United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA-600/S1-83-013 Sept. 1983
&EPA Project Summary
Study of Microbial Aerosols
Emitted from a Water
Reclamation Plant
Kerby F. Fannin and Stanley C. Vana
The purpose of this investigation
was to determine the occurrence of
selected microorganisms in the air in
the vicinity of the O'Hare Water Recla-
mation Plant (OWRP), Des Plaines,
Illinois. The contribution of the OWRP
to ambient microbial aerosols was de-
termined by comparing baseline, or
preoperational, observations during fall
and spring/summer months to those
made after operation was initiated.
Three sampling sites were positioned
< 150 m, 150 to 250 m, and > 250 m
downwind, while one location was up-
wind of the center of the two-stage
activated sludge aeration tanks. De-
pending upon the wind direction, the
first downwind site was frequently
positioned at < 5 m from the edge of
the aeration tanks, with the other
downwind sites proportionally nearer
to this tank boundary.
Air sampling volumes were based
upon predetermined sensitivity levels
for each group of microorganisms. At
each site, multistaged impactor and
slit samplers were used to determine
total aerobic bacteria-containing par-
ticle concentrations and particle size
distributions. In addition, "large volume"
air samplers, that included electro-
static precipitator and cyclone scrubber
samplers, were used to detect aerosols
of standard plate count organisms,
total coliforms, fecal coliforms, fecal
streptococci. Salmonella sp., other or-
ganisms within the total coliform group,
coliphages of Escherichia coli C3000,
and animal viruses detectable with
Buffalo green monkey kidney (BGMK)
and WI-38 cell cultures.
Low concentrations of several aero-
bic bacteria species and of certain coli-
phages were present in the air sur-
rounding the newly constructed acti-
vated sludge plant before operation
was initiated. After plant operations
began at 21 to 67% of its design capac-
ity of approximately 270,000 mVd
[72 million gallons per day (MDG)], the
frequency of detection of all micro-
organisms studied increased at the
< 150 m downwind locations. The geo-
metric mean total aerobic bacteria-
containing particle (TABCP) concen-
trations, determined with slit samplers,
increased from 59 to 218 colony form-
ing units (cfu)/m3 during the night-
time and from 34 to 57 cfu/m3 during
the daytime. The TABCP concentra-
tions determined with Andersen sam-
plers increased from 125 to 281 cfu/m3
during the nighttime and from 87 to
234 cfu/m3 during the daytime.
Using large volume scrubber (LVS)
samplers at the first downwind loca-
tion, standard plate count (SPC) or-
ganism geometric mean concentra-
tions during the fall nighttime increased
from 55 to 1325 cfu/m3 and during
the fall daytime from 49 to 220 cfu/m3.
Increases from 0.30 to 5.03 cfu/m3 for
total coliforms, 0.12 to 1.02 cfu/m3 for
fecal coliforms, 0.14 to0.66 cfu/m3for
fecal streptococcus organisms, and
0.004 to 0.095 most probable number
plaque-forming units (mpnpfu)/ m3 for
coliphages were also observed at this
first downwind site after operations
started. At 150 to 250 m downwind from
the center of the aeration tanks aerosol
concentrations of total coliforms, fecal
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coliforms, fecal streptococci, and coli-
phages were significantly higher during
plant operations than before such opera-
tions started. When the aerosol concen-
trations of these organisms atthe>250
m downwind site during plant opera-
tions were compared to preoperation
concentrations, however, no significant
(p < 0.01) differences could be detected
from any group except for the coliphages.
Microbial aerosol concentrations
were generally higher during the night-
time than during the daytime. The total
coliform bacteria in aerosols during
plant operations were predominantly
Enterobacter sp., Escherichia sp., and
Klebsiella sp., respectively. Animal
viruses were detected at < 150 m
downwind from the center of the aera-
tion tanks in BGMK but not in WI-38
cells in two of twelve downwind air
samples having total assay volumes of
385 to 428 m3. Of the three virus
isolates, two were identified as cox-
sackievirus B-1. The other virus was
not identified by the antisera pools
used.
