Reverse Electrodialysis System Research Articles

WITHDRAWN: Concentrate Management of Spent Geothermal Water Treated with Two- Step Membrane Processes for Agricultural Irrigation

This study examines a two-step membrane treatment to improve water quality by targeting electrical conductivity in reverse osmosis (RO) concentrate from spent geothermal water. The process involves RO treatment followed by electrodialysis reversal (EDR). Water samples were collected during different seasons to assess quality under varying conditions.Following the initial treatment by XLE-RO membrane test system, the large-pilot membrane (LPM-RO) concentrate achieved salt rejection of 98.6%, while the mini-pilot membrane (MPM-RO) concentrate achieved salt rejection of 95.6%. Conductivity values were 48.6µS/cm for LPM-RO and 226µS/cm for MPM-RO concentrate. Further passing the product water obtained from XLE-RO membrane through the EDR system improved overall product water quality. Treated LPM-RO product water had conductivities of 3.71µS/cm (5V) and 2.36µS/cm (10V). For MPM-RO product water, conductivities were 11.98µS/cm (5V) and 2.64µS/cm (10V). In this study, an additional experiment investigated the EDR treatment of RO concentrate without undergoing initial RO pretreatment. After the experiment, although the salt rejection reached 97.65%, it was observed that the product water quality at the end of the 90-minute treatment was 74.6µS/cm with lower quality as compared to when the RO concentrate underwent initial RO pre-treatment. Hence, the combination of RO-EDR can be successfully utilized to treat geothermal water concentrate for better quality which could be utilized in irrigation. This two-step membrane treatment shows potential for higher-quality water reclamation for various processes.

High‐Strength, Thin PBO Nanofiber Membrane with Long‐Term Stability for Osmotic Energy Conversion

AbstractIon‐selective membrane embedded in a reverse electrodialysis system can achieve the conversion of osmotic energy into electricity. However, the ingenious design and development of pure polymer membranes that simultaneously satisfy excellent mechanical strength, long‐term stability, high power density, and increased testing area is a crucial challenge. Here, high‐strength, thin PBO nanofiber membranes (PBONM) with 3D nanofluidic channels and a thickness of 0.81 µm are prepared via a simple vacuum‐assisted filtration technology. The thin PBONM exhibits excellent mechanical properties: stress of 235.8 MPa and modulus of 16.96 GPa, outperforming the state‐of‐the‐art nanofluidic membranes. The obtained PBONM reveals surface‐charge‐governed ion transport behavior and high ion selectivity of 0.88 at a 50‐fold concentration gradient. The PBO membrane‐based generator delivers a power density of 7.7 and 40.2 W m−2 at 50‐fold and 500‐fold concentration gradient. Importantly, this PBONM presents excellent stability in response to different external environments including various saline solutions, pH, and temperature. In addition, the maximum power density of PBONM reaches up to 5.9 W m−2 under an increased testing area of 0.79 mm2, exceeding other membrane‐based generators with comparable testing areas. This work paves the way for constructing high‐strength fiber nanofluidic membranes for highly efficient osmotic energy conversion.

Superstable osmotic energy conversion based on strong cellulose membrane

In recent years, the reverse electrodialysis system (RED) has attracted significant attention because of its sustainable and pollution-free characteristics. Ion-selective membranes function as a core component for RED to directly convert salinity gradient energy into electric power. However, traditional membranes composed of 2D inorganic and organic materials currently require complex preparation technologies, high cost, or consume petrochemical resources and lead to environmental issues. In this study, we developed a sustainable, large-scale, ultra-thin (∼30 µm), and mechanical strong (>89 MPa) cellulose membrane via a phase inversion strategy of positively charged cellulose (namely PPC membrane). By coupling sufficiently positive groups and nanoscale pores, our PPC membrane demonstrates a power density of 2.2 W/m2 under 0.01/0.5 M salinity gradient and a low internal resistance ∼11 kΩ. More importantly, the prepared PPC membrane shows high structural integrity even enduring 300-day water soaking with various pH of 3–12, which indicates its long-term stable power output in harsh conditions. The PCC membrane exhibits great potential for advanced ion-sieving applications.

