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CDI vs RO vs EDI: 3 Desalination Methods Compared
- Tech Inc
- 6 days ago
- 2 min read
CDI vs RO vs EDI: Which Desalination Technology is Right for You?
When selecting a desalination or deionization technology, engineers must balance water quality requirements, energy costs, and operational complexity. Capacitive Deionization (CDI), Reverse Osmosis (RO), and Electrodeionization (EDI) each serve different niches in the water treatment landscape. This guide compares these three technologies to help you make an informed decision.
Technology Overview
Capacitive Deionization (CDI) is an electrochemical process that removes dissolved ions by adsorbing them onto porous carbon electrodes under an applied voltage. CDI is most efficient for low-to-moderate salinity water (TDS below 3,000 mg/L) and offers the advantage of low energy consumption and chemical-free operation.
Reverse Osmosis (RO) is the most widely deployed desalination technology, using semi-permeable membranes and high pressure to separate dissolved solids from water. RO achieves salt rejection rates above 99% and handles up to 45,000 mg/L.
Electrodeionization (EDI) combines ion-exchange resins with an electric field to continuously regenerate the resin bed without chemicals. EDI is a polishing technology typically placed after RO to produce ultrapure water with resistivity above 15 MΩ·cm.
Detailed Comparison Table
Parameter | CDI | RO | EDI |
Feed TDS Range | 100–3,000 mg/L | 500–45,000 mg/L | 1–40 mg/L (post-RO) |
Product Water Quality | 50–90% salt removal | 95–99.8% rejection | >15 MΩ·cm resistivity |
Energy Consumption | 0.1–1.5 kWh/m³ | 2.0–8.0 kWh/m³ | 0.1–0.6 kWh/m³ |
Recovery Rate | 70–90% | 40–85% | 90–95% |
Chemical Requirements | Minimal | Antiscalants, cleaning chemicals | None |
Operating Pressure | Ambient | 10–80 bar | 1–4 bar |
Selective Ion Removal | Yes (voltage-tunable) | No | No |
Capital Cost | Medium | Medium-High | High |
When to Choose Each Technology
Choose CDI when treating low-to-moderate salinity water where energy efficiency is paramount. CDI excels in selective ion removal applications. Choose RO for broad-spectrum desalination across all salinity levels. Choose EDI when ultrapure water is the target and RO permeate needs further polishing. Many facilities combine these technologies: RO for primary desalination followed by EDI for final polishing, or CDI as an energy-efficient alternative for lower-salinity streams.
FAQ
Q: Can CDI replace RO for desalination? A: CDI is not a direct replacement for RO in high-salinity applications. CDI is most efficient below 3,000 mg/L TDS, while RO handles up to 45,000 mg/L.
Q: Why does EDI require RO permeate as feed? A: EDI ion exchange resins can only handle low ionic loads. Feed water above 40 mg/L TDS overwhelms the resin capacity faster than the electric field can regenerate it.
Q: What is the typical lifespan of each system? A: CDI electrode stacks last 5–10 years, RO membranes 3–5 years, and EDI modules 5–8 years.
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Tech Inc. provides complete desalination and deionization solutions including CDI systems, RO membranes, and EDI modules. Visit techincresearch.com for customized system design.
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