Desalination Rate Research Articles

Numerical Simulation of Seawater Desalination Effect in The Micro-Nanochannel

In recent years, the study on the micro-nanochannel in the microfluidic technology has been made significant progress for which when inner walls charged can function similarly as ion permselective membrane. This article constructed one symmetric model with three parallel microchannels connected with two sets of nanochannel arrays and explained the mechanism of desalination within the channel by using numerical simulation method. For example, when the voltage difference, Vcn, across the nanochannel array is equal to 10 VT, the desalting efficiency can have reached nearly 90%; as the Vcn is increased continuously to 20VT, the desalination rate will definitely exceed 99% and as the Vcn increases the rate increases more slowly.

Tip and Inner Wall Modification of 4.9 nm Diameter Multi-Walled Carbon Nanotubes and Its Nanocomposite Polyamide Reverse Osmosis Membrane.

The tip and inner surface of large diameter multi-walled carbon nanotubes (MWCNTs) (4.9 nm diameter) were functionalized on the tip and inner surface to improve the rate of desalination and maintain high water flux. The modified MWCNTs-doped reverse osmosis membranes were fabricated by interfacial polymerization using trimesoyl chloride (TMC) solution in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized MWCNTs. The functionalized MWCNTs were analyzed by X-ray photoelectron spectroscopy (XPS), thermal gravity analysis (TGA), high resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy and other techniques. The obtained results showed that changes occurred in the structure of the carbon nanotubes with the inner diameter becoming smaller, and the dispersibility and stability were improved. Carboxyl, acyl chloride, amide and amino groups were successfully grafted on the tip and interior of MWCNTs. The surface characteristics of the prepared membranes were studied by scanning electron microscopy (SEM) and contact angle analysis. The desalination performance of the membranes was investigated in terms of water flux and salt rejection. The experimental results revealed that the incorporation of the modified MWCNTs (especially containing hydrophilic groups such as carboxyl groups) into the polyamide layer of RO membranes led to a significantly increase of the water flux and salt rejection.

Self-pumped evaporation for ultra-fast water desalination and power generation

Getting fresh water and electricity by utilizing low-grade thermal energy are attractive to deal with the global resource crisis. Here, a self-pumped evaporation regime based on charged carbon nanotubes membrane is reported, which can purify water and output power efficiently with thermal energy supplied. Using molecular dynamics simulations, ultra-high desalination rates of 3.6 ± 0.5 g/(cm2s) and power generation rates of 170 ± 24 W/cm2 were gotten with temperature difference of 40 K. The causes of the super rates include high pump capacity, low thermal resistance, and low irreversibility. This study shows a promising approach to desalinate water and generate power efficiently by consuming low-grade heat.

Enhancing the permeability of TFC membranes based on incorporating polyamide matrix into MWCNTs framework

Reverse osmosis (RO) technology can get rid of small molecular contaminants and salts with a very high efficiency, so that it has exhibited promising potential for addressing the emerging problem of a clean water shortage. In this paper, one new thin film composite (TFC) membrane with a novel MWCNT/polyamide (MWCNT/PA) composite rejection layer had been manufactured via interfacial polymerization (IP) method under negative pressure. The MWCNTs framework was first fabricated on surface of PVDF substrate and then the polyamide matrix was filled into the framework by IP process between the two monomers (M-phenylenediamine and trimesoyl chloride) under negative pressure. The novel rejection layer obviously enhanced the water flux and antifouling performance without harming the desalination rate in RO process. The improved performances can be attributed to the larger amount of hydrophilic MWCNTs which were embedded into the rejection layer and worked as water channels. Meanwhile, this research also revealed that enhancing the density of water channels in polyamide rejection layer and the hydrophilicity of membrane surface could effectively improve the TFC membrane performance.

