NaCl Removal Research Articles

Multi-faceted effects of NaCl on salt-tolerant microalgae Golenkinia sp. SDEC-16

The salt-tolerant microalgae are extremely few and salt-tolerance mechanism is unclear, requiring urgent exploration of salt-tolerance mechanism of known microalgae. This study was first to reveal the salt-tolerance mechanism of Golenkinia sp. SDEC-16 by investigating the growth and metabolism under different salinities and high salinity long-term cultivation. SDEC-16 can survive under high salinity and resume normal growth after NaCl removal. Under long-term stress, SDEC-16 had higher lipid content and productivity than BG11. However, the suppressed Fv/Fm (58.4%) and Fv/F0 (84.0%) along with the increased reactive oxygen species (×6.6), and superoxide dismutase (×1.7) during the treatment revealed NaCl-induced photosynthetic inhibition and oxidative stress. RNA sequencing results showed inhibition of the photosynthetic system, and the enhancement of pathways such as nitrogen metabolism, energy metabolism, and lipid synthesis contributed to the good function of chloroplast, energy supply, and metabolic activity of SDEC-16. This study provides theoretical support for large-scale microalgal cultivation in seawater.

Nutrient status and production of fodder beet irrigated with saline-sodic water in Mediterranean calcareous soils

ABSTRACT The impact of drip irrigation with saline-sodic water on the nutrient status and productivity of fodder beet (Beta vulgaris) was evaluated in rainy and dry Mediterranean cropping seasons. Two field experiments were conducted during two growing seasons (winter and summer) in calcareous soil (31% CaCO3) of Sais area, Northwestern Morocco. The rainfall was 337 mm for winter and 53 mm for summer. Four salinity levels of irrigation water (ECi) were investigated: control (1ds m−1), 4, 6, and 10 ds m−1. The ECi levels were prepared by adding sodium chloride (NaCl, laboratory grade, 99.5%) to water. The results showed that the soil salinity (ECs) was related to the growing season and the irrigation water salinity (ECi). The depressive effect of salinity on the whole plant dry biomass (−25% as average) was observed only in the summer crop cycle at different ECi ≥ 4 ds m−1 compared to control. The plant NaCl uptake for both seasons could be predicted by a linear model: Y (kg ha−1 of NaCl) = 36.3 ECi + 23.6 Q − 101.3 (adjusted R2 = 0.88) where Q = total dry biomass (t ha−1). Saline-sodic irrigation water reduced the contents of boron, calcium, and magnesium in the plants. The exchangeable sodium percentage (ESP) in the soil exceeded 41% at ECi ≥ 4 ds m−1 for both seasons. The study demonstrated that fodder beet escapes the negative impact of salt stress in the rainy season. However, the high ESP recorded at harvest did not reveal the efficacy of fodder beet in NaCl removal from the soil.

Membrane‐assisted capacitive deionization: Effect of Poly(vinyl alcohol) cross‐linking on the properties of ion exchange membranes

AbstractNovel composite electrodes were developed for application in membrane capacitive deionization (MCDI). Activated carbon (AC) was dispersed in a solution of poly(vinyl alcohol) (PVA) mixed with polyacrylic acid (PAA) or poly dimethyl diallyl ammonium chloride (PDMDAAC), and cast onto the surface of an AC‐based modified graphite electrode, prepared by phase inversion, to form a composite membrane further cross‐linked with glutaraldehyde (GA). The effect of the cross‐linking on the chemical structure of the PVA‐based membranes was determined by attenuated total reflectance Fourier‐transform infrared (ATR‐FTIR) spectroscopy. Cyclic voltammetry was conducted to examine the specific capacitance of the composite electrodes. Desalination experiments were then performed with MCDI unit cells to study the effect of cross‐linking on the desalination efficiency. It was proved that after optimization, the synthesized composite electrodes exhibited one and a half times higher NaCl removal capacity and three times higher adsorption rate as compared to that of a conventional CDI cell using commercial ion exchange membranes (IEMs) with almost the same energy consumption. The enhanced desalination performance was attributed to the optimized properties of the selected polymers and the improved adhesion of IEMs to the electrodes. This research paves the way for the application of new materials in MCDI processes for improved water desalination.

