Reverse Electrodialysis Process Research Articles

Cost-optimal design of reverse electrodialysis process for salinity gradient-based electricity generation in desalination plants

Salinity gradient-based technologies offer a solution for desalination plants seeking clean, uninterrupted electricity to support their decarbonization and circularity. This work provides cost-optimal designs of a large-scale reverse electrodialysis (RED) system deployed in a desalination plant using mathematical programming. The optimization model determines the hydraulic topology and RED units' working conditions that maximize the net present value (NPV) of the RED process recovering salinity gradient energy between brine and treated wastewater effluents. We examine how electricity, carbon and membranes prices, desalination plant capacity, and membrane resistance may affect the NPV-optimal design's competitiveness and performance. We also compare the conventional series-parallel configuration and the NPV-optimal solution with recycling and added reuse alternatives. In the context of soaring electricity prices and strong green financing support, with the use of high-performing, affordable membranes (∼10 €/m2), RED could save 8 % of desalination plant energy demand from the grid, earning 5 M€ profits and LCOE of 66–126 €/MWh, comparable to other renewable and conventional power technologies. The optimization model finds profitable designs for the entire range of medium-capacity desalination plants. The findings underscore the optimization model effectiveness in streamlining decision-making and exploiting the synergies of full-scale, RED-based electricity in the energy-intensive water sector.

Effect of channel roughness on the particle diffusion and permeability of carbon nanotubes in reverse electrodialysis process applying molecular dynamics simulation

Innovative technology and methods are crucial for making pure and refreshing water. Two main methods are present to delete soluble salts from water: membrane processes and thermal processes. A beneficial membrane technique is reverse electrodialysis. This research used molecular dynamics (MD) simulation to investigate how channel roughness affected particle diffusion and permeability in carbon nanotubes (CNTs) via the reverse electrodialysis process. The results indicate that adding roughness in the CNT duct increased the force between the primary fluid and the duct. Using an armchair-edged CNT structure maximized the electric current in the sample. Furthermore, the roughness increased the intensity of force in the channel, which was due to gravity, leading to a decrease in the mobility of fluid particles. Additionally, several broken hydrogen bonds inside the simulation box increased from 116 to 128 in the duct sample with roughness.

Continuous Selective Reverse Electrodialysis Process Based on Salt-Lake Brines and Its Thermodynamic Analysis

Continuous Selective Reverse Electrodialysis Process Based on Salt-Lake Brines and Its Thermodynamic Analysis

Enhancement of power density and hydrogen productivity of the reverse electrodialysis process by optimizing the temperature gradient between the working solutions

Reverse electrodialysis (RED) is an emerging technology that converts the salinity gradient energy (SGE) embedded in two solutions of different concentrations into electricity or hydrogen productivity. Given that two solutions containing SGE in nature are often at different temperatures, this study experimentally investigated the effects of the temperature and salinity ratio of the working solutions on the performance of RED systems. The results show that the power density and hydrogen productivity of RED systems could be markedly improved by adjusting the imposed temperature difference on the basis of the salinity gradient. The degree of improvement mainly depends on the magnitude and direction of the temperature difference between the high- and low-concentration solutions. The enhancement effect was more pronounced under a negative temperature difference (NTD) than under a positive temperature difference (PTD). Additionally, the improvement in system performance owing to the temperature difference was not affected by the endothermic or exothermic effects of different solutes in the water. At a NTD of 25℃ and a concentration of 0.1 M aqueous NaOH as the electrode solution, a RED system based on LiBr solution with a salinity ratio of 4.5 M/0.02 M as the working solution achieved a maximum power density of 0.754 ± 0.006 W∙m−2 and the highest hydrogen productivity of 1.128 ± 0.019 mol∙m−2∙h−1, which was 15.1% and 5.5% higher than the hydrogen productivity under LiCl and NaCl solution conditions, respectively. These results show the great potential of LiBr solution in the field of RED hydrogen productivity.

