EPA-6GO/R-99-089
Environmental Protection
A9eix:y October 1999
<&EPA Research and
Development
QUANTIFICATION OF METHANE EMISSIONS
AND DISCUSSION OF NITROUS OXIDE, AND
AMMONIA EMISSIONS FRCM SEPTIC TANKS,
LATRINES, AND STAGNANT OPEN
SEWERS IN THE WORLD
Prepared for
Policy and Program Evaluation Division
Prepared by
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
-------
FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a. compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building 8 science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available io the public through the National Technical Information
Service, Springfield, Virginia 22161.
-------
EPA-600/R-99-089
October 1999
QUANTIFICATION OF METHANE EMISSIONS
AND DISCUSSION OF NITROUS OXIDE, AND AMMONIA EMISSIONS
FROM SEPTIC TANKS, LATRINES, AND
STAGNANT OPEN SEWERS IN THE WORLD
Michiel R.J. Doom and David S Liles
ARCADIS Geraghty & Miller
4915 Prospectus Drive, Suite F
Durham, North Carolina 27713
EPA Contract Ho. 68-D4-0005
Work Assignment No. 3-020
and EPA Contract N
-------
ABSTRACT
This study is a fi.st attempt to estimate global and country-specific methane (CHa) emissions
from open sewers and cm-site wastewater treatment systems, including latrines and septic sewage tanks.
It is the follow-up of an earlier report that includes CH4 and N2O estimates from treated industrial and
domestic wastewater. This study uses an emission factor that expresses CH4 emissions in terms of
removed Chemical Oxygen Demand (CODrem(Jve(i).
Combined global CH, emissions from latrines, septic sewage tanks, and stagnant, open sewers
are estimated to be 29 teragrarns per year (Tg/yr), with lower and upper bound ranges of 14 and 49 Tg/yr.
These ranges reflect boundaries in the parameters that could be quantified through measurements, i.e.,
the emission factor and COD loadings. Major uncertainties in the estimates are associated with the
degrees to which wastewater in developing and eastern European countries is treated in latrines or septic
tanks, or removed by sewer. Also, the amount of wastewater that is discharged into stagnant, open
sewers and the degree to which anaerobic decomposition takes place in these sewers are highly
uncertain.
Latrines in rural areas of developing countries such as China and India are believed to be the
single most significant source of methane, accounting for roughly 12 Tg/yr. Total emissions from
stagnant, open sewers are estimated at around SO Tg/yr. Trends in these emissions in the future will
likely be driven by changes due to health considerations. Although significant gains have been made in
the provision of sanitation services in cities, these efforts have been nullified by rapid urban population
growth. In rural areas of developing countries, lack of sanitation is not likely to become a significant
health problem and no trends towards other sanitation systems are expected. Consequently, both rural
latrines and urban stagnant, open sewers arc expected to remain significant sources of methane emissions
in the future.
An appendix to this report includes a discussion of nitrogen cycle effects in these systems to
qualify ammonia (NH3) and nitrous oxide (N,O) emissions from these systems. It was concluded that
these systems are not likely to contribute any significant quantity of NH} and NjO to the atmosphere.
-------
TABLE OF CONTENTS
Page
List of Tables . iv
List of Figures iv
List of Terms v
1.0 Introduction and Background 1
2.0 Residential, Domestic, and Industrial Wastewatcr 3
2.1 Effect of Income and Urbanization 5
3.0 On-Site Treatment Systems and Open Sewers 8
3.1 On-Site Treatment Systems 8
3.1.1 Septic Tanks, Aqua Privies, and Cesspools 8
3.1.2 Standard Latrines 9
3.1.3 Bucket Latrines/Ntghtsoil Collection, Vault Latrines 9
3.1.4 Extent of Use of On-Site Treatment Systems 10
3.1.4.1 Developing Countries 10
3.1.4.2 Developed Countries 12
3.2SewfrSystems 14
3.2.1 Extent of Sewerage 15
3.2.1.1 Potential for Anaerobic Decomposition in Sewers 16
3.2.2 Extent of Centralized Treatment 17
4.0 Methane Emission Estimation Methodology, Activity Data, and Global and
Country-Specific CH4 Emission Estimates 18
4.1 Methodology 18
4.2 Activity Data 19
4.3 Methane Emission Estimates and Uncertainties 27
4.4 Trends 30
5.0 References 32
Appendix A Executive Summary of "Estimates of Global Greenhouse Gas
Emissions from Industrial and Domestic Wastewater Treatment." 35
Appendix B Summary of Nitrogen Cycle Effects on Ammonia and Nitrous Oxide
Emissions from Septic Tanks, Latrines, and Stagnant Open Sewers 41
-------
LIST OF TABLES
Table 2-1. Typical Composition of Fresh Domestic U.S.-Wastcwatcr 5
Table 2-2. Available BOD5 and COD Loadings for Municipal Wastewater
in Different Regions in the World 6
Table 2-3. Country-specific Population, Urbanization, and Residential Wastewater
BOD/COD Generation Data ?
Table 3-1. Sewage Disposal and Treatment for Europe, Turkey, and Israe! 13
Table 4-1. Country-specific WWT Practices and Methane Emissions for
Rural Population 20
Table 4-2. Country-specific WWT Practices and Methane Emissions for
Urban High-Income Population 22
Table 4-3. Country-specific WW f Practices and Methane Emissions for
Urban Low-Income Population 24
Table A-1. Summary of Global GHG Estimates for Domestic and Industrial WWT 40
Table B-1. Septic Tank Influent and pH Values from Two Sources 44
LIST OF FIGURES
Figure 3-1. Overview of Global Sanitation by Technology Type for 82 Developing
Countries
Figure 4-!: Global Estimates of CH4 Emissions from Stagnant, Open Sewers,
Septic Tanks, Latrines, and WWT Plants
11
27
-------
LIST OF TERMS
APPCD Air Pollution Prevention and Control Division
BOD Biochemical Oxygen Demand
CH, Methane
CO Carbon Dioxide
C( =D Chemical Oxygen Demand
El A Environmental Protection Agency
FTIR Fourier Transform Infrared
GHG Greenhouse Gas
g/cap/day gram per capita per day
mg/1 milligram per liter
NH, ammonia
NH4* ammonium
N,O Nitrous Oxide
OPM/TM Open Path Monitoring Transect Method
POTW Publicly Owned Treatment Works
Tg/yr Teragram per year
VOC Volatile Organic Compound
W WT Wastewater Treatment
-------
CHAPTER 1
INTRODUCTION AND BACKGROUND
Many waslcwater management and treatment systems, including sewers, centralized wastewater
treatment plants, as well as off-site treatment systems, such as septic sewage systems and latrines, are
suspected of being significan* sources of methane (CE,), .utrous oxide (NjO), and ammonia (NHj).
Methane is an importar.i greenhouse gas (GHG), while N2O is a secondary GHG. Ammonia is a gas that
plays an important role in acid rain and small airborne particle formation, as well as in nitrogen
deposition.
In the Unite.l States, the Air Pollution Prevention and Control Division (APPCD), National Risk
Management Reseai^h Laboratory, Office of Research and Development of the U.S. Environmental
Protection Agency (EPA), has been managing a program to develop estimates of GHG emissions from
waste sources, including was-.. ater sources, and to compile information on cost-effective control
technologies. As a first step in assessing the relative importance of wastewater as a source for CH4
emissions, APPCD conducted a desk study in 1991-1992, which was summarized in a Report to
Congress (USEPA, 1994). The study targeted anaerobic lagoons as the primary source of suspected CH4
emissions from wastewater.
From this initial study, APPCD concluded that major data limitations existed for quantifying
actual emissions from wastewater sources including the fraction of wastewater subject to anaerobic
decomposition, and the outflow and composition of industrial wastewater. APPCD initiated a field test
program to develop more accurate GHG emission factors based on actual emission measurements and to
improve country-specific activity data for industrial and domestic wastewater treatment (WWT). The
field test program involved the use of the open path monitoring/transect method (OPM/TM) technique
with Fourier Transform Infrared (FTIR) spectroscopy to measure emissions from two beef processing
plants, one chicken processing plant, and two facultative municipal WWT lagoons. Wastcwaler and
process data were collected during the tests to allow for the development of emission factors. The field
test results and discussion are documented in Eklund and LaCosse (1997). In conjunction with the field
tests, research was undertaken to improve the quality of available activity data. Findings and country-
specific and global CH4 and N2O estimates from treated wastewater arc documented in a report entitled:
"Estimates of Global Greenhouse Gas Emissions from Industrial and Domestic Wastewater Treatment"
(Doom, et al., 1997), produced under HP A Contract No. 68-04-0100. The executive summary of this
report is included as Appendix A. In ihc text, this report is referred to as the "Emissions-from-WWT
report."
-------
One of the findings from the treated wastewaler study was that anacrobically degrading
wastewaler that is not treated at centralized WWT facilities may be a significant source of GHG
emissions. Such wastewater sources include decentralized (on-site) anaerobic treatment systems, such as
latrines and septic sewage tanks, as well as wastewater in stagnant, anaerobic sewers in developing
countries. This study estimates CH, emissions from these sources, using the emission factor and
methodology for treated domestic sewage from the Emissions-from-WWT report. Furthermore, this
report provides background information and country- or region-specific activity data on various on-site
treatment and sewer systems,
Because sanitation system choice and availability is strongly dependent on population density
and per capita income, this study differentiates between country-specific rural, urban high-income, and
urban low-income population groups. For example, in developing countries, high-income urban
populations usually have access to some convenient type of sewage disposal system, whereas the urban
low-income population may have little or no access. In rural areas, which have low population densities,
there is less urgency for a sewage treatment or removal system from a sanitation perspective; people may
use on-site systems or the surrounding fields. Also, the per capita cost for sewer infrastructure is
inversely proportional to population density.
Also, this report includes a discussion of nitrogen cycle effects in septic tanks, latrines, and
stagnant, open sewers on NH, and N2O emissions (Appendix B). Because of the complex pathway ,i of
organic nitrogen decomposition, nitrogen emissions could not be quantified. However, knowledge of the
nitrogen cycle in septic ianks, latrines, and stagnant, open sewers suggests that anaerobic wastewater in
these systems does not contribute any significant quantity of Nil, and N2O to the atmosphere. This
discovery indicates that the estimation of global GHG and NH, emissions can safely overlook the
production of NHj and NjO from seotic tanks, latrines, and stagnant, open sewers at a global level.
-------
CHAPTER 2
RESIDENTIAL, DOMESTIC, AND INDUSTRIAL WASTEWATER
Metcalf & Eddy (1991) define residential wastewater as the spent water originating from all
aspects of human sanitary water usage, consisting of wastewater from toilets, baths, kitchens, and
laundry-rooms, (Note that this definition does not express the source of the wastewater. Hence,
residential wastewater also includes wastewater that is generated as a result of human sanitary water
usage at home, at the work place, or at recreational facilities, such as restaurants, theaters, or sports
clubs.)
Domestic (or municipal1) wastewater is defined as ail wastewater that is discharged into
municipal sewers to be removed from the premises and to be treated at a central municipal WWT plant2
or disposed of via an outfall. Domestic wastewater sources include non-point sources, such as
greengrocers, butchers, bakers, and workshops. In addition, a certain amount of raw or semi-treated
industrial wastewater is often discharged into municipal sewers. In countries with adequate regulations
and enforcement, industrial discharges to municipal sewers are limited to those kinds of wastewater that
are treatable at the local POTW. These types of wastewater would include wastewater from the food and
beverage industry, the textile industry, and from certain sectors of the organic chemicals industry. In
other countries the situation may be radically different and industrial wastewater may be discharged
indiscriminately into municipal sewers (Doom ct at., 1997).
Quantification of the fraction of industrial organic BOD and/or chemical oxygen demand (COD)
in residential wastewater is difficult. The amount of wastewater COD in absolute and in relative terms
(per unit of output or per liter of wastewater), is highly variable and depends on the type of product and
industrial process. Industries that produce limited wastewater COD outflows may be permitted to direct
all outflow to municipal sewers, whereas industries with iarge wastewater COD outflows in the same
country arc more likely to be required to apply on-sitc WWT. The establishment of on-site treatment
may be regulatory driven or it may be company policy for other reasons, such as public image
maintenance. Also, depending on local regulations and the enforcement thereof will vary from country
to country and certain corporations may apply comprehensive on-site WWT in some countries, whereas
the same corporations may apply no or limited WWT in other countries for the same industrial process
(Doom, etaL, 1997).
The fraction of COD removed from the industrial wastewater stream depends on the type of
treatment system. The primaiy treatment system of some plants may be designed to remove most or all
The terms municipal and domestic wastewater often are usoti interchangeably throughout the literature.
Municipal WWT plants are often referred to as pubftciy owned rreaimerj! works {POTW) in the United States.
-------
organic COD, e.g., when the COD has remaining commercial value as is the case with sugar.
Conversely, other primary treatment systems may be designed to remove only inorganic solids or toxic
compounds and deliberately leave the organic COD in the wastewater stream for treatment at the
municipal WWT plant. In addition, the type of treatment will depend on the geographic location of the
industry, For example, industrial processes that require large amounts of process water and that produce
large quantities of wastewater (e.g., pulp and paper mills) are likely to be located near a fresh water
source, such as a river or lake. The location on the river bank also allows for convenient discharge of the
wastewater, be it raw or purified. In this situation, the plant is unlikely to release wastewater to
municipal sewers.
Included in the Emissions-from-WWT report are estimates for the quantity of COD that is
discharged to city sewers for different industrial categories for the major producing countries. These
estimates cannot easily be combined with the data for municipal wastewater from the 'same report
because the rr.ost populous countries (which produce the most residential wastewater COD) are not
necessarily equal to the countries with the highest wastewafer COD output per industrial category, [n
order to estimate the contribution of industrial COD to municipal sewers, it was decided to use the global
average. The quantity of COD from industrial wastewater that is discharged into municipal sewers
around the world is estimated at 18 Tg/yr (Emissions-from-WWT report, Table 18, COD-to-City-Sewers
column); data from Table 17 and 19 in the Emissions-from-WWT report were combined to estimate the
total global residential COD per year that is discharged into municipal sewers, i.e., 73 Tg/yr.