Fabrication of porous carbon nanofiber webs from polyacrylonitrile and cellulose acetate for NaCl removal from water using capacitive deionization

Abstract Capacitive deionization (CDI) has shown potential in addressing freshwater scarcity. CDI's electrode design is a key to better performance as it determines the extent of water purification. For carbon electrodes, the pore structure is an important factor influencing removal kinetics and ion storage. Herein, porous carbon nanofibers with diameters ranging from 277 to 348 nm were fabricated from blends of polyacrylonitrile (PAN) and cellulose acetate (CA) through electrospinning and carbonization. Surface area and pore properties were adjusted by varying the proportions of the precursors while ensuring no adverse alteration to the products' tangible properties. Enhanced pore structure and specific surface area were evident in the blend-based carbon nanofibers. The blend ratio of 2:8 (CA:PAN) had a high specific surface area of 925.47 m2/g and a pore volume of 0.7884 cm3/g. Correspondingly, a high specific capacitance of 177.5 F/g was attained. Desalination performance was determined in batch mode using 500 mg/L NaCl solution. A salt adsorption capacity of 6.57 mg/g and charge efficiency of 0.46 was obtained for the blend that had 20% CA. The carbon nanofibers demonstrated good desalination stability when used repetitively indicating their excellent potential for practical application.

Reactivation of redox active materials boosts the performance of electrochemical desalination with coupling energy storage.

Aqueous redox flow battery (RFB) desalination is considered as an emerging technology for both freshwater production and energy storage. However, the desalination capacity of desalination RFB is constrained by the amount of redox active materials. To break through this innate limit, a tandem redox strategy is reported to boost the desalination capacity of desalination RFB through reactivating the depleted redox active materials to achieve relay desalination. Taking zinc/sodium ferrocyanide as the proof-of-concept model, the introduction of 5.6 g Prussian blue (PB) as a reactivator could boost the desalination capacity by ∼106.1%, reaching to 651.2 mAh, compared with the theoretical limit of 315.9 mAh. This system can afford the desalination of 34-47 mL seawater with 85%-91% NaCl removal and as low as 8.17 kJ/mol (2.27 Wh/L) salt energy consumption using only 15 mL of catholyte, while providing 55.6-42.5 Wh/L electrical energy for other purposes, outperforming the reported desalination RFBs so far. This study represents a paradigm shift to rational design for desalination RFB and may broaden the implications in desalination, energy storage, and other related fields.

Double-photoelectrode redox desalination of seawater

High energy consumption and low salt removal rate are key barriers to realizing practical electrochemical seawater desalination processes. Here, we demonstrate a novel solar-driven redox flow desalination device with double photoelectrodes to achieve efficient desalination without electrical energy consumption. The device consists of three parts: one photoanode unit, one photocathode unit, and one redox flow desalination unit sandwiched between the two photoelectrode units. The photoelectrode units include a TiO2 photoanode and a NiO photocathode sensitized with N719 dye, triiodide/iodide redox electrolyte, and graphite paper integrated electrodes decorated with 3,4-ethylene-dioxythiophene. Two salt feeds are located between two ferro/ferricyanide redox flow chambers. Under light illumination, high-quality freshwater is obtained from brackish water containing different concentrations of NaCl from 1000 to 12,000 ppm with a high NaCl removal rate. The device can work in multiple desalination cycles without significant performance declines. Furthermore, natural seawater with an ionic conductivity of 53.45 mS cm−1 is desalinated to freshwater. This new design opens opportunities to realize efficient and practical solar-driven desalination processes.

