Direct Contact Membrane Distillation Research Articles

Definition of Exergetic Efficiency in the Main and Emerging Thermal Desalination Technologies: A Proposal

Increasing attention is being given to reduce the specific energy consumption in desalination processes, which translates into greater use of exergy analysis. An exergetic analysis provides relevant information related to the influence of the efficiency of a single component in the global plant performance and in the exergy cost of the product. Therefore, an exergy analysis identifies the main improvement potentials in a productive thermodynamic process. Related to desalination technologies, many previous papers deal with the calculation of the parameters involved in the exergy analysis, the exergetic efficiency of different processes, plants, and technologies among them. However, different approaches for formulating the exergetic efficiency have been suggested in the literature, often without sufficient understanding and consistency. In this work, these formulations, applied to the main desalination components and processes, are compared and critically reviewed. Two definitions of exergy efficiency are applied to the desalination components of the three main thermal desalination processes (multieffect distillation–thermal vapour compression, multistage flash distillation, and direct-contact membrane distillation). The results obtained for the exergy efficiency of the MED-TVC, MSF, and DCMD processes for the input–output approach are 21.35%, 17.08%, and 1.28%, respectively, compared to the consumed–produced approach that presented 3.1%, 1.58%, and 0.37%, respectively. The consumed–produced approach seems to better fit the thermodynamic behaviour of thermal desalination systems.

Modeling pore wetting in direct contact membrane distillation—effect of interfacial capillary pressure

In this study, we aimed to develop a model for computing direct contact membrane distillation (DCMD) performance, taking into account capillary pressure effects at the liquid–gas interface within membrane pores. We developed a simulation model to investigate how factors such as pore radius, feed/permeate temperature, pressure, and contact angle influenced the distance of liquid intrusion into the pore, the weight flow rate in a single pore, and the temperature at the liquid–gas interface. The model predicted that the permeation rate would decrease with an increase in the feed pressure when the permeate pressure was kept constant and also when the pressure difference between the feed and permeate was kept constant. It also predicted that the permeation rate would increase with an increase in the permeate pressure when the feed pressure was kept constant. The model also indicated that partial pore wetting would be enhanced with an increase in feed pressure when the pore size was as large as 1 μm but would diminish when the pore size was as small as 0.1 μm. According to the model, partial pore wetting diminished with a decrease in the permeate pressure. The model’s predictions were in line with the trends observed in the experimental DCMD flux data by many authors, particularly those regarding the effects of feed and permeate temperature and the effect of contact angle. The model’s predictions were compared with the experimental data recorded in the literature, validating the model’s accuracy.

Enhancing the Permeate Flux Improvement of Direct Contact Membrane Distillation Modules with Inserted S-Ribs Carbon-Fiber Filaments

Three widths of manufacturing S-ribs carbon-fiber filaments acting as turbulence promoters were implemented into the flow channel of direct contact membrane distillation (DCMD) modules to augment the permeate flux improvement in the present study. Attempts to reduce the disadvantageous temperature polarization effect were made by inserting S-ribs turbulence promoters in improving pure water productivity, in which both heat- and mass-transfer boundary layers were diminished due to creating vortices in the flow pattern and increasing turbulence intensity. The temperature polarization coefficient ttemp was studied and found to enhance device performance (less thermal resistance) under inserting various S-ribs carbon-fiber thicknesses and operating both cocurrent- and countercurrent-flow patterns. The permeate fluxes in the DCMD modules with inserted S-ribs carbon-fiber turbulence promoters were investigated theoretically by developing the mathematical modeling equations and were conducted experimentally with various design and operating parameters. The theoretical predictions and experimental results exhibited a great potential to considerably achieve permeate flux enhancement in the new design of the DCMD system. The DCMD module with inserted S-ribs carbon-fiber turbulence promoters in the flow channel could provide a relative permeate flux enhancement up to 37.77% under countercurrent-flow operations in comparisons with the module of using the empty channel. An economic consideration on both permeate flux enhancement and power consumption increment for the module with inserted S-ribs carbon-fiber filaments was also delineated.

