In a water system, EDI stands for Electrodeionization. It is a technology used to further purify water after initial processes like reverse osmosis.
According to the provided reference, Electrodeionization (EDI) is a continuous, chemical-free process of removing ionized and ionizable species from feedwater using DC power. This makes it a key technology for producing ultra-pure water in various industrial and commercial applications.
How EDI Technology Works
EDI combines three purification methods:
- Ion Exchange Resins: These capture dissolved ions and ionizable species from the water.
- Ion-Selective Membranes: These membranes allow specific charged ions to pass through, directing them towards waste streams.
- DC Electric Field: A direct current is applied across the system. This electric field regenerates the ion exchange resins continuously and drives the captured ions across the membranes into concentrated waste streams, effectively purifying the water flow.
Because the electric field continuously regenerates the resins, EDI operates without needing periodic shutdowns for chemical regeneration, unlike traditional ion exchange methods.
Where is EDI Used?
EDI is typically used as a final polishing step in high-purity water systems. The reference states that EDI is typically used to polish reverse osmosis (RO) permeate. This means water that has already passed through an RO system (which removes a large percentage of dissolved solids) is fed into an EDI system for further purification, achieving very low conductivity levels suitable for sensitive processes.
Common applications include:
- Pharmaceutical manufacturing
- Semiconductor production
- Power generation (boiler feedwater)
- Laboratory water
- Food and beverage processing
EDI vs. Traditional Ion Exchange
Historically, mixed bed ion exchange (IX) systems were the standard for achieving high-purity water after RO. However, EDI offers significant advantages. The reference identifies EDI as a smart alternative to — and effective replacement of — conventional mixed bed ion exchange (IX).
Here's a comparison of key features:
| Feature | Electrodeionization (EDI) | Conventional Mixed Bed Ion Exchange (IX) |
|---|---|---|
| Process | Continuous | Batch (requires shutdown for regeneration) |
| Regeneration | Electrical (using DC power) | Chemical (using acids & bases) |
| Chemicals | Chemical-free operation | Requires handling & disposal of chemicals |
| Water Quality | Consistent, stable product water | Quality fluctuates before/after regeneration |
Benefits of Using EDI in a Water System
Implementing EDI technology offers several benefits for water purification:
- Continuous Operation: Provides uninterrupted supply of high-purity water.
- Environmentally Friendly: Eliminates the need for hazardous regeneration chemicals, reducing chemical handling, storage, and waste disposal costs and risks.
- Lower Operating Costs: Reduces expenses associated with chemical purchase, wastewater treatment, and labor for regeneration procedures.
- Consistent Water Quality: Delivers stable and predictable purified water quality over time.
- Scalable: Systems can be sized and configured to meet varying flow rate requirements.
In summary, EDI is a modern, efficient, and environmentally sound method for producing high-purity water by removing residual ions after primary purification steps like reverse osmosis, providing a continuous, chemical-free alternative to traditional ion exchange.
