A hierarchical model for novel schemes of electrodialysis desalination

Electrodialysis (ED) is a new advanced separation process that is commonly utilized for producing drinking water from water bodies as well as for the treatment of industrial effluents. ED process is applied on commercial scale. Basically, an ED process consists of an ion exchange membrane and the diving force necessary for applicability of the process is electric potential. Due to the presence of electric potential ions from one solution after passing through ion selective membrane barrier are transferred to another solution. The main factors on which ED process performance depends on concentration of ion in raw water, flow rate, concentration of feed, current density, membrane properties and cell compartments geometry. Fouling which is produced by foulants including organics, colloids and biomass on the inside membrane internal structure or on the outside surface results in reduction of process separation efficiency and energy consumption is enhanced. Fouling increases the membrane resistance and selectivity of membrane is reduced by fouling. Therefore, some methods are proposed to reduce fouling in ED system such as pre-treatment of feed solution, zeta potential control, membrane properties modification and flowrate optimization. It is a need of an hour to suggest a reducing method less energy and thus minimum operating and investment cost. Electrodialysis Reversal (EDR) system can be as regarded as best option because no extra chemicals are required and life of membrane increased by it. In EDR fouling progress is broken by revering electric potential (applied electric field). This paper elaborates ED process briefly and presents an overview of literature review on different kinds of fouling mechanisms. Also, different cleaning methods have been briefly described for enhancing efficiency of ED process.

Hybridization of electrodialysis (ED) and batch reverse osmosis (BRO) process is used to reduce the brine volume and water production cost. The ED process has the benefit of high water volume recovery in brackish water desalination, while reverse osmosis can produce pure water at a low production cost. Here, a simple hybrid process layout is preferred in which the ED process is kept in the reject stream of the BRO process and permeate from both ED and BRO is mixed. Recovery of the ED process is kept at 70% which can decide the blending ratio of ED and BRO permeates. The capital cost and operating cost of ED and BRO processes are used to calculate water production cost. The water production cost from the hybrid ED–BRO process is found to be 0.22 $ m−3 of freshwater when the feed concentration is 1,100 ppm. The cost increases from 0.20 to 0.34 $ m−3 with feed concentration from 1,000 to 2,000 ppm. In the cost, a major portion comes from the capital equipment in which the highest contributor is the membrane for both ED and BRO processes.

Micellar-enhanced electrodialysis: Influence of surfactants on the transport properties of ion-exchange membranes

Numerous attempts have been made to develop ion-exchange membranes with low resistance for various applications such as electrodialysis and fuel cells. In this study, the strategies of immersion precipitation and dry-casting were combined, to control the membrane porosity with the purpose of improving the physical and electrochemical properties of ion-exchange membranes. The porosity was tuned using the time of membrane exposure to an elevated-temperature environment. In addition to controlling the porosity to balance the membrane electrical resistance with the diffusion caused by the concentration gradient, it was experimentally shown that the porosity can influence the IEC and water uptake of the membrane and, thus, further affect the resistance. Furthermore, the surface hydrophilicity was characterized by water contact angle measurements; the results revealed that the porous membranes were more hydrophilic than the dense membranes. As demonstrated by experimental data for desalination by electrodialysis, it was found that a membrane dried at 60 °C for 1 h had the highest desalination efficiency. This is mainly because porous membranes facilitate the transport of ions. Compared to membranes with higher porosity, the membrane prepared with a 1-h aging time had more steric hindrance, which can decrease the diffusion of ions, so that a superior desalination efficiency can be obtained. To further investigate the impact of the density of −SO32– functional groups on the electrodialysis process, membranes with various weight ratios of poly(ether sulfone) (PES) to sulfonated poly(ether sulfone) (SPES) were prepared. With increasing content of SPES, the physical and electrochemical properties of the newly developed porous membranes were changed. A membrane with higher density of functional groups was found to have a higher desalination efficiency, because of the electrostatic effect of the membrane. These results were consistent with the current efficiency. Under optimal membrane preparation conditions, the obtained membrane had a high IEC (1.75 mmol/g) and water uptake (168%). The desalination efficiency reached 95%, and the current efficiency reached 100%. It was concluded that the performance of a porous membrane with controllable porosity can enhance the electrodialysis (ED) process with respect to energy efficiency and desalination efficiency. New methods of fabricating membranes with pores such as immersion precipitation and dry-casting are thought to be potential routes to decreasing the electrical resistance.