Accordingly, this report uses 18/73 or 25 percent for the overall fraction of industrial wastewater COD in
municipal sewers.
Domestic wastewater that has not received indiscriminate industrial discharges typically contains
only components that arc organic in nature (carbohydrates, lipids, proteins, soaps) and may be
considered somewhat homogeneous. An indication of the average composition of U.S. municipal
wastewater is given in Table 2-1.
-------
TABLE 2-1, Typical Composition of Fresh Domestic U.S. Wastewater
COMPONENT
Soiids, Total
Dissolved, Total
Mineral
Organic
Suspended
Mineral
Organic
Total SetHeabie
Solids
Five day biochemical
oxygen demand
(BODJ
VOC's
Typical pH
RANGE
(mg/ir
730-
1,180
400 - 700
250-450
150 - 250
180-300
40 - 70
140-230
150 -180
160-280
<1
RANGE
(o^sap/day)"
277 -448
152 - 266
95- 171
57-95
68-114
15-27
53-87
57-68
61 - 106
7.0 - 7.5
COMPONENT
Organic Carbon, Total
Chemical oxygen
Demand (COD)
Total Nitrogen
Organic
Free ammonia
Nitrates and nitrites
Phosphorus, Total
Chlorides
Alkalinity (as calcium
carbonate)
Oil and Grease
RANGE
(mgtir
200 - 500
550 - 700
40-50
15-20
25-30
0
10-15
50-60
100-125
90-110
RANGE
(0/eap/day)**
76 - 190
209-266
15-19
6-8
10-11
0
4-6
19-23
38-48
34-42
Based on Muiitek (1987). -
" milligrams per liter.
** grams per capita per day. Assumed water consumption of 100 gal. (380 liter) per capita.
Assumed medium use of garbage disposals, moderate income population.
'As did ihc Emissions-from-WWT report, this report uses daily per capita organic loadings rates
to quantify residential and domestic organic wastewater outflow. Residential daily per capita BOD
loadings depend on diet, metabolism, and body weight, as well as cleansing, bathing, laundering, and
food preparation habits, including the use of kitchen garbage disposals. Table 2-2 includes available
BOD and COD loadings for residential wastewater in different regions in the world, including those from
the Emissions-from-WWT report. In the table, the per capita BOD loadings used in the Emissions-from-
WWT report reflect the lower range of the loadings from Mullick (I987) and Laak (1980). Based on the
data represented in Table 2-2 it was estimated that the ratio between municipal wastewater BOD and
organic COD is approximated at 2.5.
2.1 EFFECT OF INCOME AND URBANIZATION
As mentioned in the Introduction and Background Section, this report distinguishes between
rural, urban high-income, and urban low-income populations, because availability and choice of sewage
disposal system are dependent on income and population density. According to the World Bank's World
Development Report on Poverty (1990) in Bartone (1994), about one quarter of the world's urban
-------
population lives in absolute poverty and many more live in substandard conditions. In this report, 75
percent of the urban population for most developing countries has been classified as low-income, which
is higher than what is indicated by the aforementioned Report on Poverty. The choice of this value is
based on expert judgment by the authors and reflects relative sanitary conditions only and should not be
construed as an indication of other factors that determine poverty or privation. For countries in "Other
Asia" a Jaw-income fraction of 50 percent is used instead of 75 percent. This region includes many oil-
producing countries, which arc assumed to have a larger middle- and high-income- class compared to
other developing Asian countries. For developed and eastern European countries, the distinction
between urban high-income and low income was not made.
Table 2-3 provides country-specific population and urbanization data (from UNEP, 1993), as
well as BOD and COD loading rates. The COD ranges (g/cap/day) from Table 2-2 were converted into
the low, mean, and high estimates of "Total COD Generation" (Tg/yr) by multiplying by the population
(?) and by 365 (days/year).
TABLE 2-2 M.jilaMe BOD, and COD Loadings for Municipal Wastewater
in Different Regions in the World
REGION OR
COUNTRY
USA
USA
Developing
countries
Eastern Europe
OECD (ex. U.S.)
USA
Developing
countries
Eastern Europe
OECD countries
(ex. U.S.)
WASTE
Excreted
Toilet tissue
Bath, laundry,
kitchen wastewater
Total residential
Total residential
wastewater
(use for septic
tanks, cess pools,
and latrines.)
Total wastewater
(use for stagnant
sewers)
BOD, LOADING
(g/cap/day)
27 ±8
10±5
±50
87 ±25
65 + 15
35 + 10
45 ±10
60 ±15
COD LOADING
(g/capAiay)
70±20
40 + 20
±90
200 ±50
160 + 70
90 ±40
110 + 45
140+65
200 ±87
113 ±50
138 ±58
175 ±81
REFERENCE
Laak (1980),
Muliick(1987)
from Doom, et at.
(1997)
25% added for
industrial wastewater
(only for city sewers)
-------
TABLE 2-3. COUNTRY-SPECIFIC POPULATION, URBANIZATION, AND RESIDENTIAL WASTEWATER
BOD/COD GENERATION DATA
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
Zimbabwe
Other Africa
ASIA
China
Ma
Indonesia .
Pakistan
Bangladesh
Japan
Other Asa
EUROPE
Russia
Germany
United Kingdom
France
Mali'
Other OECD
Other Europe
NORTH AMERICA
United States
Canada
Population
(P)
(million)
127
59
S&
43
12
492
1,238
931
201
135
128
126
726
150
81
58
58
58
113
217
263
29
LATIN AMERICA AND CARIBBEAN
Brazil
Mexico
Others
AUSTRALIA AND NEW
Australia
TOTAL
161
94
225
?EALAND
18
Fraction of Population (U) that Is
Rural
0.65
0.58
0.76
0,51
0,71
0.60
0.74
0.74
0.71
0,68
0,84
0.23
0.50
0.34
028
0.11
0.27
0.31
0.20
0.35
0.2S
0.23
0,25
0.27
0,25
0.15
Urban
total
0,35
0.44
0.24
0.49
0.29
0.40
0.26
056
0.29
0.32
0.16
0.77
0.50
0.66
0.72
0.89
0.73
0.69
0.80
0.65
0.7S
0.77
0,75
0.73
0,75
0.85
hlgh-
fetcome
0.09
0.11
0.06
0.12
0.07
0.10
0.07
0.07
0.07
0.08
0.04
0.77
0.25
0.66
0.72
OJ9
0.73
0.69
0,80
0.65
0.75
0.77
0.19
0.18
0.19
0.85
k>w-
kicome
0.26
0.33
0,18
0.37
0.22
0.30
0.20
050
052
0,24
0.12
0
0.2S
0
0
0
0
0
0
0
0
0
0.56
055
0.56
0
BOO
Generation
(g/c«p/day)
35+MO
35W-10
3S+/-10
40+/-1Q
4W-10
35+/-10
35+MO
35*MQ
354/-10
35+MO
3S+A10
55+/-15
3S+/-1Q
SO+/-10
60V-1S
B(W-1S
60+/-15
WW-1S
60+M5
erw-is
6SW-1S
60+/-15
35+/-10
35+/-10
35*MO
60^-15
SJ70
Total COO
Generation (COD)
-taw
3
1
1
1
0
11
28
21
S
3
3
5
17
5
3
2
2
2
5
9
13
t
4
2
5
1
154
(Tg/yr)
mean
4
2
1
2
0
16
40
30
6
4
4
6
23
7
4
3
3
3
6
12
17
2
5
3
7
1
212
high
5
2
1
2
1
20
51
38
8
6
5
a
30
8
6
4
4
4
8
15
20
2
7
4
9
1
270
-------
CHAPTER 3
ON-SITE TREATMENT SYSTEMS AND OPEN SEWERS
This section describes different on-site treatment systems and provides information on the extent
to which they are used throughout the world. Also included is background information that defines the
degree to which each system is anaerobic. In addition, this section provides country- or region-specific
activity data on the availability of sewer systems, as well as a discussion on the possible anaerobicity of
sewers.
3.1 ON-SITE TREATMENT SYSTEMS
On-site treatment systems include standard latrines, septic sewage systems, and systems that
require some type of manual collection, such as bucket latrines. The use of septic sewage systems is
common in rural and suburban areas throughout most countries in the world, including eastern Europe
and the United States. Latrines are widely used in developing countries. Below, the most common on-
site treatment systems are introduced.
3.1.1 Septic Tanks. Aqua Privies, and Cesspools
All these systems consist of a water-filled tank in which solids are allowed to settle (Rybczynski,
v
1979). They can receive wastewater from one or several dwellings. In a cesspool, the liquid waste is
presumed to soak away. When the cesspool is fitted with an outlet pipe, it is indistinguishable from a
septic tank or aqua privy. The effluent from an aqua-privy usually flows to a soak-away area, but may
also be fed into a sewer system (Feachem and Cairncross, 1978). Aqua privies and cesspools are not
very common compared to septic tanks (WHO/UNICEF, 1993} and are excluded from further discussion.
A septic tank is a horizontal, continuous-flow, one-story sedimentation tank that accepts all
wastewater from an individual dwelling or a group of houses, including bath-, kitchen-, and laundry-
water. The wastewater is allowed to flow slowly to permit settleable suspended matter to settle to the
bottom, where it is retained until anaerobic decomposition is established. Digested solids will form a
permanent sludge at the bottom of the tank and require periodic removal with a vacuum truck.
(Depending on the size of the tank and the number of users, pumping should be done every couple of
years.) Gases resulting from anaerobic composition, including CH4, carbon dioxide (CO,), and hydrogen
sulftde, are vented from the septic tank through a vent stack or thrcugh the effluent outlet pipe.
Recommended retention time for the wastewater in the tank is one to three days (Ipurks and Minnis,
1994).
-------
Effluent from the septic tank consists of partially treated wastcwater that still contains most non-
settleabie (dissolved and suspended) solids. It is discharged below the ground surface into a drainage
field that is composed of a gravel and/or sand bed that is permeable to the effluent and to air. The
drainage field is designed to provide secondary treatment by natural processes in the soil. These
processes are physical, chemical, and biological. The soil acts as a filter, as well as an adsorption
mechanism to remove remaining solids, nutrients, and pathogens. In addition, aerobic organisms in the
soil digest the organic effluent matter (RHI, 1992). The combination of septic tank and drainage field is
referred to as a septic sewage system.
The BODj removal efficiency in a septic tank is around 50 percent, whereas, the organic solids
removal efficiency is around 80 to 90 percent (Metealf & Eddy, 1991). The discrepancy between the two
numbers can be explained by the dissolved BOD, which is not removed in the septic tank.
3.1.2 Standard Latrines
Standard pit latrines are traditional "hole in the ground" solutions that consist of an enclosed
structure and a squatting plate above the hole, which may be either dug or bored (referred to as "bore-
hole latrines"). Simple pit latrines are prone to smell and fly problems and in many cases the design has
been modified to reduce these problems. Improvements include latrines with vent pipes (VIP latrines) or
offset pits to enable hand flushing (pour flush latrines). Pits are used until full, then either abandoned
and relocated, or emptied and reused. The pits are unlined but may be reinforced, for example, by using
oil drums with the tops and bottoms removed. Liquids are presumed to soak away and solids
decomposition can be classified as anaerobic (Burks and Minnis, 1994). In this study, latrines are
assumed to have an efficiency of 100 percent.
Latrines may serve individual households or larger groups of up to several hundred people and
may be fitted with several squatting plates and partitions for privacy (World Bank, 1979; Rybczynski,
1979; Feachem and Caimcross, 1978). These systems are widely used throughout rural and urban
settings in developing countries (WHO/UMCEF, 1993).
3.13 Backet Latrlnes/Nightsoll Collection. Vault Lalrines
These systems have in common the need for regular emptying. One of the oldest and generally
least hygienic systems used in urban areas is the bucket latrine. A squatting slab or seat is placed
directly above a bucket to collect excreta. The bucket location is at the outside wall of the dwelling ana
is accessible from the street or alley. The bucket is emptied every day or every several days by a
sweeper who manually carries the bucket to a transfer or collection station. Vault latrines are more
convenient and hygienic than bucket latrines because they allow for a water seal. Excreta plus small
-------
amounts of water for flushing are stored in sealed vaults under or beside the house. These vaults are
emptied about once every two weeks by vacuum truck (or by hand-dipping if the infrastructure does not
allow for motorized transport) (Feachem and Caimcross, 1978; Foster, 1980).
Until the late 1970s, bucket and vault latrine systems were widespread in urban locations in
eastern Asia, including Japan, Taiwan, China, Korea, and Malaysia. Also, bucket latrines were fairly
popular in African cities and towns. For example, between 50 to 80 percent of residential sewage in four
cities in Japan was collected as nightsoil, and in Kumasi, Ghana, a city of 500,000 inhabitants (in 1978),
50 percent of the population made use of bucket latrines (World Bank, 1979). Traditionally, the
nightsoil would be sold to local farmers as fertilizer, however, demand for nightsoil has decreased
significantly. As an alternative disposal method, nightsoil would be trenched for land treatment or fed
into city sewer lines to be treated at the local WWT plant (World Bank, 1979). Nevertheless, with ever-
increasing pressure on civil services, due to rapid urbanization, lack of operating funds, and
modernization of agriculture, many nightsoil collection systems have broken down and septage is
dumped uncontrolled into the nearest wetland, manhole, or open sewer (Bartone, 1990). In addition,
bucket latrines are widely seen as undesirable because of their unsanitary nature (World Bank, 1979).
Biological degradation in a bucket latrine, and especially in a vault, may be partially anaerobic.
However, in the short time frame before collection, the nightsoil is not likely to undergo significant
degradation. Depending on the disposal method, the collected nightsoil may still be a source of CH^ for
example if it is dumped into an open anaerobic sewer. Assessment of the actual fraction of nightsoil that
may degrade anaerobica'ly would, at best, be a coarse guess.
