Many municipalities tap into the benefits of EDR water treatment
Diagram of a hollow fibre UF membrane.
No one wants to drink radium.
Or nitrates. Or arsenic.
Methods like electrodialysis
reversal (EDR), provide
treatment options.
Just ask the citizens of Washington,
Iowa. In 1979, Washington was notified
by the Iowa Department of
Natural Resources that the city was in
violation of the radium standard for
drinking water. Even then, radium was
recognized as a carcinogen. The city
evaluated a number of options for
improving the water quality and
removing the radium from the water.
They decided on implementing the
process known as EDR, a relatively
new variation on the electrodialysis
process which had been commercialized
by Ionics. The technology was
incorporated in the 1950s.
Today, there are many other examples
of cities, towns and municipal
organizations that have found EDR
demineralization to be an economical,
high-performance way to transform
unusable water into safe drinking
water. Major applications for EDR
include: the purification of drinking
water from brackish sources; demineralization
of water from industrial
processes; reuse of municipal effluent;
and reduction of mineral concentrations
in wastewater.
A self-cleaning process
EDR is a variation on the electrodialysis
process, in that it uses electrode
polarity reversal to automatically
clean membrane surfaces. The electrodialysis
process uses a driving force of
direct current (DC) power to transfer
ionic species from the source waterfeed
water through cation (positively
charged ions) and anion (negatively
charged ions) transfer membranes to a
concentrate wastewater stream, creating
a more dilute stream.
EDR works the same way, except
that the polarity of the DC power is
reversed two to four times per hour.
When the polarity is reversed, the
sourcewater dilute and concentrate
compartments are also reversed. The
alternating exposure of membrane surfaces
to the product dilute and brine
concentrate streams provides a selfcleaning
capability that enables purification
and recovery of up to 94% of
the feed water.
There are currently a number of
alternatives to the EDR technology for
treating and reducing contaminants in
drinking water and feed water.
Probably the most well-known of these
is reverse osmosis (RO). Both EDR
and reverse osmosis use semipermeable
membranes to filter out dissolved
ions from water. But where RO uses
the application of pressure to overtake
osmotic pressure and shift the water
flow force water through the membranes,
EDR uses voltage potential
and polarity reversal to flush out the
unwanted particles to force contaminants
through the membranes.
An evolving technology
Over the last 10 to 15 years, numerous
advances in membrane and system
technology are claimed for EDR, both
in terms of performance and cost effectiveness.
Improved membrane
technology now allows for one-step
machine manufacture of ion exchange
membranes, reducing costs and lowering
membrane resistivity. And new
high performance spacers (placed
between the membranes) allow better
transport of contaminants like nitrates,
speeding the process, reducing the
number of membrane stacks required
and shrinking costs.
Major improvements to EDR system
design are claimed in the form of
the next generation Ionics EDR 2020®
system. This new design streamlines
the process flow with simpler
hydraulics and standardized components,
substantially lowering the capital
and operating costs of EDR demineralization.
It features the new
spacer technology, as well as a more
compact design that is said to be easy
to install in an array of configurations.
The new generation EDR systems,
with up to half as many membrane
stacks, standardized components and
simpler hydraulics, have demonstrated
a 30% reduction in capital cost savings.
Contact Ionics, Incorporated: Francine
Bernitz, e-mail: fbernitz@ionics.com
or Antonia von Gottberg, e-mail: avongottberg@ionics.com.
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