Membrane Distillation Research Articles

Sustainable apple juice concentration: A fusion of pasteurization and membrane distillation

Apple juice concentrate offers significant advantages in terms of transportation and storage. However, the conventional concentration method is known for its high energy consumption and has been observed to negatively affect the quality of the apple juice. This study investigated an efficient and sustainable process combining pasteurization and membrane distillation (MD) for apple juice concentration. The effects of operational conditions on flux, membrane fouling control, product quality and energy consumption were evaluated. When a single MD was used as a pre-concentration method, apple juice could be concentrated by more than 3.65 times. The final product with a total soluble solids (TSS) content of 60 °Brix after VE re-concentration has better quality, especially in terms of acidity and total phenols content. The flux recovery rate of hydraulic washing can reach more than 96 %. The MD pre-concentration process used uncooled pasteurized apple juice as the feed reduced the energy consumption by 60.6 % compared with thermal concentration.

Performance of capacitive deionizing membrane distillation (CDIMD) process for the organic sewage treatment and how operating parameters can affect it

To solve the fouling issue of traditional membrane distillation (MD) technique, a newly-designed hybrid purification system integrating capacitive deionization (CDI) with MD technology was established for the organic sewage treatment in this study, namely capacitive deionizing membrane distillation (CDIMD) technology. Complexes formation via cross-linking among protein, divalent cations, and polysaccharide, an archcriminal inducing MD fouling, was remarkably alleviated in the CDIMD system considering that negatively-charged organics were clearly divided away from those divalent cations in an electric field circumstance. The CDIMD performance was deeply explored in this study focusing on the impact mechanisms of core operational parameters. An appropriate increment of feed temperature (60–65 °C) and feed flow velocity (15.72–17.82 mm/s) contributed to the anti-fouling performance of CDIMD. Considering the side reactions at voltage >1.2 v, setting working voltage at around 1.2 v seemed to be optimal for CDIMD operation. With an overall consideration of pure water production and anti-fouling performance, a properly thicker CNTs layer (40–60 μm) efficiently enhanced the fouling mitigation of CDIMD. A frequent switching of electric field direction (9/1 min) facilitated the timely regeneration of electrode and composite membranes, accordingly promoting a reliable purification of organic wastewater by CDIMD technique.

Hydrophobic C60-modified PVDF membrane with micro-nano structures for mitigating CaSO4 scaling in direct contact membrane distillation (DCMD)

Membrane scaling is a non-negligible problem for membrane distillation (MD) in the treatment of high-salinity wastewater (e.g., calcium sulfate and calcium carbonate). In this study, fullerene (C60) was adhered to a polyvinylidene fluoride (PVDF) membrane using a polydimethylsiloxane (PDMS) solution to create a micro-nano structure, fabricating the C60/PDMS-PVDF membrane. This membrane was then re-immersed in a PDMS solution to further reinforce the C60 nanoparticles on the surface, forming the PDMS/C60/PDMS-PVDF membrane. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the membrane surface morphology. Fourier transform infrared (FT-IR) was used to explore the membrane chemical composition. Liquid entry pressure (LEP) and water contact angle (WCA) measurements were employed to assess the membrane wettability. The results showed that C60-modification created the micro-nano structure on the membrane surface. The WCA of the PVDF membrane was 112.7 ± 2.4°, with a sliding angle far greater than 90°, whereas the PDMS/C60/PDMS-PVDF membrane exhibited a WCA of 147.9 ± 3.2° and a sliding angle of 6.3°. Compared to the virgin PVDF membrane, the LEP value of the PDMS/C60/PDMS-PVDF membrane increased from 68.4 ± 2.7 kPa to 87.2 ± 3.3 kPa. In direct contact membrane distillation (DCMD), a CaSO4 solution (2 g/L) was used to test the membrane performance. After 48 hours of operation, the flux of the PDMS/C60/PDMS-PVDF membrane remained at approximately 3.57 kg/(m2·h), and the salt rejection rate was over 99.96 %. This could be attributed to the C60 modification forming a micro-nano structure on the membrane surface, which trapped an air layer. This air layer could reduce the contact area between the crystal and the membrane, decrease nucleation probability, and shorten the residence time of liquid on the membrane surface. Additionally, the PDMS/C60/PDMS-PVDF membrane exhibited superior stability during the ultrasonic destruction experiment due to the encapsulation of PDMS. In summary, a novel hydrophobic membrane with a micro-nano structure was fabricated through C60 modification, offering superior anti-scaling properties and stability in treating high-salinity wastewater.

