Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and other treatments with significant environmental benefits. ED technologies can be used in operations of concentration, dilution, desalination, regeneration, and valorisation to reclaim wastewater and recover water and/or other products, e.g., heavy metal ions, salts, acids/bases, nutrients, and organics, or electrical energy. Intense research activity has been directed towards developing enhanced or novel systems, showing that zero or minimal liquid discharge approaches can be techno-economically affordable and competitive. Despite few real plants having been installed, recent developments are opening new routes for the large-scale use of ED techniques in a plethora of treatment processes for wastewater.

Preparation of novel multi-walled carbon nanotubes nanocomposite adsorbent via RAFT technique for the adsorption of toxic copper ions

In the present work, polymer-coated multiwalled carbon nanotube (MWCNT) was prepared via RAFT method. First, a novel trithiocarbonate-based RAFT agent was prepared attached chemically into the surface of MWCNT. In addition, the RAFT co-polymerization of acrylic acid and acrylamide monomers was conducted through the prepared RAFT agent. In the next age, the surface morphology and chemical properties of the prepared components were fully examined by using FTIR, ¹HNMR, SEM, TEM, XRD and TGA/DTG techniques. Finally, the modified MWCNT composite was employed as an excellent adsorbent for the adsorption of copper (II) ions. The results indicated that ion adsorption basically relies on adsorbing time, solution pH, initial copper concentration, and adsorbent dosage. Further, the adsorption kinetics and isotherm analysis demonstrated that the adsorption mode was fitted with the pseudo-second-order and Langmuir isotherm models, respectively. Based on the results of thermodynamic study, the ion adsorption process was endothermic and spontaneous. Finally, based on the experimental results, the surface functionalized MWCNT with hydrophilic groups could be successfully used as a promising selective adsorbent material in wastewater treatment.

Study on the fouling mechanism and cleaning method in the treatment of polymer flooding produced water with ion exchange membranes

The complex interactions between organic and inorganic foulants in polymer flooding produced water (PFPW) play a significant role in membrane fouling characteristics during the treatment processes with ion-exchange membranes (IEMs). In order to ensure the desalination capacity of IEMs during electrodialysis, this work systematically investigated the fouling mechanism and cleaning properties with different synthetic solutions as feed water. The results demonstrated that the desalination rates of the IEMs decreased by 39.73%, 43.05%, 45.81% and 52.72% when fouled by HPAM, HPAM-inorganic (i.e., CaCl₂ and NaHCO₃), oil emulsions and oil–HPAM-inorganic, respectively. The results of membrane resistances and SEM images indicated that organic foulant (i.e., HPAM) and inorganic components have a synergistic effect on the fouling of IEMs. The membrane cleaning method using acid–base-sodium dodecyl benzene sulfonate (SDBS) was proposed here to recover the performance of the IEMs after being fouled by feed solution containing oil–HPAM-inorganic compounds. The desalination rate of the IEMs after membrane cleaning increased from 39.62% to 81.39%. This indicated that the acid–base cleaning alone eliminated the inorganic precipitation and gel layer, and the subsequent SDBS cleaning removed the dominant oil emulsion layer.

The fouling and cleaning mechanism of ion exchange membranes in polymer flooding produced water treatment were investigated.

Polymers in separation processes

Application of polymer materials as membranes and ion-exchange resins was presented with a focus on their use for the recovery of metal ions from aqueous solutions. Several membrane techniques were described including reverse osmosis, nanofiltration, ultrafiltration, diffusion and Donnan dialysis, electrodialysis and membrane extraction system (polymer inclusion and supported membranes). Moreover, the examples of using ion-exchange resins in metal recovery were presented. The possibility of modification of the resin was discussed, including hybrid system with metal cation or metal oxide immobilized on polymer matrices or solvent impregnated resin.

Ceramic anion-exchange membranes based on microporous supports infiltrated with hydrated zirconium dioxide

Anion-exchange membranes were produced by infiltrating microporous ceramic supports with particles of hydrated ZrO₂. These membranes can be applied to the electrodialytic treatment of harsh industrial effluents.

Retrieval of CO2 from a carbonate solution for its sequestration by a novel electrochemical decarbonizing and ingathering method

Under an electrical force the migration rate of carbonate ions in a low residence resin chamber was accelerated and CO₂ gas was released through an acidic chamber.