What is the Difference Between EDI and DI Water?

Electrodeionization (EDI) and deionization (DI) are two advanced water purification technologies used to produce ultra pure water. Although they share some similarities, their working principles and capabilities differ significantly.

Understanding the key differences between EDI and DI is essential to determine which process best suits your application’s water purity requirements. As a professional EDI module supplier, I am writing this guide to compare these technologies to help you make an informed decision.

How Do EDI and DI Water Systems Work?

DI and EDI both use ion exchange to remove dissolved salts and minerals from feedwater. However, their methods differ:

DI Water Systems

DI systems pass feedwater through cation and anion exchange resins. These resins contain positively and negatively charged sites which attract and bind oppositely charged ions.

As water passes through the mixed bed resins, undesirable ions like calcium, magnesium, chloride, and sulfate get exchanged for hydrogen (H+) and hydroxyl (OH-) ions. The resulting deionized water contains almost entirely H+ and OH- ions which instantly recombine to form pure H2O molecules.

After the exchange capacity is exhausted, the resins must go through chemical regeneration to restore their ion removal capability. The frequency of regeneration depends on the feedwater quality and throughput volume.

EDI Systems

EDI also utilizes ion exchange resins, but it regenerates them electrically instead of chemically. The key components of an EDI module are:

• Ion exchange resins
• Cation-permeable membranes
• Anion-permeable membranes
• Oppositely charged electrodes

Feedwater enters dilute flow compartments packed with resins for ion removal. Simultaneously, a DC voltage applied across the electrodes causes cations and anions to migrate out of the dilute channels into adjacent concentrate channels.

The ion selective membranes prevent the ions from remixing while allowing water passage. The electric field continuously regenerates the resins while removing extracted ions into the waste.

Purity Levels of EDI and DI Water

Both DI and EDI can produce extremely pure water, but EDI takes it to another level in terms of residual conductivity and overall quality:

• DI water typically achieves 0.1 to 1 μS/cm conductivity corresponding to less than 5 ppb silica and 10 ppb TOC
• EDI water can reach 0.06 μS/cm conductivity corresponding to less than 1 ppb silica and TOC

So while DI removes over 99% of ionic impurities, EDI can eliminate 99.9% and produce water nearing theoretical purity levels.

Key Differences Between EDI and DI Water

Below is a comparison of some vital characteristics of EDI and DI processes:

Power usage: EDI consumes more power for running the electric field. DI just needs pumping power.

Chemical usage: DI depends on hazardous acids/caustics for resin regeneration. EDI uses no chemicals.

Water recovery: ~75% for DI vs. 90% for EDI. Less water gets wasted as concentrate.

Scalability: DI can handle higher capacities cost-effectively. Large EDI systems become very expensive.

Pretreatment needs: EDI requires extensive pretreatment like high-pressure RO to avoid fouling issues.

Applications of EDI and DI Water

When to Choose EDI

EDI should be your technology of choice when you need:

• Ultra pure water with conductivity below 0.1 μS/cm
• Consistent and reliable quality without fluctuations
• Low TOC levels for high-end applications
• Complete elimination of ions without leaks or slippage
• High final product water recovery rate
• Chemical-free and environmentally friendly process

Typical EDI applications:

• Final polish for pharmaceutical WFI systems
• Semiconductor fab rinsing and cleaning
• High purity clinical diagnostics
• HPLC mobile phase preparation
• Nuclear reactor cooling systems

When to Choose DI

DI offers a cost-effective way to produce extremely pure water for applications like:

• Industrial pure steam generation
• Laboratory water
• Optics and photolithography
• Automated analytical instruments
• Medical equipment rinsing
• Power industry feedwater

DI is more economical for larger volumes where slightly higher conductivity can be tolerated. The modular construction also allows easy capacity upgradations.

Conclusion

EDI utilizes a sophisticated electro-deionization technique to make the highest purity water practically achievable. The electrical regeneration of resins eliminates all chemicals while extracting almost 100% of dissolved ions.

DI also offers phenomenally pure water at excellent value. It has simpler pretreatment needs and can handle higher capacities in a scalable manner. DI is ideal if target conductivity requirements are moderately strict rather than ultra stringent.

So consider your feedwater quality, target water purity specs, capacity demand, operating budgets and environmental factors while deciding between EDI and DI systems. Their techno-economic evaluation will guide you to the optimal choice.