Waste 8

- 1 

# 8. Waste

Waste management and treatment activities are sources of greenhouse gas emissions (see Figure 8

- 1 ). Landfills accounted for approximately 17.5 percent of total U.S. anthropogenic methane (CH 4 ) emissions in 201 1 , the third largest contribution of any CH 4 source in the United States. Additionally, wastewater treatment and composting of organic waste accounted for approximately 2.8 percent and less than 1 percent of U.S. CH 4 emissions, respectively. Nitrous oxide (N 2 O) emissions from the discharge of wastewater treatment effl uents into aquatic environments were estimated, as were N 2 O emissions from the treatment process itself. N 2 O emissions from composting were also estimated. Together, these waste activities account for less than 2 percent of total U.S. N 2 O emissions. Nit rogen oxides (NO

x ), carbon monoxide (CO), and non

- CH 4 volatile organic compounds (NMVOCs) are emitted by waste activities, and are addressed separately at the end of this chapter. A summary of greenhouse gas emissions from th e Waste chapter is presented i n Table 8

- 1 and Table 8

- 2

.

Figure 8

- 1 : 2011 Waste Chapter Green house Gas Sources

Box 8

- 1 : Methodological Approach for Estimating and R eporting U.S. Emissions and S inks

In following the UNFCCC requirement under Article 4.1 to develop and submit national greenhouse gas emission inventories, the emissions and sinks presented in this report and this chapter, are organized by source and sink categories and calculated using internationally

- accepted methods provided by the Intergovernmental Panel on8

- 2 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

Climate Change (IPCC). 246 A dditionally, the calculated emissions and sinks in a given year for the U nited S tates are presented in a common manner in line with the UNFCCC reporting guidelines for the reporting of inventories under this international agreement. 247 The use of consistent methods to calculate emissions and sinks by all nations providing their inventories to the UNFCCC ensures that these reports are comparable. In this regard, U.S. emissions and sinks reported in this inventory report are comparable to emissions and sinks r eported by other countries. Emissions and sinks provided in this inventory do not preclude alternative examinations, 248 but rather this inventory presents emissions and sinks in a common format consistent with how countries are to report inventories under t he UNFCCC. The report itself, and this chapter, follows this standardized format, and prov ides an explanation of the IPCC methods used to calculate emissions and sinks, and the manner in which those calculations are conducted.

Overall, in 201 1 , waste activities generated emissions of 127.7 Tg CO 2 Eq., or just under 2 percent of total U.S. greenhouse gas emissions.

Table 8

- 1 : Emissions from Waste (Tg CO 2 Eq.)

Gas/Source 1990 2005 2007 2008 2009 2010 2011

CH 4 164.0 130.5 129.8 131.9 131.4 124.7 120.8

Landfills 147.8 112.5 111.6 113.6 113.3 106.8 103.0

Wastewater Treatment 15.9 16.5 16.6 16.6 16.5 16.4 16.2 Composting 0.3 1.6 1.7 1.7 1.6 1.5 1.5

N 2 O 3.8 6.4 6.7 6.8 6.7 6.8 6.9

Domestic Wastewater

Treatment 3.5 4.7 4.8 4.9 5.0 5.1 5.2 Composting 0.4 1.7 1.8 1.9 1.8 1.7 1.7

Total 16 7.8 136

. 9 136.5 138.6 138.1 131.4 127.7 Note: Totals may not sum due to independent rounding.

Table 8

- 2 : Emissions from Waste (Gg)

Gas/Source 1990 2005 2007 2008 2009 2010 2011

CH 4 7,810 6,217 6,183 6,280 6,258 5,936 5,751

Landfills 7,037 5,357 5,314 5,409 5,397 5,083 4,907

Wastewater Treatment 758 785 791 791 786 779 770 Composting 15 75 79 80 75 73 74

N 2 O 12 21 21 22 22 22 22

Domestic Wastewater

Treatment 11 15 16 16 16 16 17 Composting 1 6 6 6 6 5 6 Note: Totals may not sum due to independent rounding.

Carbon dioxide

, CH 4 , and N 2 O emissions from the incineration of waste are accounted for in the Energy sector rather than in the Waste sector because almost all incineration of municipal solid waste (MSW) in the United States

occurs at waste

- to

- energy facil ities where useful energy is recovered. Similarly, the Energy sector also includes an estimate of emissions from burning waste tires and hazardous industrial waste, because virtually all of the combustion occurs in industrial and utility boilers that recov er energy. The incineration of waste in the United States

246 See http://www.ipcc

- nggip.iges.or.jp/public/index.html

. 247 See http://unfccc.int/national_reports/annex _i_ghg_inventories/national_inventories_submissions/items/5270.php

. 248 For example, see http://www.epa.gov/aboutepa/oswer.html

.Waste 8

- 3

in 201 1 resulted in 12.4 Tg CO 2 Eq. emissions, nearly half of which is attributable to the combustion of plastics. For more details on emissions from the incineration of waste, see Section 3.3.

It is additionally noted that in this chapter methodological guidance was taken from the 2006 IPCC Guidelines for

National Greenhouse Gas Inventories

. This latest guidance from the IPCC best represents the understanding of emissions profiles from activitie s in the waste sector. The use of the most recently published calculation methodologies by the IPCC, as contained in the 2006 IPCC Guidelines for waste source categories is fully in line with the IPCC good practice guidance for methodological choice to imp rove rigor and accuracy. In addition, the improvements in using the latest methodological guidance from the IPCC has been recognized by the UNFCCC’s
Subsidiary Body for Scientific and Technological Advice in the conclusions of its 30th Session 249 , Numerous U .S. inventory experts were involved in the development of the 2006 IPCC Guidelines, and their expertise has provided this latest guidance from the IPCC with the most appropriate calculation methods that are then used in this chapter.

Box 8

- 2 : Waste Data from the Greenhouse Gas Reporting Program

On October 30, 2009, the U.S. EPA published a rule for the mandatory reporting of greenhouse gases from large GHG emissions sources in the United States. Implementation o f 40 C FR Part 98 is referred to as EPA’s Greenhouse Gas Reporting Program (GHGRP) . 40 CFR part 98 applies to direct greenhouse gas emitters, fossil fuel suppliers, industrial gas suppliers, and facilities that inject CO 2 underground for sequestration or ot her

reasons and requires reporting by 41 industrial categories. Reporting is at the facility level, except for certain suppliers of fossil fuels and industrial greenhouse gases. In general, the threshold for reporting is 25,000 metric

tons or more of CO 2 E q. per year.

EPA’s GHGRP dataset and the data presented in this inventory report are complementary and, as i ndicated in the respective plann ed improvements sections for source categories in this chapter, EPA is analyzing how to use facility

- level GHGRP da ta to improve the national estimates presented in this inventory. Most methodologies

used in EPA’s GHGRP are consistent with IPCC, though for EPA’s GHGRP, facilities collect detailed information specific to their operations according to detailed measuremen t standards

. This may differ with the more aggregated data collected for the inventory to estimate total, national U.S. emissions. It should be noted that

t he definitions for source categories in the GHGRP may differ from those used in this inventory in meeting the UNFCCC reporting guidelines. In line with the UNFCCC reporting guidelines, the inventory report is a comprehensive accounting of all emissions from source catego ries identified in the IPCC guidelines

. Further information on the reporting categorization s in EPA’s GHGRP and specific data caveats associated with monitoring methods in EPA’s GHGRP has been provided on the EPA’s GHGRP website. 250

EPA presents the data co llected by EPA’s GHGRP through a data publication tool 251 that allows data to be viewed in several formats including maps, tables, charts and graphs for individual facilities or groups of facilities.

249 These Subsidiary Body for Scientific and Technological Advice (SBSTA) conclusions state, “The SBSTA acknowledged

that the 2006 IPCC Guidelines contain the most recent scientific methodologies available to estimate emissions by sources and removals by sinks of greenhouse gases (GHGs) not controlled by the Montreal Protocol, and recognized that Parties have gained experience with t he 2006 IPCC Guidelines. The SBSTA also acknowledged that the information contained in the 2006 IPCC Guidelines enables Parties to further improve the quality of their GHG inventories.” See

< http://unfccc.int/resource/docs/2009/sbsta/eng/03.pdf >
250 See

< http://www.ccdsupport.com/confluence/display/ghgp/Detailed+Description+of+Data+for+Certain+Sources+and+Processes>.

251 See < http://ghgdata.epa.gov >

.8

- 4 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1 

# 8.1 Landfills (IPCC Source Category 6A1)

In the United States, solid waste is managed by landfilling, recovery through recycling or composting, and combustion through waste

- to

- energy facilities. Disposing of solid waste in modern, managed landfills is the most commonly used waste management tech nique in the United States. More information on how solid waste data are collected and managed in the United States is provided in Box 8

- 3 and Box 8

- 4 . The municipal solid waste (MSW) and industrial waste landfills referred to in this section are all modern landfills that must comply with a variety of regulations as discussed in Box 8

- 5 . Disposing of waste in illegal dumping sites is not considered to have occurred in years later than 1980 and these sites are not considered to contribute to net emissions in this section for the inventory time frame of 1990 to 2011. MSW landfills, or sanitary landfills, are sites where MSW is managed to prevent or minimize health, safety, and environmental impacts. Waste is deposited in different cells and covered daily with soil; many have e nvironmental monitoring systems to track performance, collect leachate, and collect landfill gas. Industrial waste landfills are constructed in a similar way as MSW landfills, but accept waste produced by industrial activity, such as factories, mills, and mines.

After being placed in a landfill, organic waste (such as paper, food scraps, and yard trimmings) is initially decomposed by aerobic bacteria. After the oxygen has been depleted, the remaining waste is available for consumption by anaerobic bacteria , which break down organic matter into substances such as cellulose, amino acids, and sugars. These substances are further broken down through fermentation into gases and short

- chain organic compounds that form the substrates for the growth of methanogeni c bacteria. These methane

- (CH 4 ) producing anaerobic bacteria convert the fermentation products into stabilized organic materials and biogas consisting of approximately 50 percent biogenic carbon dioxide (CO 2 ) and 50 percent CH 4 , by volume. Landfill biog as also

contains trace amounts of non

- methane organic compounds (NMOC) and volatile organic compounds (VOC) that either result from decomposition by

- products or volatilization of biodegradable wastes (EPA 2008).

Methane and CO 2 are the primary constituen ts of landfill gas generation and emissions. However, the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines set an international convention to not report biogenic CO 2 released due to landfill decomposition in the Waste sector (IPCC 2006). C arbon dioxide emissions are estimated and reported for under the Land Use/Land Use Change and Forestry (LULUCF) sector (see Box 8

- 6 ). Additionally, emissions of NMOC and VOC are not estimated because they are considered to be emitted in trace amounts. Nitrous oxide (N 2 O) emissions from the disposal and application of sewage sludge on landfills are also not explicitly modeled as part of greenhouse gas emissions from lan dfills. N 2 O emissions from sewage sludge applied to landfills as a daily cover or for disposal are expected to be relatively small because the microbial environment in an anaerobic landfill is not very conducive to the nitrification and denitrification pr ocesses that result in N 2 O emissions. Furthermore, the 2006 IPCC Guidelines (IPCC 2006) did not include a methodology for estimating N 2 O emissions from solid waste disposal sites “because they are not significant.” Therefore, only CH 4 generation and

emis sions are estimated for landfills under the Waste sector.

Methane generation and emissions from landfills are a function of several factors, including: (1) the total amount of

waste

- in

- place, which is the total waste landfilled annually over the operation al lifetime of a landfill; (2) the characteristics of the landfill receiving waste (e.g., composition of waste

- in

- place, size, climate, cover material); (3)

the amount of CH 4 that is recovered and either flared or used for energy purposes; and (4) the amou nt of CH 4 oxidized as the landfill gas passes through the cover material into the atmosphere. Each landfill has unique characteristics, but all managed landfills practice similar operating practices, including the application of a daily and

intermediate c over material over the waste being disposed of in the landfill to prevent odor and reduce risks to public health. Based on recent literature, the specific type of cover material used can affect the rate of oxidation of landfill gas (RTI 2011). The most c ommonly used cover materials are soil, clay, and sand. Some states also permit the use of green waste, tarps, waste derived materials, sewage sludge or biosolids, and contaminated soil as a daily cover. Methane production typically begins one or two years after waste is disposed of in a landfill and will continue for 10 to 60 years or longer as the degradable waste decomposes over time.

In 2011, landfill CH 4 emissions were approximately 103.0 Tg CO 2 Eq. (4,907 Gg of CH 4 ), representing the third largest s ource of CH 4 emissions in the United States, behind natural gas systems and enteric fermentation. Emissions from MSW landfills, which received about 69 percent of the total solid waste generated in the United States, accounted for about 94 percent of tota l landfill emissions, while industrial landfills accounted for the remainder. Approximately 1,900 to 2,000 operational MSW landfills exist in the United States, with the largestWaste 8

- 5

landfills receiving most of the waste and generating the majority of the CH 4 emitted (EPA 2010; BioCycle 2010; WBJ 2010). Conversely, there are approximately 3,200 MSW landfills in the United States that have been closed since 1980 (for which a closure data is known, WBJ 2010). While the number of active MSW landfills has

decreas ed significantly over the past 20 years, from approximately 6,326 in 1990 to approximately 2,000 in 20 10, the average landfill size has increased (EPA 2010; BioCycle 2010; WBJ 2010 ). The exact number of active and

closed dedicated industrial waste landfil ls is not known at this time, but the Waste Business Journal total of landfills that accept industrial and construction and demolition debris for 2010 is 1,305.

