OPERATORS MANUAL
ORION II
Orion II 500-10000 Operators
Page 90 of 95
Manual Part no: DOMAON0100 Issue A
April 2008
9.2 CEDI
9.2.1 What is Continuous Electrodeionisation
Continuous Electrodeionisation (CEDI) is a continuous process for producing high purity water using
ion-selective membranes, ion exchange resins, and electricity. DC electric potential is the driving
force for removing ions from the feed stream while continuously regenerating the resins. The CEDI
process produces consistent and predictable water quality, better than 99% salt removal, with a RO
feed water conductivity of less than 25 µS/cm.
9.2.2 Technology Description
The CEDI module comprises alternating cation- and anion-permeable membranes. The spaces
between the membranes are configured to create liquid flow compartments with inlets and outlets.
The compartments bound by the anion membrane facing the anode and the cation membrane facing
the cathode are dilute compartments and the compartments bound by the anion membrane facing
the cathode and cation membrane facing the anode concentrate compartments.
The dilute compartments are filled with alternating layers of cation, anion and/or an intimate mixture
of both resins. Liquid to be deionised flows
sequentially through the layers of resins.
A transverse DC electrical field is applied by an external power source using electrodes at the
bounds of the membranes and compartments. When the electric field is applied, ions in the liquid
are attracted to their respective counter-electrodes. The result is that the dilute compartments are
depleted of ions and the concentrate compartments are concentrated with ions.
