Membrane and Desalination Technologies - TCE Moodle Website

Desalination of Seawater by Thermal Distillation and Electrodialysis Technologies 547
Fig. 12.15. Deposition and displacement of colloidal particulates during EDR operation.
The EDR system has a wide flow capacity ranging from 500 gal/d up to 1.6 million gal/d.
By using multiple stages (stacks in series), the systems are designed to handle a wide range of
treatment needs. It is able to reduce TDS with an efficiency of 50–95%.
The major advantage of EDR over RO is that it is not necessary to feed chemicals at remote
water treatment sites. EDR and RO compete with one another on many desalting projects.
EDR offers advantages over RO on some applications. It can be applied to reclaim the
RO concentrate of approximately 8,000 mg/L TDS. The combined RO–EDR system in
Fig. 12.16 can yield up to 96% of recovery (18). EDR is not affected as many feed water
constituents as RO. The EDR can take raw water with turbidity up to 2 nephelometric
turbidity unit (NTU), whereas the RO cannot function well if the turbidity is above 1 NTU.
The oil & grease (O&G) of raw water to the EDR is up to 1 mg/L, whereas the raw water to
RO must be O&G free.
Particles and microorganisms are not removed by the EDR (also ED). Hence, posttreatment
of the product water becomes necessary. Filtration and disinfection by chlorination can