3.1.4 Extent of Use of On-Sjte Treatment Systems
3.1.4.1 Developing Countries
Figure 3-1 provides an overview of global sanitation coverage by technology type based on a
survey from 82 developing countries (WHO/UNICEF, 1993). Technology types specified in the
WHO/UNICEF survey are: house connection and small bore sewer, septic (sewage) system, various
types of latrines, and "other." The survey distinguishes between urban high-income, urban low-income,
and rural populations, but does not define the income cut-off 3-4. The WHO/UNICEF survey does not
include information on the disposal method or possible off-site treatment, i.e., it is unclear if sewered
wastewater is treated at a WWT plant or disposed of via an outfall.
3 It is assumed Chat the urban-high income is represented by the upper and middle classes, which typically are small far
developing countries. The urban low-income population is represented by the slum dwellers and other tower dasses. The rural
population is also expected to be tow-income.
4 The WHOWN1CEF document includes data for different continents ana! geographical areas, i.e.. Africa, Western Asia,
Asia & Pacific, and Latin America & Caribbean. These data have been incorporated into the spreadsheets used to calculate
emissions.
10
-------
Figure 3-1. Overview of Global Sanitation by Technology Type for 82 Developing Countries
According to Figure 3-1,92 percent of the urban high-income population in the surveyed
countries has some type of coverage, compared to only 30 percent of the urbm low-income population
and 42 percent of trie rural population. Consequently, 70 percent of the urban low-income population
and S8 percent of the rural population has no access to a sanitation system. Wastes from these
populations are assumed to be disposed of indiscriminately in the environment where it will likely
degrade aerobically and not contribute to CH4 emissions. People in rural areas may perhaps build out-
houses over a Jake or stream or they may use designated areas of the surrounding bush (Marks, 1993).
The category "Others" in Figure 3-1 was not specified in the text. It was assumed by the authors
that this category includes bucket latrines/nightsoil collection systems and vault latrines by default. This
category is one percent for high-income populations and less than five percent for the low-income and
rural groups. Because bucket latrines/nightsoil collection systems and vault latrines play a minor role,
they are not considered further as significant potential GHG sources.
11
-------
3.1.4.2 Developed Countries
Table 3-1 includes comprehensive data on urban and rural sewerage coverage and the use of on-
site disposal systems for European countries, including Turkey, and Israel (WHO, 1990; Artcmcl, 1995).
In WHO (1990) on-sitc disposal systems are classified as either "adequate" and "inadequate," but these
terms were not defined in the text. It was assumed by the authors that septic sewage systems are
considered adequate, and that cesspools and latrines are considered inadequate cm-site disposal systems.
According to Table 3-1. most European urban residents have home sewer connections. Only in Greece,
Hungary, Poland, Romania, and the former Yugoslavia septic sewage systems are being used by more
than 10 percent of the urban population. Eastern European sewage treatment and disposal data were
based on anecdotal data from Poland (Jocewicz, 1997). Urban Poland has a sewer infrastructure that
accepts 90 to 100 percent of domestic sewage. A small amount of urban residents may make use of
septic tanks (five percent). Only 40 percent of rural residents have sewer connections. The use of septic
tanks is widespread in rural Poland (80 percent) and latrines are also in use. The respondents had
different views on the degree to which sewered wastewater is treated Estimates vary from 50 to 95
percent. It is believed that the situation is better for urban sewage. The best guess is that between almost
70 and 95 percent of urban domestic sewage is treated, whereas, about 50 percent of rural sewered
wastewater is treated.
The status of WWT is different for rural Europe compared to urban Europe. In rural areas, the
use of septic sewage systems is widespread. In many countries more than 50 percent of the rural
population uses septic sewage systems. It is important to note that the rural population in Europe is
relatively small, because most countries are highly urbanized (Table 2-3). Therefore, the total population
that does not use sewers for wastewater disposal is also relatively small. Cesspools and/or latrines are
still being used in rural areas in some European countries, including Albania, Hungary, Romania, former
Yugoslavia, and the former Union of Soviet Socialist Republics (USSR).
-------
TABLE 3-1. SEWAGE DISPOSAL AND TREATMENT FOR EUROPE, TURKEY AND ISRAEL
COUNTRIES
All units In percent
Albania
Austria
Belgium
Bulgaria
Czechoslovakia (former)
Denmark
Finland
France
Germany (DDR) (lorrnerS
Germany (FBG) (former)
Gre«9
Hungary
Iceland
Ireland
Israel
Italy
Luxembourg
Netherlands
Norway
Poland
Portugal
Romania
Spain
Sweden
Switzerland
Turkey
USSR (former)
United Kingdom
Yugoslavia (former)
Urban
36
58
96
68
77
85
60
73
85
85
S3
64
91
57
65
69
84
89
75
62
34
54
78
84
62
61
65
89
55
Sewerage Coverage
and On-site
Treatment
RURAL
_ Sept Inade-
GoiAiiSif " -"- -
sewer Tank quate
50 40 10
20 80
54 46
56 40 4
55 40 5
1 99
10 90
63 37
70 30
86 14
54 40 6
S 80 15
100 0
23 74 3
60 40
58 42
83 7
18 82
0 100
43 50 7
9 86 S
14 76 10
40 60
70 30
82 16
20 85 15
60 30 10
89 11
33 57 10
Sewerage Coverage
and On-site
Treatment
URBAN
_ Sept Inade-
Sewer _ ,
Tank quate
90 S S
100
98 2
85 1 14
85 10 5
99 1
91 9
100
91 9
97 3
SO 35 5
76 20 4
100
99 1
93 7
96 4
100
100
94 6
79 16 5
83 12 5
73 22 5
100
100
100
56 36 8
90 10
100
84 12 4
WWT"
None Prim, Sec. Ten.
10 5 80 5
55 45
56 45
34 2 64
5 25 6S 5
1 1 99
60 40
11 81 8
82 18
4 10 82 4
90 10
30 15 54 1
10 15 70 5
70
8 6 B4
15 7 75 3
23 9 34 34
37. 40 23
55 20 23 2
20 18 62
74 17 9
1 23 76
17 28 55
70 14 16 0
10 BO 10
27 54 11 9
DISCHARGE
TREATED WW TO
_ Surface . .
Sea waters Land
100
98 2
49 51
20 80
95 5
99 1
96 4
10 90
52 48
100
5 95
TO 29 1
34 65 1
80 20
46 54
100
50 45 S
DISCHARGE RAW
SEWAGE TO
- Surface . .
Sea waters Und
100
85 15
3 97
25 75
60 40
99 1
38 12
10 90
100
100
96 4
42 43 15
100
100
1 7 92
Sources: WHO (1990); and Artemel (1995) for Turkey,
* Primary WWT consists ol processes such as sedimentation and screening.
Secondary WWT is biological treatment.
Tertiary WWT may consist of enemical processes, reoxiflallon, ehlorinatton, ate.
-------
Twenty-five percent of the total U.S. population uses septic sewage systems for sewage
treatment (U.S. Department of Commerce, 1990), whereas, the degree of urbanization is 75 percent. In
this study it is assumed that 90 percent of the rural population of the United States uses septic sewage
systems. Only eight percent of the rural population has sewer connections and the remaining two percent
is assumed to use latrines. Septic tanks are used by five percent of urban U.S. inhabitants. These ratios
were also adopted for Canada and Australia,
3.2 SEWER SYSTEMS
A conventional (closed) sewer is defined as an artificial, usually underground conduit for
carrying off sewage and/or rainwater run-off. Sewers that are built solely for the purpose of carrying off
rainwater are called storm sewers. Storm sewers do not contain significant loadings of organics and are,
therefore, not considered to be potential GHG emission sources. Typically, a closed sewer system
consists of a service line that runs from the dwelling to a collector in the street The collector carries the
sewage by gravity to an interceptor sewer. If topography dictates, the collector sewer may discharge to a
pump station, which transports the sewage via a force main to another collector or interceptor at a higher
elevation. Ultimately, the collection system delivers the sewage to a wastewater treatment plant or
discharges the sewage in a river, lake, ocean, or other natural system.
Sewer lines do not necessarily transport sewage to a WWT plant. Instead they may also serve
outfalls that discharge into an ocean, sea, lake, or river. Outfalls are used all over the world for the
disposal of untreated or semi-treated wastewater. In many countries outfalls are used to dispose of
wastewater that is either untreated or has received some type of preliminary or primary treatment
(Proctor, 1989; Andreadakis et al, 1993). For example, an outfall that serves part of Rio de Janeiro,
Brazil, dumps six cubic meters per second (136 million gallons per day) of raw wastewater into the
Atlantic Ocean (Jordao and Leitao, 1990).
Sewers may be open or closed (covered or underground). In most developed countries and in
high-incom urban areas in other countries, sewers are usually closed and underground. Underground
location is most sanitary and prevents the accumulation of solid debris, such as trash, branches or rocks.
Wastewater in closed, underground sewers is not subject to insolation and will stay relatively cool,
compared to surface water, including water in open sewers. In urban areas in developing countries and
some developed countries, sewer systems often consist of networks of canals, gutters, and ditches, which
arc referred to as open sewers.
The United Nations and some other international organizations labeled the period between 1980
and 1990 "The International Drinking Water Supply and Sanitation Decade." During this period,
substantial absolute advances were made in providing more people from developing countries with
14
-------
adequate drinking water facilities. (Rotival, 1987.) Also, many improvements were made in the level of
sanitation in different areas of the world, however these were often outpaced by urban population
growth. The reiative success in providing cities with water has generated greater volumes of both
domestic and industrial wastewater to bo managed. As cities densify, the per household volumes of
wastewater exceed the infiltration capacity of local soils and require some other drainage system.
(Bartone, 1994.) Hence, cities in arid areas in developing countries also can be expected to have open
sewers, although these sewers will have less flow than similar sewers that accept substantial amounts of
rain water.
3.2.1 Extent of Sewerage
In many developing countries, sewerage infrastructure does not retch large sections of the
population (see Figure 1). Especially in rural areas and urban slums, sewerage is virtually non-existent
(WHO/UMCEF, 1993;Draaijer, 1994 in Doom etai, 1997). The lack of sewerage in rural areas in
developing countries is rarely a large pollution or sanitation problem because the population density is
low. However, in urban areas lack of adequate sanitation and sewerage can easily become a health issue
and may also result in serious degradation of the environment. When wastewater is not sewered offer
treated in adequate on-site systems, it accumulates in the direct environment, where it will degrade over
time and likely contribute to the pollution of ground and surface water.
Official statistics on the extent of sewerage often do not acurately represent the actual situation.
For example, the section of the urban low-income population that consists of slam dwellers may not be
included in the count, thereby increasing the ratio of people with adequate sanitation coverage.5 Also,
official publications may not account for inadequate or malfunctioning sewer or treatment systems
(Bartone, 1990).
In Africa in the mid-eighties, only 14 percent of the population had a sewerage connection. In
Latin America and the Middle East, official figures indicate that 41 percent of the urban population has
sewers (capitals and other large cities have 50 to 85 percent; for secondary cities this number is 10
percent). In Asia and the Pacific, less than 20 percent of the total urban population has sewer-to-house
connections. (Bartone, 1990; WHO/UMCEF, 1993.) For reasons mentioned earlier in this Chapter
these numbers should be treated with caution.
3 Sanitation is defined as a sanitary means of excreta disposal and sanitation coverage is the proportion ol the population
with access lo a sanitary facility for human excreta disposal in the dwelling or within a convenient distance tan the user's dwelling,
15
-------
3.2.1.1 Potential for Anaerobic Decomposition in Sewers
Anaerobic biodegradation reaction kinetics in open sewers depends on multiple parameters
including, residence time, water temperature, and dissolved oxygen content. No qualitative data were
found that pertain particularly to wastewater behaviour in open sewers. It may be expected, however that
dissolved oxygen in fresh sewage can. be depleted within a few hours (Hulshoff-Pol, 1986 in Doom, et
al, 1997). As a result, actual CH,, generation resulting from anaerobic degradation may also start within
a similar time frame, because active anaerobic organisms are already present in the sewage. In
developing countries, open sewers are often clogged with debris, partially or entirely blocking the flow
of wastewater and thereby increasing the residence time. In addition, nisny developing countries have a
sunny, tropical climate, leading to relatively high water temperatures in open sewers. Consequently,
wastewater in open sewers in many developing countries is likely to be septic and a likely source for CH4
emissions. This conclusion is supported by anaecdotal evidence from Wiegant and Kalker, 1994;
Draaijer, 1994; and Doppenberg, 1994, (all in Doom et al., 1997) who provide anecdotal evidence that
wastewater in many open sewers in various developing countries is practically stagnant, and brownish or
black in color, and is visibly emitting gases. In this report it is assumed that 75 percent of wastewater in
open sewers in developing countries will degrade anaerobically. This number is based on professional
judgment by the authors using the anecdotal evidence provided above. The remaining 25 per-ont may
degrade aerobically or not at all, due to the presence of compounds that are toxic to the pertinent
bacteria.
It is unclear if closed municipal sewers in developed countries are also a source of CH4.
Although, closed sewers are typically designed to avoid anaerobic conditions to prevent hydrogen sulfide
generation, anaerobic conditions can develop in certain sections of the sewer system, for instance, pump
station wet wells and force mains which have no head space. A Research Triangle Institute (RTI) field
study found CH, emissions at manholes in sewers in Durham, North Carolina. As part of the RTI study,
a preliminary estimate of CH4 emissions from sewers was developed, based on the estimated total
number of manholes in the United States; roughly 0,16 Tg/yr (Thomeloe, 1997). Additional research is
required to produce a more reliable CH4 emissions estimate from closed sewers and this possible source
category is not considered further in this study.
Excessive discharge of organics in rivers, lakes, or wetlands of limited capacity may also lead to
local anaerobic conditions, but these conditions are not likely to cause CH, emissions. The reason is that
rivers, lakes, or wetlands that are receptacles for anoxic organic wastewater are presumed to have a
facultative top-layer, preventing these emissions. Also, organics discharged into oceans are unlikely to
produce anaerobic GHGs emissions because the salt water environment is not conducive to anaerobic
16
-------
bacteria and other chemical and/or biochemical degradation mechanisms are likely to prevail (Wiegant
and Kalker, 1994 in Doom et al., 1997).
