February 4, 2009
TECHNICAL SUPPORT DOCUMENT FOR
WASTEWATER TREATMENT: PROPOSED RULE
FOR MANDATORY REPORTING OF
GREENHOUSE GASES
Climate Change Division
Office of Atmospheric Programs
U.S. Environmental Protection Agency
February 4, 2009
-------
CONTENTS
1. Industry Description 3
2. Total Emissions 3
3. Review of Existing Programs and Methodologies 4
4. Types of Emissions Information to be Reported 4
4.1 Types of Emissions to be Reported 4
4.2 Other Information to be Reported 4
5. Options for Reporting Threshold 6
5.1 Emissions-based thresholds 6
5.2 Other threshold options 11
6. Options for Monitoring Methods 11
6.1 Calculating Methane Generation 12
6.2 Methane Combustion at Anaerobic Digesters 15
6.3 Calculating Methane Combustion of Anaerobic Digesters 16
6.4 Nitrous Oxide Emissions 17
6.5 Estimating Total Generation and Emissions 17
6.6 Calculating CH4 Generation and Emissions Using Digester Gas Collection Data 18
6.7 Direct Measurement of Emissions 18
7. Options for Estimating Missing Data 18
8. QA/QC Requirements 18
2
-------
1. Industry Description
Both domestic and industrial wastewater treatment systems may result in direct emissions
of CH4 and N2O, depending on the treatment operations in place and the quality of the
wastewater to be treated. Wastewater is treated to remove soluble organic matter,
suspended solids, pathogenic organisms, and chemical contaminants. Centralized
wastewater treatment systems may include a variety of processes, ranging from primary
treatment for solids removal to secondary biological treatment (e.g., activated sludge,
lagoons) for organics reduction to tertiary treatment for nutrient removal, disinfection,
and more discrete filtration.
Methane emissions from wastewater treatment systems are primarily a function of how
much organic content is present in the wastewater system and how the wastewater is
treated. Methane is produced by the anaerobic decomposition of organic content, as
measured by the biochemical oxygen demand (BOD) of the wastewater. The production
of direct N2O emissions from wastewater treatment depends on the amount of nitrogen
(N) entering the system. For direct N2O emissions to occur, the wastewater must first be
handled aerobically where ammonia (NH3) or organic nitrogen is converted to nitrates
and nitrites (nitrification), and then handled anaerobically where the nitrates and nitrites
are reduced to nitrogen gas (N2), with intermediate production of N2O and nitric oxide
(NO) (denitrification). These emissions are most likely to occur in treatment systems
designed to achieve biological denitrification.
Wastewater treatment at oil/water separators onsite at petroleum refineries can result in
indirect emissions of CO2 that are considered anthropogenic.
In the United States, approximately 79 percent of domestic wastewater is collected and
treated centrally.1 Industries that have the potential to produce significant CH4 emissions
from wastewater treatment—those with high volumes of wastewater generated and a high
organic wastewater load—include pulp and paper manufacturing; meat and poultry
processing; vegetables, fruits, and juices processing; starch-based ethanol production; and
petroleum refining.
2. Total Emissions
As of 2004, there are 16,583 centralized wastewater treatment plants in the United States
and its territories2, and approximately 15,600 onsite wastewater treatment systems at
industrial facilities in the United States.3 Approximately 4,700 industrial wastewater
treatment systems are operated at industries with a potential to produce significant CH4
emissions.
In 2006, CH4 emissions from domestic wastewater treatment were estimated to be 16.0
million metric tons of carbon dioxide equivalent (mmtC02e) and CH4 emissions from
1 U.S. Census Bureau 2007
2 Clean Watersheds Needs Survey 2004 Report to Congress
3 2004 Permit Compliance System data
3
-------
industrial wastewater treatment were estimated to be 7.9 mmtCC^e. Direct N2O
emissions from domestic wastewater treatment were 8.1 mmtCC^e. Emissions at
centralized plants (domestic and industrial wastewater) were 10.9 mmtCC^e CH4 and 0.3
mmtC02e N2O, or 11.2 mmtCC^e in total. Wastewater treatment systems account for 4
percent of total anthropogenic CH4 emissions and 2 percent of anthropogenic N2O
emissions in the United States.
