreatment displayed TSS and turbidity removals above 90% and TOC removal close to 55%. The PW constituents such as benzene, toluene, ethylbenzene, xylene (BTEX), and total petroleum hydrocarbons (TPH) were analyzed and quantified throughout the cascade of the treatments. The volatiles like BTEX were mainly removed by air floatation, while saturated hydrocarbons such as TPH were retained by the hydrophobic membrane. The MD long-term stability without any in-place cleaning was evaluated, and the membrane withstood for twenty two days without wetting, suggesting that optimizing oxidation pretreatment is critical for mitigating the fouling in MD. Results suggest that organic fouling in PW could be effectively reduced by the pretreatment, but further treatment is required to mitigate the scaling, which resulted in MD wetting. • Evaluated chlorine dioxide pretreatment for the treatment of real produced water • Pretreated produced water was desalinated using membrane distillation. • With optimal oxidant dosage, long-term MD continued for extended period. • Studied organics removal efficiency through the cascade of treatments [ABSTRACT FROM AUTHOR]

Unconventional oil and gas production raises concerns regarding sustainable management of high salinity wastewaters generated in this process. Membrane distillation (MD) is a thermal desalination process capable of treating hypersaline brines such as produced water. The low single pass recovery in MD systems operated in a single stage requires a large recycle stream to achieve the desired recovery, resulting in high energy consumption and operating cost. Multistage configurations in continuous recirculation operation mode offer the potential to reduce the energy intensity of MD systems. However, rigorous analysis is needed to assess the performance of MD configurations when operating in multi-stage mode. We present an optimization-based comparison of economic and energetic performance for five configurations of MD (including DCMD, AGMD, PGMD, CGMD, and VMD) operating in multi-stage continuous recirculation mode. Our findings demonstrate that multistage operation reduces the treatment cost and energy intensity of all MD configurations compared to single stage MD, with the greatest benefit for VMD and PGMD. AGMD with five stages outperforms other configurations with 3.58 $/m3 feed treatment cost, followed by VMD, CGMD, DCMD, and PGMD with 3.8, 4.2, 5.4, and 9.06 $/m3 feed treatment costs corresponding to twelve, eight, eight, and sixteen stages, respectively. • Developed an optimization framework for comparing five multistage MD configurations. • Continuous recirculation mode is analyzed for produced water treatment. • Treatment cost and energy intensity are compared for the five MD configurations. • Multistage MD offers energy and economic benefits over single stage MD. • AGMD outperforms all other configurations with lowest treatment cost. [ABSTRACT FROM AUTHOR]

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 SrSO 4 , 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. • Laboratory-scale DCMD studies confirmed feasibility of produced water treatment\ • Demonstrated steady-state AGMD 0.8 gpm pilot-scale operation for 120 h • Achieved 50% water recovery with 99.7% ion rejection with real produced water • Pretreatment of produced water to remove iron and sulfate may be required. • Precipitation of Ba and Ca in the system did not affect AGMD performance. [ABSTRACT FROM AUTHOR]

A superomniphobic polyvinylidene fluoride (PVDF-F) membrane was fabricated through electronspinning to obtain an excellent antiwetting and antifouling property for the effective and efficient treatment of real produced water. Compared with pristine PVDF and hydroxyl functionalized PVDF (PVDF-O) membrane, PVDF-F membrane had a larger pore diameter, while its pure water flux was found to be lower than both. Neither liquids with high surface tension (water, ethanol) or low surface tension (sodium dodecyl sulfate (SDS) as surfactant, mineral oil) could wet the PVDF-F surface even up to 3 min of contact. During membrane distillation (MD) of 3.5 wt% of aquoues NaCl solution, PVDF-F could withstand 0.4 mM SDS solution without any wetting as seen from the conductivity of the permeate, which was not the case for the PVDF and PVDF-O membranes. After 18 h of MD operation using produced water, a significantly thick fouling layer was found on the PVDF and PVDF-O membranes containing Ca 3 (PO4) 2 , Sr 3 (PO 4) 2 and Mg 3 (PO 4) 2. However, PVDF-F had a very thin and reversible organic fouled layer, causing only 40% reduction in permeate flux and with a low permeate conductivity of 20 μS cm−1. This layer was easily removed by cleaning using distilled water and 80% of the flux was recovered. On the 2nd and 3rd MD cycle, the reduction in permeate flux was within 10%. The superomniphobic PVDF-F nanofibrous membrane was run for three successful consecutive MD cycles during produced water processing without any significant fouling as well as wetting. • Modified nanofibrous membrane was fabricated through chemical vapor deposition. • Superhydrophobic and superoleophobic surface was developed for MD. • The modified membrane had an excellent antiwetting and antifouling property. • High salinity produced water from hydraulic fracturing process was treated. • The modified membrane exhibited high separation efficiency with good regeneration. [ABSTRACT FROM AUTHOR]

