Seawater Desalination Applications Research Articles

Capillary-Flow-Optimized Heat Localization Induced by an Air-Enclosed Three-Dimensional Hierarchical Network for Elevated Solar Evaporation.

Solar evaporation is a cost-effective way for obtaining clean water using renewable energy. However, many solar evaporation devices still show unsatisfactory performance and suffer from inefficient utilization of absorbed solar energy. Herein, numerical simulations of solar evaporation demonstrate that the heat management is a key factor governing the solar evaporation efficiency. This prediction is confirmed through using a bilayered solar steam generation architecture [hollow glass microsphere-carbon black (HS-CB)] both in laboratory- and pilot-scale studies. The HS-CB consists of a CB film as a solar-thermal conversion layer and three-dimensional hierarchical polyvinylidene fluoride skeleton cross-linking HSs as a heat localization and water-transporting layer. A balance between thermal insulation and capillary-driven water transport can be reached by tuning the porosity of the thermal-insulating layer, thus inducing optimized heat localization. The proposed structure evaporates water with an efficiency of 82.1% under 1 sun irradiance (1 kW m-2) in the laboratory and can even stably produce 4.63 L m-2 d-1 (average efficiency of 37%) of purified water from highly concentrated industrial waste water in the pilot study, demonstrating its promising potential for applications in seawater desalination and brackish water purification.

Separating photo-thermal conversion and steam generation process for evaporation enhancement using a solar absorber

Solar steam generation is an effective method combining solar energy utilization with water treatment. Photo-thermal conversion and steam generation are typically integrated to enhance the evaporation process, which have wide applications in seawater desalination, waste water treatment, sterilization and power plant fields. However, the photo-thermal enhancement for different evaporation areas remains unclear, and there are a number of important issues for membrane process (e.g., blockage of pore structures and contamination of nanoparticles). To overcome these issues, we herein propose a separating design involving a C-TiO2 absorber and a polyvinyl alcohol fiber material as the photo-thermal and steam generation units, respectively. A C-TiO2 absorber with good spectral and photo-thermal conversion characteristics was prepared. And the evaporation enhancement effect was investigated with different evaporation areas by experiments and simulations. The equivalent evaporation rate reached the maxima with the evaporation area and decreased thereafter for this separating design. The optimum behavior was achieved when the evaporation region area to photo-thermal area ratio of ca. 2.06, providing guidance for large-scale use. These results can be explained in terms of the changed thermal gradient generated between the center C-TiO2 film and the evaporation region. The design achieved equivalent evaporation rates and evaporation efficiencies of 1.24 kg·m−2·h−1 and 77.83%, respectively, paving the way for the further improvement of solar steam generation processes.

Ion concentration polarization and its application in molecular preconcentration in micro-nanofluidic systems

The combination of ion concentration polarization (ICP) phenomenon and micro-nanofluidic technologies provided novel solutions to the problems of biomolecular detection, ion separations and desalinations etc. This paper makes a brief introduction to ICP and the latest advances in the related theoretical and simulation research, with especial emphases on electroosmotic flow of the second kind and its deterministic role in the formation of over limiting currents. Subsequently, ICP in dumbbell-shaped and H-shaped micro-nanofluidics systems is introduced, along with its application in preconcentration, seawater desalination and current rectification systems. Latest theoretical advances ICP-based electrokinetic concentration is reviewed. Lastly, future work in terms of new functionalities, industrial development and theoretical investigations are suggested.

N-doped graphene /carbon hybrid aerogels for efficient solar steam generation

Efficient solar-thermal energy conversion is critical for utilization of abundant solar energy in solar power-based concentration systems, photochemical plants and seawater desalination technologies, etc. However, conventional processes for solar steam generation generally rely on high-temperature heating of bulk liquids, which requires highly concentrated solar energy and suffers from high energy and optical losses. Therefore, it is still critical to explore and design solar absorption materials with high solar-thermal conversion efficiency. Herein, we report the preparation of a nitrogen-doped graphene/carbon hybrid aerogel (NGCA) using graphene oxide (GO) and melamine form (MF) for highly efficient solar steam generation by a simple dip-coating processes, air drying and carbonization at different temperatures. The NGCA carbonized at 600 °C (NGCA-600) exhibits excellent stability, efficient light absorption, good hydrophilicity for water supply and abundant micro-pores for vapor escape, therefore, it can achieve 90% solar-thermal conversion efficiency under the light density of 1 kW m−2. This cost-effective and reusable solar-thermal convertible material could be ideal for practical applications in seawater desalination, water purification and sterilization.

