Method For Seawater Desalination Research Articles

Biomimetically spider web-like hydrogels for high-efficiency solar evaporators

With the increasing population, the shortage of freshwater resources has become a problem faced by human beings. Although many hydrogel solar evaporators achieved high evaporation rates by increasing the intermediate water content to reduce the enthalpy of water evaporation, it is still challenging to explore effective photothermal materials to construct efficient hydrogel solar evaporators. Here, inspired by the spider web structure, interconnected porous hydrogels were proposed by cross-linking heterojunctions and polymers. For the first time, MXene heterojunction is applied to solar evaporators. The introduction of SnS2 greatly improves the light absorption of MXene, at the same time, benefiting from the multi-scale macro/micro fiber network structure, MXene-SnS2 hydrogel (MSH) has a good “lock-in” performance, which makes the heat locally distributed near the evaporable water. As a result, the MSH evaporator has a low enthalpy of evaporation, with an evaporation rate of 3.3606 kg m−2 h−1 in 3.5 wt% salt water, and can maintain 1.9 kg m−2 h−1 even in 10.5 % brine. The evaporators present superior purification performance for seawater, could maintain high and stable evaporation performance for 72 h. This design principle and excellent performance provide a potential method and design concept for seawater desalination.

Solar/microwave-driven composite membrane evaporation and its application in seawater desalination

Increased economic growth and population expansion has heightened the demand for water resources, leading to escalating levels of water scarcity. Sustainable seawater desalination methods, powered by renewable energy, offer promising solutions to the long-standing global water shortage. This study presents a method for seawater desalination that employs eco-friendly materials. The approach involves utilizing metakaolin-based porous geopolymer (GP) as the base material, and depositing graphene oxide (GO) to create a graphene oxide geopolymer (GOGP) composite membrane. The membrane undergoes in-situ self-reduction to obtain reduced graphene oxide geopolymer (rGOGP). The study examines the composition, microstructure, and water evaporation performance of the composite membrane under both solar/microwave-driven. The results show that, under microwave conditions with a frequency of 2450 MHz and power of 400 W, the evaporation rate can reach up to 4.13 kg·m−2·h−1, doubling the evaporation rate achieved through solar-driven evaporation at an equivalent efficiency level. Furthermore, the evaporation rate of the composite membrane remains consistent when exposed to high-concentration saltwater of 15 wt%. Notably, the removal rates of Na+, K+, Ca2+, and Mg2+ all exceed 99 %, meeting the drinking water requirements established by the World Health Organization. This study provides a novel approach to seawater desalination utilizing environmentally friendly materials and clean energy sources.

Plant transpiration inspired biomass-derived solar evaporator for highly efficient solar vapor generation

The interface solar evaporation is an energy-saving and environmentally friendly method for seawater desalination and sewage purification. In this work, a biomimetic solar evaporator (ppy@AZL) inspired by plant transpiration was designed to achieve high efficient vapor generation. The ppy@AZL evaporator was made of zizania latifolia as raw material, has a cellulose skeleton with high water transport after alkalization and was decorated with photothermal polypyrrole to form bionic branches and leaves, and has excellent photothermal conversion performance. The evaporation performance and potential application of ppy@AZL evaporator in seawater desalination and sewage treatment were studied. The results indicated that the average evaporation rate of the ppy@AZL in simulated seawater (3.5 wt%) under the irradiation of one sun (1 kW m−2) was 2.239 kg m−2 h−1, and the photothermal conversion efficiency was 93.4 % in this work. In addition, the ppy@AZL evaporator has excellent evaporation rate of 2.668 kg m−2 h−1 in 9 h outdoor continuous evaporation experiment of simulated seawater (3.5 wt%), and can continuously and stably generate vapor. Therefore, this study provided a new solar evaporator with low-cost, simple preparation, better salt resistance, and high evaporation performance for seawater desalination and sewage treatment.

Photo-Fenton-Active MIL-88A/CNT-Based PVA Hydrogel for Solar-Driven Water Evaporation and Simultaneous Volatile Organic Compound Removal.

