A Citizen's Guide to
Air Stripping
What Is Air Stripping?
Air stripping is the process of moving air through
contaminated groundwater or surface water in an
above-ground t'eatment system. Air stripping removes
chemicals called "volatile organic compounds" or" VOCs."
VOCs are chemicals that easily evaporate, which means
they can change from a liquid to a vapor (a gas). The
air passing through contaminated water helps evaporate
VOCs faster. After treating the water, the air and chemical
vapors are collected, end the vapors are either removed
or vented outside if VOC levels are low enough. Air
stripping is communly used to treat groundwaier as
part of the "pump and treat" cleanup method. (See .A
Citizen's Guide to Pump and Treat [EPA 542-12-017].)
How Does It Work?
Air stripping uses either an air stripper or aeration tank
to force air through contaminated water and evaporate
VOCs. The most common type of air stripper is a
packed-column air stripper, which is a tal tank fillec with
pieces of plastic, steel, or ceramic packing material.
Rising Air and
Vnpora to TreatiTwinl
Contaminated
Water Enters
Air SUFp|Xr
Water Is Sp-ayed Over
Packing Uaurla.
Witor Trice tot
TtvouQh ft« Picking
IMNM
Air
Bto»n In
Ch
Water Out
Contaminated water is pumped above ground and
into the top of the tank and sprayed over the top of the
packing material. The water trickles downward through
the spaces between the packing material, forming a thin
film of water that increases its exposure to air blown in at
the bottom of the tank. A sieve-tray air stripper is similar
in design but contains several trays with srrall holes. As
water flows across the trays, a fan at the bottom blows
air upwards through the holes, increasing air exposure.
Aeration tanks are another type of design that remove
VOCs by bubbling air into a tank of contaminated water.
Rising air and vapors accumulate at the top of the air
stripper or aeration tank where they are collected for
release or treatment. Treated water flows to the bottom.
where it is collected and tested to make sure it meets
cleanup requirements. The water may be further treated,
if necessary, to achieve required levels. Clean water
may be pumped back underground, into local surface
waters, or to the municipal wastewater treatment plant
Aeration tanks are typically shorter than packed-column
or sieve-tray air strippers. The size and type of air
stripper used will depend on the types and amounts of
contaminants as well as the quantity o* water requiring
treatment.
How Long Will It Take?
The flow of water through an air stripper or aeration
tank may take only a few minutes, depencing on the
size of the device and the rate of water flow through it.
However, cleanup of all the contaminated water at a site
can take several months to years. The actual cleanup
lime will depend on several factors. For example, it will
take longer where:
• Contaminant concentrations are high or the source
of dissolved contaminants has not been completely
removed
• The amount of v/ater requiring treatment is large.
Groundwater cannot be pumped at a fast rate.
Buildup of mineral deposits or algae on the packing
material require frequent removal.
Packed-Column Air Stripper
These factors vary from site to site.
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Is Air Stripping Safe?
Air stripping is generally considered to be safe to use. Air strippers may be
brought lu the bite so lhat contaminated water does not have to De transported
to a cleanup facility. Contaminated water is contained throughout cleanup so lhat
there is little chance for people to come into contact with it. The treated water
usually may be returned to the groundwater or discharged to surface water. The
cherrical vapors produced by air stripping are treated, if necessary, to ensure
unsafe levels of vapors are not released.
How Might It Affect Me?
Installation of the air stripper
and treatment equipment
may require use of heavy
machinery, especially at
large contaminated sites.
Area neighborhoods may
experience some increased
truck traffic as the equipment
is delivered. Large tanks or
columns may be visible from
the street and may need
to operate for many years.
However, care is taken to
make sure the operation of
ar strippers is as quiet as
possible.
Air stripper and trfialrrtfiot building
Why Use Air Stripping?
Air stripping is an effective
way of removing VOCs from
contaminated water and is
commonly used as part of
grnundwater pump and treat
systems at sites around the
country, Air strippers can be
brought to the site eliminating
the need to pump contaminated
water for offsite treatment.
Sample plastic packing material.!Photo from Mass
Transfer, Ltd.)
Example
Air stripping is part of the
treatment tor four ground water
pump and treat systems
operating at the \orth Indian
Qend Wash Superfund site
in Arizona. Ground water at
the site is contaminated with
an industrial solvent called
trichloroethene {TCE) and
other VOCs. Contamination
extends ever an area of about
8 square miles anc :o depths
over 100 feet.
The first pump and treat
system began operating in
1994 The ylhers were adced
later to improve cleanup. Tne
packed-column air strippers
remove VOC vapors, which
arc then treatec with activated
carbon and another method
called "ultraviolet oxidafcon."
Cleaned water is discharged
to an area irrigation network
and reservoir. As of 2011, over
40,000 pounds of TCE had
been removed, anc cleanup
cf tome areas was rtearty
ccnpJele. The systems are
expected to operate for another
40 '.o 70 years to dean up the
entire site.
For More Information
For more information on this
and other technologies n the
Citizen's Guide Series, con:act
U.S. EPA
Technology Innovation &
Reid Servces Diviaon
Technology Assessment B'anch
(703)603-9910
NOTE: This fact sfieef is intended soiely as general information to the public. It is not intended, nor can it be relied upon, to create any rights
enforceable by any party in litigation with the United Statos. or to ondcrss the use of products or services provided by specific venocrs The
Agency also reserves the nght to change tn>s fact sheet at any time without puolic notice.
United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
151023]
EPA 542 F 12 002
September 2012
www.epa.BOv/superfund/sites
www.clum.org
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