Electrodialysis (ED) is an emerging membrane-based electroseparation technology for desalination, water treatment, and ionic pollutant removal. Compared to conventional separation methods such as reverse osmosis, ED offers several advantages including lower energy consumption, higher selectivity, and lower fouling propensity. Further, coupling ED with renewable electricity sources enables it to be far more sustainable than competing technologies (reverse osmosis and evaporation) across a wide range of scales. However, the design and operation of ED systems are still challenging due to the complex interactions between the membrane, the electrolytes, and the applied electric field. To address this issue, advanced process models are required to provide accurate predictions of ED performance and to guide system optimisation. Existing ED models tend to be highly dependent on empirical parameters and thus are only applicable to a narrow range of process conditions and require several data sets to validate. Therefore, in this work we aimed to develop a glabal model of ED without reliance on experimental training data.Herein, we present a novel circuit-based model for ED. The model considers the membrane stack as a series of resistors, where the membranes and electrolytes are represented as separate resistive elements. Crucially, the membrane resistance is calculated directly from the electrostatic interaction between ions and fixed charge groups, rather than from manufacturer data or empirical sub-model. This allows for consideration of the ion identity and electrolyte concentration when determining the membrane resistance. Ohm's law is used to relate the applied voltage and stack electrical resistance to a current density, which is then converted to a flux using Faraday's law and current efficiency model. Historically, current efficiencies are calculated from transport numbers provided from membrane manufactures and assumed constant. A novel model for the current efficiency has been developed by us in which the current efficiency is a function of the trans-membrane concentration difference. A space-wise material balance is employed to determine the concentration profile along the stack, while a time-wise material balance tracks the changes in reservoir concentration for recirculating batch experiments.To validate the model, desalination experiments were conducted on a PC BED 1-4 recirculating batch system and compared the model predictions with experimental data. The model demonstrated excellent matching on a range of variables across a range of conditions, including current density, current efficiency, and ion concentration.The proposed model has various applications in ED process modelling, optimisation, and economic analysis. It can be used to evaluate the impact of different design parameters such as membrane thickness, membrane charge density, and flow rate on system performance as well as to optimise these.In summary, the circuit-based model presented in this work offers a robust and versatile tool for ED process simulation and optimisation, which can be used for effective and efficiency desalination and water treatment. Two major advancements presented include models for the membrane electrical resistance and current efficiency, which have historically been considered constant. Figure 1

New anhydrous proton conducting membranes based on poly(vinyl acohol) (PVA), tetraethyl orthosilicate (TEOS) and sulfosuccinic acid (SSA) were prepared in a single step using the solution casting method, with the aim to improve the mechanical properties of PVA membranes. SSA has been used as a sulfonating agent for crosslinking the membrane structure and also as a source of protons. TEOS has been used as crosslinking agent to increase the thermal and mechanical properties of the membranes and membranes stability in aqueous environment. In order to verify that all the substances were immobilized into the matrix, the membranes were analyzed by means of Fourier transform infrared spectroscopy (FTIR).The thermal, mechanical and rheological properties of the membranes were investigated by means of thermogravimetry (TGA), dynamic mechanical analysis (DMA) and Ares G2 rheometer. Water uptake (Wu) of composite membranes was determined. The properties were investigated for various PVA solutions and for each dried membrane. The analysis of mixed PVA solutions exhibited unique behaviour of viscosity with increasing the crosslink density. TGA and DMA measurements showed increased thermal and mechanical resistance of membranes depending on the extent of their crosslinking. Due to incorporation TEOS, the resistance of PVA membranes to the aquatic environment has increased. These properties can increase the resistance of the membranes during the processes occurring in the fuel cells.

Wastewater and by-product treatments are substantial issues with consequences for our society, both in terms of environmental impacts and economic losses. With an overall global objective of sustainable development, it is essential to offer eco-efficient and circular solutions. Indeed, one of the major solutions to limit the use of new raw materials and the production of wastes is the transition toward a circular economy. Industries must find ways to close their production loops. Electrodialysis (ED) processes such as conventional ED, selective ED, ED with bipolar membranes, and ED with filtration membranes are processes that have demonstrated, in the past decades and recently, their potential and eco-efficiency. This review presents the most recent valorization opportunities among different industrial sectors (water, food, mining, chemistry, etc.) to manage waste or by-product resources through electrodialysis processes and to improve global industrial sustainability by moving toward circular processes. The limitations of existing studies are raised, especially concerning eco-efficiency. Indeed, electrodialysis processes can be optimized to decrease energy consumption and costs, and to increase efficiency; however, eco-efficiency scores should be determined to compare electrodialysis with conventional processes and support their advantages. The review shows the high potential of the different types of electrodialysis processes to treat wastewaters and liquid by-products in order to add value or to generate new raw materials. It also highlights the strong interest in using eco-efficient processes within a circular economy. The ideal scenario for sustainable development would be to make a transition toward an eco-circular economy.