Parametric analysis of reverse electrodialysis process for improved power generation: Influence of spacer thickness, feed solution flow rate, membrane, and concentration

Reverse electrodialysis (RED) technology produces electrical energy from a salinity gradient by transporting ions through ion-exchange membranes (IEM). Although research into this technology has recently seen considerable growth, there is still interest in improving its efficiency. As a result, a mathematical model to study the RED process was developed using Aspen Custom Modeler software, focusing on three membranes (Fumasep (FAD/FKD), Fujifilm Type 10, and Selemion (AMV/CMV)). A parametric analysis was conducted, considering spacer thickness, salinity gradient, and feed-solution flow rates. Evaluation of internal resistance, gross power density, and net power density was also performed. Results showed that using a thicker spacer (270 μm) in the high compartment and a thinner spacer (150 μm) with a high Reynolds number in the low compartment led to higher net power densities of 2.17 W·mcp−2 and 6.74 W·mcp−2 for Fumasep (FAD/FKD) membrane with (brackish/seawater) and (brackish/brine), respectively. Among the membranes tested, Fumasep (FAD/FKD) and Fujifilm Type 10 had similar results, with the former slightly exceeding the latter. However, the Selemion membrane (AMV/CMV) performed poorly in all tests.

The influence of divalent ions on the osmotic energy conversion performance of 2D cation exchange membrane in reverse electrodialysis process

As reverse electrodialysis (RED) technology evolves, achieving high-performance osmotic energy conversion (OEC) necessitates porous membranes with exceptional ion selectivity and permeability. Two-dimensional membranes crafted from graphene oxide (GO) or MXene stand out for their immensely high surface charges, which facilitate superb ion selectivity during transport. Their unique layered stacking structure further yields ultra-small nanochannel radii, bolstering ion selectivity while maintaining high permeability. This makes them prime candidates for osmotic energy conversion. However, the presence of divalent ions in natural seawater readily alters the surface charge density and interlayer spacing of these 2D membranes, significantly impacting their OEC performance, resulting in a power density reduction of about 6 % -10 %. Prior research focused on the ionic properties of divalent ions but overlooked their impact on the nanochannel structure, including changes in interlayer spacing and surface charge density. This study thus delves into the OEC performance variations of GO and MXene 2D layered membranes under varying divalent ion concentrations and salt ratios. Starting from the ion properties of divalent ions and their impact on the nanochannel structure, combined with simulation research, explain their mechanism of action. This research offers theoretical foundations for the future design and application of 2D layered membranes, providing novel solutions and insights to tackle critical challenges like enhancing power density and adapting to real seawater conditions.

Sustainable energy recovery from salt-lake brines through a novel selective reverse electrodialysis process

The salinity gradient energy (SGE) in salt-lake brines can be exploited as a sustainable energy source through reverse electrodialysis (RED). However, the composition of brines is notably intricate. In order to avoid the adverse effects of multivalent cations on RED in brines, we introduced a novel selective reverse electrodialysis (SRED) here. The results demonstrate that when increasing the salinity ratio between high and low concentration feeds (HCFs, LCFs) from 20 to 60, the SRED maximal maximum power density (Pd,max) improves from 0.069 to 0.109 W/m2. The feed salinity has less obvious effect on SRED. Moreover, the role of Mg2+ on the adverse effects is regulated. The maximal Pd,max of SRED is 1.13 ∼ 1.23 times higher than that of the conventional RED at the Mg2+ concentrations of 4861.00 ∼ 14583.00 ppm in HCFs and 40.51 ∼ 121.53 ppm in LCFs. This suggests that SRED is a feasible and efficient strategy for capturing SGE in salt-lake brines.

Assessment of Data Capture Conditions Effect on Reverse Electrodialysis Process Using a DC Electronic Load

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.

Nanofluidic osmotic power generation from CO2 with cellulose membranes

The diffusion of chemical species down concentration gradient is a ubiquitous phenomenon that releases Gibbs free energy. Nanofluidic materials have shown great promise in harvesting the energy from ionic diffusion via the reverse electrodialysis process. In principle, any chemicals that can be converted to ions can be used for nanofluidic power generation. In this work, we demonstrate the power generation from the diffusion of CO2 into air using nanofluidic cellulose membranes. By dissolving CO2 in water, a power density of 87 mW/m2 can be achieved. Using monoethanolamine solutions to dissolve CO2, the power density can be increased to 2.6 W/m2. We further demonstrate that the waste heat released in industrial and carbon capture processes, can be simultaneously harvested with our nanofluidic membranes, increasing the power density up to 16 W/m2 under a temperature difference of 30 °C. Therefore, our work should expand the application scope of nanofluidic osmotic power generation and contribute to carbon utilization and capture technologies.

