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DISINFECTION AND FLUSHING
OF AIRCRAFT DRINKING WATER SYSTEMS
Background
Hie goal of this project was to better understand
how aircraft drinking water systems become
contaminated with bacteria and to investigate
remedies. Under the Aircraft Drinking Water
Rule, drinking water systems in commercial
United States flagged aircraft are categorized as
Transient Non-Community Water Systems. As
such, airline employees collect total coliform
bacteria samples and conduct disinfection and
flushing of the water system on a routine,
approved schedule. Generally, coliform bacteria
are not harmful, but, when detected in water
systems, they indicate that other potentially
harmful fecal bacteria could be present. National
data indicate that the drinking water systems in
some aircraft models have experienced more
positive total coliform water samples from the
aircraft lavatory than from the galley location,
even though both taps are served by the same
onboard water tank. The presence of colifonns in
these tap water samples suggests either cross
contamination via aerosols from the lavatory
wastewater disposal system or bacterial
colonization of the water system during normal
passenger use of lavatory facilities. This project
focused on identifying the bacteria that are the
potential sources of these positive total coliform
assays, on locating potential hotspots for bacterial
colonization within aircraft plumbing materials,
and on investigating the effectiveness of the
airline industry's current disinfection and
flushing procedures.
Approach
A Materials Cooperative Research and
Development Agreement was signed by the
U.S. Environmental Protection Agency's
(EPA's) Office of Research and
Figure 1: Mock aircraft water system
constructed at EPA's Test and Evaluation
Facility in Cincinnati, Ohio.
Development (ORD), Boeing Commercial
Airplanes, and air carriers in EPA Region 6
to share equipment and technical expertise.
This Regional Applied Research Effort
(RARE) project, part of the ORD program
to respond to the high-priority, near-term
research needs of EPA's regional offices,
consisted of two phases. Phase 1 was
focused on isolating coliform bacteria from
commercial aircraft. EPA Region 6 and
ORD scientists worked with regional air
carriers and their contract water testing
laboratories to have positive total coliform
water samples shipped overnight to the
EPA's ORD laboratory in Cincinnati for
concentration and isolation studies. Aliquots
of the media were cultured on solid nutrient
media to recover isolates, which were then
identified to the species level using both
biochemical testing and DNA sequencing
methods.
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U.S. Environmental Protection Agency
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In Phase 2 of the project, a mock up of a Boeing
737 aircraft water system was constructed (Figure
1).	The coliform strains isolated and identified in
Phase 1 were used to conduct seeding studies in
the mock system to understand the possible
locations within the aircraft drinking water
plumbing system that were susceptible to
bacterial colonization. Once the mock system had
been contaminated with coliform bacteria,
researchers tested the effectiveness of various
decontamination procedures used by the air
carriers to disinfect any residual coliforms.
Results arid Impact
With assistance from the project's air carrier
collaborators, 38 positive total coliform samples
from 35 different aircraft were received. Most of
the positive samples were from lavatories with
one sample from a galley location. A total of 161
bacterial isolates were recovered by ORD. The
isolated bacteria are commonly found in the
environment. Aliquots of these isolates were
incubated 111 sections of the plumbing material
that makes up the aircraft water systems (Figure
2),	and the ability of the microorganisms to form
bioftlms (i.e., to stick and grow on the pipe wall)
was assessed. The three isolates with the greatest
biotilm forming potential were used to inoculate
the mock system.
