Desalination Efficiency Research Articles

Design of Multi-Layer Graphene Membrane with Descending Pore Size for 100% Water Desalination by Simulation Using ReaxFF.

The performance of a desalination membrane depends on a specific pore size suitable for both water permeability and salt rejection. To increase membrane permeability, the applied pressure should be increased, which creates the need to improve membrane stability. In this research article, a molecular dynamics (MD) simulation was performed using ReaxFF module from Amsterdam Modeling suite (AMS) software to simulate water desalination efficiency using a single and multi-layer graphene membrane. The graphene membrane with different pore sizes and a multi-layer graphene membrane with descending pore size in each layer were designed and studied under different pressures. The stability of the membrane was checked using Material Studio 2019 by studying the dynamics summary. The single-layer graphene membrane was evaluated under pressures ranging from 100 to 500 MPa, with the salt rejection ranging from 95% to 82% with a water permeability of 0.347 × 10-9 to 2.94 × 10-9 (mm.g.cm-2s-1.bar-1), respectively. Almost 100% salt rejection was achieved for the multi-layer graphene membrane. This study successfully demonstrated the design and optimization of graphene membrane performance without functionalization.

Interfacial Charge-Modulated Multifunctional MoS2/Ti3C2Tx Penetrating Electrode for High-Efficiency Freshwater Production.

Freshwater production is critical in terms of solving the global water shortage. Aiming at improving freshwater production capability and ensuring its quality, an interfacial charge-modulated MoS2/Ti3C2Tx-modified carbon fiber (CF/MoS2/Ti3C2Tx) penetrating electrode is designed. To maximize the desalination and degradation efficiencies of CF/MoS2/Ti3C2Tx, a photocatalytic component is introduced into the membrane capacitive deionization (PMCDI) device. High desalination capability is derived from the lamellar architecture structure of MoS2/Ti3C2Tx. Meanwhile, excellent degradation performance is due to the formation of two photoelctrocatalytic activity centers, directionally generating singlet oxygen (1O2) and hydroxyl radical (•OH). The intercalated Cl- (desalination) as the electron transfer bridge optimizes the charge distribution of MoS2/Ti3C2Tx, reinforcing the photoelectrocatalytic activity (degradation). The formation of the electron-deficient (desalination) and electron-rich (regeneration) regions at the terminated O atom of Ti3C2Tx accelerate the generations of •OH and 1O2, respectively. In perspective, a mutual promotion process of desalination and degradation is achieved for high-efficiency production of high-quality freshwater.

Development of an effective operation system in a magnesium-air desalination cell for electricity production with nitrogen and phosphorus removal

A magnesium-air desalination cell system is developed for electricity production alongside concurrent desalination and wastewater treatment. Synthetic wastewater at three concentrations is used as an anolyte and catholyte with and without a recirculation system to investigate effective operation methods. The operation time was 20 h, and the anolyte was changed every 3 h. The maximum conductivity reduction efficiency (desalination efficiency) at a high concentration of synthetic wastewater was 77.4 % and 51.6 % in operation systems with and without recirculation, respectively. Measured concurrently, the maximum electric energy production (EEP) was 23.8 Wh m−3 in the system with recirculation and 15.6 Wh m−3 in the system without recirculation. The increase of voltage drop in operation without recirculation was due to the high internal resistance of the membrane induced to lower EEP in contrast to the membrane in operation with recirculation. During operation, struvite was produced at high initial concentration of synthetic wastewater in bulk solution and confirmed through Fourier transform-infrared spectroscopy and X-ray diffraction. Ammonia and phosphorous removal was high at high initial concentration of synthetic wastewater. The results indicate that the magnesium-air desalination cell holds great potential for electricity production, salt reduction, and wastewater treatment.

