Electrodeionization (EDI) is an awesome technology for producing ultra pure water. But over time, the performance of EDI modules can drop off due to contaminant buildup.
In this guide, I’ll walk you through everything you need to know to keep your EDI system running in tip-top shape.
How to Know When Your EDI Modules Are Getting Gunked Up
Let’s start with the signs that your EDI system needs some TLC:
- Pressure difference between inlet and outlet increases by 45%
- Concentrate pressure difference up by 45%
- Resistivity of product water drops significantly
- Concentrate flow rate drops by 35%
- Voltage exceeds initial baseline by 20%
See any of those issues? It likely means contaminants are starting to block things up inside your EDI modules.
The good news? With the right maintenance plan, you can often restore performance to like-new levels.
Onwards!
What Causes EDI Modules to Get Contaminated
There are 5 main culprits when it comes to EDI module contamination:
1. Particles
Inlet particles ≥5μm can get logged in the EDI flow channels. This reduces flow distribution and performance.
Solution: Add a security filter (≤0.2μm) on the inlet line. And remember to flush all pipes during installation.
2. Scaling
If the feedwater has excess hardness or high recovery rates, scaling can occur rapidly in the concentrate and cathode channels.
This type of fouling is usually carbonate scale caused by calcium and magnesium ions. Acid cleaning can remove it.
3. Organic Fouling
Too much organic material in the feedwater can foul up the ion exchange resins and membranes.
Circulating a high pH cleaning solution through the system helps remove organics.
4. Microbial Growth
Microbes love the environment inside EDI systems. So bacterial/algae growth is common over time.
This biofouling is also removed by alkaline or acidic cleaning solutions.
5. Iron/Metal Oxides
Iron and other metals can “poison” ion exchange resins. This gunks things up and hurts performance.
How Feedwater Contaminants Impact EDI Performance
Let’s do a quick rundown of how specific feedwater pollutants impact EDI systems:
- Hardness: Forms scale on membranes and resins, increasing differential pressure.
- Organics: Lower efficiency of membranes and resins by “coating” them.
- Particles: Can literally clog resin beds and membranes. Big pressure losses.
- Metals: “Poison” ion exchange resins, hurting efficiency.
- Oxidizers: Chemically attack and degrade ion exchange resins.
- CO2: Produces carbonate scale in concentrate. Also reduces resistivity of product water.
The takeaway is that it’s incredibly important to remove these contaminants upstream to prevent fouling issues downstream.
Now let’s get into how to safely clean EDI modules when you need to restore performance.
Precautions When Chemically Cleaning EDI Modules
Before breaking out the cleaning chemicals, keep these safety tips in mind:
- Wear proper PPE at all times
- Isolate equipment pipes before cleaning
- Verify electrical power is OFF
- Keep pressure below 0.15 MPa
- When cleaning the exterior, use only mild detergents and damp cloths
Accidents happen. Don’t let haste put you or your team at risk.
Solutions for Cleaning Contaminated EDI Modules
When EDI performance drops off due to fouling, here are some recommended cleaning approaches:
Cleaning Solution Matrix
Here’s an overview of cleaning solutions matched to common EDI contamination issues:
| Problem | Solution 1 | Solution 2 | Solution 3 |
|---|---|---|---|
| Concentrate Chamber Scaling | ✅ | ||
| Freshwater Chamber Scaling | ✅ | ||
| Organic Fouling | ✅ | ||
| Organic Fouling + Scaling | ✅ | ||
| Microbial Fouling | ✅ | ||
| Microbial Fouling + Scaling | ✅ | ||
| Severe Microbial Fouling | ✅ | ||
| Severe Microbial Fouling + Scaling | ✅ |
Overview of Cleaning Protocols
Here’s what each cleaning protocol entails step-by-step:
| Step | Solution 1 | Solution 2 | Solution 3 |
|---|---|---|---|
| 1 | Acid Clean | Acid Clean | Alkaline Clean |
| 2 | Rinse | Rinse | Rinse |
| 3 | Regeneration | Regeneration | |
| 4 | Disinfection |
And so on…
Time and Chemical Requirements
Generally, each step takes 30-60 minutes. Regeneration takes at least 120 minutes.
For chemicals, plan on needing about 80 liters of cleaning solution per m3/hour of EDI treatment capacity.
Approved Cleaning Chemicals
For safety, make sure all chemicals used are reagent grade or better. Approved options include:
- Hydrochloric acid (HCl)
- Sodium hydroxide (NaOH)
- Sodium hypochlorite (NaClO)
- Hydrogen Peroxide (H2O2)
And there you have it!
Monitor those performance metrics. And when your EDI system needs some TLC, follow the cleaning tips in this guide to get back to maximum performance.
Let me know in the comments if you have any other questions!