Transport in Ion-Exchange Membranes with Ternary Solutions of Salt, Water and Alcohol Relevant for (Reverse) Electrodialysis

Leaching of Li-ion battery components in sulfuric acid followed by precipitation with ethanol has been proposed as a route for material recycling [1]. Cobalt, copper and lithium were then recovered as sulphate salts. The final mixture of dilute salts, water and ethanol may be further processed using ion-exchange membranes and electrodialysis to separate salts and water from ethanol, with the aim of increasing salt recovery and allowing for the re-use of the spent ethanol. We investigate the effect of alcohol on the transport numbers, resistance and the thermodynamic properties of the membrane and the aqueous solutions of alcohol, water and salt. This has implications for the electrodialysis of alcohol-containing mixtures, as well as for the application of this working fluid to a power-producing reverse electrodialysis system.[1] S. Aktas, D. J. Fray, O. Burheim, J. Fenstad & E. Açma, Recovery of metallic values from spent Li ion secondary batteries.

Salinity gradient energy conversion by custom-made interpolymer ion exchange membranes utilized in reverse electrodialysis system

Reverse electrodialysis (RED) is one of methods to extract salinity gradient energy between two aqueous solutions with different salt concentrations. In this work, custom-made interpolymer ion exchange membranes were employed in the RED stack. The effects of divalent (Mg2+, Ca2+ and SO42-) and monovalent (Li+, K+ and Cl-) ions in the feed solutions prepared from NaCl salt as a function of such process parameters as number of membrane pairs, flow rate, and salinity ratio on power generation by the RED method were studied. It was shown that the maximum power density of 0.561 W/m2 was reached by using three membrane pairs using 1:45 of salt ratio with a feed flow rate of 120 mL/min using only NaCl salt in the feed solutions. The maximum power density was 0.398 W/m2 at 120 mL/min of the flow rate of the feed solutions composed of 90 wt% NaCl and 10 wt% KCl by using a salt ratio of 1:30 while the lowest power density of 0.246 W/m2 was obtained with a feed flow rate of 30 mL/min in the presence of SO42- ions with a similar salt ratio. Consequently, it was seen that while the presence of divalent ions in NaCl solutions had negative impact on power generation by RED system, the addition of monovalent ions having smaller hydrated radius than that of the Na+ ions contributed positively to the power generation.

Temperature-gated nanocellulose membrane for enhanced and controllable osmotic energy harvesting

Reverse electrodialysis system (REDs) based on nanochannels membrane has been widely investigated for high-performance osmotic energy harvesting. However, restricted by the non-renewable, low power density, and uncontrolable ion transport of membrane materials, the existing membrane-based REDs are usually unregulated and unintelligent, which greatly prohibits their practical applications. Herein, a temperature-gated nanochannels membrane is constructed by the functionalized Cladophora nanocellulose for controllable osmotic energy harvesting, in which the thermo-responsive nanocellulose is obtained by grafting with poly(N-isopropylacrylamide) (PNIPAM) brushes via the atom-transfer radical polymerization (ATRP) method. Based on this membrane, the output from the osmotic energy harvesting system can be regulated and boosted by alternating the temperature switches reversibly and stably. A maximum power density up to approximately 10.1 W/m2 is achieved under a 50-fold salinity gradient at 50 °C, which is remarkably superior to most of the reported cellulose-based nanofluids. Besides, the REDs based on this membrane is designed as a self-powered flexible and wearable thermometer, which can be employed to detect human health. Overall, this strategy first develops cellulose-based nanochannels membrane with both intelligent response and enhanced energy output, which anticipates the wide potential for pushing the osmotic energy into real-world applications.

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.

Scaled-up multistage reverse electrodialysis pilot study with natural waters

A multistage reverse electrodialysis system was studied at the REDstack research facility (the Afsluitdijk, the Netherlands) for over 30 days to describe the performance of such configuration under natural water conditions. The experiments were done with two 0.22 × 0.22 m2 stacks in series comprising 32 cell pairs (3.1 m2 of membrane area) for stage 1 and 64 cell pairs (6.2 m2 membrane area) for stage 2. The total gross power density at the available salinity gradient was stable at around 0.35 W∙m−2. The total net power density, corrected for the initial pressure drop of the stacks, was 0.25 W∙m−2 at an energy efficiency of 37 %. Throughout the operation, due to increased stack pressure drop, the actual total net power density lowered to 0.1 W∙m−2. A distinct behaviour was found for multivalent ions in each stage. For stage 1, Ca2+ and SO42− were transported from the river water to the seawater side, so-called uphill transport. For stage 2, uphill transport was not found, in line with Donnan potential calculations. Stack autopsy revealed microorganisms with sizes ten times larger than the cartridge filter nominal pore size (5 µm) and biofilm covering part of the spacer open area, both contributing to the increasing pressure drop in the stacks. This study showed that stable gross power densities and high energy efficiencies were obtained from feeding natural waters to a multistage reverse electrodialysis system, independent of fouling. In addition, it emphasized the importance of maintaining pumping power losses low for a viable deployment of the technology.

