United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-97/094 January 1998
Project Summary
Field Measurement of
Greenhouse Gas Emission
Rates and Development of
Emission Factors for Wastewater
Treatment
Bart Eklund and Jeffrey LaCosse
A research project was conducted to
measure emissions of greenhouse
gases (GHGs) from wastewater treat-
ment (WWT) and disposal facilities. The
overall objective of the research under
the base statement of work area for
this contract is to develop more reli-
able estimates of GHG emissions from
industrial and domestic WWT systems.
Most previous research for these
sources has used a mass balance ap-
proach to estimate potential methane
(CH4) emissions, but in this study emis-
sions of CH4 and other GHGs were mea-
sured under field conditions, which
should improve the reliability of the
emission estimates.
Field sampling was performed at five
sites, including WWT systems in the
beef and chicken processing industries
and two publicly owned treatment
works (POTWs). Ambient air was mea-
sured immediately downwind of the la-
goons using a Fourier Transform Infra-
red (FTIR) approach. The FTIR light
beam was directed along a path of sev-
eral hundred feet and the absorbance
of gases was measured. The target
compounds of interest included CH4,
carbon dioxide (CO2), nitrous oxide
(N2O), carbon monoxide (CO), ammo-
nia (NH3), and certain volatile organic
compounds (VOCs). The source term
(i.e., emission rate) can be determined
from information about the average
downwind ambient concentration (mea-
sured by the FTIR method) and the
atmospheric dispersion characteristics
at the time of sampling. In addition,
samples of influent and effluent waste-
water and sludge were collected. Emis-
sion factors were developed in terms
of grams of species emitted per gram
of precursor in the influent wastewa-
ter; e.g., g CH4/g biological oxygen de-
mand (BOD). The emission factors will
be combined with activity factor data
to develop national and global emis-
sions inventories.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory's Air Pollution
Prevention and Control Division, Re-
search 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
A GHG generally can be defined as any
molecule which absorbs infrared light in
the spectral region of 5 to 20 |jm These
molecules include water vapor (H2O), CO2,
CO, CH4, certain VOCs, and N2O. Rea-
sonably accurate global balances of GHGs
are needed as input to climatic models for
estimating long-term global temperature
changes.
A large number of natural and anthropic
activities produce or release GHGs. The
emphasis of this program was on emis-
sions from WWT facilities. The decomposi-
tion of organic waste may occur aerobi-
cally (i.e., with oxygen) or anaerobically
(i.e., without oxygen). Aerobic decomposi-
tion of organic carbon results in the pro-
duction of CO2, while anaerobic decompo-
sition results in the production of CH4and
CO2. Given a sufficient amount of time,
essentially every atom of carbon in waste
streams is converted to either CO2 or CH4.
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In terms of their ability to retain heat in the
atmosphere, however, CO2 and CH4 are
not equivalent. A given mass of CH4 is 58
times stronger a GHG than the same mass
of CO2 (it is 21 times stronger on a mo-
lecular basis). Therefore, the relative
amount of anaerobic versus aerobic de-
composition is of interest.
The overall objective of the research
under the base statement of work area for
this contract was to develop more reliable
estimates of GHG emissions from indus-
trial and domestic WWT systems. National
and global inventories of CH4 emissions
from WWT facilities have been published.
These estimates, however, are based on
various assumptions and very limited data.
Most previous research for these sources
has used a mass balance approach to
estimate potential CH4 emissions, but in
this study emissions of CH4 and other
GHGs were measured under field condi-
tions, which should improve the reliability
of the emission estimates.
The overall objectives of this study were:
1) Identify industries and WWT processes
that have the greatest potential for mea-
surable emissions of CH4; 2) Select the
most promising sites for testing in those
industries; 3) Perform ambient air mea-
surements using an open path monitoring
(OPM) approach with a FTIR spectros-
copy instrument; 4) Collect and process
data and characterize the influent and ef-
fluent wastewater quality at the field sites;
and 5) Use the field data to develop emis-
sion factors for each target compound.
The target compounds of interest included
CH4, CO2, N2O, CO, NH3, and certain
VOCs.
