Membrane Distillation Process Research Articles

Synergetic effect on fouling alleviating of membrane distillation in urine resource recovery by thermally activated peroxydisulfate pretreatment

Given that the spontaneous precipitation of minerals caused by urea hydrolysis and abundant organic compounds, membrane fouling became a major obstacle for urine recovery by membrane distillation (MD). Herein, this study developed a combined system (TAP-MD) by integrating thermally activated peroxydisulfate (TAP) and MD process to inhibit membrane fouling and improve separation efficiency. Based on the TAP-MD system, the separation performance was improved significantly, improving nutrient recovery efficiency and quality of reclaimed water. More than 80% of water could be recovered from urine, and about 94.13% of total ammonia nitrogen (TAN), 99.02% of total nitrogen (TN), 100% of total phosphate (TP), and 100% of K+ were rejected. The mechanism for alleviating urine-induced fouling was systematically and intensively studied. With TAP pretreatment, the TAN concentration of pretreated urine was kept at a low level steadily and the pH was at neutral or weakly acidic. Hence, inorganic scaling represented by carbonate and phosphate precipitates were significantly inhibited by creating unfavorable solvent environment for crystallization with TAP pretreatment. Additionally, aromatic proteins were found as the main organic foulants. According to the secondary structure of protein, the proteins were degraded by the cleavage of peptide bonds by TAP pretreatment. Meanwhile, the hydrophilicity of protein increased, which reduced the hydrophobic interaction of protein and membrane surface and thus alleviated protein-induced membrane fouling. This study revealed the inorganic and organic foulants in urine that caused membrane fouling and demonstrated the mechanism of membrane fouling alleviation by TAP-MD system. The experimental results will be instrumental in better understanding the mechanisms of membrane fouling induced by urine and optimize MD process for resource recovery from urine.

Improvement of anti-wetting and anti-scaling properties in membrane distillation process by a facile fluorine coating method

In this work, a fluorine coating material has been employed to improve membrane performance during membrane distillation process. The coating operation is easy and fast without additional modification of membrane morphology nor chemistry. After coating, pore structure of the membrane has remained unchanged, while surface free energy of the membrane has been drastically lowered. Low surface free energy endows the coated membrane with exceptional high anti-wetting and anti-scaling property. In membrane distillation test with the presence of surfactant or scaling agent, the coated membrane has significantly outperformed the pristine membrane. Moreover, the coated membrane has exhibited excellent performance in water recovery test from synthetic seawater, showing great promise for practical applications.

High-performance robust graphitic carbon nitride nanosheets embedded membranes for desalination through direct contact membrane distillation

Two-dimensional (2D) graphitic carbon nitride (g-C3N4)-based membranes have recently received widespread attention due to their fantastic separation performance. In the present investigation, for the first time, we assessed the desalination performance of membranes incorporated with g-C3N4 nanosheets through the membrane distillation (MD) process. For this purpose, different concentrations (0–0.06 wt.%) of synthesized nanosheets were embedded within the hydrophobic PVDF matrix by simple phase inversion method. Upon loading 0.03 wt.% g-C3N4, the water contact angle and LEP augmented from 80.5° and 6 bar for the pure PVDF membrane to 95.2° and 8 bar, respectively. Adding the g-C3N4 nanosheets also improved both the tensile strength and the elongation at break by 21.32% and 36.46% than the pristine membrane, respectively. The mixed matrix membranes favorably improved MD performance; so that, 0.03 wt.% g-C3N4 embedded membrane exhibited a flux of 27.63 kg/m2h with an enhancement of 70% relative to its pure counterpart. Continuous testing for up to 24 h filtration of a 3.5 wt.% NaCl solution still showed a stable flux and almost complete salt rejection for the mentioned mixed matrix membrane. The anti-fouling properties of the membranes were also improved by incorporation of the g-C3N4 nanosheets. The 0.03 wt.% gCN embedded membrane recovered about 90% of the original permeation flux after 20 h desalination operations using real seawater as a feed solution. This work holds promise for developing next-generation MD membranes with superior desalination performance in terms of water vapor permeability and salt rejection.

