Seawater Desalination Technology Research Articles

Analysis of Boron Removal By Capacitive Deionization

Climate change and water overextraction are some of the reasons for a growing global water stress, with seawater desalination being the leading solution worldwide. The state-of-the-art technology for seawater desalination is reverse osmosis (RO), utilizing mechanical pressure to push seawater through membranes, leaving the dissolved species in the brine. However, boron, which is considered toxic in high concentrations, is poorly removed by RO. This is because under normal conditions boron is present as boric acid, a small neutrally-charged compound. The most common technique to overcome this problem includes multiple RO stages combined with chemical dosage of the effluent, ensuring boron is present as borate, a charged species, present in high pH conditions.Capacitive deionization (CDI) is an emerging membraneless technique for water treatment and desalination, based on electrosorption of salt ions into microporous electrodes. Large internally-generated pH gradients develop during CDI operation, and thus CDI can potentially remove boron without chemically adjusting the feed pH. Here, we present a novel theoretical framework predicting the adsorption of boron in micropores, while considering pH-dependent chemical surface groups in the micropores, ion transport in the macropores, and local electrolyte pH. Moreover, we account for association and dissociation reactions of boron-consisting compounds in the electrolyte[1].We analyzed the effects electrodes order have on pH dynamics, where panels a. and b. in the attached figure present spatiotemporal plots of the pH for the case where cathode is placed upstream (panel a., cat-an) and the anode placed upstream (panel b., an-cat). This analysis shows that higher pH in the anode are expected for the an-cat configuration, counter to common-wisdom in the field. Panel c. follows this trend, by presenting the removed boron as a function of scaled flow velocity for both configurations. The results show, both experimentally and theoretically, that an-cat configuration should be preferred. Similarly, we found that an optimum charging voltage exists, even without accounting for parasitic reactions. Moreover, we found that also the discharging voltage significantly affects boron removal. Overall, CDI is a promising technology for boron removal, but a deep theoretical understanding of the problem is crucial towards future optimization.

Enhanced capacitive deionization properties of activated carbon doped with carbon nanotube-bridged molybdenum disulfide

The shortage of freshwater supplies has restricted societal development. Capacitive deionization (CDI) is an emerging technology for desalination of seawater or brackish water, the performance of which is highly dependent on electrode materials. In this work, a molybdenum disulfide/carbon nanotube composite (CNTs-b-MoS2) with high capacitance was successfully synthesized using a hydrothermal method. The composite exhibited a specific capacitance of 112.79 F g−1. To reduce costs and determine the practicality of using CNTs-b-MoS2 for CDI, we combined activated carbon (AC) with CNTs-b-MoS2 as a CDI electrode. The research demonstrated that after doping with 5% (mass ratio) CNTs-b-MoS2, the specific capacitance and electrosorption capacity of AC were significantly improved and the maximum desalination capacity of CNTs-b-MoS2/AC reached 8.19 mg g−1. The low dosage of CNTs-b-MoS2 combined with the high specific surface area of AC avoided the shortcomings of CNTs-b-MoS2, namely low specific surface area and high cost. Moreover, the outstanding conductivity of CNTs-b-MoS2 improved the conductivity and enhanced the adsorption capacity of AC, giving CNTs-b-MoS2/AC potential as an advanced, low-cost CDI electrode material.

Optimization of Evaporation and Condensation Architectures for Solar-Driven Interfacial Evaporation Desalination.

Solar-driven interfacial evaporation is an ideal technology for seawater desalination, and the corresponding system is mainly composed of a solar evaporator and a condensing collector. The traditional scheme focuses on the evaporation efficiency of the evaporator. Still, it ignores the influence of condensing collection scheme on the overall efficiency, which is one of the obstacles to the practical use of solar seawater desalination. Here, we reported a new solar-driven interfacial evaporation seawater desalination system by studying the influence of the condensation architecture, i.e., vapor flow by a fan and an air pump, sidewall material, transparent cover shape and material, evaporation level, and transparent cover heating, on the apparent collection efficiency of the system. The apparent collection efficiency was up to over 90% after optimization. This study is expected to promote the practical application of solar evaporation desalination technology.