The estimated annual quantity of waste placed in MSW landfills increased 26 percent from abou t 205 Tg in 1990 to 258 Tg in 2011 (see Annex 3.13). Net CH 4 emissions have fluctuated from year to year, but a slowly decreasing trend has been observed over the past decade despite increased waste disposal amounts. For example, from 1990 to 2011, net C H 4 emissions from landfills decreased by approximately 30 percent (see Table 8

- 3 and Table 8

- 4 ). This decreasing trend can be attributed to a 21 percent reduction in the amount of decomposable materials (i.e., paper and paperboard, food scraps, and yard trimmings) discarded in MSW landfills over the time series (EPA 2010) and an increase in the amount of landfill gas collected and combusted (i.e., used for energy or fl ared), resulting in lower net

CH 4 emissions from MSW landfills. 252 For instance, in 1990, approximately 954 Gg of CH 4 were recovered and combusted from landfills, while in 2011, approximately 8,177 Gg of CH 4 were combusted, representing an average

annual in crease in the quantity of CH 4 recovered and combusted from 1990 to 2011 of 11 percent (see Annex 3.13). In 2011, an estimated 71 new landfill gas

- to

- energy (LFGTE) projects and 29 new flares began operation (EPA 2012). While the amount of landfill gas co llected and combusted continues to increase every year, the rate of increase in collection and combustion no longer exceeds the rate of additional CH 4 generation from the amount of organic MSW landfilled as the U.S. population grows.

The total amount of MSW generated is expected to increase as the U.S. population continues to grow. The percentage of waste landfilled, however, may decline due to increased recycling and composting practices. Additionally, the quantity of recovered CH 4 that is either flare d or used for energy purposes is expected to continually increase as a result of 1996 federal regulations that require large MSW landfills to collect and combust landfill gas (see 40 CFR Part 60, Subpart Cc 2005 and 40 CFR Part 60, Subpart WWW 2005), as we ll as voluntary programs that encourage CH 4 recovery and use such as EPA’s Landfill Methane Outreach Program (LMOP), and federal and state incentives that promote renewable energy (e.g., tax credits, low interest loans, and Renewable Portfolio Standards).

252 Due to a lack of data specific to industrial waste landfills, landfill gas recovery is only estimated for M SW landfills.8

- 6 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

Table 8

- 3 : CH 4 Emissions from Landfills (Tg CO 2 Eq.)

Activity 1990 2005 2007 2008 2009 2010 2011

MSW Landfills 172.6 241.2 254.2 259.2 262.9 266.6 270.2

Industrial Landfills 11.6 15.4 15.5 15.7 15.8 15.9 16.0

Recovered

Gas

- to

- Energy (13.3) (55.9) (62.6) (67.2) (74.2) (82.5) (88.0)

Flared (6.7) (75.7) (83.2) (81.5) (78.6) (81.4) (83.7)

Oxidized a (16.4) (12.5) (12.4) (12.6) (12.6) (11.9) (11. 4 )

Total 147.8 112.5 111.6 113.6 113.3 106.8 103.0 Note: Totals may not sum due to independent rounding. Parentheses indicate negative values.

a Includes oxidation at both municipal and industrial landfills. Oxidation at MSW landfills is accounted for after

CH 4 recovery.

Table 8

- 4 : CH 4 Emissions from Landfills (Gg)

Activity 1990 2005 2007 2008 2009 2010 2011

MSW Landfills 8,219 11,486 12,106 12,343 12,519 12,694 12,868

Industrial Landfills 554 732 740 746 752 758 761

Recovered

Gas

- to

- Energy (634) (2,660) (2,980) (3,198) (3,532) (3,927) (4,190)

Flared (321) (3,606) (3,961) (3,880) (3,743) (3,876) (3,986)

Oxidized a (782) (595) (590) (601) (600) (565) (545)

Total 7,037 5,357 5,314 5,409 5,397 5,083 4,907 Note: Totals may not sum due to independent rounding. Parentheses indicate negative values.

a Includes CH 4 oxidation at municipal and industrial landfills. Oxidation at MSW landfills is accounted for after CH 4

recovery.


# Methodology

CH 4 emissions from landfills were estimated as the CH 4 produced from MSW landfills, plus the CH 4 produced by industrial waste landfills, minus the CH 4 recovered and combusted from MSW landfills, minus the CH 4 oxidized before being released into the atmosphere:

CH 4,Solid Waste = [CH 4,MSW + CH 4,Ind − R] − Ox

wh ere,

CH 4,Solid Waste = CH 4 emissions from solid waste

CH 4,MSW = CH 4 generation from MSW landfills,

CH 4,Ind = CH 4 generation from industrial landfills,

R = CH 4 recovered and combusted (only for MSW landfills), and

Ox = CH 4 oxidized from MSW and industrial waste landfills before release to the atmosphere.

The methodology for estimating CH 4 emissions from landfills is based on the first order decay model described by the IPCC (IPCC 2006). Methane generation is based on natio nwide waste disposal data; it is not landfill

- specific.

The amount of CH 4 recovered, however, is landfill

- specific, but only for MSW landfills due to a lack of data specific to industrial waste landfills. Values for the CH 4 generation potential (L 0 ) and de cay rate constant (k) used in the first order decay model were obtained from an analysis of CH 4 recovery rates for a database of 52 landfills and from published studies of other landfills (RTI 2004; EPA 1998; SWANA 1998; Peer, Thorneloe, and Epperson 1993) . The decay rate constant was found to increase with average annual rainfall; consequently, values of k were developed for 3 ranges of rainfall, or climate types (wet, arid, and temperate). The annual quantity of waste placed in landfills was apportioned to the 3 ranges of rainfall based on the percent of the U.S. population in each of the 3 ranges. Historical census data were used to account for the shift in population to more arid areas over time. An overview of the data sources and methodology used t o calculate CH 4 generation and recovery is provided below, while a more detailed description of the methodology used to estimate CH 4 emissions from landfills can be found in

Annex 3.13.Waste 8

- 7

National MSW landfill waste generation and disposal data are obtained from the BioCycle State of Garbage surveys, published approximately every two years. The State of Garbage (SOG) survey is the only continually updated nationwide survey of waste disposed in landfills in the United States. The SOG surveys use the principle s of mass balance where all MSW generated is equal to the amount of MSW landfilled, combusted in waste

- to

- energy plants, composted, and/or recycled ( BioCycle 2010). This approach assumes that all waste management methods are tracked and reported to state a gencies. Survey respondents are asked to provide a breakdown of MSW generated and managed by landfilling, recycling, composting, and combustion (in waste

- to

- energy facilities) in actual tonnages. The survey reported data are adjusted to exclude non

- MSW m aterials (e.g., industrial and agricultural wastes, construction and demolition debris, automobile scrap, and sludge from wastewater treatment plants) that may be included in survey responses. All state disposal data are adjusted for import/export; importe d waste is included in a particular state and exported waste is not. Where no waste generation data are provided by a state in

the SOG survey, the amount generated is estimated using the average nationwide waste per capita rate multiplied by that particul ar state’s population.

National landfill waste generation data for 1989 through 2008 were obtained from the SOG survey for every two years (BioCycle 2006, 2008, and 2010). National landfill waste generation data for the years in

- between the BioCycle State of Garbage surveys (e.g., 2001, 2003, 2005, 2007, 2009, 2010, and 2011) were extrapolated based on BioCycle data and the U.S. Census population The most recent SOG survey was published in 2010 for the 2008 year. Waste generation data will be update d as new reports are published. Because the SOG survey does not account for waste generated in U.S. territories, waste generation for the territories was estimated using population data obtained from the U.S. Census Bureau (2009, 2012) and national per cap ita solid waste generation from the

survey (2010).

Estimates of the quantity of waste landfilled from 1989 to the current inventory year are determined by applying a waste disposal factor to the total amount of waste generated (i.e., the SOG data). A was te disposal factor is determined for each year an SOG survey is published and equals the ratio of the total amount of waste landfilled to the total amount of waste generated. The waste disposal factor is interpolated for the years in

- between the BioCycle

s urveys, as is done for the amount of waste generated for a given survey year.

Estimates of the annual quantity of waste landfilled for 1960 through 1988 were obtained from EPA’s Anthropogenic Methane Emissions in the United States, Estimates for 1990: Report to Congress (EPA 1993) and an extensive landfill survey by the EPA’s Office of Solid Waste in 1986 (EPA 1988). Although waste placed in landfills in the 1940s and 1950s contributes very little to current CH 4 generation, estimates for those years were included in the first order decay model for completeness in accounting for CH 4 generation rates and are based on the population in those years and the per capita rate for land disposal for the 1960s. For calculations in this inventory,

wastes landfil led prior to 1980 were broken into two groups: wastes disposed in landfills (Methane Conversion Factor, MCF, of 1) and those disposed in dumps (MCF of 0.6). All calculations after 1980 assume waste is disposed in managed, modern landfills. Please see Ann ex 3.13 for more details.

Methane recovery is currently only accounted for at MSW landfills since no comprehensive data regarding gas collection systems have been published for industrial waste landfills. The estimated landfill gas recovered per year a t MSW landfills was based on a combination of three databases: the flare vendor database (contains updated sales data collected from vendors of flaring equipment), a database of landfill gas

- to

- energy (LFGTE) projects compiled by LMOP (EPA 2012), and a dat abase developed by the Energy Information Administration (EIA) for the voluntary reporting of greenhouse gases (EIA 2007). Based on the information provided by the EIA and flare vendor databases, the CH 4 combusted by flares in operation from 1990 to the c urrent inventory year was estimated. Information provided by the EIA and LMOP databases were used to estimate CH 4 combusted in LFGTE projects over the time series. The three databases were carefully compared to identify landfills that were in two or all three of the databases to avoid double or triple counting CH 4 reductions.

The flare vendor database estimates CH 4 combusted by flares using the midpoint of a flare’s reported capacity while

the EIA database uses landfill

- specific measured gas flow. As t he EIA database only includes data through 2006; 2007 to 2011 recovery for projects included in the EIA database were assumed to be the same as in 2006. This quantity likely underestimates flaring because these databases do not have information on all fla res in operation. The EIA database is no longer being updated and it is expected that data obtained from the EPA’s Greenhouse Gas Reporting Program (GHGRP) will serve as a supplemental data source for facility

- reported recovery data. Additionally, the EI A and LMOP databases provided data on landfill gas flow and energy generation for landfills with LFGTE projects. If a landfill in the EIA database was also in the LMOP and/or the flare vendor database, the8

- 8 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

emissions avoided were based on the EIA data beca use landfill owners or operators reported the amount recovered based on measurements of gas flow and concentration, and the reporting accounted for changes over time. If both flare data and LMOP recovery data were available for any of the remaining landfi lls (i.e., not in the EIA database), then the emissions recovery was based on the LMOP data, which provides reported landfill

- specific data on gas flow for direct use projects and project capacity (i.e., megawatts) for electricity projects. The flare data , on the other hand, only provide a range of landfill gas flow for a given flare size. Given that each LFGTE project is likely to also have a flare, double counting reductions from flares and LFGTE projects in the LMOP database was avoided by subtracting e mission reductions associated with LFGTE projects for which a flare had not been identified from the emission reductions associated with flares (referred to as the flare correction factor). A further explanation of the methodology used to estimate the lan dfill gas recovered can be found in Annex 3.13.

A destruction efficiency of 99 percent was applied to CH 4 recovered to estimate CH 4 emissions avoided due to the combusting of CH 4 in destruction devices, i.e., flares. The destruction efficiency value was s elected based on the range of efficiencies (86 to 99 percent) recommended for flares in EPA’s AP

- 42 Compilation of Air Pollutant Emission Factors, Chapter 2.4 (EPA 2008), efficiencies used to establish new source performance standards (NSPS) for landfills, and in recommendations for shutdown flares used in LMOP.

Emissions from industrial waste landfills were estimated from industrial production data (ERG 2012), waste disposal factors, and the first order decay model. As over 99 percent of the organic waste placed in industrial waste landfills originated from the food processing (meat, vegetables, fruits) and pulp and paper industries, estimates of industrial landfill emissions focused on these two sectors (EPA 1993). There are currently no data sources tha t track and report the amount and type of waste disposed of in industrial waste landfills in the United States. Therefore, the amount of waste landfilled is assumed to be a fraction of production that is held constant over the time series as explained in Annex 3.13. The composition of waste disposed of in industrial waste landfills is expected to be more consistent in terms of composition and quantity than that disposed of in MSW landfills.