A deep desalination and anti-scaling electrodeionization (EDI) process for high purity water preparation

Electrodeionization (EDI) is a composite desalination process that combines ion exchange and electrodialysis to achieve continuous deionization. However, the current EDI technology has demanding requirements for the feed water, and fouling in the stack often exists in practical industrial applications. For the above-mentioned issue, a novel deep desalination and anti-scaling EDI stack configuration was proposed. Different from previous configuration, a cation exchange membrane was added to the right side of the reverse anode exchange membrane to form a protective chamber, in which mixed bed ion exchange resin was filled with a certain proportion, Meanwhile, the influent of concentrated stream was supplied by dilute stream. Aiming at no fouling and maximum dilute water resistivity, the effect of operating conditions on the EDI process for the preparation of high purity water were studied. All the results demonstrated that for the feed water with a hardness of 7.9 mg·L−1 (calculated as CaCO3), with the proposed EDI stack configuration and a membrane stack voltage of 8 V, a concentrated flux of 6 L/h, a dilute flux of 32 L/h, the membrane stack can run stably for 400 h without fouling, and the dilute water resistivity can reach 16.1 MΩ·cm−1, the total desalination rate was 99.8%, the hardness ion removal rate was close to 100%, the energy consumption could be maintained at <0.03 KWh·m3. These results indicate that the proposed EDI stack configuration can broaden the limits of EDI feed water conditions and it is of great practical significance to realize the industrial application of the deep desalination and anti-scaling EDI model.

Impacto de agua distribuida en tierra desalinizada y características hidroquímicas de aguas subterráneas: análisis temporal y espacial de un estudio de caso regional en China

The influence of water resources allocation patterns on root layers soil desalination and groundwater quality were investigated by monitoring different irrigation area from People’s Victory Canal irrigation district in Huang Huai Hai plain China that had been conducted well canal combined irrigation patterns from 1954. A typical area was chosen belong to the People’s Victory Canal irrigation district from 2013 to 2015. Precipitation of the area, surface water irrigation amount, groundwater consumption amount, salinity content in 0 to 100 cm soil layer and total dissolved solids in groundwater were monitored, the ratio of canal-well water (the ratio of surface water to groundwater irrigation amount, CWWR), soil salinity spatial dynamic, desalinization rate in 0 to 100 cm soil layer and sodium adsorption ratio (SAR) of groundwater were analyzed in the area. CWWR of 1st, 2nd, 3rd branch canals ranged from 0.72 to 1.03, 2.50 to 2.63, and 0.65 to 1.26 in 2013 to 2015, respectively. The soil salinity contents for the top 100 cm horizons in the 2nd branch canal irrigation area decreased slightly by 1.63% to 8.90% compared with the values in the 1st and 3rd branch canal irrigation districts while the water resources allocation patterns were conducted two years later. Compared with the area in the hydrological period in 2013, area of average soil salinity exceeded 0.32 mS/cm for the top 20 cm horizons has decreased notably in 2014 and 2015. Compared with the values in 2014, the average TDS concentration of groundwater increased by 18.66% in the study area in 2015, while the sodium adsorption ratio (SAR) values in the above-mentioned irrigation areas decreased by 23.58%, 36.82%, and 53.37% in the normal period in 2015. The combined well-canal irrigation pattern could represent a useful water allocation method mainly because of the temporal and spatial regulation of water resources and root layer soil desalination; however, possible increases of TDS in the groundwater may cause potential ecosystem degradation risks after long-term water allocation in semi-arid areas. Thus, water allocation should be emphasized to maintain a healthy groundwater environment and sustainable stable yields of grain in combined canal-well irrigation districts

Effects of Different Irrigation Treatments on Aquaculture Purification and Soil Desalination of Paddy Fields

Aquaculture wastewater contains considerable quantities of organic matter, nitrogen, and phosphorus. Irrigation of paddy rice with aquaculture wastewater can make full use of water and fertilizer, which has practical significance for alleviating water-use conflicts in the coastal areas of Jiangsu Province and promoting soil desalinization. Our objective in this study was to evaluate the effects of water quality indexes of surface discharge in paddy fields, total nitrogen (TN) and total phosphorus (TP) losses of discharge in paddy fields, growing indexes of plants, grain yield, as well as soil salinity affected by the different irrigation treatments. To achieve this objective, experiments were conducted from May to October in 2017. There were four treatment combinations: I1W1 (shallow–frequent irrigation and aquaculture wastewater), I2W1 (shallow–wet irrigation and aquaculture wastewater), I3W1 (flooding irrigation and aquaculture wastewater), and I1W2 (shallow–frequent irrigation and fresh water). The results revealed that there was no significant difference in grain yield among the three wastewater irrigation treatments. Meanwhile, the values of water quality indexes were optimal in I3W1; the total losses of TN and TP of the I3W1 treatment were the lowest over the three important growth stages; the desalinization rate of I3W1 was the largest due to its long hydraulic retention time and large irrigation depth. The overall results suggested that the I3W1 treatment was the optimal treatment.