Stable, zero liquid discharge, and highly efficient solar-driven multistage distillation device based on tree-inspired radial water transfer

Emerging solar-driven passive multistage distillation (MSD) devices are considered one of the most promising strategies for environmentally friendly freshwater production, but salt-resistant and stability remain challenges. Here, an MSD device with a well-tolerated salt-resistant structure was designed to control the crystallization location by radial water transfer. The device is capable of producing both freshwater and salt crystals with in-situ zero liquid discharge. For a well-designed 7-stage device, the steady evaporation rate and the salt yield reached 2.21 kg m−2 h−1 and 60 g m−2 h−1 under a 1 kW m−2 light intensity and 3.5 wt% NaCl solution. In particular, the device maintained stable evaporation performance at high brine concentrations of 10 wt%, demonstrating the broad applicability of the strategy. Thus, this novel approach to the stable operation of MSD devices demonstrates a promising option for seawater desalination technology.

Towards highly salt-rejecting solar interfacial evaporation: Photothermal materials selection, structural designs, and energy management

With the development of the industry, water pollution and shortage have become serious global problems. Owing to the abundance of seawater storage on earth, efficient solar-driven evaporation is a promising approach to relieve the freshwater shortage. The solar-driven evaporation has attracted tremendous attention due to its potential application in the seawater desalination and wastewater treatment fields. Also, the solar-driven evaporation efficiency can be enhanced by designing both solar absorbers and structures. Up to now, many strategies have been explored to achieve high solar-driven evaporation efficiency, mainly including the selection of photothermal conversion materials and structure optimization. In this review, the solar absorbers, structural designs, and energy management are proposed as the keys for high performance solar-driven evaporation systems. We report four kinds of solar absorbers based on different photothermal conversion mechanisms, substrate structure designs, and energy management methods for the purpose to achieve high conversion efficiency. And we also systematically investigate the available salt-rejections strategies for seawater desalination. This review aims to summarize the current development of efficient solar-driven evaporation systems and provide insights into the photothermal conversion materials, structural designs, and energy management. Finally, we propose the perspectives of the salt-rejection technologies for seawater desalination.

Heat recovery capacity and water desalination performance of passive solar vacuum tube distiller

The direct thermal distillation utilized the solar vacuum tube was a seawater desalination technology with quite a development potentiality. Therefore, an efficient passive solar vacuum tube distiller (P-SVTD) with a heat recovery function was developed in this paper, which realized the integration operation of raw water vaporization and high-temperature steam self-pressurization. It also had the character of simultaneously carrying out boiling vaporization and interfacial vaporization. The mechanisms of photo-thermal conversion and heat-mass transfer in the whole operation process of P-SVTD were analyzed. The theoretical calculation models of water yield (msh) and heat recovery rate (HRR) were presented. The water desalination performance, temperature level of recovered heat, and HRR of P-SVTD were measured to obtain the comprehensive photo-thermal conversion efficiency (HE) of P-SVTD. The results showed that the optimal depth ratio of the vapor–liquid interface to the vaporized-pressurized cavity was 0.9718. The water yield of P-SVTD was positively correlated with the total solar irradiance on the inclined plane by the trend of an exponential function. The average temperature level of recovered heat, HRR, and HE of P-SVTD were 74.30 °C, 28.68 %, and 87.43 %, respectively. And the rejection capacity (REJ), the decreased degree of conductivity, and the pH of P-SVTD were close to 100.00 %, 100.00 %, and 7.00, respectively, which showed excellent desalination capacity. The research provided solid technical and theoretical support for promoting the large-scale application of passive solar distillation technology.