Importance of the conductivity and specific surface area of electrode particles to the desalination performance and energy efficiency of flow-electrode capacitive deionization

Different from electrodialysis for desalination, flow-electrode capacitive deionization (FCDI) removes ions via electrosorption on the surface of charged flow-electrode particles. In this study, the exact effects of the conductivity and surface area of carbon electrode particles on the desalination performance and energy efficiency of the FCDI were investigated under the constant voltage (CC) and constant current (CV) power-supply modes. The low-cost activated carbon (AC) with a large specific surface area and carbon black (CB) with a high conductivity were used as the model electrode particles. In the CC mode, increasing the CA content from 0.5 wt% to 5 wt% achieved a limited enhancement of the desalination rate and efficiency (50.2%-54.5% in 2 h), but dramatically reduced the energy consumption from 1.39 kWh/kg to 0.73 kWh/kg. In the CV mode at 1.2 V, doubling the AC content from 5 wt% to 10 wt% or mixing a small amount of CB in AC (AC:CB = 9:1 at 5 wt%) significantly improved the desalination efficiency from 65.6% to over 90%, but the energy consumption remained similarly at 0.64–0.68 kWh/kg. The conductivity of the electrode particles greatly affects the energy efficiency in the CC mode and the desalinization rate in the CV mode. The CB addition can effectively enhance the electric charge transfer between the current collectors and electrode particles. The surface area of electrode particles largely regulates the FCDI capacitance, as well as the back diffusion during the process. Accordingly, the flow-electrode property can be optimized, e.g., CB is mixed with AC at an appropriate ratio, to ensure both a high conductivity (to facilitate electron transfer) and sufficient surface area (to increase the capacitance and alleviate back diffusion) for cost-effective desalination.

Numerical and experimental investigation of phase change characteristics and desalination effect of seawater freezing desalination in narrow channels

The crystallisation characteristics of freeze desalination in narrow channels need to be explored theoretically. Phase-field method (PFM) is an effective method for determining the microstructure during phase changes. In this study, the PFM coupled with the lattice Boltzmann method (LBM) was used to study the phase change behaviour and desalination effect of seawater freezing desalination in narrow channels. The phase, concentration, temperature, and flow fields were coupled and solved. A microscopy observation experimental system with a charge-coupled device camera was established to verify the numerical results. The salinity of the crystallisation zone was obtained by examining the crystallisation region. Important variables that could impact the desalination effect, such as the flow temperature, heat flux, and flow velocity, were investigated. The results showed that the flow temperature increased the desalting rate; the desalination ratio was 20 %–27.9 % in the temperature range of 263.15–283.15 K. The heat flux increased five-fold, and the desalination rate decreased from 22.6 % to 10.1 %. Owing to the counteracting effects of convection and solute diffusion on ice crystal growth, the inflow velocity had little effect on the desalination efficiency. The present method was expected to provide technical guidance for the device development of multistage crystallisers.

Multi-objective optimization of a small-scale solar-hot-spring-geothermal brackish water direct contact membrane distillation system

A small-scale solar-hot-spring-geothermal brackish water membrane distillation (MD) system is proposed by combining hot-spring and solar components to reduce fossil energy consumptions. A performance parameter framework and carbon footprint model is developed to perform an analysis on whole life cycle of the proposed system. The results show that the solar subsystem improved heat recovery with the water generation ratio increased by 22–42 %. As the feed-side inlet temperature increases, the total Specific Energy Consumption (SEC) contribution rate of renewable geothermal and solar energies increases from 12.34 % to 20.45 %. The cold and hot sources are responsible for the largest exergic losses at 1.79 kJ/S and 0.48 kJ/S. The unit exergy cost of the solar subsystem is the highest of 0.037 $/h in terms of economic benefits. One of effective ways to improve the carbon emission reduction rate is to develop a cogeneration process for the water purification. A multi-software co-simulation methodology is proposed to explore innovative MD systems of optimal configurations, improve desalination efficiency and reduce the energy consumptions. The Non-dominated Sorting Genetic Algorithm (NSGAII) and improved NSGAII genetic algorithms (NSGAII-A and NSGAII-B) are utilized for multi-objective optimization of the MD system. Finally, the Technique for Order Preference by Similarity to Ideal Situation (TOPSIS) method based on entropy weight is employed to obtain the Pareto frontier solution set. It is indicated that NSGAII-B based on the four objective-optimal scheme is the best for the Multi-objective optimization of the MD system.

