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Featured Application: The developed methodology enables the rapid fabrication of customized lab-scale reactors, optimizing their design and manufacturing. Beyond desalination, this approach is valuable in the early R&D stages for other electrochemical flow reactors, such as fuel cells, bio-batteries, microfluidic devices, and electrolyzers. In response to the growing demand for potable water, this study presents a practical methodology for designing and fabricating a hybrid desalination system that integrates reverse electrodialysis and electrodialysis using 3D-printing technology. The hybrid system combines the energy generation potential of RED with the salt removal capabilities of ED, reducing energy consumption. Customized reactors were designed to enhance flow distribution and ion exchange, with computational fluid dynamics simulations validating the hydrodynamic performance. The reactors were fabricated using 3D printing, allowing rapid, cost-effective production, with functional reactors constructed in under 24 h. The system achieved a 15% reduction in salt concentration within one hour, with a specific energy consumption of 0.1388 Wh/m3 and a water recovery rate of 50%. These results demonstrate the functionality of the RED-ED hybrid system for achieving energy savings and performing water desalination. This methodology provides a scalable and replicable solution for water treatment applications, especially in regions with abundant salinity gradients and limited freshwater resources, while offering a multidisciplinary approach that integrates physicochemical and engineering principles for effective device development. [ABSTRACT FROM AUTHOR]

The reverse electrodialysis heat engine (REDHE) represents a transformative innovation that converts low-grade thermal energy into salinity gradient energy (SGE). This crucial form of energy powers reverse electrodialysis (RED) reactors, significantly changing wastewater treatment paradigms. This comprehensive review explores the forefront of this emerging field, offering a critical synthesis of key discoveries and theoretical foundations. This review begins with a summary of various oxidation degradation methods, including cathodic and anodic degradation processes, that can be integrated with RED technology. The degradation principles and characteristics of different RED wastewater treatment systems are also discussed. Then, this review examines the impact of several key operational parameters, degradation circulation modes, and multi-stage series systems on wastewater degradation performance and energy conversion efficiency in RED reactors. The analysis highlights the economic feasibility of using SGE derived from low-grade heat to power RED technology for wastewater treatment, offering the dual benefits of waste heat recovery and effective wastewater processing. [ABSTRACT FROM AUTHOR]

Industry, agriculture, and a growing population all have a major impact on the scarcity of clean‐water. Desalinating or purifying contaminated water for human use is crucial. The combination of thermal membrane systems can outperform conventional desalination with the help of synergistic management of the water‐energy nexus. High energy requirement for desalination is a key challenge for desalination cost and its commercial feasibility. The solution to these problems requires the intermarriage of multidisciplinary approaches such as electrochemistry, chemical, environmental, polymer, and materials science and engineering. The most feasible method for producing high‐quality freshwater with a reduced carbon footprint is demanding incorporation of industrial low‐grade heat with membrane distillation (MD). More precisely, by using a reverse electrodialysis (RED) setup that is integrated with MD, salinity gradient energy (SGE) may be extracted from highly salinized MD retentate. Integrating MD‐RED can significantly increase energy productivity without raising costs. This review provides a comprehensive summary of the prospects, unresolved issues, and developments in this cutting‐edge field. In addition, we summarize the distinct physicochemical characteristics of the membranes employed in MD and RED, together with the approaches for integrating them to facilitate effective water recovery and energy conversion from salt gradients and freshwater. [ABSTRACT FROM AUTHOR]

Salinity gradient energy presents a promising opportunity for renewable energy, gaining significant interest in the sustainable power sector. This article presents an overview of the application of ion exchange membranes and reverse electrodialysis techniques to harness energy from salinity gradients in seawater, employing anthropomorphic terminology to enhance understanding. The main focus lies in the utilization of ion exchange membrane technology for power generation, with a particular emphasis on its current implementation status and underlying operational principles. The research aims to enhance readers' comprehension of salinity gradient energy in seawater and promote awareness of "energy security" through the use of descriptive language. [ABSTRACT FROM AUTHOR]

Blue energy obtained by salinity gradient can be generated by mixing two saline solutions having different salt concentrations. According to researchers working in this area, about 80% of the current global electricity demand could potentially be covered by this energy source. There are basically two membrane technologies so-called pressure-retarded osmosis (PRO) and reverse electrodialysis (RED) that are capable to generate electrical energy from salinity gradient. The pressure driven PRO process is more suitable for energy generation from highly concentrated brines. However, RED is more favorable for power generation by mixing seawater and river water. In RED process, ion exchange membranes (IEMs) placed between two electrodes in a stack were employed for transport of ions. Thus, an electrical current is obtained at the electrodes by electron transport through redox reactions. This review gives an overview of RED as a pioneering technology for salinity gradient energy (SGE) generation. The review summarizes the recent improvements of IEMs employed for RED studies, membrane fouling and RED stack design. [ABSTRACT FROM AUTHOR]

Sub-Saharan Africa, and in particular Mozambique, has considerable potential of salinity gradient energy, which could foster coastal development. However, the lack of scientific based information hinders the development of policies and investments in harnessing this source of energy in Sub-Saharan Africa. The present study, used historical data of temperature and salinity and estimated the potential of salinity gradient power in four main estuaries in Mozambique. The theoretical salinity gradient power ranged, on average, from 843.6 MW, in Incomati River estuary to 2,800.0 MW in Zambezi Delta. The Bons Sinais Estuary and Limpopo Estuary had 1,086.8 MW and 1292.0 MW, on average, respectively. The salinity power estimated in the Mozambique estuaries studied was above the maximum power densities for electrodialysis osmotic energy storage systems, which is set at 5 W m−2, and has potential extractable energy of about 3,000MW, and could benefit about 2 million coastal rural households (about 7% of the total Mozambican population) on irrigation and lighting houses. Further studies may be focused in determining the seasonal and salinity intrusion effects on salinity power gradient in the Mozambican estuaries. [ABSTRACT FROM AUTHOR]