Surface functionalization of polytetrafluoroethylene membrane by polydopamine and quaternary ammonium compound for fouling mitigation in membrane distillation of secondary effluent

Considering the worldwide water scarcity issue, membrane distillation (MD) offers a promising solution for producing reclaimed water from secondary effluent generated by municipal wastewater treatment plants. However, prolonged operation of MD systems can result in membrane fouling, which impairs separation efficiency and shortens the membrane's lifespan. To overcome these challenges, novel surface-modified polytetrafluoroethylene (PTFE) membranes have been developed through a combination of polydopamine deposition and quaternary ammonium compound (QAC) grafting (named as PDQ membranes). The objectives of this preparation are to reduce the membrane hydrophobicity, impart anti-adhesive and bactericidal properties, and improve water permeability and antifouling performance in the MD system. In particular, the membrane coated by a QAC solution with the concentration of 40 mM (named as M3 membrane), achieved a flux of 47.0 LMH, surpassing the original PTFE membrane by 11.4%. During the long-term direct contact membrane distillation operation with the secondary effluent, the M3 membrane exhibited significantly superior antifouling capability than the PTFE membrane. Undergoing three runs of the MD process, the flux reduction of M3 was only 38.1%, whereas the flux of original PTFE membrane experienced a 71.4% decline. The PDQ membranes were also capable of providing stable distillate quality (over 40 h). Notably, the M3 demonstrated a high rejection capability, with an impressive removal efficiency of 96.9% for low molecular weight organics and 92.5% for humus-like substances. Additionally, the PDQ membrane exhibited good anti-bioadhesion and bactericidal properties. This study highlights the promising application potential of the PDQ membrane for fouling mitigation in water and wastewater treatment.

Predicting the flux of various volatile fatty acids mixtures in a membrane distillation

This study aims to predict the initial flux of various volatile fatty acids (VFAs) mixtures in direct contact membrane distillation (DCMD), focusing on understanding the interaction between the acids and improving a previous model to better suit the VFAs mixtures. The DCMD experiments were conducted under conditions of feed temperatures of 40, 50, and 60 °C, pH conditions of 3, 4.8, and 6, and VFA concentrations within the feed of 1000–4000 mg/L. The experiments investigated the influence of acids in the VFAs mixture. It was verified whether the ionization fraction of VFAs, even in multi-acid solutions, is proportionate to the flux. The correction coefficient and the overall mass transfer coefficient were introduced to enhance the model that previously used an empirical equation. The correction coefficients were derived, reflecting the interaction between acids and the hydrophobic membrane in the VFAs mixtures. A random factor experiment was conducted to verify the accuracy of the prediction model. Additionally, the sum of each VFA transport can be estimated and expressed using a common water quality measure, chemical oxygen demand. The modeling work can provide further insights into the relationship among the flux, ionization, hydrophobicity, and interactions among acids.

Facile design of amphiphobic PVDF membranes utilizing synergy of pore structure and surface fluorination: A demonstration in membrane distillation

Amphiphobic membranes have attracted much attention in membrane distillation (MD) applications, due to its potential in simultaneously resisting membrane wetting and fouling when treating complex wastewater. The current amphiphobic membranes often require non-trivial design of multilevel re-entrant structure. Here we proposed a new class of amphiphobic membranes without multilevel re-entrant surface, by creating a composite poly(vinylidene fluoride)/polyvinyl alcohol/SiO2 membrane with asymmetric structure and well-controlled small surface pores via the NTIPS method, followed by direct fluorination via chemically binding the –OH of polyvinyl alcohol and low surface energy moieties 1H,1H,2H,2H-perfluorodecyl-triethoxysilane, assisted by 3-aminopropyltriethoxysilane and trimesoyl chloride. The amphiphobic membrane showed superior liquid entry pressure above 5 bar with various simulated saline feeds containing surfactants and organic pollutants. The amphiphobic membrane demonstrated robust anti-wetting and anti-fouling performance through a series of 24-h direct contact MD experiments using the above feeds, presenting stable water flux and high rejection, e.g., flux of 50.6 kg/(m2·h) and rejection >99.9 % with feed containing 3.5 wt% NaCl, 1 mM FA, and 2 mM SDS. The results demonstrated the fabrication of robust amphiphobic membrane through simple procedure utilizing the synergy between pore structure and surface chemistry, inspiring more efforts to design adequate membranes for treating complex wastewater.