Influence of photothermal nanomaterials localization within the electrospun membrane structure on purification of saline oily wastewater based on photothermal vacuum membrane distillation

Today, synergistic combination of special nanomaterials (NMs) and electrospinning technique has emerged as a promising strategy to address both water scarcity and energy concerns through the development of photothermal membranes for wastewater purification and desalination. This work was organized to provide a new perspective on membrane design for photothermal vacuum membrane distillation (PVMD) through optimizing membrane performance by varying the localization of photothermal NMs. Poly(vinylidene fluoride) omniphobic photothermal membranes were prepared by localizing graphene oxide nanosheets (GO NSh) (1) on the surface (0.2 wt%), (2) within the nanofibers structure (10 wt%) or (3) in both positions. Considering the case 1, after 7 min exposure to the 1 sun intensity light, the highest temperature (∼93.5 °C) was recorded, which is assigned to the accessibility of GO NSh upon light exposure. The case 3 yielded to a small reduction in surface temperature (∼90.4 °C) compared to the case 1, indicating no need to localize NMs within the nanofibers structure when they are localized on the surface. The other extreme belonged to the case 2 with the lowest temperature of ∼71.3 °C, which is consistent with the less accessibility of GO NSh during irradiation. It was demonstrated that the accessibility of photothermal NMs plays more pronounced role in the membrane surface temperature compared to the light trapping. However, benefiting from higher surface temperature during PVMD due to enhanced accessibility of photothermal NMs is balanced out by decrease in the permeate flux (case 1: 1.51 kg/m2 h and case 2: 1.83 kg/m2 h) due to blocking some membrane surface pores by the binder. A trend similar to that for flux was also followed by the efficiency. Additionally, no change in rejection was observed for different GO NSh localizations.

Hybrid and boosted structures of multi-effect mechanical vapor compression for enhanced water production

Retrofitting the multi-effect mechanical vapor compression (MEMVC) process for water desalination through hybridization with membrane distillation (MD) and/or employing vapor boosting mechanism is investigated in this work. The impact of using more than one mechanical compression, their respective locations and flow rates is investigated. Integration of parallel feed scheme of MEMVC with MD owned the maximum MD water production compared to the hybrid forward feed and parallel cross feed arrangements that can reach up to 54 % enhancement. However, the contribution of the MD production to the total production of the hybrid system does not exceed 17 %. Recycling the vapor of the last three effects to boost the first effect indicated a positive impact. The MEMVC with parallel feed can achieve 134 % water production enhancement with 26 % increase in the specific energy consumption over the nominal condition, i.e., when only the steam of the last effect is recycled to the first effect. Recycling the vapor of the penultimate effect to boost the second effect illustrated superior performance compared to that of boosting the first effect. It is found that the MEMVC with forward feed can attain 61 % improvement in water production with 14 % reduction in the specific energy consumption.