Phase equilibrium conditions in cyclopentane hydrate forming systems coexisting with sodium chloride aqueous solution under atmospheric pressure and vacuum condition

The equilibrium condition measurements were performed in the cyclopentane clathrate hydrate forming systems coexisting with sodium chloride as a technological basis for the development of seawater desalination technology using clathrate hydrates. The experiments were performed in the system under vacuum condition in addition to the system under atmospheric pressure. The equilibrium conditions in the system under the vacuum condition are essential to accurately construct the phase diagram in the cyclopentane clathrate hydrate forming system without the effects of the surrounding air. The equilibrated phases were sodium chloride aqueous solution + cyclopentane clathrate hydrate + liquid cyclopentane + vapor cyclopentane in the system under the vacuum condition. The concentration of sodium chloride investigated in this study, wNaCl, was 0 ≤ wNaCl ≤ 0.210 in mass fraction. The equilibrium temperature in both systems decreased with increasing wNaCl. The equilibrium temperature at a fixed concentration of sodium chloride under the vacuum condition was lower than that under the atmospheric pressure. It was attributed to the compression by the atmospheric pressure in addition to the incorporation of molecules constituting the atmospheric air.

Assessment of the innovative freezing-melting technology for desalination of the Mediterranean seawater in the Gaza Strip, Palestine

Assessment of the innovative freezing-melting technology for desalination of the Mediterranean seawater in the Gaza Strip, Palestine

Enhanced Solar Evaporation Using a Scalable MoS2 -Based Hydrogel for Highly Efficient Solar Desalination.

Interfacial photo-vapor conversion has been suggested as a cost-effective and sustainable technology for seawater desalination. However, the conversion performance was still limited by some drawbacks, like salt accumulation and poor mechanical stability. Herein, a scalable MoS2 -based porous hydrogel (SMoS2 -PH) with good mechanical stability and salt resistance was successfully constructed through a crosslinking foaming polymerization method. With the high porosity (92.63 %), the SMoS2 -PH performed an impressive evaporation rate of 3.297 kg m-2 h-1 and photothermal conversion efficiency of 93.4 % under 1-sun illumination. Most importantly, the SMoS2 -PH could maintain high and stable photothermal properties for 15 days on the surface of seawater. We believe that the excellent salt resistance, the high photothermal conversion efficiency, the ease of scale preparation method and the available commercial MoS2 make the SMoS2 -PH a promising device for full-scale seawater desalination.

Enhanced Solar Evaporation Using a Scalable MoS2‐Based Hydrogel for Highly Efficient Solar Desalination

AbstractInterfacial photo‐vapor conversion has been suggested as a cost‐effective and sustainable technology for seawater desalination. However, the conversion performance was still limited by some drawbacks, like salt accumulation and poor mechanical stability. Herein, a scalable MoS2‐based porous hydrogel (SMoS2‐PH) with good mechanical stability and salt resistance was successfully constructed through a crosslinking foaming polymerization method. With the high porosity (92.63 %), the SMoS2‐PH performed an impressive evaporation rate of 3.297 kg m−2 h−1 and photothermal conversion efficiency of 93.4 % under 1‐sun illumination. Most importantly, the SMoS2‐PH could maintain high and stable photothermal properties for 15 days on the surface of seawater. We believe that the excellent salt resistance, the high photothermal conversion efficiency, the ease of scale preparation method and the available commercial MoS2 make the SMoS2‐PH a promising device for full‐scale seawater desalination.