Washing Methods for Remove Sodium Chloride from Oyster Shell Waste: A Comparative Study

The oyster shell is a valuable calcium resource; however, its application is limited by its high NaCl content. Therefore, to establish the use of oyster shells as a viable resource, conditional experiments were conducted to select optimum parameters for NaCl removal. For this purpose, we compared leaching methods with batch and sequential procedures, determined the volume of water used for washing, and evaluated the mixing speed. The batch system removed NaCl when washed for >24 h over a shell to water ratio of 1:5. Results from the batch experiments confirmed that washing twice can completely remove NaCl from the shells on a like-for-like basis. Additionally, the efficiency of washing was sequentially evaluated in terms of the number of washing cycles. Compared to batch experiments, continuous washing could remove NaCl in approximately 10 min at a shell to water ratio of 1:4. We found that regardless of the washing methods, the volume of water used for washing is key for enhancing NaCl removal. Consequently, increasing the volume of water used for washing coupled with a proper sorting of fine particles can help enhance the purity of calcium, which will enable the use of oyster shell as an alternate Ca-resource.

Influence of water volume on CO2 hydrate-based desalination of brine solution

The exclusion of salt from brine or produce water in the presence of hydrates is a potentials technique to produce clean water and treat produce water. However, the effect of water content on the salt exclusion efficiency is needed to provide relevant data to optimize the technology. In this work, NaCl removal efficiency in CO2 hydrate system was evaluated at varying water volumes in 2 wt% NaCl solution. The experiments were carried out at a fixed pressure of 30 bar in various water volumes of feed ranging from 200 ml to 500 ml to find out the optimum feed conditions at 2 °C. The parameters evaluated are moles of gas consumed, water recovery and removal efficiency. It was found that with increasing water volume from 300 ml to 500 ml the removal efficiency increased from 30.83 % to 60.08% at 3.5 MPa. Averagely, the water volume of 500 ml produced the highest water recovery (58.6%) and removal efficiency (41.17%) at all the pressures (2.5 MPa–3.5 MPa). The findings from this research will lead to the design of an efficient reactor for commercialization of the hydrate-based desalination system.

Green preparation of quaternized vinylimidazole-based anion exchange membrane by photopolymerization

• AEMs were prepared via environmental friendly, highly efficient and single step ultraviolet polymerization method. • Non-toxic ethanol and water were used as solvents and the reaction mass efficiency was higher than 94%. • The performance of the membrane could be finely adjusted by the varying the content of imidazolium monomer. • The prepared membrane showed excellent desalination performance with the NaCl removal ratio as high as 99%. At present, most preparation processes of ion exchange membranes inevitably involve toxic solvents and complicated synthetic procedure. Herein, we reported a one-pot ultraviolet induced polymerization route to prepare quaternized imidazole-based anion exchange membranes. During the preparation processes, only environmentally friendly ethanol and water were used as solvents. The effects of mass ratio of quaternized imidazole monomer, crosslinker and vinylimidazole comonomer diluent on membrane structures and properties were carefully investigated to optimize the performance of anion exchange membrane. In optimized conditions, reliable mechanical properties as well as good electrochemical property could be achieved. The best-performing membrane showed a resistance of 1.86 Ω·cm 2 (reaching the level of a normal homogeneous membrane) and desalination ratio as high as 99% (superior to the commercial anion exchange membrane Fuji type II (98%)). Besides, the reaction mass efficiency of all membranes was above 94%, indicating the high raw material utilization, low energy consumption and environmentally friendliness of the proposed synthetic route. This research would shed light on the development and commercialization of the green synthetic route for ion exchange membranes.

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Electro-desalination of saline solutions by multiwall carbon nanotube electrodes

Electrodes of multiwall carbon nanotube (MWCNT) with polytetrafluoroethylene (PTFE) binding were prepared for NaCl removal from water in the electrosorption system. SEM, XRD and BET analysis were used to characterize the prepared electrodes. The optimum electrosorption parameters (electrosorption temperature, NaCl concentration, electrosorption time, and potential) were studied. The maximum electrosorption capacity (15.64 mg/g) was obtained at −1.0 V, 100 min, and 30 °C. The electrosorption capacity of electrodes decreased from 15.64 mg/g to 6.15 mg/g with the temperature rise from 30 to 50 °C. Also, the kinetics of electrosorption NaCl by Electrodes was investigated by pseudo-first-order and pseudo-second-order. The results indicated that the electrosorption data will fit with the pseudo-first-order model indicating the physio-electrosorption of NaCl by Electrodes with activation energy was 19.45 kJ mol−1. The regeneration result indicated the exceptional and stable reusability of MWCNT/PTFE in the NaCl electrosorption system.