A review on evaporation improvement of solar still desalination using porous material

Recently, many studies have focused on desalination systems using solar energy sources due to low energy costs, the feasibility of usage in most weathers and no use of fossil fuels. Different materials have been proposed to enhance the temperature gradient and to gain better water productivity of the system such as porous materials, nanoparticles and phase change materials. Due to the uneven and porous surface, the porous materials raise the solar intensity absorption and the water temperature. This present review article assists to study the implementation of porous materials in evaporation enhancement of solar water desalination systems. All previous studies have demonstrated that the use of porous materials has a significant influence on the evaporation rate in solar desalination systems. Eventually, a summary of comparison in previous publications was presented and discussed in detail to assist researchers and engineers with a better design of solar still desalination systems. The achieved outcomes indicated that the energy efficiency of the solar desalination using activated carbon as a porous media was enhanced by 94.14%. Moreover, the productivity of the solar still desalination by aluminium fins and black steel wool fiber as a porous material was increased by about 42.3% and 20.9%, respectively.

Modelling Soil Water, Salt and Heat Dynamics under Partially Mulched Conditions with Drip Irrigation, Using HYDRUS-2D

Drip irrigation under mulch is a widely used technique in the arid region of northwest China. The partially mulched soil and the bare strips between mulched areas may complicate the migration of water, salt, and heat in soils, and cause lateral salt accumulation on bare soil surfaces. For investigating hydrothermal dynamics and salt distribution patterns under such circumstances, tank experiments with drip irrigation under plastic film on partially mulched soil were conducted under two intensities of drip irrigation (i.e., low (W1) and high (W2)) with the same total irrigation amount. The spatial distributions of soil water, temperature, and electrical conductivity were monitored accordingly. The two-dimensional (2D) model of soil water, salt, and heat transport under drip irrigation and partially mulched soil conditions was established using HYDRUS-2D, and kinetic adsorption during salt migration was considered. The results of the experiments showed that the uneven distribution of the hydrothermal state led to the accumulation of salt on the un-mulched soil surface. Water migrated from where the dripper was located, and heat accumulated mainly in the mulched soil. HYDRUS-2D matched reasonably well with the observed data, with an R2 higher than 0.54. Under the partially mulched conditions, lower intensity of drip irrigation (W1) show higher desalination efficiency in root zones, with less even lateral salt distribution. Scenario simulations further demonstrated that a larger total irrigation amount would result in a larger desalination zone, and drip irrigations with appropriate incremental intensity could improve salt leaching in the root zone with increased lateral migration of water.

Effect of highly saturated superhydrophilic porous media on air gap diffusion distillation considering preferential flow

Air gap diffusion distillation (AGDD) is a new and inexpensive desalination technology. As the hot stream channel and evaporation surface of AGDD, the superhydrophilic porous medium plays a decisive role in its desalination efficiency. In addition, we also found the preferential flow in the highly saturated superhydrophilic porous media in experiments, which also impairs the desalination efficiency of AGDD. However, these have not been investigated. A detailed characterization of the superhydrophilic porous media was conducted in this study, based on which a theoretical model of an AGDD process containing coupled heat and moisture transfer in highly saturated superhydrophilic porous media (SIM) was developed. The preferential flow in porous media was visualized using an infrared imaging method, and the results were incorporated into the theoretical model (SIMPF), which agreed well with the experimental data. The maximum prediction errors of SIMPF for temperature and permeate fluxes were reduced by 61.2 % and 81.8 %, compared with those of SIM. The AGDD is most affected by the preferential flow at small feed volume flow rates, with a maximum reduction in permeate flux of 24.3 %. Moreover, the effects of operating and porous media structure parameters on the AGDD performance were also investigated.

