Initial Salt Concentration Research Articles

Alginate/clinoptilolite beads as a novel adsorbent for reducing the salinity of industrial wastewater: adsorption kinetics and isotherm study

ABSTRACT Treatment and desalination of unconventional water are considered important alternatives to combat water scarcity in Tunisia. This study demonstrates a viable approach to the increasing possibility of the salinity reduction of industrial effluent through adsorption. In this work, a novel alginate complex was developed for reducing the salinity of the industrial wastewater to be reinjected and reused again within the industrial process and even in agriculture. The Calcium alginate/clinoptilolite beads (Ca-Alg/Clino beads) were prepared using sodium alginate (2%) solution and calcium chloride (4%) solution as the crosslinking agent with clinoptilolite. Batch experiments were carried out to test the adsorption capacity of the synthetised Ca-Alg/Clino beads. It was found that the salinity reduction process depends strongly on the pH, the adsorbent mass, the interaction time, and the initial salt concentration. The highest reduction efficiency and salinity reduction were achieved at pH (6-7). Batch adsorption experiments indicated that Ca-Alg/Clino beads allow an excellent salinity reduction of up to 96.83% for a dosage adsorbent/water of 2 g/L and a salinity of 6 g/L at a contact time of 20 min. The maximum adsorption capacity (qmax) was 30.1 mg/g. The optimal adsorption pH was 7. The adsorption isotherms data follow well the Langmuir model. The separation factor, RL = 0.74, indicates that the adsorption process is favourable. The kinetics data favour the pseudo-second-order model. The fabricated beads can be reused 5 times without any weight loss. This material has excellent efficiency when applied to real environmental water.

Frozen Saline Sand Can Be Highly Permeable

AbstractMass transport in frozen ground is typically regarded slow. However, a highly permeable path can exist in frozen saline sand if the unfrozen water is interconnected at the pore scale. We therefore should consider when the unfrozen water is connected and how permeable can frozen saline sand be, yet there are few studies. This research utilizes in‐situ X‐ray CT to evaluate unfrozen water connectivity and permeability in frozen saline sand considering effects of initial salt content, temperature, freezing rate, and temperature gradient. Results show that higher initial salt content and/or temperature, both of which results in a higher unfrozen water content, easily maintains unfrozen water connectivity. Rapid freezing minimizes the brine expulsion and permits a higher unfrozen water content hence better connectivity. Permeability in frozen saline sand can be several orders higher than the typically reported value, highlighting the potential presence of rapid mass transport through the connected unfrozen water.

Green Manure Mediated Improvement in Saline Soils in China: A Meta-Analysis

The application of green manure is a traditional and valuable practice to improve the fertility of saline soil. However, the impact of environmental factors, green manure types and returning methods on the changes in soil fertility and soil salinity remain poorly quantified at a large scale. In the present study, we conducted a meta-analysis to generate a comprehensive evaluation of the effects of green manure on soil organic carbon (SOC), soil salt content, and soil nutrients compared to bare soil in China. The results showed that compared with bare soil, green manure planting could significantly increase the SOC content of saline soil, reduce salt content, and improve the soil total nitrogen (N), soil available phosphorus (P) and soil available potassium (K) contents. On average, green manure significantly enhanced SOC by 34.82% (percentage change), soil total N by 32.23%, soil available P by 34.34% and soil available K by 17.43%, while reducing soil salt content by 47.75%, compared to bare soil. In areas with a mean annual temperature (MAT) of <10 °C or a mean annual precipitation (MAP) of 200–400 mm, green manure had the largest increase in SOC, soil total N, soil available P, and soil available K. The smallest increases were observed in areas with an MAT above 15 °C and MAP greater than 800 mm. Green manure types influenced the improvement effect of green manure on saline soil. Green manure mixtures were more conducive to increases in SOC, while the increases in soil total N resulting from mixed green manure were lower in comparison to those from both legumes and non-legumes. In addition, the initial salt content, experimental years, and returning method influenced the improvement effect of green manure on saline soil. Therefore, this meta-analysis identified green manure as a promising practice for significantly improved saline soil in China.

