Electrodialysis-Reverse Osmosis Technology (EDI-RO)

In a system with an ion-exchange membrane reverse osmosis (EDI) module: After reverse osmosis, ion-exchange technology is used to further purify the deionized water to achieve the final low conductivity and low silicon content levels. Therefore, in most applications, we tend to use a two-pass reverse osmosis water purification system. So, EDI uses ion-exchange membranes, ion-exchange resins, and electricity. Therefore, they can produce high-quality water without the need for regeneration downtime. EDI is a substitute for traditional mixed-bed purifiers.

What is a two-pass reverse osmosis RO system?

In a reverse osmosis system with an electro-deionization system, the two-pass reverse osmosis (DPRO) system refers to introducing the permeated water into the second RO unit to further produce purer water. Therefore, two-stage or dual-stage RO means introducing the concentrated liquid or waste liquid separately into the second RO system to recover water. So, a reverse osmosis system is simply to purify water by removing approximately 99% of total dissolved solids from the feed water. Meanwhile, a single-pass RO system simultaneously produces product water (permeated water) and waste liquid (concentrated liquid). Therefore, most reverse osmosis + EDI systems have a two-pass RO unit.

How does the two-stage reverse osmosis system work? The principle of the two-stage reverse osmosis system is as follows:

The two-stage reverse osmosis system consists of two reverse osmosis systems (the first stage and the second stage), where the volume flow capacity of the first stage is greater than that of the second stage. An intermediate water storage tank can be set between them. The permeate water or concentrated water from the first-stage reverse osmosis system can be stored in this water tank and then sent to the second-stage reverse osmosis system. Further filtration treatment or direct connection from the permeate water outlet of the first-stage reverse osmosis system to the inlet of the second-stage reverse osmosis system can be done.

During the treatment process using the electro-deionization reverse osmosis (EDI) system, pre-treatment may be necessary initially. If the application purpose is to achieve water recovery, then pre-treatment needs to be provided for the first and second-stage reverse osmosis systems. Because the water quality of the first-stage effluent is already close to saturation. On the other hand, if the application only requires first-stage pre-treatment, then only the first-stage pre-treatment may be needed. If it will be used as the permeate liquid for the second-stage treatment.

Why use a reverse osmosis system with an electro-deionization module?

Based on our experience, if the influent concentration of the electro-deionization module is lower than 20us/cm, the efficiency and service life of the module will be greatly improved. For the two-stage reverse osmosis system with an electro-deionization module, we tend to choose membrane products like those used by other well-known water treatment companies, such as Dow FilmTec membranes, IonPure or General Electric electro-deionization modules.