Reliable and efficient membrane processes for clean and sustainable production of fresh water from saline waste

AbstractBACKGROUNDIncreasing water scarcity due to growing demand highlights the urgency for innovative solutions. Seawater desalination is emerging as a crucial answer, with direct contact membrane distillation (DCMD) emerging as a promising technology in this context. In particular, membranes produced from ionic liquids constitute a well‐established avenue for the preparation of membranes by non‐solvent phase inversion (NIPS) in the field of desalination.RESULTSThe tests carried out as part of the DCMD, using PVDF membranes modified with the IL MPF6 and TBAPF6 synthesized during this study, in particular those containing 50% TBAFP6, demonstrate a notable improvement in hydrophobicity and porosity (121,48°, 79%). The results suggest that the flux of the PVDF‐TBAPF6 membrane shows a clear improvement of 300% compared to the support alone. Various parameters such as salinity, temperature and flow rate were examined, highlighting their impact on membrane performance. The low energy parameters (Ea = 43,36 Kj/mol, ΔH≠ = 40,86 Kj/mol) indicate a diffusion mechanism of vapor molecules, occurring by successive jumps through the IL interaction sites.CONCLUSIONExtensive experimental investigations have carefully anticipated the permeate flow in DCMD, aiming to efficiently extract pure water. DCMD is positioned as a promising technology for desalination and treatment of BRINE solutions. Therefore, this study can make a significant contribution to the expansion of DCMD by facilitating the prediction and optimization of operational parameters, thereby paving the way for expanded application of this technology.This article is protected by copyright. All rights reserved.

A cost-effective and high efficient Janus membrane for the treatment of oily brine using membrane distillation.

Membrane distillation technology could utilize low-grade heat to desalinate brine, but the membrane material often suffers from disadvantages of low permeation flux and weak robustness to contaminants. To address these issues, the commercial polytetrafluoroethylene (PTFE) membrane was modified by cost-effective chemicals of tannic acid and (3-Aminopropyl)-triethoxysilane (APTES) to construct hydrophilic/underwater superoleophobic nano-rough structures on the surface to enhance its flux and oil-fouling resistance in direct contact membrane distillation (DCMD). The results show that a high underwater oil contact angle of 180° is observed to the membrane surface due to the rough nanostructures functionalized by abundant hydroxyl groups. Despite the additional mass transfer resistance provided by the rough nanostructures, the flux was increased noticeably. This is mainly attributed to the strong interactions between the abundant hydroxyl groups of hydrophilic layer surface and water molecules, leading to a part of free water (FW) staying at intermediate transition state (IW). The mass transfer resistance of the hydrophilic layer itself is reduced as a consequence of decreased evaporation enthalpy of water, thereby increasing the flux. Moreover, while the flux of the pristine membrane is reduced by 84.18%, the flux of Janus membrane remains the same when treating mineral oil brine emulsions with oil concentration up to 1500 ppm in comparison with the result for 35 g/L brine solution, indicating that the Janus membrane is safe from the oil contamination. Our work provides a fine guidance for membrane distillation to treat high oily brine.&#xD.