Abstract Multi-stage reverse electrodialysis (MSRED) offers a promising way for efficient salinity gradient energy harvesting. Here, an improved model of the MSRED system under serial control strategy is proposed. The technical–economic analysis is conducted with considering discount, depreciation and different regional tax and electricity price levels under the maximum net power output conditions. Results reveal that net power output and energy efficiency both increase first with increasing stage numbers, reach their maximum values, and then decrease. For 5 M/0.05 M solutions, the optimal net power output of 4.98 kW is obtained at the stage number n = 12. The optimal stage number corresponding to the maximum net power increases with increasing feed solution concentrations. Due to the compromise between net power generation and capital cost, there exist optimal stage numbers leading to the lowest LCOE and largest NPV, respectively. Higher feed solution concentration can significantly decrease the system LCOE and increase the NPV. The optimal stage number corresponding to the maximum NPV increases with increasing feed solution concentrations. In Germany, for 5 M/0.05 M solutions, the lowest LCOE of 0.061 €·kWh−1 is achieved at n = 3 while the highest NPV over the system lifecycle of 52,005 € is obtained at n = 8. Lower tax, higher electricity price, appropriate membrane price and stage numbers, and high salinity gradient sources can significantly accelerate the commercial completeness of the MSRED systems.

Reverse electrodialysis (RED) is one of the methods able to generate energy from the salinity gradient between sea- and river water. The technique is based on the diffusion of ions through membranes that specifically allow either cations or anions to pass through. This ion current is converted into an external electric current at electrodes via suitable redox reactions. Seawater contains mainly eight different ions and the description of transport phenomena in membranes in classical terms of isolated species is not sufficient because the different particles have different velocities—in the same direction or opposite—in the same membrane. More realistic is the Maxwell–Stefan (MS) theory that takes all interactions between the different particles in account; however, such a model is complex and validation is difficult. Therefore, a simplified system is used with solely NaCl in solution, using only 9 diffusivities in the calculation. These values are estimated from the literature and are applied to an MS model of the RED process. Using experimental data of NaCl and water transport as well as power density, these diffusivities are adapted in the MS model. Reliable values for the diffusivities were obtained for the following three interactions: H2O–Na+, H2O–Cl− and Na+–Cl−. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Electrochemistry is the property of Journal of Electrochemistry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Membrane fouling inevitably occurs during nanofluidic reverse electrodialysis. Herein, the impact of multi-fouling on the energy conversion performance of negatively charged conical nanochannels under asymmetrical configurations is systematically investigated. The results reveal that in Configuration I, where a high-concentration solution is applied at the tip side, at small concentration ratios, multiple foulings reduce the electric power. In Configuration II, where a low-concentration solution is applied at the tip side, multiple foulings near the base side contribute to the electric power. Any fouling that formed near the low-concentration entrance diminished the electric power and energy conversion efficiency. Multi-fouling lowered the electrical power consumption by 69.27% and 99.94% in Configurations I and II, respectively. In Configuration I, the electric power first increased with increasing fouling surface charge density, reached its maximum value, and thereafter decreased. In Configuration II, the electric power first decreased with increasing fouling surface charge density, reached its minimum value, and thereafter increased. Large negative or positive charge densities of fouling contribute to the electric power and energy conversion efficiency. [ABSTRACT FROM AUTHOR]

Blue energy obtained by salinity gradient can be generated by mixing two saline solutions having different salt concentrations. According to researchers working in this area, about 80% of the current global electricity demand could potentially be covered by this energy source. There are basically two membrane technologies so-called pressure-retarded osmosis (PRO) and reverse electrodialysis (RED) that are capable to generate electrical energy from salinity gradient. The pressure driven PRO process is more suitable for energy generation from highly concentrated brines. However, RED is more favorable for power generation by mixing seawater and river water. In RED process, ion exchange membranes (IEMs) placed between two electrodes in a stack were employed for transport of ions. Thus, an electrical current is obtained at the electrodes by electron transport through redox reactions. This review gives an overview of RED as a pioneering technology for salinity gradient energy (SGE) generation. The review summarizes the recent improvements of IEMs employed for RED studies, membrane fouling and RED stack design.

In response to the growing demand for potable water, this study presents a practical methodology for designing and fabricating a hybrid desalination system that integrates reverse electrodialysis and electrodialysis using 3D-printing technology. The hybrid system combines the energy generation potential of RED with the salt removal capabilities of ED, reducing energy consumption. Customized reactors were designed to enhance flow distribution and ion exchange, with computational fluid dynamics simulations validating the hydrodynamic performance. The reactors were fabricated using 3D printing, allowing rapid, cost-effective production, with functional reactors constructed in under 24 h. The system achieved a 15% reduction in salt concentration within one hour, with a specific energy consumption of 0.1388 Wh/m3 and a water recovery rate of 50%. These results demonstrate the functionality of the RED-ED hybrid system for achieving energy savings and performing water desalination. This methodology provides a scalable and replicable solution for water treatment applications, especially in regions with abundant salinity gradients and limited freshwater resources, while offering a multidisciplinary approach that integrates physicochemical and engineering principles for effective device development.

