United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-90/015 July 1990
4>EPA Project Summary
Technology Assessment of the
Biological Aerated Filter
Arthur J. Condren
The innovative and alternative technol-
ogy provisions of the Clean Water Act
of 1977 (PL 95-219) provide financial
incentives to communities for using
wastewater treatment alternatives that
reduce costs or energy consumption
when compared with those for conven-
tional systems. Some of these technol-
ogies have only recently been developed
and are not in widespread use in this
country. To increase awareness of the
potential benefits of such alternatives and
to encourage their implementation where
applicable, several assessments of prom-
ising new treatment technologies have
been conducted.
The technology assessment summar-
ized here describes a recently developed
biological wastewater treatment concept
called the biological aerated filter (BAF)/
Biocarbone process* and addresses
performance and operational character-
istics, design approaches used by the
two vendors of the process, and potential
applications of that process. Recommen-
dations are provided where further
definition of process performance
response to environmental conditions is
believed warranted. Similarities and
differences of the BAF/Biocarbone
process are briefly compared with those
of conventional activated sludge sys-
tems. An alternative design method
proposed by the author based on oper-
ating and performance data from several
French Biocarbone systems is also
presented.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
*Mention of trade names or commercial products
does not constitute endorsement or recommendation
for use.
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
The BAF is a trademarked wastewater
treatment process marketed in the United
States and most of Canada by Eimco
Process Equipment Company (Eimco) of
Salt Lake City, UT. Original research and
development of the technology belongs
to the French company Omnium de
Traitements et de Valorisation (OTV) that
directly or indirectly markets their equi-
valent Biocarbone process elsewhere, but
primarily in Europe. A number of process
patents, dating back to 1978, have been
granted both in Europe and North
America.
Process Description
The BAF/Biocarbone process consists
of a granular media bed, usually of vitrified
clay particles with a specific gravity of
approximately 1.6, through which pre-
treated wastewater (minimum acceptable
pretreatment is primary clarification) is
passed in a downward gravity flow pattern
similar to either a downflow water filter
or a downflow tertiary wastewater filter.
The media bed is supported by an
uriderdrain plate that incorporates plastic
nozzles for collecting the treated waste-
water and for distributing backwash water
and air. The process air supplied to the
media (via a distribution header assembly
located 8 to 10 in. [20 to 25 cm] above
the underdrain plate) results in aerobic
biological growth on the media. The
filtering action of the media obviates the
need for a separate final clarification step.
-------
This process, therefore, provides both
biological stabilization of organic matter
and suspended solids removal in a single
vessel. As a consequence, the space
requirements of this technology can be
substantially less than for more conven-
tional secondary treatment systems.
Accumulated solids stored in the media
and excess biological growth sheared
from the media are backwashed and
removed from the bed on a predetermined
schedule, typically once a day, or on the
basis of headless buildup. The backwash
solids can be separately thickened or
returned to the plant headworks for
cothickening with the primary sludge.
When treating primary effluent, the
BAF/Biocarbone process can be
designed to achieve carbonaceous BOD
removal only [or carbonaceous BOD Pollutant Removal
removal and nitrification by selecting
appropriate loading rates. The process
can also be designed to achieve ad-
vanced secondary treatment removals of
BOD and suspended solids as well as
nitrification wittj either primary or secon-
dary effluent feed.
Plan and section views of a typical BAF/
Biocarbone unit are presented in Figure
1. A typical process flow diagram for a
complete BAF/Biocarbone treatment train
is shown in Figure 2.
Background Performance Data
OTV, through years of conducting pilot-
and full-scale Biocarbone plant evalua-
tions, has developed reliable correlations
between applied pollutant and/or hydrau-
lic loading rates and effluent quality or
percent pollutant removal.
One of these generalized correlations
extracted from an OTV brochure is
depicted in Figure 3 for two types of
media, activated carbon and biodamine
(vitrified clay particles). Influent waste-
n
h
^
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Legend
Underdrain/'Backwash Nozzles
Process Air Distribution Piping
Media Bed Surface
Effluent/Backwash Piping
Air Scour Header
Backwash Water Syphon
Process Air Header
Effluent Plenum
Influent
Side View
Flgura 1. Plan and side views of a BAF/Biocarbone module.