Investigations of nanomaterial-based membranes for efficient removal of contaminants from wastewater via membrane distillation: a critical review

The requirement for wastewater treatment is paramount in ensuring environmental sustainability and safeguarding public health. As industrialization and urbanization accelerate, the volume of wastewater generated continues to increase, containing a diverse range of pollutants and contaminants. Untreated wastewater poses serious threats to ecosystems, water bodies, and human communities, leading to pollution, waterborne diseases, and ecological imbalances. Effective wastewater treatment becomes essential to mitigate these adverse effects by removing or reducing pollutants before discharge into natural water sources. This process helps to preserve water quality, protect aquatic life, and maintain the overall health of ecosystems. Membrane distillation (MD) has emerged as a promising technology for wastewater treatment, offering an innovative approach to address the challenges associated with conventional treatment methods. In MD, a hydrophobic membrane serves as a selective barrier, allowing water vapor to pass through while preventing the passage of contaminants. This paper offers an extensive overview of the latest advancements in nanotechnology and membrane distillation applied in wastewater treatment. We will delve into different types of nanomaterials that have been used to enhance the properties of MD membranes, such as nanocomposites, nanoparticles, and nanofiber membranes. We also explore the mechanisms by which these nanomaterials improve the separation efficiency, anti-fouling properties, and durability of MD membranes. Additionally, we highlight the potential of hybrid membranes that combine different types of nanomaterials for further improving the performance of MD in wastewater treatment. We provide examples of recent studies that have investigated the use of hybrid membranes, including carbon nanotube-graphene oxide hybrid membranes, nanocomposite nanofiber membranes, and silver nanoparticle-embedded membranes. We also identify some areas for future research and development, such as the scale-up and commercialization of nanotechnology-based MD systems. In summary, this review paper highlights the potential of nanotechnology to enhance the performance of MD in wastewater treatment, leading to improved water quality and a cleaner environment.

Au-TiO2 nanoparticles enabled catalytic treatment of oil and gas produced water in slurry and vacuum membrane distillation systems

Produced water (PW) treatment and reuse provide a promising alternative to address freshwater scarcity and reduce the environmental impacts associated with PW disposal. Efficient treatment of PW is challenging due to its complex matrix and hypersalinity. This study developed innovative gold-doped titania (Au-TiO2) nanoparticles to enable effective treatment of PW collected from the Permian Basin with salinity of ∼118 g/L. The mechanisms of removing organics and ammonia in PW in slurry and vacuum membrane distillation (VMD) systems were investigated via thermocatalysis, photocatalysis, and photo-thermocatalysis. Photocatalysis and photo-thermocatalysis were found more effective for organic removal than thermocatalysis. A baseline study using glucose as a representative of easily degradable organic carbon showed that thermocatalysis and photocatalysis mineralized 23.2 % and 93.1 % glucose, respectively. However, photo-thermocatalysis and thermocatalysis degraded only 17.4 % and 7.5 % dissolved organic carbon (DOC), and 56.2 % and 49.2 % NH3-N in PW, respectively. Au-TiO2 coating on ceramic membranes improved the distillate flux of photo-thermocatalytic membrane distillation (PMD) compared to no catalysts coating in VMD (7.14 versus 6.75 kg per hour per m2). Both PMD and VMD rejected >99.9 % of salts and >96 % DOC, and PMD had slightly higher DOC and salt removal rates. In contrast, normalized permeate flux using pristine membranes (hydrophobically modified without catalysts coating) decreased to zero after 29 h of operation while normalized flux with TiO2-coated membranes under UV on and UV off were 57.5 % and 53.7 % on average, which is much lower than that with Au-TiO2 coated membranes in both UV on (91.3 %) and UV off (88.1 %) cases, indicating Au-TiO2 coating significantly improved membrane anti-fouling propensity and durability during treatment of complex PW. Targeted analysis of three groups of petroleum hydrocarbons and 70 volatile organic compounds showed that only 2-butanone and acetone were detected in the distillates with removal efficiencies of 80 % for 2-butanone in both PMD and VMD, and acetone was removed by 75.4 % in PMD and 69.2 % in VMD. Au-TiO2 nanoparticles demonstrated excellent catalytic performance for PW treatment in slurry and immobilized PMD systems.