Polymer inclusion membrane (PIM) containing ionic liquid as a proton blocker to improve waste acid recovery efficiency in electrodialysis process

Electrodialysis (ED) is a promising seawater desalination technology using electricity. However, the existing research studies on ED mainly focus on design of electrode materials and device structure. The ED is a multiscale and multi-physical process with multiple influencing parameters. Under these circumstances, the complicated ED process needs to be unified for understanding its physical essence and further optimization. In the current work, a similarity principle-based multiscale model is constructed to analyze ion migration mechanism inside ED device. The multiscale model is developed by correlating cation and anion concentration difference in a mesoscopic nanopore with macroscopic space charge density. On the basis of non-dimensionalization of Poisson-Nernst-Planck equations, the mesoscopic model of ED is unified with three dimensionless variables instead of eight-dimensional input parameters, which can be categorized as representative of ion absorption capability, ion transport characteristic, and nanopore characteristic. Then, the macroscopic model of ED is further unified using 6 dimensionless variables instead of 12-dimensional input parameters, and their physical meaning include ion absorption capability, ion transport characteristic, ion migration driving force, and desalination tank characteristic. The similarity principle of multiscale ED process is verified through nine dimensional different cases with identical dimensionless variables. The dimensionless cation-anion difference in nanopores of mesoscopic model varies within 0.25%, and the dimensionless outlet Na⁺ concentration of macroscopic model changes within 0.05%. Besides, a multi-physical sensitivity analysis is also carried out using the Taguchi method to clarify dominant parameters for ED. The Taguchi sensitivity analysis quantifies parameter contribution to seawater desalination rate in ED as seawater temperature 39.74%, initial ion concentration 15.94%, applied electric potential 15.91%, desalination tank length 11.45%, ion exchange membrane porosity 8.76%, and seawater flow velocity 8.19%. The current work lays a theoretical foundation for developing experimental correlations of ED, and it also contributes to rapid sampling generation in artificial intelligence prediction.

Reverse osmosis (RO) is a commonly used desalination technology, but due to high requirements concerning the quality of the feed water, there still exists permeate flux related to the operating conditions, and the solute removal rate is low. Electric fields have a facilitating effect on RO desalination performance. Previous studies have focused on investigating the combination of RO and electrodialysis (ED) processes separately, without directly exploiting their interactions. To address this issue, this study proposes a novel coupling device that combines both RO and ED technologies in a single unit and investigates their mutual enhancement effects on brackish water desalination. The results show that the coupled EDRO system can mutually enhance the performance of RO and ED processes. The permeate flux ratio of the RO membrane increased with increasing voltage, reaching a maximum value of 23.7% at a feed concentration of 10,000 mg/L. The solute rejection by the ion-exchange membrane also increased with increasing pressure, reaching a maximum value of 14.95% at the same feed concentration. In addition, the specific energy consumption of the coupled system was also reduced compared to a standalone operation, with maximum reductions of 9.5% and 19.2% for RO and 2.5% and 3.4% for ED at 5000 and 10,000 mg/L feed concentrations, respectively.

Fabrication of trimethylphosphine-functionalized anion exchange membranes for desalination application via electrodialysis process

Novel compact ion exchange membranes through suppressing reverse permeation for high-efficiency recovery of inorganic acids

Concentration of trisodium citrate by electrodialysis

A novel industrial lithium-containing wastewater depth concentrating process integrating reverse osmosis (RO) and electrodialysis (ED) into a system is presented. A systematic analytical study was accomplished to optimize the studied parameters and minimize the energy consumption. The tested parameters were as follows: RO recovery by adding pressure, ED voltage drop, the concentration of RO retentate in ED feed solution, ED volume ratio, and ED operating mode. By using RO retentate instead of initial wastewater in the ED process, water energy consumption was reduced by 3.41 times from 26.67 to 7.81 kW h/m3, while optimizing the RO retentate concentration for the ED feed solution reduced the cost to 0.47 $/kg. The results showed that RO is crucial to preconcentrate lithium salt and save energy. Furthermore, the final LiCl concentration can approach as high as 87.09 g/L with the secondary ED process (Vd:Vc = 3:1), while the energy consumption can be saved as 7.71 kW h/m3 when the experiments stopped in region 1. The concentration factor of 12.32 can be achieved to justify the feasibility of integration of a high volume ratio concentrating with a mutistage concentrating protocol. As a consequence, the hybrid RO–ED process allows for lithium salt extraction and concentrating from industrial lithium-containing wastewater, which is appropriate for industrial applications.

An attempt for improving electrodialytic transport properties of a heterogeneous anion exchange membrane