1T/2H MoS2 nanoflowers embedded in porous PDMS sponge with high salt-resistance for efficient and durable solar desalination

Solar water evaporation is emerging as one of the most cost-effective and sustainable technologies for efficient seawater desalination. However, salt crystallization during solar desalination severely limits light absorption and reduces evaporation efficiency. Balancing the desirable evaporation rate and the suppressed salt crystallization is critical for long-term solar desalination, but remains a major challenge. In this work, 1T/2H MoS2 nanoflower embedded in a macroporous PDMS sponge (MoS2/PDMS) was fabricated and used as a novel solar evaporator for efficient and durable solar desalination. Thanks to the broadband absorption of MoS2 and the thermal insulating PDMS sponge, the MoS2/PDMS sponge presents a high evaporation rate of 1.47 kg m−2 h−1 and an evaporation efficiency of 81.5 % in pure water under one sun irradiation (1 kW m−2). Importantly, the MoS2/PDMS sponge with macroporous structure and wet-state hydrophilic wettability achieves efficient and durable solar desalination in simulated seawater (3.5 wt% NaCl solution), effectively suppressing salt crystallization. This finding offers a new way to design robust evaporators with structural flexibility, efficient evaporation and durable desalting for solar desalination.

Opportunities and Challenges of Seawater Desalination Technology

Opportunities and Challenges of Seawater Desalination Technology

MXene-based flexible and washable photothermal fabrics for efficiently continuous solar-driven evaporation and desalination of seawater

Solar-driven interface evaporation (SDIE) is a promising seawater desalination technology, which can achieve long-term and efficient seawater desalination in laboratory. However, because of fragile and easily damaged, the solar absorbers are difficult to be applied in the complex and changeable actual applications. In this work, a polypyrrole/Ti3C2Tx MXene-polydopamine-fabric (PPy/MXene-PDA-fabric) was prepared by a simple two-step polymerization method in this study, which can be used as the solar absorber of the SDIE system. Due to the unique physical properties of elastic fabrics, the PPy/MXene-PDA-fabric is easy to transport and clean, making it extremely practical. Meanwhile, the combination of polypyrrole, polydopamine, and MXene photothermal materials also ensures its excellent photothermal conversion performance. The research results show that the average evaporation rate of PPy/MXene-PDA-fabric can reach 1.485 kg/m2h in nearly 100 h of evaporation test under one sun irradiation. After 12 h of continuous operation, only a tiny amount of salt accumulated on the surface of the sample, which could be continued after a simple cleaning. The evaporation rate remained stable after eight cycles. Compared with the traditional solar absorber, PPy/MXene-PDA-fabric not only ensures efficient and durable solar evaporation performance, but also dramatically improves the practicability and environmental applicability.

Cradle-to-grave life cycle assessment of membrane distillation systems for sustainable seawater desalination

Membrane distillation (MD) is an emerging seawater desalination technology capable of utilizing low-grade heat. Many studies have been dedicated to MD systems design; however, few have offered comprehensive life cycle assessment (LCA). This paper develops a cradle-to-grave LCA framework for MD systems to shed some light on the environmental performance of MD technology. The MD systems consist of direct contact/air gap MD modules, heat exchangers, pumps, pipelines, and other equipment of heat sources. The MD modules comprise membrane, housing, condenser, and spacer. The heat sources are geothermal and solar energy, with auxiliary power from the grid and renewable energy sources. Life cycle inventories of the major components of the systems are established for the assessment. The ReCiPe 2016 method is chosen in this paper, including 18 midpoint indicators and three endpoint damage indicators. Results suggest that the major environmental impacts of renewable energy-driven MD desalination plants arise from the construction materials for the heat sources and the auxiliary power consumption in the operation stage. The environmental impacts can be reduced by 24.57%-70.79% when the auxiliary electricity supply from the grid is switched to renewable energy sources.

Modeling and Structural Optimization of MSF-RO Desalination System.

