EPA-6Q0/R-97-091
September 1997
ESTIMATES OF GLOBAL
GREENHOUSE GAS EMISSIONS
FROM INDUSTRIAL AND DOMESTIC
WASTEWATER TREATMENT
Michiel R.J. Doom, Randy P. Strait, and William R. Barnard
E.H. Pechan & Associates, Inc.
3500 Westgate Drive, Suite 103
Durham, NC 27707
and
Bart Eklund
Radian International, LLC
P.O. Box 13000
Austin, TX 78720
EPA Contract No. 68-D4-0100
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
Prepared for:
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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\
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before comple \ | ||| | |||| |
II lllllll
1. REPORT NO. 2.
EPA-600/R-97-091
3. 1 1 III 1 llll 1
PB98-1
IIIIIIIII
06420
4. TITLE AND SUBTITLE
Estimates of Global Greenhouse Gas Emissions from
Industrial and Domestic Wastewater Treatment
5. REPORT DATE
September 1997
6. PERFORMING ORGANIZATION CODE
7. authoro)]^ Doom, R. Strait, and W. Barnard (Pechan);
and B. Eklund (Radian)
8. PERFORMING ORGANIZATION REPORT NO.
a_J>EHfOBMING ORGANIZATION NAME AND ADDRESS T , - , T ,
E. H. Pechan ana Assoc. ,lnc. Kaaian International, LLC
3500 Westgate Dr., Suite 103 P. 0. Box 13000
Durham, NC 27707 Austin, TX 78720
^10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D4-0100 (Pechan)
12. 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; 9/94 - 3/97
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notes ^PPCD project officer is Susan A. Thorneloe, Mail Drop 63,
919/541-2709.
is. abstract rj-rep0rt summarizes the findings of field tests and provides emission
factors for methane (CH4) and nitrous oxide (N20) from wastewater treatment
(WWT). It also includes country-specific activity data on industrial and domestic
WWT which were used to develop country-specific emission estimates for CH4 and
N20. The report concludes that WWT is unlikely to be a significant source of volatile
organic carbon and carbon dioxide emissions. Global CH4 emissions from industrial
WWT are estimated to be between 0.6 and 6.1 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. The second prin-
cipal contributor to CH4 emissions from WWT is the meat and poultry industry. Glo-
bal CH4 emissions from domestic WWT are estimated to be between 0.6 and 2.1 Tg/
yr, with a mean value of 1.3 Tg/yr. Russia is believed to be the largest contributor.
CH4 emissions from untreated domestic wastewater may be many times higher than
those of treated wastewater. The report provides rough estimates for global N20
emissions from WWT. Global emissions from anaerobic domestic WWT are estima-
ted to be 0. 5 Tg/yr, and wastewater from the meat and poultry processing indus-
tries is expected to emit about 0. 24 Tg/yr.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cos ATI Field/Group
Pollution Methane
Waste Water Nitrogen Oxide (N20)
Waste Treatment Paper Industry
Greenhouse Effect Poultry Meat
Emission
Estimating
Pollution Control
Stationary Sources
13B 07C
07B
05C.11L
04A 06H
14 G
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
106
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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NOTICE
This document has been reviewed in accordance with U.S.
Environmental Protection Agency policy and approved for publication.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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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 a 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
i i i
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ABSTRACT
To improve global estimates of greenhouse gas (GHG) emissions from wastewater
treatment (WWT), EPA's Air Pollution Prevention and Control Division (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 (FTIR) spectroscopy to
measure emissions from two meat processing plants, one chicken processing plant, and
two facultative domestic WWT lagoons. In conjunction with the field test program,
research was undertaken to improve the quality of the country-specific activity data that
included a search of the most recent literature and interviews with U.S. and European
wastewater experts.
This report summarizes the findings of the field tests and provides emission factors
for methane (CH4) and nitrous oxide (N20) from WWT. Also, the report includes country-
specific activity data on industrial and domestic WWT which were used to develop
country-specific emission estimates for CH4 and N20. The report concludes that WWT is
unlikely to be a significant source of volatile organic carbon and carbon dioxide emissions.
Global CH4 emissions from industrial wastewater treatment 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. The second principal contributor to CH4
emissions from WWT is the meat and poultry industry. Global CH4 emissions from
domestic WWT are estimated to be between 0.6 and 2.1 Tg/yr with a mean value of
1.3 Tg/yr. Russia is believed to be the largest contributor. CH4 emissions from untreated
domestic wastewater may be many times higher than those of treated wastewater.
The report provides rough estimates for global N20 emissions from WWT. Global
emissions from anaerobic domestic WWT are estimated to be 0.5 Tg/yr and wastewater
from the meat and poultry processing industries is expected to emit about 0.24 Tg/yr.
For both industrial and domestic wastewater, large relative uncertainties are
associated with estimating the overall degree of global WWT. Also, the quantification of
the fraction of the wastewater that may decompose under anaerobic conditions is
uncertain.
i v
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CONTENTS
Page
TABLES yj i
FIGURES viii
ABBREVIATIONS AND SYMBOLS ix
EXECUTIVE SUMMARY ES-1
INTRODUCTION AND BACKGROUND 1
BOD AND COD 4
FIELD MEASUREMENT OF GHG EMISSION RATES AT FIVE WWT LAGOONS . . 6
SITE SELECTION 6
RESULTS 7
CONCLUSIONS 10
ADDITIONAL INFORMATION ON GHG EMISSIONS FROM WWT 11
METHANE AND CARBON DIOXIDE 11
Stoichiometric Decomposition Models 11
Summaries of Four GHG Wastewater Studies 14
VOLATILE ORGANIC COMPOUNDS 19
NITROUS OXIDE 21
EMISSION FACTORS 24
METHANE AND CARBON DIOXIDE 24
VOLATILE ORGANIC COMPOUNDS ... 25
NITROUS OXIDE 26
ACTIVITY DATA AND METHODOLOGY DEVELOPMENT 28
INDUSTRIAL WASTEWATER 28
Composition and Output 29
Industrial Wastewater Discharged to City Sewers 40
DOMESTIC WASTEWATER 41
Composition and Output 41
Extent of Sewerage, Treatment, and Prevailing Treatment Methods 43
ESTIMATES OF GHG EMISSIONS FROM WWT 49
METHANE 49
Industrial Wastewater 49
Domestic Wastewater 53
Industrial Wastewater Discharged into Sewers 54
CARBON DIOXIDE 56
NITROUS OXIDE 56
v
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UNCERTAINTIES 58
Uncertainties Associated With the CH4 Emission Factor 58
Uncertainties Associated With Industrial Wastewater Activity Data 58
Uncertainties Associated With Domestic Wastewater Activity Data 60
Uncertainties Associated With the N20 Emission Estimates 61
TRENDS 62
REFERENCES 64
APPENDIX A: SUMMARIES OF FIVE INTERVIEWS WITH WWT EXPERTS A-l
APPENDIX B: WASTEWATER TREATMENT METHODS B-l
APPENDIX C: EFFECT OF WATER AND AMBIENT AIR TEMPERATURE ON
CH4 EMISSIONS AND COD REMOVAL RATES IN ANAEROBIC LAGOONS . . C-l
vi
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TABLES
Page
ES-1. SUMMARY OF GLOBAL CH4 AND N20 ESTIMATES FOR DOMESTIC
AND INDUSTRIAL WWT ES-4
1. COD/BOD RATIOS FOR WASTEWATER 5
2. MEASURED EMISSION RATES OF SELECTED COMPOUNDS FOR EACH
FIELD SITE 8
3. AVERAGE EMISSION FACTORS FROM FIELD TESTS 9
4. THEORETICAL CH4 AND C02 EMISSION FACTORS 13
5. DATA AND CH4 AND C02 EMISSION RATES FOR POTW IN DURHAM, NH . . . 15
6. ACTIVITY DATA FOR THE PULP & PAPER AND
FOOD & BEVERAGE INDUSTRIES 17
7. EMPIRICAL WASTEWATER AND BIOGAS DATA FOR SIX INDUSTRIES 18
8. VOC-GHGS DETECTED AT U.S. POTWS 20
9. SUMMARY OF AVAILABLE EMISSION FACTORS 25
10. RECOMMENDED EMISSION FACTORS 27
11. INDUSTRIAL WASTEWATER GENERATION ESTIMATES FOR THE
UNITED STATES, CHINA, AND THE WORLD 30
12. WASTEWATER OUTFLOW AND COMPOSITION DATA FOR SELECTED
INDUSTRIES 31
13. GLOBAL WASTEWATER DISCHARGE AND TREATMENT PRACTICES 34
14. TYPICAL COMPOSITION OF UNTREATED DOMESTIC U.S.
WASTEWATER 42
15. BOD5 AND COD LOADINGS FOR DIFFERENT REGIONS OF THE WORLD ... 43
16. POPULATION SERVED BY WWT IN DEVELOPED COUNTRIES 46
17. COUNTRY-SPECIFIC DOMESTIC WASTEWATER DATA 48
18. COUNTRY-SPECIFIC INDUSTRIAL WASTEWATER DATA AND METHANE
EMISSIONS 50
19. GLOBAL CH4 EMISSIONS FROM ANAEROBIC DOMESTIC WASTEWATER
TREATMENT 55
20. SUMMARY OF GLOBAL GHG ESTIMATES FOR DOMESTIC AND
INDUSTRIAL WWT 57
21. SENSITIVITY ANALYSIS OF INDUSTRIAL CH4 ESTIMATES 60
22. SENSITIVITY ANALYSIS OF DOMESTIC CH4 ESTIMATES 61
B-l. DESIGN CRITERIA FOR LAGOONS B-3
vi i
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FIGURES
Figure 1. Parameters Used to Develop Emission Estimation Methodology for
Industrial WWT 29
Figure 2. Urban Sanitation by Technology Type 44
Figure 3. World Methane Emissions from Anaerobic Industrial WWT 53
Figure C-l. Biogas Production and COD Removal Efficiency as a Function of
Temperature in a Pilot UASB Reactor Treating Domestic Sewage C-l
Figure C-2. COD Removal Efficiencies and CH4 Production as a Function of
Temperature C-2
Figure C-3. Monthly Water Temperatures for Two Lagoons in the Southern United
States C-5
viii
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ABBREVIATIONS AND SYMBOLS
APPCD
Air Pollution Prevention and Control Division
bod5
Biological oxygen demand (five day)
BODy
Biological oxygen demand (ultimate)
COD
Chemical oxygen demand
DAF
Dissolved Air Flotation
DOE
Department of Energy
EPA
Environmental Protection Agency
FTIR
Fourier Transform Infrared (spectroscopy)
GHG
Greenhouse gas
HRT
Hydraulic retention time
OECD
Organization for Economic Cooperation and Development
OPM/TM
Open Path Monitoring/Transect Method
POTW
Publicly owned treatment work
(T)SS
(Total) Suspended solids
UASB
Upflow Anaerobic Sludge Blanket
UNISY
United Nations Industrial Statistical Yearbook
US
United States
WW
Wastewater
WWT
Wastewater treatment
WWTP
Wastewater treatment plant
°C
Degrees Celsius
op
Degrees Fahrenheit
Gg
Gigagram (109 grams)
ha
Hectare
kg
Kilogram
1
Liter
m
Meter
mg
Milligram (10~3 gram)
Mg
Megagram (106 grams)
mgd
Million gallons per day
Tg
Teragram (1012 gram)
vol.%
Percent by volume
yr
Year
CFC
Chlorofluorocarbon
ch4
Methane
CO
Carbon monoxide
co2
Carbon dioxide
HCFC
Hydrochlorofluorocarbon
HFC
Hydrofluorocarbon
h2s
Hydrogen sulfide
n2o
Nitrous oxide
NO"
Nitrate
NOx
Nitrogen oxides
ix
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PFCs Perfluorocarbons
VOCs Nonmethane volatile organic compounds
x
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EXECUTIVE SUMMARY
Introduction
Over the last few years, knowledge on major greenhouse gas (GHG) sources has
greatly increased. This report focusses on improving global estimates of GHG emissions
from wastewater treatment (WWT) which is considered one of the larger minor sources.
GHGs emitted from WWT include methane (CH4), carbon dioxide (C02), nitrous oxide
(N20), and certain types of nonmethane volatile organic compounds (VOCs).
To improve global estimates of GHG emissions from WWT, EPA's Air Pollution
Prevention and Control Division (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 (FTIR) spectroscopy to measure emissions from two meat processing plants, one
chicken processing plant, and two facultative domestic WWT lagoons. In conjunction with
the field test program, research was undertaken to improve the quality of the country-
specific activity data that included a search of the most recent literature and interviews
with U.S. and European wastewater experts.
This report summarizes the findings of the field tests and provides emission factors
for CH4 and N20 from WWT. Also, the report includes country-specific activity data on
industrial and domestic WWT which were used to develop country-specific emission
estimates for CH4 and N20. The report concludes that WWT is unlikely to be a significant
source of VOC and C02 emissions. The report also provides background information on
WWT systems and discusses the effect of water and ambient air temperature on CH4
emissions and chemical oxygen demand (COD) removal rates in anaerobic lagoons.
Field Tests
OPM/TM using FTIR spectroscopy was used to determine emission rates. A very
large data set was generated, and up to 300 separate valid, 5-minute average emission
rate determinations were made at a given site. Typical detection limits were about
0.1 gram per second (g/sec) for most compounds, except for C02, which had a minimum
detection limit of about 150 g/sec. The high detection limit for C02 was due to high
background concentrations.
At all three meat processing plants, large amounts of CH4 were measured downwind
of the WWT system. The field tests detected significant N20 emissions only at the
anaerobic chicken processing waste lagoon. No N20 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 POTW
lagoons. However, it is highly probable that C02 was being generated, but the levels were
too small to measure given the very high background levels of C02 and the measurement
variability.
ES-1
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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 random 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 gram (g)/g COD. The average CH4
emission factor derived from the field tests is 0.96 g/g COD with a lower range of 0.26 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 CH4
emissions from COD that had been deposited in the sludge during past winters when
anaerobic microbial activity was low. For the purpose of developing CH4 emissions
estimates for this report, a CH4 emission factor of 0.3 ±0.1 g/g COD was used. This
factor reflects the upper end of the range of factors based on theoretical models and
empirical digester data, and the lower end of the range of the factors developed from the
field test results.
The report uses two separate N20 emission factors. The first emission factor (0.09 g
N20/g CODremoved) is based on the field tests and reflects a completely anaerobic
environment. It was used to estimate emissions from domestic sewage, meat, poultry,
fish, and dairy processing wastewater that is degrading under anaerobic conditions. The
second emission factor [5.1 grams per capita per year (g/capita/yr)] is based on literature
studies and pertains to anoxic processes (denitrification) as part of conventional domestic
WWT.
The equation below was used to estimate CH4 emissions from industrial wastewater.
CH4 emissions = EF * 1012 * £ {Pic * Q, * COD,. * TAJ (Tg/yi) (1)
/ C
where:
EF
Pic
Qi
COD,
TAlc
Subscript i =
Subscript c =
Emission factor (g CH4 or g N20/g CODremoved).
Industry- and country-specific product output [megagrams per
year (Mg/yr)];
Industry-specific wastewater produced per unit of product [cubic
meters per megagram (m3/Mg)];
Organics loading removed, by industry (g/m3);
Industry- and country-specific fraction of COD in wastewater
treated anaerobically;
An individual industry; and
An individual country.
ES-2
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Initially, 23 industrial categories were identified as potentially the most significant
dischargers of wastewater with high organic COD loading. Country-specific annual
industrial product output data for each industrial category (Pic) were obtained from the
United Nations, Industrial Statistical Yearbook. Typical wastewater generation rates (Qt)
and representative COD loadings {COD) were obtained for each industrial category from
various literature sources. Country-specific data for Q; and CODi were not available.
TAic expresses the country or region-specific fraction of wastewater for each
industrial category that is treated at the industrial site under anaerobic conditions. Very
few literature data were found to determine values for TAic and these are mainly based on
anecdotal information from interviews with wastewater experts. 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 underaerating of lagoons).
The methodology that was used to estimate CH4 emissions from domestic
wastewater is represented by:
CH4 emissions = EF * 10"12 * (Pc * CODc * 365 * TAC) (Tg/yr) (2)
where:
EF
Pc
CODc
TAC
Subscript c =
Emission factor (g CH4/g CODremoved);
Country population;
Country-specific per capita COD generation (g/day);
Country-specific fraction of COD treated anaerobically; and
An individual country.
The methodology uses country-specific per capita COD generation rates (CODc)
which were obtained from various literature sources. The country-specific fraction of COD
that is treated anaerobically (TAC) 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, this WWT is likely to be primarily aerobic.
GHG Emission Estimates
CH4 emissions from industrial wastewater treatment are estimated to be between
0.6 and 6.1 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 is typically treated aerobically,
it was 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.
ES-3
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Earlier estimates for global CH4 emissions from industrial WWT are significantly
higher [i.e., between 26 and 40 Tg/yr (U.S. EPA, 1994)]. The two main reasons that the
emissions in this current report are lower are, that iron and steel manufacturing and
petroleum refining are excluded as significant categories and that the fraction of
wastewater degrading anaerobically is significantly lower for most remaining categories.
(In U.S. EPA 1994, it was assumed that between 10 and 15 percent of wastewater
degrades anaerobically.)
CH4 emissions from domestic WWT are estimated to be between 0.6 and 2.1 Tg/yr
with a mean value of 1.3 Tg/yr. One earlier estimate for global CH4 emissions from
domestic WWT is 2.3 Tg/yr (U.S. EPA, 1994). Russia is believed to be the largest
contributor. In many developing countries very little wastewater is treated. Whereas
much wastewater may end up "on the ground," very significant amounts of wastewater
may also be discharged into open sewers and ditches where it may degrade anaerobically.
Consequently, CH4 emissions from untreated domestic wastewater may be many times
higher than those of treated wastewater.
Global N20 emissions from conventional domestic activated sludge WWT are
estimated at 0.004 Tg/yr. Estimated global N20 emissions from anaerobic domestic WWT
are 0.5 Tg/yr. Wastewater from the meat, poultry, fish, and dairy processing industries is
expected to contain substantial amounts of bound nitrogen, and global N20 emissions
from this source category are estimated at 0.24 Tg/yr. For the United States, emissions
are estimated to be 0.12 Tg/yr. As a comparison, previous U.S. estimates for total NzO
emissions are 0.4 Tg/yr and do not include WWT. These estimates are associated with
large uncertainties and are, at best, an indication of the relative significance of this source
category.
TABLE ES-1. SUMMARY OF GLOBAL CH4 AND N20 ESTIMATES FOR DOMESTIC AND
INDUSTRIAL WWT.