Volumetric solar steam generation enhanced by reduced graphene oxide nanofluid

Solar steam generation is a highly efficient photo-thermal conversion method that has a wide range of applications in water purification, distillation, power plants, and seawater desalination. Low steam generation efficiency was obtained for solar steam generation using traditional working media. Therefore, reduced graphene oxide (rGO) nanofluids with good stability and light absorption capability were fabricated to achieve highly efficient volumetric solar steam generation in this work. The effects of rGO mass concentration and light intensity on solar steam generation enhancement were investigated experimentally. It was found that a hot area was formed at water–air interface due to the unique lamellar structure of rGO with good light absorption characteristic, and sunlight was absorbed by the hot area to generate steam locally, which reduced thermal loss and improved evaporation efficiency. The solar steam generation enhancement achieved by the rGO nanofluids reduced evaporation costs and expanded their applicability in seawater desalination, clean water production, sterilization of waste, etc.

Oxygen plasma treated graphene aerogel as a solar absorber for rapid and efficient solar steam generation

Using optical absorption materials to heat localized water gaining water steam is a highly efficient way of solar energy utilization. Here, we introduced a new solar absorber of modified graphene aerogel (MGA) prepared by one-step hydrothermal method and oxygen plasma treatment for rapid and efficient solar steam generation. The obtained MGA possesses interconnected 3D porous networks formed by randomly construction of reduced graphene oxide (rGO) sheets and hydrophilic surface due to effective oxygen implant by oxygen plasma. Furthermore, under one sun illumination, MGA exhibited a high evaporation efficiency of 76.9%, which is not only due to the intrinsic property of rGO with excellent light absorption but also attributed to the particular structural merits of MGA—hydrophilic surface for water supplying and connected networks for steam escaping as well as porous matrix with low thermal conductivity. The cyclic tests confirmed that MGA still maintained a stable performance of solar steam generation even when it repeated multiple times. This new assembly demonstrated here is efficient and reusable for applications in rapid solar seawater desalination and wastewater treatment in remote area.

Biofabrication of gold/activated carbon/polyvinyl alcohol (Au/Ac/PVA) polymer sheet and its application in seawater desalination

Biofabrication of gold/activated carbon/polyvinyl alcohol (Au/Ac/PVA) polymer sheet and its application in seawater desalination

Detailed modeling and simulation of an out-in configuration vacuum membrane distillation process.

In this study, a detailed rigorous theoretical model was developed to predict the transmembrane flux of a shell-and-tube type vacuum membrane distillation (VMD) module for seawater desalination. Two modes of operation are used for performing the VMD, namely lumen-side feed (in-out) configuration and shell-side feed (out-in) configuration. In this study, detailed mathematical formulations are derived for an out-in configuration that is commonly used in seawater desalination applications. Experimental results and model predictions for mean permeate flux are compared and shown to be in good agreement. The results indicate that although the simple VMD model that maintains a constant permeate pressure is easy to use, it is likely to significantly overestimate the mean permeate flux when compared to the detailed model that considers the pressure build-up in the fiber lumen. The pressure build-up of water vapor in the fiber lumen is identified as the crucial factor that significantly affects the VMD performance because it directly reduces the driving force for vapor permeation through the membrane pores. Additionally, its effect is more pronounced at longer fiber lengths and higher permeate fluxes, and this is achieved at higher feed temperatures and velocities and at lower feed salinities. In conclusion, the results of the study are extremely important in module design for the practical applications of VMD processes.

Experimental study of heat transfer and scale formation of spiral grooved tube in the falling film distilled desalination

The heat transfer performance and scale formation of spiral-grooved tube in the falling film evaporator was studied experimentally compared with the conventional smooth tube. A series of experiments were performed contrastively on the two types of heat transfer tube based on a heat exchange test platform of horizontal tube falling film evaporation for desalination. The influences of various factors on heat transfer coefficients for the spiral-grooved and smooth tubes were investigated. Heat transfer experiments indicated that the heat transfer coefficient of the spiral-grooved tube can be improved by approximately 35%, comparing with the smooth tube under the same experimental conditions. The anti-scaling capability of spiral grooved tube is a little better than that of smooth tube. Their scaling layers had similar thickness under the same operation condition, and their cohesiveness with the tube was weak. Experimental findings indicated that the spiral-grooved tube was feasible for application in seawater desalination given the enhancement of heat transfer and anti-scaling characteristics.