Investigation of direct contact membrane distillation (DCMD) performance using CFD and machine learning approaches

Direct Contact Membrane Distillation (DCMD) is emerging as an effective method for water desalination, known for its efficiency and adaptability. This study delves into the performance of DCMD by integrating two powerful analytical tools: Computational Fluid Dynamics (CFD) and Artificial Neural Networks (ANN). The research thoroughly examines the impact of various factors, such as inlet temperatures, velocities, channel heights, salt concentration, and membrane characteristics, on the process's efficiency, specifically calculating the water vapor flux. A rigorous validation of the CFD model aligns well with established studies, ensuring reliability. Subsequently, over 1000 data points reflecting variations in input factors are utilized to train and validate the ANN. The training phase demonstrated high accuracy, with near-zero mean squared errors and R2 values close to one, indicating a strong predictive capability. Further analysis post-ANN training shed light on key relationships: higher membrane porosity boosts water vapor flux, whereas thicker membranes reduce it. Additionally, it was detailed how salt concentration, channel dimensions, inlet temperatures, and velocities significantly influence the distillation process. Finally, a mathematical model was proposed for water vapor flux as a function of key input factors. The results highlighted that salt mole fraction and hot water inlet temperature have the most effect on the water vapor flux. This comprehensive investigation contributes to the understanding of DCMD and emphasizes the potential of combining CFD and ANN for optimizing and innovating water desalination technology.

Gamma-irradiated janus electrospun nanofiber membranes for desalination and nuclear wastewater treatment

This study presents the fabrication of double-layer electrospun nanofibrous membranes (DL-ENMs) using polyvinylidene fluoride (PVDF) and polyether sulfone (PES) based polymers with different degrees of hydrophilicity (PES, sulfonated PES, and PES with hydroxyl terminals). A comparative analysis was carried out with single-layer electrospun nanofiber membranes (SL-ENM) with a total thickness of about 375 μm. Using feed solutions, including sodium chloride, sodium nitrate, and simulated nuclear wastewater (SNWW), the performance of DL-ENMs was evaluated for desalination and radionuclide decontamination by direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) techniques. The results showed that DL-ENMs, especially those incorporating a sulfonated PES-based hydrophilic layer, exhibited superior permeate fluxes, reaching values of 72.72 kg/m2.h and 73.27 kg/m2.h in the DCMD using aqueous feed solutions of NaCl and NaNO3, respectively, and 70.80 kg/m2.h and 41.96 kg/m2.h using aqueous feed solutions of SNWW in DCMD and AGMD, respectively. Both SL-ENMs and DL-ENMs exhibited high rejection efficiencies and decontamination factors for the feed solutions (>99.9%). In addition, the prepared ENMs were exposed to gamma radiation to evaluate their applicability in real-life applications. The result of irradiation revealed the negative impact of gamma radiation on the fluorine content of PVDF which could be a critical point in using PVDF as a hydrophobic material for decontaminating nuclear wastewater by membrane distillation.

Mass Transfer Mechanism Within Commercial PTFE Membranes In Spacer-Filled Direct Contact Membrane Distillation

The mass transfer mechanism within commercial PTFE membrane with various nominal pore sizes in spacer-filled direct contact membrane distillation (DCMD) was determined. Mass fluxes and membrane permeability (MP) values for each commercial PTFE membrane were experimentally measured. The MP values increased insignificantly with 2.3% and 4% when the inlet temperature at feed side rose from 400C to 500C in different membrane pore sizes. All investigated mass transfer models except from Dusty Gas model were good enough to simulate the mass transfer inside smaller membrane pore sizes (0.22 µm, and 0.45 µm). Compared to combined diffusion model, the predicted mass fluxes using the overall mass transfer model including the contribution of Poiseuille flow obtained better agreement with experimental results for larger membrane pore size (1 µm). The mean absolute percentage error (MAPE) values for combined diffusion model were up to 16.5% compared with the Ding et al. model or Schofield et al. model (under 3%). Regarding the root mean square error (RMSE), the combined diffusion model obtains larger values than the mass transfer model considering the Poiseuille flow contribution. Consequently, the contribution of Poiseuille flow in mass transfer mechanism within smaller PTFE membrane pores (0.22 µm, and 0.45 µm) could be ignored, however, the contribution of Poiseuille flow to the overall mass transfer should be included in case of larger membrane pores (1 µm), or the case of applied transmembrane hydrostatic pressure.