A generalized disjunctive programming model for the optimal design of reverse electrodialysis process for salinity gradient-based power generation

Reverse electrodialysis (RED) is an emerging electro-membrane technology that generates electricity out of salinity differences between two solutions, a renewable source known as salinity gradient energy. Realizing full-scale RED would require more techno-economic and environmental assessments that consider full process design and operational decision space from the RED stack to the entire system. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem that incorporates a finite difference RED stack model from our research group to define the cost-optimal process design. The solution to the GDP problem provides the plant topology and the RED units’ working conditions that maximize the net present value of the RED process for given RED stack parameters and site-specific conditions. Our results show that, compared with simulation-based approaches, mathematical programming techniques are efficient and systematic to assist early-stage research and to extract optimal design and operation guidelines for large-scale RED implementation.

Electro dialysis reversal (EDR) performance for reject brine treatment of reverse osmosis desalination system.

In this study, the performance of bench-scale EDR was evaluated using the samples taken from the 1st and the 2nd stage RO from the Brackish Water Reverse Osmosis (BWRO) plant in Eshtehard, Iran. The measurements indicated that original TDS of the aquifer brackish water was equal to 3,229–3,664 mg/L, whereas TDS of the 1st stage RO brine was between 5,500 and 7,700 mg/L, that TDS of the 2nd stage RO brine was in the range of 9,500–10,600 mg/L. A batch bench-scale EDR system of 12 l/h was used with a direct electric current at three different scenarios. In the first, the brine was fed at 20°C (as a reference regulated point). In the second, temperature (14, 20, 26.5°C), and in the third, voltage were changed (6, 12, 18, 24 V) to investigate their influences on performance of the EDR process, while the other operational parameters (feed flow rate, recovery ratio, quality of feed brine)were kept constant. Based on the data analysis using the ANOVA and DUNCAN tests for the second and third scenarios, it was observed that the optimum TDS removal efficiency of the EDR process can be at temperature of 26.5°C and voltage of 18 V. On the other hand, the successful performance of the bench-scale EDR in reducing the 29,000 mg/L TDS and the 45,000 μmhos/cm EC of the 2nd stage brine to 1,716 mg/L (TDS) and 2,640 μmhos/cm (EC) (at 26.5°C and 24V) could be considered as the main achievement of this research. Overall, the hybrid process RO-EDR-RO can be considered as the best technical, environmental and economical scenario for the development of Eshtehard Desalination Plant phase 2 at full scale.

Generalized Disjunctive Programming Model for Optimization of Reverse Electrodialysis Process

Reverse electrodialysis (RED), an emerging electrochemical technology that uses ion-selective membranes to directly draw electricity out from salinity differences between two solutions, i.e., salinity gradient energy (SGE), has the potential to be a clean and steady renewable source to reach a sustainable water and energy supply portfolio. Although RED has made notable advances, full-scale RED progress demands more techno-economic and environmental assessments that consider full process design and operational decision space from module- to system-level. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem to define the cost-optimal RED process design for different deployment scenarios. We use a predictive model of the RED stack developed and validated in our research group to fully capture the behavior of the system. The problem addressed is to determine the RED plant's topology and the working conditions for a given design of each RED stack which renders the cost-optimal design for the defined problem and scenario. Our results show that, compared with simulation-based approaches, mathematical programming techniques are an efficient and systematic approach to provide decision-making support in early-stage applied research and to obtain design and operation guidelines for full-scale RED implementation in real scenarios.

Use of the Microheterogeneous Model to Assess the Applicability of Ion-Exchange Membranes in the Process of Generating Electricity from a Concentration Gradient.