Hard-NaCl template-regulated LiCoO2 catalyst with enhanced activity for aqueous and gaseous organics elimination

Developing new and effective catalytic materials is of significant importance to the catalytic oxidation of multiphase organic pollutants. In the present work, lithium cobalt oxide (LiCoO2) was synthesized and modified via hard-NaCl template regulation for the oxidative elimination of organic dye, e.g. rhodamine B (RhB), and VOCs, e.g. benzene. Compared with the pristine sample, a medium-level NaCl addition offered a much more advanced reactivity towards RhB oxidation, with the elimination percentage rising from 31% to 60% after 20-min reaction for 50 mL 5 mg/L RhB and 4 g/L catalyst. As to benzene oxidation, the above NaCl-assisted catalyst manifested a giant step forward from the inertness of the unmodified sample, with 82%-86% of the ∼460 ppm inlet benzene being removed by the NaCl-LiCoO2 catalyst at 350 °C and 120 L/g/h in contrast to the 5% removal efficiency of the pristine sample. Characterization studies confirmed the fully developed mesoporous structure after NaCl removal, which facilitated the reactant diffusion as well as the accessibility of the catalytical sites, and the strengthened oxidativity of the NaCl-modified sample was ensured by its large number of surface adsorbed oxygen species. Besides, the C6H6-TPSR measurements gave a direct experimental evidence to the high activity of the oxygen species induced by NaCl modification. These favorable factors were all conducive to dye and VOCs oxidation.

Salinity reduction of brackish water using a chemical photosynthesis desalination cell.

In this study, a chemical photosynthesis desalination cell (CPDC) was investigated for saltwater desalination. The cell consisted of three main parts: (1) an anodic compartment where the oxidation reaction occurs, releasing electrons, (2) a cathode compartment where the required soluble oxygen is provided by microalgae photosynthesis, and (3) an electrodialysis desalination cell installed between the cathode and anode. In the anode, a novel idea was adopted to shorten the desalination duration and increase the salinity rate using a chemical oxidation reaction in combination with the biocathode. The CPDC contributed to the carbon dioxide biological sequestration (reducing air pollution), produced microalgae biomass as a source of renewable energy and generated electricity. In the investigated CPDC, microalgae were used to supply the required oxygen solution as an electron acceptor. The metal anode-microalgae biocathode battery could provide the required energy for electrodialysis. In addition, some extra electricity was generated with a maximum excess power density of 32.4W/m3 per volume of the net anodic compartment, 16.2W/m3 per volume of the net cathodic compartment, and 3.07W/m2 of membrane surface area. This study confirms the benefits of microalgae as a sustainable biocathode in microbial desalination cells (MDCs) to supply electron acceptors in an environmental-friendly manner. Compared to photosynthetic microbial desalination cells (PMDCs), the CPDC decreased the desalination time by a factor of about 4. Besides, the NaCl removal was about 69% for 12g/L NaCl concentration in the CPDC, higher than other MDCs. In addition, as a new operational factor, the internal resistance variations were determined by electrochemical impedance spectroscopy in different case studies. The results demonstrated for the first time the possibility of applying a new desalination cell (i.e. CPDC) for water desalination and power generation which only uses a source of chemical reaction and microalgae photosynthesis without the need for an external power source.

