Desalination Rate Research Articles

Pine-derived porous carbon for efficient capacitive deionization and the role of its hierarchical pore structure

Capacitive deionization (CDI) is a low-energy, eco-friendly, and economically viable technology for seawater desalination. In the desalination process of CDI, the pore structure characteristics of electrode materials play a crucial role. In this study, the carbon materials with a hierarchical pore structure were prepared through high-temperature carbonization and KOH activation using pine powder as raw material. When the pine-derived porous carbon (PPC) was used as an electrode material, it was found that its specific capacitance is remarkably consistent with the specific surface area of the mesopores. This discovery provides guidance for further optimization and regulation of biomass-derived carbon electrode materials. The desalination performance of the PPC electrode was studied in detail by CDI and flow-electrode capacitive deionization (FCDI) devices. In NaCl solution with an initial concentration of 700 ppm, the equilibrium adsorption capacities in CDI and FCDI systems are 24.96 mg g−1 and 23.12 mg g−1, respectively. Particularly in FCDI tests, the average adsorption rate reaches 23.3 μg cm−2 min−1, and the desalination rate reaches 98.96 %. The PPC shows an excellent desalination performance, making it a promising efficient electrode material for electrochemical desalination.

Plasmonic group 4 transition metal carbide interfaces for solar‐driven desalination

AbstractTo combat the dwindling supply of freshwater, solar‐driven desalination using plasmonic nanomaterials has emerged as a promising and renewable solution. Refractory plasmonic carbide nanomaterials are exciting candidates that are inexpensive and chemically robust but have not been widely explored. Herein, plasmonic carbide interfaces made of TiC, ZrC, and HfC nanoparticle aggregates loaded onto to a mixed cellulose ester (MCE) membrane were explored to gain insight into their solar‐vapor generation and desalination potential. Desalination using Atlantic Ocean water under 1 sun intensity yielded rates of 1.26 ± 0.01, 1.18 ± 0.02, and 1.40 ± 0.01 kg m−2 h−1, with efficiencies of 86%, 80%, and 96% for TiC, ZrC, and HfC, respectively. Carbide interfaces showed good stability and effectively removed heavy metal ions and salt from solutions with concentrations up to 35%. PVA hydrogel based TMC evaporators afforded rates of 3.31 ± 0.03 and 3.22 ± 0.03 kg m−2 h−1 for TiC and ZrC, respectively. The HfC‐PVA interface afforded a high solar desalination rate of 3.69 ± 0.04 kg m−2 h−1, corresponding to an efficiency of 97% under 1‐sun illumination. The hydrogel evaporators also retained their strong salt rejection action over time.

Application of a functionalized thin-film composite nanofiltration membrane in water desalination

To prepare a thin-film nanocomposite (TFN) nanofiltration (NF) membrane, characterized with high desalination rate and antifouling performance, carboxylated multi-walled magnetic 1,2,3,4-butanetetracarboxylic acid carbon nanotubes (hereafter, the C-MWCNT-MBTCA) with a choice of hydrophilic groups were initially synthesized in this study, and then incorporated into the polyamide (PA) layer via interfacial polymerization (IP). After that, the surface morphology and hydrophilicity of the fabricated NF membrane was examined by the field emission scanning electron microscopy (FESEM) and water contact angle measurements, respectively. To assess the membrane application, the solutions (2000 mg/L) of sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), calcium chloride (CaCl2), and sodium chloride (NaCl) were consistently tested. On account of the ample carboxylic acid (R-COOH) groups in the modified TFN membrane, the study outcomes revealed that the given membrane could enhance the flux along with the desalination rate upon the addition of the C-MWCNT-MBTCA (0.04 wt%). Likewise, the pure water flux significantly grew from 58.8 to 110.5 Lm-2h−1 after the utilization of the C-MWCNT-MBTCA (0.04 wt%), and the Na2SO4 removal rate promoted from 87 to 98 %. Ultimately, it was established that the C-MWCNT-MBTCA could be used as an economical modifying agent to boost the performance of NF membranes for water desalination purposes.

