[CPEO-MEF] New Device Removes Drinking Water Contaminants

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June 17, 2002

New Device Removes Drinking Water Contaminants


Two hollow-fiber membrane biofilm reactors shown in series as part of a
pilot study in southern California. [more detail]
EVANSTON, Ill. — A Northwestern University environmental engineer has
received a U.S. patent for a treatment device that renders perchlorate —
a thyroid-damaging ingredient of rocket fuel and a drinking water
problem — harmless. The applications extend beyond the safety of
drinking water and this one pollutant.

Bruce E. Rittmann, John Evans Professor of Environmental Engineering at
the Robert R. McCormick School of Engineering and Applied Science,
received U.S. Patent No. 6,387,262 for a hollow-fiber membrane biofilm
reactor, that, through a natural biochemical process of electron
transfer, turns perchlorate into innocuous chloride.

The cost-effective and environmentally friendly system also works on
nitrate, a contaminant from agricultural fertilizers that can cause
methemoglobinemia, or blue-baby syndrome, in infants, and is expected to
be successful with other oxidized pollutants, such as bromate, selenate,
heavy metals, radionuclides, and a range of chlorinated solvents,
including trichloroethylene, a problem in the semiconductor industry.

Currently there is no effective clean-up solution for perchlorate, which
was discovered in the water supplies of a large number of states in the
late 1990s, and existing methods are not always successful when dealing
with other contaminants.

"Many emerging pollutants are difficult to treat with conventional
methods," said Rittmann. "These methods do not destroy the contaminants
but simply move them from place to place, from the water to a solid
resin to a nasty brine that still contains the contaminants. Our simple
method, which destroys the contaminant, should work for almost every
oxidized pollutant, which means it has an incredible range of
applications, including being used on more than drinking water."

Rittmann has teamed up with the environmental engineering firm
Montgomery-Watson-Harza Engineers, Inc. to conduct a pilot study in La
Puenta, Calif., treating groundwater that is highly contaminated with
perchlorate and nitrate. Results have shown that the biofilm reactor can
effectively treat 0.3 gallons of water per minute, removing perchlorate
and nitrate at the same time.

The decontamination process takes advantage of a community of
microorganisms that lives as a biofilm on the outer surface of the
membranes in the system. The microorganisms, found naturally, act as
catalysts for the transfer of electrons from hydrogen gas to the
oxidized contaminant, such as perchlorate or nitrate. Chemically
speaking, the oxidized contaminants are eager to receive electrons,
which reduces them to harmless products. The hydrogen gas supplies the
electrons, and the biofilm microorganisms are the agents for the
transfer.

A bundle of 7,000 hollow-fiber membranes are in one of the pilot-study
biofilm reactors, a column approximately 5 feet tall and 18 inches in
diameter. Each membrane is like a long, very thin straw, only 280
micrometers in diameter (the width of a thick sewing thread). Hydrogen
gas is fed to the inside of the membrane fibers, and the hydrogen
diffuses through the membrane walls into the contaminated water that
flows past the fibers. At this meeting point, on the outside of the
membrane, bacteria attach to the surface because they gain energy from
the process of transferring electrons and can grow and thrive. The
contaminants are reduced to harmless end products — perchlorate to
chloride and nitrate to nitrogen gas — while the hydrogen gas is
oxidized to water.

"We are exploiting nature," said Rittmann. "Life is all about
transferring electrons. We have an extraordinarily efficient system for
bringing hydrogen and its electrons to oxidized pollutants, such as
perchlorate, and reducing them to innocuous substances."

Hydrogen gas is an ideal electron donor for biological drinking water
treatment as it is non-toxic and inexpensive, and Rittmann’s system has
been shown to be safe. Another advantage is that the performance of the
reactor can be controlled simply by adjusting the pressure of the
hydrogen gas.

Rittmann also is conducting research on the microbial ecology of the
bioreactor system in order to understand how it works. Which
microorganisms are doing the work? How fast do they work? How do they
achieve the essential reaction of electron transfer?

"By looking at the details of what’s going on in the biofilms, we can
make the system even more reliable and efficient in cleaning up some of
the most dangerous and newly discovered contaminants in drinking water,
ground water and wastewater," said Rittmann.

The current research is supported by a grant from the U.S. Environmental
Protection Agency and administered by the American Water Works
Association Research Foundation.

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