CDI vs RO vs EDI: Choosing the Right Technology

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. It is gaining traction in brackish water treatment, agricultural water recycling, and selective ion removal applications.

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 can treat water ranging from low-TDS brackish to high-TDS seawater (up to 45,000 mg/L). It is the industry standard for desalination plants, ultrapure water production, and industrial wastewater reuse.

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. It is essential in semiconductor fabrication, pharmaceutical manufacturing, and power plant boiler feed water.