The amount of CH 4 oxidized by the landfill cover at both municip al and industrial waste landfills was assumed to be ten percent of the CH 4 generated that is not recovered (IPCC 2006, Mancinelli and McKay 1985, Czepiel et al. 1996). To calculate net CH 4 emissions, both CH 4 recovered and CH 4 oxidized were subtracted fro m CH 4 generated at municipal and industrial waste landfills.



# Uncertainty and Time

- Series Consistency

Several types of uncertainty are associated with the estimates of CH 4 emissions from MSW and industrial waste landfills. The primary uncertainty concern s the characterization of landfills. Information is not available on two fundamental factors affecting CH 4 production: the amount and composition of waste placed in every MSW and industrial waste landfill for each year of its operation. The SOG survey is the only nationwide data source that compiles the amount of MSW disposed at the state

- level. The surveys do not include information on waste composition and there are no comprehensive data sets that compile quantities of waste disposed or waste compositi on by landfill. Some MSW landfills have conducted detailed waste composition studies, but landfills in the United States are not required to perform these types of studies. The approach used here assumes that the CH 4 generation potential and the rate of decay that produces CH 4 , as determined from several studies of CH 4 recovery at MSW landfills, are representative of conditions at U.S. landfills. When this top

- down approach is applied at the nationwide level, the uncertainties are assumed to be less than when applying this approach to individual landfills and then aggregating the results to the national level. In other words, this approach may over

- and under

- estimate

CH 4 generation at some landfills if used at the facility

- level, but the end result is e xpected to balance out because it is being applied nationwide. There is also a high degree of uncertainty and variability associated with the first order decay model, particularly when a homogeneous waste composition and hypothetical decomposition rates a re applied to heterogeneous landfills (IPCC 2006).

Additionally, there is a lack of landfill

- specific information regarding the number and type of industrial waste landfills in the United States. The approach used here assumes that the majority (99 percen t) of industrial waste disposed of in industrial waste landfills consists of waste from the pulp and paper and food and beverage industries. However, because waste generation and disposal data are not available in an existing data source for all U.S.

indu strial waste landfills, we apply a straight disposal factor over the entire time series to the amount of waste generated to determine the amounts disposed.Waste 8

- 9

Aside from the uncertainty in estimating CH 4 generation potential, uncertainty exists in the estima tes of the landfill gas oxidized. A constant oxidation factor of 10 percent as recommended by the Intergovernmental Panel on Climate Change (IPCC) for managed landfills is used for both MSW and industrial waste landfills regardless of climate, the type of cover material, and/or presence of a gas collection system. The number of field studies measuring the rate of oxidation has increased substantially since the IPCC 2006 Guidelines were published and, as discussed in the Potential Improvements section, eff orts are being made to review the literature and revise this value based on recent,

peer

- reviewed studies.

Another significant source of uncertainty lies with the estimates of CH 4 that are recovered by flaring and gas

- to

energy projects at MSW landfills. Three separate databases containing recovery information are used to determine

the total amount of CH 4 recovered and there are uncertainties associated with each. The LMOP database and the flare vendor databases are updated annually, while the EIA databa se has not been updated since 2005 and will essentially be replaced by the GHGRP data for a portion of landfills (i.e., those meeting the GHGRP thresholds). To avoid double counting and to use the most relevant estimate of CH 4 recovery for a given landfill, a hierarchical approach is used among the three databases. The EIA data are given precedence because CH 4 recovery was directly reported by landfills, the LMOP data are given second priority because CH 4 recovery is estimated from facility

reported LFGTE system characteristics, and the flare data are given third priority because this database contains

minimal information about the flare and no site

- specific operating characteristics (Bronstein et al., 2012). The IPCC

default value of 10 percent for uncertainty in recovery estimates was used in the uncertainty analysis when metering of landfill gas was in place (for about 64 percent of the CH 4 estimated to be recovered). This 10 percent uncertainty factor applies to 2 of the 3 databases (EIA and LMOP). For flaring without metered recovery data (approximately 34 percent of the CH 4 estimated to be recovered), a much higher uncertainty of approximately 50 percent was used (e.g., when recovery was estimated as 50 percent of the fla re’s design capacity). The compounding uncertainties associated with the 3 databases leads to the large upper and lower bounds for MSW landfills presented in Table 8

- 5

. The results of the IPCC Good Practice Guidance Tier 2 quantitative uncertainty analysis are summarized in Table

8

- 5 . In 2011, land fill CH 4 emissions were estimated to be between 47.0 and 150.2 Tg CO 2 Eq ., which indicates a range of 54 percent below to 46 percent above the 2011 emission estimate of 103.0 Tg CO 2 Eq.

Table 8

- 5 : Tier 2 Quant itative Uncertainty Estimates for CH 4 Emissions from Landfills (Tg CO 2 Eq. and Percent)

Source Gas 2011 Emission

Estimate Uncertainty Range Relative to Emission Estimate a (Tg CO 2 Eq.) (Tg CO 2 Eq.) (%)

Lower

Bound Upper

Bound Lower

Bound Upper

Bound

Landfills CH 4 103.0 47.0 150.2

- 54% +46%

MSW CH 4 88.7 33.5 136.0

- 62% +53%

Industrial CH 4 14.4 10.5 17.4

- 27% +21%

a Range of emission estimates predicted by Monte Carlo Stochastic Simulation for a 95 percent confidence interval.



# QA/QC and Verification

A QA/QC analysis was performed for data gathering and input, documentation, and calculation. QA/QC checks are not performed on the published data used to populate the inventory data set, including the SOG survey data and the publis hed LMOP database. A primary focus of the QA/QC checks was to ensure that CH 4 recovery estimates were

not double

- counted and that all LFGTE projects and flares were included in the respective project databases. Both

manual and electronic checks were made to ensure that emission avoidance from each landfill was calculated in only one of the three databases. The primary calculation spreadsheet is tailored from the IPCC waste model and has been verified previously using the original, peer

- reviewed IPCC wast e model. All model input values were verified by secondary QA/QC review.



# Recalculations Discussion

When conducted, methodological recalculations are applied to the entire time

- series to ensure time

- series consistency from 1990 through the current inventor y year. No methodological changes were made for this8

- 10 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

inventory, but the national landfill waste generation data for 2007, 2008, 2009, and 2010 were recalculated for states that did not report an amount of waste generated in the SOG 2010 survey. This recalculation was warranted after reviewing the waste generation and disposal trends over the time series, particularly for years after 2004 where a noticeable decrease in the amount of waste generated was calculated. For states that d id not report an amount of waste generated in the 2010 survey ( BioCycle 2010 ), the recalculations used the most recent SOG waste per capita data in the 2010 survey and state

- specific generation rates from the previous SOG survey ( BioCycle 2008). These

rec alculations resulted in a slight increase in the waste generated for 2007 through 2010.



# Planned Improvements

Improvements to the inventory being examined include incorporating data from the EPA’s GHGRP and recent peer

reviewed literature, modifying the d efault oxidation factor applied to MSW and industrial waste landfills, and either modifying the bulk waste degradable organic carbon (DOC) value or estimating emissions using a waste

- specific approach in the first order decay model.

Beginning in 2011, al l MSW landfills that accepted waste on or after January 1, 1980 and generate CH 4 in amounts equivalent to 25,000 metric tons or more of carbon dioxide equivalent (CO 2 Eq.) were required to calculate and report their greenhouse gas emissions to EPA through its GHGRP. The MSW landfill source category of the GHGRP consists of the landfill, landfill gas collection systems, and landfill gas destruction devices, including flares. Potential improvements to the inventory methodology may be made using the GHGRP dat a, specifically for inputs to the first order decay equation. The approach used by the inventory to estimate CH 4 generation assumes a bulk

waste

- specific DOC value that may not accurately capture the changing waste composition over the time series (e.g.,

t he reduction of organics entering the landfill environment due to increased composting, see Box 8

- 4 ). Using data obtained from the GHGRP and any publicly available la ndfill

- specific waste characterization studies in the United States, the methodology may be modified to incorporate a waste composition approach or revisions may be made to the bulk waste DOC value currently used. Additionally, GHGRP data could be analyze d and a weighted average for the methane correction factor (MCF), fraction of CH 4 (F) in the landfill gas, the destruction efficiency of flares, and the decay rate constant (k) could replace the values currently used in the inventory.

The most significan t contribution of the GHGRP data to the inventory is expected to be the amount of recovered landfill gas and other information related to the gas collection system (Bronstein et al., 2012). Information for landfills with gas collection systems reporting u nder the GHGRP will be incorporated into the inventory data set and

the measured CH 4 recovery data will be used for the reporting landfills in lieu of the EIA, LMOP, and flare vendor data. The GHGRP data undergo an extensive series of verification steps, are more reliable and accurate than the data currently used, and will reduce uncertainties surrounding CH 4 recovery when applied to the landfills in the inventory data set (Bronstein et al., 2012).

In addition to MSW landfills, industrial waste landfills a t facilities generating CH 4 in amounts equivalent to 25,000

metric tons or more of CO 2 Eq. were required to report their GHG emissions beginning in September 2012 through EPA’s GHGRP. Similar data for industrial waste landfills as is required for the MSW l andfills will be reported. Any additions or improvements to the inventory using reported GHGRP data will be made for the industrial waste landfill portion of the inventory. One possible improvement is the addition of industrial sectors other than pulp and paper, and food and beverage (e.g., metal foundries, petroleum refineries, and chemical manufacturing facilities). Of particular interest in the GHGRP data set for industrial waste landfills will be the presence of gas collection systems since recovery i s not currently associated with industrial waste landfills in the inventory methodology. It is unlikely that data reported through the GHGRP for industrial waste landfills will yield improved estimates for k and

L
o for the industrial sectors. However, EPA is considering an update to the L
o and k values for the pulp and paper

sector and are currently gathering feedback from stakeholders

.

T he addition of this higher tier data will improve the emission calculations to provide a more accurate representation of greenhouse gas emissions from MSW and industrial waste landfills, but p otential improvements to the inventory will not occur until after the deferral of GHGRP equation inputs expires in March 2013 for both MSW and industrial waste landfills, or as early as the 1990 to 2013 inventory report. Facility

- level reporting data from the GHGRP are not available for all inventory years as reported in this inventory; therefore, particular attention will be made to ensure time series consistency while incorporating data from EPA’s GHGRP that would be useful to improve theWaste 8

- 11

emissions estimates for MSW landfills. In implementing improvements and integration of data from the GHGRP, the latest guidance from the IPCC on the use of facility

- level data in national inventor ies will be relied upon. 253

As a first step toward revising the oxidation factor used in the inventory, a literature review was conducted in 2011 (RTI 2011). A standard CH 4 oxidation factor of 10 percent has been used for both industrial and MSW landfills f or all inventory reports and is currently recommended as the default for well

- managed landfills in the latest IPCC guidelines (2006). Recent comments on the inventory methodology indicated that a default oxidation factor of 10 percent may be less than oxi dation rates achieved at well

- managed landfills with gas collection and control. The impact of different landfill cover types on the rate of oxidation warrants further investigation as well.

Currently, one oxidation factor (10 percent) is applied to the total amount of waste generated nationwide. Changing the oxidation factor and calculating the amount of CH 4 oxidized from landfills with gas collection and control requires the estimation of waste disposed of in these types of landfills. The inventory me thodology uses waste generation data from the SOG surveys, which report the total amount of waste generated and disposed nationwide by state. In 2010, the State of Garbage survey requested data on the presence of landfill gas collection systems for

the fi rst time. Twenty

- eight states reported that 260 out of 1,414 (18 percent) operational landfills recovered landfill gas ( BioCycle 2010). However, the survey did not include closed landfills with gas collection and control systems. In the future, the amou nt of states collecting and reporting this information is expected to increase. The EPA’s GHGRP data set for MSW landfills could be used to fill in the gaps related to the amount of waste disposed in landfills with gas collection systems. Although the EPA ’s GHGRP does not capture every landfill in the United States, larger landfills are expected to meet the reporting thresholds and will be reporting waste disposal information by year beginning in March 2013. After incorporating the EPA’s GHGRP data, it ma y be possible to calculate the amount of waste disposed of at landfills with and without gas collection systems in the United States, which will allow the inventory waste model to apply different oxidation factors depending on the presence of a gas collect ion

system.

While research findings indicate some evidence that landfills with gas collection and control achieve a 20 percent or higher oxidation rate, there is not sufficient certainty to adopt a higher oxidation rate at this time. It is expecte d that with increased reporting by states in the State of Garbage survey, as well as the data collected through EPA’s GHGRP, the oxidation rate for at least a subset of landfills may be increased in a future inventory. A continued

effort will be made to r eview peer

- reviewed field studies that focus on oxidation specifically to determine how oxidation is affected by the presence of a gas collection system and landfill cover type and whether increasing the oxidation factor is warranted for all or only a port ion of landfills (e.g., open versus closed, or only those with gas collection systems).

Box 8

- 3 : Nationwide Municipal Solid Waste Data Sources

Municipal solid waste generated in the United States can be managed through landfilling, recycling, composting, and combustion with energy recovery. There are two main sources for nationwide solid waste management data in the United States,

 The BioCycle and Earth Engineering Center of Columbia University’s State of Garbage (SOG) in America surveys and

 The EPA’s Municipal Solid Waste in The United States: Facts and Figures reports.