The low-level concentrations of mi-
crobial aerosols observed before plant
operations began did not increase be-
yond the perimeter of the plant on the
east south, and west sides during
plant operations. Depending upon the
meteorological and diurnal conditions,
the concentration of certain micro-
organisms could occasionally increase
beyond the north plant boundary. These
concentrations, however, are very low
(< 1 cfu or mpnpfu/m3) and require
very sensitive methods for detection.
This Project Summary was developed
by EPA's Health Effects Research Lab-
oratory, Research Triangle Park, NC. to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Population growth within large urban
regions necessitates expansion of existing
wastewater treatment systems for pro-
cessing increased volumes of sewage prior
to utilization or discharge. Locating new
wastewater treatment facilities in densely
populated regions, however, requires con-
sideration of the potential environmental
and health effects of their operation. Mi-
crobial aerosols are emitted by waste-
water treatment processes into the sur-
rounding air. Activated sludge treatment,
for example, generates small bubbles by
diffused air aeration that adsorb and con-
centrate suspended bacteria and viruses
as they rise through the sewage depth in
the aeration tank to the surface boundary.
At this boundary, a surface film containing
microorganisms is disrupted as these rising
bubbles burst, releasing tiny aerosol drop-
lets containing the bubble-adsorbed, as
well as the surface film-associated micro-
organisms.
The nearly instantaneous evaporation
which may occur as these droplets be-
come suspended in air leaves dried resi-
dues referred to as droplet nuclei that are
subject to downwind dispersion. The sur-
vival and dispersion of the organisms that
may be associated with these droplet
nuclei are affected by organism character-
istics and environmental factors such as
relative humidity, temperature, irradiation,
wind velocity, atmospheric stability, and
atmospheric pollutants.
While processes of wastewater treat-
ment have shown to generate microbial-
laden aerosols that can be carried down-
wind, the occurrence of potentially infec-
tious microbial aerosols per se does not
provide evidence of associated health
risks. No conclusive evidence is yet avail-
able that demonstrates that persons resid-
ing in the vicinity of wastewater treatment
facilities are subjected to greater health
risks than those who do not dwell in such
areas. Placing such facilities in regions of
high population densities has, however,
initiated concerns regarding the health
implication of exposure to microorganism-
containing wastewater aerosols.
One such facility, the O'Hare Water
Reclamation Plant (OWRP), located in the
City of Des Plaines, Illinois, was con-
structed to be operated as part of the
regional Metropolitan Sanitary District of
Greater Chicago (MSDGC) system. The
proximity of this plant to a residential area
has been the subject of concern over the
past several years because of the potential
for exposure to plant-emitted microbial
aerosols. Because no data were available
to determine the potential for community
exposure to microbial aerosols that might
be emitted from this plant, this study was
initiated to determine the probability of
such exposure over a wide range of envi-
ronmental and meteorological conditions.
The probability of community exposure
was evaluated by comparing the preopera-
tional, or baseline, plant site microbial
aerosol contribution to the surrounding
environment to that observed after initia-
tion of plant operations. This study was
intended to provide data on whether or not
significant increases in microbial aerosols
could be attributed to facility operations
during different seasons and atmospheric
conditions.
Conclusions
1. When operating at 21 to 67% of its
design capacity, the OWRP is a source
of aerosols containing bacteria anc
viruses.
2. Significant aerosol concentration in-
creases over the baseline at < 1 50 nr
downwind from the center (or, depend
ing on the wind direction, to within 5 IT
from the edge) of the aeration tanks
were observed for total aerobic bacteria
containing particles, standard plat*
count organisms, total coliforms, feca
coliforms, fecal streptococci, and coli
phages. The total coliform aerosol;
identified were predominantly Entero
bacter sp., Escherichia sp., and Kleb
siella sp. Animal viruses from assa'
volumes ranging from 385 to428 m:
in two cell culture lines were detectei
in two of twelve downwind air samples
Of three virus isolates, two were identi
fiedascoxsackievirusB-1 and the thin
was not identified with the antiser
pool used.