Efficiency increment of CFD modeling by using ANFIS artificial intelligence for thermal-based separation modeling

This study presents a comprehensive analysis of predicting the temperature in a vacuum membrane distillation (VMD) process. The simulation was carried out via computational fluid dynamics (CFD) as well as machine learning. CFD was performed for obtaining temperature distribution in the feed solution, and the calculated temperature was used for training several machine learning models. The dataset comprises over 13,000 observations, which provide a rich source for modeling complex relationships. Three sophisticated regression models were employed: Adaptive Neuro-Fuzzy Inference System (ANFIS), Kernel Ridge Regression (KRR), and Multi-Layer Perceptron (MLP). ANFIS was chosen for its hybrid nature, combining neural networks and fuzzy logic, effectively capturing intricate non-linear relationships in data. ANFIS performance in fitting the data was compared with the other models. Hyper-parameter optimization for these models was conducted using the Tabu Search algorithm to ensure optimal performance. The ANFIS model demonstrated superior performance with an R2 score of 0.9964513 on the training set and 0.9964507 on the test set, alongside a MSE of 0.037655 and a MAE of 0.168272. The robustness of ANFIS was further confirmed by a 3-fold cross-validation mean R2 score of 0.9964579 and a standard deviation of 3.3619616e−05.

Fouling Reduction and Thermal Efficiency Enhancement in Membrane Distillation Using a Bilayer-Fluorinated Alkyl Silane-Carbon Nanotube Membrane.

In this study, we report the robust hydrophobicity, lower fouling propensity, and high thermal efficiency of the 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS)-coated, carbon nanotube-immobilized membrane (CNIM) when applied to desalination via membrane distillation. Referred to as FAS-CNIM, the membrane was developed through a process that combined the drop-casting of nanotubes flowed by a dip coating of the FAS layer. The membranes were tested for porosity, surface morphology, thermal stability, contact angle, and flux. The static contact angle of the FAS-CNIM was 153 ± 1°, and the modified membrane showed enhancement in water flux by 18% compared to the base PTFE membrane. The flux was tested at different operating conditions and the fouling behavior was investigated under extreme conditions using a CaCO3 as well as a mixture of CaCO3 and CaSO4 solution. The FAS-CNIM showed significantly lower fouling than plain PTFE or the CNIM; the relative flux reduction was 34.4% and 37.6% lower than the control for the CaCO3 and CaCO3/CaSO4 mixed salt solution. The FAS-CNIM exhibited a notable decrease in specific energy consumption (SEC). Specifically, the SEC for the FAS-CNIM measured 311 kwh/m3 compared to 330.5 kwh/m3 for the CNIM and 354 kwh/m3 for PTFE using a mixture of CaCO3/CaSO4. This investigation underscores the significant contribution of the carbon nanotubes' (CNTs) intermediate layer in creating a durable superhydrophobic membrane, highlighting the potential of utilizing carbon nanotubes for tailored interface engineering to tackle fouling for salt mixtures. The innovative design of a superhydrophobic membrane has the potential to alleviate wetting issues resulting from low surface energy contaminants present in the feed of membrane distillation processes.

Pre-concentration of lithium-rich brine via direct contact membrane distillation: Conditional analysis

The objective of this study is to employ membrane distillation (MD) for the preconcentration of lithium from Salt Lake. Considering the intricate correlation between the physical properties of the solution and the operational conditions, a theoretical estimation and verification of the mass transfer coefficient in MD process are conducted using pure water. Furthermore, a comparison is made on the effects of different cross flow velocities (CFVs) and feed temperature (FT) on MD concentration for lithium chloride solutions ranging from 0.3 g/L to 5 g/L, as well as simulated Salt Lake brine. When CFVs are set at 350 mL/min, after 600 mins of MD treatment, a permeation flux of 23.91 kg/(m2·h) is achieved for a 2 g/L lithium chloride solution. In addition, when 0.3 g/L lithium chloride solution is treated by MD for 600 mins and the FT is increased from 40℃ to 60℃, the permeate flux increases linearly from 13.21 kg/(m2·h) to 42.27 kg/(m2·h), an increase of up to 220 %, and the reject rate reaches more than 99 % at this time. This study demonstrates that employing MD process in preconcentrating lithium from Salt Lake can effectively extract valuable lithium resources through downstream processes.