3.2.2 Extent of Centralized Treatment
For most countries in the world except for European countries, data from the Emissions-frorn-
WWT report were used to quantify the extent of centralized WWT. New data were found for European
countries, including Turkey, and Israel (see Table 3-1), Unfortunately, these data do not distinguish
between rural and urban populations, nor do they include information on the former USSR, Because
most European countries are largely urbanized, the country data were copied for the urban population
and for the rural population engineering judgement was used.
According to Table 3-1, which includes data from 1990, many countries, including France,
Greece, Portugal, Italy, and Spain, do not treat most of their municipal wastewater. However, in recent
years fre situation in southern and western Europe has begun to improve. Under pressure from European
Union regulations, countries with bad WWT track records have started campaigns to improve the state of
their WWT. In addition, countries in southern Europe, such as Spain, Greece, and Turkey, have been
spurred to improve and increase local WWT due to economic pressure from the tourist industry (World
Water and Environmental Engineering, 1992). These recent changes have not been reflected in the
numbers and thuir possible impact will be discussed in the "Methane Emission Estimates and
Uncertainties" and "Trends" sections,
-------
CHAPTER 4
METHANE EMISSION ESTIMATION METHODOLOGY, ACTIVITY DATA, AND GLOBAL
AND COUNTRY-SPECIFIC CH4 EMISSION ESTIMATES
4.1 METHODOLOGY
Methodologies and activity data used to estimate CH4 emissions from treated wastewater and the
resulting CH4 emissions estimates are documented in the Emissions-from-WWT report. This report
includes CH4 emission estimates for wastewater that is not centrally treated at a POTW or industrial
WWT plant. In this report, the methodology for estimating CH, emissions for domestic wastewater from
the Emissions-from-WWT report was modified to improve the CH4 emission estimates for wastewater
that is not centrally treated. The expanded methodology differentiates between three separate source
categories: septic tanks, latrines, and stagnant, open sewers. The methodology was modified to
distinguish between urban high-income, urban 1-jw-income, and rural populations, because sewage
disposal and/or treatment options available to the three different categories vary considerably (see Figure
3-1). The distinction between urban high-income and urban low-income was not made for developed or
eastern European countries, because income differences (as reflected in sanitation provisions) are less
pronounced in these countries.
The comprehensive methodology used in this report to estimate CH4 emissions from domestic
wastewater that is not centrally treated for country c is represented by the equation below. Subscripts c, s,
and u denote country or group of countries, treatment or disposal system (stagnant, open sewers, septic
tanks, and latrines), and population-income group (urban high, urban low, rural-low), respectively.
CH4 Emissions, =£F x Pt x BODC x M x £ £[Uc xTfiax(l + I) x-AFcJ (Tgfyr)
u S
where:
EF - emission factor, 0.3 +0.1 gram CH4 per gram COD removed;
Pc - country population (from Table 2-3);
BODf = country-specific per capita BOD generation (g/day) (from Table 2-3);
M = conversion from BOD (g/cap/day) to COD (Tg/yr) (from Table 2-3);
Uc population-income group fraction (from Table 2-3);
Ta, = degree of utilization of treatment or disposal system;
ls coi.^ection for industrial BOD/COD (/, = 0.25 for sewers only), (see page 4);
AFCS = degree to which BOD/COD is degrading anaerobically in system s.
18
-------
4.2 ACTIVITY DATA
Tables 4-1,4-2, and 4-3 include comprehensive, country-specific activity data for rural, urban-
high, and urban-low populations, respectively. In the following text, the assumptions used in these tables
are discussed and the data sources summarized.
* Table 4-3 (urban low-income) contains no data for European and developed countries, because for
these countries the differentiation between urban high-income and urban low-income populations
was not made. Information on the urban populations for these countries is condensed in Table 4-2.
« Emissions-front-WWT-cohimns in Table 4-1 (rural) and Table 4-3 (urban low-income) contain only
zeroes, because it is assumed that for rural and low-income populations all sewered wastewater is
discharged without treatment, i.e., there are no WWT plants.
* To account for industrial COD discharged with residential wastewater into open sewers, the CODC
quantity is multiplied by / = 1.25 (see page 4). For latrines and septic systems, / = 0, because these
systems do not accept industrial wastewater.
For most developing countries, except rural Latin America, the degree of utilization of specified
treatment or disposal system for each income group (Taa) is primarily based on WHO/UNICEF
(1993). World Bank (1979) provided additional comprehensive information from site studies in
South Korea, Taiwan, Indonesia, Malaysia, Sudan, Nigeria, Ghana, Zambia, Colombia, and
Nicaragua- Data for latrine use in rural Latin America are based on World Bank (1979). WHO
(1990) includes data for Israel and Turkey. Engineering judgment by the authors was complemented
with anecdotal information on South Korea, China, and Turkey, to develop Tfm estimates for these
three countries.
For the urban high-income populations in developing countries, it was assumed by the authors that
some type of sewage treatment or removal system exists (i.e., the "None" category in Table 4-2 is
zero).
For the urban low-income populations in developing countries (Table 4-3), it is assumed by the
authors that 20 percent of human waste ends up on the ground or is directly disposed of into surface
water (e.g., rivers or lakes). In either case it will not contribute to CH» emissions. For the same
urban low-income populations, with the exception of "Other Asia" between 34 and 53 percent of
human waste is assumed to accumulate in open sewers or gutters. For "Other Asia" the fraction of
waste that is sewered is assumed to be higher, 68 percent, because this category includes many oil
producing and exporting countries, where sewer infrastructure is assumed to be better than in other
Asian countries.
-------
TABLE 4-1. COUNTRY-SPECIFIC WASTIWATER TREATMENT PRACTICES AND METHANE EMISSIONS
FOR RURAL POPULATION
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
Zimbabwe
Other Atrica
China
India
Indonesia
Pakistan
Bangladesh
Japan
Other Asia
EUROPE
Russia
Gtrmany
United Kingdom
France
Italy
Other OECD
Other Europt
NOaitLAMEfUCA
United States
Canada
Municipal WW Disposal (Tcs)
Septic
Tank
(%)
2
2
2
10
10
Z
0
0
a
0
0
20
5
30
20
11
37
42
50
50
90
90
Utrine
(%)
28
28
28
28
28
2B
47
47
47
47
47
0
30
10
0
0
0
0
0
to
2
2
Other
(%)
4
4
4
4
4
4
50
10
0
0
0
50
10
0
0
0
0
0
0
0
0
0
(Open)
Sewor
(%)
10
10
10
10
10
10
0
10
10
10
10
30
36
60
80
89
63
58
50
40
8
8
None
(%)
56
56
56
48
48
56
3
33
43
43
43
0
19
0
0
0
0
0
0
0
0
0
LATIN AMERICA AND CARIIB6AN
Brazil
Mexico
Others
0
0
0
45
45
45
0
0
0
10
10
10
45
45
45
AUSTRALIA AND NEW ZEALAND
Australia
TOTAL (Tg/yr)
90
2
0
8
0
V ./rMtlpWc* , j
AFcs
()
0.5
0,5
0.5
0.5
O.S
0.5
O.S
0,5
0.5
0,5
0,5
0,5
0.5
0,5
0.5
0,5
0,5
O.S
0,5
0,5
0.5
0,5
0.5
0.5
0.5
0.5
COD (snaeroblc)
'''.' !(f$fyr)
"'toil'::
0.0
0.0
0.0
0.0
0.0
0.1
0
0
0
0
0
0.1
0.2
O.Z
0.1
0.0
0.1
0.2
0.2
0.8
1.5
0.1
0
0
0
0.0
3.7
mean
0.0
0.0
0.0
0.0
0.0
0.1
0
0
0
0
0
0.1
0.3
0.3
0,1
0.0
0.2
0.2
0.3
1.0
1.9
02
0
0
0
0.1
5.0
Wflh '
0.0
0.0
0.0
0.0
0,0
0.1
0
0
0
0
0
0.2
0.4
0.5
0.2
0,0
0.2
0,3
0.4
1.3
2.3
0.2
0
0
0
0.1
6.2
AFcs
it >;W
1.0
1.0
1.0
1.0
1.0
1,0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1,0
1,0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
^ilirt^v^
'$7&SS5
> r.-Vam ;| ifiisari iJIWilptii-;:
0.5 0.7 0.9
0.2 0.3 0,4
0.1 0.2 0.2
0.2 0.2 0.3
0.1 0.1 0.1
1 .9 2.6 3.4
9.8 13.8 17.7
7.4 10.3 13.3
1.5 2.1 2.8
1.0 1.4 1.8
1.2 1.6 2.1
0.0 0.0 0,0
2.5 3.5 4.5
0.2 0.2 0,3
000
000
000
000
000
0.3 0.4 0.5
0.1 0.1 0,1
0.0 0.0 0.0
0.4 0.6 0.7
0.3 0.4 0.5
0.6 0,8 1.0
0.0 0,0 0.0
28.2 39 4 50 6
teiiifi
0.8
0.8
0.8
O.B
0.8
0.8
0.8
0.8
0.6
0.8
0.8
0.0
0.8
0.0
0,0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
0.8
0.8
0.8
0.0
Ri^^giMaSbi'' -r^W*^
0.2 0.2 0.3
0.1 0.1 0.1
0.0 0.1 0.1
0.1 0.1 0.1
0.0 D.O 0.0
0.6 0.9 1.1
0.0 0,0 0.0
1.5 2.1 2.7
0.3 0.4 0.6
0.2 0.3 0,4
0.2 0.3 0,4
00 0
2.8 3.9 5.0
00 0
00 0
0 0 " 0
00 0
00 0
00 0
00 0
00 0
00 0
0,1 0.1 0.2
0,1 0.1 0.1
0.1 0.2 0.2
00 0
63 8.8 1 1 .3
Totals may not equal sums of individual numbers due to rounding.
(continued)
-------
TABLE 4-1. COUNTRY-SPECIFIC WASTEWATER TREATMENT PRACTICES AND METHANE EMISSIONS
FOR RURAL POPULATION (CONTINUED)
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
Zimbabwe
Other Africa
ASIA
China
India
Indonesia
Pakistan
Bangladesh
Japan
Other Asia
Russia
Germany
United Kingdom
France
Italy
Other OECD
Other Europe
WWT Plant
Haw
Discharge
(%)
100
100
100
100
100
100
100
100
100
100
100
20
too
80
10
20
70
70
40
80
NQRT,H AMERICA
Unitad Slates
Canada
0
0
To
WWTP
(%)
0
0
0
0
0
0
0
0
0
0
0
BO
0
20
90
80
30
30
60
20
100
100
LATIN AMERICA AND CARIBBEAN
Brazil
MsxkX)
Others
100
100
100
0
0
0
AUSTRALIA AND NEW ZEALAND
Australia
TOTAL (Tg/yr)
20
BO
A Fes
(-)
0,5
0.5
O.S
0.2
0,2
0,S
0.5
0.5
0.5
0.5
0.5
0.1
0,5
0.4
0.1
0.1
0,1
0.1
0.1
0.1
0.1
0.1
0.5
0.5
0.5
0.1
COD (anaerobic)
low
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0,0
0,0
0,0
0,1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.2
mean
0.0
0,0
0.0
0.0
0.0
0,0
0,0
0.0
0.0
0.0
0.0
0,0
0,0
0.1
0,0
0.0
0,0
0.0
0,0
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0.3
high
0.0
0.0
0,0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.3
Methane Emissions (Tg/yr)
.'. .Septfefranks'
io« | mean j . .high .
0,0 0.0 0.0
0,0 0.0 0,0
0.0 0.0 0.0
0,0 0.0 0.0
0,0 0,0 0,0
0.0 0.0 0,0
0.0 0,0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0,0 0,1
0.0 0,1 0.1
0.0 0.1 0.2
0,0 0.0 0.1
0,0 0,0 0,0
0.0 0.0 0.1
0.0 0.1 0.1
0.0 0.1 0.2
0.2 0.3 0.8
0.3 0,6 0.9
0,0 0.0 0,1
0,0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0,0 0.0
0,7 1 ,5 2.5
^.^ni
low -;4.j .mean.
0.1 0.2
0.0 0.1
0.0 0.1
0.0 0.1
0.0 0.0
0.4 0.8
2.0 4.1
1.5 3.1
0.3 0.6
0.8 0.4
0.2 0.5
0.0 0.0
0.5 1 .0
0.0 O.t
0.0 0.0
0.0 0,0
0.0 0.0
0.0 0,0
0.0 0.0
0.1 0.1
0.0 0,0
0.0 0.0
0.1 0.2
0,1 0.1
0.1 0.2
o.o o.o
5.6 11.8
-,! , '-''
/high
0.4
0,2
0.1
0,1
0.0
1.4
7.1
S.3
1.1
0,7
0.8
0.0
i.a
0.1
0.0
0.0
0.0
0.0
0,0
0.2
0.0
0.0
0.3
0.2
0.4
0.0
20.2
?l^fil*?fc(>|w»Wah;5
0.0 0,1 0.1
0.0 0.0 0.1
0.0 0.0 0.0
0,0 0.0 0,0
0.0 0.0 0.0
0.1 0.3 0.5
0.0 0.0 0.0
0.3 0.6 1.1
0.1 0.1 0.2
0.0 0.1 0,1
0.0 0.1 0.2
0.0 0.0 0.0
0.6 1,2 2.0
0,0 0.0 0,0
0,0 0.0 0,0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0,0
0.0 0.0 0,0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.0
0.0 0.0 0.1
0.0 0.0 0.0
0.0 0.1 0.1
0.0 0.0 0.0
1.3 2.8 4.5
VWT Plant
low
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
or
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
mean [ high
0.0 0.0
0.0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0,0 0.0
0.0 0.0
0.0 0.1
0.0 0,0
0.0 0.0
0.0 0.0
0,0 0.0
0.0 0.0
0.0 0.0
0,0 0.0
0,0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.1 0.1
Totals may not equal sums ol individual numbers due to rounding.