GHG
LOWER
BOUND
(Tg/yr)
AVERAGE
(Tg/yr)
UPPER
BOUND
(Tg/yr)
REMARKS
CH„
Industrial WWT
0.6
2.4
6.1
ch4
Domestic WWT
0.6
1.3
2.1
n2o
Domestic Activated
Sludge WWT
0.004
These are rough
estimates.
No lower and upper
bounds are
available.
n2o
Domestic Anaerobic
WWT
0.5
n2o
Anaerobic WWT at
meat, poultry, fish, and
dairy processing
industries
0.24
ES-4
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Uncertainties
The specific uncertainties associated with the development of the field test emission
factor such as the representativeness of the test sites and suitability of the test
procedures are discussed in the field test report (Eklund and LaCosse, 1997). The
emission factors express CH4 and N20 emissions per mass of CODremoved as a surrogate for
the amount of available organic carbon or nitrogen in the wastewater. The ratio of COD
to actual degradable organic loading varies for different types of wastewater and is a
source of uncertainty.
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. Qt 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, local water and wastewater regulations, and the degree of
enforcement. It is expected that errors are associated with the extrapolation of data
across industries, even within the same industrial category.
ES-5
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INTRODUCTION AND BACKGROUND
A greenhouse gas (GHG) can generally be defined as any gaseous molecule which
absorbs infrared light in the spectral region of 5 to 20 micrometers. Reasonably accurate
global balances are needed for targeted GHGs for use with climatic models to estimate
long-term global temperature changes. The development of a global balance for any
compound includes identification of all major emission sources, estimation of their source
strength (i.e., emission rate), and identification of all major reaction mechanisms and
sinks, as well as, atmospheric residence times. Now that comprehensive efforts by
national and international research centers are well under way to quantify GHG
emissions from larger sources, more attention is given to secondary sources, such as
treated and untreated wastewater.1 This report focusses on improving global estimates of
GHG emissions from treated wastewater.2
Methane is believed to be the most important GHG emitted from wastewater
treatment (WWT). It is produced during the anaerobic decomposition of wastewater and
wastewater sludge. Other GHGs from WWT are carbon dioxide (C02), nitrous oxide
(N20), and certain types of nonmethane volatile organic compounds (VOCs). VOCs are
typically discarded in and with wastewater as liquids and may later be emitted especially
if the wastewater undergoes turbulence. Also C02 and N20 are products of the biological
degradation of organic matter in the wastewater.
In the United States, the Air Pollution Prevention and Control Division (APPCD),3
National Risk Management Research Laboratory, Office of Research and Development of
the U.S. Environmental Protection Agency (EPA) has conducted a program to develop
estimates of GHG emissions from waste sources and to compile information on cost-
effective control technologies for GHGs. Waste sources include landfills, livestock waste
lagoons, and wastewater. As a first step to assess the relative importance of WWT as a
source for CH4 emissions, APPCD conducted an initial desk study in 1991 - 1992 which
was summarized in a Report to Congress (EPA, 1994). The 1991 - 1992 study contained
a preliminary estimate for CH4 from WWT, with emissions from global industrial sources
between 26 to 40 teragrams per year (Tg/yr) and from domestic WWT of about 2 Tg/yr.
The methodology for estimating CH4 from industrial WWT is based on world wastewater
outflows and industry-specific average biological oxygen demand (BOD) values. The
domestic wastewater emissions methodology uses country populations and a constant to
1 Wastewater is usually classified as either domestic or industrial. Domestic wastewater is the spent water
originating from all aspects of human sanitary water usage, whereas industrial wastewater results from
industrial operations, including product handling.
2 Future research will focus on developing estimates of GHG emissions from untreated wastewater, if funding
is available.
3 Formerly named Air and Energy Engineering Research Laboratory (AEERL).
1
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express BOD discharge per capita per day. Both methodologies employ an assumed CH4
emission factor of 0.22 gram (g)/g BOD.4
In this initial study, APPCD recognized that major data limitations existed for
quantifying actual emissions from WWT sources, the fraction of wastewater subject to
anaerobic decomposition, and the outflow and composition of industrial wastewater.
Therefore, APPCD initiated a field test program to develop GHG emission factors based
on actual emissions measurements and to improve county-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 (FTIR)
spectroscopy to measure emissions from two meat processing plants, one chicken
processing plant, and two facultative municipal WWT lagoons. Wastewater and process
data were collected during the tests to allow for the development of emission factors. The
site-selection criteria, sampling and analysis procedures, and results for the field tests are
documented in a separate report (Eklund and LaCosse, 1997).
In addition, research was undertaken to improve the quality of the country-specific
activity data that included a search of the most recent literature and interviews with
European wastewater experts. Summaries of the interviews with these experts are
included in Appendix A of this report. The most important findings from this research
pertained to the extent to which domestic and industrial wastewater is treated and may
be summarized as follows:
• There is only one published source (Lexmond and Zeeman, 1995) which
provides estimates of the degree to which wastewater is treated in developing
and developed countries.
• In developing countries, as well as in Eastern Europe, only a very small
fraction of industrial wastewater is treated. Large, multi-national corporations
are more likely to treat their wastewater than local industries. Also, in some
Organization for Economic Cooperation and Development (OECD) countries
significant fractions of raw wastewater are discharged into rivers and oceans
via outfalls.
• In many countries (including developing countries and Eastern European
countries), sewer infrastructure may not reach large parts of the population,
especially in rural areas. In cities in developing countries, domestic wastewater
is often discharged into open sewers or gutters where significant anaerobic
decomposition is expected to take place.
• In most countries, it is common to discharge large portions of industrial
wastewater into public sewers to be treated at the local municipal WWT plant.
4 BOD is considered here to be the amount of BOD that is actually used up during CH„ formation (i.e.,
BODinltuont - BODeffluent). For WWT it is assumed that BODellluent equals zero.
2
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• Around the world, most domestic and industrial wastewater is treated
aerobically. Anaerobic biological treatment is only applied to specific kinds of
wastewater (e.g., from meat packing plants). Sometimes domestic and/or
industrial wastewater also is treated anaerobically, for instance, in situations
with severe space constraints or when aerobic systems are not managed
properly.
• Environmental regulations may be in place in some developing countries, but
there often is very little or no enforcement to ensure compliance with the
regulations.
• There are lagoons in use in Africa, Europe, and America. Space constraints
limit the use of lagoons in some countries in Asia.
In this current study, the methodology for estimating CH4 from industrial
wastewater has been significantly improved compared to the methodology in the Report to
Congress (U.S. EPA, 1994). The accuracy of CH4 estimates from industrial and domestic
WWT was further improved by using the validated emission factors and the more
comprehensive and better activity data set. The new methodology allows for country-
specific emission estimates and it includes industrial wastewater that is being discharged
into public sewers. The methodology for estimating CH4 emissions from domestic
wastewater was not changed compared to the Report to Congress version, with the
exception that, for both methodologies chemical oxygen demand (COD) is used instead of
BOD. COD is believed to be a better parameter for measuring organics concentrations
than BOD (see below). The improvement of the activity data is founded on better
quantitative and qualitative industrial outflow data and on better estimates for the
fraction of COD in wastewater that is treated anaerobically.
During the field tests, no emissions of VOCs and C02 were detected at any of the
sites and N20 emissions were recorded for only one site. The lack of measurable VOC and
C02 is believed to be associated with the relatively low emissions of these compounds and
constraints on the detection limits of the OPM/TM FTIR sampling technique. Techniques
with more sensitive detection limits for VOCs and C02 (e.g., flux chamber) would need to
be applied to determine the extent to which these compounds are emitted from the
lagoons tested. This report includes only rough estimates for total VOCs, C02, and N20
emissions from WWT.
As background information, generic descriptions of an activated sludge treatment5
plant and a typical lagoon system are given as Appendix B. Also, the report provides the
result of a literature study on the effect of water and ambient air temperature on CH4
emissions and COD removal rates in anaerobic lagoons (Appendix C). The chapter on
emissions estimates concludes with an uncertainty analysis and a brief discussion on
global WWT trends that may affect GHG emissions. For a more comprehensive
discussion on trends that may affect GHG emissions, information on untreated
5 The term activated sludge treatment pertains to wastewater treatment.
3
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wastewater including septic systems (for example, urban sanitation issues) must be
included.
BOD AND COD
BOD and COD are both used as expressions of the mass of organics loadings in
liquids such as wastewater in milligrams per liter (mg/1). Because both terms are used
extensively throughout this report and other wastewater literature, a short introduction
and comparison is warranted.
The BOD test is a batch-type laboratory procedure in which aerobic bacteria are
allowed to degrade organic matter in a known liquid sample (e.g., wastewater) for a
definite number of days (usually five) at 20°C with excess oxygen in the head space of the
closed reactor. The sample may be seeded with bacteria if it is expected that not enough
organisms are naturally present in the wastewater. The BOD of the organics originally
present in the sample is equal to the amount of oxygen used in the bottle over the test
period. A five day period is used almost exclusively in tests throughout the world and the
BOD value is denoted as BOD5. For the purpose of determining GHG emissions from
organic matter in wastewater, ultimate BOD (BODu) would be a more appropriate
parameter than BOD5, however, the determination of BODu takes a long time (infinite, in
theory), which makes it an impractical parameter to use. BOD5 is generally in the range
of 60 percent to 70 percent of BODu (Metcalf & Eddy, 1991).
COD analysis is a quick test that gives the maximum value for the oxygen that is
needed for chemical oxidation of all materials in the wastewater. In the COD test, a
wastewater sample is placed in a flask containing chromic acid (dichromate ions and
sulfuric acid), a strong oxidizing solution. After heating the sample-oxidant mixture on a
burner for 2 hours, the mixture is removed and the amount of dichromate remaining is
determined through titration. The amount of dichromate depleted during the test is
proportional to the COD of the sample (Metcalf & Eddy, 1991).
Aerobic bacteria use metabolisms that are different from those of anaerobic bacteria.
BOD is a measure for the activity of aerobic bacteria and is consequently not well suited
for determination of organic carbon loadings in an anaerobic environment. In addition, a
5-day BOD test will not fully degrade all of the biological material (especially proteins and
fatty acids) in wastewater. The suspended solids associated with the wastewaters also
are biodegradable and their ultimate BOD would not be exerted in the 5 days it takes to
run a standard BOD test. Consequently, for CH4, an emission factor based on COD
should be a better predictor of emissions than an emission factor based on BOD.
For wastewaters that contain only readily degradable organics, the BOD5 is equal to
the COD. When the wastewater contains organics that are not readily degradable over a
five day period, the BODu will be equal to the COD and the BOD5 will be significantly
lower than the COD. Also, if a significant concentration of inorganic compounds, such as
metal salts, is present, the COD will be higher because the oxidation of these compounds
also requires oxygen. For the purpose of studying GHG emissions from anaerobic
wastewater, this fact may not necessarily be of great significance, because wastewater
4
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with high inorganic loadings would likely be treated with physical or chemical methods as
compared to biological methods and would, therefore, not be a source of the major GHGs
(i.e., CH4 and N20). Table 1 includes empirical COD/BOD5 ratios for different types of
wastewater.
TABLE 1. COD/BOD RATIOS FOR WASTEWATER
INDUSTRY
COD/BOD5
Ratio
INDUSTRY
COD/BODb
Ratio
Beef, Pork, Poultry Slaughtering
and Processing1
3
Grain Processing, Starch
Production1,2
1.7 - 2
Dairy Products1
2
Fish Processing'
1.5
Edible Fat and Oil Processing1
1.5
Vegetables, Fruit Processing1
1.5
Sugar Refining1
1.5
Soft Drinks, Juices Production1
2.5
Coffee Processing1
3
Alcohol Production1
3
Fermentation (Yeast)2
2.5
Beer Brewing1,2
1.5 - 2.5
Paper, Pulp Production2
2
Raw Sewage3
2 - 3
From Lexmond and Zeeman (1995) (no ranges provided).
From Paques (1994) (no ranges provided).
From Lettinga, et al. (1983) and Metcalf & Eddy (1991).
5
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FIELD MEASUREMENT OF GHG EMISSION RATES AT FIVE WWT LAGOONS
In 1995, Radian Corporation and E.H. Pechan & Associates under contract with
APPCD conducted field tests at five WWT lagoons in the Midwestern, Southwestern, and
Southeastern United States. The objective of the tests was to develop emission factors for
each target compound. The target compounds of interest included CH4, C02, N20, as well
as CO, and certain VOCs. The technique used to perform ambient air measurements was
an OPM/TM approach with a FTIR spectroscopy instrument. Simultaneously, process
data were collected to characterize the influent and effluent wastewater at the field sites.
The field work involved being on site for about five days at each facility. Ambient
air measurements were made immediately upwind and downwind of the lagoons. The
FTIR light beam was directed along a path of several hundred feet and the absorbance of
gases was measured. Emission rates were determined from measurements of the ambient
concentrations and the atmospheric dispersion characteristics at the time of sampling. In
addition, a limited number of influent and effluent wastewater and sludge samples were
collected. The field test results are documented in a separate report (Eklund and
LaCosse, 1997).
SITE SELECTION
Site-selection criteria were developed to identify those industries and WWT processes
that have the greatest potential for measurable emissions of CH4 and other GHGs. The
site-selection criteria include:
• WWT system is likely to emit CH4 or other GHGs;
• Facility type is among those treating the largest annual mass of BOD/COD in
wastewater;
• WWT at specific site of interest is representative of practices within the
industry or is representative of WWT practices in developing countries;
• Influent BOD/COD loadings are relatively high;
• BOD/COD removal primarily occurs in lagoons;
• Site terrain is conducive to Gaussian plume dispersion (reasonably level
terrain, few windflow obstructions such as buildings and trees, low berms
around the lagoons or low tanks, etc.);
• No or few other significant emission sources in the area;
• Access around the lagoon for easy set-up of sampling equipment;
• Access for collecting influent and effluent samples; and
• A high degree of cooperation from the on-site WWT operators.
Site selection focused on U.S. WWT systems that employ open, anaerobic lagoon
processes to achieve high levels of BOD or COD removal. First, industries that treat
large volumes of wastewater and remove large amounts of BOD/COD were identified
using published information sources. Then, additional information was collected from
EPA regulatory personnel, project files, and reports and researches in the WWT field to
identify which industries were most likely to treat wastewater to remove high levels of
6
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BOD/COD in open, anaerobic lagoons, and to identify the most promising sites for
sampling. The most promising candidates were beef and poultry processing plants and
pulp and paper mills. Municipal WWT plants, often referred to as publicly owned
treatment works (POTWs), also were of interest because they are used to treat a
significant fraction of wastewater both nationally and globally and, also, they were
thought to be a potentially significant source of N20 emissions.
Five sites were selected for testing: two beef processing plants, one chicken
processing plant, and two POTWs. Two beef processing plant sites and two POTWs were
included to help determine the variability in emissions within a given category. Pre-
sampling surveys were conducted at these sites to confirm that they met the site-selection
criteria for sampling. All testing took place during summertime conditions.
RESULTS
OPM/TM using FTIR spectroscopy was used to determine emission rates. A very
large data set was generated, and up to 300 separate valid, 5-minute average emission
rate determinations were made at a given site. The air measurement data were reviewed
to identify those compounds found in significantly greater concentrations in the downwind
air versus the upwind air at each site. Any such compounds were likely to have been
emitted from the lagoons being tested. Many of the target analytes were found at the
same concentration levels upwind and downwind of the lagoons (i.e., they had no
quantifiable emission rate). Only CH4 and the SF6 tracer gas generally were present in
greater amounts in the downwind air.
The minimum quantifiable emission rate varied from site to site and from one
5minute period to another. The detection limit for a given compound, in terms of g/sec, is
dependent on the smallest difference between downwind and upwind concentrations that
could be identified apart from the measurement variability within each of the upwind and
downwind data sets. For each increment of 0.5 ppmv (500 ppbv) that a given compound
was present in greater concentrations downwind than upwind, its emission rate was about
1 g/sec (depending on the molecular weight of the compound). Typical detection limits
were about 0.1 g/sec for most compounds, except for C02, which had a minimum detection
limit of about 150 g/sec. The high detection limit for C02 was due to the high background
concentrations (e.g., up to 500 ppmv) and the measurement variability (e.g., % CV =
7.5 percent, or 37.5 ppmv).
At all three meat processing plants, large amounts of CH4 were measured downwind
of the WWT system. For the two beef processing plants, the concentration of CH4
exhibited an exponential-type relationship with wind speed. The downwind CH4
concentration at the chicken processing plant did not show a clear relationship between
concentration and wind speed. At the chicken processing plant, however, the range of
wind speeds was much smaller than for the meat processing plants and the number of
valid measurement periods also was much smaller, making it more difficult to identify
trends and relationships. There also was a thick grease layer present on top of the lagoon
which would tend to diminish the effect of surface winds on air emissions and which may
have affected the emission rates in other ways also. For example, the grease layer may
7
-------
trap certain emissions and release these periodically. The emission rates measured at
each site for CH4 and other selected compounds are given in Table 2.
TABLE 2. MEASURED EMISSION RATES OF SELECTED COMPOUNDS FOR EACH
FIELD SITE
SITE
GAS
AVERAGE
DOWNWIND
CONC.
AVERAGE
UPWIND
CONC.
MAXIMUM
DOWNWIND
CONC,
AVERAGE
EMISSION
RATE
PPm
ppm
ppm
g/sec
Beef Processing Plant
in SW U.S.
ch4
61.9
2.3
142
280
Beef Processing Plant
in Midwest U.S.
CH,
58.1
2.83
200
230
Chicken Processing
Plant in SE U.S.
ch4
9.80
1.92
29.9
180
n2o
563 ppb
542 ppb
586 ppb
2.6
POTW for Small Town
in Southwest U.S.0
CH„
2.20
2.14
2.46
<0.15
O
o
ro
342
351
384
<150
POTW for Very Small
Town in Southwest
U.S.3
ch4
2.11
2.16
2.81
<0.15
o
o
ro
528
668
691
<150
Methane and carbon dioxide values are shown for the POTWs for comparison purposes. No quantifiable
emissions of these compounds were detected at either POTW.
The field tests detected significant N20 emissions only at the anaerobic chicken
processing waste lagoon. No emissions (i.e., < 0.1 g/sec) were detected from the anaerobic
waste lagoons at the two beef processing plants or the facultative lagoons at the two
POTWs.
Surprisingly, no quantifiable emissions were detected from the POTW lagoons. It
was expected that either CH4 or C02 or both would be detected at greater concentrations
downwind versus upwind. The dissolved oxygen (DO) level in the lagoons exceeded
2 mg/L, indicating that BOD removal is taking place under aerobic conditions. So it is
highly probable that C02 is being generated, but the levels were too small to detect given
the very high background levels of C02 and the measurement variability. In general,
anaerobic degradation can be expected to produce a mixture of CH4 and C02 (generally
somewhere between a 50:50 and a 70:30 ratio). Therefore, emissions of C02 would be
expected wherever quantifiable emission rates of CH4 were found. The lack of
quantifiable C02 emission rates may be due to the high detection limit for C02 emission
8
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rates, as previously discussed. The absence of C02 emissions also could be due to the
consumption of C02 by cyanobacteria (blue-green algae) in the lagoons.