A subset of WWT systems that employ
anaerobic treatment processes was se-
lected for testing. Within this subset,
anaerobic lagoons were given priority over
anaerobic digesters, tanks, and sludge dis-
posal units because lagoons offered the
fewest logistical constraints to testing. Al-
though anaerobic lagoons are not exten-
sively used to treat industrial and domes-
tic waste in the U.S., other countries use
anaerobic lagoons to treat wastewater.
Because of difficulties associated with iden-
tifying sites and the expense of conduct-
ing field measurements in foreign coun-
tries, sites in the U.S. that are representa-
tive of treatment conditions in developing
countries were selected for testing.
Approach
Site selection focused on U.S. WWT
systems that employ open, anaerobic pro-
cesses to achieve high levels of BOD or
chemical oxygen demand (COD) removal.
First, industries that treat large volumes of
wastewater and remove large amounts of
BOD/COD were identified. Approximately
a dozen industries were identified as po-
tential candidates for testing. Second, a
telephone survey was conducted of in-
dustry representatives, experts in the WWT
area, and regulatory personnel to identify
industries most likely to treat wastewater
to remove high levels of BOD/COD in
open, anaerobic lagoons. The most prom-
ising candidates were beef and poultry
processing plants, and pulp and paper
mills. POTWs also were of interest be-
cause they are used to treat a significant
fraction of wastewater both nationally and
globally and, also, are thought to be a
potentially significant source of N2O emis-
sions.
Five sites were selected for testing. The
selection intentionally included sites from
several different industries: two beef pro-
cessing plants, one chicken processing
plant, and two POTWs. Two sites from
certain industries were included to help
determine the variability in emissions within
a given industry.
The field work involved being on site for
about 5 days at each facility. Ambient air
was measured immediately upwind and
downwind of the lagoons using an OPM-
transect method (OPM-TM) approach with
detection by FTIR spectroscopy. The FTIR
light beam was directed along a path of
several hundred feet and the absorbance
of gases was measured. Emission rates
were determined from measurements of
the downwind ambient concentration and
the atmospheric dispersion characteristics
at the time of sampling. In addition, a
limited number of influent and effluent
wastewater and sludge samples were col-
lected.
Emission factors were developed in
terms of grams of GHG species emitted
per gram of precursor in the influent waste-
water (e.g., g CH4/g BOD). The emission
factors will be combined with activity fac-
tor data to develop national and global
emission estimates.
Results
OPM-TM using the FTIR was used to
determine emission rates. A very large
data set was generated, and up to 300
separate valid, 5-minute average emis-
sion rate determinations were made at a
given site. The air measurement data were
reviewed to identify compounds found in
significantly greater concentrations in the
downwind air versus the upwind air at
each site. Any such compounds were likely
to have been emitted from the lagoons
being tested. Many of the target analytes
were found at the same concentration lev-
els upwind and downwind of the lagoons;
i.e., they had no quantifiable emission rate.
Only CH4, NH3, and the sulfur hexafluo-
ride (SF6) tracer gas generally were
present in greater amounts in the down-
wind air.
The minimum quantifiable emission rate
varied from site to site and from one 5-
minute period to another. The detection
limit for a given compound, in terms of
grams per second, is dependent on the
smallest difference between downwind and
upwind concentrations that could be iden-
tified apart from the measurement vari-
ability within each of the upwind and down-
wind data sets. For each increment of 0.5
ppmv (500 ppbv) that a given compound
was present in greater concentrations
downwind than upwind, its emission rate
was about 1 g/sec (depending on the mo-
lecular weight of the compound). Typical
detection limits were about 0.1 g/sec for
most compounds, except for CO2, which
had a minimum detection limit of about
150 g/sec. The high detection limit for
CO2 was due to the high background con-
centrations (e.g., 500 ppmv) and the mea-
surement coefficient of variability (e.g., CV
= 7.5%, or 37.5 ppmv).
At all three meat processing plants, large
amounts of CH4 were detected downwind
of the WWT system. For the two beef
processing plants, the concentration of CH4
(and NH3) exhibited an exponential rela-
tionship with wind speed. The downwind
CH4 concentration at the chicken process-
ing plant did not show a clear relationship
between concentration and wind speed.