Exploring the utilization of ion exchange membranes (IEMs) in salinity gradient energy harvesting, a technique that capitalizes on the salinity difference between seawater and freshwater to generate electricity, this study focuses on optimizing PVDF to Nafion ratios to create ultra-thin membranes. Specifically, our investigation aligns with applications such as reverse electrodialysis (RED), where IEMs facilitate selective ion transport across salinity gradients. We demonstrate that membranes with reduced Nafion content, particularly the 50:50 PVDF:Nafion blend, retain high permselectivity comparable to those with higher Nafion content. This challenges traditional understandings of membrane design, highlighting a balance between thinness and durability for energy efficiency. Voltage–current analyses reveal that, despite lower conductivity, the 50:50 blend shows superior short-circuit current density under salinity gradient conditions. This is attributed to effective ion diffusion facilitated by the blend's unique microstructure. These findings suggest that blended membranes are not only cost-effective but also exhibit enhanced performance for energy harvesting, making them promising candidates for sustainable energy solutions. Furthermore, these findings will pave the way for advances in membrane technology, offering new insights into the design and application of ion exchange membranes in renewable energy. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED), an emerging membrane-based technology, harnesses salinity gradient energy for sustainable power generation. Accurate characterization of electrical parameters in RED stacks is crucial to monitoring its performance and exploring possible applications. In this study, a DC electronic load module (DCELM) is implemented in a constant current condition (CC mode) for characterization of lab scale RED process, using a RED prototype in-house designed and manufactured (RU1), at different data capture setups (DCS), on which the total number of steps for data capture (NS) and the number of measurements per step (ρ) are the parameters that were modified to study their effect on obtained electrical parameters in RED. NS of 10, 50, and 100 and ρ of 10 and 20 were used with this purpose. The accuracy of resulting current and voltage steps can be enhanced by increasing NS and ρ values, and according to obtained results, the higher accuracy of resulting output current and voltage steps, with low uncertainty of the average output steps (AOS) inside the operational region of power curve, was obtained using a DCS of NS = 100 and ρ = 20. The developed DCELM is a low-cost alternative to commercial electronic load devices, and the proposed methodology in this study represents an adaptative and optimizable CC mode characterization of RED process. The results obtained in this study suggest that data capture conditions have a direct influence of RED performance, and the accuracy of electrical parameters can be improved by optimizing the DCS parameters, according to the required specifications and the scale of RED prototypes. [ABSTRACT FROM AUTHOR]

Coupling low-grade heat (LGH) with salinity gradient is an effective approach to increase the efficiency of the nanofluidic-membrane-based power generator. However, it is a challenge to fabricate membranes with high charge density that ensures ion permselectivity, while maintaining chemical and mechanical stability in this composite environment. Here, we develop a bis[2-(methacryloyloxy)ethyl] phosphate (BMAP) hydrogel membrane with good thermal stability and anti-swelling property through self-crosslinking of the selected monomer. By taking advantage of negative space charge and three-dimensional (3D) interconnected nanochannels, salinity gradient energy conversion efficiency is substantially enhanced by temperature difference. Theoretical and experimental results verify that LGH can largely weaken the concentration polarization, promoting transmembrane ion transport. As a result, such a hydrogel membrane delivers high-performance energy conversion with a power density of 11.53 W·m−2 under a negative temperature difference (NTD), showing a 193% increase compared with that without NTD. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a renewable energy-generating SGE technique using energy from salinity gradients. This research investigates the effect of membrane and feed characteristics on reverse electrodialysis (RED) power generation. Some investigations on the process parameters effect for the complement of the main study were also conducted. The generated power of RED was measured using power density analysis. The experiments were performed using artificial seawater varied from 0 to 1 g/L NaCl for diluted salt water and from 0 to 40 g/L NaCl for concentrated salt water. In a study of ions type, NaCl non-pa is used to represent monovalent ions, and MgSO4 represents divalent ions. The results showed that the highest voltage generation is 2.004 volts by 14 cells number of the RED membrane utilizing a RED self-made laboratory scale. The power density was enhanced by raising the flow rate (0.10 L/min), concentration difference (40 g/L), and the presence of electrode rinse solution. Further, the ion type (monovalent, divalent, and multivalent) influenced the resulting RED power density, where the divalent ion (MgSO4) 's power density was greater than that of the monovalent ion (NaCl). The resistance and selectivity of the membrane were the major keys for the power generation of RED

Capacitive mixing (CapMix) is a renewable method of extracting energy from the salinity difference between seawater and freshwater. In this study, we systematically investigate the system behavior and performance of the CapMix system under four operational modes namely, capacitive energy extraction based on double layer expansion (CDLE), capacitive energy extraction based on the Donnan potential (CDP), and CDP with additional charging of constant voltage (CDP-CV) and constant current (CDP-CC). The results indicate that the application of additional charging in the CDP technique can break the limits of the Donnan potential and significantly improve the system’s performance. Accordingly, in terms of energy production and average power density, CDP-CC and CDP-CV are the two superior operational modes, followed by CDP and CDLE. In addition, our results reveal that CDP-CC is determined by the accumulated charge and applied current. CDLE is dependent on the applied voltage, while CDP-CV is not sensitive to the applied voltage. Increasing the external load can considerably increase the energy production of both CDLE and CDP. In summary, the findings in this study provide practical information for the optimization and application of CapMix technologies.