Impact of surfactants used in oil and gas extraction on produced water treatment by membrane distillation

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

Decentralized biomass-based Brayton-Stirling power cycle with an air gap membrane distiller for supplying electricity, heat and clean water in rural areas

Ensuring access to essential services, such as clean water and electricity, is a key challenge for achieving sustainable development goals in rural areas. This study proposes a novel Brayton-Stirling combined cycle-based cogeneration system for utilizing locally available biomass waste to generate both electricity and clean water. The system employs an externally fired gas turbine, a Stirling engine, and an air–gap membrane distiller. Four operation modes—parallel-powered, fully-fired, straightforward, and by-pass—were modeled for their efficiency and output. Four operation modes can be switched by two three-way valves. Sunflower husk, identified as the most effective biomass source, enabled the system to achieve up to 160 kW of electricity and 0.7 m3/h of freshwater. The electrical and exergy efficiencies of the system peaked in the parallel-power mode, offering a practical solution for enhancing rural sustainability. Moreover, the by-pass mode maximized water production, highlighting its effectiveness in addressing water scarcity along with energy generation. Through a case study, the cogeneration system has demonstrated its capability in satisfying both rural electricity and water demands throughout the day by controlling the combination of different operation modes and parameters. Therefore, it provides a promising solution for advancing rural electrification and water purification in rural areas.

Glass capillary array supported membrane evaporator balancing heat and water management for double-side solar-driven interfacial evaporation

Efficient heat and water management are two important aspects for boosting solar-driven interfacial evaporation. Here, we develop a glass capillary array supported membrane evaporator (GCSE) to simultaneously achieve heat and water management. In the GCSE, a membrane at top regions enables photothermal conversion, and a glass capillary array at bottom regions serves as both water and heat management. The balance of heat and water management can be readily controlled by adjusting the number and height of glass capillary array. Moreover, the exposed bottom surface of GCSE further utilizes extra evaporation surface to boost evaporation. As a result, a high evaporation rate of 2.06 kg m−2 h−1 with an efficiency of 98.6% under 1 sun is achieved. Furthermore, the GCSE also exhibits potential applications in oil/water emulsion purification and seawater desalination.

Ammonia recovery via direct contact membrane distillation: Modeling and performance optimization

Ammonia recovery from wastewater has positive environmental benefits, avoiding eutrophication and reducing production energy consumption, which is one of the most effective ways to manage nutrients in wastewater. Specifically, ammonia recovery by membrane distillation has been gradually adopted due to its excellent separation properties for volatile substances. However, the global optimization of direct contact membrane distillation (DCMD) operating parameters to maximize ammonia recovery efficiency (ARE) has not been attempted. In this work, three key operating factors affecting ammonia recovery, i.e., feed ammonia concentration, feed pH, and DCMD running time, were identified from eight factors, by a two-level Plackett-Burman Design (PBD). Subsequently, Box-Behnken design (BBD) under the response surface methodology (RSM) was used to model and optimize the significant operating parameters affecting the recovery of ammonia though DCMD identified by PBD and statistically verified by analysis of variance (ANOVA). Results showed that the model had a high coefficient of determination value (R2 = 0.99), and the interaction between NH4Cl concentration and feed pH had a significant effect on ARE. The optimal operating parameters of DCMD as follows: NH4Cl concentration of 0.46 g/L, feed pH of 10.6, DCMD running time of 11.3 h, and the maximum value of ARE was 98.46%. Under the optimized conditions, ARE reached up to 98.72%, which matched the predicted value and verified the validity and reliability of the model for the optimization of ammonia recovery by DCMD process.

