Long-term Membrane Distillation Research Articles

Elucidating biofouling development and succession in membrane distillation using treated effluent

Biofouling in membrane distillation (MD) has several repercussions, including reduced efficiency of the MD process and limiting membrane life. Additionally, the evaluation of MD biofouling using treated effluents from wastewater treatment plants remains an unexplored area. Thus, biofouling formation and development in a long term MD process (15 days) using treated effluent from a wastewater treatment plant was explored in this study. The results revealed that flux decline occurred in four phases: i) initial decline (0–1 d), ii) gradual decline (1–5 d), iii) progressive decline (5–10 d), and iv) rapid decline (10–15 d). Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis demonstrated that the treated effluent contained humic-like substances, which deposited on the membrane surface in phase 1. Whereas biopolymers development on the membrane surface in phase 2 and 3 was linked to biofouling. Microbial community analysis revealed that the initial colonisers were predominantly thermophilic bacteria, which were different from the microbial community of the treated effluent. The biofilm-forming bacteria included Schlegelella, Meiothermus, and Vulcaniibacterium. These microorganisms proliferate and release excessive extracellular polymeric substances (EPS), leading to the development of mature biofilm on membrane surface. This helped in the deposition of organics and inorganics from the bulk feed, which led to microbial community succession in phase 4 with the emergence of the Kallotenue genus. The results suggested that organic substances and microbial communities on membrane surface at different stages in a long-term MD process had a significant influence on MD performance for high-quality wastewater reuse.

Facile preparation of superhydrophobic PVDF/MWCNTs distillation membranes: Synthesis, characteristics and separation performance

In recent years, membrane distillation (MD) has emerged as an effective solution to mitigate the high energy consumption associated with conventional fermentable sugar concentration processes. However, the inherent low mechanical strength of traditional organic membrane surfaces can result in issues related to membrane wetting during long-term MD experiments. In this work, superhydrophobic PVDF/MWCNTs (multi-walled carbon nanotubes) distillation membranes with high mechanical strength were prepared by a combination of templating and co-blending techniques. The process involved peeling the semi-gelation membrane from a sandpaper template, subsequently forming a high aspect ratio microstructure on the membrane surface via tearing and pulling. Additionally, the incorporation of MWCNTs further bolstered the mechanical strength of the membrane. At a peeling time of 90 s and a MWCNTs content of 0.08 wt%, the distillation membrane exhibited an impressive water contact angle of 153.2°, indicating it possess exceptional hydrophobicity while maintaining high mechanical strength. The separation performance of the prepared distillation membranes has been inspected by conducting both experimental analyses and computational fluid dynamics (CFD) modeling of the entire MD process. An appropriate elevation in both feed flow rate and temperature could effectively mitigate the problem of temperature and concentration polarization on the membrane surface. PVDF/MWCNTs distillation membrane demonstrated a modest reduction in permeate flux of about 11.69 % and a stable rejection rate exceeding 99.95 % throughout a 100-hour operational period, and it required only 15 h to concentration of aqueous glucose solution to 100 g/L, significantly enhancing the efficiency of the process. This study also employed a combination of experiments and simulations to optimizes the process conditions guiding the vacuum membrane distillation (VMD) process and could provide guidance for the future application of membrane distillation in the concentration of sugar solutions.

High performance bimetallic ZIF-CoZn@PVDF-HFP composite nanofiber membrane for membrane distillation based on coaxial electrospinning technology

Membrane Distillation (MD) technology stands out for its cost-effectiveness and sustainability in diverse applications, such as high-salinity wastewater treatment and seawater desalination. However, conventional MD membranes frequently encounter challenges associated with inadequate permeate flux and insufficient anti-wetting performance. In the present study, we fabricated a series of ZIF-CoZn@PVDF-HFP composite nanofiber membranes with a core–shell structure via coaxial electrospinning. Here, PVDF-HFP functions as the core, while a blend of bimetallic Zeolitic imidazolate framework ZIF-CoZn nanoparticles and PVDF-HFP constitutes the shell. Through the utilization of the coaxial technology, functional nanoparticles achieve uniform and stably dispersed on the nanofiber surface, leading to the creation of a secondary rough structure in addition to the inherent roughness of single-nozzle electrospinning. This results in a surface with a 3D-hierarchical structure. The significantly amplifies the evaporation area on the surface of the composite nanofiber membrane, thereby bolstering the permeate flux in the MD process. Additionally, the incorporation of bimetallic ZIF-CoZn nanoparticles, recognized for their superior hydrophobicity and low thermal conductivity, improves the anti-wetting and heat-insulating properties of the composite nanofiber membrane, further advancing permeate flux performance. Using a 35 g L−1 NaCl as the feed solution, the optimal 1 % ZIF-CoZn@PVDF-HFP composite nanofiber membrane demonstrated a permeate flux of 21.8 L m−2 h−1, coupled with a salt rejection rate exceeding 99.9 %. Even during long-term MD testing, it maintained excellent insulation and anti-wetting capabilities. Our research offers a convenient and effective approach for fabricating anti-wetting composite nanofiber membranes.