The world alone cannot thrive and relies on energy production and expenditure. In an ideal scenario, all the energy produced worldwide would be clean and renewable; however, that is not the case. Most developed countries have already taken steps toward a green future, except developing countries that rely heavily on fossil fuels. Determining the costs of transitioning to a purely renewable energy-reliant future is essential for a developing country like the Philippines. One viable source of renewable energy sources is salinity gradient energy. The study aims to identify if salinity gradient energy can be a viable energy source. The researchers selected specific locations across Las Piñas, specifically Zapote and Las Piñas rivers, to show if the subject Location fits the conditions as a source of salinity gradient energy. Using the mathematical model expressed by Hsu et al. (2021), Location A can only generate approximately 0.0005 kWh per cubic meter of saltwater and freshwater mixed. Location B can only generate approximately 0.0004 kWh per cubic meter of saltwater and freshwater mixed. It would take 1000 and 1250 times the amount of fresh water and salt water from Location A and Location B, respectively, to match the energy output calculated by Hsu et al. The amount of energy harnessed from these rivers is insignificant due to its concentration difference. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The power conversion of salinity gradient energy (SGE) between concentrated brine from seawater desalination and seawater by reverse electrodialysis (RED) benefits energy conservation and also dilutes the discharge concentration to relieve the damage to coastal ecosystems. However, two key performance indexes of the maximum net power density and energy conversion efficiency for a RED stack harvesting the energy usually cannot reach the optimal simultaneously. Here, an optimization study on the two indexes was implemented to improve the performance of RED in harvesting the energy. A RED model for capturing the SGE between concentrated brine and seawater was constructed, and the correlation coefficients in the model were experimentally determined. Based on the model, the effects of a single variable (concentration, flow rate, temperature, thickness of the compartment, length of the electrode) on the performance of a RED stack are analyzed. The multi-objective optimization method based on the genetic algorithm was further introduced to obtain the optimal solution set, which could achieve the larger net power density and energy conversion efficiency with coordination. The ranges of optimal feed parameters and stack size were also obtained. The optimal flow velocity of the dilute solution and the concentration of the dilute solution are approximately 7.3 mm/s and 0.4 mol/kg, respectively. [ABSTRACT FROM AUTHOR]

Hydrogen production and dye degradation can be achieved simultaneously in a hybrid system of reverse electrodialysis（RED）and electrocoagulation (EC), using current derived from the salinity gradient energy. Under the current, Fe electrode is used as the anode to produce Fe2+(subsequently oxidized to Fe3+) which combines with OH− produced from the cathode to remove the dyes, while the hydrogen gas produced by the cathode is collected by a hydrogen collection device. The experiments are carried out to investigate the effects of different initial concentrations, pH, currents, electrode rinse solution (ERS) flow rates and the addition of chlorine on the degradation rate and hydrogen production. The results indicate that the degradation rate and hydrogen production could reach 98.3% and 150 m h−1 at alkaline condition (pH = 11) and acidic condition (pH = 3) respectively, with a current of 0.4 A. The degradation rate and hydrogen production increase significantly with an increase in current. • A hybrid system of the reverse electrodialysis and electrocoagulation is experimented. • Blue energy harvest, dye degradation and H 2 production can be achieved simultaneously. • The optimal pH range for degradation and hydrogen production were analyzed. • The effects of current, initial concentration, ERS flow rate were investigated. • The effects of addition of chlorine were tested and analyzed. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is an evolving form of a renewable energy process which utilizes the salinity gradient energy from two solutions of different concentrations. One of the main problems limiting the application of PRO is the low performance of the commercially available spiral-wound modules which have poor flow distribution and high pressure drop. The present paper proposes a new spiral-wound module design for PRO application. The performance of the new module design was investigated numerically and compared with the available spiral-wound module. Compared to the available module, the power density of the new design was higher by 25% and 15% at draw concentrations of 35 g/kg and 60 g/kg respectively, while there was a 35% decrease in the pressure drop. The new spiral-wound module design presents an enhanced overall performance due to the better flow distribution and lower pressure drop, yielding a higher water flux and power density. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a promising way of harvesting salinity gradient energy (SGE). The seawater or industrial wastewater may have various pHs. Here the RED performance involving sodium salt solutions with different ion valence ratios including anions of Cl-, SO 4 2-, and PO 4 3- is experimentally investigated in symmetric and asymmetric pH configurations. In the symmetrical pH configuration, increasing the solution pH significantly weakens the energy conversion performance for the 1:1 and 1:3 salts; for the 1:2 salt, the power density and energy conversion efficiency increase and then decrease with increasing pH due to the coupling effects of OH- on the ion transportation through AEMs and CEMs. In the asymmetric pH configuration, increasing the pH of the low concentration solution decreases the power density and energy conversion efficiency. As the pH of the high concentration solution increases, the output power and energy conversion efficiency decrease and then increase for the 1:1 salt due to the coupling effects of the ion transmembrane concentration difference and OH- on the ion migration of IEMs; for the 1:2 salt, the output power and energy conversion efficiency increase and then decrease; for the 1:3 salt, OH- inhibits the hydrolysis of Na 3 PO 4 and anion migration, leading to the lowered output power density and energy efficiency. [ABSTRACT FROM AUTHOR]

Two-thirds of the world's population has limited access to potable water. As we continue to use up our freshwater resources, new and improved techniques for potable water production are warranted. Here, we present a general concept called "salinity exchange" that transfers salts from seawater or brackish water to treated wastewater until their salinity values approximately switch, thus producing wastewater with an increased salinity for discharge and desalinated seawater as the potable water source. We have demonstrated this process using electrodialysis. Salinity exchange has been successfully achieved between influents of different salinities under various operating conditions. Laboratory-scale salinity exchange electrodialysis (SEE) systems can produce high-quality desalinated water at ∼1 mL/min with an energy consumption less than 1 kWh/m3. SEE has also been operated using real water, and the challenges of its implementation at a larger scale are evaluated. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is a power generation process that harnesses the salinity gradient between two water bodies of different salinities. Using high salinity water as a draw solution, this work assesses the techno-economic feasibility of the technology to generate electricity using single and multistage systems. This work utilizes a simulator built on the rigorous Q-Electrolattice equation of state and a mass transfer model that accounts for concentration polarization, combined with the Dakota optimization tool to perform sensitivity analysis and optimization studies. The economic indicator of interest is the Levelized Cost of Electricity (LCOE), which serves to compare PRO with other sources of renewable energy. An LCOE value of USD 0.1255/kWh was obtained from the use of commercial membranes at an efficiency of 100% for the mechanical components of the PRO system. This LCOE drops to USD 0.0704/kWh when an ideal membrane is used—thus showing the improvements to economics possible with improved membrane properties. With currently obtainable membrane properties and mechanical equipment, the LCOE of a single-stage process increases to USD 0.352/kWh, which is not cost-competitive with other renewable energy sources. Setting up multistage PRO systems towards minimizing the LCOE was found to be detrimental to the net power production by the plant. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a renewable energy-generating SGE technique using energy from salinity gradients. This research investigates the effect of membrane and feed characteristics on reverse electrodialysis (RED) power generation. Some investigations on the process parameters effect for the complement of the main study were also conducted. The generated power of RED was measured using power density analysis. The experiments were performed using artificial seawater varied from 0 to 1 g/L NaCl for diluted salt water and from 0 to 40 g/L NaCl for concentrated salt water. In a study of ions type, NaCl non-pa is used to represent monovalent ions, and MgSO4 represents divalent ions. The results showed that the highest voltage generation is 2.004 Volts by 14 cells number of the RED membrane utilizing a RED self-made laboratory scale. The power density was enhanced by raising the flow rate (0.10 L/min), concentration difference (40 g/L), and the presence of electrode rinse solution. Further, the ion type (monovalent, divalent, and multivalent) influenced the resulting RED power density, where the divalent ion (MgSO4) 's power density was greater than that of the monovalent ion (NaCl). The resistance and selectivity of the membrane were the major keys for the power generation of RED. [ABSTRACT FROM AUTHOR]