Shortening of NaCl removal process using granular NaCl in fabrication of porous aluminum by sintering and dissolution process

Shortening of NaCl removal process using granular NaCl in fabrication of porous aluminum by sintering and dissolution process

Homogeneous trimethylamine-quaternized polysulfone-based anion exchange membranes with crosslinked structure for electrodialysis desalination

A series of trimethylamine quaternized crosslinked anion-exchange membranes (AEMs) based on polysulfone has been prepared by using an ultraviolet cross-linking method, which avoids the uneven reaction and undesirable aggregation of the basic functional groups (trimethylamine) by heterogeneous quaternization. The ultraviolet cross-linking method makes the reaction simpler and more controllable, compared with traditional method. By crosslinking, at 40 °C, the water uptakes of as-prepared AEMs decrease from 62.6% to 36.9%, while the linear expansion ratios reducing from 26.3% to 13.4% without significantly sacrificing the surface area resistance (increased 2.32 Ω cm2 to 2.98 Ω cm2). In addition, the introduced crosslinking yields the more robust AEMs with increased tensile strength from 4.32 to 11.89 MPa and increased elongation at break in a range of 13.8–30.9%. The significantly reduced water absorption, enhanced (dimensional and mechanical) stabilities suggest crosslinkers with more acrylate groups could promote high crosslinking within AEMs. For electrodialysis (ED) application, the optimized AEM exhibits an enhanced NaCl removal ratio of 75.0%, current efficiency of 92.7% and energy consumption of 6.06 kWh Kg−1, compared with AEM without cross-linking (61.4%; 75.9%; 6.20 kWh Kg−1). This investigation demonstrates that the as-proposed strategy has certain guiding significance for the development of advanced AEMs.

Cobalt and nickel ferrites based capacitive deionization electrode materials for water desalination applications

Capacitive deionization (CDI) is an emerging technology for water desalination and is based on electrosorption of ions onto surfaces of electrically charged electrodes. The CDI electrode materials play a significant role in determining the process efficiency. In this study, pure and mixed nickel-cobalt ferrites CoxNi1-xFe2O4 (x = 0.0, 0.3, 0.5, 0.7 and 1.0) were synthesized using the sol-gel auto-combustion method and investigated as novel CDI electrode materials. The purity, structure, and morphology of the synthesized ferrite nanoparticles were analyzed by various techniques. The electrochemical performance of the synthesized materials was investigated, and the results showed that the mixed ferrite Co0.5Ni0.5Fe2O4 electrode possessed the highest specific capacitance of 255 F/g at a scan rate of 10 mV/s. The electrodes were used to treat 250 mg/L NaCl solution in a CDI cell at 1.2 V and a feed flow rate of 10 mL/min. Under optimized experimental conditions, the highest specific salt adsorption capacity was 21.84 mg/g, corresponding to 23.43% of NaCl removal efficiency. These electrodes were highly stable and easily regenerable with less than 5% loss in electrosorption capacity for six adsorption/desorption cycles. The recyclability, stability, and enhanced electrochemical performance of the fabricated electrodes establish cobalt-nickel ferrites as a promising material for use in CDI desalination application.

The role of adsorption in microalgae biological desalination: Salt removal from brackish water using Scenedesmus obliquus

In this study, the effects of different operating conditions on the salt removal from brackish water by dry and fresh Scenedesmus obliquus (S. obliquus) were investigated to explore the mechanisms of algae biological desalination process. It was identified that, within only 30 min contact time, the salt removal increased with the increasing salinity, which was probably due to the higher NaCl concentration gradient from the bulk solution to the algae surface. Compared to other study with a longer algae cultivation period (16 days), this study demonstrated that both adsorption and absorption contributed to the NaCl removal, but adsorption played a more significant role (two thirds of the NaCl removal). The full adsorption can be reached within a relatively short period (1–30 min), and the salts removed by absorption is negligible when the contact time was short. The Langmuir isotherm adsorption model can accurately predict the NaCl adsorption, which indicated the formation of a single molecular layer on the algae surface. The FT-IR analysis further demonstrated different functional groups on the cell wall of S. obliquus can effectively combine the Na+ and Cl−. Overall, the fresh algae showed much faster adsorption kinetics. The results of this study showed promise for the search of alternative desalination technology with an environmentally friendly algae-based biological system.