Degradation of phenol in the bio-cathode of a microbial desalination cell with power generation and salt removal

In this study, the performance of a three-chamber microbial desalination cell (MDC) was assessed to simultaneously remove salt (35 g.L-1) from water and degrade phenol as a hazardous compound. Two parallel MDCs with the same configurations were run using glucose as the chemical oxygen demand (COD) at an initial concentration of 1.5 g.L-1 as the anolyte. MDC#1 operated with 10 mM phosphate buffer solution (PBS), while MDC#2 operated with bio-cathode as the catholyte for the degradation of 100 mg.L-1 of phenol. The use of MDC#1 resulted in a power density, desalination efficiency, and COD removal of 366.2 mW.m−2, 50.3 ± 4.0 %, and 79.3 ± 2.2 %, respectively. All performance parameters were improved in MDC#2 with bio-cathode so that power density, desalination efficiency, and COD removal reached 660.1 mW.m−2, 72.1 ± 3.0 %, and 92.6 ± 2.4 %, respectively. Also, more than 96 % of phenol was degraded using bio-cathode within 7 h of operation. Bio-cathode could enhance the performance of the MDC reactor through catalyzing the final reactions of electron acceptors compared to MDC#1 with a chemical cathode. In general, the results indicated that heterotrophic microorganisms, able to grow alongside autotrophic bacteria, could effectively extend the applications of MDC reactors to degrade hazardous compounds in cathode chambers.

Visualization study on preferential flow in highly saturated and super hydrophilic porous media by combining dye tracking and infrared imaging

• New method to track finger flow in highly saturated superhydrophilic porous media. • Preferential flow recurrence was observed at high saturation. • The preferential flow was found to impair desalination efficiency. • The temperature distribution was controlled by preferential flow. Air-gap diffusion distillation (AGDD) is a practical desalination technique. The highly saturated super hydrophilic porous medium as its evaporation surface has a decisive influence on the desalination efficiency of AGDD. In experiments, we found preferential flow in porous media. However, the preferential flow in highly saturated super hydrophilic porous media has not been studied, and the effect of preferential paths on evaporation from porous media surfaces remains poorly understood. The method of combining dye tracking and infrared imaging was used to visualize the process of thermal seepage in highly saturated super hydrophilic porous media. Under the condition of uniform and continuous liquid supply on the upper surface, the preferential flow characteristics of hot stream seepage in porous media are tracked; Point source infiltration experiments were carried out at room temperature to compare the difference between preferential flow in super hydrophilic porous media and general soil (sand). The experimental results of thermal seepage showed that the preferential flow greatly influences the uneven temperature distribution of the porous media, which directly impairs the desalination efficiency of AGDD. According to the coefficient of variation (CV), the preferential flow development process can be divided into three stages: stable development, exponential development, and high-speed growth. As the seepage flow is stabilized, the influence of preferential flow on the flow field and temperature field still exists and is affected by these three stages. Preferential flow characteristics were also captured in the saturated capillary rise zone at the bottom of the porous medium (below the phreatic level). The point source infiltration experiment found that the preferential flow in superhydrophilic porous medium will reappear at high saturation, which is completely different from the soil (sand) studied by previous studies. In addition, the effects of inlet temperature, flow rate, thickness, and hydrophilic, hygroscopicity on preferential flow were discussed. Increasing the flow rate and inlet temperature and reducing the thickness of the porous media can weaken the influence of preferential flow on the temperature field. But increasing the temperature only superficially weakens the preferential flow. Increasing hydrophilicity and hygroscopicity can also reduce the preferential flow.

Surface modification of commercial reverse osmosis membranes using both hydrophilic polymer and graphene oxide to improve desalination efficiency.