The removal of phenol from simulated wastewater by a reverse electrodialysis reactor (REDR) wastewater treatment system is experimentally investigated in independent or synergetic degradation circulation mode under specific conditions. Results demonstrated that the total degradation efficiencies (ηde,tot) and the total chemical oxygen demand (COD) removal efficiencies (ηCOD,tot) in an independent degradative circulation mode were better than those in a synergetic degradative circulation mode. After 2 h of treatment, the ηde,tot of phenol reached 100% and 99.7%, and ηCOD,- tot reached 59.6% and 51.3%, under two circulation modes, respectively. However, the synergistic degradation cycle mode achieved a balance between hydrogen ion production and consumption during the wastewater treatment process. When the synergetic circulation mode was applied, the pH of the wastewater was always maintained at around 3 without the addition of acid, which reduced the wastewater treatment costs. Moreover, the general current efficiency and the energy consumption of REDR in the synergetic degradative circulation mode were 51.1% and 168.8 kWh/kgCOD, respectively, after 2 h. Therefore, the implementation of REDR with a suitable circulation mode and operating conditions offered a viable alternative to achieve a win-win situation for both energy and the environment. [ABSTRACT FROM AUTHOR]

This study estimates the environmental and technical energy potential of the thermohaline conditions in the Mexico–Belize riverine estuary. Site-specific conditions were considered based on monthly water temperature, salinity, and river discharge field measurements along the Hondo River estuary from 2018 to 2019. The practical extractable energy assessment described the possibility of outlining a hypothetical ∼3 MW salinity gradient energy (SGE) plant, which could support 5.4–15.1% of houses in the main urbanised area. Low-income housing benefits can be viable for up to 7700 houses with either mechanical or natural ventilation under tropical weather conditions. Alternatively, this energy may be directed towards commercial shared zones between Mexico and Belize. SGE harnessing might be possible throughout the year with limited zero extraction periods provided by seasonal thermohaline variations in the estuary during the dry season and at mid-summer droughts. The energy potential of the Hondo River was compared with manatee presence to explore possible environmental implications from SGE harnessing. The periods of high energy potential were followed by peaks in manatee sightings with a 1–2-month delay. The SGE approach based on a small-scale energy-generation scheme for the local coastal urbanised area considering the binational framework is discussed.

Salinity gradient energy generated by the contact between seawater and river water is one of the promising renewable energies. In the reverse electrodialysis (RED), salinity gradient energy is directly translated into the electricity. The representative problem is a large electrical resistance of river water or dilute solutions. The dilute solutions are poor electrically conductive. This results in a huge energy loss when an electrical current passes through it.In this study, sodium chloride (NaCl) or poly(sodium 4-styrenesulfonate) (NaPSS) was added to the dilute solutions to increase the conductivities and enhance the power outputs of the RED cells. When NaCl was added, the power output reached 11.4 ± 0.6 µW. On the other hand, when NaPSS was added, the power output increased up to 19.6 ± 0.6 µW.

Reverse electrodialysis (RED) systems employing charged nanochannels have gained prominence for harvesting salinity gradient energy. Nevertheless, fabricating nanochannel membranes with optimal ion selectivity and high energy conversion efficiency remains a significant challenge. In this study, we develop oppositely charged bacterial cellulose (BC)/polymer composite nano-channel membranes with precisely designed nanochannel architectures by integrating chemical modification with composite material technology. Initially, BC undergoes chemical modifications, including 2,2,6,6-Tetramethylpiperidine 1-oxy radical (TEMPO) oxidation and quaternisation. Subsequently, a polymer network is integrated into the modified BC network through a polymer synthesis technique. This approach successfully yields negatively charged BC/poly(sodium p-styrene sulfonate) (NBC/PSS) composite double-networked nanochannel membranes and positively charged BC/poly(dopamine) (PBC/PDA) composite double-networked nanochannel membranes. Notably, these membranes exhibit significantly enhanced ionic conductivities, with values of 0.0008 and 0.0014 S cm−1 for the NBC/PSS and PBC/PDA composites, respectively, while also demonstrating superior ion selectivity with cation transfer numbers of 0.9 and 0.1 respectively. Furthermore, a series connection of 30 BCE/charged polymer-based RED devices successfully powers an electronic calculator. This work offers novel insights into the design of BC-based RED devices by integrating chemical modification and polymeric composite strategies for efficient salinity gradient energy generation. [ABSTRACT FROM AUTHOR]