-------
TABLi 4-2, COUNTRY-SPECIFIC WASTEWATER TREATMENT PRACTICES AND METHANE EMISSIONS
FOR URBAN HIGH-INCOME POPULATION
Country
AFRICA
Nigeria
Egypt
Ksnya
South Africa
Zimbabwe
Other Alrioa
ASIA
China
India
Indonesia
Pakistan
Bangladesh
Japan
Other Asia
EUHQgE
Russia
Germany
United Krgdom
Franca
Italy
Other OECD
Other Europe
NORTH AMERICA
United States
Canada
Municipal WW Disposal (Tcs)
Septic
Tank
{%!
32
15
32
15
15
32
18
16
18
16
IB
0
18
10
5
0
0
4
2
20
S
5
Latrine
(%)
31
S
31
15
15
31
8
8
e
8
B
0
&
0
0
0
0
0
0
0
0
0
Other
System
(%)
0
10
0
0
0
0
7
7
0
0
0
10
0
0
0
0
0
0
0
0
0
0
(Open)
Sewer
w
37
70
37
70
70
37
67
67
74
74
74
90
74
90
95
100
100
96
98
ao
95
95
Nona
(%)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LATIN AMERICA AND CARIBBEAN
Brazil
Mexico
Others
0
0
0
20
20
20
0
0
0
80
80
60
0
0
0
AUSTRALIA AND NEW ZEALAND
Australia | 5
TOTAL (Ttfyr)
0
0
95
0
,,; , - Septic/Finite ';,-^:
-XFes'"-
() -
0.5
0.5
0,5
O.S
O.S
0.5
0.5
O.S
0.5
0.5
0.5
0.5
0.5
0.5
0.5
O.S
0.5
0.5
O.S
0.5
0.5
0,5
O.S
0.5
0.5
0.5
3?1S
.: tow., . I nwan
0.0 0,1
0.0 0.0
0,0 0.0
0.0 0.0
0.0 0.0
0.2 0.3
0.2 0.2
0.1 0.2
0.0 0.0
0.0 0,0
0.0 0.0
0 0
0.4 0.5
0.2 0.2
0.1 0.1
0 0
0 0
0,0 0.0
0,0 0.0
0.6 0.8
0.2 0.3
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0,0
0 0
2,1 2.9
wMCJ.- .
.. Wgh
0,1
0,0
0.0
0.0
0.0
0.3
0,3
0.2
0.1
0,0
0.0
0
0,7
0.3
0.1
0
0
0.1
0.1
1.0
0.4
0.0
0.0
0.0
0.0
0
3.7
; .. ,;'. Y
..-W 'I'.
1.0
1.0
1.0
1.0
1.0
1,0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
t.o
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
-LaWrtes-^-;^
to*...
0.1
0.0
0.0
0.0
0.0
0.3
0.1
0.1
0,0
0.0
0.0
0
0.3
0
0
0
0
0
0
0
0
0
0.1
0.1
0.2
0
1.5
'mean
0.1
0.0
0.0
0.0
0.0
0.5
0.2
0.2
0.0
0.0
0.0
0
0.5
0
0
0
0
0
0
0
0
0
0.2
0.1
0.3
0
2.1
>^Pf
. .*i*fi'!:.
0.1
0,0
0.0
0.0
0.0
0.6
0.3
0.2
0,0
0.0
0.0
0
0.6
0
0
0
0
0
0
0
0
.0
0.2
0.1
0.3
0
2.7
0.75
0.50
0.7S
0.50
0.50
0.75
0.50
0.75
0.75
0.75
0.75
0.00
0.50
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
C.75
0.75
0.75
0.00
ij^ll&ynMait,1 |**hlglfe;;
0.1 0.1 0.2
0.1 0.1 0.1
0.0 0.0 0.0
0,1 0.1 0.1
0.0 0.0 0.0
0.4 0,5 0.7
0.8 1.1 1.4
0.9 1.2 1.6
0,2 0.3 0.4
0.2 0.2 0,3
0.1 0.1 0.1
000
1.9 2.7 3.4
000
000
0 0 0
000
000
000
000
000
000
0.5 0.7 0.9
0.3 0.4 0.5
0.7 1.0 1.3
0.0 0.0 0.0
6.2 6.7 11.1
Totals may not equal sums of individual numbers du» to rounding.
(continued)
-------
TABLE 4-2. COUNTRY-SPECIFIC WASTEWATER TREATMENT PRACTICES AND MiTHANE EMISSIONS
FOR URBAN HIGH-INCOME POPULATION (CONTINUED)
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
ambabwa
Other Africa
AS*.
China
India
Indonesia
Pakistan
Bangladesh
Japan
Other Asia
EUROPE
Russia
Germany
United Kingdom
France
Italy
Other OECD
Ofiar Europe
WWT Plant
Raw
Discharge
[%)
90
80
60
60
60
90
90
90
80
90
90
10
90
40
10
0
60
70
30
40
NORTH AMpRICA
^ United States
Canada
0
0
To
WWTP
{%L
10
ao
40
40
40
10
10
10
20
10
10
90
10
60
90
100
40
30
70
60
100
100
MVTIN AMERICA AND CARIBBEAN
Brazil
Mexico
Others
95
95
95
5
5
5
AUSTRALIA A^D NEW ZEALAND
Australia
TOTAL (Tgtyr)
0
100
AFcs
()
o,s
0.5
0.5
0.2
0.2
0.5
0.5
0.5
0.5
0,5
0.5
0.1
0.5
0.4
0.1
0.1
0.1
0.1
0.2
0.2
0.1
0.1
O.S
0,5
0.5
0.1
COD (anaerobic)
(Tg/yr)
low
0.0
0,0
0,0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.1
0,2
0.7
0.1
0.1
0.0
0,0
0.5
0,6
0.5
0.0
0.0
0.0
0.0
0.0
3.1
mean | high
0.0 0.0
0.0 0.0
0,0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
0.1 0.1
0.1 0.1
0,0 0.0
0.0 0.0
0.0 00
0.2 0.3
0,2 0.3
1.0 1.3
0.1 0.2
0.1 0.2
0.0 0.1
0.0 0.0
0.7 0.8
0.7 0.9
0.6 0.7
0,1 0.1
0.0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
4.2 5.3
Methane Emissions (Tg/yr)
Septic Tanks
tow
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.0
0.0
0
0
0
0.0
0.1
0,0
0.0
0.0
0.0
0.0
0
0.4
mean | high
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.1 0.1
0.1 0.1
0.1 0.1
0.0 0.0
0.0 0,0
0,0 0.0
0.0 0.0
0.2 0.3
0.1 0.1
0,0 0.0
0 0
0 0
0 0
0.0 0.0
0.2 0.4
0.1 0.2
0.0 0.0
0.0 0.0
0.0 0.0
0,0 0.0
0 0
0.9 1.5
Latrines
low | mean | high
0.0 O.Q 0.1
0.0 0,0 0,0
0.0 0.0 0.0
0.0 0.0 O.Q
0.0 0,0 0.0
0.1 0.1 0.3
0.0 0.1 0.1
0.0 O.P 0,1
0.0 0.0 0,0
0.0 0.0 0,0
0,0 0.0 0.0
000
0.1 0.1 0.2
000
000
000
000
000
000
000
000
000
0.0 0.1 0.1
0.0 0.0 0.1
0.0 0.1 0.1
000
0.3 0.6 1.1
'm&\$SM>*tot*r
o.o o.o 0.1
0.0 0.0 0.0
0,0 0.0 0.0
0.0 0.0 0.0
O.Q 0.0 0.0
0.1 0.2 0.3
0.2 0,3 0.6
0.2 0.4 0.6
0.0 0.1 0.2
0.0 0,1 0.1
0.0 0.0 0,1
0.4 0.8 1.4
0.1 0.2 0.4
0.1 0.1 0.2
0.1 0.3 O.S
1 .2 2.6 4.5
WWT Plant
low I mean
0.0 0,0
0.0 0.0
0.0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.1
0.0 0.1
0.1 0.3
0.0 0,0
0.0 0.0
0.0 0.0
0.0 0.0
0.1 0.2
0,1 0.2
0.1 0.2
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0,0
0.0 0,0
0.6 1.3
high
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0,1
0.5
0.1
0,1
0.0
0.0
0.3
0.4
0.3
0.0
0,0
0.0
0.0
0.0
2.1
Totals may not equal sums of individual numbers dua to rounding.
-------
TABLE 4-3. COUNTRY-SPECIFIC WASTEWATER TREATMENT PRACTICES AND METHANE EMISSIONS
FOR URBAN LOW-INCOME POPULATION
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
Zimbabwe
Other Africa
ASIA
China
indtet
Indonesia
Pakistan
Bangladesh
Japan'
OtharAsia
EUROPE
Russia
Germany
United Kingdom
France
Italy
Other OECO
Other Europe
NORTH AMiRICA
United States
Canada
LATJN AMERICA Al
Brazil
Mexico
Others
AUSTRALIA AND N
Australia
TOTAL (Tg/yr)
Municipal WW Disposal (Tcs)
Septic
Tank
(%)
17
17
17
17
17
17
14
14
14
14
14
8
Latrine
(%)
24
24
24
24
24
24
10
10
10
10
10
7
Other
System
(%) . .
5
5
5
5
5
5
3
3
3
3
3
6
(Open)
Sewer
&$
34
34
34
34
34
34
68
53
53
53
53
S3
None
(%)
20
20
20
20
20
20
S
20
20
20
20
10
3D CARIBBEAN
0
0
40
40
0 40
EWJ;EALAND*
0
0
0
40
40
40
20
20
20
'-" .
AFC*':.
.t-1 -
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
SepHe/tdhRs','-.':-' :. .
f COO (anaerobic) ,
;':.Y:. ffg/yr)
low-- |=;rtiean-^--riiah -
0.1 0.1 0.1
0.0 0.1 0.1
0.0 0.0 0.0
0.0 0.0 0,1
0,0 0.0 0.0
0.3 0.4 0.5
0.4 O.S 0.7
0.3 0.4 O.S
0.1 0.1 0.1
0.1 0.1 0.1
0.0 0.0 0.0
0.2 0.2 0.3
000
000
000
1.4 2.0 2.8
', ^i#mw,^&t
';. *&'' V COD^Ar|ibi|i
;^\ ^y ,i*W ^;;
-------
TABLE 4-3. COUNTRY-SPECIFIC WASTEWATER TREATMENT PRACTICiS AND METHANE EMISSIONS
FOR URBAN LOW-INCOME POPULATION (CONTINUED)
URBAN LOW
Country
AFRICA
Nigeria
Egypt
Kenya
South Africa
Zimbabwe
Other Africa
ASIA
China
India
Indonesia
Pakistan
Bangladesh
Japan
Other Asia
EUROPE
Russia
Germany
United Kingdom
France
Italy
OttlBf OECD
Other Europe
Raw
Discharge
(%)
100
100
too
100
100
100
100
100
100
100
100
100
NORTH AMERICA
United States
Canada
WWT Plant
To
WWTP
(%)
0
0
0
0
0
0
0
0
0
0
0
0
LATIN AMERICA AND CARIBBEAN
Brazil
Mexico
Others
100
100
100
0
0
0
AUSTRALIA AJ>lp NEW ZEALAND
Australia
TOTAL (Tg^r)
AFcs
(-)
0,5
0.5
0.5
0.2
0.2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0,5
0.5
0.5
COD (anaerobic)
(Tg/yr)
' low | mean | high
000
000
000
000
000
000
000
000
000
000
000
000
000
000
ooo
Methane Emissions (Tg/yr)
>::; .': ' "' -/.:.; '
Septic Tanks
W«:
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.1
0.0
0,0
0.0
0,0
0.0
0.0
0.0
0.0 0.0 0.0 0.3
mean [ 'high
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
0.1 0,2
0.2 0.3
0.1 0.2
0,0 0.1
0.0 0.0
0.0 0,0
0.1 0.1
0.0 0.0
0.0 0.0
0.0 0.0
0.6 1.0
;7;5 Latrlhek V ;?.
'law--. .!] mtefi
0.0 0.1
0.0 0.0
0.0 0.0
0.0 0.0
0.0 0.0
O.Z 0.3
0.1 0.2
0.1 0.2
0,0 0.0
0.0 0.0
0.0 0.0
0.1 0,1
0.2 0.3
0.1 0.2
0.2 0.5
1.0 2.2
«8h
-------
Total Ta for sewer connections in urban China is slightly higher than for other populous A.~ian
countries, including India, Indonesia, Pakistan, and Bangladesh. The Chinese government p'aces
relatively high emphasis on civil infrastructure (expert judgment by the authors). Additional
information on China regarding the construction of WWT facilities was found in Zhongxiang and Yi
(1991).
In Table 4-2, sewer connection (Ta) numbers for high-income urban Egypt, Zimbabwe, and South
Africa are 70 percent, which is higher than for other African countries. Mancy (1993) states that
Cairo, Egypt, has a sewer network which was built under colonial rule and during the era of Soviet
aid in the sixties and seventies,
Zimbabwe and South Afnsa also historically have had better sewer infrastructure for their urban
high-income populations than most other African countries (Marks, 1993).
Most !* information for European countries came from WHO (1990). Anecdotal information for
Polar ^ and its neighbors is from Jocewicz (1997).
Information on Japan is from World Bank (1979). According to this document, nightsoil collection
was widespread until the mid-seventies throughout Japan, For example, the city of Kyoto (1,5
million inhabitants) relied heavily on nightsoil collection (80 percent). Nightsoil was collected by
vacuum truck. Bartone (1990) and World Bank (1979) state that, in the countries that traditionally
relied heavily on nightsoil collection, there has been a steady decline in the use of collection and
reuse systems with the modernization of agriculture. As no recent data were found that specifically
pertain to present-day Japan, it was assumed by the authors that nightsoil collection systems in Japan
also have become incrc?singiy unpopuiar. Accordingly, it was estimated lhat in Japan in urban areas
the nightsoil collection systems have been largely replaced by sewer connections (90 percent), and
that in rural areas, 50 percent of the population have stopped using nightsoil collection in favor of
sewer connections or septic tanks.
In the United States, 25 percent of th-. total population use septic systems (U.S. Department of
Commerce, 1990). It was assumed by the authors that 90 percent of the rural population are
dependent on septic tanks, compe.i'.d to five percent of the urban population. (The United States is
75 percent urbanized.) The same Tn values were used for Canada and Australia.