3. Review of Existing Programs and Methodologies
For this proposal, EPA reviewed several protocols and programs for monitoring and/or
estimating GHG including the 2006 IPCC Guidelines, the U.S. GHG Inventory,
California AB32, California Climate Action Registry, U.S. Energy Information
Administration Voluntary GHG Reporting Program (1605b), EPA Climate Leaders, The
Climate Registry, UNFCCC Clean Development Mechanism, the EU Emissions Trading
Scheme, and the New Mexico Mandatory GHG Reporting Program. These
methodologies are primarily all based on the IPCC guidelines.
In addition, EPA reviewed programs for obtaining and recording information from
wastewater treatment plants, including EPA's Clean Watersheds Needs Survey and the
National Pollutant Discharge Elimination System (NPDES). These data sources do not
currently collect information that could be used for the purpose of estimating GHG
emissions.
4. Types of Emissions Information to be Reported
4.1 Types of Emissions to be Reported
This section includes options for reporting CH4, direct N2O, and indirect CO2 (petroleum
refineries only) emissions from wastewater treatment.
There are other sources of emissions that occur at facilities with onsite wastewater
treatment. For reporting options for combustion (including digester gas combustion and
combustion of fossil fuels used to assist digester gas combustion efficiency), refer to
EPA-HQ-OAR-2008-0508-004.
In the case of industrial facilities with onsite wastewater treatment, industrial process
emissions of GHG may be occurring onsite as well. Reporting options for wastewater
treatment at these sites are detailed here, but for reporting options for other sources of
emissions, refer to sections for that industry.
4.2 Other Information to be Reported
In order to check the reported GHG emissions for reasonableness and for other data
quality considerations, additional information about the emission sources is needed. It is
recommended that, in addition to N2O and CH4 emissions, each reporting wastewater
treatment system should also report methane generation and, if applicable, CH4
4
-------
combustion annual quantities. Additionally, it is recommended that the following data
also be submitted with the annual report:
Data to report
a. Type of wastewater treatment system
b. COD
c. Date of measurement of COD
d. Influent flow rate
e. Date of measurement of influent flow rate
f. B0 value used
g. MCF used
h. Methane emissions
i. Type of oil/water separator (petroleum refineries)
j. Emissions factor for the type of separator (petroleum refineries)
k. Carbon fraction in NMVOC (petroleum refineries)
1. Indirect CO2 emissions (petroleum refineries)
Plants with digesters
a. Total volumetric flow of biogas
b. CH4 concentration of biogas
c. Temperature at which flow is measured
d. Pressure at which flow is measured
e. Destruction efficiency used
f. Methane destruction
g. Fugitive methane
EPA considered requiring that wastewater treatment plants over the selected threshold
report CH4 generation, any CH4 combustion, and N2O emissions (for POTWs), along
with the input data to calculate these values. For petroleum refining wastewater
treatment systems, EPA also considered that CO2 generation be reported. EPA can use
the reported input data for QA/QC purposes.
EPA considered requesting plants to report only CH4 and N2O emissions or generation;
these options were not chosen because without reporting input data, including CH4
combustion data, insufficient information is available for QA/QC of the reported
emissions. EPA also considered reporting of only emissions and combustion data, but
without reporting input data; again, insufficient information is available for QA/QC of
the reported emissions.
Regarding the frequency of reporting, EPA had considered both annual and quarterly
reporting. Although emissions could fluctuate seasonally at wastewater treatment
systems, annual reporting of emissions is sufficient for these sources.
5
-------
5. Options for Reporting Threshold
5.1 Emissions-based thresholds
In evaluating thresholds for wastewater treatment, we considered emissions-based
thresholds of CH4 generation and N2O emissions at a wastewater treatment system
("generation threshold") and CH4 and N2O emissions at wastewater treatment systems
("emissions threshold") of 1,000 mtCC^e, 10,000 mtCC^e, 25,000 mtCC^e, and 100,000
mtC02e per year. The "generation threshold" is the amount of CH4 and N2O that would
be emitted from the facility if no CH4 recovery takes place. This includes all CH4
generation from all wastewater treatment system types, including digesters, and N2O
emissions. The "emissions threshold" includes the CH4 and N2O that is emitted to the
atmosphere from these facilities. In the emissions threshold, CH4 that is recovered and
combusted at digesters is taken into account and deducted from the total CH4 generation
calculated.
This section discusses the number of facilities that meet emissions-based thresholds for
wastewater treatment emissions only. For facility-level threshold analyses at industrial
facilities with onsite wastewater treatment, please see the TSD for the industry.