• The coupling of the PCC membrane surface charge to the nanopore structure confers its high-power density. • PCC membranes have the advantages of simple preparation process and low cost. • PCC membrane shows a high-power density of 9 W/m2 at a 50-fold KCl gradient. • The connection 30 series of PCC devices can output voltages up to 2.24 V to directly power calculators and LEDs. Surface charge and nanoscale porous structure of ion-selective membranes have been considered prominent in affecting conversion capability of salinity gradient energy-to-power, while the synergistic contribution of them is conventionally overlooked, thus limiting their further development toward high-performance harvesting of salinity gradient energy. Herein, bioinspired by organisms achieving effective intracellular ion transport through their surface-charged nanochannels, we designed porous-charged cellulose membrane (PCC) by simultaneously engineering surface charge and pore structure, followed by desirably chemical and structural distinctions, such as high zeta potential and sulfonic acid group content of −44 mV and 1.22 mmol/g, large porosity of 84 % and pore volume of 0.01 cm3/g (d ≤ 10 nm), while just −23 mV, 42 %, 0.0036 cm3/g and 0 mmol/g for pristine cellulose. Such distinctions endow PCC with excellent ion transport rate and capability (high t + of 0.97 and η of 44.18 % in 0.001/0.01 M), correspondingly superhigh power density of 21.6 W/m2 (0.01/5 M), which surpasses that of most membrane materials, including biomass materials, synthesized polymers, and even some composite materials. By a tandem 30 PCC units, the output voltage of the designed PCC device reaches 2.24 V, which successfully powers calculator and light-emitting diode. In addition, our PCC demonstrates excellent stability in various pH system (from 3 to 11) during 30-day testing. The PCC with environmentally friendly, low cost, and large-scale advantages demonstrates strong competitiveness in advanced membrane materials toward high-performance manipulating ion transport. [ABSTRACT FROM AUTHOR]

• The maximum treatment capacity of 1167.44 g is achieved in Mode 1 systems. • Optimization of operating conditions enhances energy efficiency and reduces costs. • Systems in Mode 2 exhibit higher energy efficiency but a lower COD removal value. • Switching modes maximize energy utilization across different application scenarios. A multi-stage reverse electrodialysis reactor (MSREDR) wastewater treatment system with an independent strategy is researched theoretically in this paper. The influences of operating conditions on the system performance and levelized costs are explored. Results illustrate that reducing the number of membrane pairs not only enhances the system performance but also decreases the levelized cost of wastewater treatment. A high concentration of concentrated solution facilitates enhancing the total COD removal value and reducing the levelized cost, but it adversely affects the energy conversion efficiency of the system. The optimal total COD removal value and energy efficiency are respectively 1164.77 g and 3.58 % under the given conditions. However, when the wastewater discharge rate from the plant is lower than the maximum treatment capacity, it transitions from a wastewater treatment mode to a combined power generation and wastewater treatment mode. Compared to the system operating in the wastewater treatment mode, the system operating in the combined power generation and wastewater treatment mode exhibits higher effective energy and energy efficiency but a lower COD removal value. This research successfully achieves the flexible adjustment of operating modes based on real-world applications, thereby maximizing energy efficiency and establishing a theoretical foundation for practical implementations. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a promising method for harvesting the salinity gradient energy (SGE) between the brine and river water. Many investigations are carried out by using the artificially brine and fresh water, bringing difficulties in reflecting the practical RED performance under the complex influences of feed solutions. This work explores the performance of the RED system for hydrogen and electricity co-generation that is driven by salinity gradient between the actual concentrated brine and natural river water, and compared with the simulative brines and river waters under six testing schemes. The results show both the working current and solutions influence the system performances, including the output voltage, power density, hydrogen production, and energy conversion efficiency. Besides, the effects of salinity gradient of feed solutions are greater than that of the presence of trace multivalent ions and anionic radical in brine. The effective monovalent ion ionic strength is vital. The experimental maximum hydrogen production and power density are 82.12 mL·h−1 and 0.124 W·m−2 respectively at the current is 0.2 A, and the total power reached 0.32 W with the energy conversion efficiency of 25%. The research offers recommendations for harnessing SGE from actual brines and freshwater to produce hydrogen. • An innovative process of energy recovery from the actual brines and freshwater was presented. • A reverse electrodialysis stack was built to produce H 2 driven by actual brine and river water. • Feasibility is analyzed based on the comparation testes by 3 brines and 3 fresh waters schemes. • Maintaining a suitable working current heightens H 2 production and total power output. • Power density is 0.149 W·m−2 and H 2 production is 82.12 ml·h−1, at the current is 0.2 A. [ABSTRACT FROM AUTHOR]

Blue energy can be harvested from salinity gradients between saline water and freshwater by reverse electrodialysis (RED). RED as a conversion technique to generate blue energy has received increasing attention in recent decades. As part of the RED system, ion exchange membranes (IEMs) are key elements to the success of future blue energy generation. However, its suboptimal performance often limits the applications and stagnates the deve­lopment of the technology. The key properties of IEMs include ion exchange capacity, perm­selectivity, and electrical resistance. The enhancement of such physical and electrochemical properties is crucial for studying energy production with acceptable output efficiency on a commercial scale. Recently, many studies have tried blending nanotechnology into the membrane fabrication process. Hybridizing inorganic nanomaterials with an organic polymeric material showed the great potential of improving electrical conductivity and perm­selectivity, as well as other membrane characteristics for power performance. In this short review, recent developments on the IEM synthesis in association with potential nanomaterials are reviewed and raising issues regarding the application and commercialization of RED-based energy production are discussed.

