IEEE Spectrum April, 2008 - 7

cialize CDI because of the
proximity of parched cities
to coal-bed gas mines, where
pressurized underground
water is used to release the
trapped gas. The by-product
is water that, though ample,
is too brackish even for most
agricultural uses. Many in the
water industry have predicted
that Australian demand
for water-purification
technology will spike as
the mining industry taps
the deep coal deposits in
Australia's largest aquifer.
The reason reverse
osmosis has dominated
the market, and hence
discouraged research into
other methods, is that
municipalities wanting
water desalination have
usually been coastal: huge
desalination plants are
built on shorelines in
the Middle East, China,
California, and Texas.

what are
the ChanCeS?

m

artin Hellman,
professor emeritus
at Stanford, used
engineering risk analysis
methods to determine
the failure rate for the
United States' nuclear
deterrence strategy and
came up with a shocking
1 percent chance per
year that a nuclear
war will break out.
More at http://www.spectrum.ieee.
org/apr08/deterrence

12

Na * iEEE SpEctrum * april 2008

Solid Smoke: superporous carbon aerogels are cDi's secret.
photo: JpL/nasa

Where the water's salt
content is high-it's about
32 000 milligrams per liter
in ocean water-reverse
osmosis is efficient and costeffective. But for inland brackish waters, in which there
might be 800 to 3500 mg/L
of salt, CDI requires less
energy, says Frost & Sullivan
analyst Afamia Elnakat.
Until recently, opportunities for inland
desalination were
scarce because, as
Elnakat says, "the
water problem just
hasn't hit anyone in
the pocket yet." But
inland droughts
are starting to
become ruinous.
In the past two
years, water levels
in northeastern
Australia have
dropped to one
quarter of their
normal depth,
causing barley and
wheat production
to plummet (and
contributing to the
country's decision
to sign onto the

Kyoto climate agreement).
Similar long-term droughts
have laid waste to water
supplies in China and in the
southwestern United States.
In these situations, CDI is a
clear winner, argues Campbell.
Its main efficiency advantage
versus reverse osmosis is that
it doesn't need pressurized
water. CDI can also save
power by allowing for "dialin" ion concentrations: for
medically pure water, for
example, the reactors can
remove all dissolved ions;
but for agriculture the water
can be somewhat saltier.
The fewer ions that need to
be removed, the longer the
reactors can go between rinses.
And deionization might
play a role in seawater
desalination too. The World
Health Organization warns
that the natural boron
content in seawater has been
linked to developmental
and reproductive disorders.
Boron ions can slip through
reverse osmosis systems.
Campbell says that CDI can
be a postosmosis "polishing"
step to filter the boron.
-Sarah Adee
www.spectrum.ieee.org

Jeff toppInG/the neW york tImes/redux

numbers of ions before they
were saturated, but they were
also prone to clogging up
with bacteria, which feed on
organic particles in the water.
Bob Campbell, CEO of
California-based Campbell
Applied Physics, which is
managing the Australia
project, tackled the problem.
With funding from Maltabased Water Resources
International, Campbell
worked with four U.S.
Department of Energy
national laboratories, among
them Lawrence Livermore.
The team developed a
proprietary ozone technology
that kills the bacteria before
they can fill the aerogel's
pores, says Lawrence
Livermore technologist Bill
Daily, who is developing
the deionization reactors
for the Australia project.
Northeastern Australia
will be the first to commer-
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Table of Contents for the Digital Edition of IEEE Spectrum April, 2008