Values for the degree to which on-site WWT systems and open sewers are anaerobic (AFC,) are
based on various references, anecdotal evidence, and engineering judgment. Septic tanks are
estimated to accommodate anaerobic degradation of approximately 50 percent of influent COD,
while latrines were assumed to be 100 percent anaerobic. AFrs for open sewers in most developing
countries was assumed to be 75 percent, based on expert judgment by the authors. As mentioned
26
-------
earlier, China, Egypt, Zimbabwe, and the countries of "Other Asia" are assumed to have slightly
higher AF^ values (50 percent) because sewer infrastructure is assumed to be somewhat better.
» All sewers in developed countries are assumed to be closed sewers and AFa for these closed sewers
is, hence negligible. (As mentioned earlier, this source category is not considered in this report).
« The AFa values for WWT plants are from the Eraissions-from-WWT report, page 48, Table 17.
43 METHANE EMISSION ESTIMATES AND UNCERTAINTIES
Country-specific CH4 emission estimates for rural, urban-high, and urban-low populations for
stagnant, open sewers, septic systems, latrines, and WWT plants are included in Tables 4-1,4-2, and 4-3.
Global CH4 emissions from the targeted source categories are estimated at 29 Tg/yr. Note that
substantial uncertainties are associated with this number. Figure 4-1 summarizes global emission
estimates for the different source categories. According to Figure "-L, latrines in rural areas are the most
significant source, emitting 12 Tg/yr. China and India account for about 60 percent of global CH4
emissions from latrines in rural areas (Table 4-1), Also, emissions from stagnant, open sewers in urban,
as well as in rural areas, are significant, i.e., 10 Tg/yr. The default estimate for CH4 emissions from
WWT plants is included for comparison purposes only. The 1.3 Tg/yr emission rate is similar to the
estimate in Doom, et al. (1997).
12
10
fc
»ft
C
o
"i
w
X
O
8 -
4
Open Sewers
Septic Systems
Latrines
WWTP
Figure 4-1: Global Estimates of CH4 Emissions from Stagnant, Open Sewers, Septic Tanks,
Latrines, and WWT Plants
The above CH4 emission estimates should be seen only as preliminary and substantial research
would be needed to reduce the level of uncertainty associated with these preliminary numbers. The
27
-------
mathematical uncertainty in this global emission estimate consists of the uncertainty in the emission
factor (0.3 ± O.I g CH4/g CODr<.movi:S) and the uncertainty in the BOD loading (Table 2-2). In a
mathematical sense, the total CH4 emissions estimate may hence be expressed as 29 with lower and
upper boundaries of 14 and 49 Tg/yr, to reflect the uncertainties associated with these two parameters.
Other significant uncertainties are associated with the activity data used in this report and could only be
defined qualitatively. Therefore, the lower and upper bound values may be too conservative to reflect ail
uncertainties associated with the estimates. Uncertainties in the various parameters used to estimate the
CH4 emissions are discussed in the ensuing text.
The degrees to which wastewater in developing countries is treated in latrines or septic tanks, or
removed by sewer, per income group is primarily based on WHO/UNICEF (1993), Data in this
document are from a survey to which 82 developing countries responded. It is likely that significant
uncertainties are associated with these data, because the questions in the survey may have been
misinterpreted or the data may have been flattered. In addition, the definitions for different WWT
systems may not have been consistently interpreted by the respondents of the surveys. Nevertheless,
there is qualitative evidence in sparse other literature, as well as anecdotal information that was used
as a qualitative verification of the ratios to which each type of treatment system is used. As
mentioned, emissions from latrines in rural China and India are estimated to "be most significant and
follow up work could be focused on verification of the degree of use of latrines in these countries.
Urbanization rates and country-specific populations are from UNEP (1993) and are believed to be
relatively accurate. However, recent increases in population and urbanization shifts are not reflected.
This report uses the same criteria as WHO/UNICEF (1993) for classifying the population as either
rural, urban low-income, and urban high-income. For the countries that were not included in
WHO/UNICEF (1993), the distinction between urban low-income and urban high-income was based
on engineering judgment.
« Bartone (1990) states that in Latin America and the Middle East, in capitals and other large cities 85
percent of the urban population may have sewer connections compared to only 10 percent in
secondary cities. First, these numbers are likely to reflect only the situation for urban high-income
residents. Secondly, sanitation coverage and choice is apparently dependent on city size, status or
function. Country capitals, especially in east European or developing countries may well receive
prcfeicntial treatment and may have better wastewalcr collection and treatment systems than
secondary cities. This phenomenon has not been accounted for in the estimates, because
urbanization data do not differentate'among different types of urban areas or cities.
* Other uncertainties are associated with the amount of wastewater that is discharged into open sewers.
Whereas, data for high-income populations may be fairly accurate, quantification of sewer use for
28
-------
low-income populations is very difficult. Low-income urban populations may make use of
communal toilets that may be fitted with some kind of sewer line, however, this line may not
necessarily be connected to a WWT plant. Instead, it may merely discharge into the nearest gutter or
canal.
One of the assumptions used in this study is that low-income humans with no access to sanitary
facilities will attempt to keep their direct environment as clean as they can, just like anyone else.
Accordingly, they will attempt to remove their body wastes from the premises. The most convenient
method is to use some type of open sewer or other body of water, such as & river. Data that
specifically pertain to open sewers and gutters, and the amount of waste that accumulates in them,
are practically non-existent. The reason is that the existing literature and research are focused on the
treatment or disposal systems themselves. As a result, the quantification of the wastes that remain
outside of these systems (end up in a gutter, canal, or field) can only be by default. Accordingly, the
estimates of the fraction of waste that accumulates in open sewers has an unknown degree of
uncertainty.
Another source of uncertainties is the degree to which open sewers in developing countries arc
anaerobic and will emit CH4. This will depend on retention time and temperature, and on other
factors including the presence of a facultative layer and possibly components that are toxic to
anaerobic bacteria (e.g. certain industrial wastewate* components). Based on anecdotal evidence, an
unknown number of stagnant, open sewers in developing countries may well be 100 percent
anaerobic. This percentage was adjusted downward to 75 percent for most countries, however, to
account for factors that may impede (total) anaerobic degradation (based on best professional
judgment by the authors). In follow-up studies, the degree of uncertainty could be reduced by
laboratory testing to determine the actual retention time that is needed for full anaerobic degradation
and the factors that impede anaerobic degradation, China and India are among the largest
contributors to CH4 emissions from stagnant, open sewers. More accurate data for tliesc two
countries are needed to improve the quality of the estimates.
The degree to which latrines and septic tanks are anaerobic is less of an uncertainty than the degree
to which open sewers are anaerobic. Latrines are very likely 100 percent anaerobic and septic tanks
were assumed to be 50 percent anaerobic (see Chapter 3). Simple field tests for septic tanks and a
laboratory test for latrines can be used to verify these assumptions.
The amount of industrial COD that is discharged into open or closed municipal sewers for each
country is very difficult to quantify. This quantity will depend on the size, type and scale of the
industrial process and the local regulations and their enforcement. Some countries may be highly
industrialtxcd, whereas others are not. But, even in developing countries with low overall levels of
29
-------
industrialization, one is likely to find semi-industrial food processing facilities that can make
significant contributions to organic waste loadings in open sewers. A default value of 25 percent
was used to account for industrial organic COD co-discharged with domestic COD. This value is
based on global industrial wastewater data from the Emissions-from-WWT report.
4.4 TRENDS
In rural areas, where lack of sanitation is not a significant health problem, no large changes in the
use of sanitation options are anticipated that would have a significant influence on CH4 emissions. In
many urbanized areas in developing countries, inadequate disposal of industrial and domestic wastewater
has become a major health, as well as an environmental issue. Although significant gains have been
made in the provision of sanitation services, the influx of migrants into cities has nullified most efforts.
In the next two decades the global urban population will continue to increase. It is estimated that in this
time frame, the number of persons living in cities in developing countries will double, increasing by
nearly 1.3 billion. The rapid growth of cities and concentration of popuiation lead to ever increasing
amounts of human wastes to be managed safely. The relative success in providing cities with water
generates greater volumes of wastewater to be managed, both domestic and industrial. As cities densify,
the per household volumes of wastewater exceed the infiltration capacity of local soils, implying that
wastewater removal will increasingly be by open sewer (Bartone, 1994). Increasing open sewer capacity
is likely to lead to increasing CH4 emissions.
In developing countries traditional sanitation and WWT projects funded with foreign aid have
generally not provided the expected results. A survey of 223 municipal WWT plants in Mexico
(installed capacity equal to 15 percent of total sewage outflow) revealed that 45 percent of the plants
were out of service and 35 percent suffered severe operational problems. A World Bank study in Algeria
showed that 33 out of 42 plants were out of service. Experience in Korea with nightsoil treatment plants
has been similar with respect to operational difficulties (Bartone, 1990). The situation with existing
sewer lines is unlikely to be much betler. It is likely that many sewers in developing countries, as well as
in eastern European countries are in need of repair.
Apart from limited financial resources, there arc also other barriers to improving the current
wastewater disposal and treatment situation in developing countries. Mancy (1993) writes that: "while
the need of financial resources is indisputable, it seems that sociostnictural and institutional variables are
the limiting factors; there exists compelling evidence that the major constraints in Egypt, as well as in the
majority of the less developed areas of the world, are not the lack of technology or financial resources;
the new outlook for the future should emphasize capacity building, which entails the ability to develop,
utilize and sustain the available resources; local communities (and their inhabitants) should not only
30
-------
participate in the planning and implementation of WWT projects, but they should also pay for the
development and sustainment of these services." Thus, in addition to the financial and infrastructure!
barriers that exist, it may be expected that the implementation of the social infrastructure, as described by
Mancy. in which sanitation service consumers are able and willing to pay, may further slow down the
badly needed improvements.
It can be concluded that the wastewater disposal and treatment situation in developing countries
is likely to get worse over the next two decades. In some cities, effects of the lack of WWT have started
to reach intolerable proportions. Perhaps catastrophic events such as cholera epidemics or toxification of
the local drinking water supply may spur drastic changes that will influence the current global trend.
Notable exceptions are developing countries that have recently experienced significant economical
growth and are beginning to have the financial means and political will to invest in wastewater
infrastructure to address their pollution problems. These countries, often dubbed "Newly Industrialized
Countries" include, Taiwan, Singapore, South Korea, and perhaps Chile and parts of Indonesia.6
(Doppenberg, 1994 in Doom et al., 1997.)
The problems associated with the lack of WWT are not limited to the developing world, but also
include the countries of the former Soviet Union, and most eastern European countries. Also, for these
countries no significant improvements in domestic WWT are expected in the near future, due to lack of
funds (Draayer, 1994 in Doom et al., 1997). There are few exceptions, such as the former German
Democratic Republic, which has had access to West German financial and technical support. Also,
possibly Czechia, Slovenia, Hungary, and Poland are experiencing significant economical growth that
may enable them to finance improved WWT on a significant scale.
Short-term improvements in regard to WWT can be expected only from developed countries that
don't have existing comprehensive WWT, including Belgium, Spain, Greece, and Turkey. These
countries are under pressure from the European Union which pushes for uniform and rigorous water and
effluent quality regulations for its members and candidate members. For example, pressure to meet such
EU regulations (in this case 90 percent reduction of load) has forced Spain to clean up its act (World
Water and Environmental Engineering, 1992).
6 Unfortunately, with Ihu rtrcent economic crisis in pans Ot'east Asia (his argument may have lost much Ol'ils
validity.
31
-------
CHAPTER 5
REFERENCES
Andreadakis, A.D., Agelakis, T.E., and D.V. Adraktas. 1993. Treatment and Disposaljaf the
Wastewater of Thessalonikj, Greece. Environment International. Vol. 19, pp 291-299.
Artemel. 1995. Environmental Opportunities in Turkey, Volume 1: Environmental Technologies Export
Market Plan. Prepared for The United States Trade and Development Agency in cooperation
withUSEPA, Artemel International, Inc., Washington, DC. December 1, 1995,
Bartone, C.R. 1990, Urban Wastewater Disposal and Pollution Control: Emerging Issues for Sub-
Sahara Africa. African Infrastructure Symposium: "Infrastructure and the Environment."
World-Bank. Baltimore, MD, January 8-9, 1990.
Bartone, C.R. 1994. Urban Sanitation, Sewerage and Wastewater Management: Responding to
Growing Household and Community Demand. The Human Face of Urban Environment.
Second Annual World Bank Conference on Environmentally Sustainable Development.
Washington, DC. September 19-21, 1994.
Burks, B.D. and M.M.Minnis. 1994. Qnsite WastewaterTreatment Systems. Chapter?. Hogarth
House Ltd., Madison, WI,
Doom, M.R.J., Strait, R.P., Barnard, W.R., and B. Eklund. 1997. Estimates of Global Greenhouse Gas
Emissions from Industrial and Domestic Wastewater Treatment. Prepared for USEPA, Air
Pollution Prevention and Control Division. Research Triangle Park, NC. EPA-60G/R-97-091.
NTIS PB98-106420. September 1997.
Eklund, B. and I. LaCosse. 1997. Field Measurements of Greenhouse Gas Emissions Rates and
Development of Emission Factors for Wastewater Treatment. Prepared for USEPA, Air
Pollution Prevention and Control Division. Research Triangle Park, NC. EPA-600/R-97-094.
NTIS PB98-117898. September 1997.
Feachem, R, and S. Cairncross. 1978. Small Excreta Disposal Systems. The Ross Institute Information
and Advisory Service. London School of Hygiene & Tropical Medicine, London, U.K.
Foster, R. 1980. "Sewage Disposal in Developing Countries: Some Thoughts." In Proceedings of
Water Pollution and Control Association, Meeting of North Western Branch, Manchester, U.K.
January 16, 1979.
Jozewic?:, W. 1997. ARCADIS Geraghly & Miller, Durham, NC. Interviewed by Miehiel Doom.