Redox‐Flow Desalination with a Voltage Range Extending up to 2 V Under Dual‐pH Conditions

AbstractThe battery‐like systems utilizing redox materials present a promising avenue for electrochemical desalination with reduced energy consumption. However, several attempts have focused on reducing the operational voltage to minimize energy consumption, and efforts to enhance the performance of such systems as energy storage devices remain limited. Herein, a system with a high energy density capable of sustaining freshwater production was proposed. Furthermore, in this proposed system, the electrolytes with different pH values were utilized to implement an operational voltage of 2 V or higher. Accordingly, an alkaline Zn electrolyte was paired with acidic MnO2 or VOSO4 electrolyte. During the process, potential side reactions such as chlorine evolution and proton crossover were not observed, even without water‐splitting reactions. Ultimately, at operational voltages exceeding 2 V, the system achieved a desalination rate of 0.104 mg/cm2/min and demonstrated maximum energy discharge of up to 2.4 Wh/L. These designed systems pave the way towards a more environmentally friendly and efficient approach to desalination.

Advancing electrodialysis with dually cross-linked PVDF-based anion exchange membranes having semi-interpenetrating networks

Electrically-driven membrane technology plays a crucial role in water treatment and purification, finding applications in various fields like saline water and wastewater desalination, saline concentration and wastewater recycling. The content of this study is based on dually cross-linking and hot-pressing on a PVDF blend, to fabricate a kind of anion exchange membranes (AEMs) having semi-interpenetrating network and thus improve the defect of the traditional heterogeneous AEMs. The research explores the impact of vinyl imidazole (VIM) and dimethylaminoethyl methacrylate (DMAEMA) monomers, primarily or dually cross-linking, and optimizes the membrane properties through a hot-pressing process. Under these optimized conditions, the resulting membranes exhibit robust mechanical properties and outstanding desalination capabilities, achieving an area resistance of 2.56 Ω cm2 (comparable to standard homogeneous membranes), a desalination rate of 97.26% (outperforming the Neosepta AMX: 76.90%), and a salt limiting concentration of 3.1 M (surpassing the heterogeneous AEM and Neosepta AMX). Notably, this synthesis method is characterized by its cheap raw material and low energy consumption. This research offers valuable insights for the advancement and large-scale implementation of anion exchange membrane desalination.

Simulation of Nanofiltration Mass Transfer for Magnesium and Lithium Separation in Salt Lakes.

A mass transfer model to predict the transport processes of magnesium and lithium ions through porous media in salt lakes has been proposed, which is a combination of the extended Nernst-Planck equation and Donnan effect, accounting for ion diffusion, electromigration, and convection within membrane pores. First, the morphological structure, thickness, surface roughness, and hydrophilicity of the membrane were characterized as fixed parameters, indicating that the surface of the nanofiltration membrane is smooth with low roughness and strong hydrophilicity, resulting in a lower desalination rate but higher water flux. Subsequently, numerical calculations based on the model were conducted to establish a reasonable transport equation for predicting the concentration and retention rate of the main magnesium and lithium ions. When compared with the experimental results, a deviation of less than 5.5% is obtained, confirming the accuracy of the model in describing ion mass transfer. Finally, computational fluid dynamics techniques were employed to simulate the model equations in both the feed and permeate subdomains, demonstrating that the flow characteristics align with reality. Thus, the established transport model exhibits higher predictive accuracy for NF ion separation than one-dimensional models.

Preparation and characterization of nanocellulose acetate and acrylate polymer composite membrane

Abstract In the present study, a nanocellulose acetate and acrylate polymer composite membrane was formed by the phase transfer technique. The physical and mechanical properties, water flux, and desalination performance of the achieved composite membrane were investigated. When 3 % (w/w) acrylate polymer, 10 % acetylated nanocellulose, and 0.3 % mass fraction of TiO2 were used for the formation of the membrane, the obtained product could reach a tensile strength of 1.97 N/mm2 and a pure water flux of 51 L/(m2 h). Moreover, the composite membrane achieved a desalination rate of 92.4 %. Thus, the obtained composite membrane could meet the performance requirements for the treatment of industrial wastewater.