Modified ceramic membranes for the treatment of highly saline mixtures utilized in vacuum membrane distillation

Membrane Distillation processes could enable the treatment of highly saline solutions and facilitate minimal (MLD) or zero liquid discharge (ZLD) applications. Ceramic membranes can be a robust alternative to polymeric membranes if they are chemically modified to exhibit hydrophobic qualities to prevent wetting, particularly for vacuum membrane distillation (VMD). This study found that the thin top layer of asymmetrically structured ceramic membranes is robust enough for highly saline and abrasive suspensions and that TiO2 membranes outperform Al2O3 membranes in respect to the mass transport due to their larger support pore size and lower thermal conductivity. A maximum permeate flux of 35 kg/(m2 h) with exceptionally high rejections were measured in VMD using a saline brine with a concentration of 350 g NaCl per kg H2O. Furthermore, a VMD mass transfer model was successfully adopted (based on the Dusty Gas Model) to facilitate the calculation of the mass transfer through asymmetrically structured TiO2 membranes. Model deficiencies such as the underestimation of polarization effects were discussed, and correction factors integrated accordingly. This was done to establish a mass transfer modelling fundament for asymmetrical ceramic membranes used in MD that can be extended in future works and possibly serve as a tool for membrane optimization.

Synthesis of hybrid membrane distillation processes with optimal structures for ethanol dehydration

Conventional distillation is the most used unit operation to separate zeotropic mixtures. However, it is combined other unit operations to separate azeotropic mixtures. This work proposes a synthesis and intensification framework to obtain hybrid membrane distillation process structures. The synthesis problem was represented by a low aggregation superstructure comprised of functional modules. Then, the superstructure was reformulated as a Mixed Integer Linear Programming (MILP) problem to derive the optimal structure. The synthesis problem does not consider any pre-established process structure or connectivity; therefore, the optimal solution must be interpreted, simulated, and validated to generate a known process structure. Finally, the validated structure was post-optimized to fine-tune the detailed design of the process structure. The presented framework was applied to separating an ethanol/water mixture. The obtained solutions attained high energy and cost savings compared to the typical pressure swing and extractive distillation.

Simultaneous Desalination and Glyphosate Degradation by a Novel Electro-Fenton Membrane Distillation Process.

The industrial effluent from glyphosate production has high salinity and refractory organic contaminants. The removal of organics and the recycling of inorganic salts from this kind of water are challenging issues. In this study, electro-Fenton (EF) and membrane distillation (MD) were coupled in a single reactor utilizing a membrane-based electrode (Mem-GDE) with the ability to bidirectionally transfer vapor and oxygen and electrochemically synthesize H2O2. The operating thermal conditions for MD significantly promoted Fenton reactions and, thus, the removal of glyphosate. During operation, Fe species deposited on the Mem-GDE and enhanced its catalytic activity and adsorptive capacity, which markedly increased the apparent reaction rate constant of glyphosate by 6 times. This novel EF-MD process simultaneously removed organics and concentrated the inorganics, which is very meaningful for decreasing the costs for subsequent crystallization and achieving high-quality crystal salts. This study provides an efficient method for the treatment of organic-inorganic hybrid wastewater.