At the chicken processing plant, however,
the range of wind speeds was much
smaller than for the meat processing plants
and the number of valid measurement pe-
riods also was much smaller, making it
more difficult to identify trends and rela-
tionships. There also was a thick grease
layer present on top of the lagoon which
would tend to diminish the effect of sur-
face winds on air emissions.
The emission rates measured at each
site for CH4, NH3, and other selected com-
pounds are given in Table 1. Surprisingly,
no emissions were detected from the
POTWs. It was expected that either CH4
or CO2 would be detected. The dissolved
oxygen (DO) level in the lagoons exceeds
2 mg/L, indicating that BOD removal is
taking place under aerobic conditions. So
it is highly probable that CO2 is being
generated, but the levels were too small
to detect given the very high background
levels of CO2 and the measurement vari-
ability. In general, anaerobic degradation
can be expected to produce a mixture of
CH4 and CO2 (somewhere between a 50:50
and a 70:30 ratio). Therefore, emissions
of CO2 would be expected wherever quan-
tifiable emission rates of CH4 were found.
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Table 1. Measured Emission Rates of Selected Compounds for Each Field Site
Site
Beef Processing Plant
inSWU.S.
Beef Processing Plant
in Midwest U.S.
Compound
CH4
NH3
NH!
Average
Downwind
Cone.
(ppm)
61.9
355 ppb
58.1
1.04
Average
Upwind
Cone.
(ppm)
2.3
0
2.83
0.277
Maximum
Downwind
Cone.
(ppm)
142
609 ppb
200
2.06
Average
Emission
Rate
(g/sec)
280
2.2
230
3.5
Chicken Processing Plant
in SE U.S.
POTWfor Small Town
in SWU.S.3
POTWfor Very Small
Town in SWU.S.3
NH3
N20
CH
NH
C02
NH
CO,
9.80
2.6 ppb
563 ppb
2.20
0.2 ppb
342
2.11
93.3 ppb
528
1.92
2.8 ppb
542 ppb
2.14
0
351
2.16
25.5 ppb
668
29.9
44.1 ppb
586 ppb
2.46
15.4 ppb
384
2.81
21 4 ppb
691
180
0.066
2.6
O.15
O.05
<150
O.15
O.05
<150
aMethane, carbon dioxide, and ammonia values are shown for the POTWs for comparison purposes. No quantifiable emissions of these
compoundswere detected at either POTW.
The lack of quantifiable CO2 emission rates
may be due to the high detection limit for
CO2 emission rates, as previously dis-
cussed. The absence of CO2 emissions
also could be due to the presence of
cyanobacteria (blue-green algae) in the
anaerobic lagoons.
The wastewater data for all three meat
processing plants are very similar, with
the two beef processing plants showing
very good agreement. All three WWT sys-
tems have high BOD removal rates (88-
95%), as well as high removal rates for
COD, total organic carbon (TOC), and ni-
trates. All three WWT systems at meat
processing plants generated large amounts
of NH3 as a by-product of the biodegrada-
tion of the wastewater. The only param-
eter that showed variable behavior from
system to system was total Kjeldahl nitro-
gen (TKN).
The two POTWs had similar influent
wastewater and exhibited similar perfor-
mance in terms of removal of BOD, COD,
TOC, TKN, and NH3. Both systems gener-
ated nitrates as a by-product of biodegra-
dation.
Activity factors were developed for each
site based on information provided by the
plant operators and from the wastewater
data. Emission factors were developed for
each site by dividing the average emis-
sion rates by the activity factors for each
site. The resulting emission factors are
given in Table 2. For CH4, the emission
factor based on COD should be a better
predictor of emissions from other facilities
than the emission factor based on BOD.
The 5-day BOD test will not fully degrade
all of the biological material in wastewa-
ters containing proteins and fatty acids.
The suspended solids associated with the
wastewaters also are biodegradable, and
their ultimate BOD would not be exerted
in the 5 days it takes to run a standard
BOD test. COD data, however, are not
always available, and estimates based on
other activity factors may be necessary.
Therefore, a variety of emission factors
are included in Table 2.