Water productivity enhancement in variable pressure humidification dehumidification (HDH) desalination systems using heat pump

Variable pressure humidification dehumidification (VPHDH), humidification compression (HC), and conventional humidification dehumidification (HDH) processes are coupled to a heat pump (HP) for enhancement of their performances and desalination rates. Process simulation of the modified processes reveals the superiority of the proposed VPHDH-HP process to HC-HP, HDH-HP and the conventional HDH processes. Due to the superiority of VPHDH processes over conventional HDH processes, coupling them to HP units as a novel idea improves the desalination rate and energy utilization. The effects of dehumidifier to humidifier pressure ratio (PD/PH), humidifier pressure, and the inlet water to air mass flow rate ratio (w/a) on desalination rate and performance ratio (PR) are studied for the VPHDH-HP process as the superior process. Increasing PD/PH within 2.0 to 3.0 range, leads to an increase in desalination rate by 215%. Increasing w/a from 1.5 to 2.0 increases the desalination rate by 15%, while the same from 2.0 to 3 leads to a 53% decrease in the desalination rate for humidifier pressure of 0.5 bara. A cost analysis yields a water cost of US $4.68/m3 in VPHDH-HP system, indicating its performance superiority against its counterparts.

Response surface modeling and optimization of electrodialysis for reclamation of RO concentrates in coal-fired power plants

ABSTRACT Response surface methodology was employed to model and optimize the electrodialysis process for Reverse osmosis concentrate (ROC) reclamation in coal-fired power plants. Predictive models were developed for simulation of different input parameters and responses of ED process. The model for responses was statistically verified by analysis of variance which generated a high coefficient of determination value. Moreover, regression analysis showed a good repeatability and agreement of the experimental data to a quadratic model. The optimum operating parameters were found to be 5.9 V of operational voltage, 1.19 m/s of flow rate and 74 min of time. And the corresponding energy consumption and desalination rate were 0.11 Wh/L and 75.3%, respectively.

Enhanced Hybrid Capacitive Deionization Performance by Sodium Titanium Phosphate/Reduced Porous Graphene Oxide Composites.

In this study, sodium titanium phosphate/reduced porous graphene oxide (NTP/rPGO) composites are used as novel electrode materials for hybrid capacitive deionization (HCDI). The composites are synthesized through assembling the NaTi2(PO4)3 precursor with etched graphene oxide under hydrothermal condition. The NTP/rPGO composites demonstrate a porous hierarchical structure, where uniformly dispersed NaTi2(PO4)3 particles are attached on the rPGO sheets, which provide abundant adsorption sites, highly conductive networks, and short diffusion lengths for salt ions. Benefiting from the redox reaction of the NTP and electrical double-layer capacity of the rPGO, the NTP/rPGO composite containing 77 wt % NaTi2(PO4)3 presents a high specific capacity of 396.42 F g–1 and a high electrosorption capacity of 33.25 mg g–1 at the voltage of 1.4 V with the initial salt conductivity of 1600 μS cm–1 (786 mg L–1). Further, it also shows excellent recycling stability and rapid desalination rate of 0.30 mg g–1 s–1 (100 times as fast as the bare graphene electrode). Therefore, the NTP/rPGO composites exhibit a promising prospect for desalination application in the HCDI system.