The harmful effects arisen from the discharge of saline wastewater have become more evident in recent years and therefore drawn much public concerns. Saline wastewater, including produced water, tannery wastewater, textile wastewater and aquaculture wastewater, contains various organic pollutants and inorganic dissolved ions. These saline wastewaters can be treated, not only to meet the discharge standard but also to offer the opportunities for water reuse and nutrient recovery. Membrane technology is a promising technology that offers attractive solutions for effective saline wastewater treatment and resource recovery. With the tremendous development made in this realm, this review is set to provide a frame of state-of-the-art approaches for saline wastewater treatment based on membrane technology and stimulate ideas to enhance the treatment efficiency and sustainability in these related works. The unique features, strengths and limitations of pressure-driven, osmotically-driven, thermally-driven and electrically-driven membrane processes in treating saline wastewater and resource recovery are discussed. This review aims to consolidate the literature related to membrane technology as a versatile tool for saline wastewater treatment, as well as to identify the current research gaps and areas of improvement related to this field. • Various membrane-based separation processes for saline wastewater treatment and resource recovery are discussed. • Pressure-driven membrane processes are reliable and effective for saline wastewater treatment and recovery. • Forward osmosis, membrane distillation and electrodialysis are feasible alternatives. • Integrations among membrane processes or with conventional treatment processes provide more holistic solutions. • The current research gaps and the future directions are highlighted. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) has shown strong promise for treating hypersaline produced water (PW) streams. Scaling and fouling on the membrane surface, however, have been identified as major challenges for commercialization and widespread application. The focus of this study was to first identify the nature of foulants and scalants on the membrane surface and then investigate the pretreatment strategies that mitigate the extent of fouling and scaling on the membrane surface. Vacuum MD (VMD) was selected for this study because of its higher flux at more moderate feed temperatures that eventually leads better assessment of fouling and scaling on the membrane surface. VMD flux tests were carried out with three different real PW samples at total dissolved solids concentrations in the range of 120–160 g/L. It was found that an efficient pretreatment prior to MD is required to mitigate the fouling potential of the organic matter, mostly suspended constituents, in PW samples. Suspended organics fouled and quickly wetted the MD membrane. Major conventional treatments, including filtration, oxidation, coagulation, air floatation, and aeration were investigated to pretreat the PW before VMD tests. A comprehensive comparative analysis is presented showing that the ultrafiltration and coagulation pretreatments displayed the best performance in mitigating the fouling and scaling, while oxidative pretreatment was found to be effective in reducing the iron concentration to less than 5 ppm. The surface of scaled membranes was carefully characterized to further evaluate the performance of each pretreatment. The components that had the highest tendency to precipitate on the membrane surface were identified as strontium sulfate, calcium carbonate, sodium chloride, iron oxide, and silica. These findings are supported by thermodynamic estimation of the saturation index. • Membrane distillation proposed for desalinating hypersaline produced water • Suspended organic matter fouls the membrane, leading to immediate membrane wetting. • Pretreatment of produced water required for long-term performance • Fouling and scaling characterized; sulfate and carbonates found as major scalants • Produced water concentrated to 290 g/L and +50% water recovery achieved [ABSTRACT FROM AUTHOR]