Table 2. Average Emission Factors
Compound
Emission Factor
Average
Range
Methane
Ammonia
Nitrous Oxide
g CH4/head of cattle
g CH4/chicken
g CH4/kg meat
g CH4/L of wastewater
g CH4/g influent BOD
g CH4/g BOD removed
g CH4/g COD removed
g NH3/head of cattle
g NH3/chicken
g NH3/kg meat
g NH3/L of wastewater
g NH3/g influent BOD
g NH3/g NH3 in effluent
g N2O/chicken
g N2O/kg meat
g N2O/L of wastewater
g N2O/g BOD removed
g TKN removed
4,200
120
37
2.7
1.5
1.6
0.96
46
0.046
0.14
0.014
0.40
0.072
1.8
1.1
0.067
0.051
1.7
3,500 - 4,800
N/A
15-74
1.6-4.6
0.40 - 3.2
0.43 - 3.4
0.26 - 2.0
37-54
N/A
0.027 - 0.24
0.0017-0.028
0.0031 - 1.2
0.020-0.13
N/A
N/A
N/A
N/A
N/A
N/A = Not applicable.
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An estimate of the uncertainty of the
emission factors was developed through
standard error propagation methods. The
derived emission factors all appear to be
reliable to within a factor of 2, based on
random error in the measurements, and
assuming that the sites and samples
accurately represent the population of interest.
It is possible that the lagoons are a sink
for suspended and colloidal material (i.e.,
insoluble BOD) and this material builds up
over time in the lagoon sediments. If so,
sediments may degrade during summer
months or whenever the sediment is re-
suspended, thereby increasing the CH4
(and CO2) emissions. However, no sea-
sonal trend is evident in the BOD effluent
levels in the long-term wastewater data
provided by the plants.
A number of previously published stud-
ies contain estimated or measured values
for the emission fluxes of CH4 from liquid
surfaces or slurries. The key comparison
is the emission flux (i.e., emission rate per
unit surface area). The average CH4 emis-
sion flux for the three meat processing
plants ranged from 6,100 to 23,000 \ig
CH4/sec-m2. Results for livestock lagoons
in previous studies (1,400 to 9,400), were
within an order of magnitude, as were
measurements at a manure tank (1,300 to
3,800). The emission flux from municipal
WWT systems, industrial WWT systems,
and rice paddies was substantially lower,
as expected given the much lower BOD
and COD levels in such waters.
Very few published emission factors
can be compared with the emission fac-
tors developed in this study. The most
widely reported emission factor for CH4 is
0.22 g CH4/g BOD. The reference for this
factor does not provide information about
how it was developed. It is very close to
the theoretical value for the anaerobic deg-
radation of glucose. The emission factors
determined in this study are substantially
higher than those based on glucose deg-
radation. Glucose is a simple sugar and
its biodegradation over short periods of
time cannot be directly compared with the
microbial degradation of complex mixtures
of amino and fatty acids, such as are
present in the wastewaters at the meat
processing plants.
Conclusions
Several conclusions can be drawn from
the study:
• The FTIR measurement approach
used in this study was successful for
the simultaneous collection of large
amounts of ambient concentration
data for CH4 and NH3;
• The use of the OPM-TM approach
using FTIR for estimating emission
rates has insufficient sensitivity for cer-
tain compounds, such as hydrogen
sulfide and total non-methane hydro-
carbons, due to limitations in the FTIR
analysis. For most of the sites, the
sensitivity for CO2 was limited by the
high background concentrations and
the variability in the background con-
centrations;
• Anaerobic WWT lagoons are a sig-
nificant source of CH
sions; and
• Lagoons at POTWs are not a signifi-
cant source of any GHG, with the
possible exception of CO2.
and NH3 emis-
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Bark Eklund and Jeffrey LaCosse are with Radian Corporation, Austin, TX 78720.
Susan A. Thorneloe is the EPA Project Officer (see below).
The complete report, entitled "Field Measurement of Greenhouse Gas Emission
Rates and Development of Emission Factors for Wastewater Treatment," (Order
No. PB98-117898; Cost: $67.00, 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:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
EPA/600/SR-97/094
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