Tuning Transpiration by Interfacial Solar Absorber-Leaf Engineering.

Plant transpiration, a process of water movement through a plant and its evaporation from aerial parts especially leaves, consumes a large component of the total continental precipitation (≈48%) and significantly influences global water distribution and climate. To date, various chemical and/or biological explorations have been made to tune the transpiration but with uncertain environmental risks. In recent years, interfacial solar steam/vapor generation is attracting a lot of attention for achieving high energy transfer efficiency. Various optical and thermal designs at the solar absorber–water interface for potential applications in water purification, seawater desalination, and power generation appear. In this work, the concept of interfacial solar vapor generation is extended to tunable plant transpiration by showing for the first time that the transpiration efficiency can also be enhanced or suppressed through engineering the solar absorber–leaf interface. By tuning the solar absorption of membrane in direct touch with green leaf, surface temperature of green leaf will change accordingly because of photothermal effect, thus the transpiration efficiency as well as temperature and relative humidity in the surrounding environment will be tuned. This tunable transpiration by interfacial absorber‐leaf engineering can open an alternative avenue to regulate local atmospheric temperature, humidity, and eventually hydrologic cycle.

Strained single-layer C2N membrane for efficient seawater desalination via forward osmosis: A molecular dynamics study

Forward osmosis (FO) has proven to be a promising membrane separation technology for seawater desalination. However, advanced porous membranes are highly demanded to improve the efficiency of FO process. The single-layer C2N, also known as nitrogenated holey graphene, has recently emerged as a promising material for nanofiltration due to its intrinsic porous structure and robust mechanical strength. In this study, molecular dynamics simulations have been conducted to investigate the seawater desalination performance of the single-layer C2N membrane in the FO process by tuning its pore size using tensile strain. The results show that with a biaxial tensile strain larger than 4%, the C2N membrane becomes permeable to the water molecules but completely impermeable to the salt ions. At the strain of 12%, a water flux as high as 14.36Lcm−2h−1 can be obtained at the moderate temperature of 338K. Interestingly, the permeation water flux shows a nonmonotonic dependence on the osmosis pressure difference across the membrane. To understand the underlying mechanism, the potential mean force profile, water density distribution and hydrogen bonding dynamics are analyzed to investigate both the diffusion of the water molecules near the membrane and in the bulk salt solution. This study is helpful for the understanding of the water permeation behavior through the C2N membrane and promoting its application in seawater desalination.

Assessing the performance of solar thermal driven membrane distillation for seawater desalination by computer simulation

A computer model was developed to simulate the performance of an integrated solar thermal driven direct contact membrane distillation (DCMD) system for seawater desalination using recorded weather data. The results highlight the importance of simulating the DCMD process together with the energy source. Indeed, when considered in isolation from the thermal energy source, increasing water cross flow velocities in the feed and distillate channels results in an increase in water flux and thermal efficiency of the DCMD module. By contrast, when coupling the DCMD module with the solar thermal collector, increasing water cross flow velocities reduces both the process water flux and thermal efficiency. This is because of the limited supply of solar thermal at any given time, and hence the feed temperature decreases when cross flow velocities increase. Thus, any benefits in the reduction of temperature polarisation due to increasing cross flow velocities are overwhelmed by the effects of feed temperature decrease on water flux and thermal efficiency. Results from our simulation also demonstrate the viability of the solar thermal driven DCMD process for small-scale seawater desalination applications. Distillate production is dependent on the availability of solar radiation during the day; nevertheless, a small system with a 7.2m2 spiral-wound DCMD module and a 22.6m2 flat plate solar thermal collector can produce over 140kg of distillate each day under real weather conditions. This is equivalent to a daily distillate production rate of 19.7kg per m2 of membrane or 6.3kg per m2 of solar thermal collector.