Aircraft water systems are commonly disinfected
and flushed using disinfectants such as chlorine
dioxide or ozone. These disinfectants, along with
a novel mixed oxidant solution, were then used
separately to disinfect the mock aircraft water
system after inoculation with the coliforms
isolated in Phase 1. Results showed that while
some of the coliforms colonized water tube
sections under laboratory conditions, isolates
were not observed to persist on or to colonize
water system tubing and fittings in dechlorinated
water in the mock system. This suggests that
coliforms do not readily form bioftlms or persist
in airplane drinking water systems. The only
place that coliforms were detected after
disinfection and flushing were on lavatory faucet
aerators when ozone or mixed oxidant solutions
had been used for disinfection. Standard aircraft
procedures for disinfecting individual aerators
(using Glyco-San® [Celeste Inc., Easton, MD ] or
Lysol® [Reckitt Benckiser LLC, Parsippany,
NJ]) were tested. After disinfection, no coliforms
were detected on the aerators. Overall, coliforms
were not detected on tubing, fittings or in the
water phase after disinfection and flushing with
chlorine dioxide, ozone or mixed oxidant
solutions. The disinfection and flushing
procedures with chlorine dioxide and ozone
appear adequate when coupled with further
disinfection (or replacement) of faucet aerators,
which is standard practice for US based
commercial air carriers.
Figure 2. Sections of aircraft water system
tubing.
The project further investigated how one
commercial product called Purogene® (Bio-Cide
International, Inc., Norman, OK) performed in
the creation of chlorine dioxide (CIO2). Purogene
is a blend of chlorine compounds containing
purified sodium chlorite, which, when activated,
produces chlorine dioxide. Laboratory scale
analyses indicated that, over time, active chlorine
dioxide increases significantly. As the
concentration of chlorine dioxide increases,
chlorite is consumed (Figure 3). Once the active
Purogene® is added to water in the aircraft water
tank, the reaction degrading chlorine dioxide is
quenched such that more active chlorine dioxide
is present, but less chlorite is available to
maintain the chlorine dioxide concentration.
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These data can be used by air carriers to
understand how long to let a Purogene® solution
activate in order to achieve the appropriate
chlorine dioxide concentration in the aircraft
water system during disinfection and flushing.
Data from the project was shared with the air
carrier community at EPA's 2016 National
Aircraft Drinking Water Conference and at the
2016 EPA International Decontamination
Research and Development Conference. Results
will also be published in the journal Water
Science and Technology: Water Supply (in-
press).
This project allowed EPA Region 6 Aircraft
Drinking Water Rule staff to better comprehend
the mechanics involved in aircraft water systems.
In addition, this RARE project has fostered
greater trust between the air carrier industry and
EPA offices by allowing EPA's regional and
ORD staff to interact with aircraft manufacturers,
air carrier maintenance teams, and air carrier
environmental staff throughout the research
effort.
Contacts:
Jatin Mistry, EPA Region 6
214.665. 7483
mistrv.iatin@epa.gov
Dr. Mark Rodgers, EPA, ORD, NRMRL
513.569.7225
rodgers.mark@epa.gov
Dr. Jeff Szabo, EPA, ORD, NHSRC
513.487.2823
szabo ,i eff@epa.gov
Dr. Michael G. Morton, Regional Science
Liaison, EPA Region 6
214.665.8329
morton.michael@epa.gov
This project was funded through
EPA's Regional Applied Research
Effort (RARE) Program, which is
administered by the Office of
Research and Development's
(ORD) Regional Science Program.
For more information, go to:
https://intranet.ord.epa.gov/regiona
1-science/regional-applied-
research-effort-rare
Chlorine Dioxide (mg/L)
Chlorite (mg/L)
12,000
10,000
8,000
6,000
25,000
22,500
20,000
17,500
15,000
12,500
10,000
7,500
5,000
2,500
0
-2,500
250 500 750 1000 1250 1500
Time (Min)
Figure 3: Increase in Purogene® chlorine dioxide
concentration and decrease in chlorite over time.
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Disclaimer
The U.S. Environmental Protection Agency (EPA) through its Office of Research and Development funded
and managed the research described herein under contract EP-C-12-014 with Aptim. It has been subjected to
the Agency's review and has been approved for publication. Note that approval does not signify that the
contents necessarily reflect the views of the Agency. Any mention of trade names, products, or services does
not imply an endorsement by the U.S. Government or EPA. The EPA does not endorse any commercial
products, services, or enterprises.
The contractor role did not include establishing Agency policy.
U.S. Environmental Protection Agency
Office of Research and Development
EPA/600/S-18/381
December 2018

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