Solar-driven interfacial water evaporation (SIWE) has emerged as a promising avenue for cost-effective freshwater production from seawater or wastewater. However, the simultaneous evaporation of volatile organic compounds (VOCs) presents a limitation for the widespread implementation of this technique. Thus, developing dual-functional evaporators capable of both desalining seawater and degrading VOCs is challenging. Herein, we fabricated an iron-based metal-organic framework MIL-88A/carbon nanotubes (CNTs) poly(vinyl alcohol) hydrogel (MCH) evaporator via the conventional freezing method for solar-driven seawater desalination and simultaneous photo-Fenton VOC degradation. Because of the superior photothermal conversion capability of CNTs, reduced thermal conductivity and water evaporation enthalpy within the hydrogel, and the photo-Fenton activity of rod-shaped MIL-88A, the MCH evaporator exhibits a higher evaporation rate of 2.26 kg m-2 h-1 under 1 sun illumination with simultaneous VOC degradation. The higher hydrophilicity and vertical channels in the MCH evaporator enable its self-salt cleaning ability, facilitating consistent seawater desalination, even in high salt concentrations up to 10 wt %. The synergistic effects of localized heating from CNTs and hydrogen peroxide activation through reactive sites of MIL-88A allow the MCH evaporator to degrade more than 93% of the added phenol during evaporation. This work presents a sustainable and efficient approach for solar-driven seawater desalination, offering simultaneous VOC degradation.

Corn straw coated with Fe3+-tannic acid bilayers as a photothermal material for solar steam generation

Recently, studies on developing a system to filter seawater into clean water using the method of water evaporation at the interface of photothermal materials and air using solar energy (solar steam generation - SSG) have attracted increasing attention from the scientific community. In those SSG systems, photothermal materials play a key role in improving water evaporation rate and efficiency. In this study, a photothermal material was fabricated by treating the corn straw with tannic acid and Fe3+ solution (cheap and environmentally friendly). The surface of photothermal material from corn stalks exhibited a good ability to absorb over 90% of light with wavelengths of 300-1500 nm due to the formation of a complex layer between Fe3+ ions and hydroxy groups (OH) of tannic acid with sizes of 200-1000 nm. Besides, corn straw consists of many vascular bundles and porous multilayers that exhibit a honeycomb-like structure, which improves the ability of water transportation and reduces the thermal conductivity of the material. Therefore, an SSG system utilising the photothermal material based on corn straw possesses a high-water evaporation efficiency of 1.58 kg m-2 h-1. This efficiency was stably maintained for a long time due to the durability of corn straw in various conditions. The corn straw-based photothermal material showed high potential for SSG utilising seawater desalination method with affordable fabrication cost and eco-friendly raw materials.

Electric Field-Enhanced Ion Rejection Rate in Freeze Desalination.

Freeze desalination is an appealing method for seawater desalination through freezing seawater. The percentage of ions in the liquid phase, which is termed ion rejection rate, is a critical factor affecting the performance of freeze desalination. Improving the ion rejection rate is an important topic for freeze desalination. In this work, we investigate the effects of electric fields on the ion rejection rate during the freezing of seawater through molecular dynamics simulations. It is found that the ion rejection rate increases with increasing electric field strength. The enhanced ion rejection rate is due to the reduction of the energy barrier at the ice-water interface caused by the electric field, which affects the orientation of water molecules and ion-water interactions. However, the electric field hinders the ice growth rate, which affects the productivity of freeze desalination. Nevertheless, the finding in this work offers a new idea to improve the ion rejection rate. Practically, a trade-off needs to be found to optimize the overall performance of freeze desalination.

Efficient evaporation of seawater desalination by novel double-interface evaporator: Photothermal conversion, water transfer and salt-resistant

Interfacial solar-driven water evaporation emerged as an established eco-friendly method for seawater desalination to combat water scarcity, yet the low water evaporation rate and cost-effectiveness limit the practicable application. Herein, we presented a double-interface evaporator with a bilayer structure (BCCu@FC). The upper layer was constructed using carbonized copper-doped biochar (BCCu), which exhibited broadband sunlight absorption and effective photothermal conversion capability for the localized surface plasmon resonance (LSPR) effect. Meanwhile, the lower layer was constructed by felt fabric (FC), which featured a large spatial network structure, guaranteeing sufficient water transportation. Therefore, BCCu@FC exhibited a high photothermal conversion efficiency of 87.05% with a 1.571 kg m-2 h-1 water evaporation rate under 1 sun illumination. Moreover, BCCu@FC further exhibited high stability and salt resistance, showing no significant salt crust formation after continuous operation for 24 h under 3.5 wt% brine. Especially, BCCu@FC could stably work under 21 wt% brine, and the salt crust re-dissolved within 4 h after the cessation of illumination. This facile and universal strategy was anticipated to pave the way for future designs and fabrication of diverse, more efficient, and cost-effective photothermal conversion devices.