Hydrogen production from water electrolysis driven by the membrane voltage of a closed-loop reverse electrodialysis system integrating air-gap diffusion distillation technology

Air-gap diffusion distillation (AGDD) technology is one of attracting desalination technology, which can be used to convert various of low and medium grade thermal energies to the salinity gradient energy (SGE) between two electrolyte solutions at different saline concentrations. The SGE is harvestable and converted to the electromotive force of a reverse electrodialysis (RED) stack. The accumulated voltage by several repeated RED units is capable to driving the electricity or hydrogen production apparatus. This paper proposes the complete mathematical model of a RED-AGDD integration system that converts the low-grade thermal energies (LGTE) to hydrogen driven by the membrane voltage sourced from the salinity gradient of KAc solutions for the first time. Accordingly, the influence behaviors of the concentration of concentrated solution (1 mol L−1 to 7 mol L−1), concentration of diluted solution (0.001 mol L−1 to 0.22 mol L−1), solution flow rate of (0.2 cm s−1 to 1.6 cm s−1), solution temperature (303.15 K to 333.15 K), and hydrogen production schemes (three cases) on hydrogen production performances are simulated and discussed. The hydrogen production and energy efficiency are achieved to be 3.7 L h−1and 0.84% respectively. It verifies that the direct scheme of hydrogen production possesses the better performance than that of the indirect scheme, and an intermediate battery is applied to improve the performance. Finally, the optimal operating conditions and parameters are obtained and presented.

MOF-Derived Nanoporous Carbon Incorporated in the Cation Exchange Membrane for Gradient Power Generation.

Ion exchange membranes (IEMs), as a part of the reverse electrodialysis (RED) system, play an important role in salinity gradient power (SGP) generation. Structure optimization of IEMs is critical to increase the power production by RED. In this work, metal organic framework (MOF)-derived nanoporous carbons (hollow zeolitic imidazolate framework (ZIF)-derived nanoporous carbons, HZCs) were incorporated in a sulfonated poly (2, 6-dimethyl-1,4-phenylene oxide) (sPPO) membrane to prepare an organic−inorganic nanocomposite cation exchange membrane (CEM). Physicochemical properties, electrochemical properties, and power generation of the synthesized nanocomposite membranes with different HZCs loading were characterized. The results show that the incorporated HZCs could tailor the microstructure of the membrane matrix, providing a superior performance of the nanocomposite membrane. With a HZCs loading of 1.0 wt.%, the nanocomposite membrane possessed the highest permselectivity of 77.61% and the lowest area resistance of 0.42 Ω·cm2, along with a super gross power density of 0.45 W/m2, which was 87.5% (about 1.87 times) higher than that of the blank sPPO membrane. Therefore, incorporating of an appropriate amount of HZCs in the ion-exchange membrane can improve the performance of the membrane, providing a promising method to increase the power generation of the RED system.

Investigations on the effects of operational parameters in reverse electrodialysis system for salinity gradient power generation using central composite design (CCD)

Reverse electrodialysis (RED) can be utilized for the production of renewable energy from salinity gradients. However, there are many key parameters that could influence the performance of RED. This study investigates the use RSM for development of a predictive power density (PD) and open-circuit voltage (OCV) model for the RED system. A three-factor central composite design (CCD) was used to quantify the effects of flow velocity (X1), salinity ratio (X2), and number of cell pairs (X3) towards PD and OCV. A total of 17 experimental data were fitted and ANOVA was used to validate the accuracy of the models. 3D and surface plots were created to foresee the optimal levels of each variable. It was found that flow velocity and salinity ratio have the most dominant influences on the RED performances as compared to number of cell pairs. The predicted PD and OCV values were found to be reasonably fit with the experimental data, validating the predictability of applied models. Therefore, this study suggests that CCD can be considered an effective tool for evaluating and optimizing the RED system using a minimum number of experiments.

Improvement in the Power Output of a Reverse Electrodialysis System by the Addition of Poly(sodium 4-styrenesulfonate)

Improvement in the Power Output of a Reverse Electrodialysis System by the Addition of Poly(sodium 4-styrenesulfonate)

Probing fouling mechanism of anion exchange membranes used in electrodialysis self-reversible treatment by humic acid and calcium ions