-------
Backwash Water
*Generally would only be needed in industrial wastewater
treatment applications with strong influent concentrations.
Dilution Water
(Optional)*
Figure 2. Typical BAF/Biocarbone system process flow diagram.
water characteristics from which the
correlations were developed include:
Parameter
Range, mg/L
BOD5
COD
TSS
TKN
NH4-N
50-150
100-300
50-150
15-30
10-25
Effluent quality from a Biocarbone unit,
based on the above influent character-
istics, is graphically depicted in Figure 4.
Pilot plant studies by OTV indicated that
ammonium nitrogen (NH4-N) removal is
governed, in part, by the organic loading
to the Biocarbone unit. As indicated in
Figure 5, an organic loading of greater
than approximately 0.19 to 0.22 Ib COD/
ft3/day (3.0 to 3.5 kg/m3/day) produces
incipient inhibition of NH4-N oxidation,
and the inhibition becomes substantially
more pronounced once the organic
loading exceeds 0.25 to 0.28 Ib COD/ft3/
day (4.0 to 4.5 kg/m3/day). The above
loading condition is of concern mainly
when primary effluent must be nitrified in
conjunction with removing carbonaceous
BOD. Nitrification of secondary effluent,
on the other hand, is governed mainly by
the TKN loading to a Biocarbone unit.
Between nitrogen loadings of 0.010 and
0.037 Ib TKN/ft3/day (0.16 and 0.59 kg/
m3/day), NH4-N removal decreases at a
relatively linear rate, from about 90% to
84%. Loadings above about 0.037 Ib TKN/
ft3/day (0.59 kg/m3/day) result in sub-
stantially reduced NH4-N removal rates.
Pilot plant studies also provided data
on the temperature dependence of
NH4-N oxidation. Based on NH4-N oxida-
tion in secondary effluent, OTV reported
removal rates to approximate the
following:
Temperature
0ฐF 0ฐC
54
64
75
12
18
24
NHj-N Removal Rate
Ib/ft3/day
0.024
0.031
0.037
kg/ms/day
0.39
0.50
0.60
Media Characteristics
The original media OTV used in their
Biocarbone process was granular acti-
vated carbon. This material had the
desirable characteristics of a porous
surface with a high surface-to-volume
ratio for enhancing biomass attachment
and a low specific gravity to allow for ease
of air scouring and backwashing, but it
was found too expensive. Subsequently,
two new media were developed, both kiln-
fired clay particles. Biodamine is an
angular shaped media that is subject to
a slight degree of abrasion during media
placement and backwashing operations.
Biodagene is a spherical shaped media
that is less subject to abrasion. Both have
a bulk dry density of about 50 Ib/ft3
(800 kg/m3). Eimco has developed an
angular media that appears to be a kiln-
fired shale. This media also has a bulk
dry density of approximately 50 Ib/ft3 (800
kg/m3).
Media gradation is one of the more
important variables responsible for the
performance of the BAF/Biocarbone
process. Gradation not only affects
effluent BOD and TSS concentrations but
also governs the rate of headless buildup
and the associated time interval between
backwashings. An OTV approximation of
effluent quality as a function of media
gradation is as follows:
Media Gradation
in. mm
Effluent Quality, mg/L
BOD5 TSS
0.079-0.157
0.118-0.236
0.157-0.325
2-4
3-6
4-8
10
20
30
10
20
30
Media in the smaller size ranges require
more frequent backwashing than larger
media sizes subjected to the same loading
rate. In general, media in the 0.079 to 0.157
in. (2 to 4 mm) range should be considered
where stringent effluent residuals are
required, lower loading rates are econom-
ically feasible, and wastewaters contain
-------
0.5
Hydraulic Loading Rate, gpm/ft2 \
1.0 1.5
2.0
Q
O
O
75
70 -
1.0lb/fP/day = 16.0 kg/ms/day
1.0 gpm/ft2 = 2.44 m3/mz/hr
Media Depth: 5.25 ft(1.6 m)
Media Size: 0.079-0.197 in.(2-5 mm)
Influent BODS: < 150 mg/L
0.2 0.3 0.4 0.5 0.6 O.p 0.8
Organic Loading Rate, Ib COD/ft3/day
0.9
Flgura 3. COD removal as functions of influent COD loading rate and influent hydraulic
loading rate fpr (wo different media.
