Eletrodialysis
Electrodialysis (ED) is a membrane process, whereby electrically charged particles, ions, are transported from a raw solution (diluate) into a more concentrated solution (concentrate) through semi permeable membrane, due to electric attraction.
The membranes are cation- or anion-selective, meaning that either positive or negative ions will pass through. This means that the negatively charged anions migrate towards the anode and the positively charged cations towards the cathode. This separation stage results in a concentration of electrolytes in the so-called concentrate loop and a depletion of charge carriers in the so-called diluate loop.
Sometimes pretreatment is necessary before the electrodialysis can take place. Suspended solids with a diameter that exceeds 10 µm need to be removed, or else they will plug the membrane pores. There are also substances that are able to neutralize a membrane, such as large organic anions, colloids, iron oxides and manganese oxide. These disturb the selective effect of the membrane. Pretreatment methods, which aid the prevention of these effects are active carbon filtration (for organic matter), flocculation (for colloids) and filtration techniques.
The membranes are cation- or anion-selective, meaning that either positive or negative ions will pass through. This means that the negatively charged anions migrate towards the anode and the positively charged cations towards the cathode. This separation stage results in a concentration of electrolytes in the so-called concentrate loop and a depletion of charge carriers in the so-called diluate loop.
Sometimes pretreatment is necessary before the electrodialysis can take place. Suspended solids with a diameter that exceeds 10 µm need to be removed, or else they will plug the membrane pores. There are also substances that are able to neutralize a membrane, such as large organic anions, colloids, iron oxides and manganese oxide. These disturb the selective effect of the membrane. Pretreatment methods, which aid the prevention of these effects are active carbon filtration (for organic matter), flocculation (for colloids) and filtration techniques.
What are the Pros and Cons of the process?
Pros
- Low energy consumption: Electrodialysis systems purify water without changing its phase so it does not require the energy to change phases. This lowers the cost and amount of energy needed.
- Limited post-treatment: Electrodialysis systems requires limited treatment to bring salt water to the required purity level and doesn't need a lot of extra treatment. It may require that the water is chlorinated to make it fit for consumption but that is a small need compared to waste water treatment plants.
- Longevity: Compared to other systems, electrodialysis uses few chemicals and is durable. In addition, its membrane can last for a period of up to 10 years. Individuals are free to enjoy a high pure water recovery rate for a long time.
- Although electrodialysis efficiently removes low molecular weight ions, it has limitations when it comes to removing heavy ions or ions with no charge. In addition, it can't remove colloids and other organic matter.
- Even though electrodialysis is an efficient water purifying systems, users must buy quality membranes that work with their systems. This means that since the membranes are specific, they can only be bought from reputable local or online retailers.