Based on the mathematical modeling and operational optimization studies of reverse osmosis (RO) and multistage flash (MSF) desalination, the structural optimization of the hybrid process was specially studied in this work with the consideration of reducing comprehensive expenses under given operational conditions. Firstly, according to the process mechanism and flowchart of the RO and MSF seawater desalination technologies, seven hybrid structures with different feed conditions were designed, and their connection equations were established for numerical calculation. Then, in order to evaluate the economic performance of the hybrid systems with different structures, the hourly average operational cost equations of RO and MSF processes were established and formulated as the comprehensive evaluation indicators. Next, with a given water production requirement, simulation calculations of the hybrid system with seven different structures were performed. The results show that the hybrid system with the fourth structure has the lowest operational cost of 4.6834 CNY/m3, and at the same time it has the lowest blowdown. However, if we take GOR or production water temperature as the target, the optimal structure of the hybrid system is the fifth or the seventh option. The obtained results are helpful in structural optimization of the hybrid system with aspects of operational cost reduction, maximum GOR, or minimizing the wastewater discharge.

Watermelon Flesh‐Derived Carbon Aerogel with Hierarchical Porous Structure for Interfacial Solar Steam Generation

Solar‐enabled interfacial steam generation is emerging as a sustainable seawater desalination technology, but its practical application is impeded by the high cost of materials and low evaporation rate. To solve these problems, a three‐dimensional (3D) carbon aerogel (CA) is prepared with hierarchical pores by the hydrothermal‐carbonization/freeze‐drying/carbonization treatment of watermelon flesh. The CA is composed of frizzy carbon thin sheets (thickness: ≈2 μm) and large pores (size: 200–400 μm), deriving from the carbonization of plant cells. Especially, plenty of ≈200 nm nanoparticles are located on these thin sheets, accompanying the formation of nanopores with a size of 200–400 nm. These hierarchical macro/nanopores can act as the “light traps,” conferring the broad (250–2500 nm) and strong photoabsorption (absorbance efficiency: 93%). Then, the CA is inserted into a ring‐like polystyrene foam to construct a 3D evaporator, which can float on seawater. Under the irradiation of simulated sunlight (1 kW m−2), the evaporator exhibits a high evaporation rate of 2.32 kg m−2 h−1and long‐term stability. Therefore, the CA acts as an efficient photothermal material for solar‐enabled desalination and also provides some insights for developing other biomass‐derived evaporators.

Methane Hydrate Formation in the Salty Water Confined in Clay Nanopores: A Molecular Simulation Study

A sound knowledge of the effects of clay surfaces and salt ions on CH4 hydrate formation is vital to understand the formation of natural gas hydrate resources and develop hydrate-based technologies, such as seawater desalination. Herein, microsecond simulations are conducted to investigate CH4 hydrate formation from fresh water and NaCl solution in kaolinite nanopores and the outside bulk phase. Simulation results show that the gibbsite surface shows strong affinity for water and salt ions, while the siloxane surface exhibits certain affinity for CH4 and hence affects hydrate formation. With two siloxane surfaces in the nanopore, hydrate formation is severely inhibited by the significantly lowered aqueous CH4 concentration, caused by surface adsorption of CH4 to form nanobubbles; salt ions greatly enhance such an inhibitory effect by promoting surface nanobubble formation and suppressing CH4 dissolution from nanobubbles. However, with one siloxane surface and one gibbsite surface presented in the nanopore, no nanobubble forms on the siloxane surface, no matter salt ions are present or not, and the inhibitory effects caused by the siloxane surface are not observed. In contrast, gibbsite surfaces are more beneficial to hydrate formation, and salt ions have little effect as most ions adsorb to the surface. Hydrate formation outside of the nanopores is obviously inhibited by salt ions, especially at high salt concentrations. Some interesting phenomena are observed, such as stochastic formation of large sI and sII hydrate domains, which then blocks the nanopore throat and hinders the mass transfer of CH4 and water, and sustained growth of large hydrate solids outside of the nanopore causes decomposition of small hydrate solids in the nanopore. Additionally, densification of salt ions in solution and formation of ion-containing hydrate cages are systematically analyzed to figure out the surface effects of kaolinite on the desalination process. These molecular insights are of scientific and engineering significance to sustainable chemistry related to exploitation of natural gas hydrate and hydrate-based seawater desalination technology.