Surface regeneration of templated PVDF membrane for efficient microalgae-rich high saline aquaculture wastewater treatment in membrane distillation

This study investigated the use of templated PVDF membranes with intermediate flushing to revive fouled membrane during membrane distillation (MD) for sustainable high saline seawater aquaculture wastewater treatment. Results showed that superhydrophobic templated membrane with intermediate physical flushing was highly effective in reducing fouling, even after 5 cleaning cycles, when treating microalgae-rich feed with algogenic organic matter and high salinity aquaculture wastewater. Specifically, the membrane restoring flux performance by up to 97.2 %, compared to only 75.6 % for pristine membranes. In this study, intermediate flushing effectively restored the advancing and reducing contact angles of fouled templated membranes, enhancing membrane regeneration and reducing surface adhesion properties. In long-term 82-h MD tests, the superhydrophobic templated membrane still demonstrated excellent separation, achieving 99.84 % rejection rate for all components and maintaining average water permeation flux of 21.4 kg/m2.h when treating microalgae-rich feed. The study suggests that the use of superhydrophobic templated membrane with surface reviving capability holds immense potential in overcoming the challenges of membrane fouling in MD, providing a sustainable treatment solution for microalgae-rich and high salinity wastewater treatment.

Omniphobic membranes in membrane distillation for desalination applications: A mini-review

Membrane processes are extensively used to provide purified water from various saline water bodies. Membrane distillation (MD), one such membrane process, is mainly used for desalinating highly saline feed waters and to provide clean water. The design of robust membranes recently received considerable attention to address wetting, scaling, and fouling issues that hampered performance in long-term MD process. The current review discusses the omniphobic membranes employed in MD process for desalinating highly saline feedwaters containing diverse low surface tension substances. Also, it summarizes the basic concepts, fabrication and modification methods involved in designing omniphobic membranes. The developed omniphobic membranes have re-entrant structures and low surface energy which effectively provided anti-wetting and anti-fouling ability against saline feedwaters containing various low-surface tension substances. Further, the review focused on future research directions for developing omniphobic membranes for MD desalination applications.

Plasma-Induced Superhydrophobicity as a Green Technology for Enhanced Air Gap Membrane Distillation

Superhydrophobicity has only recently become a requirement in membrane fabrication and modification. Superhydrophobic membranes have shown improved flux performance and scaling resistance in long-term membrane distillation (MD) operations compared to simply hydrophobic membranes. Here, we introduce plasma micro- and nanotexturing followed by plasma deposition as a novel, dry, and green method for superhydrophobic membrane fabrication. Using plasma micro- and nanotexturing, commercial membranes, both hydrophobic and hydrophilic, are transformed to superhydrophobic featuring water static contact angles (WSCA) greater than 150° and contact angle hysteresis lower than 10°. To this direction, hydrophobic polytetrafluoroethylene (PTFE) and hydrophilic cellulose acetate (CA) membranes are transformed to superhydrophobic. The superhydrophobic PTFE membranes showed enhanced water flux in standard air gap membrane distillation and more stable performance compared to the commercial ones for at least 48 h continuous operation, with salt rejection >99.99%. Additionally, their performance and high salt rejection remained stable, when low surface tension solutions containing sodium dodecyl sulfate (SDS) and NaCl (down to 35 mN/m) were used, showcasing their antiwetting properties. The improved performance is attributed to superhydrophobicity and increased pore size after plasma micro- and nanotexturing. More importantly, CA membranes, which are initially unsuitable for MD due to their hydrophilic nature (WSCA ≈ 40°), showed excellent performance with stable flux and salt rejection >99.2% again for at least 48 h, demonstrating the effectiveness of the proposed method for wetting control in membranes regardless of their initial wetting properties.