One option analyzed would require wastewater treatment systems with combined CH4
and N2O (and indirect CO2 for petroleum refineries) generation of 25,000 mtC02e (i.e.,
CH4 and N2O generated at the wastewater treatment system) to report generation and
emissions. At this threshold, facilities operating wastewater treatment systems with
emissions of 25,000 mtC02e (i.e., anthropogenic CO2, CH4, andN20 emissions
generated at a wastewater treatment system minus CH4 combusted) would be required to
report their emissions.
At this threshold, EPA estimates that 0 domestic wastewater treatment plants, 18 pulp
and paper plants, up to 63 food processing plants, 1 ethanol refinery, and 1 petroleum
refinery would be required to report under this rule when only considering emissions
from the wastewater treatment system. Due to limited plant-specific data for industrial
wastewater treatment plants, EPA made assumptions regarding the types of treatment
systems in place at the industrial operations. In general, larger facilities tend to more
often use aerobic treatment systems; therefore, these estimates can be considered a
conservatively high estimate. Table 1 presents a summary of the number of facilities and
emissions reported at the proposed threshold.
6
-------
Table 1. Estimated Number of Facilities Reporting and Emissions Reported at a
25,000 mtCOie Threshold
Estimated
Percent of All
Percent of
All Emissions
from this
Type of
Operation
Operation
Number
Facilities
Reporting
Facilities of this
Type of
Operation
Emissions
(mtCOie)
Domestic
0
0
0
0
wastewater treatment
plants
Pulp and paper
18
3.2
1,100,000
28
onsite wastewater
treatment
Food processing
<63
<1.1
<1,600,000
40
onsite wastewater
treatment
Ethanol refineries
1
0.7
33,000
31
onsite wastewater
treatment
Petroleum refineries
1
0.7
26,000
7
onsite wastewater
treatment
This section discusses the data used to analyze domestic wastewater treatment systems,
and onsite industrial wastewater treatment systems.
Domestic Wastewater Treatment. Using available activity data from EPA's Clean
Watersheds Needs Survey (CWNS) database and U.S. GHG inventory methods, EPA
estimated CH4 generation and emissions and direct N2O emissions for centralized
wastewater treatment systems. The CWNS database contains information on 15,343
plants in the U.S. Although this database may not include data on all treatment plants in
the U.S. (whose total number exceeds 16,000 plants), the data are considered
representative of all U.S. centralized wastewater treatment systems. The database
contains plant identification data, as well as information on wastewater flow, population
served, and unit operations in place. The data were analyzed to determine which plants
have primary sedimentation in place, whether the secondary treatment is aerobic or
anaerobic, and whether the plant performs biological denitrification and/or anaerobic
digestion of sludge.
EPA estimated the CH4 generated from wastewater treatment and sludge digestion, the
CH4 combusted from sludge digestion, and the direct N2O generated from wastewater
treatment. Table 2 presents a summary of emissions as estimated for the universe of
treatment systems included in the CWNS dataset. ERG next evaluated how many plants
generate (includes methane generation in digesters) or emit greenhouse gases above one
7
-------
of four thresholds: 1,000 mtCC^e, 10,000 mtCC^e, 25,000 mtCC^e, or 100,000 mtCC^e
based on estimated greenhouse gas (CH4 and N2O) emissions from wastewater treatment
including sludge digestion (indirect N2O emissions associated with nitrogen discharged in
the effluent from these plants are not included in these calculations). Table 3 presents a
summary of this analysis. For information on assumptions and details on the analysis,
please see ERG's memorandum dated July 21, 2008, Revised Threshold Analysis for
POTWs, located in the docket.
Table 2. Greenhouse Gas Emissions from Centralized Domestic Treatment Systems
Emission Type
Methane (mtC02e)
Direct Nitrous Oxide
(mtC02e)
Total Emissions
(tC02e)
Generated
16,820,573
201,226
17,021,799
Combusted
16,617,879
0
16,617,879
Emitted
202,695
201,226
403,920
Note: Emissions based on data from 15,343 plants in CWNS dataset. Nitrous oxide emissions do not
include emissions associated with nitrogen discharged to the environment in wastewater effluent.