50
ง 30
a
1
ง 20
I
10
tO/b/ftVctey= 16.0 kg/m3/day
COD
Media Type: Biodamine
Media D0pth: 5.25 ft(1.6m)
Media Sfee: 0.079-0.197 in.(2-5 mm)
Influent BOD5:< 150 mg/L
- BODS
0.2
0.3
0.4 0.5 0.6 rj.7
I
Organic Loading Rate, Ib COD/ft3/day
Figure 4. Effluent quality as a function of influent COD loading rate.
0.8
0.9
a high soluble BOD fraction. Wastewaters
with a high TSS concentration may not
be compatible with a media gradation of
0.079 to 0.157 in. (2 to 4 mm) because
of the short run time between backwash-
ings that could be incurred. Selecting
BAF/Biocarbone media gradation for a
given system influent loading may involve
a tradeoff decision of attaining advanced
secondary effluent quality with frequent
backwashing (e.g., several times per day)
versus attaining just secondary effluent
quality with relatively infrequent back-
washing (e.g., once a day).
Media gradation also defines capacity
of a bed to store accumulated solids,
which include a combination of sus-
pended solids captured in the filtration
process plus biomass produced from the
assimilation and oxidation of carbonace-
ous and nitrogenous matter. An approx-
imation of solids storage capacity, as a
function of media gradation, developed
from OTV pilot plant studies and con-
firmed at full-scale operational facilities
is as follows:
Media Gradation Solids Storage Capacity
in.
mm
Ib/ft3
kg/m3
0.079-0.157
0.118-0.236
0.157-0.315
2-4
3-6
4-8
0.06-0.09
0.14-0.17
0.19-0.22
1.0-1.5
2.2-2.7
3.0-3.5
In a BAF demonstration study at Salt
Lake City, UT, sponsored by the U.S.
Environmental Protection Agency (EPA),
media with a size range of approximately
0.098 to 0.256 in. (2.5 to 6.5 mm) were
used. Data indicated that the solids
storage capacity of these media averaged
about 0.16 Ib/ft3 (2.6 kg/m3).
Solids Production
The solids production rate in the BAF/
Biocarbone process is a function of,
among other factors, the quantities of
soluble BOD, nonbiodegradable TSS,
NH4-N, and TKN removed. OTV initially
used the historic solids production
approximation of 0.7 to 0.8 Ib solids/lb
total BOD5 removed (kg/kg). A larger data
base acquired from both pilot- and full-
scale facilities yielded the following two
modifications by OTV to their historic
solids production value:
Solids Production Rate =
0.4 Ib (kg)
Ib (kg) soluble BOD5 removed
, 1.0lb(kg)
Ib (kg) insoluble BOD5 removed (1)
-------
90
85
80
ง
o 75
I
70
65
60
0.01
Nitrogen Loading Rate, Ib TKN/ft3/day
0.02 0.03
0.04
A ) Combined
Carbonaceous BOD5
Removal and
Nitrification
of Primary Effluent
Nitrification of
Secondary Effluent
Media Type: Biodamine
Media Depth: 5.25 ft (1.6 m)
Media Size: 0.079-0.197 in.
(2-5 mm)
1.0lb/ft3/day = 16.0 kg/m3/day
0.1
0.2 0.3
Organic Loading Rate, Ib COD/ft3/day
Figure 5. NH4-N removal as functions of influent COD and TKN loading rates.
0.4
Solids Production Rate =
0.4 Ib (kg)
Ib (kg) soluble BOD5 removed
0.65 Ib (kg)
Ib (kg) TSS removed
(2)
Either of the above predicted models may
be used to approximate the net solids
production rate according to OTV.
Backwashing
The BAF/Biocarbone system must be
backwashed, normally once a day, to
ensure a specific volumetric throughput
rate of wastewater. From numerous pilot
plant studies, OTV established a need for
up to seven consecutive sets of air scours
and backwashes to clean the media bed.
