Principles of Operations
Electrodialysis depends on the following general principles:
- Dissolved salts in the water are mostly ionic that is they are either positively charged or negatively charged.
- These ions are attracted towards the opposite charged electrodes.
- The charged particles can be either allowed or prohibited to pass through membrane built for the purpose.
How Electrodialysis System Functions?
The saline solution consist of dissolved salts like Na+, Ca2+, and CO32- . These ionic salts move towards the electrode with the opposite charge when the electric current is passed through these electrodes. In these phenomena either the negatively charged particles or the positively charged particles will pass the membrane which are placed between a pair of electrodes. Membranes that is anion-selective membrane and cation-selective membrane, are arranged in an alternative fashion. Between each pair of membrane there is a spacer sheet that allows the water to flow along the face of the membrane.
Electrodialysis Process
The spacers separate the product water and the brine. Due to the action of electrodes, spacers and membranes the concentrated and the diluted solution is created in the spaces between the alternating membranes.
The spaces between the two membranes are called cells. The pair of cells consist of two cells. From one cell ions migrated. This is the dilute cell of the product water whereas in the other cell the ions concentrate. This is the concentrate cell meant for the brine stream.
One electrodialysis unit comprises of numerous pair of cells that are bound together with electrodes on the outside. The bounded cell is referred as a membrane stack. Feed water passes through all of the cells in order to provide a continuous flow of desalted water and brine to emerge from the stack. To protect the scaling chemicals can be added to the streams in the stack.
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Pre-Treatment and Post Treatment
Before actual operation feed water is firstly pre-treated in order to prevent materials from harming the membranes or clog the narrow channels in the cells from entering the membrane stack. Low pressure pump is used to push the feed water through the stack. The feed water is forced with enough power to overcome the resistance of the water as it passes through the narrow passages. In the post treatment water is stabilized and prepared for distribution. In this treatment water the pH is adjusted and the gases like hydrogen sulfide is removed.
Advantages
- Whole operation is automatic
- Requires low maintenance and can be installed easily Automatic operation of the plant, requiring very
- Whole process can remove the salts from feed water
- They can be used in industries for:
- Demineralization of cheese whey
- Fruit juices deacidification
- Stabilization of Tartaric wine
Electro deionization for pure water