Table 3. Summary of Threshold Analysis for Domestic Wastewater Treatment
Threshold
(mtC02e)
# Systems
% Systems
Emissions
(mtC02e)
% Emissions3
Emissions Threshold
1,000
59
0.4
120,362
30
10,000
0
0
0
0
25,000
0
0
0
0
100,000
0
0
0
0
Generation Threshold
1,000
1,438
9.4
270,114
67
10,000
273
1.8
184,550
46
25,000
112
0.7
143,079
35
100,000
27
0.2
79,005
20
aThe percent emissions column presents the percent of emissions from all plants in the U.S. that would be
covered based on the reporting threshold.
Industrial Wastewater Treatment. Using available activity data and U.S. GHG inventory
methods, EPA estimated greenhouse gas generation and emissions for certain industrial
wastewater treatment systems, including those located at pulp and paper mills, meat
processors, poultry processors, fruit and vegetable processors, ethanol producers, and
petroleum refiners. For each industrial category, ERG first attempted to locate any plant-
level datasets to directly calculate greenhouse gas emissions by plant, and count the
number of facilities that would exceed the thresholds of interest. Where plant-level data
were incomplete, EPA used default national-level data from the U.S. GHG Inventory to
fill in missing data. Where plant-level data were unavailable, EPA instead determined
the production levels for each industry that would trigger emissions over any of the
thresholds of interest, and used best professional judgment to estimate how many plants
would meet the production levels.
8
-------
EPA estimated CH4 emissions for the industries named above, as well as CO2 emissions
from oil/water separators at petroleum refineries. EPA did not include direct nitrous
oxide emissions associated with biological denitrification treatment onsite. The number
of industrial facilities in these categories using biological denitrification is likely low. In
addition, there are currently no established nitrous oxide emission factors for these
industries4. EPA estimated how many plants emit greenhouse gases above one of three
thresholds: 1,000 mtCC^e, 10,000 mtCC^e, 25,000 mtCC^e, or 100,000 mtCC^e based on
estimated greenhouse gas (CH4 and N2O) emissions from wastewater treatment. Table 4
presents a summary of this analysis. For certain industries where EPA identified
significant use of biogas collection in place, EPA also estimated how many plants have
generation (includes methane generation at digesters) above the thresholds. For
information on assumptions and details on the analysis, please see ERG's memorandum
dated July 17, 2008, Revised Threshold Analysis for the Estimation of Greenhouse Gas
Emissions from Individual Industrial Facilities, located in the docket.
4 The 2006 IPCC Guidelines only briefly address direct nitrous oxide emissions from centralized wastewater treatment
plants using biological denitrification, and do not discuss emissions from industrial wastewater treatment systems. In
the guidelines, the only other wastewater N20 emission factor that is offered is for domestic wastewater treatment (3.2
g N20 per person per year). Ongoing work by the Water Environment Research Foundation (WERF) may lead to
improved N20 emission factors.
9
-------
Table 4. Summary of Threshold Analysis for Industrial Wastewater Treatment
Threshold
(mtC02e)*
#
Systems
% Systems
Emissions
(mtC02e)
% Emissions
Pulp and Paper - Generation and Emissions r
"hresholds
1,000
23
4.1
1,144,351
30
10,000
22
3.9
1,135,278
29
25,000
18
3.2
1,065,422
28
100,000
1
<0.2
119,445
3.1
Meat Processing -Emissions Threshold
1,000
<616
<18
<2,024,125
<100
10,000
<45
<1.3
<1,125,000
<56
25,000
<13
<0.4
>325,000
>16
100,000
1
<0.1
>100,000
>5
Meat Processing - Generation T
ireshold
1,000
<616
<18
<2,024,125
<100
10,000
<45
<1.3
-1,125,000
>56
25,000
<19
<0.6
>425,000
>23
100,000
2
<0.1
>200,000
>10
Poultry Processing - <
feneration and Emissions Thresholds
1,000
86
16
>1,286,000
>85
10,000
50
9.3
>1,250,000
>82
25,000
NE
NE
NE
NE
100,000
0
0
0
0
Fruit and Vegetable - Generation and Emissions Thresholds
1,000
<100
<6%
<123,000
<100
10,000
0
0
0
0
25,000
0
0
0
0
100,000
0
0
0
0
Ethanol -Emissions Threshold
1,000
11
7.9
67,041
64
10,000
2
1.4
50,810
48
25,000
1
0.7
32,850
31
100,000
0
0
0
0
Ethanol - Generation Threshold
1,000
78
56
385,805
94
10,000
3
2.2
213,715
52
25,000
2
1.4
178,050
44
100,000
1
0.7
127,570
31
Petroleum Refining - Generation and Emissions Thresholds
1,000
30
21
213,871
60
10,000
8
5.6
119,246
34
25,000
1
0.7
25,914
7.3
100,000
0
0
0
0
Threshold analyzed is based on wastewater treatment emissions only.