Hierarchically Structured Nanoparticle-Free Omniphobic Membrane for High-Performance Membrane Distillation.

The functional loss of membranes caused by pore wetting, mineral scaling, or structural instability is a critical challenge in membrane distillation (MD), which primarily hinders its practical applications. Herein, we propose a novel and facile strategy to fabricate omniphobic membranes with exceptionally robust MD performance. Specifically, a substrate with a hierarchical re-entrant architecture was constructed via spray-water-assisted non-solvent-induced phase separation (SWNIPS), followed by a direct fluorinated surface decoration via "thiol-ene" click chemistry. Deionized (DI) water contact angle measurements revealed an ultrahigh surface water contact angle (166.8 ± 1.8°) and an ultralow sliding angle (3.6 ± 1.1°) of the resultant membrane. Destructive abrasion cycle and ultrasonication tests confirmed its structural robustness. Moreover, the membrane possessed excellent wetting resistance, as evidenced by the prevention of membrane pore penetration by all low-surface-tension testing liquids, allowing stable long-term MD operation to treat brine wastewater with a surfactant content of 0.6 mM. In a desalination experiment using shale gas wastewater, the omniphobic membrane exhibited robust MD performance, achieving a high water recovery ratio of ∼60% without apparent changes in water flux and permeate conductivity over the entire membrane process. Overall, our study paves the way for a nanoparticle-free methodology for the scalable fabrication of high-performance MD membranes with surface omniphobicity and structural robustness in hypersaline wastewater treatment.

Silanization enabled superhydrophobic PTFE membrane with antiwetting and antifouling properties for robust membrane distillation

A superhydrophobic polytetrafluoroethylene (PTFE) membrane (water contact angle 158 ± 5o) was fabricated based on a commercial microporous membrane by surface silanization and fluorination. The engineered PTFE membrane was characterized by various techniques, including scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, laser scanning confocal microscopy, a liquid-liquid porometer, water vapor permeation and contact angle measurements. The prepared PTFE membrane showed a slightly decreased average pore size of 0.37 μm, and thus an increased penetrating pressure of 0.38 MPa compared with the pristine commercial membrane. The developed superhydrophobic PTFE membrane had a very low surface energy of 1 mJ/m2, only one third of that of the unmodified commercial membrane. The characterization and membrane distillation (MD) separation results showed that the superhydrophobic PTFE membrane had significantly enhanced antiwetting and antifouling performances compared with the pristine commercial membrane. The developed new PTFE membrane also displayed excellent antifouling, antiwetting and long-term stability during the treatment of real challenging landfill leachate of high salinity and high organics by MD. The fabricated PTFE membrane with simultaneously antiwetting and antifouling properties opens a new avenue for treating challenging waste liquids via MD. This study also provides an important strategy to develop superhydrophobic simultaneously antiwetting and antifouling membranes for stable long-term MD applications.

Superhydrophobic composite asymmetric electrospun membrane for sustainable vacuum assisted air gap membrane distillation

Membrane distillation (MD) relies on superhydrophobic membranes that must achieve the competing goals of high liquid entry pressure (LEP) and high permeability. In this study, we developed the first superhydrophobic composite electrospun asymmetric membrane using fluorinated graphite (FG). We also provided among the first comparisons of the relative benefits of membrane asymmetry and composite coatings via 3D electrospinning and spraying. FG particles increased the roughness and reduced the zeta potential of the membranes. Superhydrophobic composite membranes had a contact angle of 157° (sliding angle of 7°) and an LEP of 327 kPa. Long-term MD testing revealed that FG particles could increase MD's sustainability while decreasing membrane wetting. Vacuum-assisted air gap membrane distillation (V-AGMD) showed that the composite asymmetric membrane outperformed the non-asymmetric version (composite nanofiber) membrane by 21 % in average water flux and 25 % in average thermal efficiency because of the asymmetric structure of the membrane. The numerical model developed for the V-AGMD system also successfully predicted the water flux generated experimentally from the composite nanofiber and composite asymmetric membranes. Our results confirmed that electrospun asymmetric FG membranes with high contact angle, low sliding angle, high permeability, and high gained output ratio (GOR) would be promising candidates for sustainable MD.