Flow electrode capacitive deionization with iron-based redox electrolyte

Flow electrode capacitive deionization (FCDI) employs carbon-based materials for electrochemical separation. Redox additives like vanadium, ferricyanide, and organic molecules have boosted desalination rates in FCDI. However, these additives must be low-cost, have chemical stability in electrolytes, and have low toxicity. We investigate two iron-based redox couples, iron chloride, and iron citrate, for their cost-effectiveness and reduced health risks. We incorporate them with activated carbon (AC) in flow electrodes, resulting in a significant enhancement of the salt removal rate, with iron chloride increasing it by 100 % and iron citrate by 23 % compared to standard AC slurries. In our system, the AC exhibits a salt removal rate of 7.8μmolcm−2min−1, while the iron chloride system reaches 15.6μmolcm−2min−1. Iron citrate flow electrodes achieve a desalination rate of 9.6μmolcm−2min−1, maintaining a pH suitable for potable water. We observe that iron chloride concentration in the flow electrode influences iron crossover and pH in the water streams, leading to acidity. Conversely, the iron citrate-based slurry maintains minimal iron crossover and a neutral pH. This study highlights iron-based redox additives as promising for FCDI slurries and the need for tailored flow electrode composition based on specific ion removal requirements.

Effect of Subsurface Drainage in Regulating Water on Desalinization and Microbial Communities in Salinized Irrigation Soils

In order to achieve water conservation and salt control in saline irrigation areas and improve the soil ecological environment of farmland in irrigation areas, this study carried out a field trial in 2020–2021 on edible sunflowers planted in saline subsurface farmland in the Hetao Irrigation District. Three irrigation level treatments and a control setup under subsurface drainage were compared. The control was with no drainage and local conventional irrigation levels (the spring irrigation amount is 240 mm and the bud stage irrigation amount is 90 mm, CK); and the three irrigation levels were conventional irrigation (the spring irrigation amount is 240 mm and the bud stage irrigation amount is 90 mm, W1), medium water (the spring irrigation amount is 120 mm and the bud stage irrigation amount is 90 mm, W2), and low water (the spring irrigation amount is 120 mm and there is no irrigation in the bud stage, W3). The results showed that soil desalinization was best in the conventional irrigation (W1) treatment and lowest in the low-water treatment (W3) under subsurface drainage. The desalinization rate was 13.54% higher in the subsurface drainage than in the undrained treatment with the same amount of irrigation water. Under subsurface drainage, the medium-water treatment (W2) increased the diversity of soil microorganisms and the relative abundance of dominant phyla such as Ascomycetes, Chlorobacterium, Acidobacterium, and Ascomycetes among soil bacteria and Ascomycetes and Tephritobacterium amongst fungi. The average sunflower yield in the treatments under subsurface drainage increased by 32.37% compared with the undrained treatment, and the medium-water treatment (W2) was the most favorable for protein and essential amino acid synthesis. Structural equation modeling indicated that desalinization rate, irrigation water utilization efficiency, bacterial Chao1 abundance and Shannon diversity, and fungal Chao1 abundance and Shannon diversity were the major influences on sunflower yield. Based on the entropy weight method TOPSIS model, 15 indicators such as soil desalinization rate, soil microbial diversity, water and nitrogen utilization rate, and sunflower yield and quality were evaluated comprehensively for each water treatment of subsurface drainage farmland. It was found that the irrigation volume under tile drainage of 210 mm (W2) had the highest comprehensive score, which could improve the soil microenvironment of the farmland while realizing water conservation and salt control in salty farmland, increase the production of high-quality crops, and be conducive to the sustainable development of agriculture; it was the optimal irrigation treatment for the comprehensive effect. The results of this study are of great significance for the realization of efficient water conservation and salt control and the protection of food security and ecological safety in the Hetao Irrigation District.