Superhydrophobic and oleophobic Nylon, PES and PVDF membranes using plasma nanotexturing: Empowering membrane distillation and contributing to PFAS free hydrophobic membranes

As freshwater demand is constantly increasing, water purification via membrane distillation (MD) emerges as a promising water production technology, especially when combined with the use of superhydrophobic membranes. Here, following our previous work [1] we extend our universal, environmentally friendly, plasma nanotexturing and hydrophobization technology for rendering practically any type of membrane superhydrophobic and oleophobic. Thus, we render three commercial porous membranes superhydrophobic, namely, polyvinylidene (PVDF 0.45 μm) (initially hydrophobic), polyethersulfone (PES 1.20 μm) and nylon (NY 1.20 μm) (both initially hydrophilic). We demonstrate superhydrophobic, superoleophobic (down to 40mn/m surface tension) and oleophobic properties (down to 30mN/m surface tension) for PVDF, PES and Nylon membranes thus paving the way for their use with low surface tension waste streams. Moreover, the technology presented herein not only improves existing hydrophobic membranes but may lead to elimination of the use of Teflon-like fluorinated hydrophobic membranes altogether in the future, thereby contributing to the PFAS (Per and Poly Fluoro Alkyl Substances) and Teflon-like membrane use reduction. We subsequently evaluated the performance of the treated membranes in direct contact membrane distillation (DCMD) for desalination of sea-like water (35 g/L NaCl). All membranes showed enhanced water flux with an increase of >13% compared to the pristine hydrophobic PVDF membranes for at least 2 h of continuous operation, with salt rejection exciding 99.99%.

Enzymatic Synthesis of Prebiotic Carbohydrates from Lactose: Integration of Osmotic Membrane Distillation with Batch Reactor System

AbstractThis study aimed to enhance galactooligosaccharide (GOS) yield by maintaining high lactose concentration levels using osmotic membrane distillation (OMD) throughout the synthesis. The main problem influencing GOS yield during transgalactosylation is the decrease of lactose concentration over extended reaction periods. By integrating OMD with a continuous stirred batch reactor, water was progressively removed from the reaction medium. Compared to a standard batch reactor, the OMD-integrated system not only increased GOS yield by a maximum of 20.1% but also reduced the time needed for equivalent lactose conversion about 15–90 min. This integration particularly boosted the formation of longer-chain GOS. A consistent GOS yield of 67% was achieved, with up to 28% lactose conversion, surpassing the non-integrated reactor’s performance. The proposed reactor design shows promise for enhancing GOS production efficiency while concurrently concentrating the reaction medium in a single step.

Enhancing the scaling resistance of corrugated polyvinylidene fluoride hydrophobic membrane in membrane distillation: Impact of CF4 plasma modification, pulse flow, and negative pressure

Membrane distillation (MD) is an emerging technology for brine concentration, but plagued by scaling/fouling/wetting in realistic applications. There has been tremendous progress in the mitigation of scaling via chemical modification to reduce the surface energy and hydraulic operation to change flow state in feed channel. But there still lacks an undisputed cognition yet which approach outperforms the others. To address this issue, this study comprehensively investigates the impact of state-of-the-art technologies on scaling mitigation based on a surface corrugated hydrophobic PVDF membrane with high flux and potential for mass production. The technology selected include CF4 plasma modification, pulse flow, and negative feed pressure from both thermodynamic and hydraulic perspectives. CF4 plasma modification resulted in a low surface energy superhydrophobic surface, but the scaling resistance of the membranes was not significantly improved. Pulse flow effectively mitigated scaling, yet the intrusion of calcium sulfate into the membrane matrix still occurred. Negative pressure at the feed channel created a stable air layer, leading to excellent stable vapor flux and distillation conductivity. The results indicated that the hydraulic operation using negative pressure at feed was an efficient approach for scaling mitigation. This study further elucidated the mechanism underlying the scaling resistance of superhydrophobic membranes and underscored the importance of hydraulic factors in enhancing the scaling resistance in MD.