Investigating the principle and application of high-frequency and high-voltage pulse AC equipment for oil–water separation of heavy crude oil

To address the challenges of oil–water separation encountered during the processing of heavy crude oil, this study meticulously examines the kinetics of demulsification under an electric field. Consequently, a cutting-edge high-frequency/high-voltage AC pulsed power supply has been innovatively developed. This device boasts a flexible voltage-adjustment mechanism, strategically enhancing the inverter output voltage incrementally throughout the pulse’s duration. This method effectively reduces the negative impact of current surges on the operational stability of crude oil desalination plants, especially during the commutation periods of the switching devices. Furthermore, it resolves the issue of premature power supply shutdowns to the desalination plant, caused by peak currents misinterpreted as critical short-circuit currents leading to pole plate breakdowns. An industrial application study conducted at Shandong Chambroad Petrochemicals Co., Ltd. Under identical operational conditions, the power supply designed in this research outperforms traditional electrical desalting transformers in several key aspects. These include a notably enhanced oil–water separation capability and significantly more stable performance. Remarkably, the desalting efficiency shows substantial improvement even at increased feed rates, under constant other conditions. The experimental findings indicate that the average rates of desalination and dehydration achieved by this power supply exceed 90%. Moreover, even when the feed rate is augmented by approximately 75% under constant operating conditions, the desalination efficiency remains 78.49% higher than that achieved by standard industrial frequency electric desalination transformers. Additionally, the desalting outcomes are predominantly unaffected by fluctuations in the initial salt content of the feedstock, demonstrating the robustness of the developed solution.

Calculating the Soil Freezing Characteristic Curve of Saline Soil With Equivalent State of Bulk Solution

AbstractThe relationship between unfrozen water content and temperature, called as soil freezing characteristic curve (SFCC), is of importance for hydrologic, engineering, environmental issues related to frozen soil. The SFCC of saline soil is essentially a result of phase equilibrium of pore solution, which is similar but not identical to that of bulk solution. However, there is still a vacancy of study on the phase equilibrium of pore solution in frozen soil. In this study, image transformation was used to establish the relationship of phase equilibrium between bulk solution and pore solution, with four introduced parameters. Then, the new model of SFCC for saline soil was proposed based on the equivalent state of bulk solution with Pitzer model and SFCC of nonsaline soil. The model was validated by the experimental data from published articles and showed good performance in calculating SFCC of saline soils regardless of soil type, phase transition path, and soil initial water‐salt condition, and some advantages when compared to other three models. All the four introduced parameters have clear physical meanings and their relationships with soil type and initial salt concentration were discussed. Finally, the evolution of phase diagram from bulk solution to pore solution at icing stage was figured out. Further studies are needed for their relationship at salt crystallization stage. Shifting the research perspective from unfrozen water content to pore solution, this study gives a new approach to research of freezing characteristic of saline soil and could promote hydrological and engineering research in cold regions.

Study on water-salt phase transition of saline soils during freezing

As the temperature decreases, when the freezing temperature is reached, the solution in the pores of saline soil undergoes ice crystallization and salt crystallization phenomena. Theoretical and experimental studies have been carried out in order to investigate the behaviour of water-salt phase transitions within the pores of saline soils. Firstly, the theoretical expression for the initial crystallization radius is given from the thermodynamic theory by considering the interphase chemical potential equilibrium and the Young-Laplace equation, and the relationship between the initial crystallization radius and temperature as well as the initial salt content is analyzed. Then, a theoretical model to predict the pore solution content and crystal content was developed in conjunction with the Van Genuchten soil-water characteristic curve model, and the water-salt phase transition behaviour of saline soils was analyzed by numerical calculations. Finally, the validity of the theoretical model was verified by a saline soil freezing test. The results show that the water-salt phase transition behaviour of the solution within the pores of saline soils is affected by temperature and initial salt content, and the water-salt phase transition behaviour mainly occurs at the early stage of freezing. Salt lowers the freezing temperature of the soil; the higher the salt content, the lower the freezing temperature, and the presence of salt inhibits the growth of ice crystals. As the temperature decreases, the precipitation of ice salt crystals during the phase transition of the soil pore solution reduces the soil porosity and decreases the channels for ion migration, resulting in a gradual increase in the soil pore volume ratio.