The wastewater data for all three meat processing plants are very similar, with the
two beef processing plants showing very good agreement. All three WWT systems have
high BOD removal rates (88-95 percent), as well as high removal rates for COD, total
organic carbon, and nitrates.
The two POTWs had similar influent wastewater and exhibited similar performance
in terms of removal of BOD, COD, and total organic carbon. Both systems generated
nitrates as a by-product of biodegradation.
Activity factors were developed for each site based on information provided by the
plant operators and from the wastewater data. Emission factors were developed for each
site by dividing the average emission rates by the activity factors for each site. The
various resulting emission factors are given in Table 3. 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
random error in the measurements, and assuming that the sites and samples accurately
represent the population of interest.
TABLE 3. AVERAGE EMISSION FACTORS FROM FIELD TESTS
COMPOUND
EMISSION FACTOR
AVERAGE
RANGE
Methane
g CH„/head of cattle
4,200
3,500 - 4,800
g CH4/chicken
120
n/a
g CH„/kg meat
37
15 - 74
g CH4/L of wastewater
2.7
1.6 - 4.6
g CH„/g influent BOD
1.5
0.40 - 3.2
g CH„/g BOD
1.6
0.43 - 3.4
g CH„/g COD
0.96
0.26 - 2.0
Nitrous Oxide
g NsO/chicken
1.8
N/A
g N20/kg meat
1.1
N/A
g N20/L of wastewater
0.067
N/A
g N20/g BOD
0.051
N/A
g Total Kjeldahl Nitrogen (TKN)
1.7
N/A
N/A = Not applicable
It is possible that the lagoons are a sink for suspended and colloidal material (i.e.,
insoluble BOD) and this material builds up over time in the lagoon sediments. If so, the
degradation of the sediments may occur during summer months or whenever the sediment
9
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is resuspended, thereby increasing the CH4 (and C02) emissions. However, no seasonal
trend is evident in the BOD effluent levels in the long-term wastewater data provided by
the plants. A discussion on the theoretical effect of lagoon water temperature on the
organics removal rates and GHG emissions is provided in Appendix C of this report.
CONCLUSIONS
Several conclusions can be drawn from the study:
• The OPM/TM FTIR measurement approach used in this study was successful for the
simultaneous collection of large amounts of ambient concentration data for CH4;
• The use of the OPM/TM FTIR technique for estimating emission rates from the
lagoons had insufficient sensitivity for certain compounds, such as H2S and VOCs,
due to limitations in the FTIR analysis. For most of the sites, the sensitivity for C02
was limited by the high background concentrations and the variability in the
background concentrations;
• Anaerobic WWT lagoons are a significant source of CH4 emissions; and
• Lagoons at POTWs are not a significant source of any GHGs, with the possible
exception of C02.
10
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ADDITIONAL INFORMATION ON GHG EMISSIONS FROM WWT
METHANE AND CARBON DIOXIDE
This section contains stoichiometric decomposition models that were used to develop
theoretical emission factors for CH4 and C02. Four literature sources were found that
included data on CH4 and C02 emissions from wastewater and summaries from these
studies are included as well.
Stoichiometric Decomposition Models
Theoretical emission factors for CH4 and C02 emissions from wastewater can be
calculated using simple, stoichiometric decomposition models that represent ultimate
decomposition analysis. Two models are presented, one for anaerobic and one for aerobic
environments. The models assume that sludge and bacterial cell mass in the wastewater
are steady state and provide two variants as a surrogate for average domestic sewage;
glucose (C6H1206) and the average stoichiometric composition of new bacterial cell matter,
as in fresh sludge (represented by C5H702N) (Metcalf & Eddy, 1991, p. 379).
The organic matter in domestic wastewater can be divided into three main classes:
proteins, carbohydrates, and fats. Proteins make up between 33 and 50 percent and will
usually have a carbon content that is somewhat higher than that of glucose, due to their
hydrocarbon chains. However, according to Mudrack and Kunst (1986), it is acceptable to
represent carbohydrates and fats by glucose.
The theoretical emission factors that are calculated here do not take other competing
degradation mechanisms into account. For example, oxygen may also be required for
oxidation of nitrogen, phosphorus, or sulphur compounds. Oxygen required for these and
other processes will increase COD values. On the other hand, the carbon content of
glucose is 40 percent by mass, whereas the carbon content of human feces is higher (40 to
55 percent) (Gloyna, 1971). Due to the higher carbon content, CH4 production from feces
can be expected to be higher than that of an equivalent mass of glucose. The increase in
CH4 generation is offset by the increase in COD to a certain degree. More information is
required to assess whether the theoretical emission factor representing real sewage differs
from the one for glucose.
Model 1: Anaerobic Process (Complete Reaction)—
Glucose
The anaerobic decomposition of glucose is represented by: C6H1206 —>3 C02 + 3 CH4.
One mole of glucose weighs 180 g and produces 3 moles of CH4, which weigh 3 x 16 =
48 g. Therefore, the CH4 production rate per gram of glucose is 48 -4- 180 = 0.27 g. The
oxidation of one mole of glucose requires six moles of oxygen (equal to 192 g), [i.e., the
BOD,j, as well as, the COD of one mole of glucose is 192 g (C6H1206 + 6 02 —> 6 C02 + 6
H20)]. Therefore, the COD of one gram of glucose 192 -f- 180 = 1.07 g 02. Accordingly,
one gram of COD correlates with 0.27 -r 1.07 = 0.25 g of CH4, which is the emission factor.
11
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As mentioned before, this model assumes that all BOD is degraded over time and the
amount of sludge and cell matter is steady state.
The C02 emission factor can be calculated in a similar way. Under anaerobic
conditions, for every gram of glucose (3 x 44) 4- 180 = 0.73 g of C02 is produced.
Accordingly, the emission factor is 0.73 -r 1.07 = 0.69 g C02 / g BOD.
Average Bacterial Cell Matter
The CH4 emission factor was also calculated for new bacterial cell matter in
wastewater, which may be expressed as C5H702N and is used as a surrogate for domestic
sewage. The complete anaerobic decomposition of any organic compound containing C, H,
O, and N is represented in Equation 3.
CaHbOcNd + [(4a-b-2c+3d)/4]HzO ^[(4a+b-2c-3d)/8]CH^[{4a-b+2c+3d)/8]C02+(d)NH^
For CsH702N, Equation 3 may be rewritten as:
2 C5H7OzN + 6 H20 —>5 CH4+ 5 C02 + 2 NH3 (4)
One mole of C5H702N weighs 113 g (dry) and produces IVi moles of CH4 equal to
40 g. Therefore, for every gram of average dry sewage, 40 113 = 0.35 g of CH4 is
produced.
c5h7o2n + 602 -»5C02 + 2HzO + NH3 (5)
As Equation 5 indicates, one mole of C5H702N requires 6 moles of 02 equal to 192 g
COD, (i.e., the COD of C5H702N is 192 -f 113 = 1.70 g). Thus, for every gram of CH4
produced, 1.70 g of COD are required and the emission factor thus becomes 0.35 -f- 1.70 =
0.21 g CH4 per gram of COD.
The C02 emission factor can be calculated in a similar way. For every gram of
C5H702N, (5 x 44) -j-113 = 1.95 g of C02 is produced. And for every gram of C02
produced, 1.70 g of COD is required. Accordingly, the emission factor is 1.95 -r 1.70 = 1.15
g C02 / g COD.
Model 2: Aerobic Process—
Glucose
The aerobic decomposition of glucose is represented by: C6H1206 + 6 02 —>6 COz +
6 HzO. For every gram of glucose, 264 -r 180 = 1.47 g of C02 is produced. As before, for
every gram of glucose, 192 -r 180 = 1.07 g 02 (COD) are needed. Accordingly, the emission
factor is 1.47 - 1.07 = 1.38 g CH4/ g CODremoved.
12
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Average Bacterial Cell Matter
The complete aerobic decomposition of any organic compound containing C, H, O,
and N is represented in Equation 6.
CaHbOcNd + [{Aa+b-2c-3d)/A\02 ->aC02 + [(b-3d)/2]H20 + bNH3 (6)
or, for C5H702N:
C5H702N + 502 ->5C02+ 2 HzO+ NH3 (7)
One mole of C5H702N weighs 113 g and produces 5 moles of C02, which weigh 5 x 44
= 220 g. Therefore, for every gram of average C5H702N, 220 -5-113 = 1.95 g of C02 is
produced. One mole of C5H702N requires 5 moles of 02 or 160 g. So, for every gram of
C5H702N, 160 -f 113 = 1.42 g of 02 (COD) are needed and the emission factor thus
becomes 1.95 -r 1.42 = 1.37 g C02/ g COD.
Table 4 summarizes the theoretical emission factors that were developed in this
chapter. Based on the CH4 emissions data in Table 4, it becomes apparent that the
0.22 g/g BOD number introduced by Orlich and used in prior reports is likely to have been
derived from similar calculations. One other theoretical value was found in the literature;
Viraraghavan and Kikkeri (1990) report a theoretical maximum value of 0.3 m3 CH4 per
kg COD for dairy wastewater at standard temperature and pressure. This converts to
0.21 g/g COD. Note that although "new bacterial cells" have a higher mass percentage of
carbon than glucose, the CH4/g COD emission factor is lower.
TABLE 4. THEORETICAL CH4 AND C02 EMISSION FACTORS
ANAEROBIC
DECOMPOSITION
AEROBIC
DECOMPOSITION
g/g COD or g/g BODu
Sewage composition
represented by:
ch4
o
o
C02
C6Hi2°6 (glucose)
0.25
0.69
1.38
C5H702N (new bacterial
cells in wastewater)
0.21
1.15
1.37
Average
0.23
0.92
1.375
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Summaries of Four GHG Wastewater Studies
Only three references were found that describe field tests to measure C02 and CH4
from WWT plants. Also, one manufacturer of anaerobic digester systems provided useful
C02 and CH4 data. Pertinent information is summarized below.
Field Test at U.S. Activated Sludge POTW—
Field tests were conducted at an activated sludge POTW in Durham, New Hampshire
over a period that ran from mid-winter to summer (Czepiel et al.; 1993.) The average
influent concentration at the plant is approximately 250 mg BOD5/l and the average
removal efficiency is 94 percent. Significant amounts of C02 were detected and some CH4
was also measured. Depending on the location in the plant different sampling techniques
were used. To take samples from nonaerated surfaces, a closed chamber technique was
used, whereas, a bag technique was used for emissions from aerated surfaces. Because
the plant is aerated (with the exception of the sludge digestion) it may be that the CH4
emitted was already present in the sewage and is merely stripped from the liquid. This
indicates that anaerobic decomposition must have taken place in the sewer lines.
As the degree of aeration is not specified, the CH4 emissions may only be
extrapolated to similar types of treatment plants. The CH4 and C02 emission rates from
Czepiel et al. are given in Table 5. Total BOD5 related emission factors for C02 and CH4
may be calculated by dividing the total yearly gas emission rates by the average total
yearly BOD that is removed. The emission factors for CH4 and C02 are 1.7 x 10"3 g CH4/g
BOD and 1.5 g COJg BOD, respectively.
Czepiel et al. include an estimate of U.S. CH4 emissions from domestic WWT and
anaerobic sludge digestion. They estimate that CH4 emissions from primary treatment
are 6,000 Mg/yr and from aerated sludge treatment, 8,000 Mg/yr (total of 0.014 Tg/yr).
The total yield from anaerobic sludge digestion is estimated at 0.84 Tg/yr. If it is
assumed that 10 percent of this CH4 leaks to the atmosphere, the total CH4 emissions
from domestic WWT would be 0.1 Tg/yr or 0.2 to 0.4 percent of total anthropogenic U.S.
CH4 emissions [Total emissions based on U.S. EPA (1994) and U.S. DOE (1994)].
14
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TABLE 5. DATA AND CH4 AND C02 EMISSION RATES FOR POTW IN DURHAM, NH
WWT
RETENTION
TIME
INFLOW
ch4
co2
REMARKS
hrs
l/day
g/yr
g/yr
Grit removal
chamber (aerated)
0.3
3.0*106 with
bod5 =
250 mg/L
0.6*105
0.4*107
Stripping of gases already
present in sewage
Primary settling
tank
2.6
0.9*105
0.1 *107
Possibly some CH4
generation
Aeration tank
16
2.2*105
36*107
Inoculation with sludge,
stripping of CH„;
C02 generation
Secondary settling
tank
10
CH4 generation is likely,
no tests were performed
Sludge holding
(partially aerated)
72
0.6*105
2.1*107
Stripping of CH4; C02
generation
Total
4.3*105
39*107
BOD5 removal efficiency
= 94%
Biogas Measurements at an Anaerobic Lagoon in Portugal—
Toprak (1995) describes a field-study at a WWT plant in Portugal. Domestic
wastewater at a community of 30,000 people is treated in a system of lagoons that
consists of one anaerobic, three facultative, and one polishing lagoons. The system is
designed for 1,200 m3/day. There are 53 such systems in Portugal and another 40 are
under construction, indicating that this type of domestic WWT is suitable for a country
such as Portugal. At the anaerobic lagoon, biogas was collected with a small flux chamber
and composition and production rates, as well as wastewater characteristics, were
recorded over a period of 62 days. From the field test results, Toprak developed a varied
range of empirical equations which are included below.
COD removal rates
The mean COD loading rate at the anaerobic lagoon was 0.17 kilogram (kg)/cubic
(m3)/day. This value is lower than the maximum design capacity of 0.42 COD kg/m3/day.
The COD removal efficiency (r|) varied between 30 and 68 percent and was dependent on
temperature. From the field data, Toprak developed a first-order kinetic model for COD
removal. The model is based on the assumption that an anaerobic lagoon is a completely
mixed reactor (Equation 8).
15
-------
(1 + t * kzQ* 67""20)
(8)
where: C0 = influent COD concentration (mg/L);
C = effluent COD concentration (mg/L);
t = mean hydraulic retention time (HRT) (days);
k20 = COD removal rate constant at 20°C (0.221 day"1);
0 = temperature correction factor (1.117); and
T = water temperature in the pond (°C).
Biogas emissions and composition
Biogas rates varied considerably, depending on influent COD loading rate, and
especially on ambient air temperature. Biogas consisted predominantly of CH4, C02, and
atmospheric N2. The CH4 component varied between 50 and 82 percent with a mean
value of 71 percent. The lowest value was achieved on days with rain. Apparently, the
rain contributes to a significant increase in dissolved oxygen. Weekly averages of biogas
emissions and composition and weekly COD removal rates were used to develop emission
factors. For CH4 the mean emission factor was 0.145 m3/kg COD, which may be converted
into 0.10 g CH4/g COD, using the ideal gas law at 20°C. Toprak remarks that this is
39 percent of the theoretical maximum value and suggests that part of the difference is a
result of the conversion of carbon into new cells. Also, the measurement techniques may
have contributed to errors and low CH4 collection rates.
Global CH4 and C02 Emissions for the Food and Beverage, and Pulp and Paper
Industries—
Lexmond and Zeeman conducted a study to determine the theoretical maximum
global CH4 and C02 emissions for domestic wastewater and wastewater from two industry
sectors, the food and beverage industry and the pulp and paper industry. Preliminary
findings of their study are summarized in Lexmond and Zeeman (1994), a more detailed
report was published in 1995 (Lexmond and Zeeman, 1995). Although the estimates are
based on a desk study using pilot scale digester test data, the report is of particular
interest because of the well developed methodology and the novel activity data.
Lexmond and Zeeman estimate that wastewater from domestic sources and from the
food and beverage and the pulp and paper industries represents over 70 percent of total
biodegradable matter present in all industrial wastewater. They further estimate that
global CH4 emissions from wastewater and wastewater sludge are between 5 and 10 Tg/y.
Uncontrolled anaerobic digestion of untreated wastewater in developing countries is
considered to be the largest source. In their report, Lexmond and Zeeman do not include
an estimate of global C02 emissions from wastewater.
16
-------
The paper and report include a methodology which uses the parameters listed in
Table 6. This methodology is similar to the one that was adopted in this document.
Lexmond and Zeeman conclude that production and utilization of digester gas would offset
a significant amount of C02, although losses from CH4 escaping to the atmosphere must
be held to a minimum.
TABLE 6. ACTIVITY DATA FOR THE PULP & PAPER AND
FOOD & BEVERAGE INDUSTRIES
DESCRIPTION
UNITS
REFERENCES,
REMARKS
PULP &
PAPER
FOOD &
BEVERAGE
Annual production
kg/yr or
m3/yr
United Nations,
Industrial Statistics
Yearbook
Wastewater
outflow =
21.2*109 m3/y
Wastewater
outflow =
7.4*109 m3/y
Wastewater per unit of
product
m3/kg or
m3/m3
Multiple references
COD for "fresh"
wastewater
g/m3
Multiple references
2,200
5,600
Fraction treated by
certain method
%
Lexmond assumes two cases: 100% aerobic and 100%
anaerobic.
Maximum CH4 producing
capacity
m3/kg
COD
Multiple references
0.026
0.31
COD removal efficiency
%
Assumption
90
90
Biological sludge yield
%
40% for aerobic systems, 10% for anaerobic systems
Empirical Anaerobic Digester Data—
Paques Environmental Technology, a manufacturer of anaerobic digester systems,
has sold and installed hundreds of anaerobic digesters at various industries and
municipal WWT plants around the world. Empirical information collected by Paques for
the beer, potato, starch, yeast, paper, and wood pulping industries is summarized in
Table 7, which includes BOD5, COD, and biogas production and composition data. These
data were used to calculate CH4 emission factors expressed in g CH4 /g COD and some of
the COD/BOD ratios in Table 1 in the Introduction.
17
-------
TABLE 7. EMPIRICAL WASTEWATER AND BIOGAS DATA FOR SIX INDUSTRIES
INDUSTRY
¦ COD
influent
BODs
COD
removed
BIOGAS
PRODUCTION
(ANAEROBIC)
BIOGAS
COMPOSITION
EMISSION FACTOR1
mg/L
x100
mg/L
x100
%
m3/
kg CODnmoved
ch4
%
C02
%
H2S*
%
g CH4 /
g CODnmov,d
Brewery
15-70
10-45
75-90
0.4-0.45
80-85
15-20
1-2
0.25
Potato
Processing
40-160
24-70
70-80
0.45-0.55
45-55
45-55
0.1
0.163
Wheat Starch
Production
15-420
9-255
65-85
0.45
70
24
0.5-
1.0
0.206
Yeast
Wastewater
65-160
30-60
65-70
0.2-0.3
60-70
30-40
1-3
0.106
Paper
Production
15-80
7.5-40
75-85
0.45
80
19
1
0.235
Pulping
20-150
10-75
50-65
0.4
75
24
1
0.196
Notes: 1 Based on ideal gas law at 25°C: 1 mole = 24.5 liters.