The seven consecutive sets constitute
one backwash sequence. Air scour and
backwash water rates and total volumes
used at several full-scale French facilities
are summarized below:
Parameter
Range of
Values
Air Scour
Rate, ft3 (m3) air/ft3 (m3)
media/min 0.43-0.52
Total Volume, ft3 (m3) air/ft3
(m3) media 5.14-6.25
Backwash Water
Rate, ft3 (m3) water/ft3 (m3)
media/min 0.33-0.35
Total Volume, ft3 (m3) water/ft3
(m3) media 2.50
The EPA BAF demonstration project used
essentially these same air scour and
backwash water rates and volumes as do
facilities that Eimco has recently installed.
Performance of Existing Facilities
North American Facilities
A 0.25-mgd (946-m3/day) Eimco facility
has been installed at Lake Wildwood, GA.
Primary effluent is being treated with the
goal of achieving a nitrified secondary
effluent containing 6 to 8 mg/L NH4-N.
This facility is operating at, or slightly
above, design flow. Another Eimco oper-
ational facility is located at Wallace, NO.
Design flow is 0.60 mgd (2,271 m3/day),
and the system is polishing the effluent
from an existing trickling filter plant to
effect additional BOD and TSS removals
as well as to achieve an NH4-N concen-
tration of 2 mg/L. Eimco's 0.60-mgd
(2,271 -m3/day) facility at Madison, FL, is
polishing effluent from an existing acti-
vated sludge system to provide supple-
mental BOD and TSS removals and
nitrification to effluent residuals of less
than 5 mg/L NH4-N. At the present time,
limited performance data have been
reported for these facilities. A 0.75-mgd
(2,839-m3/day) facility is being con-
structed at St. George, SC, and a 2.2-mgd
(8,327-m3/day) facility is also under
construction at Oneonta, AL. These latter
two facilities will be used to polish and
nitrify lagoon effluent.
-------
The aforementioned EPA demonstra-
tion project at Salt Lake City, UT, operated
from January 1983 to February 1985, also
used an Eimco system. The system was
operated to demonstrate the applicability
of this European technology to treat U.S.
strength wastewaters and to formulate
any needed design or operational mod-
ifications to ensure a specific effluent
quality. One of the system's two cells was
operated to amass information on carbo-
naceous BOD removal with nitrification;
the other cell was operated to generate
information on carbonaceous BOD re-
moval with nitrification. Data on the
performance of this pilot plant are
reported in detail in the June 1988 issue
of the ASCE Journal of Environmental
Engineering ("Biological Aerated Filter
Evaluation" by H.D. Stensel et al.).
French Facilities
OTV has designed, constructed, and
operated a number of Biocarbone facil-
ities throughout France.
The location of these operational
facilities, the type of wastewater being
treated, and their design population
equivalents are summarized in Table 1.
In addition to the above, a four-celled
323-ftz (30-m2) pilot plant has been
operated by OTV at the Colombes treat-
ment plant to optimize system design
criteria and operating conditions forfuture
reference when the City of Paris is
required to install wastewater nitrification
facilities.
On-site visits were made to four of the
French facilities: Soissons, Grasse, Val-
bonne, and Colombes. The Colombes
pilot plant was nitrifying activated sludge
treatment plant effluent at the time of the
visit. Available operating and perfor-
mance data for Soissons, Grasse, and
Colombes are summarized in Tables 2
and 3, respectively. Detailed operating
and performance data were not available
for Valbonne.
The system at Soissons was the first
full-scale facility built by OTV. A circular
design with 10 truncated, pie-shaped
units was selected, with the center of the
structure functioning as the clear well for
storing the treated wastewater used for
backwashing the units.
The Grasse Biocarbone system, which
began operation in April 1983, is similar
in appearance to the circular Soissons
facility. Wastewater being treated at this
facility during the 1984 site visits was
primarily from perfumeries located in the
City. As more of the City's collection
system is installed, the contribution of
domestic wastewater is expected to
increase from ithe 35% to 40% level noted
at the time of the site visit.
The Colombes pilot system during the
1984 site visits was composed of four
independent ;81-ft2 (7.5-m2) cells. As
previously mentioned, this system was
being operated as an experimental facility
to amass design and operational infor-
mation for future City of Paris secondary
effluent nitrification facilities.