Experimental investigation of freezing desalination using silicon oil for ice production

Because of its potential benefits in lowering process energy consumption, freezing desalination as a seawater desalination method has attracted a lot of attention. However, significant mass loss caused by extensive washing is a fundamental problem preventing the development of freezing desalination technologies. For freezing desalination technology to be widely adopted, the washing process must be eliminated. In this study, a fluid-layer-based method for separating ice is introduced. The density differences between the generated ice and the silicon oil intermediate fluid layer facilitate the separation of the product water without the need of conventional crushing or washing processes. The aim of this work is to study the feasibility and applicability of using silicon oil as an intermediary fluid layer in ice separation during the freezing desalination process. The outcomes show promise for a feasible freezing desalination technique utilizing silicon oil as an intermediate separation layer. It was also observed that as feed salinity decreases, the desalination rate increases. For instance, the distillation rate is 50.89 % and 67.3 % at an initial feed salinity equal 45,000 and 10,000 ppm, respectively. Overall, the initial feed salinity and COP are found to have an impact on specific energy usage.

Supplemented desalinated seawater using sulfuric acid activated zeolit as hydroponic medium for mustard (Brassica juncea L.)

Sufficient agricultural water for irrigation is an important factor in food production, yet available fresh water only occupies 1% of the water on the earth. Seawater, through desalination, becomes rational solution to provide agricultural water due to abundant quantities and beneficial nutrients for crops. Hydroponic using desalinated seawater as medium is an approach to accomplish food security, especially in the arid and coastal areas. This study aimed to examine the growth of mustard (Brassica juncea L.) on a blend of fresh water and desalinated seawater using sulfuric acid activated zeolite as hydroponic medium. The experiment consisted of one control (100% fresh water+AB mix) and treatments namely a blend of 70% fresh water and 30% desalinated seawater using sulfuric acid activated zeolite with various sulfuric acid concentrations i.e 0.5, 1, 1.5, 2, 2.5, 3, and 3.5 N. The growth of mustard in blend of 70% fresh water and 30% desalinated seawater was lower than fresh water. A blend of 70% fresh water and 30% desalinated seawater using 1.5 N sulfuric acid activated zeolite showed no significant different mustard growth compared with fresh water medium and the fresh weight reduction was about 24%. Insignificant different growth between optimum treatment and control indicated a simple desalination method in this study can be utilized to desalinating seawater for hydroponic medium purpose. This finding emphasized that the simple seawater desalination method in this study for hydroponic medium was promising and interesting to be further developed for sustainable water management and agriculture.

Wood-inspired biomimetic vascular evaporator for highly efficient and stable solar steam generation in harsh environments

Solar-driven interfacial evaporation has great potential in freshwater harvesting, but it remains a huge challenge to maintain the structural stability of solar evaporator in complex and harsh environments while ensuring the water evaporation capacity. Herein, inspired by the mechanical stability and water transportation capability of vascular system in natural wood, a biomimetic vascular evaporator (BVE) was prepared by ice template induced self-assembly method for high-efficiency solar energy-driven seawater desalination and wastewater purification in harsh environments. Due to the ice crystals grow vertically and sublimate, the gel was squeezed to form a structure like vascular bundles with a uniform three-dimensional network structure and parallel vascular pores. The experimental results show that the vascular structure of BVE provides effective structural stability that 1000 times of repeated compression at 80% deformation without being destroyed. Meanwhile, integrating rapid water transportation capability, thermal positioning effect, and the reduced vaporization enthalpy endow high evaporation capacity (2.37 kg m−2 h−1, 93.11% pure water efficiency) under 1 sun irradiation. In particular, the above performance of BVE allows it to maintain a high and stable freshwater production capacity in various harsh environments, such as acid and alkali solutions, organic dyes, heavy metal wastewater, and wet soil. This work provides new insights into the rational design of the bionic photothermal evaporator, and demonstrates its potential application in long-term effective wastewater purification in harsh environments.

Salt-blocking three-dimensional Janus evaporator with superwettability gradient for efficient and stable solar desalination

Solar interfacial steam power generation is a prospective method for seawater desalination. In this work, a salt-blocking three-dimensional (3D) Janus evaporator with a superhydrophobic to superhydrophilic gradient was fabricated by spraying a composite dispersion of multi-walled carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) onto the top side of a polyurethane (PU) foam and polyvinyl alcohol (PVA) solution onto the bottom side. The CNTs/PDMS composite dispersion with nanostructured CNTs and low surface energy PDMS combined with the porous structure of the PU foam rendered the top side superhydrophobic. Therefore, a layer suitable for photothermal conversion was obtained. The hydrophilic PVA combined with the porous structure of the foam rendered the bottom side superhydrophilic, facilitating water absorption and transportation. The asymmetric wettability gradient of the CNTs/PDMS-PU-PVA as a 3D evaporator caused the evaporation rate and transportation speed of water to reach a balance, and the salt was quickly dissolved at the superhydrophilic interface. This 3D salt-resistant Janus evaporator achieved an evaporation rate of 2.26 kg m-2 h−1 under 1 kW m−2 illumination.

