Electrodialysis (ED) is a process that utilizes a semipermeable membrane and a direct current electric field to selectively transport charged solute particles (such as ions) from a solution. This separation process concentrates, dilutes, refines, and purifies solutions by directing charged solutes away from water and other non-charged components. Electrodialysis has evolved into a large-scale chemical unit operation and plays a significant role in membrane separation technology. It finds wide application in industries such as chemical desalination, seawater desalination, food and pharmaceuticals, and wastewater treatment. In some regions, it has become the primary method for producing drinking water. It offers advantages such as low energy consumption, significant economic benefits, simple pretreatment, durable equipment, flexible system design, easy operation and maintenance, clean process, low chemical consumption, minimal environmental pollution, long device lifespan, and high water recovery rates (typically ranging from 65% to 80%).
Common electrodialysis techniques include electrodeionization (EDI), electrodialysis reversal (EDR), electrodialysis with liquid membranes (EDLM), high-temperature electrodialysis, roll-type electrodialysis, bipolar membrane electrodialysis, and others.
Electrodialysis can be used for the treatment of various wastewater types, including electroplating wastewater and heavy metal-contaminated wastewater. It can be employed to extract metal ions and other substances from wastewater, allowing for the recovery and reuse of water and valuable resources while reducing pollution and emissions. Studies have shown that electrodialysis can recover copper, zinc, and even oxidize Cr3+ to Cr6+ during the treatment of passivation solutions in the copper production process. In addition, electrodialysis has been combined with ion exchange for the recovery of heavy metals and acids from acid pickling wastewater in industrial applications. Specially designed electrodialysis devices, using both anion and cation exchange resins as fillers, have been used to treat heavy metal wastewater, achieving closed-loop recycling and zero discharge. Electrodialysis can also be applied to treat alkaline wastewater and organic wastewater.
Research conducted at the State Key Laboratory of Pollution Control and Resource Reuse in China studied the treatment of alkali washing wastewater containing epoxy propane chlorination tail gas using ion exchange membrane electrolysis. When the electrolysis voltage was 5.0V and the circulation time was 3 hours, the COD removal rate of wastewater reached 78%, and the alkali recovery rate was as high as 73.55%, serving as an effective pretreatment for subsequent biochemical units. Electrodialysis technology has also been used to treat high-concentration complex organic acid wastewater, with concentrations ranging from 3% to 15%, by Shandong Luhua Petrochemical Company. This method results in no residues or secondary pollution, and the concentrated solution obtained contains 20% to 40% acid, which can be recycled and treated, reducing the acid content in wastewater to 0.05% to 0.3%. In addition, Sinopec Sichuan Petrochemical Company used a specialized electrodialysis device to treat condensate wastewater, achieving a maximum treatment capacity of 36 t/h, with the ammonium nitrate content in the concentrated water reaching above 20%, and achieving a recovery rate of over 96%. The treated freshwater had an ammonium nitrogen mass fraction of ≤40mg/L, meeting environmental standards.
Post time: Sep-07-2023