When humic substances (HS) are present in the feed water, fouling of ion-exchange membranes is inevitable despite the built-in self-cleaning process of electrodialysis reversal systems (EDR). When Ca2+ is present in water, HS can readily chelate with them and form organic-Ca2+ complexes, which can foul anion exchange membranes (AEMs) in an irreversible manner. However, the elucidation of distinct processes between membrane scaling by Ca2+ and fouling by HS-Ca2+ complexes is debated. We examined the AEM fouling by Ca2+ and HS using synthetic groundwater. Well-characterized Sigma-Aldrich humic acid (HA) was used to adjust the dissolved organic carbon content in the water. Forcefully fouled AEM by HA and HA-Ca2+ was treated with 2% (w/w) NaCl and 0.03% (w/w) sodium dodecyl sulfate to destabilize the organic moieties on the membranes. The bonding types of HA-Ca2+ and HA with the membrane were examined by vibrational spectroscopy. The surface topographies were visualized by scanning electron microscopy. Both inter- and intramolecular interactions, including hydrophobic cation-π interactions among HA-Ca2+ complexes, were active in membrane fouling. Size compatibility and reduced surface charge of HA-Ca2+ (compared to HA) seems to alter the AEM self-cleaning process leading to irreversible fouling. Based on the vibrational spectral evidence, a plausible AEM fouling mechanism by HA-Ca2+ is proposed. Identification of interactions between the membrane and the foulant will provide an insight into designing appropriate self-cleaning protocols in EDR.

High-Temperature Proton Conduction in Covalent Organic Frameworks Interconnected with Nanochannels for Reverse Electrodialysis.

The crystalline porous organic framework offers a highly ordered and stable structure under hydrated conditions at high temperatures. Here, we demonstrated a method for preparing high-performance membrane buildup using "heterogeneous networks" and "polymer phase-separated nanochannels". A well-interconnected "nanochannel" with a "crystalline organic framework" forms a highly stable hybrid membrane above 80 °C under 100% hydration under acidic and basic conditions. The prepared structure provides a self-standing membrane that easily overcomes the problem faced by conventional high ion-exchange capacity (IEC)-based membranes such as swelling, gelling, fragility, and dissolving at elevated temperatures. Apart from structural stability, it also shows better chemical stability with enhanced proton conduction at elevated temperatures. This proton conduction with better structural stability in the high IEC sample confirms from thermal analysis, whereas it also offers relatively low in-plane membrane swelling as compared to the conventional membranes. These hybrid membranes were further combined with the FAA-3 membrane to manufacture a reverse electrodialysis system for generating a power output. We also evaluated the maximum power density (Pmax) of the stack theoretically and experimentally. The determined net power density (Pnet) is reported to be 0.45 W m-2 at a flow rate of 40 mL min-1. These results confirm that the developed membrane can withstand robustly under realistic ambient conditions maintaining stable cell performance.

Pilot Demonstration of Reclaiming Municipal Wastewater for Irrigation Using Electrodialysis Reversal: Effect of Operational Parameters on Water Quality.

The modification of ion composition is important to meet product water quality requirements, such as adjusting the sodium adsorption ratio of reclaimed water for irrigation. Bench- and pilot-scale experiments were conducted using an electrodialysis reversal (EDR) system with Ionics normal grade ion-exchange membranes (CR67 and AR204) to treat the reclaimed water in the Scottsdale Water Campus, Arizona. The goal is to investigate the impact of operating conditions on improving reclaimed water quality for irrigation and stream flow augmentation. The desalting efficiency, expressed as electrical conductivity (EC) reduction, was highly comparable at the same current density between the bench- and pilot-scale EDR systems, proportional to the ratio of residence time in the electrodialysis stack. The salt flux was primarily affected by the current density independent of flow rate, which is associated with linear velocity, boundary layer condition, and residence time. Monovalent-selectivity in terms of equivalent removal of divalent ions (Ca2+, Mg2+, and SO42−) over monovalent ions (Na+, Cl−) was dominantly affected by both current density and water recovery. The techno-economic modeling indicated that EDR treatment of reclaimed water is more cost-effective than the existing ultrafiltration/reverse osmosis (UF/RO) process in terms of unit operation and maintenance cost and total life cycle cost. The EDR system could achieve 92–93% overall water recovery compared to 88% water recovery of the UF/RO system. In summary, electrodialysis is demonstrated as a technically feasible and cost viable alternative to treat reclaimed water for irrigation and streamflow augmentation.