Development of watermelon rind derived activated carbon/manganese ferrite nanocomposite for cleaner desalination by capacitive deionization

Capacitive deionization (CDI) is one of the most efficient and emerging techniques for water desalination applications. This work reports the development, characterization and CDI studies of watermelon derived activated carbon (WMAC) and its MnFe2O4 composite (WMAC/MnFe2O4) for NaCl desalination. WMAC was prepared through single-step low-temperature pyrolysis by H3PO4 activation. Facile synthesis of spinel MnFe2O4 nanoparticles on WMAC surface was performed through the hydrothermal technique. Morphological, textural and physico/electro–chemical analysis showed the effect of MnFe2O4 incorporation on WMAC. The nanocomposite possessed definite crystallites, low structural disorders and sufficient magnetization for electrochemical applications. Also, the nanocomposite was dominantly composed of mesopores with a specific surface area of 483 m2/g. The high specific capacitance value of 425 F/g (scan rate – 10 mV/s) along with better stability and low charge resistance, confirmed the suitability of WMAC/MnFe2O4 as an efficient electrode material for CDI applications. NaCl removal studies using WMAC/MnFe2O4 showed an electrosorption capacity of 29.7 mg/g for the nanocomposite, with rapid desalination and good recyclability. A plausible mechanism of salt adsorption and desorption is also presented. WMAC/MnF2O4 exhibited significant application potential for the industrial desalination.

Development of antifouling nanofiltration membrane with zwitterionic functionalized monomer for efficient dye/salt selective separation

Nanofiltration (NF) membranes offer advantages to address enormous demands for textile water treatment. To meet omnipresent challenges of dye/salt selectively and antifouling performance, an efficient dye desalting and antifouling NF membrane was developed by virtue of zwitterionic functionalized monomer (zwitterionic N,N-Bis(3-aminopropyl)methylamine, ZDNMA). The structures of zwitterionic membranes can be tailored to suit the separation performance and antifouling property. The prepared zwitterionic NF membrane shows superior removal performance of methyl blue and penetration capacity of NaCl due to zwitterion desirable features of accelerating NaCl transportation. Thus, the membrane selectivity factor for NaCl/methyl blue can be as high as 857.0, accompanied by pure water flux of 10.67 L m-2 h-1 bar-1. When dealing with 0.3 g L-1 MYB and 4 g L-1 NaCl mixture solution, a high NaCl removal was achieved in 75.8% with about 8.1% dye loss after dye purification process. Furthermore, the membrane revealed antifouling performance with a 94.9% flux recovery ratio. The zwitterionic NF membrane highlights more exceptional dye desalination performance, which renders a vast potential for practical textile effluent.

Effect of NaCl removal from biodiesel‐derived crude glycerol by ion exchange to enhance dihydroxyacetone production by Gluconobacter thailandicus in minimal medium

AbstractBACKGROUNDChloride salts are major impurities in biodiesel‐derived crude glycerol that can impact dihydroxyacetone (DHA) production. Ion exchange was performed to remove these salts. DHA production from crude glycerol was investigated, before and after an ion exchange treatment in shake‐flask fermentation and batch fermentation. DHA production from treated crude glycerol was further studied in fed‐batch fermentation.RESULTSIn shake‐flask fermentation, the DHA production from the treated crude glycerol was 56.1 ± 1.87 g L−1. This is 16.2 g L−1 (41%) higher than the DHA production from crude glycerol without the ion exchange treatment at 72 h. The DHA production from the treated crude glycerol was 61.9 ± 2.57 g L−1, with a DHA production yield (DHA moles per glycerol moles) of > 99 ± 4.4% at 138 h in the batch fermentation. The DHA concentration from the treated crude glycerol was 8.1 g L−1 higher than in the crude glycerol fermentation. In fed‐batch fermentation, the DHA production was not significantly higher than that in the batch fermentation due to product inhibition when the DHA concentration reaches 65.05 ± 4.52 g L−1 or more, after 156 h.CONCLUSIONThis study shows that salt impurities in crude glycerol negatively impact the DHA production by Gluconobacter thailandicus TBRC 3351 cultured in crude glycerol minimal media. Removing chloride salts from crude glycerol can improve the DHA yield, both in the shake‐flask and the batch fermentation. Fed‐batch fermentation can also increase the DHA production, but to a lesser extent because of the product inhibition mechanism. © 2019 Society of Chemical Industry