Limited Bioweathering by Cyanobacteria in Cold, Nutrient-Limited Conditions: Implications for Microbe-Mineral Interactions and Aquatic Chemistry in Cold Environments

Solute fluxes in Antarctic meltwaters indicate microbial processes influence chemical weathering. Antarctic cyanobacterial mats dominated by Leptolyngbya glacialis enhance weathering rates at 12 °C. Yet, their effects on nutrient fluxes in colder, nutrient-limited conditions, similar to the McMurdo Dry Valleys environments, are unknown. Here, we investigate biotic and abiotic weathering rates of glaciofluvial sediments at 4 °C and compare results to previous experiments at 12 °C. We also examine the effects of nutrient and salt concentrations on weathering fluxes by comparing the effects of different media concentrations (0.1X and 0.001X: 10 and 1000 times diluted) at both temperature conditions. Our results show limited evidence of biologically mediated silica release at 4 °C, yet microbe-mineral interactions still affect nutrient fluxes, particularly for Ca, Mg, Mn, P, and N. However, a higher initial salt concentration (0.1X media) increased the concentration of solutes released under abiotic conditions. These results indicate that aqueous solutes, temperature and microbial processes are all important factors controlling weathering rates and nutrient fluxes in cold settings.

Optimizing operational parameters for highly-concentrated sodium hydroxide production via electrodialysis with bipolar membranes from concentrated brines

Sodium hydroxide necessitates the implementation of cleaner production methods that deviate from the conventional practices in the chlor-alkali industry. New sustainable sources such as concentrated brines, which are typically regarded as waste, are currently being investigated for the production of sodium hydroxide using Electrodialysis with Bipolar Membranes (EDBM). This process has the advantages of not producing gas by-products, reducing operational risks, and providing value to waste brines after converting them into acids or alkali solutions. However, the production of sodium hydroxide via EDBM using brines is limited by the low concentration of the final base (e.g. typically below 2 M), which increases the cost of transport. This study aims to overcome this limitation by optimizing parameters such as salt-to-base volume ratio, initial salt concentration, and current density values. Notably, this research is one of the few to employ Response Surface Methodology with a Central Composite Design to maximize the final sodium hydroxide concentration; two models using second-order polynomial equations were proposed. Results showed the possibility to achieve 5.3 M NaOH under a volume ratio range of 9.8:1–10:1, a current density range of 490 A/m−2 to 500 A/m−2, and an initial salt concentration in the range of 6 M NaCl. Moreover, the energetic analysis showed values of specific energy consumption in a range of 2.5 kWh kgNaOH-1-3.5 kWh kgNaOH-1 and specific productivity of the process up to 3.08 tonNaOH year−1 m−2, which are moderate in comparison with values previously presented in literature. Finally, an economic analysis showed that energy was the most significant cost component, making up 89 % of the total process cost, which was estimated to be 0.69 € kgNaOH-1 (concentration 21.2 % w/w). Overall, these high concentration values open a real chance to shift towards sustainable production of NaOH by means of EDBM from brines, highlighting the novelty of this study.