Performance of Reverse Electrodialysis System for Salinity Gradient Energy Generation by Using a Commercial Ion Exchange Membrane Pair with Homogeneous Bulk Structure

Salinity gradient energy is a prominent alternative and maintainable energy source, which has considerable potential. Reverse electrodialysis (RED) is one of the most widely studied methods to extract this energy. Despite the considerable progress in research, optimization of RED process is still ongoing. In this study, effects of the number of membrane pairs, ratio of salinity gradient and feed velocity on power generation via the reverse electrodialysis (RED) system were investigated by using Fujifilm cation exchange membrane (CEM Type 2) and FujiFilm anion exchange membrane (AEM Type 2) ion exchange membranes. In the literature, there is no previous study based on a RED system equipped with Fujifilm AEM Type II and CEM Type II membranes that have homogeneous bulk structure. Using 400 µm of intermembrane distance, maximum obtainable power density by 5 pairs of Fujifilm membranes at 1:45 salinity ratio and with a linear flow rate of 0.833 cm/s was 0.426 W/m2.

The Influence of Concentration and Temperature on the Membrane Resistance of Ion Exchange Membranes and the Levelised Cost of Hydrogen from Reverse Electrodialysis with Ammonium Bicarbonate.

The ohmic resistances of the anion and cation ion-exchange membranes (IEMs) that constitute a reverse electrodialysis system (RED) are of crucial importance for its performance. In this work, we study the influence of concentration (0.1 M, 0.5 M, 1 M and 2 M) of ammonium bicarbonate solutions on the ohmic resistances of ten commercial IEMs. We also studied the ohmic resistance at elevated temperature 313 K. Measurements have been performed with a direct two-electrode electrochemical impedance spectroscopy (EIS) method. As the ohmic resistance of the IEMs depends linearly on the membrane thickness, we measured the impedance for three different layered thicknesses, and the results were normalised. To gauge the role of the membrane resistances in the use of RED for production of hydrogen by use of waste heat, we used a thermodynamic and an economic model to study the impact of the ohmic resistance of the IEMs on hydrogen production rate, waste heat required, thermochemical conversion efficiency and the levelised cost of hydrogen. The highest performance was achieved with a stack made of FAS30 and CSO Type IEMs, producing hydrogen at 8.48× 10 kg ms with a waste heat requirement of 344 kWh kg hydrogen. This yielded an operating efficiency of 9.7% and a levelised cost of 7.80 € kg.

Generation of energy from salinity gradients using capacitive reverse electro dialysis: a review.

Energy is one of the critical resources determining the overall socioeconomic development. Global warming and natural resource demand had made the world to look into renewable energy like solar, wind, and fuel cells. Salinity gradient energy is the concept of extraction of energy from the concentration gradient between saline and clean solution. In this review, we present different novel systems to generate electricity by salinity gradients by reverse electrodialysis technology integrated with capacitive electrodes and also different types of reverse electro dialysis. This capacitive reverse electrodialysis system synergistically combines previous developments in capacitive mixing and reverse electrodialysis.This review work consists of the study of various reverse electrodialyses, comparing the recent advancements with the novel process and integrates the various results and experiments, and reviews of all reverse electrodialysis are incorporated.

Power Generation by Reverse Electrodialysis System Using Industrial Salty Wastewater in a Production Process for Magnesium Compounds from Seawater

Power Generation by Reverse Electrodialysis System Using Industrial Salty Wastewater in a Production Process for Magnesium Compounds from Seawater

Energy recovery through reverse electrodialysis: Harnessing the salinity gradient from the flushing of human urine

Urine dilution is often performed to avoid clogging or scaling of pipes, which occurs due to urine's Ca2+ and Mg2+ precipitating at the alkaline conditions created by ureolysis. The large salinity gradient between urine and flushing water is, theoretically, a source of potential energy which is currently unexploited. As such, this work explored the use of a compact reverse electrodialysis (RED) system to convert the chemical potential energy of urine dilution into electric energy. Urine’ composition and ureolysis state as well as solution pumping costs were all taken into account. Despite having almost double its electric conductivity, real hydrolysed urine obtained net energy recoveries ENet of 0.053–0.039 kWh/m3, which is similar to energy recovered from real fresh urine. The reduced performances of hydrolysed urine were linked to its higher organic fouling potential and possible volatilisation of NH3 due to its high pH. However, the higher-than-expected performance achieved by fresh urine is possibly due to the fast diffusion of uncharged urea to the freshwater side. Real urine was also tested as a novel electrolyte solution and its performance compared with a conventional K4Fe(CN)6/K3Fe(CN)6 couple. While K4Fe(CN)6/K3Fe(CN)6 outperformed urine in terms of power densities and energy recoveries, net chemical reactions seemed to have occurred in urine when used as an electrolyte solution, leading to TOC, ammonia and urea removal of up to 13%, 6% and 4.4%, respectively. Finally, due to the migration of K+, NH4+ and PO43−, the low concentration solution could be utilised for fertigation. Overall, this process has the potential of providing off-grid urine treatment or energy production at a household or building level. [Display omitted]