2 Hydrogen sulfide.
-------
VOLATILE ORGANIC COMPOUNDS
VOC emissions from municipal WWT plants have received attention because they
are a potential health hazard to plant personnel. Also, VOCs are precursors to ground-
level ozone formation. Not all VOCs are GHGs. A group of potent GHG/VOCs are the
halocarbons, which include:
• Chlorofluorocarbons (CFCs);
• Bromofluorocarbons (halons);
• Hydrochlorofluorocarbons (HCFCs);
• Hydrofluorocarbons (HFCs);
• Perfluorocarbons (PFCs); and
• Other related compounds.
Halocarbons and related compounds are powerful GHGs with, in most cases, very
high radiative forcing potentials. CFCs, halons, and some other related compounds are
being phased out in 1996, under the Rio Treaty and Montreal Protocol. HCFCs are less
stable than CFCs and consequently do not contribute as much to stratospheric ozone
depletion. Many HCFCs are toxic and are to be phased out in 2015 under the Clean Air
Act Amendments of 1990, as well as, the Montreal Protocol. HFCs have no chlorine and
thus have no effect on the ozone layer. This makes them strong, unambiguous GHGs.
For instance, HFC-134a, a CFC-replacer used in car air conditioners, has a radiative
forcing potential of 4,300 relative to C02. PFCs are strong GHGs and are emitted as a by-
product from aluminum smelting.
Chlorine containing compounds (including CFCs and HCFCs) tend to react with
tropospheric ozone (which is also a GHG) and may, as such be contributing to GHG
reduction (sink). The net global warming effect of these gases is unclear at this time.
Unfortunately, no quantitative information was found on GHG/VOCs that are
emitted from WWT. Five VOCs that were detected in wastewater air emissions are also
known GHGs [US Department of Energy (DOE), 1994], (Table 8). Other VOCs that have
been detected in air emissions from WWT may also be GHGs, although little information
was available to verify this. The VOCs most commonly found in wastewater (i.e.,
benzene, toluene, and xylenes) are not known to be GHGs. The ensuing discussion of
data found in the literature is geared towards VOC emissions from WWT, regardless of
their radiative forcing potential.
19
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TABLE 8. VOC-GHGS DETECTED AT U.S. POTWS
GREENHOUSE
GAS
GLOBAL WARMING
POTENTIAL
(CO, = 1)
PRINCIPAL USES
Dichlorodifluoro-
methane
8,300
Auto air conditioners, Chillers,
Blowing agent
Trichlorofluoro-
methane
3,900
Blowing agent, Chillers
Carbon tetrachloride
1,400
CFC feedstock, Solvents
Methylene chloride
10
Solvent
Chloroform
5
HCFC feedstock.
There are many different VOCs found in wastewater. Mihelcic et al. (1993) includes
a list of 32 VOCs that have been detected in air emissions at U.S. POTWs that receive
domestic and industrial wastewater. Industrial and commercial operations are the
predominant source for VOC loadings to POTWs. Predominant chemicals contributed by
industry are benzene, toluene, and xylenes; and to a lesser degree, methylene chloride,
trichloroethylene, and carbon tetrachloride (chloroform). Benzene, toluene, and xylenes
can be associated with petroleum refining operations, whereas, the other VOCs are
typically used as strippers and/or industrial solvents. Chloroform may have a potential to
be formed during chlorination of drinking water. No information was retrieved on
industrial wastewater characteristics and potential VOC emissions for industrial
wastewater that is treated on-site. The discussion in this chapter only pertains to VOC
emissions from municipal WWT plants.
The three primary VOC removal processes from wastewater are stripping or
volatilization, biodegradation, and sorption. In studying air emissions from WWT,
stripping is the removal mechanism of principal interest. A significant fraction of VOCs
discharged into public sewers may be stripped from the wastewater before it reaches the
WWT plant. Quigley and Corsi (1995) measured emissions for total VOCs including
benzene, toluene, xylenes, and tetrachlorethene from an interceptor in Toronto, Canada.
Measurements included, average emissions of total nonmethane hydrocarbons from a
single manhole which amounted to 2.3 Mg/yr. Quigley and Corsi also compared emissions
of several VOC species from the interceptor to those from three local POTWs in Toronto,
Canada. For all but one species, emissions at the interceptor were higher than at the
POTW. Because sewer structures can vary greatly, accurate models for estimating VOC
emissions from sewers are difficult to develop. Emissions of VOCs from sewers will
depend on the solubility of the VOC species in water, the layout of the sewer, and the
degree of ventilation and contact with the atmosphere. At municipal WWT plants,
primary treatment processes such as aerated grit chambers, and equalization basins,
especially those that require mechanical aeration, are considered to be VOC emission
sources.
20
-------
Many VOCs are also highly biodegradable. Wood et al., (1990) studied the behavior
of VOCs at a WWT plant at an organic chemicals manufacturing site and conclude that,
"a significant percentage of the pollutant loss across the equalization basin can be
accounted for by biodegradation or mechanisms other than volatilization." Hentz et al.,
(1996) state that at three Philadelphia POTWs over 85 percent (by weight) of 18 targeted
VOCs was biodegraded. Generally, in WWT plant environments, nonchlorinated VOCs
such as benzene, toluene, and xylenes are biodegradable, whereas, chlorinated VOCs are
regarded as recalcitrant. However, there is increasing evidence that some chlorinated
VOCs are also amenable to biological degradation. The three Philadelphia plants studied
by Hentz have a combined maximum capacity of 23.4 m3/sec (500 mgd) and total VOC
emissions were 9.16 Mg/yr. In another study, Chang et al. in Mihelcic et al. (1993)
estimated that 13 out of 589 Californian POTWs emit more than 9.1 Mg of 16 targeted
VOCs annually. Total VOC from WWT emissions data for California were not retrieved,
but combined POTWs in Los Angeles County were estimated to emit 429 Mg annually.
NITROUS OXIDE
Nitrification and denitrification processes are an integral part of comprehensive
WWT. Both processes are thought to be capable of producing N20, however,
denitrification may be considered the dominant mechanism in N20 formation (Debruyn et
al., 1994). For both nitrification and denitrification a carbon source is required for cell
growth and nitrification also requires oxygen. Nitrification ( NH4+ —> N02" —> N03") is the
first step in nitrogen removal and takes place in aerobic reactors such as trickling filters
or rotating biological contactors, either separate or in combination with carbonaceous
matter removal. Nitrifying bacteria are sensitive organisms and are extremely
susceptible to a wide variety of inhibitors.
During denitrification (Equation 9), N20 is formed as an intermediate product and is
usually consumed within cells, although some species excrete N20 without further
reduction (Hanaki et al., 1992). Denitrification is the second step in nitrogen removal and
takes place under anoxic conditions. The presence of dissolved oxygen will inhibit the
process, however, denitrification may not be described as an anaerobic process. The
biochemical pathways are modifications of aerobic pathways (Metcalf and Eddy, 1991).
As with nitrification, denitrification organisms are sensitive to changes in temperature
and pH. Usually, an extra carbon source is required for cell growth.
NO3 ~^NO'2 -»A/0 N20 ->Nz (9)
Hanaki et al. (1992) researched N20 emissions during denitrification from
wastewater under steady-state, laboratory conditions. Substrate containing acetate and
yeast extract (1,000 ml COD), and potassium nitrate as a nitrogen source was
continuously fed to three liter flasks containing return activated sludge from a WWT
plant. The potassium nitrate concentration, pH, and hydraulic retention time (HRT) were
varied in different experiments. It was found that favorable conditions for N20 production
21
-------
were a relatively low pH, a low COD/nitrogen (as N03) ratio, and a short HRT (i.e., less
than one day). At pH = 6.5, N20 production was significantly higher than at pH = 7.5.
Hanaki et al. conducted four sets of tests with COD/nitrogen (as N03) ratios6 of 4.5,
3.5, 2.5, and 1.5, respectively and HRTs varying from 0.5 to 10 days. The pH of the
substrate was between 7.5 and 8.5. With a COD/nitrogen (as N03) ratio of 4.5, no N20
was detected in the emitted gas at any point during the experiment. With the
COD/nitrogen (as N03) ratio being 3.5, approximately 1 percent of N20 and 99 percent N2
was detected in the early part of the test. With the COD/nitrogen (as N03) ratio being 1.5
and a HRT of 5 days, the percentage of N20 peaked at 19 percent, but decreased again to
11 percent toward the end of the test.
Next, Hanaki et al. extended the HRTs for the tests with COD/nitrogen ratios of 1.5
and 2.5. For the COD/nitrogen = 1.5 test, increase of the HRT from 5 to 7 days resulted
in a rapid decrease of the N20 concentration from 11 percent to 6.5 percent. Further
increase of the HRT to 10 days resulted in final N20 concentrations of less than
0.6 percent (COD/nitrogen = 1.5 test) and 0 percent (COD/nitrogen = 2.5 test).
Knowledge acquired by Hanaki et al. indicates that NzO production probably cannot
easily be related to one single parameter of the wastewater, such as nitrogen
concentration. N20 is an intermediate product formed during denitrification and its
formation and emissions are dependent on the incompleteness of various denitrification
reactions that are governed by parameters that include pH, HRT, and feed
concentrations.7 Consequently, it will be difficult to develop accurate emission factors.
The emission factor expressed by Hanaki et al. is 0.13 gram N20 per gram nitrogen (as
nitrate). Unfortunately they do not provide other wastewater data that allow for the
development of more practical emission factors for estimating country-specific emissions
(e.g., N20 per COD or per capita).
In another study by Debruyn et al. (1994), wastewater samples were collected at
three different WWT plants. Two of these plants treated mainly domestic wastewater, the
third plant accepted a mix of industrial and agricultural wastewater. Twenty-one
samples were kept under laboratory conditions at 25°C and the N20 concentration in the
head-space of the bottles was monitored. Since the initial rate of N20 formation in the
head space is representative of the rate of formation in an open undisturbed system, this
initial rate may be used to develop an emission factor. In order to extrapolate the initial
gas production rate to an overall emission factor, Debruyn et al. use a theoretical
biochemical model referred to as the Michaelis-Menten formalism. This approach
produces an emission calibration curve for a given wastewater composition and
temperature (i.e., 25°C). By integrating the calibration curve with the Arrhenius equation
6 The COD/nitrogen (as N03) ratio in wastewater is a basic factor governing the completeness of nitrogen
oxides reduction. If the reduction is not complete, N20 will be formed. For actual denitrification, a ratio of at
least 3.5 is necessary to permit cell matter build-up.
7 Hanaki et al. concluded that N20 production can be avoided by achieving complete denitrification by assuring
high COD/NO3-N concentrations, long HRTs, and neutral to alkaline pH.
22
-------
(which expresses gas production as a function of chemical activation energy and
temperature) it is theoretically possible to produce an N20 emission factor.
Debruyn et al. proceed with statistical manipulation of the data and ultimately
produce two rough indicative emission factors for Belgian sewage water which has a
yearly mean temperature of 12.5°C. For raw wastewater, the emission factor is 23 ±
21 jig N20/g suspended solids (SS), and for wastewater, sampled after the settling tanks,
the emission factor is 770 ± 170 pg N20/g SS. The combined total emission factor is 0.8 ±
0.2 mg N20/g SS.
In another study Czepiel and others monitored N20 emissions at an activated sludge
POTW in Durham, NH (Czepiel et al., 1995). As did Debruyn et al., and Hanaki et al.,
Czepiel et al. conclude that N20 is generated in anaerobic sections of the WWT layout as
an intermediate byproduct of denitrification. Potential sources are sewer lines, primary
settling tanks, secondary clarification tanks, sludge holding tanks, and sludge transfer
pipes. At the Durham POTW it was found that mechanical aeration (stripping) was a key
release mechanism for N20. Czepiel et al. (1995) emphasize that they found no
correlation between temperature and N20 emissions. Emission factors derived from the
Durham field tests include per capita emissions of 3.2 g N20/yr and flow based emissions
of 1.6xl0"5 g N20/1 of wastewater treated for an activated sludge system. Expressed per
gram of SS, the emission factor is 0.14 mg/g SS.
23
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EMISSION FACTORS
Table 9 includes the available emission factors for GHGs from WWT. As mentioned
in the previous chapter, conclusions of the field test report assert that anaerobic lagoons
are a significant source of CH4 emissions and that facultative lagoons that treat municipal
wastewater are not a significant source of any GHGs, with the possible exception of C02.
METHANE AND CARBON DIOXIDE
CH4 emission factors based on theoretical models and on empirical industrial
digester data are within the range of 0.11 to 0.25 g/g COD. The lowest value is for
industrial yeast production wastewater, and the highest value is for brewery wastewater.
Toprak found an emission factor of 0.1 g/g COD for a municipal lagoon, which is lower
than the other emission factors for domestic wastewater. Toprak's lower value may
possibly be explained by an anticipated strong effect of local weather (rain, wind, ambient
air temperature) on dissolved oxygen levels and, hence on CH4 generation and emission
rates. Also, the lagoon water temperature varied from 17.3 to 25.3°C; the 17.3°C value is
considerably lower than the minimum for CH4 generation conditions.
The average CH4 emission factor (0.96 g/g COD) based on the APPCD field tests is
higher than all other values, although the lower range of the field test factor (0.26 g/g
COD) is within the range of the other data. The emission factor developed from the
poultry processing lagoon data is higher than the ones from the two meat processing
wastewater lagoons. If the data from the poultry processing lagoon are excluded, the
average emission factor based on the field tests would be 0.42 g/g COD.
The most likely explanation for the fact that the average APPCD field test emission
factors are higher than other factors from the literature is that the field test emission
rates also account for CH4 emissions from COD that had been deposited in the sludge
during the previous winter. Appendix C contains a discussion on the effect of water and
ambient air temperature on CH4 emissions and COD removal rates in anaerobic lagoons.
Based on this information, it is possible that emissions from a lagoon in summer in a
mediterranean climate (hot summers and fairly cold winters), such as in the field test
areas, are significantly higher than the yearly average.
For the purpose of developing CH4 emissions estimates for this report, a CH4
emission factor of 0.3 ±0.1 g/g COD was used. This factor reflects the upper end of the
range of factors based on theoretical models and empirical digester data, and the lower
end of the range of the factors developed from the field test results.
The field test report is inconclusive about C02 emissions from anaerobic lagoons.
Instead, a theoretical emission factor for C02 emissions from wastewater was used, which
is included in Table 9.
24
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TABLE 9. SUMMARY OF AVAILABLE EMISSION FACTORS
GAS
REFERENCE
D/l1
TYPE OF
STUDY
REMARKS
EMISSION
FACTOR2
ch4
This report
D
Theoretical
Anaerobic
0.21 to 0.25 g/g COD
Eklund and
LaCosse, 1997
I
Field tests
APPCD
Meat processing.
Anaerobic lagoons
0.26 - 2.0 g/g COD
Orlich, 1990;
EPA,1994
D
Limited field
study
Based on glucose.
Lagoons
0.22 g/g BOD
Toprak, 1995
D
Field tests
Anaerobic lagoon
0.10 g/g COD
Paques, 1994
I
Empirical
Anaerobic digesters. Six
types of industrial
wastewater.
0.11 to 0.25 g/g COD
Lexmond and
Zeeman, 1994
I
Full- and pilot-
scale digesters
Food & Beverage industry
0.22 g/g COD
Pulp & Paper industry
0.019 g/g COD
Czepiel et al., 1993
D
Field tests
Activated sludge plant.
1.7x10"3 g/g BODs
o
o
This report
D
• Theoretical
Aerobic
1.37 g/g COD
n2o
Eklund and
LaCosse, 1997
I
Field tests
APPCD
Chicken processing,
Anaerobic lagoon
1,700 mg/g TKN
51 mg/g BOD
89 mg/g COD
76 mg/g TSS
Schon et al., 1993
D/l
Comprehensive
literature study
Plants that employ
nitrification/ denitrification.
Anoxic process
0.08 mg/l wastewater
7,000 mg/capita/yr
Debruyn et al.,
1994
D
Laboratory
Anoxic process
Raw wastewater
Secondary wastewater
0.023 mg/g TSS
0.77 mg/g TSS
Czepiel et al., 1995
D
Field tests
Anoxic process
Raw wastewater
Secondary wastewater
0.007 mg/ g TSS
»
0.13 mg/ g TSS
Overall
3,200 mg/capita/yr
0.016 mg/l wastewater
Domestic/Industrial wastewater,
per unit removed.
VOLATILE ORGANIC COMPOUNDS
The field tests found no speciated VOC emissions and only emission factors for total
VOCs were found in the literature. Total VOC emissions from municipal WWT plants
25
-------
have been estimated as a part of several studies. Melcer (1994) describes results of the
Joint Emission Inventory Program, a working group of 22 of the 23 major POTWs in the
South Coast Air Basin. According to this program, POTWs in the Basin emitted
149 Mg/yr of VOCs which was less than 0.03 percent of basin wide emissions. As a
comparison, the two largest sources in California, solvent utilization and highway
vehicles, were estimated to emit 517,093 and 662,241 Mg in 1991 (U.S. EPA, 1993a). The
biggest point source in the United States, a chemicals plant in Kentucky, emitted
22,680 Mg/yr directly to the air (U.S. EPA, 1993b). Hence, it may be concluded that
domestic WWT is an insignificant source of total VOC emissions compared to other VOC
sources, such as highway vehicles and solvents.
Certain types of industrial wastewater (i.e., from petroleum refineries) may be a
significant source of VOC emissions. The Joint Emission Inventory Program (Melcer,
1994) found that two out of 22 POTWs tested produced unusually high VOC levels. These
were the only two facilities that accepted petroleum refinery wastewater. However, even
with the petroleum wastewater included, the POTW emissions remained significantly
smaller than emissions from other sources. No further information was available to
quantify VOC emissions from petroleum refinery wastewater.
Theoretically, relatively small emissions of specific VOCs from other industrial
processes may also be significant, due to their relatively high global warming potentials
(see Table 9). For example, dichlorodifluoromethane and trichlorofluoromethane have
global warming potentials of 8,300 and 3,900 times that of C02, respectively. The
question is, will these and other strong GHG/VOC end up in wastewater. The two
aforementioned VOCs are primarily used as blowing agents (e.g., styrofoam production)
and in chillers. These processes imply utilization of VOCs in a gaseous or volatile state
and it is unlikely that substantial amounts of these compounds would find their way into
wastewater streams. However, this assumption is based on expert judgement. To
estimate speciated emissions from industrial sources, an in-depth study of the various
industrial processes that use specific VOCs is required, accompanied by extensive testing.
