Ion Exchange
7 October 2020
Post treatment
9 October 2020

Electrodeionization (EDI)

Electrodeionization (EDI) is a process that removes ionizable species from liquids using electrically active media and an electrical potential between an anode and a cathode to influence ion transport. A typical system has at least one product channel through which liquid to be processed is flowed. The product channel is filled with a mixed bed of ion exchange resin ion exchange materials. These ion exchange materials are either anion specific or cation specific. The liquid to be purified is flowed into the product channel while an electrical potential is applied to the system. The ion exchange materials in the product channel selectively cause the ions in the liquid to attach to the bead surfaces where they are transferred from bead to bead toward the electrode (anode or cathode) they favor. Once they pass through the ion selective membrane, they are passed to ion exchange materials in the waste channels. A liquid is also flowed through each waste channel that removes the ions from the ion exchange materials and carries them to waste.

Electrodeionization (CEDI)

EDI provides continuous demineralization at recovery rates of 90% or more. In EDI, just as in conventional ion exchange, cations and anions in the feed water are exchanged for hydrogen and hydroxyl ions in the ion exchange resins, producing demineralized water. The key operational difference is that with EDI, the ion exchange resin is regenerated continuously, while with conventional ion exchange, chemical regeneration is performed intermittently.
Continuous electro-deionization (CEDI) is the most advanced generation of ion exchange technology and it is achieved electrochemically, by means of ion conducting membranes and an imposed electric current. The continuous electro-regeneration enables CEDI systems to produce multi-megohm water without the need for chemical regeneration or downtime so CEDI is a chemical-free operation and therefore environmentally friendly, a continuous production, and has extremely low operating costs when compared to chemically regenerated ion exchange technology.
CEDI is often selected for projects requiring ultra-high purity water, as well as for projects with stringent wastewater requirements. It is typically used in industries requiring higher purity than RO alone can produce.

Advantages of EDI

Conventional ion exchange is a viable treatment option for applications where high-flow and high conductivity requirements are not critical. In other situations, however, cost comparisons between ion exchange and continuous deionization may reveal potential economic advantages.
The biggest difference is that continuous electrodeionization eliminates all chemical regeneration and waste neutralization steps. While capital equipment costs may be higher with continuous deionization systems, operating expenses are lower because there are no regeneration chemicals, and labor or maintenance costs are less. There are significant tangible cost benefits associated with the elimination of regeneration. The costs of regeneration labor and chemicals are replaced with a small amount of electrical consumption.
Continuous electrodeionization systems do not require duplexing (two separate treatment units) which can increase the cost, complexity and size of the system.
Additional benefits of chemical-free CEDI technology include:No waste neutralization, smaller footprint, more consistent operation, minimal maintenance.