10
-------
NE = not estimated. Data were unavailable to estimate whether systems over this threshold occur in the
U.S.
5.2 Other threshold options
EPA considered several other threshold options for reporting emissions:
1. All wastewater treatment plants regardless of size, treatment processes, or control
technology.
2. All anaerobic wastewater treatment plants.
3. Plants of a certain size (influent value or population served by plant).
4. Plants of a certain design capacity.
EPA also considered other thresholds, including requiring all wastewater treatment plants
regardless of size, treatment processes, or control technology to report. EPA determined
that this option would result in reporting from over 15,000 wastewater treatment systems
in the United States, many of whom are small emitters.
EPA also considered requiring all wastewater treatment plants with anaerobic wastewater
treatment systems to report. However, wastewater treatment plants that operate
anaerobic systems tend to be very small and manage wastewater for very small
populations. In fact, the plants with the most potential to emit greenhouse gases are large
wastewater treatment plants that operate aerobic systems, and digest their sludge on site.
EPA also considered requiring plants of a certain size to report, based on wastewater flow
treated or population served by the system. However, EPA generally found that the flow
and population are not highly correlated with emissions from wastewater treatment
because there are many factors that influence these emissions, including system type and
the amount of industrial co-discharge.
Finally, EPA considered plants of a certain design capacity to report. However, this is a
weak indicator of emissions from a wastewater treatment plant, because there are many
other factors that influence the emissions, including wastewater influent BOD or COD
and N content, and system type.
6. Options for Monitoring Methods
One option for the monitoring method involves the use of activity data, such as measured
BOD or COD, and N influent, and operational characteristics (e.g., type of management
system), with the Intergovernmental Panel on Climate Change (IPCC) Tier 1 method to
calculate CH4 generation and N2O emissions and measured values for gas combustion.
This approach allows the use of default factors, such as a system emission factor, for
certain elements of the calculation, and encourages the use of site-specific data wherever
possible. The cost of such an approach is usually low, but the uncertainty can be high.
For additional information on this method, please see IPCC 20065 and EPA 20086.
5 IPCC 2006. Chapter 6: Wastewater Treatment and Discharge. IPCC (Volume 5 Waste). Available at
http://www.ipcc-nggip.iges.or.ip/public/2006gl/pdf/5 Volume5/V5 6 Ch6 Wastewater.pdf.
11
-------
6.1 Calculating Methane Generation
Domestic Wastewater Treatment. To estimate the amount of CH4 emissions from
domestic wastewater treatment, plant-specific values of BOD in the influent to the
treatment system are determined by periodic sampling and testing (see the section below
on Sampling and Testing Programs for more details). Next, the maximum amount of
methane that could potentially be produced by the wastewater under ideal conditions is
calculated by multiplying the BOD by the maximum methane producing capacity of the
wastewater (B0). The default B0 value for wastewater is 0.6 kg CH4/kg BOD, as shown in
the 2006IPCC Guidelines for National Greenhouse Gas Inventories, Volume 5, Chapter
6, Table 6.2.
Most wastewater treatment systems will not produce the maximum amount of methane
possible from the BOD because the conditions in the systems are not ideal for methane
production. The CH4 producing potential of a specific system is represented by a
parameter known as the methane conversion factor (MCF). This value ranges from 0 to
100 percent and reflects the capability of a system to produce the maximum achievable
CH4 based on the readily biodegradable organic matter present in the wastewater. A
higher MCF equates to a higher CH4 producing potential. MCF values for various types
of treatment systems are presented in the 2006 IPCC Guidelines for National Greenhouse
Gas Inventories, Volume 5, Chapter 6, Table 6.3.
The equations proposed to calculate CH4 generation at domestic wastewater treatment
systems are presented below:
CH^ (domestic wastewater) = X [Flow * BOD * Bo* MCF]
month
Where:
CH4 = Annual CH4 mass emissions from domestic wastewater
treatment (kg/year)
Flow = Monthly flow treated through anaerobic treatment system
(m3/month)
BOD = Average monthly organics loading in wastewater entering
anaerobic treatment system (kg/m3)
Bo = Maximum CH4 producing potential of domestic wastewater
(default value of 0.60 kg CH4 /kg BOD)
MCF = CH4 correction factor, indicating the extent to which the organic
content (measured as BOD) degrades anaerobically
In some cases, the wastewater may be treated prior to entering the anaerobic treatment
step(s). When sludge is removed in these primary treatment steps, the amount of BOD
treated anaerobically is less than the total BOD entering the POTW. In this situation, the
facility should ensure that the BOD measurement represents the wastewater treated
anaerobically.