Nevertheless, it may be asserted that total VOCs from WWT are insignificant compared
to other sources.
NITROUS OXIDE
As mentioned in the previous chapter, N20 is an intermediate byproduct of
decomposition of nitrogen bearing organic compounds (proteins and urea) in wastewater.
N20 is generated, as well as absorbed during denitrification and many uncertainties are
associated with the development of reliable N20 emission factors. Currently, not enough
is understood about N20 generation and emission mechanisms to develop easy-to-use N20
emission factors for WWT.
The emission factors based on data from field tests (Table 9) reflect a completely
anaerobic environment whereas the other emission factors from the literature pertain to
anoxic processes as part of conventional WWT. Therefore, the field test emission factor
and the group of literature emission factors are presented separately.
26
-------
The N20 field test emission factors are expressed as emissions per BOD, COD, total
suspended solids (TSS), and TKN. However, this report includes only comprehensive
COD data and as such, only the COD-based emission factor (i.e., 0.09 g/g COD) can be
used to estimate emissions. As insufficient information is available regarding the
uncertainties associated with the relationship between COD and N20 emissions, estimates
derived from the use of this emission factor will be speculative. This emission factor
pertains to wastewater types that contain nitrogen, including: domestic sewage; meat,
poultry, and fish processing; and dairy products. Other types of industrial wastewater are
not expected to contain much nitrogen.
Debruyn et al. (1994) and Czepiel et al. (1995) present emission factors expressed in
terms of N20 emissions per g TSS for both raw and semi-treated domestic wastewater.
Because each emission factor pertains to wastewater with different concentrations, the
emission factors cannot be added together without further modification, nor can they be
easily extrapolated. This report does not contain comprehensive TSS data and
consequently, the emission factors based on TSS were not used.
Debruyn et al. (1994) present no other emission factors with a different format.
However, Czepiel et al. (1995) modified the TSS emission factor to a per capita and per
year (capita/yr) basis. Also Schon et al. (1993) include an N20 emission factor on a
capita/yr basis. The average emission factor based on Schon et al. (1993) and Czepiel et
al. (1995) is 5.1 g/capita/yr for domestic wastewater that is treated in activated sludge
WWT plants.
Table 10 shows the emission factors that are used in this report to calculate GHG
emissions from WWT.
TABLE 10. RECOMMENDED EMISSION FACTORS
GHG
EMISSION FACTOR
APPLICATION, REMARKS
ch4
0.3 ± 0.1 g/g COD
Based on theoretical mass
balance, empirical, and field
test data.
cw
O
o
1.37 g/g COD
Based on simplified theoretical
mass balance.
n2o
0.09 g/g COD
Anaerobic WWT.
Large uncertainties.
5.1 g/capita/yr
Generic emission factor for all
wastewater treated with
activated sludge processes.
27
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ACTIVITY DATA AND METHODOLOGY DEVELOPMENT
This chapter presents the methodologies and activity data used to prepare country-
specific CH4, C02, and N20 emission estimates for industrial and domestic WWT. No
methodology was developed for estimating VOC emissions which are classified as GHGs
from WWT because, as discussed in the previous chapter, no emissions data were found
that could be used to prepare the estimates. The methodologies and activity data are
discussed together because the methodologies are limited by the type and amount of
activity data available.
Some of the data used for developing country-specific CH4 emissions estimates can
also be used to develop estimates for C02 and N20 emissions based on emission factors
that were not derived from the field tests. These estimates are limited to the
multiplication of the emission factor with the appropriate activity data and do not require
particular methodology development. The global C02 and N20 emissions estimates are
included in the next chapter with the country-specific CH4 estimates.
Equation 10 represents a generic methodology applicable to both domestic and
industrial wastewater. The emission factor to estimate CH4 emissions from WWT is
defined as a function of the amount of organic material that is biodegraded expressed in
COD (g/yr).
CHa Emissions = EF * 10'12 * P * Q * COD * TA (Tg/yi)
(10)
where: EF = Emission factor (g CH4/g CODremoved);
P = Population, or industry-specific product output (Mg/yr);
Q = Wastewater outflow (m3/capita/yr) or wastewater produced per
unit of product (m3/Mg);
COD = Organics loading removed (g/m3); and
TA = Fraction of COD in wastewater treated anaerobically.
INDUSTRIAL WASTEWATER
Basically there are three interdependent types of activity data that must be
quantified to estimate emissions from industrial WWT: country-specific, industry-specific,
and treatment-specific data (see Figure 1). Area A in Figure 1 represents country-specific
industrial outputs. Area B represents WWT methods that are typical for a certain
country or larger geographical area. For example, in South East Asia, land may be
unavailable for lagoons due to high population densities and industries would have to
make use of on-site digesters or crude disposal means, such as outfalls. Area C
represents WWT methods that may be considered typical for a certain industry.
28
-------
INDUSTRIES
COUNTRIES
Figure 1. Parameters Used to Develop Emission Estimation Methodology for Industrial
WWT.
For example, wastewater from the meat packing industry is known to decompose well
under anaerobic conditions. It may be assumed that meat packing plants that do perform
WWT are likely to make use of anaerobic techniques, regardless of their geographical
location.
Below, a qualitative and quantitative determination is made of the industrial
categories that generate wastewater with CH4 emissions. Also, in this section a
percentage to express the degree to which wastewater is treated anaerobically is assigned
to each country-specific and industry-specific commodity output data combination.
Composition and Output
Industrial wastewater results from a myriad of industrial processes which use water
for a variety of purposes, including production, refinement, transportation and handling.
The water used in the various industrial processes is usually altered considerably and
may contain contaminants including nutrients, SS, bacteria, and toxic substances, such as
VOC and heavy metals. Large quantities of water are also used for cooling purposes,
however, cooling water is not a potential source of GHGs. Some global and national
estimates for total industrial wastewater generation were found in the literature (see
Table 11).
29
-------
TABLE 11. INDUSTRIAL WASTEWATER GENERATION ESTIMATES FOR THE UNITED
STATES, CHINA, AND THE WORLD
COUNTRY
WASTEWATER
GENERATION
(1(f m3/day)
REFERENCE
REMARKS
United States
182
U.S. EPA; 1980
Manufacturing and minerals industry
(1988 data).
United States
24
U.S. EPA; 1989
Industrial to municipal WWT plants. The
difference with the above estimate implies a large
degree of on-site industrial WWT.
China
71
Zhongxiang and Yi;
1991
74% discharged without treatment. Also report a
domestic wastewater generation of 23 million
m3/day (1987 data).
World
1,300
U.S. EPA; 1994
Industrial wastewater outflow.
World
588
U.S. EPA; 1994
Same as above, but excluding Iron & Steel and
Non-ferrous metals.
Wastewater generation can be expressed in liters per unit of product and varies from
industry to industry. The amount, composition, and concentration of wastewater
produced will depend on the type of product, the type of manufacturing processes, as well
as process efficiency, regulatory requirements and compliance with the requirements, and
good house keeping. Within the same industrial category in the same country,
wastewater composition may also be highly variable. For example, wastewater from one
pharmaceutical plant may be very different from wastewater from another pharmaceutical
plant and will depend on the types of processes and raw materials used to manufacture
various products. The production process may be batch-wise with different discharges of
wastewater at different times and locations throughout the plant. There may also be
more than one wastewater stream within a plant. For instance, at a food processing
plant, highly contaminated process water may receive primary treatment on site, whereas
water from rinsing operations with limited contamination may be discharged separately to
the sewer.
Twenty-three industrial categories were identified as the potentially most significant
dischargers of wastewater with high organic COD loadings (as opposed to inorganic COD
loadings, such as metals). These 23 industrial categories are listed in Table 12. Typical
wastewater generation rates expressed in m3/Mg of product representative BOD and COD
loadings are also included in Table 12. Industrial wastewater data provide indirect
information on the efficiency of operation and on the plant output and are, therefore, often
considered confidential by plants. Normally, only BOD5, and to a lesser degree COD, are
routinely measured by plant personnel. Fortunately, BOD5 and preferably COD are also
considered to be most practical for correlation with CH4 generation.
30
-------
TABLE 12. WASTEWATER OUTFLOW AND COMPOSITION DATA FOR SELECTED INDUSTRIES
INDUSTRY TYPE
WW Gen.
WW Gen.
Range
WW Generation Reference
BOD
BOD
Range
BOD Reference
COD
COD
Range
COD Reference
units:
mJ/Mg
m'/Mg
g/i
g/i
g/i
g/i
Animal Feed
ndf
ndf
ndf
Alcohol Refining
24
16-32
Curi, 1985; Metcalf & Eddy,
1991
ndf
3-11
extrapolated from COD data
11
5-22
Hulshoff Pol et al., 1986
Beer & Malt
6.3
5.0-9.0
Merritt, 1983; Jansen, 1994
1.5
1-4
Paques, 1994; Jansen, 1994;
Merritt, 1983
2.9
2-7
Paques, 1994; Jansen, 1994;
Hulshoff Pol, 1986
Coffee
ndf
5.4
2-9
Gathuo et al., 1991
9
3-15
Gathuo et al., 1991
Coke
1.5
1.3-1.7
Dulaney, 1982; Wurm, 1974
ndf
0.1
extrapolated from COD data
0.1
Wen et al., 1991
Dairy Products
7
3-10
Merritt, 1983; Metcalf & Eddy,
1991
2.4
1-4
Viraraghavan and Kikkeri, 1990
2.7
1.5-5.2
Viraraghavan and Kikkeri, 1990;
Lettinga et al., 1980
Drugs & Medicines
ndf
0.9
Elsevier, 1991
5.1
1-10
Elsevier, 1991; Lanting and
Franklin, 1993
Explosives
ndf
ndf
ndf
Fish Processing
ndf
8-18
same as Meat & Poultry
1.5
Forsht, 1974
2.5
Forsht, 1974
Meat & Poultry
13
8-18
Eklund & LaCosse, 1997
2.5
2-3
Eklund & LaCosse, 1997
4.1
2-7
Eklund & LaCosse, 1997
Organic Chemicals
67
0-400
Hund & Forsht, 1987; Metcalf &
Eddy, 1991
1.1
1-2
Hund & Forsht, 1987
3
0.8-5
Hund & Forsht, 1987; Wood, 1990
Paints
ndf
1-10
expert judgement
ndf
ndf
1-10
same as Dmgs & Med.
Petroleum Refineries
0.6
0.3-1.2
Dennis, 1982
0.4
1-8
Dennis, 1982; Elsevier, 1991
1.0
0.4-1.6
Dennis, 1982; Elsevier, 1991
Plastics & Resins
0.6
0.3-1.2
same as Petroleum Refineries
1.4
1-2
Hund & Forsht, 1987
3.7
0.8-5
Hund & Forsht, 1987
Pulp & Paper (combined)
162
85-240
Weyerhaeuser, 1995;
Merritt, 1983
0.4
0.3-8
Weyerhaeuser, 1995; Paques, 1994
9
1-15
Paques, 1994
Soap & Detergents
ndf
1.0-5.0
same as Vegetable oils
ndf
0.3-0.8
same as Vegetable oils
ndf
0.5-1.2
same as Vegetable oils
Soft Drinks
ndf
2.0
expert judgement
ndf
1.0
expert judgement
ndf
2.0
expert judgement
Starch Production
9
4-18
Curi, 1985
2.0
1-25
Paques, 1994
10
1.5-42
Paques, 1984; Hulshoff Pol et al.,
1986
Sugar Refining
ndf
4-18
same as Starch Prod.
ndf
2-8
extrapolated from COD data
3.2
1-6
Lettinga et al., 1980
Textiles (natural)
172
100-185
Brown, 1995; Gorsuch, 1982
0.4
0.3-0.8
Brown, 1995; Gorsuch, 1982
0.9
0.8-1.6
Brown, 1995; Dulaney, 1982
Vegetable Oils
3.1
1.0-5.0
Merritt, 1983
0.5
0.3-0.8
Merritt, 1983, Amstel et al., 1987
ndf
0.5-1.2
extrapolated from BOD data
Vegetables, Fruits & Juices
20
7-35
Merritt, 1983; Metcalf & Eddy,
1991
1.0
0.5-2
Merritt, 1983
5.0
2-10
Lettinga et al., 1980
Wine & Vinegar
23
11-46
expert judgement
0.7
0.2-1.4
expert judgement
1.5
0.7-3.0
expert judgement
Notes: ndf = no data found
When no multiple data are available, the range is assumed to be -50/+100%
-------
Wastewater outflows can be obtained by multiplying industry-specific production
outputs with generation rates (m3/kg product). Country-specific annual industrial output
data are compiled by the United Nations and published in the Industrial Statistical
Yearbook (United Nations, 1992a and United Nations, 1992b). Country-specific
commodity production outputs per industry category for 1990 are included in a large
spreadsheet, named UNISY (after the yearbook) which is not included in this report.
Earlier CH4 emission estimates by EPA (U.S. EPA, 1994) included iron and steel
wastewater as a separate category but, according to Olin et al., (1987), 99 percent of the
organic loading in wastewater from iron and steel mills results from coke manufacturing.
Accordingly, coke manufacturing was added in Table 12 , instead of iron and steel.
However, the United Nations Statistical Yearbook only provides data for iron and steel
and not for coke making. The world coke output was calculated by using a coke-to-iron
ratio based on data from Quarterly Coal Report (DOE 1993) in combination with U.S. and
world iron and steel output data. Strictly speaking, coke consumption should only be
related to pig iron manufacturing and not to steel manufacturing. As no separate iron
and steel data were available, this distinction is ignored.
The UNISY did not provide data for the petroleum refining category and instead
information from Petroleum Supply Annual (U.S. DOE, 1990) was used. According to
Petroleum Supply Annual, the finished petroleum products output for 1990 was 715 Tg.
To produce an estimate for the output for the rest of the world, it was assumed that the
United States produces 33 percent of all petroleum products.
Data reduction on UNISY was performed by eliminating all countries with
populations less than one million.8 Also, the animal feed, coffee processing, drugs and
medicines, and explosives categories were eliminated, because they have relatively minor
industrial outputs according to UNISY. For example, both the coffee industry and the
vegetable oil industry are known for their highly concentrated wastewater, but the total
world coffee production is only 1 percent of vegetable oil production and thus relatively
minor. As the UNISY data base contains over 100 countries, and each country may
represent several or most industrial categories, further data reduction was necessary.
Between two and four Major Producing Countries for each industrial category were
identified and all other countries were labeled "rest of the world." The major producing
countries represent between 50 and 75 percent of world total for that particular industry.
In order to assign a numerical value to the prevailing industry-specific and country-
specific WWT methods, the targeted industries from Table 12 first were classified into five
groups: Animal Products; Industrial Plant Processing; Vegetables, Fruits and Textiles;
Pulp and Paper; and Organic Chemicals and Related Products. Industries within each
group are considered to generate wastewater that is comparable in chemical, biological,
and physical composition, as well as by overall treatment method or lack thereof.
A total of 61 countries was eliminated, representing a population of 14 million. Most countries that were
eliminated are so-called island states.
-------
For each of these five groups the country- or region-specific percentage of on-site
treatment was estimated, compared to raw discharge or discharge into sewers. Next, the
fraction of organic matter treated anaerobically was estimated. Both estimates were
combined into a single factor TAic which expresses the country or region-specific fraction
of wastewater for each industrial group that is treated at the industrial site under
anaerobic conditions. Estimates for TAk for each of the five industry categories are
included in Table 13, as well as the general assumptions used. TAic includes three types
of on-site anaerobic treatment conditions: intended anaerobic treatment in a wastewater
digester or lagoon; sludge storage and handling;9 and undesired anaerobic conditions, as a
result of overloading or mismanagement.
The five aforementioned industrial groups are described below in detail. The
methodology for calculating CH4 emissions from industrial wastewater used in this report,
as adapted from Equation 10, is presented in the next chapter in combination with the
emission estimates.
Group 1. Animal Products-
This group includes the meat, poultry, dairy, and fish processing industries.
Wastewater from these industries is high in animal proteins and fats. It usually is
relatively strong with high BOD and total organics loadings. In many countries, most
cattle and poultry slaughtering and also dairy production is expected to be small scale,
taking place at the farm or the home. Wastewater associated with home slaughtering or
creaming would be classified as domestic wastewater. It is assumed that the UNISY
commodity numbers do not reflect these small scale activities and purely relate to
industrial operations.
In developed countries and perhaps also in some developing countries industrial
meat packing plants (including tanneries) and poultry processing plants are often large-
scale operations, generating proportionally large wastewater outflows. These plants,
typically provide primary WWT that would include anaerobic lagoons. Secondary
treatment would consist of facultative lagoons, after which the treated wastewater is land
applied or otherwise discharged.
9 Actual anaerobic sludge treatment is not included as a CH4 source, although the emission factors used in
this report to account for some sludge storage and handling. Up to 40 percent of COD (in an aerobic WWT
process) may be turned into sludge. Sludge is removed from the site to be dumped elsewhere (landfills or
oceans) or it rtiay be treated on site by various methods. According to Metcalf & Eddy (1991, p. 814),
anaerobic sludge digestion is the dominant sludge stabilization process. The digestion process generates
significant amounts of CH„ and is designed to recover and utilized or flare the CH4. Some CH4 from
anaerobic sludge digesters may however, leak to the atmosphere. Detailed research on CH„ or other GHG
emissions from sludge treatment is beyond the scope of this report.
33
-------
TABLE 13. GLOBAL WASTEWATER DISCHARGE AND TREATMENT PRACTICES
MEAT, POULTRY, DAIRY, AND FISH PROCESSING INDUSTRY
Country
Raw
To sewers
Treated
Treated on
TAIC**
Discharge to
Discharge*
or treated
on Site
Site
city sewers
on site
(anaerobic)
(%)
(%)
(%)
(%)
(%)
(%)
A
100-A
B
C
(100-A)*B*C
(100-A)(100-B)
Africa
60
40
95
90
34
2
Japan (other than fish)
10
90
80
90
65
18
Japan (fish)
10
Other Asia
70
30
80
90
22
6
Russian Federation
50
50
50
90
23
25
Germany
0
100
80
90
72
20
United Kingdom
0
100
80
90
72
20
France
0
100
80
90
72
20
Italy
0
100
80
90
72
20
Other OECD
0
100
70
90
63
30
Other Europe
50
50
50
90
23
25
United States
0
100
85
90
77
15
Canada
0
100
85
90
77
15
Latin America
50
50
70
90
32
15
Australia
0
100
80
90
72
20
Average Rest of the
3512
World
Notes
Percentages reflect amounts of COD and not volumes of water.