Research on the economic and environmental impacts of China's seawater desalination industry with different technologies in the macroeconomic system

Reverse osmosis (RO) and multiple-effect distillation (MED) are China's main seawater desalination technologies. This paper made the cost analysis of RO and MED industries, compiled China's 2007, 2012 and 2017 input-occupancy-output tables with RO and MED industries specially separated, then estimated their economic and environmental impacts in China's macroeconomic system. Results show that RO and MED had a similar pulling effect on China's economy, and their pulling effects were higher than the average level of all 50 industries. From 2007 to 2017, the ranking of direct CO2 emission coefficient of MED industry rose from 5th to 3rd, and that of RO industry rose from 12th to 8th. Expanding the unit output of the seawater desalination industry brought more CO2 emission than the average level of all industries. Unit production of MED brought more CO2 emission than that of RO. With the CO2 emission APL model, the upstream three energy production industries, which had the strongest connection with the CO2 emission of RO and MED industries were identified. To reduce CO2 emission from RO and MED industries, it is practical to take CO2 emission reduction measures on the upstream three energy production industries.

Flexible MXene-based Janus porous fibrous membranes for sustainable solar-driven desalination and emulsions separation

Sustainable solar energy driven seawater desalination technology is currently deemed as a promising pathway to overcome the shortage of freshwater resources, but solar water evaporation material suffers from serious salt-fouling, low freshwater yield, and poor long-term performance in seawater. Herein, a Janus photothermal porous fibrous membrane, composed of hydrophobic MXene/Poly(dimethylsiloxane) coatings and a hydrophilic polylactic acid/TiO2 nanofluids porous fibrous membrane, was prepared. During the solar-driven seawater desalination process, the hydrophilic fibrous membrane, functioned as salt-rejection barrier, induced by TiO2 nanofluids and transport seawater to the surface through its microporous channels; the MXene/PDMS coatings acted as a photothermal layer and generated localized heat at the water-vapor interface upon light irradiation. The solar-thermal test results show that, the Janus porous fibrous membrane displays stable solar-thermal conversion efficiency of 60%, freshwater yield of 1 kg m-2 h-1 and low ion concentration (≤1 ppm) under 1 sun irradiation in direct contact mode, which is superior to other literatures reported. With synergistic effect of TiO2 nanofluids and MXene, the Janus fibrous membrane exhibits a high salt rejection rate of 99.95%, and antibacterial activity as high as of 100%. Notably, benefiting from opposite wettability of Janus porous fibrous membrane, the as-prepared membranes also display excellent separation flux and high separation accuracy (>99.95%) in various surfactant-stabilized oil/water emulsions. It is anticipated that this versatility of Janus porous fibrous membrane has excellent photothermal conversion capability and separation properties, making it have great application potential in using sustainable solar energy to collect freshwater from seawater, medical service wastewater and other application in environmental protection.

Experimental Study on Humidifier Performance in a Humidification-Dehumidification System

The characteristic of Humidification-dehumidification seawater desalination technology is flexible scale. It is suitable for dispersive fresh water demand and easy to couple with low-grade energy. In this study, an experimental platform of humidifier performance is designed to investigate the influence of spray flow, spray liquid temperature, air flow, hole diameter, pitch of holes and the number of sieve plates on moisture content of humid air at outlet and evaporation capacity. The results show that, when the spray flow and temperature increase, the moisture content of outlet air and evaporation capacity increase. The evaporation capacity increases when the extent of the air flow increasing is more than that of the moisture content decreasing. When the spray flow is 0.025kg/s, the evaporation capacity is the highest when the sieve plate with the hole diameter of 3.0mm and the holes pitch of 9.0mm is used. For other flow conditions, the evaporation rate is the highest when the sieve plate with the hole diameter of 2.5mm and the hole pitch of 7.5mm is used. The evaporation capacity with double sieve plates is higher than that with single sieve plate. The research of this paper provides guidance for practical application of the HDH seawater desalination system.