6 EPA 2008. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006. Chapter 8: Waste.
http://www.epa.gov/climatechange/emissions/usinventorvreport.html
12
-------
Industrial Wastewater Treatment. To estimate the amount of CH4 emissions from
industrial wastewater treatment, plant-specific values of COD are determined by periodic
sampling and testing (see the section below on Sampling and Testing Programs for more
details). Next, the maximum amount of methane that could potentially be produced by
the wastewater under ideal conditions is calculated by multiplying the COD by the
maximum methane producing capacity of the wastewater (B0). The default B0 value for
wastewater is 0.25 kg CH4/kg COD, as shown in the 2006IPCC Guidelines for National
Greenhouse Gas Inventories, Volume 5, Chapter 6, p.6.21.
Most wastewater treatment systems will not produce the maximum amount of methane
possible from the wastewater because the conditions in the systems are not ideal for
methane production. The CH4 producing potential of a specific system is represented by a
parameter known as the methane conversion factor (MCF). This value ranges from 0 to
100 percent and reflects the capability of a system to produce the maximum achievable
CH4 based on the readily biodegradable organic matter present in the wastewater. A
higher MCF equates to a higher CH4 producing potential. MCF values for various types
of treatment systems are presented in the 2006 IPCC Guidelines for National Greenhouse
Gas Inventories, Volume 5, Chapter 6, Table 6.8.
The equation proposed to calculate CH4 generation at industrial wastewater treatment
systems is presented below:
CH^ (industrial wastewater) = £ [Flow * COD * Bo* MCF]
month
Where:
CH4 = Annual CH4 mass emissions from industrial wastewater
treatment (kg/year)
Flow = Monthly flow treated through anaerobic treatment system
(m3/month)
COD = Average monthly organics loading in wastewater entering
anaerobic treatment system (kg/m3)
Bo = Maximum CH4 producing potential of industrial wastewater
(default value of 0.25 kg CH4 /kg COD)
MCF = CH4 correction factor, indicating the extent to which the organic
content (measured as COD) degrades anaerobically
In addition, the equation proposed to calculate indirect CO2 emissions from oil/water
separators at petroleum refineries is presented below:
ECC>2 = Y*[FFsep * VH20 * C * 44/12 * metricton/lOOOkg]
month
Where:
ECO2 = Annual emissions of CO2 (metric tons/yr)
13
-------
EFsep = Emissions factor for the type of separator (kg
NMVOC/m3 wastewater treated)
Vh2o = Monthly flow treated through oil/water separator
(m3/month)
C = Carbon fraction in NMVOC (default = 0.6)
44/12 = Conversion - carbon to carbon dioxide
Metric tons/1000 = Conversion factor from kg to metric tons
Sampling and Testing Programs. Samples and measurements taken for the purpose of
estimating whether emissions reach a reporting threshold must be representative of the
plant's activities. To develop an appropriate testing program, the following four factors
need to be addressed:
1) Sampling Location. The plant must identify the sampling location that will provide a
valid estimation of BOD (for POTWs) or COD (for industrial facilities) entering the
wastewater treatment system. The plant should select a location where the wastewater
flow is measurable and that is easily and safely accessible. The sample location should
represent the wastewater influent for the time period that is monitored.
2) Sample Collection Method. There are two basic sample collection methods: "grab"
and "composite." A "grab" sample is a single sample collected at a particular time and
place. When the quality and flow of the waste stream being sampled is not likely to
change over time, a grab sample is appropriate. A "composite" sample is a collection of
individual samples. For flowing streams, such as treatment system influent, the individual
samples are usually collected at a regular time or volume interval (e.g., every hour or
every 1,000 liters). A composite sample is desirable when the sampled waste stream
varies significantly over time. The quality and flow of POTW influent wastewater varies
diurnally. For this reason, a 24-hour flow-weighted composite will provide the most
representative sample of POTW influent. Industrial facilities should also collect 24-hour
flow-weighted composites, unless they can demonstrate that the quality and flow into the
treatment system does not vary. In this case, industrial facilities should collect 24-hour
time-weighted composites to characterize changes in wastewater due to production
fluctuations, or a grab sample is the influent flow is equalized resulting in little
variability.