Recent Progresses in Preparation and Characterization of RO Membranes

Reverse osmosis (RO) is a water purifcation technology that uses a semipermeable membrane to remove ions, molecules, and larger particles for the production of drinking water. The frst RO membrane for seawater desalination, wastewater treatment and other applications were made of cellulose acetate. But, the polyamide thin-flm composite membrane that can tolerate wide pH ranges, higher temperatures, and harsh chemical environments is the most popular, currently. To further improve the membranes’ performances, the recent trend in polymer-based membrane research has been focused to investigate various types of nanocomposite membranes, in which nanosized fllers such as SMCNT, MWCNT, graphene, graphene oxide, silica, or zeolite are incorporated. However, there are many challenges to commercialize the application of these membranes. Nowadays, it is a norm to characterize membranes by the advanced characterization techniques such as Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy and others for studying the physical and chemical properties of membranes and to co-relate those properties to the performances of the membranes. In this work, different aspects of RO membranes and proposed characterization methods, as well as recent progresses have been reviewed, comprehensively.

Reduced Graphene Oxide–Polyurethane Nanocomposite Foam as a Reusable Photoreceiver for Efficient Solar Steam Generation

Solar steam generation driven by local hot spots is an efficient route to use solar energy. We introduce a novel photoreceiver composed of reduced graphene oxide (rGO) and polyurethane (PU) matrix for highly efficient solar steam generation. The rGO nanosheets covalently cross-linked to PU matrix provide excellent stability and broad optical absorption, together with the property of thermal insulation served by PU resulting in rapid increase of local thermal under illumination. Moreover, the hydrophilic segments and the interconnected pores of rGO/PU can be worked as water channels for replenishment of surface water evaporated. With excellent mechanical and chemical stability, the functional rGO/PU foam exhibited a solar photothermal efficiency of ∼81% at a light density of 10 kW/m2. The novel macro design demonstrated here is low cost, simple to prepare, and highly stable, being suitable for a series of practical applications in massive seawater desalination, solar steam generation, and sterilization of ...

Seawater desalination using air gap membrane distillation-an experimental study on membrane scaling and cleaning

The connection between operating temperature and membrane scaling/cleaning during an air gap membrane distillation (AGMD) process of seawater has been systematically elucidated in this study. Experimental and mathematically simulated data demonstrate the profound influences of feed salinity and membrane scaling on water flux at various operating temperatures. Feed salinity exerted significant impacts on water flux at high operating temperatures because of aggravated polarization effects. Membrane scaling and the subsequent membrane cleaning efficiency were also strongly affected by operating temperatures. Indeed, membrane scaling was more severe and occurred at a lower water recovery when operating at 60-50 °C (feed-coolant temperature) compared to that at 35-25 °C. Moreover, membrane cleaning with fresh water and vinegar was less effective for the membrane scaled at 60-50 °C compared to 35-25 °C. Finally, membrane cleaning using vinegar was much more efficient than fresh water. Given the availability of vinegar at household level, vinegar cleaning can potentially be a low cost and readily accessible approach for MD maintenance for small scale seawater desalination applications in remote coastal communities.

Anti-fouling and high water permeable forward osmosis membrane fabricated via layer by layer assembly of chitosan/graphene oxide

To date, forward osmosis (FO) has received considerable attention due to its potential application in seawater desalination. FO does not require external hydraulic pressure and consequently is believed to have a low fouling propensity. Despite the numerous privileges of FO process, a major challenge ahead for its development is the lack of high performance membranes. In this study, we fabricated a novel highly-efficient FO membrane using layer-by-layer (LbL) assembly of positive chitosan (CS) and negative graphene oxide (GO) nanosheets via electrostatic interaction on a porous support layer. The support layer was prepared by blending hydrophilic sulfonated polyethersulfone (SPES) into polyethersulfone (PES) matrix using wet phase inversion process. Various characterization techniques were used to confirm successful fabrication of LbL membrane. The number of layers formed on the SPES-PES support layer was easily adjusted by repeating the CS and GO deposition cycles. Thin film composite (TFC) membrane was also prepared by the same SPES-PES support layer and polyamide (PA) active layer to compare membranes performances. The water permeability and salt rejection of the fabricated membranes were obtained by two kinds of draw solutions (including Na2SO4 and sucrose) under two different membrane orientations. The results showed that membrane coated by a CS/GO bilayers had water flux of 2–4 orders of magnitude higher than the TFC one. By increasing the number of CS/GO bilayers, the selectivity of the LbL membrane was improved. The novel fabricated LbL membrane showed better fouling resistance than the TFC one in the feed solution containing 200ppm of sodium alginate as a foulant model.