Peroxymonosulfate enhanced Fe(III) coagulation coupled with membrane distillation for ammonia recovery: Membrane fouling control process and mechanism

Membrane fouling limited the application of membrane distillation (MD) process in resource recovery. In this research, the peroxymonosulfate (PMS) enhanced Fe(III) coagulation process was proposed and proved its effectiveness in eliminating natural organic matter (NOM) and emerging organic contaminants (EOCs). Fe(III)/PMS process significantly enhanced the removal of dissolved organic carbon (DOC), turbidity, and UV254, compared to conventional Fe(III) coagulation. Thiamphenicol (TAP) represented the EOCs in the digestate, and Fe(III)/PMS could significantly degrade TAP (86 % degradation). In this course, phenols/quinones served as electron shuttles to induce the Fe(III)/Fe (II) redox cycle. The activation of PMS was boosted, generating the primary reactive substance sulfate (SO4−) radical with intense oxidative properties. In addition, membrane distillation achieved recovery of 93 % of TAN from coagulation effluent without membrane fouling. No tryptophan-like, tyrosine-like, xanthate, and other soluble microbial byproducts were detected on the membrane surface following Fe(III)/PMS pretreatment. The innovation of this study was revealing that the complexation of Fe(III) with NOM could promote Fe (II) regeneration and enhance PMS activation, active substance formation and contaminants degradation. New insights into the role of NOM in the Fe(III)/Fe(II) redox cycle were gained and the development of advanced oxidation process (AOP) coupled membrane technology was promoted to mitigate membrane fouling.

High molecular weight cellulose acetate membrane electrospinning: Parameters experimental optimization

Cellulose acetate (CA) drew great efforts in the membrane fabrication field, as it is a biodegradable polymer. However, electrospinning of CA with high molecular weight, which affects the spinnability, is still challenging. In this study, CA, with a relatively high molecular weight, was electrospuned at differentconditions to produce uniform and bead-free fibers. The target application of the optimized CA membrane is the membrane distillation process, which requires a low fiber diameter and narrow distribution. Results of the preliminary study revealed that the minimum and maximum limits for the investigated factors are CA concentration (13-17 wt%), tip-to-collector distance (TCD) (9-18 cm), applied voltage (14–20 Kv), and flowrate (0.5–2 ml/h). Electrospinning parameters optimization was designed using response surface methodology (RSM) with Box-Behnken Design (BBD) model. The considered parameters were CA concentration, TCD, and applied voltage. The prepared membranes' morphological structure and average fiber diameter were analyzed using SEM analysis and ImageJ software. With p-values less than 0.0001 and an R2 value of 0.9729, the analysis of variance (ANOVA) demonstrated that the suggested quadratic empirical model significantly agreed with the experimental investigation. The optimal parameters were, therefore, a concentration of 13 wt% CA, an applied voltage of 16.47 Kv, and a TCD of 17.99 cm. The verification experiment revealed a relative error value of 7.5%.

Membrane flux response technology for early warning of initial surface scaling in membrane distillation

Membrane distillation (MD) is a promising green separation technology for the treatment of high salinity wastewater attributed to excellent salt rejection, which is significant in relevant environmental and chemical engineering application. However, membrane scaling is an inevitable issue during long-term membrane distillation process. Thus, we developed a membrane flux response technology with data processing method to in-situ monitor the membrane scaling according to the reduction of permeate flux. By real-time analyzing the derivative of deviation between theoretical and experimental fluxes, early warning of initial membrane surface scaling was observed at initial nucleation stage. Besides, such timely detection was also achieved under different temperatures and flow velocities of feed solution, even for the poor light transmittance aqueous solution (such as NiSO4 and CoSO4 solution), which exhibited wide application potential on diverse high salinity wastewater systems. In addition, the metastable zone width of salt solution within MD system was obtained for the efficient operation design. To sum up, membrane flux response technology provides an early warning at imminent membrane scaling, which will maintain the great separation effect for a fresh feed solution after a facile cleaning by pure water, indicating the extension of device lifetime.