Malaysia has a great potential to harness energy in water due to its long coastline within the South China Sea and the Straits of Malacca. Malaysia’s energy mix could be improved using marine current energy devices (MCEDs) to replace fossil fuel and it is predictable energy compare to hydropower, solar photovoltaic (PV), and biomass. However, MCEDs is not been fully developed in Malaysia. The objectives of this paper are to provide a useful background for policymakers or researchers in the types of MCEDs and potential sites location of MCEDs that are applicable in Malaysia. This review also discusses the issues and challenges of MCEDs in Malaysia. Five types of MCEDs were discussed including tidal range device, tidal stream turbine, wave energy converter, ocean thermal energy conversion, and salinity gradient energy. These MCEDs are compared for their suitability of application in Malaysia. Among all MCEDs, tidal stream turbine is identified as high potential and commercially viable in Malaysia. However, ocean characteristics in Malaysia are low kinetic energy-flux density, low current speed, low tide, and shallow water; only fulfill the minimum requirement of tidal stream turbine making the tidal stream energy resources not significant enough to contribute to the nation’s energy mix. Therefore, using diffuser augmented tidal stream turbines to increase the flow velocity should be studied thoroughly.

The energy requirements for desalination have made it an expensive process, however, it is still a viable and cost-effective means of water purification amidst freshwater scarcity. The management and disposal of brine is an external and extra desalination cost due to the effect of brine on the environment. The integration of Pressure Retarded Osmosis (PRO) with the Reverse Osmosis (RO) technique as modelled in this paper enhances brine management. The brine is fed back into the PRO unit to create a salinity gradient for water transfer via membrane and generate salinity gradient energy. The hybrid desalination model is designed to be powered by grid-tied offshore wind power. The use of wind power, a clean, renewable energy source devoid of carbon emission, as the main power source to drive the RO unit reduces the cost and effect of carbon emissions from the grid. The proposed model is assessed using Levelized cost of energy (LCOE), Annualized cost of the system (ACS), and cost of water (COW) as economic matrices. In contrast, loss of energy probability is used as a reliability matrix. Obtained results show a LCOE of 1.11 $/kW, ACW of $110,456, COW of 0.13 $/m3, loss of energy probability of 0.341, a low total carbon emissions of 193,323 kgCO2-e, and zero brine production. Results show that the proposed model is economically viable, technically reliable, environmentally friendly, and generally sustainable. [ABSTRACT FROM AUTHOR]

In this study, a novel irreversible cyclic model of a capacitive mixing blue heat engine mainly consisting of super capacitors, charging and discharging circuits, a heat source, as well as two water sources with given salt concentrations is established for harvesting salinity gradient energy and waste heat. Additionally, the effects of the charging voltage and ratio of the minimum to maximum surface electric charge density on the thermodynamic efficiency and power output of the cycle are discussed. The maximum power output of the cycle is calculated. The optimized ranges of efficiency and power output as well as the temperatures of two isothermal processes are determined. It is established that during the isoelectric quantity process, there is not only an increase in thermal voltage owing to the temperature difference, but also an increase in concentration voltage owing to the salinity gradient. Consequently, the blue heat engine can obtain higher energy conversion efficiency than a conventional heat engine. When the temperature ratio of the heat source to the heat sink is 1.233, the maximum efficiency can reach approximately 36%. The results obtained can promote the application of capacitive mixing technology in real life, reducing the consumption of fossil fuels. [ABSTRACT FROM AUTHOR]

Salinity gradient energy has gained attention in recent years as a renewable energy source, especially employing reverse electrodialysis technology (RED), which is based on the role of ion exchange membranes. In this context, many efforts have been developed by researchers from all over the world to advance the knowledge of this green source of energy. However, the influence of divalent ions on the performance of the technology has not been deeply studied. Basically, divalent ions are responsible for an increased membrane resistance and, therefore, for a decrease in voltage. This work focuses on the estimation of the resistance of the RED membrane working with water flows containing divalent ions, both theoretically by combining the one-thread model with the Donnan exclusion theory for the gel phase, as well as the experimental evaluation with Fumatech membranes FAS-50, FKS-50, FAS-PET-75, and FKS-PET-75. Furthermore, simulated results have been compared to data recently reported with different membranes. Besides, the influence of membrane resistance on the overall performance of reverse electrodialysis technology is evaluated to understand the impact of divalent ions in energy generation. Results reflect a minor effect of sulfate on the gross power in comparison to the effect of calcium and magnesium ions. Thus, this work takes a step forward in the knowledge of reverse electrodialysis technology and the extraction of salinity gradient energy by advancing the influence of divalent ions on energy recovery.

Membrane-based osmotic energy harvesting is a promising technology with zero carbon footprint. High-performance ion-selective membranes (ISMs) are the core components in such applications. Recent advancement in 2D nanomaterials opens new avenues for building highly efficient ISMs. However, the majority of the explored 2D nanomaterials have a negative surface charge, which selectively enhances cation transport, resulting in the underutilization of half of the available ions. In this study, ISMs based on layered double hydroxide (LDH) with tunable positive surface charge are studied. The membranes preferentially facilitate anion transport with high selectivity. Osmotic energy harvesting device based on these membranes reached a power density of 2.31 W m -2 under simulated river/sea water, about eight times versus that of a commercial membrane tested under the same conditions, and up to 7.05 W m -2 under elevated temperature and simulated brine/sea water, and long-term stability with consistent performance over a 40-day period. A prototype reverse electrodialysis energy harvesting device, comprising a pair of LDH membranes and commercial cation-selective membranes, is able to simultaneously harvest energy from both cations and anions achieving a power density of 6.38 W m -2 in simulated river/sea water, demonstrating its potential as building blocks for future energy harvesting systems., (© 2024 The Authors. Small published by Wiley‐VCH GmbH.)