The paper shows the possibility of using a microheterogeneous model to estimate the transport numbers of counterions through ion-exchange membranes. It is possible to calculate the open-circuit potential and power density of the reverse electrodialyzer using the data obtained. Eight samples of heterogeneous ion-exchange membranes were studied, two samples for each of the following types of membranes: Ralex CM, Ralex AMH, MK-40, and MA-41. Samples in each pair differed in the year of production and storage conditions. In the work, these samples were named “batch 1” and “batch 2”. According to the microheterogeneous model, to calculate the transport numbers of counterions, it is necessary to use the concentration dependence of the electrical conductivity and diffusion permeability. The electrolyte used was a sodium chloride solution with a concentration range corresponding to the conditional composition of river water and the salinity of the Black Sea. During the research, it was found that samples of Ralex membranes of different batches have similar characteristics over the entire range of investigated concentrations. The calculated values of the transfer numbers for membranes of different batches differ insignificantly: ±0.01 for Ralex AMH in 1 M NaCl. For MK-40 and MA-41 membranes, a significant scatter of characteristics was found, especially in concentrated solutions. As a result, in 1 M NaCl, the transport numbers differ by ±0.05 for MK-40 and ±0.1 for MA-41. The value of the open circuit potential for the Ralex membrane pair showed that the experimental values of the potential are slightly lower than the theoretical ones. At the same time, the maximum calculated power density is higher than the experimental values. The maximum power density achieved in the experiment on reverse electrodialysis was 0.22 W/m2, which is in good agreement with the known literature data for heterogeneous membranes. The discrepancy between the experimental and theoretical data may be the difference in the characteristics of the membranes used in the reverse electrodialysis process from the tested samples and does not consider the shadow effect of the spacer in the channels of the electrodialyzer.

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.

Benchmarking empirical models for THMs formation in drinking water systems: An application for decision support in Barcelona, Spain

Drinking water treatment plants (DWTPs) face changes in raw water quality, which affect the formation of disinfection by-products. Several empirical modelling approaches have been reported in the literature, but most of them have been developed with lab-scale data, which may not be representative of real water systems. Therefore, the application of these models for real-time operation of DWTPs might be limited. At the present study, multiple linear regression (MLR) and multi-layer perceptrons (MLP) were benchmarked using field-scale data for predicting the THMs formation in a case-study DWTP in Barcelona, Spain. After fitting the studied models, MLR exhibited good fit with the validation data set (R2 = 0.88 and MAE = 4.0 μg·L−1) and described the most plausible input-output relationships with field-scale data. The MLR predictive model was incorporated into an environmental decision support system (EDSS) for assessing the THMs formation at two critical points of the distribution network. A Monte Carlo scheme was applied for quantifying uncertainty of model predictions at these points, considering low and high water quality scenarios and different degrees of treatment by an electrodialysis reversal process. The results show that the use of the proposed EDSS can help in real operation of complex drinking water systems, which face important changes in water quality throughout the year.

Surface Modifications of Anion Exchange Membranes for an Improved Reverse Electrodialysis Process Performance: A Review.

Reverse electrodialysis (RED) technology represents a promising electro-membrane process for renewable energy harvesting from aqueous streams with different salinity. However, the performance of the key components of the system, that is, the ion exchange membranes, is limited by both the presence of multivalent ions and fouling phenomena, thus leading to a reduced generated net power density. In this context, the behavior of anion exchange membranes (AEMs) in RED systems is more severely affected, due to the undesirable interactions between their positively charged fixed groups and, mostly negatively charged, foulant materials present in natural streams. Therefore, controlling both the monovalent anion permselectivity and the membrane surface hydrophilicity is crucial. In this respect, different surface modification procedures were considered in the literature, to enhance the above-mentioned properties. This review reports and discusses the currently available approaches for surface modifications of AEMs, such as graft polymerization, dip coating, and layer-by-layer, among others, mainly focusing on preparing monovalent permselective AEMs with antifouling characteristics, but also considering hydrophilicity aspects and identifying the most promising modifying agents to be utilized. Thus, the present study aimed at providing new insights for the further design and development of selective, durable, and cost-effective modified AEMs for an enhanced RED process performance, which is indispensable for a practical implementation of this electro-membrane technology at an industrial scale.