The SOG surveys collect state

- reported data on the amount of waste generated and the waste managed via different management options: landfilling, recycling, composting, and combustion. The survey asks for actual tonnages instead of percentages in each was te category (e.g., residential, commercial, industrial, construction and demolition, organics, tires) for each waste management option. If such a breakdown is not available, the survey asks for total tons landfilled. The data are adjusted for imports and exports so that the principles of mass balance are adhered to, whereby the amount of waste managed does not exceed the amount of waste generated. The SOG reports present survey data aggregated to the state level.

253 See: http://www.ipcc

- nggip.iges.or.jp/meeting/pdfiles/1008_Model_and_Facility_Level_Data_Report.pdf8

- 12 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

The EPA Facts and Figures reports use a m aterials flow methodology, which relies heavily on a mass balance approach. Data are gathered from industry associations, key businesses, similar industry sources, and government agencies (e.g., the Department of Commerce and the U.S. Census Bureau) and a re used to estimate tons of materials and products generated, recycled, or discarded nationwide

. The amount of MSW generated is estimated by adjusting the imports and exports of produced materials. MSW that is not recycled, composted, or combusted is

ass umed to be landfilled. The data presented in the report are nationwide totals.

The State of Garbage surveys are the preferred data source for estimating waste generation and disposal amounts in the inventory because they are considered a more objective, numbers

- based analysis of solid waste management in

the United S tates

. However, the EPA Facts and Figures reports are useful when investigating waste management trends at the nationwide level and for typical waste composition data, which the State of Gar bage surveys do not ask

for.

In this inventory, emissions from solid waste management are presented separately by waste management option, except for recycling of waste materials. Emissions from recycling are attributed to the stationary combustion of

f ossil fuels, and are presented in the stationary combustion chapter in the Energy sector, although the emissions estimates are not called out separately. Emissions from solid waste disposal in landfills and the composting of solid waste materials are pres ented in the Landfills and Composting chapters in the Waste sector of this report. In the United States, almost all incineration of MSW occurs at waste

- to

- energy facilities or industrial facilities where useful energy is recovered, and thus emissions from waste incineration are accounted for in the Incineration chapter of the Energy sector of this report.

Box 8

- 4 : Overview of the Waste Sector

As shown in Figure 8

- 2 and Figure 8

- 3 , landfilling of MSW is currently and has been the most common waste management practice. A large portion o f materials in the waste stream are recovered for recycling and composting, which is becoming an increasingly prevalent trend throughout the country. Materials that are composted would have normally been disposed of in a landfill.

Figure 8

- 2 : Management of Municipal Solid Waste in the United States, 2010 (BioCycle 2010)Waste 8

- 13

Figure 8

- 3 : MSW Management Trends from 1990 to 2010 (EPA 2011)

Table 8

- 6 presents a typical composition of waste disposed of at a typical MSW landfill in the United States over time. It is important to note that the actual compos ition of waste entering each landfill will vary from that presented

in Table 8

- 6 . Understanding how the waste composition changes over time, specifically for the deg radable waste types, is important for estimating greenhouse gas emissions. For certain degradable waste types (i.e ., paper and paperboard), the amounts discarded have decreased over time due to an increase in recovery (see Table 8

- 6 and Figure 8

- 4 ). Landfill ban legislation affecting yard trimmings resulted in an increase of composting from 1990 to

2008. Table 8

- 6 and Figure 8

- 4 do not reflect the impact of backyard composting on yard trimming generation and recovery estimates. The recovery of food trimmings has been consistently low. Increased recovery of degradable

materials reduces the CH 4 generation potential and CH 4 emissions from landfills.8

- 14 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

Table 8

- 6 : Materials Discarded in the Municipal Waste Stream by Waste Type, percent (EPA 2011)

Waste Type 1990 2005 2007 2008 2009 2010 Paper and Paperboard 24.5% 24.5% 21.7% 19.7% 14.8% 15.3%

Glass 5.7% 5.7% 5.5% 5.3% 5.0% 4.8%

Metals 7.7% 7.7% 7.9% 8.0% 8.0% 8.3%

Plastics 15.7% 15.7% 16.4% 16.0% 15.8% 16.3%

Rubber and Leather 3.5% 3.5% 3.6% 3.7% 3.7% 3.8%

Textiles 5.5% 5.5% 5.9% 6.2% 6.3% 6.4%

Wood 7.4% 7.4% 7.5% 7.6% 7.7% 7.8%

Other a 1.8% 1.8% 1.9% 1.9% 1.9% 1.9% Food Scraps b 17.9% 17.9% 18.2% 18.6% 19.1% 19.3% Yard Trimmings c 7.0% 7.0% 6.7% 6.6% 7.6% 8.1%

Miscellaneous Inorganic Wastes 2.1% 2.1% 2.1% 2.2% 2.2% 2.2%

a Includes electrolytes in batteries and fluff pulp, feces, and urine in disposable diapers. Details may not add to totals due to rounding. Source: EPA 2011

.

b Data for food scraps were estimated using sampling studies in various parts of the country in combination with demographic data on population, grocery store sales, restaurant sales, number of employees, and number of prisoners, students, and patients in institutions. Source: EPA 2010

.

c Data for yard trimm ings were estimated using sampling studies, population data, and published sources documenting legislation affecting yard trimmings disposal in landfills. Source: EPA 2010

.

Figure 8

- 4 : Percent of Recovere d Degradable Materials from 1990 to 2010, percent (EPA 2011)

Box 8

- 5 : Description of a Modern, Managed Landfill

Modern , managed landfills are well

- engineered facilities that are located, designed, operated, and monitored to ensure compliance with federal , state, and tribal regulations. Municipal s olid waste (MSW) landfills must be designed to protect the environment from contamina nts which may be present in the solid waste stream. Requirements for affected MSW landfills may include:

 Siting requirements to protect sensitive areas (e.g., airports, floodplains, wetlands, fault areas, seismic impact zones, and unstable areas)

 Design requirements for new landfills to ensure that Maximum Contaminant Levels (MCLs) will not be exceeded in the uppermost aquifer (e.g., composite liners and leachate collection systems)Waste 8

- 15

 Leachate collection and removal systems

 Operating practices (e.g. , daily and intermediate cover, receipt of regulated hazardous wastes, use of landfill cover material, access options to prevent illegal dumping, use of a collection system to prevent

stormwater run

- on/run

- off, record

- keeping)

 Air monitoring requirements ( explosive gases)

 Groundwater monitoring requirements

 Closure and post

- closure care requirements (e.g., final cover construction), and

 Corrective action provisions.

Specific federal regulations that affected MSW landfills must comply with include the 40 CFR Part 258 (Subtitle D of RCRA), or equivalent state regulations and the New Source Performance Standards (NSPS) 40 CFR Part 60 Subpart W W. Additionally, state and tribal requirements may exist. For more information regarding federal MSW landfill regulati ons, see http://www.epa.gov/osw/nonhaz/municipal/landfill/msw_regs.htm

.

Box 8

- 6 : Biogenic Wastes in Landfills

Regarding the depositing of wastes of biogenic origin in landfills (i.e., all degradable waste), e mpirical evidence shows that some of these wastes degrade very slowly in landfills, and the C they contain is effectively sequestered in landfills over a period of time (Barlaz 1998, 2006). Estimates of C removals from landfilling of forest products, yard trimmings, and food scraps are further described in the Land Use, Land

- Use Change, and Forestry chapter, based on methods presented in IPCC (2003) and IPCC (2006).



# 8.2 Wastewater Treatment (IPCC Source Category 6B)

Wastewater treatment processes can produce anthropogenic CH 4 and N 2 O emissions. Wastewater from domestic 254
and industrial sources is treated to remove soluble organic matter, suspended solids, pathogenic organisms, and chemical contaminants. Treatment may either occur on site, most commonly throug h septic systems or package plants, or off site at centralized treatment systems. Centralized wastewater treatment systems may include a variety of processes, ranging from lagooning to advanced tertiary treatment technology for removing nutrients. In the United States, approximately 20 percent of domestic wastewater is treated in septic systems or other on

- site systems, while the rest is collected and treated centrally (U.S. Census Bureau 2011 ).

Soluble organic matter is generally removed using biologic al processes in which microorganisms consume the organic matter for maintenance and growth. The resulting biomass (sludge) is removed from the effluent prior to discharge to the receiving stream. Microorganisms can biodegrade soluble organic material in wastewater under aerobic or anaerobic conditions, where the latter condition produces CH 4 . During collection and treatment, wastewater may be accidentally or deliberately managed under anaerobic conditions. In addition, the sludge may be further biodegra ded under aerobic or anaerobic conditions. The generation of N 2 O may also result from the treatment of domestic wastewater during both nitrification and denitrification of the N present, usually in the form of urea, ammonia, and proteins. These compounds are converted to nitrate (NO 3 ) through the aerobic process of nitrification. Denitrification occurs under anoxic conditions (without free oxygen), and involves the biological conversion of nitrate into dinitrogen gas (N 2 ). N 2 O can be an intermediate pro duct of both processes, but has typically been associated with denitrification. Recent research suggests that higher emissions of N 2 O may in fact originate from nitrification (Ahn et al. 2010).

254 Throughout the inventory , emissions from domestic wastewater also include any commercial and industrial wastewater collected and co

trea ted with domestic wastewater.8

- 16 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

The principal factor in determining the CH 4 generation poten tial of wastewater is the amount of degradable organic material in the wastewater. Common parameters used to measure the organic component of the wastewater are the Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Under the same conditio ns, wastewater with higher COD (or BOD) concentrations will generally yield more CH 4 than wastewater with lower COD (or BOD) concentrations. BOD represents the amount of oxygen that would be required to completely consume the organic matter contained in t he wastewater through aerobic decomposition processes, while COD measures the total material available for chemical oxidation (both biodegradable and non

- biodegradable). Because BOD is an aerobic parameter, it is preferable to use COD to estimate CH 4 prod uction. The principal factor in determining the N 2 O generation potential of wastewater is the amount of N in the wastewater. The variability of N in the influent to the treatment system, as well as the operating conditions of the treatment system itself, also impact

the N 2 O generation potential.

In 2011, CH 4 emissions from domestic wastewater treatment were 0.36 Tg CO 2 Eq. (360 Gg). Emissions remained fairly steady from 1990 through 1997, but have decreased since that time due to decreasing percentages o f wastewater being treated in anaerobic systems, including reduced use of on

- site septic systems and central anaerobic treatment systems. In 2011, CH 4 emissions from industrial wastewater treatment were estimated to be 8. 6 Tg CO 2 Eq. (4 09 Gg). Industrial emission sources have increased across the time series through 1999 and then fluctuated up and down with production changes associated with the treatment of wastewater from the pulp and paper manufacturing, meat and poultry processing, fruit a nd vegetable processing, starch

- based ethanol production, and petroleum refining industries. Table 8

- 7 and Table 8

- 8 provide CH 4 and N 2 O emission estimates from domestic and

industrial wastewater treatment.

With respect to N 2 O, the United States identifies two distinct sources for N 2 O emissions from domestic wastewater: emissions from centralized wastewater treatment processes, and emissions from effluent from centralized treatment systems that has been discharged into aquatic environments. The 2011 emissions of N 2 O from centralized

wastewater t reatment processes and from effluent were estimated to be 0.3 Tg CO 2 Eq. (1 Gg) and 4.9 Tg CO 2 Eq. (15.7 Gg), respectively. Total N 2 O emissions from domestic wastewa ter were estimated to be 5.2 Tg CO 2 Eq. (16.7 Gg). N 2 O emissions from wastewater treatmen t processes gradually increased across the time series as a result of increasing U.S. population and protein consumption.

Table 8

- 7 : CH 4 and N 2 O Emissions from Domestic and Industrial Wastewater Treatment (Tg

CO 2 Eq.)

Activity 1990 2005 2007 2008 2009 2010 2011

CH 4 15.9 16.5 16.6 16.6 16.5 16.4 16.2

Domestic 8.8 8.3 8.1 8.0 8.0 7.8 7.6

Industrial* 7.1 8.2 8.5 8.6 8.5 8.6 8.6

N 2 O 3.5 4.7 4.8 4.9 5.0 5.1 5.2

Domestic 3.5 4.7 4.8 4.9 5.0 5.1 5.2

Total 19.4 21.2 21.4 21.5 21.5 21.5 21.4

* Industrial activity includes the pulp and paper manufacturing, meat and poultry processing, fruit and vegetable processing, starch

- based ethanol production, and petroleum refining

industries. Note: Totals may not sum due to independent rounding.

Table 8

- 8 : CH 4 and N 2 O Emissions from Domestic and Industrial Wastewater Treatment (Gg)

Activity 1990 2005 2007 2008 2009 2010 2011

CH 4 758 785 791 791 786 779 770

Domestic 421 396 385 383 380 370 360

Industrial* 338 389 405 409 406 409 409

N 2 O 11 15 16 16 16 16 17

Domestic 11 15 16 16 16 16 17 * Industrial activity includes the pulp and paper manufacturing, meat and poultry processing, fruit and vegetable processing, starch

- based ethanol production, and petroleum refining industries.Waste 8

- 17

Note: Totals may not sum due to independent rounding.



