In the field of modern industry and environmental protection, water treatment technology has been a key research direction. With the increasingly serious problems of water shortage and environmental pollution, how to carry out water treatment efficiently has become the focus of scientists and engineers. Bipolar membrane electrodialysis (BMED), as an emerging electrochemical separation technology, has received extensive attention and research because of its high efficiency, energy saving, and environmental protection.
The basic principle of BMED is a membrane separation technology that combines the properties of electrodialysis and electrolysis of water. Its core component is a bipolar membrane, which generally consists of an anion-exchange resin layer (AL) and a cation-exchange resin layer (CL) sandwiched in the middle by a bipolar interface (also known as a transition layer, a catalytic layer, a composite layer, an interfacial layer, etc).
Fig.1 Electrodialysis with bipolar membranes cell to treat saltcontaining wastewater.
Under the action of the DC electric field, the water (H2O) between the anion and cation membrane composite layers dissociates into hydrogen ions (H+) and hydroxide ions (OH-), and undergoes ion-directed migration, passing through the CL and the AL, respectively, to act as a systematic source of H+ and OH- ion supply. The H+ and OH- are then timely replenished, mainly through the dissociation of water in the transition zone, and the depleted water in turn passes through the transition layer, the catalyst layer, and the interface layer. replenishment and the depleted water is compensated by osmosis of water from the surrounding solution into the middle of the membrane.
The basic BMED device is driven by an electric field, and the ions in the water selectively migrate between these membranes to achieve separation and purification.
Advantages of Bipolar Membrane Electrodialysis
- High efficiency - BMED can effectively separate ions in water and improve the efficiency of water treatment.
- Energy efficient - BMED requires less energy than traditional water treatment methods. This is because it relies primarily on electric fields to drive ion migration, rather than physical methods through chemicals or high temperatures and pressures.
- Environmentally friendly - The BMED process does not require the addition of chemicals, avoiding secondary pollution. Meanwhile, the H+ and OH- generated through water electrolysis can be used to adjust the pH of wastewater, further reducing the impact on the environment.
- Adjustability - The separation effect can be flexibly controlled by adjusting the electric field strength and operating conditions, which is suitable for different types and concentrations of wastewater treatment.
Application of Bipolar Membrane Electrodialysis
Based on the characteristics of the bipolar membrane, equipped with different cation exchange membranes, anion exchange membranes, and other accessories, it can be assembled into different forms of BMED in the form of two-compartment, three-compartment, four-compartment, five-compartment, and so on.
Acid/alkali preparation function
- Inorganic salt preparation corresponding to acids and bases: sodium sulfate, sodium chloride, lithium sulfate, sodium nitrate, ammonium chloride, etc.
- Organic acid and alkali corresponding to organic acid salt preparation: tartaric acid, gluconic acid, citric acid, vitamin C, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, etc.
Acid and alkali wastewater treatment
BMED can effectively separate acid and alkali components in wastewater and realize acid and alkali recovery and wastewater neutralization. For example, acid and alkali wastewater treatment in chemical and electroplating industries, can significantly reduce the cost of wastewater treatment and improve the utilization rate of resources.
High salt wastewater treatment
BMED is outstanding in higH-salt wastewater treatment. Through the process of electrodialysis, the salts in wastewater can be concentrated, reducing wastewater discharge while recovering valuable salt compounds.
Heavy metal wastewater treatment
When treating wastewater containing heavy metal ions, BMED can efficiently separate and recover heavy metal ions, reducing pollution to the environment.
Food and pharmaceutical industry
The application of BMED in the food and pharmaceutical industries is also becoming more and more widespread. For example, in the production of amino acids and organic acids, BMED can be used to separate and purify the products, improving production efficiency and product purity.
Challenges and Prospects of Bipolar Membrane Electrodialysis
Despite its many advantages, BMED technology still faces some challenges in practical applications. For example, the cost of bipolar membranes is high, and the stability and durability of long-term operation need to be further improved. In addition, for the treatment of wastewater with complex compositions, how to optimize the operating conditions and membrane materials is also an urgent problem.
However, with the development of material science and electrochemical technology, the performance of BMED will continue to improve and the range of applications will continue to expand. In the future, BMED is expected to play a greater role in industrial wastewater treatment, resource recovery, environmental protection, and other fields, contributing to the realization of the goal of sustainable development. We are looking forward to the further development and maturity of bipolar membrane electrodialysis technology, which will bring more green and cleanness to our lives.
Reference
- Novel and Emerging Membranes for Water Treatment by Electric Potential and Concentration Gradient Membrane Processes. Advances in Membrane Technologies for Water Treatment (2015).