Thin continuous membrane coating with high surface energy for comprehensive antifouling seawater distillation

Membrane distillation (MD) has prominent advantages such as treating high-salinity wastewater with a low-grade thermal energy, high salt rejection, and zero discharge. However, organic fouling and mineral scaling are two major challenges for hydrophobic MD membranes when used for practical applications. Commonly, improving organic fouling- and mineral scaling-resistance require oppositely enhanced wetting properties of membrane, thus is difficult to simultaneously realize dual resistance with one membrane. Here, we proposed to use underwater thermodynamically stable high-surface-energy coating to modify the hydrophobic membrane with Janus structures comprising different surface energy. The underlayered structure meets the hydrophobicity requirements of the MD membrane, while the coating layer realizes dual resistance to organic and inorganic foulants. Theoretical analysis and experimental proof reveal that the membrane with the high-surface-energy coating layer outperforms the pristine one with approximately 10 times of longevity. This strategy provides a new way for the use of high-surface-energy materials in versatilely fouling-resistant MD process.

Triple-layer nanofiber membrane with improved energy efficiency for treatment of hypersaline solution via membrane distillation

A new triple-layer, electrospun nanofiber membrane was fabricated in sequential electrospinning steps for enhancing the thermal efficiency of the membrane for desalination of high-salinity solution in a membrane distillation process. The membrane structure is designed to form a Janus structure comprised of two hydrophobic layers made of polyvinylidene fluoride and polystyrene at the top and middle, respectively, and one hydrophilic layer made of polyacrylonitrile at the bottom layer (support). The low thermal conductivity of the polystyrene layer and the Janus structure of the membrane could considerably enhance the flux and thermal performance of the membrane for desalination of hypersaline solution. The experimental results demonstrated that the designed membrane achieved high permeate flux and high energy efficiency compared with single and dual-layer membranes when used for treatment of high salinity solution. The results further showed that increasing feedwater salinity dropped the permeate flux of the single-layer membrane by over 50 % and reached 10 L/m2h, while for the triple-layer membrane, it just dropped 20 % for the feed salinity of 200 g/l. Moreover, the triple-layer membrane showed 20 % higher energy efficiency at the same operation conditions. Furthermore, a simulation model was developed and validated via the experimental results to understand the effect of various parameters.

Application of vacuum membrane distillation process for lithium recovery in spent lithium ion batteries (LIBs) recycling process

The feasibility of using vacuum membrane distillation (VMD) for lithium recovery by concentrating the discharged leachate from spent lithium ion batteries (LIBs) recycling process was evaluated. The performance of VMD was compared with that of direct contact membrane distillation (DCMD) in terms of water flux, concentration rate, membrane wetting, and economic feasibility. VMD achieved a higher volume concentration factor (VCF) of 45 compared to the VCF of 25 achieved by DCMD in the LiCl feed solution. In the Li2SO4 feed solution, VMD and DCMD were concentrated to VCF15 and VCF 17, respectively, before wetting occurred. The stability of the MD process was verified using feed solutions containing nickel and manganese, which are cathode materials that can cause scaling even at low concentrations. Low concentrations of nickel and manganese did not significantly affect the maximum VCF or wetting; however, high concentrations of nickel and manganese affected the stability of the MD process. VMD exhibited a higher flux and 32 % lower thermal energy consumption than DCMD. Furthermore, the expected cost of Li2CO3 production with VMD for leachate concentration was $8.31–10.65/kg. The VMD concentration process is a feasible option for recovering lithium from the discharged leachate from spent LIBs recycling process.

Membrane Distillation for Desalination and Current Advances in MD Membranes

Desalination is a great technique to address the growing demand for water because it is essential for humans. Water treatment and desalination are two common uses for the membrane-based, non-isothermal MD (Membrane Distillation) process. It works at low pressure and temperature, and heat from waste and solar energy can meet the process's heat requirements. In MD, dissolved salts and nonvolatile contaminants are rejected as the vapors go through the membrane's pores and start condensing at the permeate side. However, because to the lack of a suitable and adaptable membrane, biofouling, wetting and water efficacy are the main problems for MD. Many researchers have recently worked on membrane composites and attempted to create effective, appealing, and unique membranes for membrane distillation. This review article talks about water shortages in the 21st century, the rise of desalination, the use of membrane distillation (MD), recent developments in membrane distillations, developments in pilot scale MD technologies, New developments in membrane fabrication and modification, the desired properties of membranes, and desalination membranes.