Productivity Prediction for the Progressive Freeze Desalination Process Using Heat and Mass Transfer Modeling

AbstractPredicting the productivity of the freeze desalination process is of key importance. This paper describes an analytical method to predict the productivity for the progressive freeze desalination process utilizing the rectangular channel crystallizer design. The mass of ice produced during the process is considered a measure of productivity. The model was developed using heat and mass transfer modeling. The effect of coolant temperature (from −8 to −16 °C), liquid flow rate (4400–6000 mL min−1), and initial salt concentration of the liquid (1.5–7 wt%) on the mass of ice produced was investigated. The analytical results of the mass of ice produced were compared with the experimental data. A plausible match was found between the analytical and experimental results, with an error range between 6 % and 9 %. The model can predict the mass of ice produced for given values of the initial salt concentration of the liquid, initial mass of the liquid, salt concentration of thawed ice, liquid flow rate, and coolant temperature.

Infiltration and Leaching Characteristics of Soils with Different Salinity under Fertilizer Irrigation

Salt and nutrient transport and transformations during water infiltration directly influence saline soil improvement and the efficient use of water and fertilizer resources. The effects of soil initial salinity (18.3 g/kg, 25.5 g/kg, 42.2 g/kg, 79.94 g/kg, and 165 g/kg, respectively, labeled S1 to S5) on the infiltration and leaching characteristics of water, salt, and nitrogen were analyzed via a one-dimensional vertical fertilizer infiltration experiment. Meanwhile, the estimation models of cumulative infiltration and wetting front, including the effect of soil initial salinity, were established. The results showed that, with the increase in soil initial salinity, the cumulative infiltration within the same time decreased, and the migration time of wet front to 45 cm was longer. The time required for S5 to reach the preset cumulative infiltration was more than six times that of S1, and, for the wet front migration to 45 cm, the time requirement for S5 was about four times that of S1. In the established Kostiakov model and wetting front model, the coefficients all decreased with the increase in soil initial salinity, and the test index R2 values both reached 0.999. In the Kostiakov model, coefficient K had a linear relationship with the natural logarithm of initial soil salt content, while index a had a direct linear relationship with initial soil salt content. The cumulative leachate volume decreased with the increase in soil initial salinity, and the corresponding data of S3 and S5 were reduced by 37% and 57.3%, respectively, compared with S1. The electrical conductivity values of S1, S3, and S5 were 15.4, 209.8, and 205.6 ms/cm, respectively, being affected by the initial content in soil, soil moisture transport rate, and exogenous potassium nitrate (KNO3) addition. The NO3−-N concentrations in the leachates of S1, S3, and S5 at the end of leaching were 55.26, 16.17, and 3.2 mg/L, respectively. Based on the results of this study, for soil with high initial salinity, the conventional irrigation amount (2250 m3/ha) of the general soil in the study area could not meet the requirements of leaching salt. These results can provide a reference for the formulation of irrigation and fertilization strategies for soils with different salinity and contribute to the sustainable development of saline soil agriculture and the ecological environment.

Models for Considering the Thermo-Hydro-Mechanical-Chemo Effects on Soil–Water Characteristic Curves

The soil–water characteristic curve (SWCC) is widely used as a tool in geotechnical, geo-environmental, hydrology, and soil science fields for predicting and interpreting hydro-mechanical behaviors of unsaturated soils. Several previous studies focused on investigating the influence of initial water content, stress history, temperature, and salt content on the SWCC behavior. However, there is still limited understanding to be gained from the literature on how we can systematically incorporate the influence of complex thermo-hydro-mechanical-chemo (THMC) effects into interpreting and predicting the behavior of unsaturated soils. To address that knowledge gap, in this study, the coupled influence of temperature, initial stress state, initial density, soil structure, and chemical solution effects was modeled using established SWCC equations from the literature. The methodology for incorporating the coupled effects of these influential factors is presented herein. Furthermore, we evaluated the SWCC models proposed in this study, enabling us to provide a comprehensive discussion of their strengths and limitations, using the published SWCC data from the literature. The developments outlined in this paper contribute toward facilitating a rigorous approach for analyzing the THMC behaviors of unsaturated soils.