Effects of di-ions structure of the core layer ionomer on anion exchange membrane characteristics of anti-protein fouling and electrodialysis desalination

To investigate the effects of di-ions structure of the core layer ionomer on anti-protein fouling and electrodialysis (ED) desalination performance of the tailored anion exchange membranes (AEMs), three highly conductive structural-controlled ionomers containing aliphatic bridging cage quaternary di-ammoniums, aliphatic liner quaternary di-ammoniums, and aromatic quaternary di-ammoniums respectively have been synthesized. With the help of the previously established bi-directional in-situ interpenetration method, a series of double-sided anti-fouling AEMs were successfully fabricated from the gradient cross-linked anti-fouling thin layer CA(2% SA-0.10Ca) and the tailored ionomers. These AEMs have basic and electrochemical properties suitable for ED applications, and significant anti-protein fouling ability. The results of the ED desalination evaluations at high current density with salted egg white confirm further that DABCO-MeI-CA having aliphatic-bridging-cage-di-ions with the best electrochemical properties displays the best ED performance (desalination rate (DR) = 32.16%, energy consumption (EC) = 0.27 kWh kg−1) and good ED stability. Its ED performance is better than that of commercial AMX, with an increase of 20.74% in DR and a reduction of 34.15% in EC. Protein biuret detections verify no protein-through-membrane pollution occurred in the tests. The properties of DABCO-MeI-CA are promising for high current density ED desalination of organic macromolecule-contaminated salted systems.

Carbon felt (CF) acted as an “ionic capacitor” to enhance flow electrode capacitive deionization (FCDI) desalination performance

Flow electrode capacitive deionization (FCDI) is a new ion removal technology with sustainable deionization performance. However, the interface resistance has a significant impact on ions migration in FCDI. We therefore introduced a novel FCDI device that incorporated a layer of carbon felt as an “ionic capacitor” between the flow electrode and the ion exchange membrane, termed CF-FCDI. Mechanism exploration results revealed that the addition of carbon felt reduced device resistance, shorten electron transfer pathways, improved charge efficiency, and increased ion migration rate. Experimental results demonstrated that the improved CF-FCDI device achieved 44 % higher desalination rate compared to traditional device. In addition, long term operation experiments confirmed the stability of CF-FCDI device, highlighting its potential as a viable desalination solution. The findings of this study provided valuable insights for further development of FCDI and offered a promising solution for its applications such as seawater desalination.

Solvent-free fabrication of pore-filling cation-exchange membranes for highly efficient desalination

The traditional route for ion-exchange membrane fabrication usually involves complex procedures that require substantial quantities of organic solvents and optionally undergo post-modification utilizing strong base or acid. Here, we develop a completely green route for cation-exchange membrane fabrication via a simple soaking pore-filling polymerization method using water as the sole solvent. The resulting pore-filling cation-exchange membranes (PFCEMs) exhibited high ion exchange capacity, moderate water uptake, robust mechanical properties, low area resistance (1.3 Ω cm2) and high limiting current density (181 mA cm−2), leading to superior performance for salt desalination. Benefiting from the superior electrochemical properties, PFCEM achieved an ideal desalination rate of 93.4 %, which was comparable to that of the flagship commercial Neosepta CMX membrane (91.5 %). In addition, the low membrane cost and satisfactory long-term stability of the PFCEMs indicated promising features for their scale-up in industrial production and applications.

Integrating FeOOH with bacterial cellulose-derived 3D carbon nanofiber aerogels for fast and stable capacitive deionization based on accelerating chloride insertion

Faradic capacitive deionization (FDI), as an emerging research branch of capacitive deionization (CDI), has shown its great potential to relieve global water stress owing to its high desalination capacity/efficiency, flexible scale, and zero secondary pollution characteristics. However, the slow desalination kinetics and poor cyclic stability of the anion-capturing electrode of current FDI systems greatly limit its practical application. Herein, we proposed a strategy of interweaving FeOOH nanospindle inside the 3D network structure of carbon nanofiber aerogel to construct a 3D network structure (CNFAs@FeOOH) and further used it as a chloride capture electrode for FDI. As a result, the FDI system equipped with CNFAs@FeOOH enjoys excellent desalination performance with an ultrahigh desalination rate of up to 0.33 mg g−1 s−1. More importantly, the CNFAs@FeOOH-based FDI system enjoys excellent cycling stability with no significant decrease in 100 cycles and only 17.85 % decrease in 200 cycles.