Machine learning and computational approaches for designing membrane distillation modules

Membrane distillation (MD) is a promising emerging water desalination technology. Commercialization of MD modules has been hindered by ineffective heat recovery and temperature polarization effect. Although hollow fiber (HF) membranes provide the highest area-per-module, they are under-investigated compared to flat-sheet membranes due to the interconnection of geometric, thermal, and hydrodynamic parameters in HF MD process. In this work, the parameters impacting HF MD module design are performed based on multiscale and deep neural network (DNN) models. MD experiments are conducted to train and validate the machine learning and multiscale models. The developed models are used either to explain the effects of geometric, thermal, and hydrodynamic parameters on the permeate flux or to predict the flux of a given set of parameters. The results revealed an increase in flux with the flow rate, velocity, and feed temperature. However, it decreased with shell diameter and module length. Compared to the experimental fluxes, flux predictions using multiscale and DNN approaches were within 14% and 1.2%, respectively. The DNN model converged to a mean squared error of 1.21% (R2 = 0.96) within a few minutes and demonstrated its potential as a favorable tool for module design optimization due to its accuracy, speed, and low computational requirements. The present study effectively exhibits the advantages of using machine learning as a next-generation model for fast module design, optimization, and scale-up of MD technology.

A luminescent thermosensitive coating for a non-invasive and in-situ study of thermal polarization in hollow fiber membranes

A new non-invasive method to evaluate the thermal polarization is herein proposed for hollow fiber (HFs) membranes during the Direct Contact Membrane Distillation (DCMD) process. The goal was reached by using a temperature-sensitive phosphorescent molecular probe such as Tris(phenanthroline) ruthenium(II) chloride (Ru(phen)3) and an infrared camera (IR) camera, to map, in-situ, the thermal profile directly at the membrane surface which is in contact with the hot feed water solution. The molecular probe was immobilized, by means of a perfluoropolyether (PFPE)-based coating, on the surface of a polypropylene HF in order to obtain a thermosensitive polymerized coating. The produced HFs were fully characterized in order to demonstrate the successful embodiment of the molecular probe on the surface of the membrane and their suitability, in terms of pore size, hydrophobicity and stability, for DCMD application. The luminescent activity of the immobilized Ru(phen)3 complex was measured by a bifurcated optical fiber, one branch was used to excite the molecular probe and the other branch was able to constantly monitor the molecular emission which was dependent on the temperature along the HF surface. The HFs were tested in DCMD at different feed temperatures (40 °C, 50 °C, 60 °C) and constant conditions of streams flow rate and distillate temperature (Qf = 90 L/h; Qp = 24 L/h; Tp = 13 °C). The obtained results clearly demonstrated the possibility of studying the thermal polarization phenomenon occurring during DCMD, with the temperature profile developed on the HF surface monitored, for the first time, at molecular level using a non-invasive technique. This approach can shed the light on better understanding this phenomenon and the possible strategies for its mitigation and counteraction.

Operational strategy preventing scaling and wetting in an intermittent membrane distillation process

The solar-powered membrane distillation (SPMD) process can improve the energy efficiency by using solar energy as a heat source. However, the SPMD process can only be intermittently operated due to the variation of the daily solar irradiation. In this study, effects of intermittent modes (IMs with/without temperature variations (IM-1/IM-2)) and continuous mode (CM) on scaling and wetting are investigated according to three types of shutdown protocols (P1: non-draining, P2: draining, P3: flushing after draining). A direct contact membrane distillation coupled with a real-time visualization system using the normalized light intensity and SEM-EDS are used for analysis of the MD performance in each condition. Consequently, scaling and wetting tendencies of SPMD at P3 are lowest among the tested shutdown protocols. Furthermore, scaling and wetting in CM and IM (IM-1 and IM-2) at P3 show low differences, indicating that shutdown protocols have a more profound effect than temperature variations and operation mode.