Nanofiber membranes immobilized with in-situ grown nanoparticles for enhanced wetting resistance in direct contact membrane distillation

Immobilizing nanoparticles (NPs) onto the hydrophobic nanofiber membrane surface is an effective method to enhance its resistance to pore wetting in membrane distillation (MD) due to construction of a hierarchical structure. However, loading NPs onto the fabricated membrane through post-treatment techniques (e.g., electrospray, physical vapor deposition etc.) results in agglomeration of NPs and their weak attachment with membrane surface. To address this issue, we utilize precipitation and crystallization methods to achieve in-situ growth of zinc oxide (ZnO) NPs onto nanofiber surface for intensifying their interaction. Morphological characterization demonstrated that the size and amount of in-situ grown ZnO NPs could be controlled by varying reaction time and concentration of precipitation agent. Furthermore, the resultant nanofiber membrane with higher contact angles (163°) showed stable water flux and effective salt rejection in presence of surfactant and oil. Finally, the kinetics of wetting progression monitored by ultrasonic time-domain reflectometry (UTDR) further confirmed that the early partial wetting induced by surfactants was significantly restrained owing to the hierarchical structure generated by the in-situ grown ZnO NPs. This study suggested the modified nanofiber membrane presented outstanding wetting resistance to low-surface-tension foulants and promise for desalination in MD.

Membrane hydrophobicity enhanced by non-solvent induced separation strategy for improving membrane distillation performance

Development of high-performance hydrophobic layer using green and economic method is still urgently on demand for wide applications of membrane distillation (MD). In this study, a novel Janus membrane was prepared by electrospinning polystyrene with the water addition on the surface of hydrophilic electrospun nanofiber substrate. With increasing water content to 3wt%, the hydrophobic layer is completely converted to be nanofiber-dominate morphology that could be beneficial for water vapor permeation during MD process. The surface roughness, water contact angle value and porosity of the hydrophobic layer are enhanced by the water addition, and the optimized Janus membrane with the hydrophobic layer prepared at the water content of 2wt% could achieve a high water flux of 33.1L/m2h and superior salt rejection of >99.9% when 3.5wt% NaCl solution was used as the feed solution. The as-prepared Janus membrane shows better performance stability and reusability than the control membrane (without the water addition) within the 24-h continuous operation duration. Our work demonstrates that the proper water addition could be used as a green strategy for fabricating efficient electrospun nanofiber membranes for the direct contact membrane distillation (DCMD) processes.

Novel integration of thermoelectric distiller with direct contact membrane distillation

A thermoelectric distiller (TED) integrated with a direct contact membrane distillation (DCMD) unit was proposed and numerically investigated. The mathematical models of the hybrid TED--–DCMD system were developed and validated. In the proposed hybrid system, the TED provides the heating demand of the DCMD desalination unit in four novel configurations of TED-DCMD integration. The first configuration integrates the TED-DCMD by adding a DCMD heat exchanger coil inside the condensation tank of a TED, while the second configuration involves two TED condensation tanks with each tank containing a DCMD heat exchanger coil. The third configuration also consists of two TED tanks with an external heat exchanger where thermal energy from the TED produced water is transferred to the DCMD feed stream. The fourth configuration is a modification of the second configuration with a thermal recovery from TED produced water for inlet feed water preheating. To investigate the performance (distillate productivity, specific energy consumption, coefficient of performance, and ratio of TED productivity) of each integrated TED-DCMD configuration, the effects of different operating parameters such as DCMD feed flow rate, TEM current, number of TEMs, and TED produced water temperature were examined. Findings indicated that the third configuration is the most energy efficient, with specific energy consumption (SEC) reaching a minimum value of 217 kWh/m3 at low current operation of 2.1 A, and feed flow rate of 4.0 L/min for 8.0 TEMs in the TED. A maximum freshwater productivity and COPh of 2.74 kg/s and 3.24, are attained by the 4th and 3rd configurations, respectively. Results also indicated that elevating the current input encourages higher water productivity. Meanwhile, higher values of SEC and water productivity are attained when operating TED at saturation temperature.