* To surface water or land "treatment."
" TAic = the country or region-specific fraction of wastewater for each industrial category that is treated at the industrial
site under anaerobic conditions.
References: Draaijer, 1994; Doppenberg, 1994; Wiegant and Kalker, 1994; and Lexmond and Zeeman, 1995.
General Assumptions
Anaerobic lagoons are common for this category.
Throughout the world, a considerable amount of activity for these industrial categories may take place at a very small scale (e.g.,
home slaughtering).
It is assumed that the commodity output numbers do not reflect small scale processing.
Nor do the assumptions for WWT practices.
It is assumed that most Japanese fish waste is dumped in the sea.
It is assumed that all large operations in developed countries have their own primary treatment facilities.
Hence the relatively low "Raw Discharge" values and the relatively high "Treated on Site" values.
High column B numbers for some countries are indicative of the absence of sewers.
34
-------
TABLE 13 (continued)
ALCOHOL REFINING, BEER, WINE, VEGETABLE OIL, SUGAR, AND STARCH
INDUSTRIES
Country
Raw
To sewers
Treated
Treated on
TK**
Discharge into
Discharge*
or treated
on Site
Site
city sewers
on site
(anaerobic)
(%)
(%)
(%)
(%)
(%)
(%)
A
100-A
B
C
(100-A)*B*C
(100-A)(100-B)
Africa
60
60
95
30
17
3
Japan
5
95
80
10
8
19
Other Asia
60
40
95
30
11
2
Russian Federation
20
50
50
30
8
25
Germany
0
100
40
10
4
60
United Kingdom
0
100
40
10
4
60
France
0
100
40
10
4
60
Italy
10
100
40
10
4
60
Other OECD
10
90
40
10
4
54
Other Europe
20
50
50
30
8
25
United States
0
100
80
10
8
20
Canada
0
100
80
10
8
20
Latin America
60
60
60
35
13
24
Australia
0
100
80
10
8
20
Average Rest of the
1110
World
Notes
Percentages reflect amounts of COD and not volumes of water.
* To surface water or land "treatment."
** TAh = the country or region-specific fraction of wastewater for each industrial category that is treated at the industrial site
under anaerobic conditions.
References: Draaijer, 1994; Doppenberg, 1994; Wiegant and Kalker, 1994; and Lexmond and Zeeman, 1995.
General Assumptions
Aerobic (aerated) lagoons most are common for this category.
In developed countries, in some cases anaerobic digesters are also used.
Raw or semi-raw wastewater is often discharged into sewers for treatment at the local POTWs.
Except for wineries and some breweries, these industries are typically large, often multi-national operations that are assumed to
have their own primary or comprehensive WWT.
Relatively high values in column C for developing countries indicate assumed anaerobic conditions resulting from possible
overloading and/or underaeration.
35
-------
TABLE 13 (continued)
VEGETABLES, SOFT DRINKS,
JUICE, AND TEXTILE INDUSTRIES
Country
Raw
To sewers
Treated
Treated on
TA»
Discharge into
Discharge*
or treated
on Site
Site
city sewers
on site
(anaerobic)
(%)
(%)
(%)
(%)
(%)
(%)
100-A
B
(100-A)*B*C
(100-A)(100-B)
Africa
70
30
95
20
6
2
Japan
10
90
10
10
1
81
Other Asia
70
30
80
20
5
6
Russian Federation
50
50
5
20
1
48
Germany
0
100
5
0
0
95
United Kingdom
0
100
5
0
0
95
France
0
100
5
0
0
95
Italy
10
90
5
0
0
86
Other OECD
10
90
5
15
1
86
Other Europe
50
50
5
20
1
48
United States
0
100
5
0
0
95
Canada
0
100
5
0
0
95
Latin America
60
40
60
20
5
16
Australia
0
100
5
0
0
95
Average Rest of the
430
World
Notes
Percentages reflect amounts of COD and not volumes of water.
* To surface water or land "treatment."
** TAh = the country or region-specific fraction of wastewater for each industrial category that is treated at the industrial site
under anaerobic conditions.
References: Draaijer, 1994; Doppenberg, 1994; Wiegant and Kalker, 1994; and Lexmond and Zeeman, 1995.
General Assumptions
Typically wastewater from these categories is directly discharged to sewers to be treated at POTWs. (Low "Treated on Site"
values for developed countries.)
For developing countries column B values are high, implying that if there is treatment it will be at the industrial site, since there
are no city sewers.
In developing countries, where there are no sewers/POTWs, lagoons may be common.
Relatively high "Treated on Site (anaerobic)" values for developing countries, account for possible anaerobic situations due to
overloading or underaerating.
36
-------
TABLE 13 (continued)
PULP AND PAPER INDUSTRY
Country
Raw
To sewers
Treated
Treated on
TAlc"
Discharge into
Discharge*:¦
or treated
on Site
Site
city sewers
on site
(anaerobic)
(%)
(%)
(%)
(%)
(%)
(%)
A
100-A
B
C
(100-A)*B*C
(100-A)(100-B)
Africa
25
75
100
20
15
0
Japan
0
100
100
1
1
0
Other Asia
25
75
100
20
15
0
Russian Federation
20
80
100
25
20
0
Germany
0
100
100
1
1
0
United Kingdom
0
100
100
1
1
0
France
0
100
100
1
1
0
Italy
0
100
100
1
1
0
OECD
5
95
100
1
1
0
Other Europe
10
90
100
15
14
0
United States
0
100
100
1
1
0
Canada
0
100
100
1
1
0
Latin America
25
75
100
20
15
0
Australia
0
100
100
1
1
0
Average Rest of the
120
World
Notes
Percentages reflect amounts of COD and not volumes of water.
* To surface water or land "treatment."
** TAic = the country or region-specific fraction of wastewater for each industrial category that is treated at the industrial
site under anaerobic conditions.
References: Draaijer, 1994; Doppenberg, 1994; Wiegant and Kalker, 1994; and Lexmond and Zeeman, 1995.
General Assumptions
Aerobic (aerated) lagoons are common for this category.
Large multi-national companies assumed to have adequate WWT.
Also, it is assumed that pulp and paper plants are not typically located near cities and, therefore, conduct their own WWT.
Relatively high values in column C for developing countries indicate assumed anaerobic conditions resulting from possible
overloading and/or underaeration.
37
-------
TABLE 13 (continued)
ORGANIC CHEMICALS, PETROLEUM REFINING,
PLASTICS AND RESINS,
COKING,
DETERGENTS, PHARMACEUTICALS, AND PAINT INDUSTRIES
Country
Raw
Discharge*
To sewers
or treated
on site
Treated
on Site
Treated on
Site
(anaerobic)
TAk**
Discharge into
city sewers
(%)
(%)
(%)
(%)
(%)
(%)
A
100-A
B
C
(100-A)*B*C
(100-A)(100-B)
Africa
60
40
90
10
4
4
Japan
10
90
70
4
3
27
Other Asia
60
40
90
10
4
4
Russian Federation
50
50
50
10
3
25
Germany
0
100
70
4
3
30
United Kingdom
0
100
70
4
3
30
France
0
100
70
4
3
30
Italy
5
95
70
4
3
29
Other OECD
10
90
70
10
6
27
Other Europe
20
80
50
10
4
40
United States
0
100
80
4
3
20
Canada
0
100
80
4
3
20
Latin America
60
40
80
10
3
8
Australia
0
100
70
4
3
30
Average Rest of the
World
310
Notes
Percentages reflect amounts of COD and not volumes of water.
* To surface water or land "treatment."
** TA,C = the country or region-specific fraction of wastewater for each industrial category that is treated at the industrial site
under anaerobic conditions.
References: Draaijer, 1994; Doppenberg, 1994; Wiegant and Kalker, 1994; and Lexmond and Zeeman, 1995.
General Assumptions
Typically chemical or physical primary treatment, followed with an aerobic phase.
In developed countries, effluent from primary treatment is discharged into sewers.
Typically large processing plants, in part multi-nationally owned, which are assumed to have adequate WWT.
38
-------
In some countries dairy wastewater may be treated aerobically, and fish wastewater
may be treated with physical purification methods, such as centrifuging. Fish and dairy
operations are nevertheless classified with meat and poultry processing because of the
similarities in biological and chemical composition. Errors resulting from the broadness of
this classification are not expected to significantly affect emissions estimates, because
commodity outputs for dairy products and processed fish are relatively small compared to
poultry and meat outputs.
Group 2. Industrial Plant Processing-
This group includes alcohol, beer, wine, vegetable oil, sugar, and starch production.
Processes associated with these industries involve the conversion of mono-culture crops to
refined products. All processes, with the exception of vegetable oil production, are
characterized by a refining or fermentation step in which the original raw material is
modified extensively. Raw materials for the alcohol, beer, vegetable oil and starch
production consist of grains or seeds. Sugar is made from cane or beets, the latter
containing starch as raw material. Wine is the exception here, as its raw material is
fruit, however, the extensive alteration and fermentation justifies its classification with
alcohol and beer production.
Wastewater from this group is considered to be high in vegetable organics (as
opposed to animal organics). Processing plants within this group (with the exception of
some wineries and some European breweries) are usually large in size and produce
proportionally large amounts of wastewater. In developing countries the plants are often
foreign owned. Industrial categories that are foreign owned and that operate relatively
large plants are assumed to have appropriate WWT. Comprehensive treatment or
primary treatment (removing most organics) is, therefore, assumed to take place on site
and usually is in aerated lagoons. However, certain steps in the treatment process may
be anaerobic, for instance, due to under-aeration or overloading of lagoons. Values in the
column entitled "Treated on Site (anaerobic)" in Table 13 reflect this possible condition for
developing countries and Eastern European countries.
Group 3. Vegetables, Fruits and Textiles-
This group includes vegetable processing, juice and soft drinks production, and
textiles. Wastewater from these industries is usually moderately contaminated with plant
organics and is typically discharged into the public sewer system (if there is a sewer
system) sometimes after preliminary treatment, such as screening. Textiles wastewater
consists of dyes which may be chemically different from vegetable waste, although dyes
made from plants are also popular. However, textile wastewater is also always
discharged to public sewers and is also moderately polluted with organics (Brown, 1995).
Typically, industries in this group may vary significantly in size from large plants
owned by multi-national corporations to small green-grocer type operations. Typical for
this industry is that the wastewater outflows may be batch wise and that the wastewater
composition and loading may vary significantly from batch to batch. A cannery or
bottling hall would typically process a certain product, for one or several shifts, after
which the lines are cleaned and a new type of product is started up. This is the reason
that, even for modern operations, it is preferred to have the municipal WWT plant treat
the wastewater, for then the concentration and outflow variations can be absorbed more
39
-------
easily. Of course, as operations vary in size and the wastewater is not terribly strong,
raw wastewater may also be discharged to surface water in certain countries.
Group 4. Pulp and Paper Industry-
Pulp and paper mills require large amounts of water and will always be situated on
rivers. The industry produces large quantities of wastewater that is unique in
composition (cellulose instead of starches and/or sugars). Due to their size, pulp and
paper mills are often owned by large corporations. Large corporations, especially multi-
national ones, are expected to receive more scrutiny from local governments, compared to
small businesses. As a result, environmental clean-up efforts, including WWT, by large
companies are expected to be fairly high throughout the world. Comprehensive treatment
or primary treatment (removing most organics) is, therefore, assumed to take place on site
and usually is in aerated lagoons. However, certain steps in the treatment process may
be anaerobic, for instance, due to under-aeration or overloading of lagoons. Values in the
column entitled "Treated on Site (anaerobic)" in Table 13 reflect this possible condition for
developing countries and Eastern European countries. The percentage "Treated on Site
(anaerobic)" for developed countries is assumed to be 1 percent and reflects anaerobic
conditions that may occur in tertiary lagoons.
Group 5. Organic Chemicals and Related Products-
This group includes the organic chemicals, plastics and resins, petroleum refining,
coking, detergents, pharmaceuticals, and paint industries. Facilities in this group are
usually large in size and are owned by multi-national corporations. Wastewater is
usually weak, but may also be moderately to very strong for the production of certain
organic chemicals. It may likely contain VOCs, petroleum derivatives, and other
substances that may be toxic to bacteria.
Typically, production plants use equalization basins or stabilization ponds to reduce
variations in composition and concentration of the wastewater and to allow for any
possible (aerobic) biological break down of susceptible organics. However, compared to the
other groups wastewater from this group is likely to vary significantly in composition. As
a result, WWT methods are also highly diverse, including different types of physical and
chemical treatment, as well as, aerobic treatment (e.g., in trickling filters). Anaerobic
treatment is generally not well suited for this group, because anaerobic bacteria are
vulnerable to composition variations and are easily upset by inhibitory compounds in the
wastewater, which include, but are not limited to certain salts containing heavy metals
and/or sulfides, and anthropogenic VOCs. (Alabaster, et al., 1991.) In developed
countries, preliminary treatment may be at the industrial site, after which the
wastewater is invariably discharged into the public sewer. In developing countries all
treatment may be at the site or other scenarios may exist that range between raw
discharge to full treatment. It was assumed that between 4 and 10 percent of treatment
at the site is anaerobic, reflecting the possible use of digesters as well as possible
overloading of lagoons.
Industrial Wastewater Discharged to Citv Sewers
Often, raw industrial wastewater or industrial wastewater that underwent
preliminary treatment at the industrial site is discharged into city sewers. In the sewer
-------
line systems and ultimately at the WWT plant (if present) this industrial wastewater will
become thoroughly mixed with domestic wastewater. Industrial wastewater that is
discharged into city sewers is classified as domestic wastewater in this report.
In countries with wastewater regulation enforcement, industrial wastewater discharges
into sewers are limited to biologically treatable waste, in order not to affect the WWT
system at the municipal WWT plants. In other countries where there may be little or no
enforcement, any type of wastewater may be discharged into sewers, which may result in
impeding proper functioning of the municipal WWT plants. Table 13, which defines
global wastewater discharge and treatment practices for the five aforementioned industry
groups also includes country-specific estimates of the fraction of industrial wastewater
(expressed in COD) that is discharged into city sewers.
DOMESTIC WASTEWATER
Composition and Output
Domestic wastewater is the spent water originating from all aspects of human
sanitary water usage. Domestic wastewater contains components that are typically
organic in nature (carbohydrates, lipids, proteins, soaps) and it may be considered
somewhat homogeneous. An average composition is given in Table 14. It is typically
generated from households from the use of toilets, baths, laundry, and kitchens. Domestic
wastewater sources include sources other than households, such as institutions, offices,
shops, schools, and recreational facilities. Municipal WWT plants that treat domestic
wastewater typically employ biological, aerobic treatment. (Appendix B includes generic
information on municipal sewage treatment operations.)
In order to develop emissions estimates from domestic WWT three methods were
evaluated for estimating organic domestic wastewater loadings were evaluated: (1) the
use of water consumption data; (2) the use of wastewater generation data; (3) the use of
per capita organics loadings.
Generic water consumption data are available from various handbooks, for example,
the World Resources Institute publishes country-specific per capita water consumption
rates (World Resources Institute, 1994). Adjustments may be made by estimating the
water consumption at the house (e.g., lawn watering) and water losses and/or gains in
sewer lines (leakages, influx of storm- or groundwater).
41
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TABLE 14. TYPICAL COMPOSITION OF UNTREATED DOMESTIC U.S. WASTEWATER
POLLUTANT
RANGE
(mg/L)
POLLUTANT
RANGE
(mg/L)
Solids Total
730-1,180
Total Organic Carbon
200-500
Dissolved, Total
400-700
COD
550-700
Mineral
250-450
Total Nitrogen (as N)
40-50
Organic (Volatile)
150-250
Organic
15-20
Suspended
180-300
Free ammonia (NH3)
25-30
Mineral
40-70
Nitrates and Nitrites
0
Organic
140-230
Total Phosphorus (as P)
10-15
Total Settleable Solids
150-180
Chlorides
50-60
bod5
160-280
Alkalinity [as calcium
carbonate (CaC03)]
100-125
Trace amounts of paints,
-< 1
Oil and Grease
90-110
motor oils, nail polish
Typical pH
7.0-7.5
removers, etc.
Based on Mullick (1987). Assumptions are: water consumption of 100 gallons (380 I) per capita, no industrial
wastewater, median use of garbage disposals, and moderate income population.
Non-industrial per capita water use rates for the United States lie between 100 and
166 gallons [380 and 630 liters (1) per day] (Mullick, 1987; Corbitt, 1990; and Metcalf &
Eddy, Inc., 1991). It is estimated that 60 to 85 percent of water used becomes
wastewater, largely depending on lawn watering requirements (Metcalf & Eddy, 1991).
This converts into a daily per capita domestic wastewater generation rate of around 60 to
141 gallons (228 to 536 1). The amount of wastewater produced can be multiplied with
the average organics concentration to obtain organics loadings. This method is not
considered very reliable, because it is difficult to estimate which fraction of the water
consumed will become wastewater. In addition, wastewater quantities may increase
considerably as a result of the inflow of stormwater into the sewer systems.
Next it was attempted to base the methodology directly on wastewater generation
rates. However, except for the United States,10 sparse information is available on
domestic wastewater generation rates. Some studies provide data that pertain to specific
sites. For example, Toprak (1993) gives a number of 200 1 per day per capita for the city
of Izmir, Turkey, but such a local rate may not be representative for the whole country.
Also, some handbooks provide generic wastewater generation rates, as well as average
composition data. Country-specific per capita wastewater generation rates are likely to
vary significantly, depending on local climate, cultural habits, and economic levels. As
10 According to the 1988 Needs Survey (U.S. EPA, 1989), there were 15,711 POTWs in operation in the United
States in 198'8, serving a population of 176 million, and treating 37,866 million gallons per day (MGD) of
wastewater and possibly some stormwater. The rest of the population would have septic systems, or no
treatment. About 17 percent or 6,437 MGD of this wastewater was considered to be industrial with the other
31,429 MGD being commercial and domestic wastewater.
42
-------
with wastewater quantities generated from water consumption rates, it is difficult to
estimate the influence of stormwater inflow.
Given the uncertainties associated with the use of water consumption and
wastewater generation rates, it was preferred to look directly at organics loadings
expressed in grams of BODs per capita/day. The quantity of organic waste products in the
wastewater is independent of stormwater inflow or other types of dilution. Table 15
contains BOD5 loadings for different regions in the world, which are largely dependent on
diet, metabolism, and body weight. An advantage of this method is that a per capita
discharge rate is not likely to be independent of the person's location (e.g., home or office).
OECD countries were grouped together, although the United States is in a category by
itself. The higher U.S. number is due to widespread use of garbage disposals in the
United States.
