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Objective:
During
winter months at Department of Defense (DoD) air bases, large
amounts of aircraft deicing fluids (ADF) that contain primarily
propylene glycol, ethylene glycol, and additives are used
to ensure flight safety throughout certain adverse weather
conditions. Due to its high biological oxygen demand (BOD),
the runoff from these events must be directed either to stabilization
ponds, the sanitary sewer, or an on-site treatment system,
which may result in high treatment costs or possible overload
conditions. This project validated that constructed wetlands
are an efficient, cost-effective technology for the treatment
of ADF runoff by installing and monitoring a 0.6-acre, pilot,
subsurface-flow treatment wetland.
Technology
Description:
The
subsurface-flow treatment wetland was constructed at Westover
Air Reserve Base (ARB), Massachusetts, by excavation, installation
of a liner, and provision of a porous medium, through which
the wastewater flows, either vertically or horizontally. The
upper layer is a finer medium, into which fast-growing, opportunistic
species (e.g., Phragmites species) are planted to develop
dense root systems. These root systems provide a complex microenvironment
for a multitude of naturally occurring physical, chemical,
and biological removal mechanisms to occur (i.e., sorption,
retention and microbial degradation), attenuating the ADF
contaminants. A subsurface flow design was selected because
it provided insulation from cold temperatures, greater media
area for microbial attachment, and no susceptibility to bird
air-strike hazards.
Results:
Heavy
snows during 2002-2003 at Westover ARB provided the opportunity
to assess the treatment wetlands. A BOD removal rate (i.e.,
loading rate) of 220 kilograms per hectare per day was achieved
during the first season of operation. Peak BOD input concentrations
between 1,000 and 15,000 milligrams per liter (mg/L) were
reduced by more than 50 percent to as low as 133 mg/L during
5 of the 10 deicing events. However, the pilot-constructed
wetland was too small for the higher than anticipated frequency
and severity of deicing events encountered during this first
season. Improved performance is anticipated during the 2003-2004
deicing season, when the plant life will be more mature and
acclimated to the incoming ADF runoff.
Benefits
and Implications:
Constructed
wetlands are a low-cost alternative for the sustainable treatment
of ADF runoff. The nature of the technology is passive and
requires very little operation and management effort, especially
when compared to more active and resource-intensive alternative
treatment technologies currently available off-the-shelf.
The cost of a full-scale installation at Westover ARB was
estimated at $800,000, with an operating cost of $4,000 per
year. On an annualized basis, this would represent a one-third
cost savings over alternative treatment options.
(Project Completed - 2004)
References:
1.
ESTCP Cost and Performance Report. May 2004. (PDF File
Format)
Principal
Investigator:
Mr. Jeff
Karrh
Naval Facilities Engineering Service Center
1100 23rd Avenue, ESC411
Port Hueneme, CA 93043-4370
Telephone: (850) 982-1272
Fax: (805) 982-4304
E-mail: jeff.karrh@navy.mil
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