# Methodology

Domestic Wastewater CH 4 

## Emission Estimates

Domestic wastewater CH 4 emissions originate from both septic systems and from centralized treatment systems, such as publicly owned treatment works (POTWs). Within these centralized systems, CH 4 emissions can arise from aerobic systems that are not well managed or that are desig ned to have periods of anaerobic activity (e.g., constructed wetlands), anaerobic systems (anaerobic lagoons and facultative lagoons), and from anaerobic digesters when the captured biogas is not completely combusted. CH 4 emissions from septic systems wer e estimated by multiplying the United States population by the percent of wastewater treated in septic systems ( 20 percent), an emission factor (10.7 g CH 4 /capita/day) and converting that to Gg/year. Methane emissions from POTWs were estimated by multiplyi ng the total BOD 5 produced in the United States by the percent of wastewater treated centrally (80 percent), the relative percentage of wastewater treated by aerobic and anaerobic systems, the relative percentage of wastewater facilities with primary treat ment, the percentage of BOD 5 treated after primary treatment (67.5 percent), the maximum CH 4 - producing capacity of domestic wastewater (0.6), and the relative MCFs for aerobic (zero or 0.3) and anaerobic (0.8) systems with all aerobic systems assumed to be well

- managed. Methane emissions from anaerobic digesters were estimated by multiplying the amount of biogas generated by wastewater sludge treated in anaerobic digesters by the proportion of CH 4 in digester biogas (0.65), the density of CH 4 (662 g CH 4 /m 3

CH 4 ) , and the destruction efficiency associated with burning the biogas in an energy/thermal device (0.99). The methodolog ical equations are:

Emissions from Septic Systems = A

= US POP × (% onsite) × (EF SEPTIC ) × 1/10^9 × Days

Emissions from Centrally Treated Aerobic Systems = B = [(% collected) × (total BOD 5 produced) × (% aerobic) × (% aerobic w/out primary) + (% collected) × (total BOD 5 produced) × (% aerobic) × (% aerobic w/primary) × (1

- % BOD removed in prim. treat.)] × (% operations not well

manag ed) × (B

o ) × (MCF

- aerobic_not_well_man) × 1/10^6

Emissions from Centrally Treated Anaerobic Systems = C = [(% collected) × (total BOD 5 produced) × (% anaerobic) × (% anaerobic w/out primary) + (% collected) × (total

BOD 5 produced) × (% anaerobic) × (% anae robic w/primary) × (1

- %BOD removed in prim. treat.)] × (B

o ) × (MCF

anaerobic) × 1/10^6

Emissions from Anaerobic Digesters = D = [(POTW_flow_AD) × (digester gas)/ (per capita flow)] × conversion to m 3 × (FRAC_CH 4 ) × (365.25) × (density

of CH 4 ) × (1

- DE) × 1/ 10^9

Total CH 4 Emissions (Gg) = A + B + C + D

where,

US POP = U.S. population

% onsite = Flow to septic systems / total flow

% collected = Flow to POTWs / total flow

% aerobic = Flow to aerobic systems / total flow to POTWs

% anaerobic = Flow to anaerobic systems / total flow to POTWs % aerobic w/out primary = Percent of aerobic systems that do not employ primary treatment % aerobic w/primary = Percent of aerobic systems that employ primary treatment % BOD removed in prim. treat. = 32.5% % oper ations not well managed = Percent of aerobic systems that are not well managed and in which some anaerobic degradation occurs % anaerobic w/out primary = Percent of anaerobic systems that do not employ primary treatment % anaerobic w/primary = Percent o f anaerobic systems that employ primary treatment8

- 18 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1 EF SEPTIC = Methane emission factor (10.7 g CH 4 /capita/day)

– septic systems Days = days per year (365.25)

Total BOD 5 produced = kg BOD/capita/day × U.S. population × 365.25 days/yr

B
o = Maximum CH 4 - produ cing capacity for domestic wastewater (0.60 kg

CH 4 /kg BOD)

1/10^6 = Conversion factor, kg to Gg

MCF

- aerobic_not_well_man. = CH 4 correction factor for aerobic systems that are not well managed (0.3)

MCF

- anaerobic = CH 4 correction factor for anaerobic sy stems (0.8)

DE = CH 4 destruction efficiency from flaring or burning in engine (0.99 for enclosed flares)
POTW_flow_AD = Wastewater influent flow to POTWs that have anaerobic digesters (gal) digester gas = Cubic feet of digester gas produced per person p er day (1.0

ft 3 /person/day) (Metcalf and Eddy 2003 ) per capita flow = Wastewater flow to POTW per person per day (100 gal/person/day)

conversion to m 3 = Conversion factor, ft 3 to m 3 (0.0283)
FRAC_CH 4 = Proportion CH 4 in biogas (0.65) density of CH 4 = 662 (g CH 4 /m 3 CH 4 )

1/10^9 = Conversion factor, g to Gg

U.S. population data were taken from the U.S. Census Bureau International Database (U .S. Census 201 2) and include the populations of the United States, American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the Virgin Islands. Table 8

- 9 presents U.S. population and total BOD 5 produced for 1990 through 2011, while Table

8

- 10 presents domestic wastewater CH 4 emissions for both septic and centralized systems in 2011. The proportions

of domestic wastewater treated onsite versus at centrali zed treatment plants were based on data from the 1989, 1991, 1993, 1995, 1997, 1999, 2001, 2003, 2005, 2007, 2009 , 2011 American Housing Surveys conducted by the U.S. Census Bureau (U.S. Census 2011), with data for intervening years obtained by linear inte rpolation. The percent of wastewater flow to aerobic and anaerobic systems, the percent of aerobic and anaerobic systems that do and do not employ primary treatment, and the wastewater flow to POTWs that have anaerobic digesters were obtained from the

199 2, 1996, 2000, and 2004 Clean Watershed Needs Survey (EPA 1992, 1996, 2000, and 2004). Data for intervening years were obtained by linear interpolation and the years 2004 through 2011 were forecasted from the

rest of the time series. The BOD 5 production rate (0.09 kg/capita/day) and the percent BOD 5 removed by primary treatment for domestic wastewater were obtained from Metcalf and Eddy (2003). The CH 4 emission factor (0.6 kg

CH 4 /kg BOD 5 ) and the MCF used for centralized treatment systems were taken from IPCC (2006), while the CH 4 emission factor (10.7 g CH 4 /capita/day) used for septic systems were taken from Leverenz et al. (2010). The CH 4 destruction efficiency for methane recovered from sludge digestion operations, 99 percent, was selected based on th e range of efficiencies (98 to 100 percent) recommended for flares in AP

- 42 Compilation of Air Pollutant Emission Factors, Chapter 2.4 (EPA 1998), efficiencies used to establish new source performance standards (NSPS) for landfills, and in recommendations for closed flares used by the Landfill Methane Outreach Program (LMOP). The cubic feet of digester gas produced per person per day (1.0 ft 3 /person/day) and the proportion of CH 4 in biogas (0.65) come from Metcalf and Eddy (2003). The wastewater flow to a POTW (100 gal/person/day) was taken from

the Great Lakes

- Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers, "Recommended Standards for Wastewater Facilities (Ten

- State Standards)” (2004).

Table 8

- 9 : U.S. Population (Millions) and Domestic Wastewater BOD 5 Produced (Gg)

Year Population BOD 5
1990 253 8,333

2005 300 9,853

2007 305 10,039

2008 308 10,132

2009 311 10,220

2010 314 10,303

2011 316 10,377Waste 8

- 19

Source: U.S. Census Bureau (2012); Metcalf & Eddy 2003.

Table 8

- 10 : Domestic Wastewater CH 4 Emissions from Septic and Centralized Systems (2011)

CH 4 emissions (Tg CO 2 Eq.) % of Domestic Wastewater CH 4 Septic Systems 5.0 66.4%
Centralized Systems 2.5 33.6%

Total 7.6 100%

Note: Totals may not sum due to independent rounding.



## Industrial Wastewater CH 4 

## Emission Estimates

Methane emission estimates from industrial wastewater were developed according to the methodology described in IPCC (2006). Industry categories that are likely to produce significant CH 4 emissions from wastewater treatment were identified. High volumes of wastew ater generated and a high organic wastewater load were the main criteria. The top five industries that meet these criteria are pulp and paper manufacturing; meat and poultry processing; vegetables, fruits, and juices processing; starch

- based ethanol produ ction; and petroleum refining. Wastewater treatment emissions for these sectors for 2011 are displayed in Table 8

- 11 below. Table 8

- 12 contains production

data for these industries.

Table 8

- 11 : Industrial Wastewater CH 4 Emissions by Sector (2011)

CH 4 emissions (Tg CO 2 Eq.) % of Industrial Wastewater CH 4 Pulp & Paper 4.1 48% Meat & Poultry 3.7 43%

Petroleum Refineries 0.6 7% Fruit & Vegetables 0.1 1%

Ethanol Refineries 0.1 1%

Total 8.6 100% Note: Totals may not sum due to independent rounding.

Table 8

- 12 : U.S. Pulp and Paper, Meat, Poultry, Vegetables, Fruits and Juices, Ethanol, and Petroleum Refining Production (Tg)

Year Pulp and

Paper a Meat

(Live Weight Killed) Poultry

(Live Weight Killed) Vegetables,

Fruits and

Juices Ethanol Petroleum Refining

1990 128.9 27.3 14.6 38.7 2.7 702.4

2005 131.4 31.4 25.1 42.9 11.7 818.6

2007 135.9 33.4 26.0 44.7 19.4 827.6

2008 134.5 34.4 26.6 45.1 26.9 836.8

2009 137.0 33.8 25.2 46.5 31.7 822.4

2010 137.0 33.7 25.9 43.2 39.5 848.6

2011 137.0 33.8 26.2 42.9 41.5 858.8

a P ulp and paper production is the sum of wood pulp production plus paper and paperboard production.

Methane emissions from these categories were estimated by multiplying the annual product output by the average outflow, the organics loading (in COD) in the outflow, the percentage of organic loading assumed to degrade anaerobically, and the maximum CH 4 pr oducing potential of industrial wastewater (B

o ). Ratios of BOD:COD in8

- 20 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

various industrial wastewaters were obtained from EPA (1997a) and used to estimate COD loadings. The B

o value used for all industries is the IPCC default value of 0.25 kg CH 4 /kg COD (I PCC 2006).

For each industry, the percent of plants in the industry that treat wastewater on site, the percent of plants that have a primary treatment step prior to biological treatment, and the percent of plants that treat wastewater anaerobically

were d efined. The percent of wastewater treated anaerobically onsite (TA) was estimated for both primary treatment ( %TA p ) and secondary treatment ( %TA
s ) . For plants that have primary treatment in place, an estimate of COD that is removed prior to wastewater tr eatment in the anaerobic treatment units was incorporated.

The methodological equations are:

CH 4 (industrial wastewater) = [P  W  COD  %TA p  B
o  MCF] + [P  W  COD  %TA
s  B
o  MCF]

%TA p = [%Plants

o  %WW a,p  %COD p ]

%TA
s = [%Plants

a  %WW a,s  %COD
s ] + [%Plants t  %WW a,t  %COD
s ]

where,

CH 4 (industrial wastewater) = Total CH 4 emissions from industrial wastewater (kg/year)

P = Industry output (metric tons/year)

W = Wastewater generated (m 3 /metric ton of product)

COD = Organics loading in waste water (kg/m 3 )

%TA p = Percent of wastewater treated anaerobically on site in primary treatment

%TA
s = Percent of wastewater treated anaerobically on site in secondary treatment

%Plants

o = Percent of plants with onsite treatment

%WW a,p = Percent of wastewater treated anaerobically in primary treatment

%COD p = Percent of COD entering primary treatment

%Plants

a = Percent of plants with anaerobic secondary treatment

%Plants t = Percent of plants with other secondary treatment

%WW a,s = Percent of wastewat er treated anaerobically in anaerobic secondary treatment

%WW a,t = percent of wastewater treated anaerobically in other secondary treatment

%COD
s = percent of COD entering secondary treatment

B
o = Maximum CH 4 producing potential of industrial wastewater ( default value of 0.25 kg CH 4 /kg COD)

MCF = CH 4 correction factor, indicating the extent to which the organic content (measured as COD) degrades anaerobically

As described below, the values presented in Table 8

- 13 were used in the emission calculations and are described in detail in Aguiar and Bartram (2008).