A novel cycle model of the capacitive salinity/heat engine mainly consisting of nano-porous super-capacitors is established for harvesting mixed free energy caused by salinity difference between the river water and the seawater, and the thermal energy due to the temperature difference. The heat engine is charged and discharged in the cycle of a low temperature brine and a high temperature fresh water, respectively. The analytical expressions of the cyclic work output and efficiency are given. General performance characteristics of the capacitive salinity/heat engine are analyzed. The temperature of the heat reservoir and salt concentration of seawater are optimized to improve the efficiency of the capacitive salinity/heat engine. The optimal selection ranges of several main parameters are provided. When the Stern distance is equal to 1 nm and the charging voltage is equal to 3.5V, the energy conversion efficiency of the capacitive salinity/heat engine is about 40%, while the pure thermal efficiency in the cycle is about 16.9%. The energy conversion efficiency of the capacitive salinity/heat engine is significantly larger than that of the capacitive heat engine. The results obtained can facilitate the application of this technology to real life, which can reduce the consumption of fossil fuels. [ABSTRACT FROM AUTHOR]

Divalent ions have a negative effect on the obtained power and efficiency of the reverse electrodialysis (RED) process when using natural waters. These effects can largely be attributed to the interaction between the various ions and the membranes, resulting in a decreased membrane voltage, an increased membrane resistance, and uphill transport of divalent ions. The aim of this study was to investigate the causes of these differences and, if possible, to find underlying causes. The approach mainly followed that in literature articles that specifically focused on the effect of divalent ions on RED. It transpired that seven publications were useful because the methodology was well described and sufficient data was published. I found two widely shared misconceptions. The first concerns the role of the stack voltage in uphill transport of divalent ions; itis often thought that the open circuit voltage (OCV) must be taken into account, but it is plausible that the voltage under working conditions is the critical factor. The second debatable point concerns the methodology used to make a series of solutions to study the effect of divalent ions. Typically, solutions with a constant number of moles of salt are used; however, it is better to make a series with a constant ratio of equivalents of those salts. Moreover, it is plausible that the decreased voltage can be explained by the inherently lower Donnan potential of multi-charged ions and that increased resistance is caused by the fact that divalent ions—with a lower mobility there than the monovalent ions—occupy relatively much of the available space in the gel phase of the membrane. While both resistance and voltage play a decisive role in RED and probably also in other membrane processes like electrodialysis (ED), it is remarkable that there are so few publications that focus on measurements on individual membranes. The implications of these results is that research on the effect of divalent ions in RED, ED and similar processes needs to be more structured in the future. Relatively simple procedures can be developed for the determination of membrane resistance in solutions of mixtures of mono- and divalent salts. The same applies to determining the membrane potential. The challenge is to arrive at a standard method for equipment, methodology, and the composition of the test solutions.

Reverse electrodialysis (RED) power generation using seawater (SW) and river water is expected to be a promising environmentally friendly power generation system. Experiments with large RED stacks are needed for the practical application of RED power generation, but only a few experimental results exist because of the need for large facilities and a large area of ion-exchange membranes (IEMs). In this study, to predict the power output of a large RED stack, the power generation performances of a lab-scale RED stack (40 membrane pairs and 7040 cm2 total effective membrane area) with several IEMs were evaluated. The results were converted to the power output of a pilot-scale RED stack (299 membrane pairs and 179.4 m2 total effective membrane area) via the reference IEMs. The use of low-area-resistance IEMs resulted in lower internal resistance and higher power density. The power density was 2.3 times higher than that of the reference IEMs when natural SW was used. The net power output was expected to be approximately 230 W with a pilot-scale RED stack using low-area-resistance IEMs and natural SW. This value is one of the indicators of the output of a large RED stack and is a target to be exceeded with further improvements in the RED system.

This study is the first comprehensive life cycle assessment (LCA) of reverse electrodialysis (RED), a technology that converts salinity gradient energy into electricity. Our goal is to identify RED system components of environmental concern and provide insights on potential environmental impacts. We conduct an attributional LCA of two RED scenarios: large‐scale energy generation from natural bodies of water and smaller‐scale energy generation from industrial processes. A functional unit of 1 MWh of net electricity production enables comparison to existing renewable energy technologies, including wind and solar photovoltaics. Under theoretical, favorable conditions, environmental impacts from RED are found to be comparable to, and often lower than, established renewable energy technologies. Processes associated with membrane manufacture are primary contributors to six of the nine evaluated impact categories. Under baseline assumptions, impacts are an average of 50% higher for the Natural Water scenario compared to the Concentrated Brine scenario because of the increased power density achieved with concentrated brines. This early‐stage LCA demonstrates that the expected environmental impacts of RED are comparable to existing renewable technologies and a large improvement over fossil‐based generation. However, eutrophication, ecotoxicity, and carcinogenic impacts are larger for RED than other technologies under some assumptions. [ABSTRACT FROM AUTHOR]

Perchlorate (ClO4 –) is a toxic anion that inhibits iodine uptake by the thyroid gland and subsequently disrupts thyroid hormone production. In this study, the feasibility of using reverse electrodialysis (RED) was examined for the treatment of perchlorate in salt (5% NaCl; w/v) water. RED uses direct electricity, produced by salinity gradients in a membrane stack, to drive the electrochemical treatment of wastewater. Operational conditions such as salinity gradient (S.G.), number of membrane pairs, and stack solution flowrates were varied and their effects on electricity generation and perchlorate reduction were investigated. Experimental batch results showed that a higher number of membrane pairs and salinity gradient gave higher values of power density, which also resulted in higher abatement of perchlorate. In contrast, the reduction of perchlorate was lowered upon increasing the stack solution flowrate. The maximum abatement of perchlorate (38.76%) was achieved using 15 pairs of cation and anion exchange membranes and 5 M/0.005 M salinity ratio (S.G. 1,000) of high and low concentrated NaCl solutions at 1.5 mL/min stack solution flowrate. This study successfully demonstrated that RED can be a sustainable alternative method for the abatement of perchlorate in salt waters. [ABSTRACT FROM AUTHOR]