The Valbonne system was designed to
achieve nitrification and partial denitrifi-
cation along with carbonaceous BOD5
removal. Three units are operated in an
aerobic state to nitrify, and one unit is
operated in an anoxic state to denitrify.
The Valbonne facility was placed in
operation in October 1982. Between that
time and the site visits in 1984, on the
average, only one to two effluent samples
per month had been analyzed for ran-
domly selected pollutant parameters. The
available data, though limited, indicated
the facility had consistently achieved high
removals of BOD5, TSS, and NH4-N with
effluent residuals in the ranges of 5 to
10 mg/L for BOD5 and TSS and 1 to 5
mg/LforNH4-N.
Table 1. Basic Information on Existing Biocarbone Facilities
Location '
Le Havre
Valbonne
Hochfelden
Soissons '.
Grasse '
Le Touquet
Sanary-Bandol
Luneville '_
Type of Wastewater
Secondary Effluent
Municipal
Industrial (Brewery)
Municipal-lndustiral (Slaughterhouse)
Municipal-Industrial (Perfumery)
Municipal
Municipal
Municipal
Design Population
Equivalent
5,000
16,000
25,000
40,000
52,000
53,000
35,000
33,000
Table 2. Operating Data for Soissons, Grasse, and Colombes
Parameter
Facility Location
Soissons
Grasse
Colombes
Operating Period 11/82-6/84 1/84-5/84 7 months
Avg. Inf. Flow >
mgd | 0.97 1.00
mVctey j 3,460 3,790
Avg. Hydraulic Loading
gpm/ft2 0.28 0.48 0.75
m3/m2/day \ 0.69 1.17 1.84
Avg. BOD5 Loading
Ib/ft3/day | 0.11
kg/rtf/day I 7.74
Avg. COD Loading
Ib/ft3/day \ 0.20 0.47
kg/rrfl/day i 3.22 7.57
Avg. NH4-N Loading
Ib/ft3/day \ 0.02
kg/ma/day [ 0.32
i
Avg. Empty Bed Contact
Time(min) | 756
Wastewater Temperature, "F (ฐC)
Avg. ' 57(13.7) 58(14.7)
Range 46-69(8-20.5) 53-65(11.5-8.5)
Backwash Waterflow (% of Inf. Flow)
Avg. 33.2 22.2
Range 17.5-63.3 19.3-27.4
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Table 3. Performance Data for Soissons, Grasse, and Colombes
Parameter
Avg. BODS (mg/L)
Influent
Primary Effluent
Final Effluent
Avg. COD (mg/L)
Influent
Primary Effluent
Final Effluent
Avg. TSS (mg/L)
Influent
Primary Effluent
Final Effluent
Avg. NH4-N (mg/L)
Influent
Primary Effluent
Final Effluent
Soissons
298
161
10
616
299
61
281
111
10
36
30
12/8$
Facility Location
Grasse
'
-
7,243+
825
777
382+
85
25
Colombes
29*
4
35*
6
25.7*
7.7
system feed was secondary effluent.
Effluent BOD5 and TSS concentrations
from the pilot plant facility were independ-
ent of influent wastewater quality as well
as independent of EBCT. Ammonium
nitrogen removal was best described by
the mathematical expression:
Effluent NH4-N,rng/L =
Influent NH4-N. mg/L
0.060 (EBCT)
(6)
*System influent is secondary effluent.
+lncludes backwash water pollutant load.
^Average of 12 mg/L for all wastewater temperatures; average of 8 mg/L for wastewater
temperatures above 54ฐ F (12ฐ C).
Design Approaches
Based on findings from their own
research and development, the OTV and
Eimco staffs developed generalized
approaches to facility design. These
extensive design protocols are presented
in the full report.
After exarnining OTV's and Eimco's
design approaches and analyzing avail-
able full-scale system performance data,
the author formulated an alternative
design approach. A review of certain of
OTV's and Eimco's system performance
functions, which were primarily based on
pollutant mass loadings, coupled with
performance data from the Soissons and
Colombes full-scale facilities indicated
complementary mathematical equations
that potentially allowed for prediction of
actual effluent quality.