Various methods have been applied to modify the surface of reverse osmosis (RO) membranes to modify the membrane performance to enhance the flux, rejection, and resistance to various factors of fouling. Hence, the main objective of the current study is to modify the surface of commercial RO membranes using the synergistic effect of the hydrophilic polymer and graphene oxide (GO). GO nanosheets were firstly synthesized by the modified hummer method, then characterized by FTIR, XRD, and SEM analyses. Then, the polyacrylic acid (PAA) was grafted on the membrane surface for membrane fabrication. Furthermore, effective factors of grafting such as monomer concentration, time, and temperature of polymerization were optimized. After that, different amounts of GO nanosheets were loaded in PAA optimized layer. Then, the effect of GO loading on the RO membrane structure and performance was investigated. The outcomes of membrane characterization demonstrated that modified RO membranes had a smoother surface, more negative surface charge, a little better hydrophilicity, and more thickness. Moreover, the results of PAA and GO optimization were shown that grafting 1.5mM of PAA and loading 0.1wt% of GO nanosheets give the best membrane performance. This membrane (GO 0.1@1.5M PAA/RO) between all modified membranes has the most water flux (37.1L/m2h), the highest NaCl rejection (98%), and the best antifouling efficiency. Ultimately, it was concluded that the grafting of GO@PAA on the surface of a commercial RO membrane is an efficient approach for the enhancement of desalination and antifouling performance of this kind of membrane.

Efficient water purification and desalination using hydrogel and aerogel solar evaporators based on different carbon materials

Interfacial solar evaporation, which utilizes abundant and clean solar energy for wastewater desalination purification, is emerging as an environmental-friendly and energy-efficient technology for producing clean water. In this paper, sodium alginate (SA) gel evaporators based on different carbon materials were proposed. A simple and convenient evaporator was constructed by comparing the network properties of hydrogels and aerogels, as well as the photothermal conversion efficiencies of CNTs and graphene. CNTs-SA-hydrogel (CSH) had higher evaporation rate and better water purification than CNTs-SA-aerogel (CSA), with the evaporation rate of 1.60 kg m-2h−1 and ion removal rate of 99 %.However, the evaporation performance and desalination efficiency of graphene-SA-aerogel (GSA) were better than those of graphene-SA-hydrogel (GSH). In particular, GSA gave the bestperformancewith a pure water evaporation rate of 1.73 kg m-2h−1. Even in a 20 wt% high-salt wastewater, it could generate steam consistently with an evaporation rate of 1.56 kg m-2h−1 without any significant performance degradation. In addition, it also had outstanding desalination ability and could completely decolorize in organic dyes. Therefore, this study provides a new idea to further promote the rapid development and application of interfacial solar steam generation in desalination and purification of seawater.

A process for CO2 capture and brine salinity reduction through reaction with potassium hydroxide: A multi-stage evaluation

Solvay and modified Solvay processes are facing a major challenge in reducing brine salinity to a level suitable for agriculture and industry. This challenge arises as a result of competing reactions and mixing limits between CO2 gas and brine. Another challenge is the high solubility of sodium bicarbonate (NaHCO3), which results in a low overall desalination efficiency. Previous studies established the effectiveness of a modified Solvay process based on potassium hydroxide (KOH). The first objective of this study is to evaluate a multi-stage treatment for a modified Solvay process on the basis of potassium hydroxide (KOH) to achieve an additional reduction in ion removal from high-salinity brines and an increase in CO2 capture as compared to previously obtained under optimal operating conditions. Three different methods were investigated. The first method evaluated the effectiveness of adding ammonium bicarbonate (NH4HCO3) in reducing the solubility of NaHCO3. Even though the Na+ and Cl− concentrations were reduced by 56.2% and 40%, respectively, the total CO2 uptake slightly improved by 1.2% (67.8 g CO2/1000 ml of treated brine). In the second method, the addition of extra KOH in subsequent stages was investigated to overcome the pH reduction observed in the first method. There was an ∼ 47.3% improvement in CO2 uptake from the first method. Furthermore, the percentages of Na+ and Cl− removal were increased to 65% and 64.5%, respectively. In the third method, the recovery of Ca2+ and Mg2+ was approximately 76.3% and 94.6%, respectively, following the pre-treatment step (filtration), followed by the same stages as in the second method. Reducing these ions decreased the competitive reactions and thus increased CO2 solubility and reactivity with KOH, resulting in higher cumulative CO2 uptake from all stages to 108.2 g CO2/1000 ml, which was 8.3% more than the second method. Additionally, solid products were characterized using scanning electron microscopy, X-ray diffraction, FTIR and Raman analysis. Finally, the dynamic behaviour of the reactor was evaluated using step changes in the inlet gas and liquid flow rate. The results are promising in terms of the reactor system's adaptability to large-scale processes.