Thermal desalination technologies are required for minimal and zero liquid discharge (MLD/ZLD). However, conventional and emerging thermal desalination technologies, such as mechanical vapor compression (MVC) and membrane distillation (MD), are usually highly expensive to implement or/and energy intensive to operate. In this study, we develop a novel desalination technology by using a vapor-compression pump to assist membrane distillation (MD). Comparing the energy efficiencies of the novel heat-pump assisted MD (HPMD), MVC, and conventional MD under similar operating conditions, demonstrates that HPMD is an energy-efficient thermal desalination technology. Furthermore, through process modeling, we provide guidelines for HPMD system design and show that the HPMD can theoretically obtain low energy consumption (~10 kWh of electrical energy per cubic meter of produced fresh water or gain output ratio, GOR, of ~60) and high water vapor flux (i.e., >60 L m−2 h−1). We conclude by highlighting promising applications of HPMD for MLD/ZLD, enabled by its high energy efficiency, low capital cost, and modularity. • We develop a novel heat-pump assisted membrane distillation (HPMD) technology. • Energy efficiency of HPMD is comparable to MVC and significantly greater than conventional MD. • HPMD can simultaneously achieve superior energetic and kinetic efficiencies. • HPMD has the potential to be widely applied in minimal/zero liquid discharge processes. [ABSTRACT FROM AUTHOR]

Treatment and management of produced water are of great significance but critical challenges remain due to the huge quantity and complexity of the liquid waste. Here we propose and demonstrate an integrated membrane based system combining electrodialysis, nanofiltration and membrane distillation (ED-NF-MD) for highly efficient treatment of oilfield produced water. Our new system enables zero liquid discharge (ZLD) by concentrating the produced water to an extremely high concentration (up to 373,000 mg/L) at a high water recovery of 99.8% without chemical (e.g. soda or anti-scalants) adding. To the best of our knowledge, such performance is the highest in terms of the final concentration and water recovery among various ZLD technologies. ZLD of our membrane system mainly comes from the metathesis by ED that separates the scaling ions into different streams, thereby creating a scaling-free environment. Basic economic evaluation shows that the total specific energy consumption for ZLD in the whole ED-NF-MD system includes a minimal electrical energy requirement (33 kW·h/m3) and a large thermal energy requirement for MD (154 kW·h/m3). The novel membrane based system shows great potential in realizing real ZLD in produced water treatment by minimizing scaling and thus highly concentrating the feed solution. Unlabelled Image • We demonstrate a new integrated membrane system for produced water treatment. • Our membrane system enables zero liquid discharge without adding chemicals. • High final concentration and high water recovery are achieved. • A scaling-free environment is achieved by electrodialysis metathesis. [ABSTRACT FROM AUTHOR]

Direct contact membrane distillation (DCMD) was investigated for the treatment of oil-field produced water using a hydrophobic polypropylene (PP) membrane with 0.2 μm pore size. The DCMD performance was studied under different feed temperatures ranged from 40 °C to 80 °C while the cooling temperature was maintained at 23 °C. Increasing the feed water temperature resulted in a higher permeate water flux. Stable and reliable DCMD membrane performance was observed for all used membranes. The obtained results indicated the great potential of DCMD to treat hypersaline oil-field produced water with an overall rejection of salts higher than 99.9% and that of total organic carbon (TOC) greater than 93.3%. This was due to the presence of volatile organic compounds in oil-field water. Pre-treatment of produced water using 0.45 μm filter did not show much effect on the DCMD performance. A slight gradual reduction of the permeate flux was observed due to fouling phenomenon. A simple washing the membrane with de-ionized water was found to be an effective method for cleaning the membrane and restoring the permeate flux indicating the absence of irreversible fouling. • Direct contact membrane distillation (DCMD) was investigated for the treatment of oil-field produced water. • Rejection of DCMD of hypersaline was >99.9% and 93.3% for TDS and TOC, respectively. • Feed temperature increased DCMD flux without affecting its rejection. • MCMD fouling was minimal and reversible when treating hypersaline oil-field produced water. [ABSTRACT FROM AUTHOR]