Alleviation of water flux decline in osmotic dilution by concentration-dependent hydraulic pressurization

Forward osmosis has motivated practical applications in seawater desalination and agricultural irrigation due to its potential advantage of osmotic dilution. However, water flux decline accompanies with continuous dilution of the DS, which will cause extra membrane expenditure, until final osmotic equilibrium. Without the help of additional driving force, it is impossible to reduce driving force loss in OD. In this study, concentration-dependent hydraulic pressure is exactly introduced as an auxiliary driving force. Investigations on water flux decline behavior in OD showed that water fluxes at lower initial concentration difference, lower initial solution volume and AL-DS orientation suffered more severe decline; furthermore, it implied that additional hydraulic pressure could alleviate adverse effects of greater concentration difference variation generated by pressure-induced water flux increment on water flux. For given dilution of the DS, minimized change in bulk FS concentration was conducive to ensure the effectiveness of constant hydraulic pressure on reducing water flux decline. Validation experiments demonstrated that current model equations were more appropriate under lower hydraulic pressures, and stable water flux also relied on concentration difference variation corresponding to applied hydraulic pressure. Potential implications were highlighted in the context of technical progress of membrane preparation and application potential of OD.

Evaluation of Solar Parabolic Trough Collector for the Application of Seawater Desalination

Solar parabolic trough collector (PTC) was considered for seawater desalination under various flow and thermodynamic conditions while being subjected to a diurnal solar beam with seawater directly running through the PTC absorber. PTC are more economical and cost effective as well as they may yield the simplest systems. The governing equations applied to the PTC absorber were deduced from the energy and mass conservation principles and consequently numerical solutions were obtained using finite difference method. The numerical simulations were generated utilizing an in-house developed computer programs. The PTC was coupled directly with multi flash chambers. The results revealed that fresh water generation is sensitive to the vapor content of the saturated water in the PTC absorber as well as to the operating pressure; whereby the rate was observed to vary from 1.3 m3/day to slightly above 2.7 m3/day for the same PTC aperture area and under the same solar flux in the range of operations that were considered; thus demonstrating the importance of the operational conditions. Also, the results indicated that PTC are adequate for capturing solar energy by revealing that the rate of fresh water production was uniform for significant time of the sunshine period.

Incorporation of N-Methyl-d-glucamine Functionalized Oligomer into MIL-101(Cr) for Highly Efficient Removal of Boric Acid from Water.

Polymeric resins are practically important adsorbents in a wide variety of applications, but they generally suffer from low surface areas and limited functionalized adsorption sites owing to their closely compacted and tangled polymeric chains. A metal-organic framework (MOF)-polymer composite with enhanced adsorption capacity against the compacted polymeric resins was reported. The strategy to incorporate functionalized oligomer within the cavities of the MOF was demonstrated by the preparation of MIL-101(Cr) incorporated with N-methyl-d-glucamine-based organosiloxane polymer. The resulting MOF composite shows high efficiency for the removal of boric acid from water because of exceptionally high loading of functional groups responsible for the boron adsorption. This material offers promising perspectives for boron removal applications in seawater desalination.

Plasmonic near-touching titanium oxide nanoparticles to realize solar energy harvesting and effective local heating.

Through the excitation of plasmon resonance, the energy of plasmonic nanoparticles either reradiates through light scattering or decays into energetic electrons (absorption). The plasmon-induced absorption can greatly enhance the efficiency of solar energy harvesting, local heating, photodetection and photocatalysis. Here, we demonstrate that heavily self-doped titanium oxide nanoparticles (TiO1.67 analogue arising from oxygen vacancies in rutile TiO2) with the plasmon resonance dominated by an interband transition shows strong absorption to build a broadband perfect absorber in the wavelength range from 300 to 2000 nm covering the solar irradiation spectrum completely. The absorptivity of the fabricated array is greater than 90% in the whole spectral range. And the broadband and strong absorption is due to the plasmon hybridization and hot spot generation from near-touching TiO1.67 nanoparticles with different sizes. What is more, the local heating of a TiO1.67 nanoparticle layer is fast and effective. The temperature increases quickly from 30 °C to 80 °C within 200 seconds. This local heating can realize rapid solar-enabled evaporation which can find applications in large-scale distillation and seawater desalination. These findings actually open a pathway for applications of these newly developed plasmonic materials in the energy and environment fields.