Thermodynamic and kinetic study of fluorinated gas hydrates for water purification

AbstractThis study investigated and compared the thermodynamic stability, kinetic behaviour, and effectiveness of a water purification process using pentafluoroethane (HFC125a) and 1,1,1,2‐tetrafluoroethane (HFC134a) as guest molecules. The hydrate phase equilibria of each fluorinated gas (F‐gas) in pure water and NaCl solution were predicted using the Hu‐Lee‐Sum correlation, which agreed well with the experimental results from our previous studies. Under the same subcooling temperature of 3 K (at 0.3 MPa), the rate of hydrate growth with HFC134a was faster than that of HFC125a in the absence or presence of NaCl. In situ Raman spectroscopy confirmed that the HFC134a and HFC125a molecules occupy only a large cage of structure II hydrate. The Raman shifts of CH and CC bands in all phases (gas, liquid, and hydrate phases) of HFC125a shifted to higher wavelengths than those of HFC134a due to the increase in the number of fluorine atoms. The change in the salinity was studied to evaluate the effectiveness of an F‐gas hydrate‐based water purification process. In addition, the desalination efficiency of the HFC134a and HFC125a hydrates was compared by separating hydrate crystals from the slurries. The results showed that the desalination efficiency (or total dissolved solids removal efficiency) of HFC134a hydrate was higher than that of HFC125a hydrate. This study proves the importance of the water purification process using hydrates.

Study of the Seawater Desalination Performance by Electrodialysis.

The global scarcity of freshwater resources has greatly contributed to the development of desalination technologies, in which electrodialysis desalination is one of the most widely used and highly regarded methods. In this work, the first step was to design and assemble a experiment module for electrodialysis desalination. The ion removal efficiency and single membrane mass transfer flux of electrodialysis desalination were investigated. The results show that the desalination performance of the module is improved by increasing the voltage gradient, increasing the concentration of seawater and electrolyte and decreasing the membrane surface flux and that the optimum operating conditions for the module at 24 V operating voltage are feedstock concentration of 35 g/L, electrolyte concentration of 1.42 g/L which and system flow rate of 15 L/h. The results of the study will help to better investigate electrodialysis desalination technology.

Freestanding Activated Carbon Nanocomposite Electrodes for Capacitive Deionization of Water.

Freshwater reserves are being polluted every day due to the industrial revolution. Man-made activities have adverse effects upon the ecosystem. It is thus the hour of need to explore newer technologies to save and purify water for the growing human population. Capacitive deionization (CDI) is being considered as an emerging technique for removal of excess ions to produce potable water including desalination. Herein, cost-effective activated carbon incorporated with carbon nanotubes (CNT) was used as a freestanding electrode. Further, the desalination efficiency of the designed electrodes was tuned by varying binder concentration, i.e., polyvinylidene difluoride (PVDF) in the activated carbon powder and CNT mixture. PVDF concentration of 5, 7.5, 10, and 12.5 wt% was selected to optimize the freestanding electrode formation and further applied for desalination of water. PVDF content affected the surface morphology, specific surface area, and functional groups of the freestanding electrodes. Moreover, the electrical conductivity and specific surface area changed with PVDF concentration, which ultimately affected the desalination capacity using the freestanding electrodes. This study paves the way to produce cost effective carbon-based freestanding electrodes for capacitive deionization and other applications including battery electrodes.