Thermoeconomic analysis of seawater desalination methods in Bandar Abbas power plant

Thermoeconomic analysis of seawater desalination methods in Bandar Abbas power plant

Theoretical and experimental study of a new freezing desalination system assisted by ultrasound

Compared with traditional seawater desalination methods, freezing desalination has gotten more attention for its advantages in reducing energy consumption and environmental protection. In this study, a new freezing desalination assisted by ultrasonic is proposed to improve desalination efficiency. A detailed freezing desalination model is established based on phase transition analysis and ultrasonic-assisted freezing theory. The experiment system is also developed to analyze the desalination process. The factors such as temperature, interface transformation and salinity in the process of droplet freezing under the action of ultrasound were analyzed and discussed. The result showed that the salinity of the droplet residual brine could decline to less than 2.4% when the initial salinity was 5% and droplet diameter was 2 mm after 1 min centrifugal treatment. After the treatment, the salinity of the existed ice-brine mixing was decreased below 0.2%. According to experiments and simulation analysis, the application of ultrasonic wave in freezing desalination can effectively increase the freezing speed of droplets and improve the efficiency of desalination. This study will contribute to the application of ultrasonic in the freezing desalination.

Designing salt transmission channel of solar-driven multistage desalination device for efficient and stable freshwater production from seawater

Solar-driven passive multistage distillation (MSD) device provides a new approach for environmentally friendly freshwater production. However, the MSD device easily forms salt crystals on the evaporation surface when treating brine, resulting in performance degradation. Here, we design an MSD device with an effective salt-resistant structure to enable rapid and automatic removal of high-concentration brine by a gravity drive. The structure was optimized by laboratory experiments and simulation. As a result, the stable freshwater production rate of the 4-stage device can reach 1.98 kg m−2 h−1 under a 1 kW m−2 light intensity. In particular, the MSD device can work stably at a high light intensity of 4 kW m−2 with an evaporation rate of 8.26 kg m−2 h−1, making its freshwater yield more than 1.7 times higher than that of a device without a salt-blocking structure. In summary, we explored a new method for salt removal in MSD devices, which is a meaningful method for long-term seawater desalination.

Corrigendum to “A greener seawater desalination method by direct-contact spray evaporation and condensation (DCSEC): Experiments” [Appl. Therm. Eng. 179 (2020) 115629

Corrigendum to “A greener seawater desalination method by direct-contact spray evaporation and condensation (DCSEC): Experiments” [Appl. Therm. Eng. 179 (2020) 115629

Photothermal Diatomite/Carbon Nanotube Combined Aerogel for High‐Efficiency Solar Steam Generation and Wastewater Purification

Solar‐driven interface evaporation is a sustainable and green method for seawater desalination and wastewater purification which has attracted great attention due to the expectation to solve the global fresh water crisis. Currently, its commercial application is still limited by high cost, a complicated preparation process, and unsatisfying photothermal conversion efficiency, which are difficult to be achieved simultaneously. Herein, a nontoxic, high efficient, low cost, and facile strategy to fabricate a solar steam generator is demonstraterd, in which biocompatible agar powder, carbon nanotubes, and diatomite are combined to achieve an aerogel. All materials involved are commercially available. The aerogel exhibits a water evaporation rate of 1.67 kg m−2 h−1 with 91% conversion efficiency under one sun illumination, and can produce drinkable water from sea water, lake water, and even strong acid/alkaline water with nearly 100% rejection of organic dyes. Most importantly, the cost to produce such an aerogel is only 6.67 $ m−2, and is expected to produce 5–8 kg m−2 of fresh water per day under natural sunlight, which is enough for a family of three to live normally for one day. Present high‐efficient and economic water purification system provides promise for commercial application in seawater desalination and wastewater purification.

Hyperstable and compressible plant fibers/chitosan aerogel as portable solar evaporator

Solar interfacial evaporation is an effective zero-energy method for seawater desalination, and solar evaporator is the key component in this evaporation system. Despite a great deal of solar evaporators have been reported, the poor portability of large-scale evaporators as well as high costs and materials toxicity still restrict their applications. In this work, a portable solar evaporator was constructed with low-cost plant fibers from papermaking pulp, using a facile method in absence of any toxic cross-linkers and solvents. The evaporator exhibited excellent stability and flexibility, and endured tremendous and repeated compression over 100 times. A large-scale evaporator could be compressed to reduce storage space by 78%, which would be portable for individuals. The evaporator presented a high evaporation rate of 1.38 kg m-2h−1, and solar-to-vapour conversion efficiency of 84.27% under one sun irradiation. The portable solar evaporator was salt-rejecting, and worked well under harsh conditions of high salinity and different pH values. The entire material cost of this potable solar evaporator is approximately 1.75 U.S. dollar m−2, much lower than those of conventional solar evaporators. This study provides a new approach for preparing portable and cost-effective solar evaporator.

