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Electrodialysis (ED)
Electrodialysis removes contaminants from water by using an electric current to pull ionic impurities through ion selective membranes and away form the purified water. ED is cost competitive to reverse osmosis especially when used to make drinkable water from clean brackish feedwater.
ED has several drawbacks when producing laboratory grade water and is rarely used in laboratory settings. First it is limited in the contaminants it can remove. It cannot remove organics, pyrogens and elemental metals which have weak or nonexistent surface charges because they are attached to the membranes. Secondly, the system requires a skilled operator and routine maintenance. Large membranes which bear a significant charge, some colloids and detergents, can plug the membranes' pores reducing their ionic transport ability and requiring frequent cleaning. Even more problematically, ED releases hydrogen gas which is potentially dangerous and liberates caustic soda, which can cause scaling. Last, and probably not least, it is relatively expensive. It requires more than the normal amount of electricity to produce, and purification beyond the potable level is not economically due to increased power costs and the extremely expensive material costs of the platinum and stainless steel materials needed to build it.
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