Effect of hydraulic retention time on the electro-bioremediation of nitrate in saline groundwater

Bioelectrochemical systems (BES) have proven their capability to treat nitrate-contaminated saline groundwater and simultaneously recover value-added chemicals (such as disinfection products) within a circular economy-based approach. In this study, the effect of the hydraulic retention time (HRT) on nitrate and salinity removal, as well as on free chlorine production, was investigated in a 3-compartment BES working in galvanostatic mode with the perspective of process intensification and future scale-up. Reducing the HRT from 30.1 ± 2.3 to 2.4 ± 0.2 h led to a corresponding increase in nitrate removal rates (from 17 ± 1 up to 131 ± 1 mgNO3−-N L−1d−1), although a progressive decrease in desalination efficiency (from 77 ± 13 to 12 ± 2 %) was observed. Nitrate concentration and salinity close to threshold limits indicated by the World Health Organization for drinking water, as well as significant chlorine production were achieved with an HRT of 4.9 ± 0.4 h. At such HRT, specific energy consumption was low (6.8·10−2 ± 0.3·10−2 kWh g−1NO3−-Nremoved), considering that the supplied energy supports three processes simultaneously. A logarithmic equation correlated well with nitrate removal rates at the applied HRTs and may be used to predict BES behaviour with different HRTs. The bacterial community of the bio-cathode under galvanostatic mode was dominated by a few populations, including the genera Rhizobium, Bosea, Fontibacter and Gordonia. The results provide useful information for the scale-up of BES treating multi-contaminated groundwater.

Numerical simulation of indirect freezing desalination using lattice Boltzmann method

With the increasing demand for freshwater for drinking, industrial, and agricultural purposes, desalination of seawater is a significant solution. Freezing desalination is a less costly process compared to other thermal methods; thus, it can be a proper alternative choice in the desalination industry. Numerical simulation of this process is advantageous in the design and optimization of this technology. The modeling of this process with common computational fluid dynamics methods is computationally expensive due to the small time scale of freezing. In this study, we develop a lattice Boltzmann method to solve the momentum and energy equations. This method is coupled with the finite difference discretization of species transport equation for the concentration of salt. A two-dimensional cavity filled with 35 g/L saltwater with one cold surface is investigated. The desalination process at three different times is analyzed. Also, the effect of changing the position of the cold wall in the presence of gravity is examined. The left and top surface cooling presents higher desalination efficiency as the purification efficiency is twice as the bottom surface cooling in terms of brine salt concentration. It was also found that reducing the temperature of the cold wall can have a more significant effect on desalination efficiency rather than changing the position of the cooling surface. The brine concentration obtained from the top cooling surface after 30 min at 250 K was 7.803%, while that of the bottom surface cooling after 10 min at 230 K was 8.40%.

Durable superhydrophobic polyvinylidene fluoride membranes via facile spray-coating for effective membrane distillation

Membrane wetting and fouling substantially limits application and deployment of membrane distillation process. Designing high-performance superhydrophobic membranes offers an effective solution to solve the challenge. In this work, a highly durable superhydrophobic surface (water contact angle of 170.8 ± 1.3°) was constructed via a facile and rapid spray-coating of extremely hydrophobic SiO2 nanoparticles onto a porous polyvinylidene fluoride (PVDF) substrate for membrane distillation. The superhydrophobic membrane coated by fluorinated SiO2 nanoparticles exhibited a superior physicochemical stability in a wide range of extreme environments (i.e., NaOH, HCl, hot water, rust water, humic acid solution, ultrasonication, and high-speed water scouring). During 8-h continuous membrane distillation desalination experiment, the coated superhydrophobic membrane experienced a consistently stable water vapor flux (ca. 19.1 kg·m−2·h−1) and desalination efficiency (99.99 %). Additionally, such a stable superhydrophobicity endowed the spray-coated PVDF membrane to overcome membrane wetting and fouling during membrane distillation of highly saline solutions containing foulants (i.e., humic acid and rust). Results reported in this study provides a useful concept and strategy in facile construction of robust superhydrophobic membranes via spray-coating for effective membrane distillation.