Desalination of produced water in the gulf petrochemical industry is a continuing challenge to major research groups in the field. With a focus on produced water from desalination plants, it has become crucial to define and follow specific protocol in wastewater purification technologies. In this work, an optimized guideline for direct contact membrane distillation (DCMD) was developed and implemented. A bench-scale DCMD unit was performed under optimum process parameters of feed and distillation inlet temperatures of T Feed = 60 °C and T Dist = 20 °C, respectively. A low flow rate of 0.03 L/min was used to avoid wetting of the fabricated membrane. A hydrophobic polystyrene flat sheet was prepared in the labs using a custom-made electrospinning apparatus. The effect of varying concentrations on the hydrophobic polystyrene membrane was studied using a high concentration brine feed (C1 ≈ 75,500 ppm) and another feed of lower concentration (C2 ≈ 25,200 ppm). A high salt rejection rate of 99% was achieved. The morphological structure, pore size and fiber length was analyzed using SEM. Conductivity measurements have confirmed an improved permeate quality of 99%. Thus, as per the DCMD performance of the polystyrene membrane, the generated permeate indicates that the membrane performance may have scalable potential contribution to industrial wastewater purification. • Electrospun hydrophobic membranes in direct contact membrane distillation. • Membrane performance with synthetic brine mimics Qatari desalination plants. • Improved permeate quality of 99% and salt rejection up to 99% from thermal brine. [ABSTRACT FROM AUTHOR]

The limited clean water resource has urged the need to extract fresh water from non-conventional sources. Produced water (PW) is a potential source of fresh water, particularly for oil-producing countries experiencing water stress issue. The engagement of membrane-based desalination technology in the field of PW treatment brings about new possibility of water reclamation. This review highlights the state-of-the-art membrane-based technologies including both stand-alone and their hybrid system, for PW treatment and reclamation. While reverse osmosis continues as a reliable option for PW treatment, emerging technologies like forward osmosis and membrane distillation have attained increasing attentions from the desalination community. To pave a way for practical applications of membrane technologies for PW desalination, the recent advances in term of membrane properties improvement, operating condition optimization, and membrane cleaning protocols are reviewed. Finally, the challenges and future outlooks of current PW desalination technologies are also highlighted. • State-of-the-art PW desalination technologies are reviewed. • Merits and limitation of RO, FO and MD PW desalinations are discussed. • Strategies of improving membrane-based PW desalination are reviewed. • Challenges are identified and the future perspectives are proposed. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) has shown promise for desalination of produced water (PW), but there are very few studies reported on the performance of MD with real PW and the characteristics of the fouling and scaling in MD. Among different MD configurations, sweeping gas MD (SGMD) is the least studied configuration. Here we report the application of SGMD for treating high-salinity PW (123 g L−1). The SGMD operating conditions were first carefully optimized through pure water MD experiments by varying operating conditions. The flux evaluation was accompanied by a detailed Aspen Custom Modeler simulation based on the electrolyte-NRTL thermodynamic model to better understand the heat and mass transfer in the feed and permeate channel. Supported by experiments, modeling results confirmed the partial condensation of the vapor in the permeate channel. Additionally, it was concluded that the saturation of the sweeping gas is controlling the overall mass transfer through the membrane. Selected membranes and optimized conditions were then used to conduct short-term and long-term performance tests with PW. In long-term MD test, the concentration of the PW increased by a factor of two (50% water recovery), while the membrane exhibited small flux decline. Elemental analysis showed that strontium and sodium were the major scalant compounds. • Aspen Custom Modeler (ACM) with e-NRTL thermodynamic model was used to predict the SGMD flux. • Modeling and experiments suggest that the sweep gas in the permeate side controls and limits the SGMD flux. • Produced water was concentrated to 250,000 mg L-1, and no membrane wetting was observed in long-term SGMD tests. • Characterization of the fouled and scaled membranes showed that organic matter can increase the possibility of membrane wetting. • Although at low concentration, strontium and iron were found to be the major scalants on the scaled membranes. [ABSTRACT FROM AUTHOR]