A numerical analysis of the electromagnetic field effect on direct contact membrane distillation performance

Using an advanced CFD model, this study attempts to determine how electromagnetic field (EMF) affects the performance of the direct contact membrane distillation (DCMD) process. The influence of electromagnetic fields (EMF) on the permeate flow, evaporation efficiency (EE), and temperature polarization coefficient (TPC) of the DCMD process are studied using a thorough theoretical model linked with a CFD model. Experiments conducted in-house with and without the EMF influence are used to verify the CFD model. High magnetic potency propagates the turbulence in the feed channel, hence boosting the driving force and transport phenomena for vapor transport to the permeate side. Permeate flux increased by 30%, and EE increased by 15% when the magnetic field strength was raised from 0 to 0.5 T, particularly at a lower intake feed velocity (0.02 m/s) and temperature of 333.05 K. In contrast, with the same magnetic potency (0.5 T) at a higher velocity at an input feed temperature, there is less improvement in EE (5%) and permeate flux (12%) due to the elevated turbulence intensity at high feed velocity. This research contributes to studies aimed at elucidating how electromagnetic fields affect separation processes such as MD, opening the door for more tuning and use of the fascinating phenomenon.

Membrane distillation with electrospun omniphobic membrane for treatment of hypersaline chemical industry wastewater

Hypersaline chemical industry wastewater comprises various species with complex characteristics, challenging the proposal treatment of such wastewater. Membrane distillation (MD) is a promising technology to realize the zero liquid discharge treatment of wastewater, due to its high salt rejection and insensitivity to the feed concentration. However, the practical application of the MD process is hindered by membrane wetting and fouling issues. Herein, we developed an innovative strategy to fabricate a robust omniphobic membrane via bio-inspired silicification and fluorosilanization on an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofiber mat. The polydopamine/polyethylenimine (PDA/PEI) deposition time was optimized based on the results of membrane morphology, wettability, and pore structure measurements. The MD process achieved a stable flux using the omniphobic membrane even when treating feed solution containing sodium dodecyl sulfate (SDS). In addition, the omniphobic membrane significantly outperformed the pristine membrane in treating hypersaline chemical industry wastewater. This work provides a novel method for fabricating robust electrospun omniphobic membranes for high-performance treatment of hypersaline chemical industry wastewater via the MD process.

Field demonstration of intensified membrane distillation for treating oilfield produced waters from unconventional wells

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.

Integrated Electrocoagulation, Ultrafiltration, Membrane Distillation, and Crystallization for Treating Produced Water.

Produced water (PW) generated from hydraulic fracturing operations was treated using an integrated electrocoagulation, ultrafiltration, membrane distillation, and crystallization process (EC UF MDC). The aim was to determine the viability of this integrated process for maximizing water recovery. The results obtained here indicate that optimizing the various unit operations could lead to increased recovery of PW. Membrane fouling limits all membrane separation processes. A pretreatment step to suppress fouling is essential. Here, removal of total suspended solids (TSS) and total organic carbon (TOC) was achieved by electrocoagulation (EC) followed by ultrafiltration (UF). The hydrophobic membrane used in membrane distillation may be fouled by dissolved organic compounds. Reducing membrane fouling is essential to increase the long-term durability of the membrane distillation (MD) system. In addition, combining membrane distillation with crystallization (MDC) can help reduce scale formation. By inducing crystallization in the feed tank, scale formation on the MD membrane was suppressed. The integrated EC UF MDC process can impact Water Resources/Oil & Gas Companies. Conservation of surface and groundwater is possible by treating and reusing PW. Additionally, treating PW reduces the amount of PW disposed in Class II disposal wells and promotes more environmentally sustainable operations.