Jordao, E.P. and J.R. Leitao. 1990. Sewage and Solids Disposal: Are Processes Such as Ocean Disposal
Proper? The Case of Rio de Janeiro. Brazil. Water Science and Technology, Vol. 22, No. 12,
pp. 33-43, 1990.
Laak, R. 1980. Wastewater Engineering Design for Unsewercd Areas. Ann Arbor Science Publishers,
Ann Arbor, MI. ISBN 0-250-40373-0
32
-------
Mancy, K.H. 1993, "A New Perspective on Rural Water Supply ana Sanitation." Water Science
Technology, Vol. 27, No. 9, pp 1-5.
Marks, R.F. 1993. "Appropriate Sanitation Options for Southern Africa." Water Science &
Technology, Vol. 28, No. 7, pp 1-10.
Metcalf& Eddy, Inc. 1991. Wastewater Engineering: Treatment Disposal and Reuse. Third Edition.
McGraw-Hill Book Company. New York, NY. ISBN 0-07-041690-7.
Mullick.M.A. 1987. Wastewater Treatment Processes in the Middle East. The Book Guild Lt. Lewes,
Sussex, U.K. ISBN 0-86-332-336.
Proctor, D. 1989. Current U.K. Research into the Design and Operation of Long Outfalls. Water
Science and Technology, Vol. 21, No, 1, pp. 47-54,
RHI. 1992. Understanding Septic Systems. For the Department of Health and Human Services,
Administration of Children and Families, Office of Community Services. Rural Housing
Improvement. Inc. Winchendon, MA.
Rotival, A.H. 1987. Status of the International Drinking Water Supply and Sanitation Decade. In
"Resource Mobilization for Drinking Water and Sanitation in Developing Nations." Proceedings
of the International Conference, San Juan, PR. May 26-29, 1987. Published by the American
Society of Civil Engineers, 345 East 47* Street, New York, NY.
Rybczynski, W. 1979. "Onsite Systems for Developing Areas." In: "individual Onsite Wastewater
Systems." Proceedings of the Sixth National Conference, 1979. Ann Arbor Science Publishers,
Aim Arbor, MI.
Thome !oa, S. 1996. Interviewed by Michie! Doom of ARCADIS Oeraghty & Miller, July 1996.
United Nations Environment Programme (UNEP). 1990. Environmental Data Report. Second Edition,
1989/1990. Blackwel! Publishers, Oxford, U.K.
United Nations Environment Programme (UNEP). 1993. United Nations Environment Programme.
Environmental DataReport 1993-1994. Blackwell Publishers, Oxford, U.K. ISBN 0-631-
19043-0.
U.S. Department of Commerce. 1990. Economics and Statistics Administration, Bureau of Census.
1990 Census. Washington, DC.
USEPA. 1994. International Anthropogenic Methane Emissions:Estimates for 1990. Report to
Congress, Prepared for U.S. EPA, Office of Policy Planning and Evaluation, Washington, DC.
Prepared by U.S. EPA, Office of Research and Development, Washington, DC. KPA/230-R-93-
010. 1994.
WHO. 1990. "Internationa} Drinking Water Supply .and Sanitation Decade." Final Evaluation Report.
World Health Organization Regional Office for Europe. Edited by Oltio Spinoza, EUR/CWS/
Oil (1). Copenhagen, Denmark.
33
-------
WHO/UNICEF. 1993. "Water Supply and Sanitation Monitoring Report. 1993." WHO/UNICEF Joint
Monitoring Programme. The Chief, Water and Environmental Sanitation Section. UNICEF,
DH40B, New York, NY.
World Bank. I:)79. "Country Studies in Appropriate Sanitation Alternatives." Prepared for the project
entitled: "Appropriate Technology for Water Supply and Waste Disposal in Developing
Countries." The World Bank Energy, Water and Telecommunications Department, Public Utility
Notes. P.U. Report No. RES 21. March 1979. Washington, DC.
World Water and Environmental Engineering. 1992. Waste Recovery, Spanish Review. World Water
and Environmental Engineering. September 1992.
Zhongxiang, Z. and Q. Yi. 1991. Water Savings and Wastewater Reuse and Recycle in China. Water
Science and Technology, Vol. 23, pp. 2135 - 2140.
34
-------
APPENDIX A
EXECUTIVE SUMMARY OF
"ESTIMATES OF GLOBAL GREENHOUSE GAS EMISSIONS FROM INDUSTRIAL AND
DOMESTIC WASTEWATER TREATMENT."
Doom, M.R.J., Strait, R.P., Barnard, W.R., and B. Eklynd. 1997. Prepared for USEPA, Air Pollution
Prevention and Control Division. Research Triangle Park, North Carolina. EPA-6QO/R-97-09I, NTIS
PB98-106420. September 1997.
Project Officer: Susan A. Thorneloe, U.S. Environmental Protection Agency, Air Pollution Prevention
and Control Division, National Risk Management Research Laboratory,
Research Triangle Park, NC 27711
INTRODUCTION
To improve global estimates of greenhouse gas (GHG) emissions from WWT, EPA's APPCD
initiated a field test program to develop GHG emission factors based on actual emissions measurements
and to improve country-specific activity data for industrial and domestic WWT. The field test program
involved the use of the open path monitoring/transect method (OPM/TM) technique with Fourier
Transform Infrared (FT1R) spectroscopy to measure emissions from anaerobic waste lagoons at two beef
processing plants, one chicken processing plant, and facultative lagoons at two POTWs. The field tests
and results are documented i:. a separate report: Eklund and LaCosse, 199?.7 In conjunction with the
field test program, research was undertaken to improve the quality of the country-specific activity data,
which included a search of the most recent literature and interviews with U.S. and European wastewater
experts.
The Emissions-from-WWT-report summarizes the findings of the field tests and provides
emission factors for CH, and N,O from WWT. Also, the report includes country-specific activity data on
industrial and domestic WWT, which were used to develop country-specific emission estimates forCH,
and N2O. The report concludes that WWT is unlikety to be a significant source of VOCs and COt
emissions. Also, the report provides background information on WWT systems and discusses the effect
of water and ambient air temperature on CIIj emissions and COD removal rates in anaerobic lagoons.
References ysed in [his summary are provided in the Reference seclion of the foport
35
-------
FIELD TESTS
Using FTIR spectroscopy, OPM/TM was used to determine emission rates. A large data set was
generated, and up to 300 seoarate, valid, five-minute-average emission rate determinations were made at
a given site. Typical detection limits were about 0.1 g/sec for most compounds, except for COZ, which
had a minimum detection limit of about 150 g/sec. The high detection limit for CO2 was due to high
background concentrations.
At ail three meat processing plants, large amounts of CH4 were measured downwind of the
WWT system. The field tests detected significant N2O emissions only from the anaerobic waste lagoons
at the chicken processing plant. No N2O emissions were detected from the anaerobic waste lagoons at
the two beef processing plants or the facultative lagoons at the two POTWs. Surprisingly, no emissions
of any GHG were detected from the facultative POTW lagoons. However, it is highly probable that CO2
was being generated, but at levels too small to detect given the high background levels of CO2 and the
measurement variability.
With the help of activity factors provided by the plant operators and from the wastewater
analyses, emission factors were developed for each site. An estimate of the uncertainty of the emission
factors was developed through standard error propagation methods. The derived emission factors all
appear to be reliable to within a factor of two, based on tandom error in the measurements, and assuming
that the sites and samples accurately represent the population of interest.
EMISSION FACTORS AND METHODOLOGY
Average CH4 emission factors based on theoretical models and on empirical industrial digester
data are between 0.11 and 0.25 g/g COD. The average CH4 emission factor derived from the field tests
range from 0.26 to 0.96 g/g COD. The most likely explanation for the fact that the average APPCD field
test emission factors are higher is that the field test emission rates also account for CH,, emissions from
COD that had been deposited in the sludge during past winters, when anaerobic microbial activity is low.
In the report, an emission factor of 0.3 ± 0.1 g/g COD was used to develop CH4 emission estimates. This
factor reflects the tipper end of the range of factors based on theoretical models and empirical digester
data, as well as the lower end of the range of !he factors developed from ihe field test results. The range
for the emission factor (i.e., ± O.I g Cll/g C()D,t.IIMVl.j) is based on expert judgment and accounts for the
uncertainties associated with the use of COD and the extrapolation to different types of wastewater. This
emission factor is believed to be conservative {i.e., on the high side).
-------
The report uses two separate N,O emission factors. The first emission factor (0.09 g N2O/g
COD,eniowd) is based on the field test at the chicken processing plant and reflects a completely anaerobic
environment. It was used to estimate emissions from domestic sewage, and meat, poultry, fish, and dairy
processing waste water that is degrading under anaerobic conditions. The second emission factor (5.1
g/capita/yr) is based on literature studies and pertains to anoxtc processes (denitrification) as a part of
conventional domestic WWT.
The equation below was used to estimate CH4 emissions from industrial wastewater. The
methodology is also applicable for estimating N2O emissions from anaerobic WWT.
CH4 Emissions = EF x Zt Sc (Pie x Q x COD, x TA^ /100) x W" (Tg/yr)
where: EF = Emission factor (g CH, or g N,O/g CODreroqvc<,);
Pic = Industry-and country-specific output
[Megagrams per year (Mg/yr)];
Qj = Wastewater produced per unit of product (mVMg);
COD, = Organics loading removed (g/ms);
TAir = Percentage of COD in wastewater treated anaerobically (%};
Subscript c denotes country;
subscript / denotes industrial category within country c.
Initially, 23 industrial categories were identified as the potentially most significant dischargers of
wastewater with high organic COD loading. Country-specific annual industrial output data for these
industrial categories were obtained from tlic United Nations* Industrial Statistical Yearbook. Typical
wastewater generation rates expressed in cubic meters per Mg of product (mVMg} and representative
COD loadings were obtained from various literature sources.
TAle expresses the country- or region-specific fraction of wastewater for each industrial category
that is treated at the industrial site under anaerobic conditions. Very little literature data were found to
determine values for TAif\ therefore, the TAlc values are based mainly on anecdotal information from
interviews with wastewater exports, In general, only a small fraction of wastewater is treated, even in
several "developed" countries. Except for meat processing plants, industrial WWT is usually aerobic.
Nevertheless, anaerobic conditions are expected to exist in certain sections of the plant (i.e., sludge
storage) or due to mismanagement (e.g., overloading or undcraerating of lagoons).
The equation on page 38 was adapted to estimate CH, emissions from domestic wastewater:
37
-------
CH4 Emissions = EF x £t ( Pf x 365 x CODf x TA,/100) x Iff" (Tg/yr)
where: EF = Emission factor (gCH4/gCODremo«d);
Pf = Country population;
CODf = Country-specific per capita COD generation (g/day); and
TAC = Country-specific percentage of COD in wastewater treated
anaerobically.
The methodology uses per capita COD generation rates (COD^), which were obtained from
various literature sources. The country-specific fraction of COD that is treated anaerobically (TA&) was
again based on anecdotal information, As with industrial WWT, only a small fraction of domestic
wastewater is treated. In countries that do have comprehensive WWT, the WWT is likely to be primarily
aerobic.
GHG EMISSION ESTIMATES
Table A-I summarizes the Global CH4 and N2O estimates for domestic and industrial WWT.
CH4 emissions from industrial WWT are estimated to be between 0.6 and 6.1 teragrams per year (Tg/yr)
with a mean value of 2.4 Tg/yr. The biggest contributor to industrial CH4 emissions from WWT is the
pulp and paper industry in developing and eastern European countries. Although pulp and paper
wastewater typically is treated aerobically, it is assumed that 15 percent of the COD in pulp and paper
wastewater in developing and eastern European countries decomposes under anaerobic conditions as a
result of poor wastewater management practices. The second principal contributor to CH4 emissions
from WWT is the meat and poultry processing industry.
Earlier estimates for global CH4 emissions from industrial WWT are significantly higher (i.e.,
between 26 and 40 Tg/yr) {USEPA 1994). The emissions in this report are lower for two reasons: iron
and steel manufacturing and petroleum refining are excluded as significant categories, and the fraction of
wastewater degrading anaerobically is significantly lower for most remaining categories. (In USEPA
1994 it was assumed that between 10 and 15 percent of wastewater degrades anaerobically.)
-------
TABLE A-1. Summary of Global GHG Estimates for Domestic and industrial WWT
GHG
CH.
CH4
N2O
NjO
N2O
SOURCE
Industrial WWT
Domestic WWT
Domestic Activated
Sludge WWT
Domestic Anaerobic
WWT
Anaerobic WWT at beef,
dairy, poultry and, fish,
processing industry
LOWER BOUND
-------
For both industrial and domestic wastewater, large relative uncertainties are associated with
quantifying the overall extent of global WWT. Also, the quantification of the fraction of the wastewater
that may decompose under anaerobic conditions is uncertain,
The estimates for industrial wastewater, furthermore, depend on quantification of the wastewater
outflow and concentration per unit of product. Q, and COD, values depend on the product, the
production process, and the efficiency of the process. The type and efficiency of the industrial process
are likely to be dependent on plant scale, availability and cost of water, lo, al water and wastewater
regulations, and the degree of enforcement. For these reasons, it is expected that significant errors are
associated with the extrapolation of data.
-------
APPENDIX B
SUMMARY OF NITROGEN CYCLE EFFECTS ON AMMONIA AND NITROUS OXIDE
EMISSIONS FROM SEPTIC TANKS, LATRINES, AND STAGNANT OPEN SEWERS
INTRODUCTION
The relatively targe concentration of nitrogen present in domestic wastewater necessitates an
understanding of the nitrogen cycle within septic tanks and other methods of dealing with human waste,
such as latrines and stagnant, open sewers. Canter and Knox (1985) determined that an average of 38
mg/1 of Total Kjeldahl Nitrogen (TKN) is present in influent wastewaters of septic tanks serving single
households. Of this 38 mg/1, 12 mg/1 or 32 percent was found to be in the form of ammonium (NH4*).