Understanding Ammonia and Water Transport in Direct Contact Membrane Distillation toward Selective Ammonia Recovery

Understanding Ammonia and Water Transport in Direct Contact Membrane Distillation toward Selective Ammonia Recovery

Evaluating the efficiency of modified hydrophobic PVDF membrane for the removal of PFOA substances from water by direct contact membrane distillation

This study addresses the global issue of the contamination of water resources by per- and poly-fluoroalkyl substances (PFAS). PFAS are notoriously difficult to remove due to their resilient alkyl-fluorinated chains. We examined the potential of hydrophobic PVDF membranes in direct contact membrane distillation (DCMD) to eliminate perfluorooctanoic acid (PFOA) from Water. For desalination, both commercial and custom-made PVDF membranes exhibited a permeate flux of approximately 13 LMH, with salt rejections of 98.39 % and 99.95 %, respectively. In the case of PFOA removal, the fabricated PVDF membrane outperformed its commercial counterpart. It boasted an initial permeate flux of 16 LMH and a PFAS rejection of 95.8 %, compared to the commercial membrane's 13 LMH and 67.31 %. Furthermore, the custom membrane exhibited superior resistance to fouling, experiencing less flux decline. Employing response surface methodology (RSM), we identified the optimal combination of feed concentration (30 ppm), (60 °C), and flow rate (1.5 LPM) to yield a flux of 9 LMH and a PFOA rejection of 95.41 %. Feed temperature emerged as the most influential factor in DCMD performance. This study offers a novel approach to concentrating and removing emerging contaminants from wastewater and highlights the efficacy of tailored membrane technology in addressing pressing environmental challenges.

Performance evaluation of novel superhydrophobic electrosprayed-electrospun nanofibrous membranes for water recovery using direct contact membrane distillation

Direct contact membrane distillation is a reliable way to produce fresh water from challenging wastewater streams. In this study, a novel electrosprayed-electrospun nanofibrous membranes (EENFMs) were fabricated using a two-step approach to reclaim water from hypersaline streams and wastewater containing trace organic contaminants. The synthesized SBA-15 was modified using fluoroalkylsilane and electrosprayed onto an electrospun PVDF-co-HFP support layer to form the EENFMs. The superhydrophobic/omniphobic membrane possessed multidirectional micro-nano scale roughness with a water contact angle of ≃ 154˚ and a low contact angle hysteresis of ≃ 6˚. The EENFM was challenged with synthetic feed solutions containing 3.5, 7.0, and 10.5 wt% NaCl and was found to exhibit stable fluxes and > 99% rejection. The M2′ membrane exhibited a steady flux of ∼ 6.5 Lm−2h−1 and permeate conductivities < 50 μScm−1 for up to 3600 min of operation for a feed solution of 10.5 wt% NaCl solution. M2′ proved to be suitable to recover water from wastewater feeds containing pesticides such as imidacloprid, carbendazim, chlorpyrifos, lambda-cyhalothrin, and quinalphos (total feed organic carbon content ∼ 350 ppm) and produced a stable flux of 8.5 Lm−2h−1 with an organic carbon rejection > 98%. Alkaline wash using sodium hydroxide was found to be efficient in recovering membrane performance and alleviating membrane fouling for 3 cycles of operations (8 h each) compared to the DI water wash. This regeneration method proved efficient, with ∼ 100% recovery of initial flux and surface superhydrophobicity. The present study indicates that these EENFMs are potential candidates for further evaluation to improve water recovery from industrial brines.