3) Monitoring Frequencies. To establish a monitoring frequency, the plant should
estimate the variability of the BOD or COD concentration by reviewing existing influent
data. A highly variable waste stream should be measured on a more frequent basis than a
waste stream that is relatively consistent over time (particularly in terms of flow and
pollutant concentration). We recommend a monitoring frequency of no less than one time
per month; ideally the frequency would be weekly, with the option of reducing frequency
if BOD or COD loads into the system are generally consistent throughout the year. Some
facilities may already be required by their NPDES permit to collect influent BOD or
COD samples on a daily or weekly basis, and should use all data available for the
calculation of a monthly mean BOD or COD mass load.
14
-------
At some POTWs the BOD load will vary seasonally, including plants that serve a
seasonal population (such as seasonal resorts, winter retirement communities, or
colleges). Flows and BOD loads may decrease in summer, when populations move to
northern regions or students go on vacation. Loads may increase during the time the
resort is in use. If the POTW knows it has seasonal variations, it should monitor during
the season with the highest loads.
Similarly, some industrial plants undergo seasonal variations in production, such as fruit
and vegetable processors that may undergo higher production activities following the
harvest of a particular crop.
4) Analytical Methods. For domestic wastewater treatment systems, BOD is the most
widely used parameter of organic pollution in wastewater, and is typically measured as
"5-day BOD" (BOD5). BOD measures the amount of dissolved oxygen used by
microorganisms in the biochemical oxidation of organic matter. In general, the sample is
seeded to provide sufficient nutrients and oxygen for the duration of the incubation
period. The typical incubation is five days, and the typical temperature is 20°C.
COD is a widely used parameter of organic pollution in industrial wastewater. Chemical
oxygen demand (COD) is a measure of the capacity of water to consume oxygen during
the decomposition of organic matter and the oxidation of inorganic chemicals such as
ammonia and nitrite. The basis for the COD test is that nearly all organic compounds can
be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions.
Analytical methods for industrial and municipal wastewater pollutants must be conducted
in accordance with the methods specified pursuant to 40 CFR Part 136, which references
one or more of the following:
• Test methods in Appendix A of 40 CFR Part 136;
• Standard Methods for the Examination of Water and Wastewater, 18th Edition;
• Methods for the Chemical Analysis of Water and Wastewater; and
• Test Methods: Methods for Organic Chemical Analysis of Municipal and Industrial
Wastewater.
6.2 Methane Combustion at Anaerobic Digesters
If the wastewater treatment plant has an anaerobic digester, such as those used to digest
biosolids at domestic wastewater treatment plants, EPA proposes that the CH4
combustion of the digester be measured. Direct measurement to determine CH4
combustion from anaerobic digesters depends on two measurable parameters: 1) the rate
of gas flow to the combustion device; and 2) the CH4 content in the gas flow. These can
be quantified by directly measuring the gas stream to the destruction device(s). The gas
stream may be measured by continuous metering or monthly sampling.
For continuous metering, the recommended instrumentation measures both flow and gas
concentration. Several direct measurement instruments also use a separate recorder to
15
-------
store and document the data. A fully integrated system that directly reports CH4 content
requires no other calculation than summing the results of all monitoring periods for a
given year. Internally, the instrumentation is performing its calculations using algorithms
similar to Equation B below.
For monthly sampling, the two primary instruments used are a gas flow meter and a gas
composition meter. The gas flow meter must be installed as close to the gas combustion
device as possible to measure the amount of gas reaching the device. Two procedures are
used for data collection in the monthly monitoring method:
1. Calibrate monitoring instrument in accordance with the manufacturer's
specifications.
2. Collect four sets of data: flow rate (ft3/minute); CH4 concentration (percent);
temperature (°R); and pressure (atm). The measurements should be taken before
any treatment equipment and using a monitoring meter specifically for CH4 gas.
The amount of CH4 destroyed during the month is calculated using Equation B. Monthly
data for V, C, T, P and t (see below) are summed to calculate an annual total.