Air-gap diffusion distillation: Theory and experiment

A novel Air-Gap Diffusion Distillation (AGDD) technology operated at normal atmospheric pressure was proposed in this paper. In this plant, cold and hot streams flow counter-currently and the strong hydrophilic porous medium is employed as the hot stream channel to control its flow. The operation characteristics of AGDD were investigated and analyzed theoretically and experimentally. Influences of structure and operation parameters on the performances were discussed deeply. The results showed the water productive flux and Gained Output Ratio (GOR) for the AGDD with one air-gap combination were 0.7244 kg·m−2·h−1 and 1.16 respectively when the thickness and height of air-gap, inlet temperatures of cold and hot streams, mass flow rate of cold stream were 5 mm, 0.9 m, 25 °C, 65 °C and 4 kg·h−1 respectively. When the air-gap height was enlarged to 1.8 m and the mass flow rate of cold stream reduced to 2 kg·h−1, the water productive flux and GOR were 0.5255 kg·m−2·h−1 and 5.01 respectively. The results also indicated that the thermal resistance of heat transfer in the AGDD mainly sourced from the air-gap. The variations of structure or operation parameters did not influence on the desalination rate of AGDD which was higher than 99.8% during experiments.

Assess Effectiveness of Salt Removal by a Subsurface Drainage with Bundled Crop Straws in Coastal Saline Soil Using HYDRUS-3D

The low permeability of soil and high investment of salt management pose great challenges for implementation of land reclamation in coastal areas. In this study, a temporary soil leaching system was tested in which bundled maize straw (straw drainage module, SDM) was operated as a subsurface drainage tube and diluted seawater was used for leaching. A preliminary field experiment was conducted in coastal soil-filled lysimeters to examine the system’s feasibility and a numerical model (HYDRUS-3D) based on field measured data was designed to simulate the entire leaching process. The simulation results showed that the soil water velocity and the non-uniformity of salt distribution were apparently enhanced in the region approaching the drain outlet. The mass balance information indicated that the amount of water drained with SDM accounts for 37.9–66.0% of the total amount of leaching water, and the mass of salt removal was about 1.7 times that of the salt input from the diluted seawater. Additional simulations were conducted to explore the impacts of the design parameters, including leaching amount, the salinity of leaching water, and the number of leaching events on the desalination performance of the leaching system. Such simulations showed that the salt removal efficiency and soil desalination rate both were negatively related to the seawater mixture rate but were positively associated with the amount of leaching water. Increasing the leaching times, the salt removal efficiency was gradually decreased in all treatments, but the soil desalination rate was decreased only in the treatments leached with less diluted seawater. Our results confirmed the feasibility of the SDM leaching system in soil desalination and lay a good foundation for this system application in initial reclamation of saline coastal land.

Novel low-cost cation exchange membrane containing hydrophilic cross-linked structure for enhanced electrodialysis properties

Abstract A new mechanism for effecting ion transfer in the CEM was obtained, which was used to guide the preparation of CEM in a cheaper manner. In this paper, a series of CEMs, based on different ratios of sulfonated polyether sulfone (SPES) and polyvinyl pyrrolidone (PVP), were prepared. The ionic conductivity of S-5/P-5 was 0.076 S/cm at 70 °C, while the ionic exchange capacity was only 0.46 mmol/g. Electrodialysis (ED) experiments showed that S-5/P-5 exhibited better ED properties than a comparable commercial CEM. The desalination rates of S-5/P-5 and a commercial CEM were 94.3 and 93.7%, respectively, while the energy consumption of S-5/P-5 was lower than that of the commercial CEM. However, the cost of S-5/P-5 was about one-fourth that of a commercial CEM. The measured ionic conductivity and improved desalination properties of the prepared CEMs were attributed to their increased proper hydrophilicity, which facilitated ion transport. This study provided a simple method for lowering the cost and enhancing the CEM properties by properly increasing their hydrophilicity.