3. At 1 50 to 250 m downwind from th
center of the aeration tanks, no sic
mficant increases in microbial aeros<
concentrations were observed durin
the daytime after the plant began opei
ations. When considering both daytim
and nighttime samples, however, sic
mficant increases were observed fc
total coliforms, fecal coliforms, feci
streptococci, and coliphages. The cor
centrations of these organisms at 1 5i
to 250 m downwind sites decrease
substantially from those observed ;
the < 1 50 m downwind location
during plant operations. These concei
trations decreased by 85% (5.0 1
0.77 cfu/m3) for total coliforms, t
76% (1.02 to 0.24 cfu/m3) for fee
coliforms, by 33% (0.66 to 0.4
cfu/m3) for fecal streptococci, and I
68% (0.004 to 0.002 mpnpfu) fi
coliphages.
4. Aerosol concentrations did not signi
cantly increase after the plant bega
operations for any bacteria studied
sampling distances beyond 250
downwind from the center of the aer
tion tanks. The frequency of detectic
did, however, increase from 38 to 79
for total coliforms, from 0 to 63% f
fecal coliforms, and from 69 to 89% f
fecal streptococci. Coliphageconce
trations were, however, significan1
higher and their frequency of detectii
increased from 22 to 86% after tl
plant began operations.
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5 Bacteria aerosol concentrations were
directly related to sewage flow rate
within 1 50 m downwind of the center
of the aeration tanks during the fall
season of plant operations, but, at
downwind locations greater than 1 50
m downwind, inverse correlations were
observed at night.
6. During plant operations, bacteria aero-
sol concentration was directly related
to wind velocity during the spring/
summer season at locations < 250 m
downwind of the center of the aeration
tanks. Before operations, negative cor-
relations were found at upwind and
1 50 to 250 m downwind locations.
7. Bacteria aerosol concentrations were
directly related to temperature at loca-
tions within 1 50 m downwind of the
aeration tanks during plant operations.
At nighttime, however, negative corre-
lations were observed at locations >
250 m downwind and upwind.
8. Bacteria aerosol concentrations were
generally inversely related to relative
humidity.
9. Fecal streptococci and coliphages ap-
pear to be more stable in aerosols than
the other indicator bacteria studied.
10. Low-level concentrations of bacteria
and coliphages were present in the air
in the vicinity of the OWRP before the
plant began operations. These con-
centrations did not increase beyond
the perimeter of the plant on the east,
south, and west sides during plant
operations. Depending upon the me-
teorological and diurnal conditions,
the concentration of certain micro-
organisms could occasionally increase
beyond the north plant boundary.
These concentrations, however, are
low (< 1 cfu or mpnpfu/m3), and
require very sensitive methods for
detection.
Recommendations
1. Selected microbial aerosol parameters
should be monitored at the OWRP
boundary during the nighttime when
the plant begins operation at full capac-
ity. These data should then be com-
pared to the baseline observations
made in this study to determine wheth-
er significant concentration increases
occur at higher sewage flow rates.
2. Coliphages and fecal streptococci ap-
pear to be stable as aerosols and are
recommended as indicators of poten-
tial sewage-borne aerosol contamina-
tions.
This report was submitted m fulfillment
of Grant No. R-806062 by IIT Research
Institute and The Institute of Gas Tech-
nology under the sponsorship of the U.S.
Environmental Protection Agency. This
report covers a period from July 24, 1 978
to June 30, 1981, and work was com-
pleted as of October 31, 1981.
Kerby F. Fannm is with the Institute of Gas Technology, Chicago, IL 60616, and
Stanley C. Vana is with the IIT Research Institute, Chicago, IL 60616
Walter Jakubowski is the EPA Project Officer (see below).
The complete report, entitled "Study of Microbial Aerosols Emitted from a Water
Reclamation Plant," (Order No. PB 83-234 906; Cost $14.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U S Environmental Protection Agency
Research Triangle Park, NC 27711
US GOVERNMENT PRINTING OFFICE 1983-659 017-7193
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