Characterization of Poly(Acrylic) Acid-Modified Heterogenous Anion Exchange Membranes with Improved Monovalent Permselectivity for RED.

The performance of anion-exchange membranes (AEMs) in Reverse Electrodialysis is hampered by both presence of multivalent ions and fouling phenomena, thus leading to reduced net power density. Therefore, we propose a monolayer surface modification procedure to functionalize Ralex-AEMs with poly(acrylic) acid (PAA) in order to (i) render a monovalent permselectivity, and (ii) minimize organic fouling. Membrane surface modification was carried out by putting heterogeneous AEMs in contact with a PAA-based aqueous solution for 24 h. The resulting modified membranes were firstly characterized by contact angle, water uptake, ion exchange capacity, fixed charge density, and swelling degree measurements, whereas their electrochemical responses were evaluated through cyclic voltammetry. Besides, their membrane electro-resistance was also studied via electrochemical impedance spectroscopy analyses. Finally, membrane permselectivity and fouling behavior in the presence of humic acid were evaluated through mass transport experiments using model NaCl containing solutions. The use of modified PAA-AEMs resulted in a significantly enhanced monovalent permselectivity (sulfate rejection improved by >35%) and membrane hydrophilicity (contact angle decreased by >15%) in comparison with the behavior of unmodified Ralex-AEMs, without compromising the membrane electro-resistance after modification, thus demonstrating the technical feasibility of the proposed membrane modification procedure. This study may therefore provide a feasible way for achieving an improved Reverse Electrodialysis process efficiency.

Performance parameters analysis of reverse electrodialysis process: Sensitive to the repeating unit pairs, inflow velocity and feed concentration

Performance parameters analysis of reverse electrodialysis process: Sensitive to the repeating unit pairs, inflow velocity and feed concentration

Application of reverse electrodialysis to site-specific types of saline solutions: A techno-economic assessment

Salinity gradients are a non-conventional source of renewable energy based on the recovery of the Gibbs free energy related to the mixing of solutions at different concentrations. Reverse Electrodialysis is a promising and innovative technology able to convert this energy directly into electric current. The worldwide availability of salinity gradients is limited to those locations where water bodies at different salinity levels are present. The present work analyses a number of different scenarios worldwide, in locations where salinity gradients are naturally available or generated by anthropogenic activities. A techno-economic model of the Reverse Electrodialysis process is presented. The model is used to evaluate the energy that can be harvested in each real scenario using a reverse electrodialysis plant and relevant results are reported in terms of power densities and energy yields. Finally, an economic analysis based on the estimation of the Levelized Cost Of Electricity (LCOE) for each scenario is presented, and perspective considerations are reported. Results suggest that competitive values of LCOE may be achieved in some scenarios.

Electrodialysis reversal for industrial reverse osmosis brine treatment

Reverse osmosis (RO) brine typically contains high salinity and dissolved organics. Among the different approaches for RO brine management, electrodialysis reversal (EDR) offers high potential due to its moderate energy consumption, anti-scaling and anti-fouling properties, ability to produce highly concentrated brine and ease of operation. However, despite the potential benefits associated with EDR, its application for industrial RO brine management has yet to be adequately explored. This study aimed to evaluate the feasibility of a lab-scale EDR system for water recovery from industrial RO brine and minimizing the volume of the resulting concentrated brine. The relatively high concentration of organic and inorganic foulants such as hardness, sulfate and alkalinity in the industrial RO brine necessitate the assessment of anti-fouling and anti-scaling properties of the ion exchange membranes. In this study, it was noted that the limiting current to prevent polarization during electrodialysis process, in the lab-scale EDR system, was 0.89 A. Total organic carbon (TOC) removal efficiency was about 7.1% and no organic fouling was observed even after 6 d of continuous operation. This observation was probably attributed to the nature of organic foulants present in the industrial RO brine, the majority of which were low molecular weights (LWMs). However, the resistance of the EDR system increased during 8 h of operation due to high scaling potential of the EDR concentrate stream. Overall, the EDR process was able to achieve 85% water recovery and the volume of industrial RO brine was reduced by approximately 6.5 times.