Decreasing Seawater Desalination Footprint by Integrating Bipolar-Membrane Electrodialysis in a Single-Pass Reverse Osmosis Scheme

Reverse osmosis (RO) is currently the most cost-efficient method for seawater (SW) desalination; however, producing high-quality water with a low boron concentration typically requires a two-pass process, which increases the required area and chemical consumption. We propose a sustainable and economic pathway for boron removal in a single RO step, thus reducing the area footprint. At the same time, chemicals are produced onsite from the RO brine using bipolar membrane electrodialysis (BMED), thus reducing the chemical footprint. We conducted BMED using natural and synthetic feed solutions and studied the acid and base production kinetics and electricity consumption to assess the feasibility. In terms of energy efficiency, the divalent cationic impurities in the feed are more detrimental than the anionic ones. We found that monoselective cation-exchange membranes are not efficacious in eliminating these, and hence, precipitation/nanofiltration before BMED is essential. As a BMED feed, the nanofiltered SWRO brine was the best option over SW or nanofiltered SW. Economical analysis shows that as compared to purchasing chemicals, BMED integration can reduce the process cost by 45%. In addition, the results point to the flexibility of the proposed design that increases its robustness toward fluctuation in chemicals and electricity prices.

Research on Key Technologies of Ocean Thermal Desalination

Due to the process of urbanization and industrialization, the crisis of freshwater resources has become a problem to be solved by mankind. Although the traditional low-temperature multi-effect distillation method, multi-stage flash evaporation method and reverse osmosis membrane method seawater desalination currently occupy the mainstream position [1], Low-temperature multi-effect distillation method brine evaporation temperature cannot exceed 70 °C, reverse osmosis membrane method has the characteristics of high requirements for seawater pretreatment, and multi-stage flash evaporation method has the defect of high energy consumption. Therefore, ocean temperature difference can be used as a renewable energy source. Due to the huge reserves, about 10TW (10x1012W) that can be developed and utilized in the world is recognized by the international community as one of the most potential energy sources[2]. This article first describes the significance of the development of ocean temperature difference energy and the current research status of ocean temperature difference energy seawater desalination; secondly, it takes the ocean temperature difference energy seawater desalination method as the research object, based on the technical difficulties of ocean temperature difference energy seawater desalination and the process of the seawater desalination method that reduces the temperature difference. Four aspects put forward the main factors to improve the performance of the system; finally, it is concluded that the transformation of the key technological achievements of the ocean temperature difference energy seawater desalination method will provide more energy-saving, environmentally friendly, and more efficient for the comprehensive development and utilization of marine engineering, offshore oil drilling platforms, and islands. High-quality freshwater resources.

Improved Formation Kinetics of Carbon Dioxide Hydrate in Brine Induced by Sodium Dodecyl Sulfate

Due to high efficiency and low cost, hydrate-based desalination is investigated as a pretreatment method for seawater desalination. To improve the formation rate of hydrates, the effect of sodium dodecyl sulfate (SDS) on CO2 hydrate formation from a 3.5 wt.% NaCl solution was measured at 275 K and 3 MPa. X-ray diffraction (XRD) and cryo-scanning electron microscopy (cryo-SEM) were used to measure the crystal structure and micromorphology of the formed hydrates. The results showed that the induction time of CO2 hydrate formation reduced from 32 to 2 min when SDS concentration increased from 0.01 to 0.05%, the hydrate conversion rate increased from 12.06 to 23.32%, and the remaining NaCl concentration increased from 3.997 to 4.515 wt.%. However, as the SDS concentration surpassed 0.05 wt.%, the induction time increased accompanied by a decrease in the hydrate conversion rate. XRD showed that the CO2 hydrate was a structure I hydrate, and SDS had no influence on the hydrate structure. However, cryo-SEM images revealed that SDS promoted the formation of hydrates by increasing the specific surface area of the formed hydrates and folds; rods and clusters could be found on the surface of the CO2 hydrate. Thus, the best SDS concentration for promoting CO2 hydrate formation was approximately 0.05 wt.%; desalination was most efficient at this concentration.