Table 8

- 13 : Variables Used to Calculate Percent Wastewater Treated Anaerobically by Industry (%)

Variable Industry

Pulp

and Paper Meat

Processing Poultry

Processing Fruit/

Vegetable Processing Ethanol

Production

– Wet Mill Ethanol

Production

– Dry Mill Petroleum

Refining

%TA p 0 0 0 0 0 0 0

%TA s 10.5 33 25 4.2 33.3 75 100

%Plants o 60 100 100 11 100 100 100

%Plants a 25 33 25 5.5 33.3 75 100

%Plants t 35 67 75 5.5 66.7 25 0

%WW a,p 0 0 0 0 0 0 0

%WW a,s 100 100 100 100 100 100 100

%WW a,t 0 0 0 0 0 0 0

%COD p 100 100 100 100 100 100 100

%COD s 42 100 100 77 100 100 100

Source: Aguiar and Bartram (2008) Planned Revisions of the Industrial Wastewater Inventory Emission Estimates for the

1990

- 2007 Inventory. August 10, 2008.Waste 8

- 21

Pulp and Paper . Wastewater treatment for the pulp and paper industry typically includes neutralization, screening, sedimentation, and flotation/hydrocycloning to remove solids (World Bank 1999, Nemerow and Dasgupta 1991). Secondary treatment (storage, settling, and biological treatment) mainly consists of la gooning. In determining the percent that degrades anaerobically, both primary and secondary treatment were considered. In the United States, primary treatment is focused on solids removal, equalization, neutralization, and color reduction (EPA 1993). The vast majority of pulp and paper mills with on

- site treatment systems use mechanical clarifiers to remove suspended solids from the wastewater. About 10 percent of pulp and paper mills with treatment systems use settling ponds for primary treatment and th ese are more likely to be located at mills that do not perform secondary treatment (EPA 1993). However, because the vast majority of primary treatment operations at U.S. pulp and paper mills use mechanical clarifiers, and less than 10 percent of pulp and paper wastewater is managed in primary settling ponds that are not expected to have anaerobic conditions, negligible emissions are assumed to occur during primary

treatment.

Approximately 42 percent of the BOD passes on to secondary treatment, which consis ts of activated sludge, aerated stabilization basins, or non

- aerated stabilization basins. No anaerobic activity is assumed to occur in activated sludge systems or aerated stabilization basins (note: although IPCC recognizes that some CH 4 can be emitted f rom anaerobic pockets, they recommend an MCF of zero). However, about 25 percent of the wastewater treatment systems used in the United States are non

- aerated stabilization basins. These basins are typically 10 to 25 feet deep. These systems are classif ied as anaerobic deep lagoons (MCF = 0.8).

A time series of CH 4 emissions for 1990 through 2001 was developed based on production figures reported in the

Lockwood

- Post Directory (Lockwood

- Post 2002). Published data from the American Forest and Paper Asso ciation, data published by Paper Loop, and other published statistics were used to estimate production for 2002 through 2011 (Pulp and Paper 2005, 2006, and monthly reports from 2003 through 2008; Paper 360 ◦ 2007). The overall

wastewater outflow was estim ated to be 85 m 3 /metric ton, and the average BOD concentrations in raw wastewater was estimated to be 0.4 gram BOD/liter (EPA 1997b, EPA 1993, World Bank 1999). The COD:BOD ratio used to convert the organic loading to COD for pulp and paper facilities was 2 (EPA 1997a).

Meat and Poultry Processing . The meat and poultry processing industry makes extensive use of anaerobic lagoons in sequence with screening, fat traps and dissolved air flotation when treating wastewater on site. About 33 percent of meat pro cessing operations (EPA 2002) and 25 percent of poultry processing operations (U.S. Poultry 2006) perform on

- site treatment in anaerobic lagoons. The IPCC default B

o of 0.25 kg CH 4 /kg COD and default MCF of 0.8 for anaerobic lagoons were used to estimate the CH 4 produced from these on

- site treatment systems. Production data, in carcass weight and live weight killed for the meat and poultry industry, were obtained from the USDA Agricultural Statistics Database and the Agricultural Statistics Annual Reports (USDA 2012). Data collected by EPA’s Office of Water provided estimates for wastewater flows into anaerobic lagoons: 5.3 and 12.5 m 3 /metric ton for meat and poultry production (live weight killed), respectively (EPA 2002). The loadings are 2.8 and 1.5 g BOD/liter for meat and poultry, respectively. The COD:BOD ratio used to convert the organic loading to COD for both meat and poultry facilities was 3 (EPA 1997a).

Vegetables, Fruits, and Juices Processing . Treatment of wastewater from fruits, vegetables , and juices processing includes screening, coagulation/settling, and biological treatment (lagooning). The flows are frequently seasonal, and robust treatment systems are preferred for on

- site treatment. Effluent is suitable for discharge to the sewer. This industry is likely to use lagoons intended for aerobic operation, but the large seasonal loadings may develop limited anaerobic zones. In addition, some anaerobic lagoons may also be used (Nemerow and Dasgupta 1991). Consequently, 4.2 percent of th ese wastewater organics are assumed to degrade anaerobically. The IPCC default B

o of 0.25 kg CH 4 /kg COD and default MCF of 0.8 for anaerobic treatment were used to estimate the CH 4 produced

from these on

- site treatment systems. The USDA National Agricult ural Statistics Service (USDA 2012) provided production data for potatoes, other vegetables, citrus fruit, non

- citrus fruit, and grapes processed for wine. Outflow and BOD data, presented in Table 8

- 14 , were obtained from EPA (1974) for potato, citrus fruit, and apple processing, and from EPA (1975) for all other sectors. The COD:BOD ratio used to convert the organic loading to COD for all fruit, veget able, and juice facilities was 1.5 (EPA 1997a).

Table 8

- 14 : Wastewater Flow (m 3 /ton) and BOD Production (g/L) for U.S. Vegetables, Fruits,
and Juices Production

Commodity Wastewater Outflow (m 3 /ton) BOD (g/L)8

- 22 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1 Vegetables

Potatoes 10.27 1.765 Other Vegetables 8.69 0.794

Fruit Apples 3.66 1.371

Citrus 10.11 0.317

Non

- citrus 12.42 1.204 Grapes (for wine) 2.78 1.831

Ethanol Production . Ethanol, or ethyl alcohol, is produced primarily for use as a fuel component, but is also used in industrial applications and in the manufacture of beverage alcohol. Ethanol can be produced from the fermentation of sugar

- based feedstocks (e.g., molasses and beets), starch

- or grain

- based feeds tocks (e.g., corn, sorghum, and beverage waste), and cellulosic biomass feedstocks (e.g., agricultural wastes, wood, and bagasse). Ethanol can also be produced synthetically from ethylene or hydrogen and carbon monoxide. However, synthetic ethanol compri ses only about 2 percent of ethanol production, and although the Department of Energy predicts cellulosic ethanol to greatly increase in the coming years, currently it is only in an experimental stage in the United States. According to

the Renewable Fuels Association, 82 percent of ethanol production facilities use corn as the sole feedstock and 7 percent of facilities use a combination of corn and another starch

- based feedstock. The fermentation of corn is the principal ethanol production process in the United States and is expected to increase through 2012, and potentially more; therefore, emissions associated with wastewater treatment at starch

- based ethanol production facilities were estimated (ERG 2006).

Ethanol is produced from corn (or other starch

- based feedstocks) primarily by two methods: wet milling and dry milling. Historically, the majority of ethanol was produced by the wet milling process, but now the majority is produced by the dry milling process. The wastewater generated at ethanol produc tion facilities is handled in a variety of ways. Dry milling facilities often combine the resulting evaporator condensate with other process wastewaters, such as equipment wash water, scrubber water, and boiler blowdown and anaerobically treat this

wastew ater using various types of digesters. Wet milling facilities often treat their steepwater condensate in anaerobic systems followed by aerobic polishing systems. Wet milling facilities may treat the stillage (or processed stillage) from the ethanol ferment ation/distillation process separately or together with steepwater and/or wash water.

CH 4 generated in anaerobic digesters is commonly collected and either flared or used as fuel in the ethanol production process (ERG 2006).

Available information was compi led from the industry on wastewater generation rates, which ranged from 1.25 gallons per gallon ethanol produced (for dry milling) to 10 gallons per gallon ethanol produced (for wet milling) (Ruocco 2006a,b; Merrick 1998; Donovan 1996; and NRBP 2001). COD concentrations were also found to be about 3 g/L (Ruocco 2006a; Merrick 1998; White and Johnson 2003). The amount of wastewater treated anaerobically was estimated, along with how much of the CH 4 is recovered through the use of biomethanators (ERG 2006). Methane emissions were then estimated as follows:

Methane = [Production × Flow × COD × 3.785 × ([%Plants o × %WW a,p × %COD p ] + [%Plants a × %WW a,s × %COD s ] + [%Plants t × %WW a,t × %COD s ]) × B o × MCF × % Not Recovered] + [Production × Flow × 3.785 × COD × ([%Plants o × %WW a,p × %COD p ] + [%Plants a × %WW a,s × %COD s ] + [%Plants t × %WW a,t × %COD s ]) × B o × MCF × (% Recovered) × (1

- DE)] × 1/10^9

where,

Production = gallons ethanol produced (wet milling or dry milling)

Flow = gallons wastewater generated per gallon ethanol produced (1.25 dry milling, 10 wet milling)

COD = COD concentration in influent (3 g/l)

3.785 = conversion, gallons to liters

%Plants o = percent of plants with onsite treatment (100%)

%WW a,p = percent of wastewater treated anaerobically in primary treatment (0%)

%COD p = percent of COD entering primary treatment (100%)

%Plants a = percent of plants with anaerobic secondary treatment (33.3% wet, 75% dry)

%Plants t = percent of plants with other secondary treatment (66.7% wet, 25% dry)

%WW a,s = percent of wastewater treated anaerobically in anaerobic secondary treatment (100%)Waste 8

- 23 %WW a,t = percent of wastewater treated anaerobically in other secondary treatment (0%)

%COD s = percent of COD entering secondary treatment (100%)

B o = maximum methane prod ucing capacity (0.25 g CH 4 /g COD)

MCF = methane conversion factor (0.8 for anaerobic systems)

% Recovered = percent of wastewater treated in system with emission recovery

% Not Recovered = 1

- percent of wastewater treated in system with emission recovery

DE = destruction efficiency of recovery system (99%)

1/10^9 = conversion factor, g to Gg

A time series of CH 4 emissions for 1990 through 2011 was developed based on production data from the Renewable Fuels Association (RFA 2012).

Petroleum Refining . Petr oleum refining wastewater treatment operations produce CH 4 emissions from anaerobic wastewater treatment. The wastewater inventory section includes CH 4 emissions from petroleum refining

wastewater treated on site under intended or unintended anaerobic cond itions. Most facilities use aerated biological systems, such as trickling filters or rotating biological contactors; these systems can also exhibit anaerobic conditions that can result in the production of CH 4 . Oil/water separators are used as a primary treatment method; however, it is unlikely that any COD is removed in this step.

Available information from the industry was compiled. The wastewater generation rate, from CARB (2007) and Timm (1985), was determined to be 35 gallons per barrel of finished p roduct. An average COD value in the wastewater was estimated at 0.45 kg/m 3 (Benyahia et al. 2006).

The equation used to calculate CH 4 generation at petroleum refining wastewater treatment systems is presented

below:

Methane = Flow × COD × B
o × MCF

where,

Flow = Annual flow treated through anaerobic treatment system (m 3 /year)

COD = COD loading in wastewater entering anaerobic treatment system (kg/m 3 )

B
o = maximum methane producing potential of industrial wastewater (default value of 0.25

kg CH 4 /kg COD)

MCF = methane conversion factor (0.3)

A time series of CH 4 emissions for 1990 through 2011 was developed based on production data from the Energy Information Association (EIA 2012).



## Domestic Wastewater N 2 

## O Emission Estimates

N 2 O emissions from domestic wastewater (wastewater treatment) were estimated using the IPCC (2006) methodology, including calculations that take into account N removal with sewage sludge, non

- consumption and industrial/commercial wastewater N, and emissions from advance d centralized wastewater treatment plants:

 In the United States, a certain amount of N is removed with sewage sludge, which is applied to land, incinerated, or landfilled (N SLUDGE ). The N disposal into aquatic environments is reduced to account for the se wage sludge application.

 The IPCC methodology uses annual, per capita protein consumption (kg protein/[person

- year]). For this inventory, the amount of protein available to be consumed is estimated based on per capita annual food availability data and it s protein content, and then adjusts that data using a factor to account for the fraction of protein actually consumed.

 Small amounts of gaseous nitrogen oxides are formed as byproducts in the conversion of nitrate to N gas in anoxic biological treatment systems. Approximately 7 g N 2 O is generated per capita per year if wastewater treatment includes intentional nitrification and denitrification (Scheehle and Doorn 2001). Analysis of the 2004 CWNS shows that plants with denitrification as one of their unit operations serve a population of 2.4 million people. Based on an emission factor of 7 g per capita per year, approximately 21.2 metric tons of additional N 2 O may have been emitted via denitrification in 2004. Similar analyses were completed for each yea r in the8

- 24 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1

inventory using data from CWNS on the amount of wastewater in centralized systems treated in denitrification units. Plants without intentional nitrification/denitrification are assumed to generate 3.2 g N 2 O per capita per

year.