TABLE 15. BODs AND COD LOADINGS FOR DIFFERENT REGIONS OF THE WORLD
BODs LOADING1
(g/capita/day)
COD LOADING"
(g/capita/day)
Developing Countries
35 ± 10
90 ±40
Eastern European Countries
45 ± 10
110 ±45
OECD Countries (except U.S.)
55 ± 15
140 ±65
United States
65 ± 15
160 ± 70
Based on Lexmorid and Zeeman (1995); Metcalf & Eddy (1991); Mullick (1987);
U.S. EPA (1994), and Polytechnisch Zakboekje (1984).
COD/BOD ratio = 2.5. See Table 1. Values are rounded to nearest 10.
Extent of Sewerage. Treatment, and Prevailing Treatment Methods
In many developing countries, sewerage infrastructure does not reach large sections
of the population. Especially in rural areas and urban slums, sewerage is virtually
nonexistent (WHO/UNICEF, 1993; Draaijer, 1994). In rural areas, the lack of sewerage is
not necessarily a problem and people use designated areas of the surrounding land
(Marks, 1993). Also, domestic sewage may be treated on the premises in pit latrines or
septic sewage systems. As previously discussed, emissions from untreated wastewater
and wastewater treated in latrines and septic tanks are not addressed in this report. As
population densities increase, lack of adequate sanitation, including sewerage may become
a health issue and the concentration of untreated sewage may be a source of GHGs.
Often, official published figures are flattered. For example, slum dwellers may not
be included, or people with bucket latrines may be counted as served by WWT (Bartone,
1990). For the mid-eighties, it was estimated that in Africa only 14 percent of the urban
population has a sewerage connection. In Latin America and the Middle East, official
figures indicate that 41 percent of the urban population has sewers (capitals or other
43
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large cities 50 to 85 percent; for secondary cities this number is less than 10 percent). For
Asia and the Pacific, less than 20 percent of the total urban population has sewer-to-
house connections (Bartone, 1990). Figure 2 provides an overview of sanitation by
technology type based on a survey of 63 developing countries (WHO/UNICEF, 1993).
Conventional
Sewer
1 Urban High-
income
~ Urban Low-
income
Small-bore
Sewer
Septic Tank Latrine
Sanitation Technology Type
Other
Unserved
Source: WHO/UNICEF, 1993.
Figure 2. Urban Sanitation by Technology Type
When there are sewer lines but no treatment facilities, the raw sewage is discharged
into a river, lake, or ocean. Pipes that transport raw sewage some distance from the coast
and discharge it below sea level are called outfalls. Outfalls are used all over the world
for wastewater discharge, with the exception of wealthy OECD countries (Draaijer, 1994).
Andreadakis et al. (1993) report that the city of Thessaloniki in Greece (100,000
inhabitants) uses an outfall to discharge raw sewage. There is a primary treatment plant
that is inoperative because effluent standards are not being met. An outfall that serves
part of Rio de Janeiro, Brazil dumps an average of 6 m3/sec (136 MGD) of raw wastewater
into the Atlantic Ocean (Jordao and Leitao, 1990). Organics that are discharged into
rivers, lakes, or oceans are not considered to contribute to the GHG effect, because they
.are assumed to be facultative.
44
-------
On its way to the discharge location sewage may undergo significant biodegradation
depending on residence time and temperature. The residence time may be high or even
infinite due to poor design and overloading of the sewer system. In developing countries,
sewers may be mere open gutters which are prone to clogging as a result of dumping of
solid waste (Doppenberg, 1994; Wiegant and Kalker, 1994). Stagnant sewage, especially
in warm countries will rapidly turn septic and is thought to be a significant source of CH4
(Draaijer, 1994).
Whereas, country-specific data on the extent of sanitation, including sewer
connections are fairly easily obtained, very few literature sources exist that give
numerical information on the extent of WWT. Country-specific data on the extent of
WWT were found for China. The Chinese Government estimates that 31.7 gigagrams
(Gg) of wastewater (including 23.9 Gg of industrial wastewater) is produced annually.
About 74 percent of this is discharged without treatment. In 1984, sewage disposal in
urban Beijing was about 700 million m3/yr, of which only 15 percent was treated. A WWT
plant of 500,000 m3/day is planned to come on line in 1990, which would cover 42 percent
of the wastewater outflow. (Zhongxiang and Yi; 1991.)
In developed countries, the extent of wastewater treatment is generally higher than
in developing countries. Table 16 gives an overview of the extent to which domestic
wastewater is treated at municipal WWT plants in developed countries (UNEP, 1990).
The information in Table 16 is somewhat dated and may not reflect the current status of
WWT in Europe. Under pressure of 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 the status of local WWT due to economic pressure from the tourist
industry. For example, for many decades Spanish effluent received only rudimentary
treatment before being discharged into rivers and seas; in 1990, only 40 percent of
Spanish wastewater was treated. Under pressure to meet European Union regulations
(90 percent reduction of load), Spain has begun a rigorous program to improve its track
record and all over the country activated sludge WWT projects are now being initiated.
Two plants under construction in Zaragossa and Ibiza will be furnished with a full cover
to minimize air emissions. [World Water and Environmental Engineering (WWEE),
1992.]
If treated, domestic sewage may be treated in one or more lagoons, or at
conventional (aerated activated sludge) WWT plants. Lagoons can be found in most
regions of the world, however, lack of available land for the lagoon itself, as well as for
the application of effluent, impedes their utilization. This is the case in densely populated
parts of Asia (Doppenberg, 1994). The successful employment of partially aerated lagoons
to serve small communities is reported from Thailand (Koottatep et al., 1994). The
expansive use of lagoons is also reported from Latin America, the United States, Canada,
Africa, and Europe, with the exception of the United Kingdom (Wiegant and Kalker, 1994;
Racault, 1994; Evans et al., 1993; Doppenberg, 1994). There are approximately 2,000
lagoons in France and 1,000 in Germany and one third of all POTWs in the USA only use
lagoons, as compared to activated sludge (Mara et al., 1992).
45
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TABLE 16. POPULATION SERVED BY WWT IN DEVELOPED COUNTRIES
PERCENT OF POPULATION SERVED.
Total
Served by Primary
WWT only
Served by
Primary and
Secondary WWT
Austria
67
5
62
Belgium (1979)
23
no data
23
Canada
62
15
47
Denmark
98
8
90
Finland
74
0
74
France (1984)
50
no data
59
Germany (BRD)
(1983)
87
8
79
Greece (1985)
1
no data
1
Ireland (1980)
11
no data
11
Italy (1980)
30
no data
no data
Japan
39
no data
no data
Luxembourg (1985)
83
14
69
Netherlands
90
7
83
New Zealand (1985)
88
8
85
Norway
43
6
37
Portugal
12
4
8
Spain (1985)
29
13
16
Sweden
100
1
99
Switzerland
85
no data
85
Turkey (1985)
4
2
2
Turkey ( 1993),
(small towns)*
26
no data
no data
United Kingdom
84
6
78
United States (1984)
74
15
59
1987 data, unless otherwise indicated.
This table does not include treatment by septic sewage systems.
* From Sarikaya and Eroglu (1993).
In spite of the relative abundance of lagoons in different areas of the world, these
lagoons have limited capacities and usually only serve small communities with no more
than a few thousand inhabitants. For example, the Province of Ontario, Canada is
reported to have 512 domestic WWT plants, 137 of which consist of lagoons. The lagoon
plants serve small populations of 100 to 3,000 (Evans et al., 1993). If we assume that all
46
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lagoon plants serve communities with the maximum reported number of 3,000 residents,
these lagoon plants only serve 5 percent of the Ontario population. Domestic WWT by
lagoons is considered a simple technology most suitable for small scale applications. For
large scale domestic WWT applications, it is expected that aerated systems will be
preferred over facultative lagoons because these systems have a larger capacity and use
up less land space.
When assessing the extent of treatment it is important to take into consideration
that in many countries conventional (aerated) WWT plants are not working properly
(Mancy, 1993). In Eastern Europe, civil engineering development was arrested 40 years
ago and as a result, there are many antiquated WWT plants, most of which are not
running (Draaijer, 1994). 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 (Bartone,
1990). In Algeria, a World Bank study showed that 33 out of 42 plants were out of
service. Experience in Korea with night soil treatment plants has been similar with
respect to operational difficulties (Bartone, 1990). Lagoons also may be prone to
operational failure, for example, they may receive loads that are too high in BOD and
turn anaerobic. Such lagoons and ill managed or overloaded municipal WWT plants are
expected to be a source of CH4 and possibly other GHG emissions.
Available country-specific information on BOD and COD loadings, and the assumed
type and extent of treatment are summarized in Table 17. The methodology for
calculating CH4 emissions from domestic wastewater used in this report, as adapted from
Equation 10, is presented in the next chapter in combination with emission estimates.
47
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TABLE 17. COUNTRY-SPECIFIC DOMESTIC WASTEWATER DATA
Country
Population
To City
Sewer
Land
Septic Tank,
Latrine
Raw
Discharge
To
WWTP
Anaer-
obic
WWT
Aerobic
WWT
TA,*
(10u)
(%)
(%)
(%)
(%)
IIP)
(%)
(%)
AFRICA
Nigeria
127
10
50
40
90
10
50
50
0.5
Egypt
59
10
50
40
80
20
50
50
1.0
Kenya
28
10
50
40
60
40
50
50
2.0
South Africa
43
40
30
30
60
40
20
80
3.2
Zimbabwe
12
40
30
30
60
40
20
80
3.2
Other Africa
492
10
50
40
90
10
50
50
0.5
ASIA
China
1,238
15
20
65
90
10
50
50
0.8
India
931
15
50
35
90
10
50
50
0.8
Indonesia
201
15
40
45
80
20
50
50
1.5
Pakistan
135
15
50
35
90
10
50
50
0.8
Bangladesh
128
15
50
35
90
10
50
50
0.8
Japan
126
90
0
10
10
90
5
95
4.1
Other Asia
726
15
20
65
90
10
50
50
0.8
EUROPE
Russia
150
70
0
30
50
50
40
60
14.0
Germany
81
80
0
20
0
100
5
95
4.0
United Kingdom
58
90
0
10
0
100
5
95
4.5
France
58
80
0
20
5
95
5
95
3.8
Italy
58
80
0
20
10
90
5
95
3.6
Other OECD
113
70
0
30
25
75
5
95
2.6
Other Europe
217
70
0
30
50
50
10
90
3.5
NORTH AMERICA
United States
263
70
0
30
0
100
5
95
3.5
Canada
29
70
0
30
0
100
5
95
3.5
LATIN AMERICA AND CARIBBEAN
Brazil
161
40
40
20
95
5
50
50
1.0
Mexico
94
40
40
20
95
5
50
50
1.0
Others
224
40
40
20
95
5
50
50
1.0
AUSTRALIA AND NEW ZEALAND
Australia
18
70
5
25
5
95
5
95
3.3
Notes: WWTP
TA„
Wastewater treatment plant
Country-specific fraction of COD that is treated anaerobically
Assume a margin of error of a factor of 2 (i.e., -50%, +100%)
References for Africa:
References for Asia:
References for Europe:
References for North America:
References for Australia
and New Zealand:
Bartone, 90; Draaijer, 94; WHO/UNICEF, 93; Doppenberg 94; Marks, 93; Alabaster, 91.
Bartone, 90; Draaijer, 94; WHO/UNICEF, 93; Doppenberg 94; Koottatep, 94; UNEP, 90.
Doppenberg, 94; UNEP, 90; Draaijer 94; WWEE, 92; Racault, 94; Mara et al., 92.
Evans et al., 93; UNEP, 90.
WHO/UNICEF, 93; Jordao and Leitao, 90; UNEP, 90.
-------
ESTIMATES OF GHG EMISSIONS FROM WWT
METHANE
Industrial Wastewater
The generic methodology in Equation 10 was modified to develop emissions
estimates for CH4 from industrial wastewater. Equation 11 provides the methodology for
estimating CH4 from industrial wastewater.
CH4 emissions = EF * 10'12 * ( Pjc * Q, * COD, * TAic ) (Tg/yr) (11)
where: EF = Emission factor (g CH4/g CODremoved);
Pic = Industry- and country-specific product output (Mg/yr);
Qi = Industry-specific wastewater produced per unit of product
(m3/Mg);
CODt = Organics loading removed, by industry (g/m3);
TAk = Industry- and country-specific fraction of COD in wastewater
treated anaerobically;
Subscript i = An individual industry; and
Subscript c = An individual country.
For each industry group, the countries with the highest product outputs were
identified and all other remaining countries were grouped "Rest of the World" (see
Table 18). Outputs Pk were taken from the UNISY data base. Table 18 includes
industry-specific wastewater generation rates Q, and average, industry-specific COD data,
which came from Table 12. Country-specific data for Qt and CODi were not available.
TAk, the industry- and country-specific fractions of COD in the wastewater that is
expected to be treated anaerobically, were retrieved from Table 13. The product of the
aforementioned parameters representing the amount of the COD in the wastewater that
is expected to be treated anaerobically was multiplied by the emission factor of 0.3 ± 0.1 g
CH4/g COD.
Based on the information in Table 18, CH4 emissions from industrial wastewater
treatment are estimated to be between 0.6 and 6.1 Tg/yr with a mean value of 2.4 Tg/yr.
According to Table 18, the biggest contributor to industrial CH4 emissions from WWT is
the pulp and paper industry (see Figure 3). Although pulp and paper wastewater is
typically treated aerobically, it was assumed that up to 15 percent of the COD in treated
pulp and paper wastewater in developing and Eastern European countries may degrade
under anaerobic conditions as a result of poor wastewater management.
49
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TABLE 18. COUNTRY-SPECIFIC INDUSTRIAL WASTEWATER DATA AND METHANE EMISSIONS
INDUSTRY TYPE
COUNTRY
Output
Wastewater
COD
Total
COD
COD to City
Methane Emissions
Generation
COD
Anaer.
(Tg/yr)
(m /Mg) | (10s l/yr)
(g/i)
(Tg/yr)
(%>
(Tg/yr)
(%)
(Tg/yr)
(Gg/yr)
low
mean i
high
low
j mean j
high
Group 1. Animal Products
Meat & Poultry
United States
28.59
131
372
2
4.1 (
7
1.5
77
1.17
ii M
0.2
114
j 352 |
801
Meat & Poultry
Germany
6.74
13 j
88
2
4.1 j
7
0.4
72
0.26
ifcfl
0.1
25
| 78 j
177
Meat & Poultry
Russia
6.64
13 j
86
2
4.1 |
7
0.4
23
0.08
ill
0.1
8
j 24 |
56
Meat & Poultry
Brazil
5
131
68
2
4.1 |
7
0.3
32
0.09
liflfi
0.0
9
| 27 j
61
Meat & Poultry
United Kingdom
4.17
13|
54
2
4.1 |
7
0.2
72
0.16
0.0
16
! 48 |
109
Meat & Poultry
Japan
3.53
131
46
2
4.1 |
7
0.2
65
0.12
life-:.
0.0
12
| 37 |
84
Meat & Poultry
Ukraine
3.01
131
39
2
4.1 |
7
0.2
23
0.04
§:Mi.
0.0
4
i 11 !
25
Meat & Poultry
Rest of the world
17.2
131
224
2
4.1 j
7
0.9
35
0.32
liM
0.1
31
| 96 I
219
Dairy Products
United States
6.46
7 j
45
1.5
2.7 |
5.2
0.1
77
0.09
III!!?
0.0
10
I 28 I
72
Dairy Products
France
4.97
7 j
35
1.5
2.7 j
5.2
0.1
72
0.07
illl
0.0
8
! 20 |
52
Dairy Products
Germany
3.71
7j
26
1.5
2.7 j
5.2
0.1
72
0.05
0.0
6
| 15 I
39
Dairy Products
Russia
2.41
7j
17
1.5
2.7 j
5.2
0.0
23
0.01
0.0
1
! 3 |
8
Dairy Products
Rest of the world
14.6
71
102
1.5
2.7 |
5.2
0.3
35
0.10
0.0
11
I 29 I
74
Fish Processing
Japan
5.39
13|
70
1.25
2.5 |
5
0.2
10
0.02
1111
0.0
2
| 5 j
14
Fish Processing
Rest of the world
12.5
131
163
1.25
2.5 |
5
0.4
35
0.14
111--
0.0
14
! 43 |
114
Group 2. Industrial Plant Processing
Alcohol Refining
Brazil
11.78
241
283
5
11 i
22
3.1
13
0.40
WMi
0.7
37
i 121 |
324
Alcohol Refining
United States
3.11
241
75
5
11 !
22
0.8
8
0.07
0.2
6
| 20 j
53
Alcohol Refining
Rest of the world
16
24!
386
5
11 !
22
4.3
11
0.47
11°§;
0.4
43
! 140 !
374
Wine & Vinegar
France
6.55
23.I
151
0.7
1.5 |
3
0.2
4
0.01
1:®
0.1
1
! 3 I
7
Wine & Vinegar
Italy
5.49
23 j
126
0.7
1.5 |
3
0.2
4
0.01
1:®:
0.1
1
j 2 j
6
Wine & Vinegar
Spain
2.34
23 j
54
0.7
1.5 |
3
0.1
4
0.00
0.0
0
! 1 !
3
Wine & Vinegar
Rest of the world
14
23|
327
0.7
1.5 !
3
0.5
11
0.05
10
0.0
5
I 16 |
43
Vegetable Oils
United States
6.76
3.1 [
21
0.5
0.9 !
1.2
0.0
8
0.00
20
0.0
0
I 0 |
1
Vegetable Oils
Malaysia
6.14
3.11
19
0.5
0.9 I
1.2
0.0
11
0.00
2
0.0
0
I 1 I
1
Vegetable Oils
China
5.44
3.11
17
0.5
0.9 I
1.2
0.0
11
0.00
2
0.0
0
! 1 I
1
Vegetable Oils
Brazil
4.12
3.1 i
13
0.5
0.9 j
1.2
0.0
13
0.00
24.
0.0
0
! o |
1
Vegetable Oils
Rest of the world
35
3.1 j
108
0.5
0.9 j
1.2
0.1
11
0.01
10
0.0
1
! 3 j
6
Sugar Refining
India
23.31
9 j
210
1
3.2 I
6
0.7
11
0.07
2
0.0
5
! 22 |
55
-------
TABLE 18 (continued)
cn
INDUSTRY TYPE
COUNTRY
Output
Wastewater
COD
Total
TAk
COD
COD to City
Methane Emissions
Generation
COD
Anaer.
Sewers
(Tg/yr)
(ma/Mg) j (10s
l/yr)
(g/i)
(Tg/yr)
<%)
(Tg/yr)
(%)
(Tg/yr)
(Gg/yr)
low
mean j
high
low
i mean :
high
Sugar Refining
Ukraine
12.18
91
110
1
3.2 !