Effect of prior salt experience on desalination capacity of the halophyte Arthrocnemum macrostachyum

We studied the capacity of extreme halophyte, Arthrocnemum macrostachyum, to desalinize an experimentally-salinized soil under non-leaching conditions. Furthermore, we tested the effect of salt pre-exposure of this species on its phytodesalination capacity. The presence of the halophyte, independently salt pre-exposure, decreased salinity of the sanilized soil by 31% after 30 days; reducing the negative effects on emergence of both test cultures, barley and wheat. Plants of A. macrostachyum pre-treated without salt showed 4-fold higher relative desalination rate than those grown with optimum salinity (with higher initial biomass). Thus, previous salt exposure was as determinant as plant biomass for desalinizing capacity. In conclusion, pre-exposure to salt of halophytes must be taken into account for desalination programs.

Enhancing the water desalination and electricity generation of a microbial desalination cell with a three-dimensional macroporous carbon nanotube-chitosan sponge anode

Microbial desalination cells (MDCs) are promising bioelectrochemical systems that are being investigated for simultaneous seawater desalination, electricity generation, and wastewater treatment. Anode materials play an important role in determining the performance of MDCs. In this study, a three-dimensional (3D) macroporous sponge was coated with compatible and conductive carbon nanotube-chitosan (CNT-CS) as a composite electrode for MDCs. Experimental results showed that the flexible CNT-CS sponge exhibited a high capacitance (159.4F/g at 20mVs−1), good cycling stability (96% specific capacitance retention after 1000 cyclic voltammetry cycles) and low resistance. Moreover, the MDC with a CNT-CS sponge anode generated a high power density of 1776.6mW/m2 (per electrode area) and desalination rate of 16.5mgh−1, which are significantly higher than those of commercial carbon felt electrodes under the same conditions. The improved MDC performance can be attributed to the continuous 3D macroporous structure of the sponge anode promoting the bacterial loading capacity on the electrode surface. Moreover, the presence of CNTs also further enhances extracellular electron transfer. Our results demonstrate that an MDC operating with a 3D CNT-CS sponge anode offers an effective means for manufacturing high-performance MDCs with wide applicability to bioelectrochemical systems.

A stable operation method for membrane capacitive deionization systems without electrode reactions at high cell potentials

A method for operating membrane capacitive deionization (MCDI) systems without electrode reactions at a high cell potential was studied. The charge supplied to the cell was controlled to suppress Faradaic reactions. The maximum allowable charge (MAC) that can be supplied to a carbon electrode without electrode reactions was measured to be 58 C/g. Adsorption experiments were conducted while supplying a charge of 55 C/g (95% of the MAC value) in constant-current (CC) and constant-voltage (CV) mode. The cell potential increased to 1.42 V in CC (1.43–4.29 mA/cm2) mode, but the concentration and pH of the effluent were kept constant. In addition, the effluent pH was stable in CV (1.25–2.0 V) mode. The salt adsorption capacities and charge efficiencies were approximately 15.5 mg/g and 92%, respectively, regardless of the current densities and cell potentials applied to the cell. With increasing cell potential, the concentration polarization in the feed stream was intensified, resulting in an increase in cell resistance. It was thought that electrode reactions did not occur at a high cell potential because of the high voltage drop due to the cell resistance. The higher the cell potential (or current density) is, the faster the desalination rate in MCDI operation. It is expected that this operation method applying the MAC concept will contribute to the stable operation of MCDI systems and an improvement in desalination performance.

Insulating plasmonic photothermal heat of Ag nanoparticles by a thin carbon shell

Plasmonic photothermal effect of metal nanoparticles has been used for efficient cancer therapy and catalysis. Here, we show the insulation of Plasmonic photothermal heat generated in Ag nanoparticles by a thin carbon shell and their application for solar desalination of seawater. Ag, carbon and Ag with carbon shells (Ag@C) nanoparticles were synthesized by a hydrothermal method. The absorption of Ag@C core/shell nanoparticles almost covers the whole visible light spectrum from red to violet, which can be tuned by changing the thickness of the carbon shells and the size ratio of Ag cores to carbon shells. Ag@C core/shell nanoparticles with the size of 50 nm@18 nm exhibit a photothermal conversion efficiency 44% higher than carbon nanoparticles. Importantly, it is observed that carbon shells have excellent heat insulation property so that the temperature decay lifetime of Ag nanoparticles is enhanced by 49% after coating with a thin carbon shell of 18 nm. Ag@C nanoparticles supported by anodic aluminum oxide (AAO) templates exhibit a desalination rate 1000% higher than the direct evaporation of seawater under simulated solar irradiation and 220% higher than that of AAO templates supported carbon nanospheres.