N 2 O emissions from domestic wastewater were estimated using the following methodology:

N 2 O TOTAL = N 2 O PLANT + N 2 O EFFLUENT

N 2 O PLANT = N 2 O NIT/DENIT + N 2 O WOUT NIT/DENIT

N 2 O NIT/DENIT = [(US POPND ) × EF 2 × F IND

- COM ] × 1/10^9

N 2 O WOUT NIT/DENIT = {[(US POP × WWTP)

- US POPND ]× F IND

- COM × EF 1 } × 1/10^9

N 2 O EFFLUENT = {[(((US POP × WWTP)

– (0.9 × US POPND )) × Protein × F NPR × F NON

- CON × F IND

- COM )

- N SLUDGE ] × EF 3 × 44/28} × 1/10^6

where,

N 2 O TOTAL = Annual emissions of N 2 O (Gg)

N 2 O PLANT = N 2 O emissions from centralized wastewater tre atment plants (Gg)

N 2 O NIT/DENIT = N 2 O emissions from centralized wastewater treatment plants with

nitrification/denitrification (Gg)

N 2 O WOUT NIT/DENIT = N 2 O emissions from centralized wastewater treatment plants without

nitrification/denitrification (Gg)

N 2 O EFFLUENT = N 2 O emissions from wastewater effluent discharged to aquatic environments (Gg)

US POP = U.S. population

US POPND = U.S. population that is served by biological denitrification (from CWNS)

WWTP = Fraction of population using WWTP (as opposed to septic systems)

EF 1 = Emission factor (3.2 g N 2 O/person

- year)

– plant with no intentional denitrification

EF 2 = Emission factor (7 g N 2 O/person

- year)

– plant with intentional denitrification

Protein = Annual per capita protein consumption (k g/person/year)

F NPR = Fraction of N in protein, default = 0.16 (kg N/kg protein)

F NON

- CON = Factor for non

- consumed protein added to wastewater (1.4)

F IND

- COM = Factor for industrial and commercial co

- discharged protein into the sewer system

(1.25)

N SLUDGE = N removed with sludge, kg N/yr

EF 3 = Emission factor (0.005 kg N 2 O

- N/kg sewage

- N produced)

– from effluent

0.9 = Amount of nitrogen removed by denitrification systems (EPA 2008)

44/28 = Molecular weight ratio of N 2 O to N 2
U.S. population data were taken from the U.S. Census Bureau International Database (U.S. Census 2012) and include the populations of the United States, American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the Virgin Islands. The fraction of the U.S. populatio n using wastewater treatment plants is based on data from the 1989, 1991, 1993, 1995, 1997, 1999, 2001, 2003, 2005, 2007, 2009 , and 2011 American Housing Survey (U.S. Census 2011). Data for intervening years were obtained by linear interpolation. The emi ssion factor (EF 1 ) used to estimate emissions from wastewater treatment for plants without intentional denitrification was taken from IPCC (2006), while the emission factor (EF 2 ) used to estimate emissions from wastewater treatment for plants with

intentio nal denitrification was taken from Scheehle and Doorn (2001). Data on annual per capita protein intake were provided by U.S. Department of Agriculture Economic Research Service (USDA 2009). Protein consumption data for 2005 through 2011 were extrapolated f rom data for 1990 through 2004. An emission factor to estimate emissions from effluent (EF 3 ) has not been specifically estimated for the United States, thus the default IPCC value (0.005 kg N 2 O

- N/kg sewage

- N produced) was applied. The fraction of N in pr otein (0.16 kg N/kg protein) was also obtained from IPCC (2006). The factor for non

- consumed protein and the factor for industrial and commercial co

discharged protein were obtained from IPCC (2006). Sludge generation was obtained from EPA (1999) for 1988

, 1996, and 1998 and from Beecher et al. (2007) for 2004. Intervening years were interpolated, and estimates for 2005 through 2011 were forecasted from the rest of the time series. An estimate for the N removed as sludge (N SLUDGE ) was obtained by determi ning the amount of sludge disposed by incineration, by land application (agriculture or other), through surface disposal, in landfills, or through ocean dumping. In 2011, 277 Gg N was removed with sludge. Table 8

- 15 presents the data for U.S. population, population served by biologicalWaste 8

- 25

denitrification, population served by wastewater treatment plants, available protein, protein consumed, and nitrogen

r emoved with sludge.

Table 8

- 15 : U.S. Population (Millions), Population Served by Biological Denitrification (Millions), Fraction of Population Served by Wastewater Treatment (%), Available Protein (kg/person

- year), Protein Consumed (kg/person

- year), and Nitrogen Removed with Sludge (Gg

- N/year)

Year Population Population ND WWTP Population Available Protein Protein Consumed N Removed

1990 253 2.0 75.6 38.7 29.6 215.6

2005 300 2.4 78.8 41.7 32.0 260.3

2007 305 2.3 79.4 42.1 32.3 265.9

2008 308 2.2 79.4 42.2 32.4 268.7

2009 311 2.2 79.3 42.4 32.5 271.4

2010 313 2.1 80.0 42.6 32.7 274.2

2011 316 2.1 80.6 42.8 32.8 277.0

Table 8

- 16 : Fate of Sludge Removed by Domestic Wastewater Treatment

Disposal Practices Distribution ( 1000 kg N) 1990 1995 2000 2005 2010 2011

Incineration 35,027.35 37,806.16 38,399.04 38,595.85 38,301.05 38,215.54 Land Application 77,378.34 97,230.98 113,311.73 129,196.74 144,113.04 147,054.99 Ag 52,198.15 69,001.16 83,522.63 98,080.96 112,014.99 114,778.24

Other 25,180.19 28,229.81 29,789.11 31,115.78 32,098.05 32,276.75 Surface Disposal 20,325.19 16,142.13 10,243.93 4,586.01 2,558.71 2,275.43

Landfill 72,962.21 75,945.15 74,158.54 71,407.98 67,609.40 66,790.83
Ocean Dumping 8,294.65

- - - - - Other 1,645.76 6,353.98 11,312.32 16,478.76 21,661.26 22,702.30



# Uncertainty and Time

- Series Consistency

The overall uncertainty associated with both the 2011 CH 4 and N 2 O emission estimates from wastewater treatment and discharge was calculated using the IPCC Good Practice Guidance Tier 2 methodology (2000). Uncertainty associated with the parameters used to estimate CH 4 emissions include that of numerous input variables used to model emissions from domestic wastewater, and wastewater from pulp and paper manufacture, meat and poultry processing, fruits and vegetable processing, ethanol production, and petroleum refining. Uncertainty associated with the parameters used to estimate N 2 O emissions include that of sewage sludge disposal, t otal U.S. population, average protein consumed per person, fraction of N in protein, non

- consumption nitrogen factor, emission factors per capita and per mass of sewage

- N, and for the percentage of total population using centralized wastewater treatment pl ants.

The results of this Tier 2 quantitative uncertainty analysis are summarized in Table 8

- 17 . Methane emissions from

wastewater treatment were es timated to be between 11.5 and 20.7 Tg CO 2 Eq. at the 95 percent confidence level (or in 19 out of 20 Monte Carlo Stochastic Simulations). This indicates a range of approximately 29 percent below to 28 percent above the 2011 emissions estimate of 16.2 Tg CO 2 Eq. N 2 O emissions from wastewater treatment were estimated to be between 1.2 and 10.2 Tg CO 2 Eq., which indicates a range of approximately 77 percent below to 97 percent above the 2011 emissions estimate of 5.2 Tg CO 2 Eq.

Table 8

- 17 : Tier 2 Quantitative Uncertainty Estimates for CH 4 Emissions from Wastewater Treatment (Tg CO 2 Eq. and Percent)

Source Gas 201 1 Emission

Estimate Uncertainty Range Relative to Emission

Estimate a (Tg CO 2 Eq.) (Tg CO2 Eq.) (%)8

- 26 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1 Lower

Bound Upper

Bound Lower

Bound Upper

Bound

Wastewater Treatment CH 4 16. 2 11.5 20.7

- 2 9 % + 28 %

Domestic CH 4 7. 6 5. 6 9. 6

- 26% +2 7 %

Industrial CH 4 8.6 4.6 12.7

- 4 7 % + 48 %

Wastewater Treatment N 2 O 5. 2 1.2 10. 2

- 77% +9 7 %

a Range of emission estimates predicted by Monte Carlo Stochastic Simulation for a 95 percent

confidence interval.

Methodological recalculations were applied to the entire time

- series to ensure time

- series consistency from 1990 through 2011. Details on the emission trends through time are described in more detail in the Methodology section,

above.



# QA/QC and Verification

A QA/QC analysis was performed on activity data, documentation, and emission calculations. This effort included a Tier 1 analysis, i ncluding the following checks:

 Checked for transcription errors in data input;

 Ensured references were specified for all activity data used in the calculations;

 Checked a sample of each emission calculation used for the source category;

 Checked that parameter and emission units were correctly recorded and that appropriate conversion factors were used;

 Checked for temporal consistency in time series input data for each portion of the source category;

 Confirmed that estimates were calculated and reporte d for all portions of the source category and for all years;

 Investigated data gaps that affected emissions estimates trends; and

 Compared estimates to previous estimates to identify significant changes.

All transcription errors identified were corrected. The QA/QC analysis did not reveal any systemic inaccuracies or incorrect input values.



# Recalculations Discussion

Production data were updated to reflect updated USDA NASS datasets. This resulted in minor changes to the emission estimates from the previous inventory. In addition, population updates from the U.S. Census resulted in minor changes to domestic wastewater treatment emission estimates from 2000 through 2010.



# Planned Improvements

The methodology to estimate CH 4 emissions from domestic wastewater treatment currently utilizes estimates for the percentage of centrally treated wastewater that is treated by aerobic systems and anaerobic systems. These data come from the 1992, 1996, 2000, and 2004 CWNS. The question of whether activity data for wastewater treatment systems are sufficient across the time series to further differentiate aerobic systems with the potential to generate

small amounts of CH 4 (aerobic lagoons) versus other types of aerobic systems, and to di fferentiate between anaerobic systems to allow for the use of different MCFs for different types of anaerobic treatment systems, continues to be explored. The CWNS data for 2008 were evaluated for incorporation into the inventory, but due to significant c hanges in format, this dataset is not sufficiently detailed for inventory calculations. However, additional information and other data continue to be evaluated to update future years of the inventory.

For industrial wastewater emissions, data recently coll ected by EPA’s Office of Air for pulp and paper mills and petroleum refineries is being evaluated to determine if sufficient information is available to update the estimates of wastewater generated per unit of production and the percent of industry wastewa ter treated anaerobically in these industries ( %TA). Initial evaluations of EPA’s Office of Air data for pulp and paper manufacturing indicate there is sufficient information to update emission estimates in the next inventory year

. Data collected in 2012 u nder the EPA’s GHGRP will also be investigated for updating this variable. In examining data from EPA’s GHGRP for use in improving the emission estimates for the industrial wastewater category, particular attention will be made toWaste 8

- 27

ensure time series consis tency, as the facility

- level reporting data from EPA’s GHGRP are not available for all inventory years as reported in this inventory. In implementing improvements and integration of data from EPA’s GHGRP, the latest guidance from the IPCC on the use of fac ility

- level data in national inventories will be relied

upon. 255 For all industries, EPA will continue to review new research on industrial wastewater characteristics, utilization of treatment systems, and associated greenhouse gas emissions as it becomes av ailable. Before the incorporation of any new data, EPA will ensure it is representative of industry conditions.

Currently, it is assumed that all aerobic wastewater treatment systems are well managed and produce no CH 4 and that all anaerobic systems have a n MCF of 0.8. Efforts to obtain better data reflecting emissions from various types of municipal treatment systems are currently being pursued.

With respect to estimating N 2 O emissions, the default emission factors for indirect N 2 O from wastewater effluen t
and direct N 2 O from centralized wastewater treatment facilities have a high uncertainty. Research is being conducted by WERF to measure N 2 O emissions from municipal treatment systems. In addition, a literature review

has been conducted focused on N 2 O em issions from wastewater treatment to determine the state of such research and identify data to develop a country

- specific N 2 O emission factor or alternate emission factor or method. Such data will continue to be reviewed as they are available to determine if a country

- specific N 2 O emission factor can or should be developed, or if alternate emission factors should be used.

Previously, new measurement data from WERF were used to develop U.S.

- specific emission factors for CH 4 emissions from septic systems a nd incorporated it into the inventory emissions calculation. Due to the high uncertainty of the measurements for N 2 O from septic systems, estimates of N 2 O emissions were not included. Appropriate emission factors for septic system N 2 O emissions will contin ue to be investigated as the data collected by WERF indicate that septic soil systems are a source of N 2 O emissions.

In addition, the estimate of N entering municipal treatment systems is under review. The factor that accounts for

non

- sewage N in wastewa ter (bath, laundry, kitchen, industrial components) also has a high uncertainty. Obtaining data on the changes in average influent N concentrations to centralized treatment systems over the time series would improve the estimate of total N entering the sy stem, which would reduce or eliminate the need for other factors for

non

- consumed protein or industrial flow. The dataset previously provided by the National Association of Clean Water Agencies (NACWA) was reviewed to determine if it was representative of the larger population of centralized treatment plants for potential inclusion into the inventory. However, this limited dataset was not representative of the number of systems by state or the service populations served in the United States, and therefore

c ould not be incorporated into the inventory methodology. Additional data sources will continue to be researched with the goal of improving the uncertainty of the estimate of N entering municipal treatment systems.