A closed-loop integrated process of bipolar membrane electrodialysis and resin adsorption for resource recovery from high-salinity phenolic wastewaters: Salicylic acid manufacturing wastewater as a representative

Phenolic compounds stand as consequential chemical precursors, boasting an extensive array of industrial applications. The worldwide yield of such compounds attained 17 million tons annually, and a substantial volume of effluent characterized by elevated phenolics content along with inorganic salinity was emanated from the manufacturing processes, which would exert profound deleterious impacts upon the ecosystem and aquatic environment. Scant literature was available regarding efficacious treatment of these high-salinity phenolic wastewaters and complete recovery of its constituents currently. In this study, initially, various high-salinity phenolic wastewaters were treated in bipolar membrane electrodialysis (BMED) system, and the migration behavior of constituents was investigated. Drawing upon the migration patterns and the efficacy of BMED, a closed-loop integrated process of BMED and resin adsorption was proposed to thoroughly address this kind of wastewater and attain comprehensive material reclamation. Because of the wide use of salicylic acid (SA) all over the world, the enormous production in China, and the complexity of the sewage which contained rich Na2SO4, phenol, and SA from manufacturing process, SA manufacturing wastewater was selected as the representative sample. For the BMED process, the desalination rate got 99.4 % under the optimum conditions. The concentrations of H2SO4 and NaOH obtained were 0.56 and 0.78 mol/L. The preliminary separation of phenol and SA was realized during desalination. Then, the effluent of BMED feed compartment was injected into two-stage resin unit. The satisfactory regeneration of both spent resins was achieved, and high-purity phenol and SA were obtained. No contaminants were undetected in the effluent, allowing for the reuse of the effluent within BMED. The complete resource utilization of SA manufacturing wastewater was realized, indicating the viability of proposed integrated process for treating and resource recovering of analogous high-salinity industrial phenolic wastewater.

Facial synthesis of FeOOH array-anchored carbon fiber as flow-through chloride-capturing electrode for ultrafast and super-stable capacitive deionization

Faradic-based capacitive deionization (FDI) has been recognized as one of the most promising technologies to solve the freshwater crisis, yet was plagued by two most serious issues, i.e., slow desalination kinetics and poor cyclic stability. Herein, an ultrafast and super-stable FDI system is successfully developed based on the employment of a pseudocapacitive material as flow-through chloride-capturing electrode. While the pseudocapacitive material, anchoring FeOOH arrays on the surface of commercial carbon fiber cloth (CF@FeOOH) ensures high desalination durability by preventing possible FeOOH aggregation through the carbon fiber framework, the unique flow-through electrode enables fast mass transfer by channeling the feed stream inside its microchannels. Consequently, the FDI system equipped with flow-through CF@FeOOH electrodes displays an excellent desalination rate of 0.48 mg g−1 s−1 with ultra-robust cyclic stability (no reduction after 60 cycles and only 14.9 % capacity reduction after 150 cycles), while maintaining its high desalination capacity of 52.04 mg g−1, exemplifying the critical importance of both delicate material design and rational cell architecture.

Development in desalination and wastewater treatment: state of the art challenges, role of solar energy, and recommendations

Abstract Water purification is crucial to ensure the availability of safe and clean water for protecting human health and helping in a sustainable environment. This review explicitly provides an overview of the major developments related to seawater desalination and wastewater treatments as a unit. Anticipating these traditional independent facilities will operate together in the future mainly for economic benefits. The advances in seawater desalination are primarily focused on the production of membranes using different types of nanoparticles (CeO2, UiO-66, CS-NPs) and carboxylated multi-walled CNTs into a polyamide that provides high salt rejection (as high as 90%) with excellent selectivity and permeability. Further, the use of nanoporous reduced graphene oxide (rGO) membranes provided 27.7–62.6% desalination rates and up to 96.8% salt rejection, along with protection against membrane fouling. Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) showed excellent rejection of divalent ions during desalination. It is anticipated that the use of solar energy for membrane and thermal desalination may be promising since it reduces the reliance on fossil energy and significantly minimizes greenhouse gas emissions (up to 94%). Solar energy can integrate with the reverse osmosis (RO) process bearing the cost of energy-intensive compressors, making the RO economically attractive.