Dual-Ion Electrochemical Deionization System with Binder-Free Aerogel Electrodes.

Desalination devices such as capacitive deionization (CDI) have been developed for many years as an approach to relief freshwater shortage. However, due to the limitation of physical adsorption capacity of CDI, the salt removal capacity is unable to reach high value. To enhance the desalination capacity effectively, battery materials are employed to fabricate a dual-ion electrochemical deionization (DEDI) device. Herein, a binder-free DEDI system with two free-standing aerogel electrodes is reported. A Na3 V2 (PO4 )3 /graphene hybrid aerogel is used as sodium electrode and a AgCl/graphene hybrid aerogel is used as chloride electrode. With electric current passing through, sodium and chloride ions are released or absorbed by two aerogel electrodes. This system achieves super high desalination capacity, excellent cycling stability, and rapid desalination rate. The desalination capacity is as high as 107.5 mg g-1 after 50 cycles with the current density of 100 mA g-1 . The outstanding desalination performance of this system shows a synergistic effect of combining battery materials with graphene for deionization and promises a new potential alternative of future desalination design.

A fully-packaged ship-shaped hybrid nanogenerator for blue energy harvesting toward seawater self-desalination and self-powered positioning

Lately, hybridization of triboelectric nanogenerator (TENG) has shown great potential in collecting ocean-wave energy with low frequency and irregular amplitude, and hybridization of TENG with electromagnetic generator (EMG) can enable the broadband energy harvesting with the fully-packaged design. Here, a ship-shaped hybridized nanogenerator (SHNG) consistsing of three TENGs and an EMG has been proposed, from which the TENGs works in freestanding rolling and contact-separation modes. In this design, the rolling of magnetic cylinder makes the TENG easy to be driven by water wave due to the low frictional resistance. Moreover, the unique structural design is beneficial to the packaging, ensuring the isolation of the SHNG from the external water environment and thus providing stable electrical output. Under an operating frequency of 2 Hz, the contact-separation TENG and EMG are able to produce a peak power of about 800 µW with a resistive load of 20 MΩ and 9 mW with a resistive load of 100 Ω, respectively. In terms of charging capacitors, the SHNG can achieve higher charging voltage and faster charging speed than that of the individual TENG or EMG. To accomplish impedance match between the TENG and EMG, a transformer was employed to decrease the impedance of the TENG. The SHNG has been demonstrated to effectively desalinate seawater, and its desalination rate reaches 29.4% in 3 h. The SHNG has also been proved to power a digital temperature-humidity meter and drive a radio-frequency emitter to form a self-powered wireless positioning system. This work not only renders an innovative approach toward effective blue energy harvesting, but also presents a great prospect for enabling self-desalination and self-powered marine rescue systems.

An internal-integrated RED/ED system for energy-saving seawater desalination: A model study

Salinity gradient energy extracting by a reverse electrodialysis (RED) unit using for electrodialysis (ED) desalination process is a potential way to achieve energy-economic and sustainable production of freshwater. However, the parameters in RED and ED unit synergistically influence the desalination process, resulting to the hybrid process controlled by multi-parameters. Modeling of an RED/ED is a simple way to describe the desalination process and reveal the effects of these parameters on the performance of system and then to find the better adaption of RED/ED. In this study, a model of an internal-integrated RED/ED hybrid system is first established. It found that the ratio of desalination in RED/ED is higher than 90%. The brine/river is the alternative combination to realize seawater desalination with a desalination rate of 0.38 h m2/mol. The desalination capacity of RED/ED (0.43–2.6 mol/h·m2) is much higher than that of the external-integrated RED + ED system (0.10–0.15 mol/h·m2), but it is of simpler configuration and has a lower energy requirement. Moreover, the RED/ED system is preferred for using in the pre-desalination process. The outcome of this model is helpful in the design of practical RED/ED systems, and points out the development potential of RED/ED in practical applications.