Pore‐scale freezing of a sandy saline soil visualized with micro‐computed tomography

AbstractSandy saline soils are widely distributed and commonly experience seasonal or long‐term freezing, yet the freezing process in these soils is rarely studied. This research utilized in situ X‐ray computed tomography (CT) to visualize pore‐scale freezing processes in sandy saline soils under various initial water and salt contents. Micron‐resolution observations of pore ice and unfrozen water produced new insights into the preferential orientation and grouping of pore ice crystals, intersections between different pore ice crystal groups causing anisotropic behavior, decreasing pore ice crystal size under faster freezing rates, and the formation of interconnected networks of both pore ice and unfrozen water upon freezing. From a thermodynamic perspective, the salt content in the unfrozen liquid is dependent on the local temperature as described by water–salt phase diagram. Furthermore, the local volume ratio between unfrozen water and pore ice reflects the initial salt content and salt mass transfer occurring due to both diffusion and fluid flow processes. This work improves the understanding of complex freezing phenomena in sandy saline soils through high‐resolution evidence of crystallization patterns, transformation mechanisms, and coupled heat‐mass transfer.

Towards spatiotemporal-resolved spectroscopic measurement of freezing desalination using femtosecond laser filaments

Freezing desalination can produce freshwater from seawater or industrial wastewater by ice crystallization with low energy consumption and less corrosion, and is promising for alleviating current stress on the world's water supply. However, the salt rejection dynamics during the freezing process is less understood due to the lack of real-time, high spatiotemporal-resolved detection methods. Here we present a proof-of-principle, quantitative, and simultaneous multi-salt detection approach for the measurement of salt rejection dynamics in salt-contaminated water at the ppm level using an ultrashort-pulsed femtosecond laser propagating in the filamentation regime. We show that this approach of filament-induced plasma spectroscopy possesses the abilities for both monitoring the change of salt concentration in the remaining unfrozen water during the freezing process and imaging the spatial concentration distributions of metal contaminants on the resultant ice surface. With this approach, we find that the initial salt concentration in water plays an essential role in the efficiency of the freezing desalination process, which shows a metal-species-dependent characteristic. Our results pave the way towards real-time, online, and high spatiotemporal-resolved detection of salt rejection dynamics of freezing desalination by ultrashort-pulsed lasers.

Effect of porous layer and initial salt gradient on improving SGSP stability: Transient numerical simulation and theoretical analysis

The salt gradient solar pond (SGSP) is a low-cost and large-scale solar energy capture and storage device. The stability of the non-convective zone (NCZ) is critical for the well-functioning and efficiency of SGSP. To understand when and how SGSP lost its effectiveness, the turbulent double-diffusive convection in solar ponds was first solved numerically with a Large Eddy Simulations (LES) model. The simulations show that attaching a porous layer or increasing the initial salt concentration effectively delays the destruction of NCZ. By increasing the initial salt concentration from 5.2% to 20.8%, the destruction time increases from 7 to 22 h. By attaching a porous layer, the overturn time can increase by about 8 h, resulting in a temperature rise from 46 °C to 73 °C in the storage layer. The flow field analysis shows that both interface erosion and turbulent mixing in NCZ cause the destruction of NCZ. The stability analysis shows that the turbulent mixing decreases the salinity gradient in NCZ, making it more susceptible to erosion. By inhibiting the turbulent mixing, the porous layer at the bottom can effectively delay the arrival of NCZ destruction. Thus, the heat storage capacity and stability of solar ponds are enhanced.