A computational fluid dynamics study on TPMS-based spacers in direct contact membrane distillation modules

Feed spacers are incorporated in membrane modules to enhance fluid mixing, thereby enhancing membrane flux. Previous experimental work showed that triply periodic minimal surfaces (TPMS)-based spacers induce significant improvements in membrane distillation (MD) performance, which was attributed to the suppression of membrane boundary layer, reducing heat and mass transfer resistance. To corroborate those findings, in this study, we assess the performance of TPMS spacers in direct contact MD (DCMD) modules using computational fluid dynamics (CFD). Results showed that the Fischer-Koch S TPMS spacer topology achieved twice the flux of the empty channel case and exhibited a 13 % increment in flux compared to the net-type spacer, but this improvement was accompanied by a higher pressure drop in the feed channel. Therefore, a normalized power ratio (NPR) was used to evaluate the overall performance of spacers. For Reynold number (Re) ranging between 200 and 1200, Fischer-Koch S spacer had a 12 % improvement in NPR compared to the net-type spacer and resulted in higher shear stress near the membrane surface, indicating a promising mean for mitigating fouling in membrane distillation. This research highlights the importance of utilizing novel spacers in membrane distillation and showcases the power of CFD tools in optimizing the process.

Experimental investigation of varying design parameters on the production rate and temperature polarisation of a DCMD system

Much of the research in the analysis of Temperature polarisation (TP) and the productivity of a membrane distillation (MD) system tends to concentrate on operational conditions. However, substantial enhancements in permeate flux can be realised through the incorporation of fundamental design modifications. This research showed that TP can be successfully mitigated almost to a level of non-existence, by manipulating the module orientation and flow channel height of an in-house designed direct contact membrane distillation (DCMD) system. Notably, at higher flow channel heights, changing the module orientation from the default horizontal position with the feed side on top (FST) to a sideway orientation led to a remarkable 90% increase in the permeate flux of the DCMD module. Permeate side on top (PST) and sideways orientations performed significantly better than FST for larger channel heights, while at low channel heights, the improvement was slight. Temperature measurements proved that thermal convective currents and secondary flows played a vital role in assisting or opposing TP and cannot be disregarded when investigating the hydrodynamics of a DCMD system. The impact of flow directions was insignificant with different channel heights, while the proximity of the flow inlets played a pivotal role in shaping the temperature profiles along the membrane.

Engineered eco-friendly composite membranes with superhydrophobic/hydrophilic dual-layer for DCMD system

Considerable advancements have been made in the development of hydrophobic membranes for membrane distillation (MD). Nonetheless, the environmentally responsible disposal of these membranes poses a critical concern due to their synthetic composition. Herein, an eco-friendly dual-layered biopolymer-based membrane was fabricated for water desalination. The membrane was electrospun from two bio-polymeric layers. The top hydrophobic layer comprises polycaprolactone (PCL) and the bottom hydrophilic layer from cellulose acetate (CA). Additionally, silica nanoparticles (SiO2 NPs) were electrosprayed onto the top layer of the dual-layered PCL/CA membrane to enhance the hydrophobicity. The desalination performance of the modified PCL-SiO2/CA membrane was compared with the unmodified PCL/CA membrane using a direct contact membrane distillation (DCMD) unit. Results revealed that silica remarkably improves membrane hydrophobicity. The modified PCL-SiO2/CA membrane demonstrated a significant increase in water contact angle of 152.4° compared to 119° for the unmodified membrane. In addition, PCL-SiO2/CA membrane has a smaller average pore size of 0.23 ± 0.16 μm and an exceptional liquid entry pressure of water (LEPw), which is 3.8 times higher than that of PCL/CA membrane. Moreover, PCL-SiO2/CA membrane achieved a durable permeate flux of 15.6 kg/m2.h, while PCL/CA membrane showed unstable permeate flux decreasing approximately from 25 to 12 kg/m2.h over the DCMD test time. Furthermore, the modified PCL-SiO2/CA membrane achieved a high salt rejection value of 99.97% compared to a low value of 86.2% for the PCL/CA membrane after 24 h continuous DCMD operation. In conclusion, the proposed modified PCL-SiO2/CA dual-layer biopolymeric-based membrane has considerable potential to be used as an environmentally friendly membrane for the MD process.