Reverse osmosis plus EDI

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Ultrapure water production

Plant with EDI (electrodeionization)

Plants with EDI produce ultrapure water (output conductivity <0.1 µS/cm). They are available both in a complete version with a reverse osmosis system, or as a solitary EDI system (see photo).
The inlet water must be osmotic with a conductivity between 4 and 20 µS/cm.

Operation:
Two elements of water treatment are grouped together in EDI: electrolysis and ion exchange. These two techniques make it possible to eliminate substances with a low energy requirement.

An EDi module includes several cells.
The cell is made up of:
one chamber for the diluted (ultrapure water) and two chambers for the concentrate. In the chambers for the concentrate, ion-selective membranes are inserted in an alternate way, allowing only anions or cations to pass.
We also find a mixed-bed resin.
By inserting current continuously, an electromagnetic field is created which causes the ions to pass towards the anodes or cathodes. These ions are then ejected towards the drain when they are near the contacts.

Water quality

  1. incoming (permeate)
    Osmotic water with a conductivity between 4 and 20 µS/cm, carbon dioxide (CO2) max. 10 mg/l, SiO2 max. 0.5 mg/l, colloidal index max. 0.25, hardness <0.1 ° f.
  2. outgoing (diluat = ultrapure water)
    Ultrapure water with a conductivity below 0.1 µS/cm.
    This conductivity can be influenced by free carbon dioxide (CO2). Because of the gaseous form, carbon dioxide is less attracted to the electric field, compared to other substances present in water. It follows that, in ultrapure water these substances are more present and increase the conductivity. To have a correct conductivity (<0.1 µS/cm) it is necessary to remove this CO2, this is done by adding NaOH or a membrane degasser.
    EDI systems hold (osmotized water inlet):
    ions:> 99%
    Free CO2:> 99%
    Silicate:> 90%
    TOC: 60 – 90%

EDI implants are available in two versions, one including reverse osmosis, the other only an EDI implant (to be added to an existing reverse osmosis).

The flow rates range from 150 up to 2,200 liters per hour (see specific table).

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