A facile method for synthesis of bismuth oxide nanoparticles on anion exchange resin and its salt removal ability for saline water

In this work, a method was applied to produce bismuth oxide nanoparticles on anion exchange resin (AR@Bi2O3), which was then applied effectively for removing salts in aqueous solution of NaCl and real-world saline water. The results from SEM, EDX, XRD, and FTIR confirm the preparation of AR@Bi2O3 with a crystalline structure and high purity as well as the effective adsorption of salt on the surface of the material. The salt removal was investigated under various conditions of contact time, solution pH, adsorbent mass, initial salt concentration, and solution temperature. The salt adsorption of AR@Bi2O3 reached an equilibrium capacity of 280 mg/g after 45 min, which is best described by the intraparticle diffusion model. Moreover, pH 5 was found to be the optimal value for salt adsorption and Freundlich is the best model for describing the adsorption process, which was a spontaneous process (∆G < 0). The adsorption capacity of the AR@Bi2O3 material likely remained stable at over 260 mg/g even after 10 cycles of adsorption-regeneration, indicating a great potential for practical application of AR@Bi2O3 in saline water treatment.

Biosignature preparation for ocean worlds (BioPOW) instrument prototype

In situ sampling missions to detect biosignatures on ocean worlds requires thorough sample preparation to manage the expected chemical complexity of such environments. Proposed instruments must be capable of automatic liquid sample handling to ensure sensitive and accurate detections of biosignatures, regardless of the initial chemical composition. Herein, we outline the design, build, and test of the integrated Biosignature Preparation for Ocean Worlds (BioPOW) system capable of purifying amino acids from icy samples. This four step modular instrument 1) melts ice samples, 2) purifies amino acids via cation exchange chromatography, 3) concentrates via vacuum drying, and 4) derivatizes amino acids to volatilize and enable detection with downstream analytical instruments. Initial experiments validated the thermal performance of the system by melting ice in the sample cup (1 mL sample, 3°C–28°C, &amp;lt;5 min, 1.4 kJ) and heating the derivatization tank past the concentration temperature (20°C–60°C, 12 min, 3.6 kJ) to the derivatization temperature (60°C–90°C, 25 min, 7.5 kJ). Later experiments investigated important factors for automatic cation exchange using a design of experiments approach, and found that initial salt concentration, sample and eluate flow rates, and water wash volumes all play significant roles in reducing conductivity (1.1 x–6.7 x) while maintaining phenylalanine yields between 31% and 94%. The modules were then integrated into a 12 cm × 20 cm × 20 cm fieldable platform for analysis, and the maturation of this design for future spaceflight is discussed.

Facile Synthesis of Citric Acid Functionalized Fe3O4@Activated Carbon Magnetic Nanocomposite for Efficient Adsorption of Brilliant Green Dye from Wastewater

AbstractOwing to the impact of brilliant green dye on potable water contamination, citric acid functionalized magnetic nanocomposite in presence of activated carbon was prepared for easy, quick, and efficient removal of the dye from water. Batch adsorption studies were conducted to maximize the adsorption efficiency by optimizing contact time, initial dye concentration, pH, dosage, and salt concentration. The maximum efficiency of the citric acid functionalized Fe3O4@activated carbon was found to be 773 mg g−1. The efficiency of the monolayer adsorption process as depicted from the Langmuir model is explained based on the hydrogen bonding, electrostatic interaction, and porosity of the adsorbent. The adsorption process follows a pseudo‐second order kinetics model which can also be correlated to the relatively quick adsorption process. The saturation magnetization of the nanocomposites prepared in presence of activated carbon was found to be 35.2 emu/g, which makes it effective for quick magnetic separation. Built on the findings, we report an economical, efficient, and satisfactory alternative adsorbent for the abatement of brilliant green dye from coloured wastewater and contaminated water sources.

Study on Purification of Emulsified Waste Liquid by Non-thermal Plasma

This paper uses the Non-thermal Plasma produced by dielectric barrier discharge to treat the emulsion waste liquid. The effects of discharge time, peak voltage, and initial concentration of waste liquid and inorganic salt on Chemical Oxygen Demand COD degradation and turbidity removal rate were studied. The primary and secondary order of influencing factors of the COD degradation rate of emulsion cutting waste liquid is discharge time > peak voltage > initial concentration of emulsion cutting waste liquid > inorganic salt type. That is to say, when 0.3000 g of anhydrous calcium chloride is added to the emulsion waste liquid prepared according to the ratio of 1:200, the peak discharge voltage is 30 kV, the discharge time is 4 hours, and the COD degradation rate is the best. The experimental results show that the COD degradation rate is 87.48%. The primary and secondary order of factors affecting the turbidity removal rate of emulsion-cutting waste liquid is peak voltage > inorganic salt type > initial concentration of emulsion-cutting waste liquid > discharge time. The experimental results show that the turbidity removal rate of emulsion waste liquid is 93.21%.