At Soissons, where the feed to the
Biocarbone system was primary effluent,
the following mathematical relationships
were developed for predicting effluent
BOD5, TSS, and NH4-N:
Effluent BOD5, mg/L =
Influent BODS, mg/L
0.13 (EBCT)
Effluent TSS, mg/L =
Influent TSS, mg/L
0.09 (EBCT)
(3)
(4)
Effluent NH4-N, mg/L = (5)
Influent NH4-N, mg/L (Effluent BOD5, mg/L)0-5
0.064 (EBCT)
where EBCT is the empty bed contact time
in minutes.
A similar set of analyses was under-
taken on the performance of the
Colombes pilot plant facility, where the
Predicted values have been compared
with actual values for effluent BOD5 at
Soissons (Table 4). Similar tables for the
other effluent pollutant concentrations are
given in the full report.
Technology Application
North American and French systems
performance data indicate that the BAF/
Biocarbone process is capable of yielding
an effluent of secondary treatment or
advanced secondary treatment quality. As
evidenced by performance of the EPA
demonstration facility at Salt Lake City, UT,
an effluent containing approximately 25
to 30 mg/L each of BOD5 and TSS can
be achieved at an EBCT of about 45 min
when treating a dilute, primary clarified
domestic wastewater. Data from the
Soissons, France, facility indicated that a
stronger primary clarified municipal
wastewater can be treated to yield an
effluent containing less than 10 mg/L
each of BOD5> TSS, and NH4-N at an EBCT
Table 4. Predicted versus Actual Effluent BOD5 Concentrations for the Soissons Facility
Month
11
12/82
1/83
2
3
4
5
6
7
8
9
10
11
12/83
1/84
2
3
4
5
6
Wastewater
Temp., ฐC
12.8
10.0
10.0
8.0
10.7
11.0
13.8
17.5
19.5
20.5
17.7
16.0
14.5
12.2
10.0
11.0
11.5
13.0
15.8
18.0
EBCT,
min
93
79
86
104
98
79
104
149
184
195
177
223
213
222
173
189
217
232
155
148
Influent
BOD5, mg/L
195
182
162
136
184
186
169
147
139
137
135
175
256
185
141
180
140
57
147
150
Effluent
BOD5, mg/L
30
17
12
12
13
12
10
. 8
8
6
7
7
9
7
8
6
7
6
6
6
Predicted
Effluent
BODS, mg/L
16
18
14
10
14
18
13
8
6
5
6
6
9
6
6
7
5
2
7
8
-------
of approximately 140 min. The process
can also be used for polishing secondary
effluent, as evidenced by the Colombes,
France, facility data that produced an
effluent containing an average of 4 mg/
L BODS and 6 mg/L TSS and achieved
an average NH4-N removal of 18 mg/L
at an EBCT of about 60 min.
To illustrate the application of the BAF/
Blocarbone process, two example
designs are developed in the full report
to upgrade an existing 1.0-mgd (3,785-
m3/day) primary clarification system to (1)
a secondary treatment system at similar
capacity and (2) an advanced secondary
treatment system of similar capacity using
the BAF/Biocarbone process. In the first
case, the goal !is to achieve effluent BOD5
and TSS concentrations of 30 mg/L or
less. Nitrification is not a process require-
Arthur J. Condren Is with James M. Montgomery, Consulting Engineers, Inc
Pasadena, CA 91109-7009. \
Richard C. Brenner is the EPA Project Officer (see below).
The complete report, entitled "Technology Assessment of, the Biological Aerated
Filter," (Order No. PB90-188 806/AS; Cost: $23.00, subject to change) will be
available only from: I
National Technical Information Service ',
5285 Port Royal Road I
Springfield, VA 22161
Telephone: 703-487-4650 \
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U.S. Environmental Protection Agency
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ment In the second case, effluent goals
are 4 mg/L for BOD5, 6 mg/L for TSS,
and less than 7 mg/L for NH4-N.
Estimates of capital costs and average
daily power requirements are developed
for these two example designs.
The full report was submitted in
fulfillment of Contract No. 68-03-1821 by
James M. Montgomery, Consulting
Engineers, Inc., under the sponsorhip of
the U. S. Environmental Protection
Agency.
*U.S. Government Printing Office: 1990-748-012/20045
United States
Environmental Protection
Agency
Center for Environmental Research
Information [
Cincinnati OH 45268 !
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