The value used for N content of sludge co ntinues to be investigated. This value is driving the N 2 O emissions for wastewater treatment and is static over the time series. To date, new data has not been identified that would be able to establish a time series for this value. The amount of sludge pr oduced and sludge disposal practices will also be investigated. In addition, based on UNFCCC review comments, improving the transparency of the fate of sludge produced in wastewater treatment will also be investigated.

A review of other industrial wastewa ter treatment sources for those industries believed to discharge significant loads of BOD and COD has been ongoing. Food processing industries have the highest potential for CH 4 generation due to the waste characteristics generated, and the greater likeli hood to treat the wastes anaerobically. However, in all cases there is dated information available on U.S. treatment operations for these industries. Previously, organic chemicals, the seafood processing industry and coffee processing were investigated to estimate their potential to generate CH 4 . Due to the insignificant amount of CH 4 estimated to be emitted and the lack of reliable, up

- to

- date data, these industries were not selected for inclusion in the industry. Preliminary analyses of the beer and mal t and dairy products industries has been performed. These industries will continue to be investigated for incorporation. Other industries will be reviewed as necessary for inclusion in future years of the inventory using EPA’s Permit Compliance System and Toxics Release inventory.

In addition, available datasets will be reviewed to provide further information on the fates of sludge removed by

domestic wastewate r treatment in the next inventory report.

255 See: http://www.ipcc

- nggip.iges.or.jp/meeting/pdfiles/1008_Model_and_Facility_Level_Data_Report.pdf.8

- 28 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1 

# 8.3 Waste Incineration (IPCC Source Category

6 C )

As stated earlier in this chapter, CO 2 , N 2 O, and CH 4 emissions from the incineration of waste are accounted for in the Energy sector rather than in the Waste sector because almost all incineration of municipal solid waste (MSW) in

the United States occurs at waste

- to

- energy facilities where useful energy is recovered. Similarly, the Energy sector also includes an estimate of emissions from burning waste tires and hazardous industrial waste, because virtually all of the combustion occurs in industrial and utility boilers that recover energy. The incineration of waste in the United

States in 201 1 resulted in 12.4 Tg CO 2 Eq. emissions, nearly half of which is attributable to the combustion of plastics. For more details on emissions from the incineration of waste, see Section 3.3 of the Energy chapter

.

Addition al sources of emissions from waste incineration include n on

- h azardous i ndustrial w aste i ncineration and

m edical w aste i ncineration . As described in Annex 5 of this report, d ata are not readily available for these sources and emissions estimates are not pro vided

. Further investigations will be made, including assessing the applicability

of state

- level data collected for EPA’s National Emission Inventory (NEI) 256

.



# 8.4 Composting (IPCC Source Category 6D)

Composting of organic waste, such as food waste, garden (y ard) and park waste, and sludge, is common in the United States. Advantages of composting include reduced volume in the waste material, stabilization of the waste, and destruction of pathogens in the waste material. The end products of composting, depend ing on its quality, can be recycled as fertilizer and soil amendment, or be disposed in a landfill. Approximately 400 composting facilities operate in the United States (WBJ 2010).

Composting is an aerobic process and a large fraction of the degradable organic carbon in the waste material is converted into carbon dioxide (CO 2 ). Methane (CH 4 ) is formed in anaerobic sections of the compost, but it is oxidized to a large extent in the aerobic sections of the compost. Anaerobic sections are created in comp osting piles when there is excessive moisture or inadequate aeration (or mixing) of the compost pile. The estimated CH 4 released into the atmosphere ranges from less than 1 percent to a few percent of the initial C content in the material (IPCC 2006). De pending on the N content of the feedstock and how well the compost pile is managed, nitrous oxide (N 2 O) emissions can be produced. The formation of N 2 O is complicated, but is mainly associated with anaerobic conditions. Emissions vary and range from less than 0.5 percent to 5 percent of the initial content of the material (IPCC 2006).

From 1990 to 2011, the amount of material composted in the United States has increased from 3,810 Gg to 18,449 Gg, an increase of approximately 384 percent. From 2000 to 2 011, the amount of material composted in the United States has increased by approximately 24 percent. Emissions of CH 4 and N 2 O from composting have increased by the same percentage. In 2011, CH 4 emissions from composting (see Table 8

- 18 and Table 8

- 19 ) were 1.5 Tg CO 2 Eq. (74 Gg), and N 2 O emissions from composting were 1.7 Tg CO 2 Eq. (5.5 Gg). The wastes composted primarily include yard trimmings (grass, leaves, and tree and brush trimmin g s) and food scraps from residences and commercial establishments (such as grocery stores, restaurants, and school and factory cafeterias). The composted waste quantities reported here do not include backyard composting. The growth in composting since th e 1990s is attributable to primarily two factors: (1) steady growth in population and residential housing, and (2) the enactment of legislation by state and local governments that discouraged the disposal of yard trimmings in landfills. In 1992,

11 state s and the District of Columbia had legislation in effect that banned or discouraged disposal of yard trimmings in landfills. Currently, 23 states and the District of Columbia, representing about 50 percent of the

256 See < http://www.epa.gov/ttn/chief/eiinformation.html >Waste 8

- 29

nation’s population, have enacted such leg islation (EPA 2010). The total amount of waste composted has decreased slightly since 2008, by approximately 8 percent.

Table 8

- 18 : CH 4 and N 2 O Emissions from Composting (Tg CO 2 Eq.)

Activity 1990 2005 2007 2008 2009 2010 2011

CH 4 0.3 1.6 1.7 1.7 1.6 1.5 1.5

N 2 O 0.4 1.7 1.8 1.9 1.8 1.7 1.7

Total 0.7 3.3 3.5 3.5 3.3 3.2 3.3

Table 8

- 19 : CH 4 and N 2 O Emissions from Composting (Gg)

Activity 1990 2005 2007 2008 2009 2010 2011

CH 4 15 75 79 80 75 73 74

N 2 O 1 6 6 6 6 5 6



# Methodology

Methane and N 2 O emissions from composting depend on factors such as the type of waste composted, the amount and type of supporting material (such as wood chips and peat) used, temperature, moisture content and aeration during the process.

The emissions shown in Table 8

- 18 and Table 8

- 19 were estimated using the IPCC default (Tier 1) methodology (IPCC 2006), which is the product of an emission factor and the mass of organic waste composted (note: no CH 4 recovery is expected t o occur at composting operations):

where,

E i = CH 4 or N 2 O emissions from composting, Gg CH 4 or N 2 O,

M = mass of organic waste composted in Gg,

EF i = emission factor for composting, 4 g CH 4 /kg of waste treated (wet basis) and 0 .3 g

N 2 O/kg of waste treated (wet basis) (IPCC 2006), and

i = designates either CH 4 or N 2 O.

Estimates of the quantity of waste composted (M) are presented in Table 8

- 20 . Estimates of the quantity composted

for 1990 and 1995 were taken from the Characterization of Municipal Solid Waste in the United States: 1996 Update (Franklin Associates 1997); estimates of the quantity composted for 2000, 2005, 2006 , 2007, 2008, and 2009

were taken from EPA’s Municipal Solid Waste In The United States: 2009 Facts and Figures (EPA 2010); estimates of the quantity composted for 2010 were taken from EPA’s Municipal Solid Waste In The United States: 2010 Facts and Fig ures (EPA 2011); estimates of the quantity composted for 2011 were calculated using the 2010 quantity composted and a ratio of the U.S. population in 2010 and 2011 (U.S. Census Bureau 2012). The estimated quantity of waste composted in 2010 was revised bas ed on updated information (EPA 2011).

Table 8

- 20 : U.S. Waste Composted (Gg)

Activity 1990 2005 2007 2008 2009 2010 2011

Waste Composted 3,810 18,643 19,695 20,049 18,824 18,298 18,449

Source: EPA 2008 and EPA 2011.8

- 30 In ventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

– 2 01 1



# Uncertainty and Time

- Series Consistency

Little is known about the site

- specific operating conditions at the composting facilities in the United States. The generation of CH 4 and N 2 O emissions is highly dependent on the characteristics of the feedstock material (e.g., moisture content, C to N ratio, size), on the climate, and on the operating and maintenance practices (e.g., use of a shredder/grinder to maintain consistency in size of the feedstock material, frequency of pile rotation, addition of moisture, application of finished compost on the pile). The estimated uncertainty from the 2006 IPCC Guidelines is ±50 percent for the Tier 1 methodology. Emissions from composting in 2011 were estimated to be between 1.6 a nd 4.9 Tg CO 2 Eq., which indicates a range of 50 percent below to 50 percent above the actual 2011 emission estimate of 3.3 Tg CO 2 Eq. (see Table 8

- 21 ).

Table 8

- 21 : Tier 1 Quantitative Uncertainty Estimates for Emissions from Composting (Tg

CO 2 Eq. and Percent)

Source Gas 2011 Emission

Estimate Uncertainty Range Relative to Emission Estimate (Tg CO 2 Eq.) (Tg CO 2 Eq.) (%)

Lower

Bound Upper

Bound Lower

Bound Upper

Bound
Composting CH 4 , N 2 O 3.3 1.6 4.9

- 50% +50%

Methodological recalculations were applied to the entire time series to ensure time

- series consistency from 1990 through 2011. Details on the emission trends through time are described in more detail in the Methodology section,

above.



# QA/QC and Verification

A QA/QC analysis was performed for data gatheri ng and input, documentation, and calculation. A primary focus of the QA/QC checks was to ensure that the amount of waste composted annually was correct according to the latest

EPA Municipal Solid Waste In The United States: Facts and Figures report.



# Recal culations Discussion

The estimated amount of waste composted in 2010 was updated based on new data contained in EPA’s Municipal Solid Waste In The United States: 2010 Facts and Figures (EPA 2011). The amounts of CH 4 and N 2 O emissions

estimat es presented in Table 8

- 18 and Table 8

- 19 were revised accord ingly.



# Planned Improvements

For future Inventories, additional efforts will be made to improve the estimates of CH 4 and N 2 O emissions from composting. For example, a literature search may be conducted to determine if emission factors specific to various composting systems and composted materials are available. Further cooperation with estimating emissions in cooperation with the LULUCF Other section will be made.



# 8.5 Waste Sources of Indirect Greenhouse

Gases

In addition to the main greenhouse gases address ed above, waste generating and handling processes are also sources of indirect greenhouse gas emissions. Total emissions of NO

x , CO, and NMVOCs from waste sources for the years 1990 through 20 11 are provided in Table 8

- 22

.Waste 8

- 31

Table 8

- 22 : Emissions of NO x , CO, and NMVOC from Waste (Gg)

Gas/Source 1990 2005 2007 2008 2009 2010 2011

NO x + 2 2 2 2 2 2

Landfills + 2 2 2 2 2 2

Wastewater Treatment + + + + + + + Miscellaneous a + + + + + + + CO 1 7 7 7 7 7 7

Landfills 1 6 6 6 6 6 6

Wastewater Treatment + + + + + + + Miscellaneous a + + + + + + + NMVOCs 673 114 111 109 76 76 76

Wastewater Treatment 57 49 48 47 33 33 33

Miscellaneous a 557 43 42 41 29 29 29

Landfills 58 22 21 21 14 14 14

a Miscellaneous includes TSDFs (Treatment, Storage, and Disposal Facilities under the Resource Conservation and Recovery Act [42 U.S.C. § 6924, SWDA § 3004]) and other waste categories. Note: Totals may not sum due to independent rounding.

+ Does not exceed 0.5 Gg.



# Methodology

Due to the lack of data available at the time of publication, emission estimates for 2010 and 2011 rely on 2009 data

as a proxy. E mission estimates for 2009 were obtained from preliminary data (EPA 2010, EPA 2009), and disaggregated based on EPA (2003), which, in its final iteration, will be published on the National Emission Inventory (NEI) Air Pollutant Emission T rends web site. Due to redevelopment of the information technology systems for the NEI, publication of the most recent emissions for these pollutants (i.e., indirect greenhouse gases) was not available for this report 257 . Emission estimates of these gases were provided by sector, using a “top down” estimating procedure

 emissions were calculated either for individual sources or for many sources combined, using basic activity data (e.g., the amount of raw material processed) as an in dicator of emissions. National activity data were collected for individual source categories from various agencies. Depending on the source category, these basic activity data may include data on production, fuel deliveries, raw material processed, etc.



# Uncertainty and Time

- Series Consistency

No quantitative estimates of uncertainty were calculated for this source category. Methodological recalculations were applied to the entire time

- series to ensure time

- series consistency from 1990 through 20 11

.

257 For a n overview of the activities and the schedule for developin g the 2011 National Emissions Inventory, with the goal of producing Version 1 in the summer of 2013 , see < http://www.epa.gov/ttn/chief/eis/2011nei/2011plan.pdf >