Calcium carbonate particle synthesis in a confined and dynamically thinning layer on a spin-coater – In situ deposition for cell adhesion

We have designed a new method for the in situ synthesis of CaCO3 particles via spin-coating while simultaneously controlling their distribution on the surface. CaCO3 is synthesized by simultaneously adding CaCl2 and Na2CO3 solutions to a rotating surface on a spin-coater. During the transient liquid film evaporation on the spin-coater, as the film layer progressively thins, the CaCO3 particles nucleate and grow while confined within that thinning layer on the spin-coater. The evaporation of the volatile component increases the global concentration of solids, resulting in the deposition of precipitates (CaCO3 particles). The growth rate, particle size, and coverage were theoretically and experimentally analyzed by adjusting the process parameters, initial salt concentrations, rotational speed, and post-deposition treatment. Experimental findings indicated that increasing the rotational speed resulted in formation of smaller particle sizes, while the concentration of the precursors directly influenced the average diameter of the particles. Raman spectroscopy analysis demonstrated that vaterite particles synthesized from lower salt concentrations exhibited a more intense signal than those synthesized from higher salt concentrations. Furthermore, higher salt concentrations led to increased particle coverage, while higher rotational speeds resulted in decreased particle coverage on the substrate. We explored the potential of such coatings in biomedicine and tissue engineering by seeding MC3T3-E1 cells on the CaCO3 particle-coated glass substrates. Surfaces functionalized with CaCO3 particles exhibited enhanced cell proliferation and adhesion.

Collaborative optimization of regeneration unit and power generation unit in reverse electrodialysis heat engine for low-grade heat recovery

Reverse electrodialysis heat engine (REDHE) emerges great potential to harvest the low-grade heat (LGH) produced during the industrial processes and renewable energy utilizations. In the closed-loop system, the power generation unit converts the salinity gradient power (SGP) to electric energy using the reverse electrodialysis (RED) cells, and the regeneration unit recovers the salinity gradient based on LGH. As two units are in series, the regeneration and power generation units should be collaboratively optimized to achieve a high performance of REDHE. Herein, a framework which can unitedly simulate the both units is built, which enables to divide the total efficiency of REDHE to the respective efficiencies of units. LiBr solution as the working fluid and the effects of initial salt concentration, concentration of the high concentration (HC) solution and temperature in RED cells are considered. Results show that the total efficiencies increase with the concentration of HC solution and the RED temperature due to the production of more chemical energy in the regeneration unit. However, a non-monotonic trend of the total efficiency with the initial concentration is discovered, which increases from 4.91% to 5.42% and then decreases to 4.69% when the initial concentration raises from 20 wt% to 25 wt% and then reaches 30 wt% at RED temperature of 25 ℃. Although enhancing the RED temperature to 50 ℃ leads the total efficiencies increase to 6.25%, 7.13% and 6.38%, respectively, the trend is unchanged. The respective efficiencies of units explain the phenomenon by that a higher salinity can decrease the efficiency of the power generation unit by reducing the ionic selectivity in the RED cells, but enhance the efficiency of the regeneration unit. Therefore, the highest total efficiency reached at initial concentration of 25 wt% is the trade-off between the efficiencies of two units. This study indicates that increasing the concentration of HC solution, the RED temperature, and carefully selecting a compromise initial concentration are helpful to achieve a high energy efficiency in a REDHE.