Carbon Reduction Path and Economic Analysis of Seawater Desalination in China under the “Dual Carbon” Goal

Carbon Reduction Path and Economic Analysis of Seawater Desalination in China under the “Dual Carbon” Goal

Comparative Assessment of the Phytodesalination rates of Duckweed and Water Hyacinth in Brackish Water

Brackish surface water is a challenge for mostestuarinecommunities to meet the water requirement for agricultural purposes. Desalination plantson the other hand,are costlyandenergy consuming method to run. This research compares the possible use of duckweed andwater hyacinth for their Phytodesalinationrates of brackish water. Three replicates containing about 100 g of each aquatic macrophytes in a trough with 10 litres of brackish water (salinity 7.69 ppt) were studied daily for 6 days. Electrical conductivity (EC), pH, total dissolved solids (TDS) and salinity were the measured water parameters thereafter, the treatment means were calculated. Results showed that maximum reductions of most of the water parameter were observed after 3 days of the research for both aquatic macrophytes. A reduction of EC by 16.4 %, TDS by 16.3 % and salinity by 20.7 % for duckweed while for water hyacinth, a reduction of EC by 20 %, TDS by 19 % and salinity by 29.1 % were observed. Thereafter, both aquatic macrophytes started showing signs of nutrient starvation and a reduced rate of desalination. This can be addressed by removingthe spent and wilting aquatic plantsand re-introducingfresh onesin 3 days intervalsuntil desalination is achieved. Anova shows that there was significant difference between pre-and post-treatment values at 95 %confidence level in EC for both duckweed and water hyacinth treatment and also in TDS and salinity for water hyacinth treatment. This suggests potency of water hyacinth in the desalination of brackish water for crop irrigation and other agricultural purposes.

Nanoarchitectonics of ultrafine molybdenum carbide nanocrystals into three-dimensional nitrogen-doped carbon framework for capacitive deionization.

Molybdenum carbide (MoC) has emerged as a promising material for capacitive deionization (CDI), but the poor electrochemical kinetics in conventional MoC owing to the bulk structure and low electric conductivity limit its CDI performance. To address this challenge, herein, we develop a novel strategy to synthesize ultrafine MoC nanocrystals that are embedded within a three-dimensional nitrogen-doped carbon framework (NC/MoC). This synthesis method involves the space-confined pyrolysis of molybdate precursors within metal-organic frameworks (MOFs). In this process, molybdates are confined into the MOF crystalline structure, where MOFs provide a confined reactor and carbon source. The resulting NC/MoC with the uniformly distributed MoC nanocrystals provides sufficient active sites for the electrosorption of salt ions, while the MOF-derived NC matrix facilitates charge transfer and provides the space-confined effect for preventing the possible aggregations of MoC nanocrystals during the CDI process. The NC/MoC exhibits an impressive salt adsorption capacity (SAC, 84.2 mg g-1, 1.2 V), rapid desalination rate, and high cycling stability (91.4% SAC retention after 200 cycles), better than those of most previously reported carbon-based CDI materials. Besides, the possible mechanisms are systematically investigated by ex situ characterization and density functional theory calculations. This study opens up new avenues for the construction of metal carbide-based nanocrystals for CDI and other electrochemical applications.

A novel strategy for retarding membrane wetting under electrical field: Embedding silver nanowires into UiO-66-NH2/graphene oxide composite thin membrane

Membrane distillation (MD) is a promising desalination technology that combines traditional distillation processes with membrane separation technology, but when the feed solution contains amphiphilic substances such as surfactant, the hydrophobic membrane is prone to being wetting, which hinders its widespread application. In this study, a novel Janus membrane was developed by embedding Zr-MOF and silver nanowires into the modified graphene oxide composite membrane to improve its separation performance, and the effect of high-concentration SDS on the membrane performance was studied. The experimental results showed that the conductive membrane exhibited excellent performance when powered on for 5 min every 2.5 h under 2 V voltage. The flux stabilized at 19.6 L/(m2h) with a desalination rate up to 99.9 % and no obvious signs of membrane wetting. It was found that the effect of electric field caused a negative charge on the membrane surface, forming a charge repulsion force with the SDS. Simultaneously, intermittent electrical flotation can effectively remove SDS that has accumulated on the membrane surface, thus achieving efficient and stable operation of MD system. Moreover, a machine learning approach with Catboost was applied to predict and unveil the complex effects on membrane performance, providing a deep insight to treat wastewater containing surfactant.