The influence of storage time on the performance of polypropylene membranes applied for membrane distillation

Membrane distillation (MD) has recently attracted great attention as an emerging technology for desalination and wastewater treatment. Although a large number of important studies have been done to investigate the influence of the membranes preparation factors on their structure, morphology and separation efficiency, so far, the impact of the membranes storage time on the MD process performance has not been dealt with in depth. Therefore, the main aim of this study was to investigate the impact of the stabilization period of new polypropylene (PP) membranes on the polymer degradation during the MD process. The findings of the present research demonstrated that the PP membranes resistance to thermal and mechanical degradation during the long-term MD process can be ensured by extending their storage time. On the other hand, it has been reported that the membranes storage time did not affect their wettability. Moreover, it has been noted that reducing the feed temperature to 333 K ensures the limitation of the membrane aging behaviour. In addition, the results obtained clearly showed that the mechanical strength of PP does not depend on the overall changes in its crystallinity, but on the transformation of the amorphous-crystalline connections responsible for the elasticity of the polymer. The membranes stored for over two years were successfully used for separation of NaCl solution (200 g/L) and desalination of Baltic Sea water, and the values of salt rejection were similar to those obtained using membranes produced by various companies. Undoubtedly, findings of this study are of essential importance for the future of the PP membranes application in the MD technology.

One-step preparation of omniphobic membrane with concurrent anti-scaling and anti-wetting properties for membrane distillation

Membrane scaling represents one of the significant challenges for membrane distillation (MD), especially when treating hypersaline brines. This work presents a one-step dip-coating method to develop an omniphobic membrane. The commercial polyvinylidene fluoride (PVDF) hydrophobic porous membranes were immersed into the epoxy acrylic (EA) resin and fluorosilane (1H,1H,2H,2H-Perfluorodecyltrimethoxysilane, PFTS) mixture followed by a heating cross-linking process. EA/PFTS ratio of 1:1 (v/v) gave the best performance regarding surface morphology, surface chemical composition, surface energy, and mechanical property. The resultant PVDF-(EA/PFTS)-1:1 membrane demonstrated excellent wetting resistance and omniphobicity during the penetration of deionized water, 30% and 60% ethanol in water, and kerosene, giving 141°, 124°, 106°, and 116° contact angles, respectively. It also exhibited excellent scaling resistance in concentrating 14.7 mM gypsum solution and actual reverse osmosis (RO) brine. The permeate flux and conductivity were maintained at about 14 kg m−2 h−1 and below 3 μS cm−1, respectively. More than 99% salt rejection (actual RO brine) was achieved during a long-term continuous MD operation for 80 h. The PVDF-(EA/PFTS)-1:1 membrane exhibited excellent anti-scaling and anti-wetting properties. A series of capillary experiments confirmed that the membrane's surface pores achieved the gas-wetting state. The increase in the membrane surface hydrophobicity, the reduction in the surface pore size, and the toughening of the surface pores contributed to the formation of a stable gas-liquid interface on the modified membrane surface that can enhance the anti-scaling and anti-wetting performance.

Asymmetric superwetting Janus structure for fouling- and scaling-resistant membrane distillation

Membrane distillation (MD) via hydrophobic membranes is a highly effective technology for recovering pure water from hypersaline solutions. However, organic fouling and mineral scaling are two prominent challenges faced by membranes when used for practical applications. Commonly, fouling- and scaling-resistance require hydrophilic and superhydrophobic modification of MD membrane, respectively, which seems contradictory to realize both. Therefore, literature rarely report to address both issues to facilitate MD process. Herein, a membrane with an asymmetric superwetting Janus structure, including a thin superhydrophilic coating on a superhydrophobic bulk membrane, was constructed. The coating layer, based on alginate, alleviated fouling and scaling due to the superhydrophilicity and mineral precipitation resistance, while the underlayered polytetrafluoroethylene (PTFE) membrane provided robust hydrophobicity, enabling a successful MD process without the membrane being exposed to water. The coated PTFE membrane with the superwetting Janus structure exhibited much higher and more stable vapor flux than the pristine PTFE membrane in the MD process for the treatment of both oil- and solvent-contaminated seawater. Importantly, the coating imparted a high scaling resistance to the PTFE membrane during long-term MD operation for seawater desalination, thereby producing a water vapor flux six times that of the pristine PTFE membrane. The anti-scaling mechanism of the asymmetric superwetting Janus structure has also been proposed as a charge and hydration effect from the coating layer. This study may provide a promising strategy for the design of fouling- and scaling-resistant membrane materials and structures.