Performance of tube heat pipe solar collector with phase change material for seawater desalination system

Abstract Unlimited seawater resources resulted for utilization of desalination systems using seawater treatment process emerges as a promising technology for addressing the continually escalating need for freshwater. At present, the most notable desalination processes that are reverse osmosis, membrane distillation, multistage desalination, multiple-effect distillation, and electrodialysis, require energy generated by fossil fuels to obtain fresh water. Among the noteworthy sources of renewable energy, solar energy stands out with its manifold applications. The use of solar energy has strong advantages, such as a low maintenance and operation costs. In this study, a novel solar desalination system is introduced, which integrates tube heat pipe solar collector (THP-SC) equipped with phase change material (PCM). The aim of this research is to evaluate the performance of THP-SC equipped with PCM and without PCM. The feedwater sample used is water. Parameters measured for 24 hours were temperature, solar radiation, ambient air temperature, relative humidity, and wind speed. The greatest recorded solar radiation at noon (11.52 a.m.) is 900 W/m2 while the maximum recorded ambient temperature at 12.45 p.m. is 35.2°C. The experimental study showed that from morning to afternoon (06.00-15.00), the temperature of the evaporator section of the heat pipe on the THP-SC without PCM (46.70-56.21°C) was higher than the temperature of the evaporator section of the heat pipe on the THP-SC with PCM (33.18-44.43°C). This is because solar radiation will heat the PCM first before heating the heat pipe. PCM can store heat energy and release it at night. This can be seen from the water temperature in THP-SC with PCM (28.39-36.03) which is higher than the water temperature in THP-SC without PCM (27.17-34.01) at night, but the temperature difference is not significant. This can be caused by the large amount of heat lost to the environment in THP-SC with PCM, it is best to coat the heat pipe tube with insulation and create a vacuum to reduce heat loss.

Enhanced water permeability and antifouling properties of cross-linked graphene oxide composite membranes with tunable d-spacings

Low flux and membrane fouling are major challenges in membrane distillation (MD) for treating concentrated wastewater. This study compared the performance of GO composite membranes with different interlayer distances, by covalently bonding the terminal amine groups of ethylenediamine (EDA) and 1,12-diaminododecane (DADD) with the carboxyl groups present on the GO sheets. The results indicated that the GO-DADD/PTFE membrane, with longer carbon chain cross-linking, achieved the highest flux and antifouling properties. At 70 °C, the pure water flux reached 68.5 kg/m2·h, and the fluxes for treating NaCl, HA containing NaCl, and BSA containing NaCl were 29.8 %, 37.1 %, and 38.5 % higher than the uncrosslinked GO/PTFE, and 95.7 %, 121.2 %, and 146.9 % higher than the PTFE membrane, respectively. Through mathematical models for mass and heat transfer, the study identified the key to this enhancement as the increased d-spacing within the GO layer due to cross-linking, which weakened the Kelvin effect and enhanced the vapor partial pressure on the hot side. The unique surface structure and electrostatic interactions induced by long-chain cross-linking further boosted the antifouling effect. These modifications not only overcome the typical trade-off between retention rates and flux but also offer a scalable and efficient solution for advanced membrane distillation applications.

A study on the measurement conditions for determining liquid entry pressure values of hydrophobic membranes

Liquid entry pressure (LEP) is a method for evaluating resistance to wetting by gradually increasing the pressure on the membrane in contact with the liquid. Despite the potential impact of pressure increase rate on LEP value determination, there is a scarcity of related research. In this study, the relationship between membrane characteristics and LEP value was analyzed by increasing the pressure by 0.1 bar at intervals ranging from 10 s to 30 min, using solutions with or without 1 mM SDS. In addition, the wetting phenomenon in direct contact membrane distillation (DCMD) and the duration to resist water penetration at a certain pressure were evaluated using LEP and membrane characteristics. As the rate of pressure increase accelerated, the measured LEP value tended to rise, showing a relatively wide range of variation for the same membrane. To ensure the efficiency and reproducibility of LEP measurements, it is recommended to increase the pressure at 5-min intervals. While the durability of resistance to water penetration under relatively high pressure was greatly influenced by membrane thickness, membrane hydrophobicity was more crucial for preventing the wetting phenomenon in DCMD.