C = V x (Cone/100) x 0.0423 x (520/T) x (P/l) x (t) x (0.454/1000)
Where:
V = Total volumetric flow (ft3/minute)
Cone = CH4 concentration (percent)
0.0423 = Density of methane at 520R or 60°F (pounds/standard ft3)
T = Temperature at which flow is measured (°R)
P = Pressure at which flow is measured (atm)
t = Time period since last monthly measurement (minutes)
0.454/1000 = Conversion factor, pounds to metric tons
6.3 Calculating Methane Combustion of Anaerobic Digesters
To estimate CH4 combustion at a digester, apply the destruction efficiency of the
combustion equipment to the value for C estimated above.
D = C x DE
Where:
DE = CH4 destruction efficiency from flaring or burning in engine (default
is 0.99)7
7 EPA 1998. U.S. Environmental Protection Agency (1998) "AP-42 Compilation of Air pollutant
Emission Factors." Chapter 2.4, Table 2.4-3, page 2.4-13. Downloaded from:
http://www.epa.gov/ttn/chief/ap42/ch02/final/c02s04.pdf.
16
-------
6.4 Nitrous Oxide Emissions
To estimate the amount of direct wastewater N2O emissions at the treatment plant, the
average annual service population is multiplied by a default emission factor and a factor
to represent the contributions from industrial wastewater (default = 1.25). Note that this
method does not consider N2O emissions that may be generated from nitrogen discharged
to the environment in effluent from treatment systems.
The equations proposed to calculate direct N2O emissions from wastewater treatment
systems are presented below:
E = N20plant = N2OMT/DEMT + N20woutnit/denit
N20mT/DENIT= [PoPnd X EF2 x Fmd.com] x 1/10A9
N2OWOUTNIT/DENIT = {(Pop - USpoPNDX F^d-com) X EFl} X 1/10A9
Where:
N2OPLant = Annual N20 emissions from centralized wastewater treatment plants (kg)
N2Omt/denit = N20 emissions from centralized wastewater treatment plants with
nitrification/denitrification (kg)
N20Wout nit/denit = N20 emissions from centralized wastewater treatment plants without
nitrification/denitrification (kg)
Pop = Service population
Popnd = Service population that is served by biological denitrification
EFi = Emission factor (3.2 g N20/person-year)
EF2 = Emission factor (7 g N20/person-year)
Find-com = Factor for industrial and commercial co-discharged protein into the sewer
system (default value 1.25)
6.5 Estimating Total Generation and Emissions
Generation from a wastewater treatment plant can be estimated by converting the CH4
emissions from the system (A+B+C) and the N2O emissions from the system (E) into
common units of CO2 equivalents, then summing them.
Generation = A + B + C + E
Emissions from a system can be estimated by adding the CH4 emissions from the system
(A+B+C) and the N2O emissions from the system (E), then subtracting the CH4
combustion from anaerobic digestion (D) (taking into account the destruction efficiency):
All parameters should be converted to a common unit (CO2 equivalents) before the
calculation occurs.
Emissions = A + B + C- D + E
17
-------
6.6 Calculating CH4 Generation and Emissions Using Digester Gas Collection Data
EPA also considered using gas collection data (metered) and an estimate of collection
system efficiency to calculate generation. The advantage of this method is that it uses
metered data. However, it is difficult to estimate collection efficiency, and studies have
given greatly varying values for collection efficiency.
6.7 Direct Measurement of Emissions
Direct measurement is another option EPA considered. This method allows for site-
specific measurements, but it is very costly and might not be accurate if the measuring
system has incomplete coverage. A direct measurement system must be complete both
spatially (in that all emissions pathways are covered) and temporally (as emissions can
vary greatly due to changes in influent and conditions at the plant).
7. Options for Estimating Missing Data
On the occasion that a facility lacks sufficient data to determine the emissions from
wastewater treatment over a period of time, EPA considered requiring that the facility
apply an average facility-level value for the missing parameter from the previous year.
The rule would then require a complete record of all parameters determined from
company records that are used in the GHG emissions calculations (e.g., production data,
biogas combustion data, etc.).
8. QA/QC Requirements
In evaluating options for QA/QC requirements, EPA considered requiring reporters to
maintain records on wastewater flow and influent BOD (for POTWs) or COD (for
industrial facilities) entering the treatment system and records on gas flow and CH4
content to any combustion device; EPA could use these data to check the estimated
emissions submitted by the entity. EPA considered requesting reporters to use EPA-
provided national emission factors for CH4 and N2O per capita and system type to check
against calculated emissions, but believes there is too much variability to compare
average national data to a specific system.
18
------- |