Oriented shish-kebab like ultra-high molecular weight polyethylene membrane for direct contact membrane distillation

The special bioinspired structure will help membranes to improve the antifouling properties during the membrane distillation (MD) process. Here, a new MD utilized membrane with oriented shish-kebab structure was prepared by stirring the ultra-high molecular weight polyethylene (UHMWPE)/decalin solution to induce the shish-kebab crystals to grow on a polyester mesh along the flow field, and then coated with fluororesin to decrease the surface energy. The multi-stage extraction drying technology was adopted to reduce the membrane shrinkage in the dry process and make the shish-kebab membranes have high porosity (77.5%). More interesting, when the water flows along the shish direction, just like the fish gill works, the membrane has better resistance to NaCl, CaCO3 scaling, due to the nanoscale structure can intensify the interfacial nanoscale turbulent flow and hinder the crystal deposition. Specifically, the membrane has a high-water recovery of 92.5% and a low conductivity increase (from 2.76 to 8.33 μS/cm in 70 h) in the long-term MD process.

Exploration of time series model for predictive evaluation of long-term performance of membrane distillation desalination

Owing to the inherent complications in membrane distillation (MD) operations, it has become a challenge to acknowledge swiftly and appropriately to safeguard the quality of effluent, particularly when the processing cost is a prominent concern. Membrane wetting in MD operations is a major concern during long-term performance. In this study, machine learning (ML) methodologies were utilized to overcome the limitations of conventional mechanistic modeling. ML applications have never been explored to investigate how operational factors, such as water flux and salt flux, are affected during long-term MD performance. Furthermore, time-dependent factors were neglected, making it difficult to analyze the relationship between effluent quality and operational factors. Therefore, this study demonstrates a novel ML-based framework designed to enhance the performance of MD. The ML-based framework consists of an autoregressive integrated moving average (ARIMA) and utilizes a unique pathway to explain the impact of time series among operational factors. The accuracy of forecasting has been explored by utilizing 180 h (180 datasets), that was further used and divided into training (165 datasets) and test datasets (15 datasets). Eventually, the ARIMA model demonstrated a highly precise relationship order between the model and experimental data, which can be further used to forecast membrane performance in terms of wetting and fouling. The selected ARIMA model (3,2,1) appears to be an adequate model for water and salt flux data which has been effectively used to capture the course of permeate water and salt flux by producing the smallest forecast RMSE. The RMSE values were observed to be 0.22 and 0.05 for water and salt flux respectively, which can better predict long time series with high frequency. These frameworks can be applied for the early prediction of membrane wetting if ample high-resolution data are available.

Membrane Distillation of Saline Water Contaminated with Oil and Surfactants.

Application of the membrane distillation (MD) process for the treatment of high-salinity solutions contaminated with oil and surfactants represents an interesting area of research. Therefore, the aim of this study is to investigate the effect of low-concentration surfactants in oil-contaminated high-salinity solutions on the MD process efficiency. For this purpose, hydrophobic capillary polypropylene (PP) membranes were tested during the long-term MD studies. Baltic Sea water and concentrated NaCl solutions were used as a feed. The feed water was contaminated with oil collected from bilge water and sodium dodecyl sulphate (SDS). It has been demonstrated that PP membranes were non-wetted during the separation of pure NaCl solutions over 960 h of the module exploitation. The presence of oil (100–150 mg/L) in concentrated NaCl solutions caused the adsorption of oil on the membranes surface and a decrease in the permeate flux of 30%. In turn, the presence of SDS (1.5–2.5 mg/L) in the oil-contaminated high-salinity solutions slightly accelerated the phenomenon of membrane wetting. The partial pores’ wetting accelerated the internal scaling and affected degradation of the membrane’s structure. Undoubtedly, the results obtained in the present study may have important implications for understanding the effect of low-concentration SDS on MD process efficiency.

Novel PVDF membrane with sandwich structure for enhanced membrane distillation

Membrane distillation (MD) holds great potential in the desalination of high concentration brines but need improvement to achieve sustained permeate flux and durable performance in long-term MD operation. In this study, a novel Janus membrane with sandwich structure was fabricated. Detailly, the microporous PVDF membrane was single-side modified with a bio-inspired hydrophilic polydopamine/polyethylenimine (PDA/PEI) coating, then a hydrophobic nanofiber layer was constructed via forcespinning on the other side as an anti-wetting layer. As the PDA/PEI deposition time increases from 0 to 1.5 h, the contact angle of the modified PVDF membrane surface decreases gradually from 124.6° to 31.3° with little change in membrane morphology and pore structures, resulting in an upward trend of permeate flux up to 50.9 LMH at a feed temperature of 70 °C. The rough forcespun nanofiber layer endows the membrane surface with good hydrophobicity, which brings improved LEP (136.4 kPa) and operation durability for the membrane during MD process. Moreover, numerical simulations were conducted to verify and predict the permeate flux variation of MD membranes under different operation conditions, revealing the superiority of the sandwich-structured Janus membrane combined with the experimental results. Finally, the optimized PDA-PVDF-NF membrane was used for the desalination of model inland brine, exhibiting stable MD performance with high permeate flux of 25 LMH, ~100% salt rejection, and excellent water recovery during a continuous operation as long as 96 h.