Metcalf & Eddy (1991) report that total nitrogen in domestic wastewater ranges from 20 mg/1 to 85 mg/1
(Tchobanoglous and Burton, 1991),
The presence of these concentrations of nitrogen in domestic sewerage is associated with a
complex set of nitrogen inputs into the "average" wastewater. One source of organic nitrogen in
domestic wastewater is the decomposition of animal and plant proteins in the digestive tract The death
and decomposition of fecal bacteria both within the digestive tract and following expulsion also
contributes nitrogen to domestic wastewater. In addition, the human body excretes nitrogenous wastes in
the form of urea. Additional sources of nitrogen may be found as a result of the use of household
cleaning products and other chemical sources that are household-specific,
AMMONIA OR REDUCED NITROGEN
Septic Tank Reduced Nitrogen
Despite the complexity of influent nitrogen sources, bacterial processes convert most nitrogen in
domestic wastewater to reduced aitrogen (Mctcalf & Eddy, p. 1040), Reduced nitrogen is a relative term
used in this memo to discriminate between forms of ox.idiy.cd nitrogen, such as nitrite and nitrate, and
types of nitrogen without bonds with negative ions. Examples of reduced nitrogen are ammonia (NHj)
and N!I4+. The only exception to the prevalence of reduced nitrogen in domestic wastewater would be
nitrate that was present in the potable water used For domestic purposes. Because the preponderance of
nitrogen in domestic wastewater is reduced nitrogen, this section will focus on the fate of reduced
nitrogen in aqueous, anaerobic systems. This fate is both microbially mediated and determined by
chemical properties of the water.
Microbial mediation of the fate of reduced nitrogen in water is dependent on the types of
bacterial populations present as a dircci result of the presence or absence of oxygen as a terminal electron
41
-------
acceptor. In the presence of oxygen, bacterial nitrification converts reduced nitrogen first to nitrite, and
then to nitrate (Brock and Madigan, 1988), Septic tank influent and the water within septic tanks are
largely anaerobic because the rate of biotic oxygen usage outstrips the rate of atmospheric oxygen
transfer into the wastewater. Because the microorganisms responsible for nitrification are obligately
aerobic, nitrification is an unlikely fate for reduced nitrogen in domestic wastewater. Under anaerobic
conditions, reduced nitrogen is stable in a microbiological sense (Brock and Madigan, 1988).
The pH is the most important chemical factor involved in the fate of reduced nitrogen in septic
tanks. The chemical property ff pH determines the speciation of reduced nitrogen in aqueous systems.
At pH levels above 7, the equilibrium of the following reactions are displaced to the left.
AW, + H2O ++NHS + Off
or
Below pH 7, NH4+ is predominant (Tchobanoglous and Burton, 199 1). Hem (1989) states that the
transformation of aqueous ammonia (NHj) in solution to the NH/ ion is half complete at pH 9.24.
Because ihe pH of septic tanks is expecled to be close to neutral (see Table B-l), reduced nitrogen is
predominantly present as the NH^-ion. The importance of this reaction equilibrium in determining the
fate of reduced nitrogen during septic tank wastewater treatment is that gaseous NHj is volatile and NH/
is not (Sundstrom and Klci, 1979).
Due to the microbiological stability of reduced nitrogen in anaerobic environments and the
chemical tendency of NH^ to become the nonvolatile NH4*-ion at pH values typical of septic tanks (pH =
7 ± 1), NH3 emissions from these on-site wastewater treatment systems are anticipated to be negligible.
This hypothesis is supported by the work of many researchers who have studied the fate of NH«+ in the
effluent of septic tanks. Aravena et al. (1993) in Gerritse ct al. (1995) stale that nitrogen leaches from
the studied septic tank into the soil mainly as NH4* and then is oxidized to nitrate. Canter and Knox
(1985) state that, due to the prevalence of anaerobic conditions in septic tanks, organic nitrogen is
converted to NH4'. In discussing the fate of nitrogen in septic tank effluent, Ritter and Eastbum (1988)
state that, "under saturated conditions, NH/ -nitrogen would eventually be leached to the ground water."
Whelan and Titamnis (1982) concur that NH4' is the predominant form of nitrogen in septic tank effluent
due to the anaerobic nature of" these wastewater treatment systems. During their studies of the fate of
nitrogen in septic tank effluent, all of these researchers established that septic tanks achieve very little
nitrogen removal from domestic wastewater.
42
-------
Table B-1. Septic Tank influent and Effluent pH Values from Two Sources
REFERENCE
Whelan and Titamnis, 1982
Canter and Knox, t985
SAMPLE SOURCE
5 Septic Tank Effluents
(Mean t Standard deviation)
Septic Tank Influent
(85% of the time less than)
PH
(standard units)
6,6 ±0.1
7.4 ± 0,1
7.0 ±0.1
6.9 ± 0.2
6.9 ± 0.3
7.15-8.7
The fate of NH/-ions leaving septic tanks seems well established. These NH4*-ions are available
for uptake and conversion to organic nitrogen by soil bacteria during incorporation into bacterial
proteins. More important, the NH4*-ions in septic tank effluent also undergo the nitrification process in
aerobic soils which support the necessary bacterial communities. Nitrate contamination of gioundwater
as a result of the nitrification of septic tank effluent is well documented. Plant uptake and the bacterial
denitrification processes are the ultimate fate of septic tank nitrogen that has been converted to nitrate.
Reduced Nitrogen In Latrines And Stagnant. Open Sewers
Though no data have been located, the chemical and microbiological characteristics associated
with septic tanks are believed to be prevalent in both latrines and stagnant open sewers. Both of these
forms of wastewater arc expected to be anaerobic and to be neutral or acidic with regard to pH. Both of
these chemical characteristics suggest that the fate of reduced nitrogen in latrines and stagnant, open
sewers does not involve gaseous nitrogenous emissions.
NITROUS OXIDE
Nitrous Oxide from Septic Tanks
The potential for the release of nitrous oxide (N,O) from septic tanks is also of interest. Nitrous
oxide results from the incomplete reduction of nitrate during a bacterial process called denitrification
(Brock and Madigan, 1988). By definition, denitrification is not possible in the absence of nitrate, which
serves microorganisms as an alternative terminal electron acceptor in the absence of oxygen. Though
septic tanks represent suitable environments for denitrification because they arc anaerobic, the
concentration of nitrate in the tank is expected to be limited. Only the nitrate present in the potable water
associated with domestic life, or present as a result of ihc introduction of a chemical into the potable
water (i.e. photographic development) would be available to facilitate denitrification. In most developed
-------
countries, nitrate concentrations in potable water supplies arc monitored and in some cases regulated due
to the negative human health aspects associated with elevated concentrations of nitrate. Without
consistent, substantial concentrations of nitrate, denitrification does not take place. Because septic tanks
do not support denitrification in the absence of nitrate, N2O emissions from septic tanks will be
negligible.
The NH/-ions present in septic tank effluent could undergo nitrification to form nitrate in
aerobic soil surrounding the drain field and then be transported to regions that would support
denitrification and lead to the formation of N,O. This type of nitrogen fate would be highly site specific
and a significant lag time would be expected for the transport and bacterial conversion necessary to form
N,O.
Nitrous Oxide from Latrines and Stagnant Open Sewers
As with septic tanks, N2O emissions from latrines and stagnant, open sewers would be dependent
on the availability of nitrate to serve as a terminal electron acceptor. Also, nitrate concentrations in any
water added to latrines and open sewers along with the actual waste will be the primary source of nitrate
in these anaerobic systems. Though the extent of nitrate in water added to latrines and open sewers is not
documented here, the potential for nitrate to be present in water used for these purposes is much greater
in areas of the world that rely on latrines and stagnant sewers as means of handling domestic wastewater.
This higher potential for the presence of significant nitrate concentrations is associated with the expected
primitive state of enforced drinking water regulations in countries where open sewers are used to
transport domestic wastewater.
As with NlI4*-ions in septic tank drain field effluent, NH4*-ions seeping into soils surrounding
unlincd latrines and open sewers could undergo nitrification to nitrate. If transported to a subsurface area
where anaerobic conditions prevail, the nitrate formed in this manner could undergo denitrification and
subsequently result in the emission of N2O. This fate of nitrogen would be equally site specific and
could also be accompanied by a substantial time lag between the expulsion of the waste and the emission
ofN2Ogas.
-------
SUMMARY AND CONCLUSION
Data associated with the operation of septic tanks and scientific judgment were used to generate an
understanding of the nitrogen cycle associated with on-site septic tank treatment of domestic wastewater.
This nitrogen cycle characterization can be applied to latrines and stagnant, open sewers because the
microbiological and chemical conditions are expected to be identical to the conditions within septic
tanks. Knowledge of the nitrogen cycle in septic tanks, latrines, and stagnant, open sewers suggests that
anaerobic wastewater does not contribute any significant quantity of NH3 and N20 to the atmosphere.
This discovery indicates that the estimation of nitrogenous air emissions can safely overlook the
production of NH3 arid N2O from septic tanks, latrines, and open sewers at a global level,
REFERENCES FOR APPENDIX B
Aravena, R., Evans, M.L., and J.A. Cherry. 1993. Stable Isotopes of Oxveen and Nitrogen in Source
Identification of Nitrate from Septic Systems. Ground Water, No. 31, pp. 180-186.
Brock, T.D. and M. T. Madigan. 1988. Biology of Microorganisms. Fifth edition, p. 572, pp. 630 and
575, Prentice Hall, Englewood Cliffs, NJ.
Canter, L.W. and R.C.Knox. 1985. Septic Tank System Effects on Ground Water Quality, pp. 50 and
p ">, Lewis Publishers, Chelsea, MI.
Gerritsc, R.G., Adeney, J.A., and J. Hosking. 1995. Nitrogen Losses from a Domestic Septic Tank
System on the Darling Plsteau in Western Australia. Water Resources, Vol. 29, No. 9, pp. 2055-
2058.
Hem,J.D. 1989. Study andInterpretation of the Chemical Characterises of Natural Water. U.S.
Geological Survey Water-Supply Paper 2254, U.S. Government Printing Office, Washington,
D.C.
Mctcalf& Eddy, Inc. 1991. Wastewater Engineering: Treatment Disposal and Reuse. Third Edition,
McGraw-Hill Book Company. New York, NY. ISBN 0-07-041690-7.
Ritter, W.F. and R.P. Eastburn, 1988. A Review of Denitrification in On-Site Wastewater Treatment
Systems. Environmental Pollution, Vol. 51, pp. 49-61.
Tchobanogtous, G. and F.L. Burton. 1991. Wastewater Engineering Treatment Disposal and Reuse, pp.
109 and p. 87. McGraw-Hill, Inc., New York, NY.
Sundslrom, D.W, and M K. Klei. 1979. Wastewater Treatment, p. 331, Prentice-Hall, Inc., Englewood
Cliffs, NJ.
Whelan, B.R. and Z.V. Titamnis. 1982. Daily Chemical Variability of Domestic Septic Tank Effluent.
Water, Air, and Soil Pollution, No. 17, pp. 131-139.
45
-------
TECHNICAL REPORT DATA
(Please read Imuucriota an the revene before compietinx)
r:tf ORT NO.
EPA- 6DO/R-99- 089
3. RECIPIENT'S ACCESSION NO.
Preasslgned FB2000-101018
4,TiTi.E,-,.%fDsuaTiTLEQ!,antif|cation of Methane Emissions
anc Discussion of Nitrous Oxide, and Ammonia Emis-
sions from Septic Tanks, Latrines, and Stagnant Open
Sewers in the World
6. PERFORMING ORGANIZATION CODE
. REPORT DATE
October 1999
7. AUTHOR(S)
Michiel R. J.
Doom and David S. Liles
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
ARCADIS Geraghty aud Miller
4915 Prospectus Drive, Suite F
Durham, North Carolina 27713
10. PROGRAM ELEMENT NO.
ft'. fcoNYtfXCT/tiKTMf'NO.
68-D4-Q005, WA 3-020
1?. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE Of REPORT AND PERIOD COVERED
Final; 10/97-1/99
14. SPONSORING AGENCY CODE
EPA/600/13
is,SUPPLEMENTARY NOTES APpCD project officer is Susan A, Thorneloe, Mail Drop 63, 919 /
541-2709.
16. ABSTRACT The report gives results of a first attempt to estimate global aricl country-
specific methane (CH4) emissions from sewers and on-site wasfcewater treatment
systems, including latrines and septic sewage tanks. It follows a report that includes
CH4 and nitrous oxide (N2O) estimates from treated industrial and domestic waste-
water. The study uses an emission factor tint expresses CH4 emissions in terms
of removed Chemical Oxygen Demand. Combined global CH4 emissions from lat-
rines, septic sewage tanks and stagnant open sewers are estimated to be 29 Tg/yr,
with lower and upper bound ranges of 14 and 49 Tg/yr. respectively. These ranges
reflect boundaries in the parameters that could be quantified through measurements;
i. e., the emission factor and Chemical Oxygen Demand loadings. Major uncertain-
ties in the estimates are associated with the degrees to which wastewater in devel-
oping and eastern European countries is treated in latrines or septic tanks, or re-
moved by sewer. Also, the amount of wastewater that is discharged into stagnant
open sewers and the degree to which anaerobic decomposition takes place in these
sewers are highly uncertain. Latrines in rural areas of developing countries such
as China ai.1 India are believed to be the single most significant source of CH4, ac-
counting for roughly 12 Tg/yr.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Emission
Septic Tanks
Sanitary Sewers
Methane
Nitrogen Oxide (N2O)
Ammonia
Greenhouse Effect
Pollution Control
Stationary Sources
Latrines
Open Sewers
13B
14G
07C
07B
04 A
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS {This Report)
Unclassified
21. NO. OF PAGES
51
2O. SECURITY CLASS fTHIipage)
Unclassified
EPA Form 5220-1 (9-73)
46
-------
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
National Risk Management Research Laboratory
Technology Transfer and Support Division
Cincinnati, Ohio 45268
OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE. S3OO
AN EQUAL OPPORTUNITY EMPLOYER
If your address is incorrect, pi east change on the above label
tear oft; and return to the above address.
If YOU do not desire to continue receiving these technical
reports. CWfCK WMf O; teat off labef, ami return it to the
above address.
Publication No. EPA- eoo/R-99-089
------- |