Plasmonic Titanium Nitride Nano-enabled Membranes with High Structural Stability for Efficient Photothermal Desalination.

Herein, we demonstrate the desalination performance of a solar-driven membrane distillation (MD) process, where upon light illumination, a highly localized heating of plasmonic titanium nitride nanoparticles (TiN NPs) immobilized on a hydrophobic membrane provides the thermal driving force for the MD operation. The engineered TiN photothermal membrane induces vapor generation directly at the feed-membrane interface upon solar irradiation, thereby eliminating the need to heat the entire bulk feed water. The results indicate that the average vapor flux through the TiN photothermal membrane without any auxiliary feed heating was recorded as 1.01 L m-2 h-1, which corresponds to the solar-thermal efficiency of 66.7% under 1 sun solar irradiance. The superior performance of the photothermal MD process is attributed to the broadband optical absorption and excellent light-to-heat conversion properties of the plasmonic TiN NP layer, which enabled efficient interfacial water heating at the membrane surface and increased the net driving force for vapor transport. Results also reveal the high mechanical stability of the TiN photothermal coating layer during long-term photothermal MD operations. We believe that the TiN photothermal membranes fabricated using a relatively inexpensive and nontoxic material via the simple technique with high stability and photothermal conversion efficiency will provide a path forward for developing the solar-driven MD applications.

Co-axially electrospun superhydrophobic nanofiber membranes with 3D-hierarchically structured surface for desalination by long-term membrane distillation

Electrospun nanofiber membranes (ENMs) have gained increasing interest in membrane distillation (MD) applications due to their high surface area, high hydrophobicity and porosity, and controllable pore size and membrane thickness. However, despite these advantages, ENMs still suffer from wetting issues in MD. Co-axial electrospinning is an attractive strategy for the one-step fabrication of non-woven membranes with core-sheath structures and improved wetting resistance for MD application. In the present study, we investigated poly (vinylidene fluoride-co-hexafluoropropylene) (PH) as the core and PH/silica aerogel (SiA) as the sheath to obtain superhydrophobic co-axial composite ENMs. The surface characterization results indicated that the active layer (i.e., PH) of the co-axial ENMs was rough, highly porous (>80%), and superhydrophobic (contact angle >160°). Further, the co-axial ENMs possessed small pore sizes (<0.39 μm) and a suitable liquid entry pressure (>1.72 bar). Upon the application in long-term (one month) direct contact MD testing using a 3.5 wt% NaCl solution as the feed, high water vapor flux and salt rejection of 14.5 L/m2h and 99.99% were achieved, respectively, when applying the optimal 4 wt% SiA solution loading at the sheath. The ENMs fabricated using the versatile co-axial electrospinning showed great potential for long-term applications in direct contact MD desalination.

Performance of sweeping gas membrane distillation for treating produced water: Modeling and experiments

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.

Influencing Factors of DCMD for Treatment of RO Concentrate Wastewater on Water Reclamation

Direct Contact Membrane Distillation(DCMD) device with PVDF as the core was introduced to treat concentrated Reverse-Osmosis(RO) wastewater on water reclamation. Effects of feed temperature, feed flow rate and permeate flow rate on flux were investigated. Furthermore, variation low of permeate flux and the main water quality during long-term membrane distillation(MD) performance were discussed. It can be concluded from the result that the permeate flux were increased with the feed temperature. When the temperature difference between hot-side and cool-side reached 35°C, the permeate flux was 7.15 kg/(m2•h), and then the growth trend of flux slowed down. The permeate flux were increased with the increase of feed flow rate and permeate flow rate, and the peak reached 8.2 kg/(m2•h) in the whole process. The permeate flux stabilized at 7.1～8.36 kg/(m2•h) during 16 hours long term experiment performance and the permeate water quality were kept steadily.