6
0.4
8
0.03
mm
0.1
2
I 8 :
21
Sugar Refining
Brazil
10.15
9 j
91
1
3.2 |
6
0.3
13
0.04
t! ?lf
2
! 11 |
29
Sugar Refining
Cuba
8.05
9 j
72
1
3.2 |
6
0.2
13
0.03
24
0.1
2
! 9 |
23
Sugar Refining
United States
6.27
9j
56
1
3.2 !
6
0.2
8
0.01
:i!i!
0.0
1
i 4 |
11
Sugar Refining
Rest of the world
87
9!
785
1
3.2 |
6
2.5
11
0.28
|:II!
llliil
17
! 83 !
207
Malt & Beer
United States
25.89
6.31
163
2
2.9 |
7
0.5
8
0.04
lictsi
0.1
5
j 11 I
37
Malt & Beer
Germany
13.01
6.3!
82
2
2.9 I
7
0.2
4
0.01
mi
illllll
1
I 3 I
9
Malt & Beer
Indonesia
11.29
6.3!
71
2
2.9 !
7
0.2
11
0.02
IIS!
0.0
3
I 7 |
22
Malt & Beer
United Kingdom
8.29
6.3}
52
2
2.9 |
7
0.2
4
0.01
Illl!
0.1
1
! 2 |
6
Malt & Beer
China
6.92
6.3|
44
2
2.9 !
7
0.1
11
0.01
!!!!!!
0.0
2
| 4 !
13
Malt & Beer
Japan
6.71
6.31
42
2
2.9 |
7
0.1
8
0.01
ill!
0.0
1
! 3 |
9
Malt & Beer
Rest of the world
62
6.3|
391
2
2.9 !
7
1.1
11
0.12
IK!
0.1
17
I 37 !
120
Starch Production
United States
11
9j
99
1.5
10 |
42
1.0
8
0.08
20
0.2
2
I 24 I
133
Starch Production
Europe
8.5
9!
77
1.5
10 j
42
0.8
8
0.06
ill!!
0.4
2
! 18 !
103
Starch Production
Rest of the world
10.5
9 j
95
1.5
10 I
42
0.9
11
0.10
im
0.1
3
| 31 j
175
Group 3. Vegetables, Fruits, and Textiles
Veg., Fruits, & Juices
United States
8.68
20 i
174
2
5 j
10
0.9
0
0.00
:!?si
0.8
0
! 0 I
0
Veg., Fruits, & Juices
Germany
4
20:
80
2
5 !
10
0.4
0
0.00
iifP
0.4
0
i o |
0
Veg., Fruits, & Juices
Rest of the world
18.7
20!
374
2
5 !
10
1.9
4
0.07
i-3cy
0.6
6
j 22 !
60
Textiles (natural)
China
9.73
172|
1,673
0.8
0.9 I
1.6
1.5
3
0.05
0.1
8
i 14 !
32
Textiles (natural)
United States
4.4
172!
756
0.8
0.9 |
1.6
0.7
0
0.00
0.6
0
I 0 I
0
Textiles (natural)
India
3.32
172!
571
0.8
0.9 j
1.6
0.5
3
0.02
iiiii-
0.0
3
\ 5 I
11
Textiles (natural)
Rest of the world
15.9
1723
2,735
0.8
0.9 :
1.6
2.5
4
0.10
0.7
18
I 30 I
70
Soft drinks
Indonesia
24.48
2:
49
1
2 !
4
0.1
3
0.00
0.0
0
| 1 !
2
Soft drinks
United States
15
2!
30
1
2 1
4
0.1
0
0.00
!!§!!:
0.1
0
! o I
0
Soft drinks
Rest of the world
63.9
2:
128
1
2 !
4
0.3
4
0.01
ill!
0.1
1
i 3 !
8
Group 4. Pulp & Paper
Pulp & Paper
Canada
9.07
162!
1,469
1
8.5 j
15
12.5
1
0.12
IISPI
0.0
3
I 37 j
88
Pulp & Paper
United States
6
162 j
972
1
8.5 j
15
8.3
1
0.08
!!;§!
wmm.
2
I 25 j
58
Pulp & Paper
Japan
3.5
162!
567
1
8.5 !
15
4.8
1
0.05
ilsi
:;!!®!!
1
I 14 I
34
Pulp & Paper
Rest of the world
13.4
1621
2,171
1
8.5 |
15
18.5
12
2.21
Mob
52
| 664 :
1,563
-------
TABLE 18 (continued)
cn
N>
INDUSTRY TYPE
COUNTRY
Output
Wastewater
COD
Total
TA„
COD
COD to City
Methane Emissions
Generation
COD
Anaer.
Sewers
(Tg/yr)
(m3/Mg) | (10s
l/yr)
(g/i)
(Tg/yr)
<%)
(Tg/yr)
(%)
(Tg/yr)
(Gg/yr)
low
mean j
high
low
mean :
high
Group 5. Organic Chemicals and Related Products
Organic Chemicals
France
15.6
67!
1,045
0.8
3
5
3.1
3
0.09
30
0.9
5
28 !
63
Organic Chemicals
Germany
14.84
67 j
994
0.8
3
5
3.0
3
0.09
30
0.9
5
27 :
60
Organic Chemicals
India
11.24
671
753
0.8
3
5
2.3
4
0.09
4
0.1
5
27 !
60
Organic Chemicals.
Japan
26.65
67 j
1,786
0.8
3
5
5.4
3
0.16
27
9
48 !
107
Organic Chemicals
United States
101
67 j
6,767
0.8
3
5
20.3
1
0.20
20
00:'lil0::;O:
11
61 :
135
Organic Chemicals
Rest of the world
60
67|
4,020
0.8
3
5
12.1
3
0.36
I'fOix:
19
109 !
241
Soap & Detergents
China
2.58
3.1!
8
0.5
0.9
1.2
0.0
4
0.00
0.0
0
0 !
0
Soap & Detergents
United States
3.87
3.1!
12
0.5
0.9
1.2
0.0
1
0.00
gsSP":
0.0
0
0 !
0
Soap & Detergents
Rest of the world
26
3.1!
81
0.5
0.9
1.2
0.1
3
0.00
0.0
0
1 |
1
Paints
United States
4.18
0.6!
2.5
1
5.1
10
0.0
1
0.00
WM10;
0.0
0
0 !
0
Paints
Indonesia
6.38
0.6:
3.8
1
5.1
10
0.0
4
0.00
&!!
0.0
0
0 !
1
Paints
Rest of the world
14.3
0.6:
8.6
1
5.1
10
0.0
3
0.00
0.Q
0
o i
1
Petroleum Refineries
United States
715
0.6!
429
0.4
1
1.6
0.4
1
0.00
0.1
0
1 I
3
Petroleum Refineries
Rest of the world
1,435
0.6!
861
0.4
1
1.6
0.9
3
0.03
10
0.1
2
8 !
17
Plastics and Resins
Germany
16.33
671
1,094
0.4
1
1.6
1.1
3
0.03
30
0.3
3
10 j
21
Plastics and Resins
Japan
13.55
67!
908
0.4
1
1.6
0.9
3
0.03
27
0.2
2
8 !
17
Plastics and Resins
United States
24.28
67!
1,627
0.4
1
1.6
1.6
1
0.02
20
0.3
1
5 !
10
Plastics and Resins
Rest of the world
54
67!
3,618
0.4
1
1.6
3.6
3
0.11
10
0.4
9
33 I
69
Coke
United States
21
0.8!
17
0.05
0.1
0.2
0.0
1
0.00
20
0.0
0
o !
0
Coke
World
243
0.8|
194
0.05
0.1
0.2
0.0
3
0.00
10
0.0
0
o !
0
Total Global (Tg/yr):
131
8.6
18
0.6
2.6
6.4
-------
Other industries
17%
Pulp & Paper
29%
Sugar Refining
5%
Alcohol Refining
11%
Organic Chemicals
12%
Meat & Poultry
26%
Figure 3. World Methane Emissions from Anaerobic Industrial WWT.
The second principal contributor to CH4 emissions from WWT is the meat and
poultry industry which is known to use anaerobic lagoons. Also, the alcohol, sugar
refining industries, and organic chemicals manufacturing are major contributors to CH4
emissions from WWT. Again, it was assumed that for these industries some anaerobic
WWT conditions may occur resulting in CH4 emissions.
Earlier estimates for global CH4 emissions from industrial WWT are significantly
higher [i.e., between 26 and 40 Tg/yr (U.S. EPA, 1994)]. The two main reasons that the
emissions in this current report are lower are that iron and steel manufacturing and
petroleum refining are excluded as significant categories and that the fraction of
wastewater degrading anaerobically is significantly lower for most remaining categories.
(In U.S. EPA 1994, it was assumed that between 10 and 15 percent of wastewater
degrades anaerobically.)
Domestic Wastewater
The methodology for calculating CH4 emissions from domestic wastewater used in
this report is represented by Equation 12, adapted from Equation 10.
CH4 emissions = EF * 10"12 * ]T (Pc * CODc * 365 * TAC) (Tg/yi) ¦ (12)
C
53
-------
where: EF = Emission factor (g CH4/g CODremoved);
Pc = Country population;
CODc = Country-specific per capita COD generation (g/day);
TAC = Country-specific fraction of COD treated anaerobically; and
Subscript c = An individual country.
Country populations P are readily available in the literature and region-specific per capita
COD generation rates come from Table 15. Country-specific COD loadings in domestic
wastewater and information on the country-specific fraction of COD that is treated
anaerobically (TAC) is included in Table 19. TAC does not only represent anaerobic
lagoons; WWT plants that are predominantly aerobic may have an anaerobic primary
treatment step. Also, certain pockets of the aerobic WWT process (e.g., holding tanks or
maturation ponds may be intentionally, or unintentionally anaerobic and in addition there
may be on-site sludge storage or holding under anaerobic conditions). As previously
mentioned, actual sludge treatment is excluded from this research.
The product of the aforementioned parameters representing the amount of the COD
in the wastewater that is expected to be treated anaerobically was multiplied by the
emission factor of 0.3 ± 0.1 g CH4/g COD. Table 19 includes estimates of the amount of
CH4 that is emitted from anaerobic domestic WWT for different regions of the world.
According to Table 19, CH4 emissions from domestic WWT are estimated to be between
0.6 and 2.1 Tg/yr with a mean value of 1.3 Tg/yr. Russia is believed to be the largest
contribute. The country is expected to have an advanced sewer line network, but lacks
the financial and technical means to perform proper WWT. This situation is expected to
result in anaerobic conditions. Earlier estimates for global CH4 emissions from domestic
WWT are 2.3 Tg/yr (U.S. EPA, 1994).
Industrial Wastewater Discharged into Sewers
Equation 11 was adapted to obtain an estimate of global CH4 emissions from
industrial wastewater that is discharged into municipal sewers to be treated at municipal
WWT plants.
CH4 emissions = EF * CODtotal * TAC average (Tg/yr) (13)
where: EF = Emission factor (g CH4/g CODremoved);
CODtotal = Total COD (Tg/yr) discharged into municipal sewers;
TAC = Country-specific fraction of COD that is treated anaerobically;
and
Subscript c = An individual country.
Wastewater from this source category is likely to mix completely with domestic
wastewater and will undergo the same transportation and degradation routes as domestic
COD. Accordingly, TAC for domestic wastewater may be used. The average global TAC
54
-------
TABLE 19. GLOBAL CH4 EMISSIONS FROM ANAEROBIC DOMESTIC WASTEWATER
TREATMENT
Country
Population
BOD
Total COD
Generation1
TA.
COD Treated
(anaerobic)
CH4 from Anaerobic
Wastewater Treatment
(Million)
(g/capita/
day)
(Tg/yr)
(%)
(Gg/yr)
(Gg/yr)
low
mean
high
low
mean
high
low
mean
high
AFRICA
Nigeria
127
35+/-10
2.9
4.1
5.2
0.5
14
20
26
3
6
10
Egypt
59
35+/-10
1.3
1.9
2.4
1.0
13
19
24
3
6
10
Kenya
28
35+/-10
0.6
0.9
1.1
2.0
13
18
23
3
5
9
South Africa
43
40+/-10
1.2
1.6
2.0
3.2
37
50
62
7
15
25
Zimbabwe
12
40+/-10
0.3
0.4
0.5
3.2
10
13
17
2
4
7
Other Africa
492
35+/-10
11.2
15.7
20.2
0.5
56
79
101
11
24
40
ASIA
China
1,238
35+/-10
28
40
51
0.8
212
297
381
42
89
153
India
931
35+/-10
21
30
38
0.8
159
223
287
32
67
115
Indonesia
201
35+/-10
4.6
6.4
8.3
1.5
69
97
124
14
29
50
Pakistan
135
35+/-10
3.1
4.3
5.5
0.8
23
32
42
5
10
17
Bangladesh
128
35+/-10
2.9
4.1
5.3
0.8
22
31
39
4
9
16
Japan
126
55+/-15
4.6
6.3
8.0
4.1
186
256
326
37
77
130
Other Asia
726
35+/-10
17
23
30
0.8
124
174
224
25
52
89
EUROPE
Russia
150
50+/-10
4.8
6.8
8.9
14.0
670
956
1,243
134
287
497
Germany
81
60+/-15
3.3
4.4
5.6
4.0
133
178
222
27
53
89
United Kingdom
58
60+/-15
2.4
3.2
4.0
4.5
107
143
179
21
43
72
France
58
60+/-15
2.4
3.2
4.0
3.8
91
121
151
18
36
60
Italy
58
60+/-15
2.4
3.2
4.0
3.6
86
114
143
17
34
57
Other OECD
113
60+/-15
4.6
6.2
7.7
2.6
122
162
203
24
49
81
Other Europe
217
60+/-15
8.9
12
15
3.5
312
416
520
62
125
208
NORTH AMERICA
United States
263
65+/-15
13
17
20
3.5
462
588
714
92
176
286
Canada
29
60+/-15
1.2
1.6
2.0
3.5
41
55
68
8
16
27
LATIN AMERICA AND CARIBBEAN
Brazil
161
35+/-10
3.7
5.2
6.6
1.0
37
52
66
7
15
27
Mexico
94
35+/-10
2.1
3.0
3.8
1.0
21
30
38
4
9
15
Others
224
35+/-10
5.1
7.2
9.2
1.0
51
72
92
10
21
37
AUSTRALIA AND NEW ZEALAND
Australia
18
60+/-15
0.7
1.0
1.2
3.5
26
34
43
5
10
17
Total Global (Tg/yr):
154
212
270
3.1
4.2
5.4
0.6
1.3
2.1
' A factor of 2.5 was used to convert BOD to COD.
55
-------
from Table 17 is estimated to be about 4 percent and it is estimated that about 17.2 Tg/yr
of industrial COD is discharged into municipal sewers (see Table 18). As with other
industrial and domestic wastewater, the emission factor (0.3 g CH4/g COD). CH4
emissions from industrial wastewater that is treated at municipal WWT plants are
estimated to be 0.2 Tg/yr.11
CARBON DIOXIDE
The field test report (Eklund and LaCosse, 1997) concludes that facultative lagoons
that treat municipal wastewater are not a significant source of any GHGs, with the
possible exception of C02. The report mentions that OPM/FTIR results were not
conclusive for C02 emissions from anaerobic lagoons. No other emissions information on
C02 emissions from WWT was found and Table 15 contains no C02 emission factors, other
than the theoretical emission factor which was based on a stoichiometrical mass balance
calculation (i.e., 1.37 g COJg COD) (pp. 12 and 13).
The theoretical emission factor can be used to develop an estimate of maximum C02
emissions by assuming that all COD in wastewater decomposes aerobically. The total
amount of COD generated from industrial and domestic sources is estimated to be about
343 Tg/yr (see Table 18 and 19), and total global C02 emissions from industrial and
domestic wastewater combined are estimated to be 470 Tg/yr. Human wastewater
generation is the single largest source (290 Tg/yr). The global pulp and paper, and
organic chemicals manufacturing industries account for 69 percent of C02 emissions from
all industrial sources. As a comparison, C02 emissions from U.S. fossil fuel combustion
are estimated to be 5,000 Tg/yr (U.S. EPA, 1993b).
NITROUS OXIDE
N20 emissions from WWT can be associated with the anaerobic or anoxic
decomposition of organic matter containing proteins and other organic nitrogen
compounds (page 27). The following emission factors were suggested to estimate NzO
emissions from WWT: 5.1 g/capita/yr for conventional12 domestic WWT; and 0.09 g/g COD
for anaerobic WWT that is either domestic or industrial. Aerobic industrial WWT may
also have denitrification, but currently no emission factor exists for this source category.
By using data from Table 17 it was estimated that 734 million people in the world
are served by conventional WWT including aerobic and facultative lagoons. Consequently,
global N20 emissions from conventional domestic WWT are estimated at 5.1 x 734 =
3,743 Mg/yr (0.004 Tg/yr).
Estimated global N20 emissions from anaerobic domestic WWT are 0.09 x 5.4 =
0.5 Tg N20/yr. The amount of COD in global domestic wastewater that is treated under
11 This does not include emissions for untreated industrial wastewater in sewers or gutters.
12 Most conventional WWT is expected to be activated sludge WWT with nitrification/denitrification.
56
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anaerobic conditions is 5.4 Tg/yr (Table 19). For the United States, it was estimated that
4 percent of COD in domestic wastewater is treated under anaerobic conditions which is
equivalent to 0.59 Tg/yr (Tables 17 and 18). Thus, U.S. N20 emissions from anaerobic
domestic WWT can be estimated at 0.05 Tg/yr. These estimates are coarse estimates and
are provided only to illustrate the potential significance of the source categories. They do
not include potential emissions from other anaerobic domestic wastewater sources, such
as septic tanks, latrines, and possibly certain sewers that may have anaerobic sections.
Wastewater from the meat, poultry, fish, and dairy processing industries is expected
to contain substantial amounts of bound nitrogen. According to Table 18, the amount of
COD in anaerobic wastewater from these industries is estimated to be 2.7 Tg/yr.
Consequently, global N20 emissions from this source category are estimated at 0.09 x 2.7
= 0.24 Tg N20 per year. For the United States, the amount of COD from this source
category is estimated at 1.3 Tg/yr, resulting in estimated emissions of 0.12 Tg N20/yr.
As a comparison, current U.S. estimates for total N20 emissions are 0.4 Tg/yr and do not
include WWT. These estimates are associated with large uncertainties and are, at best,
an indication of the relative significance of this source category.
Some other absolute and relative estimates were found in the literature. Czepiel
et al. (1995) estimated that for the United States N20 emissions from conventional
activated sludge WWT were 1,200 Mg/yr or 0.3 percent of national emissions. Schon et
al., (1993) estimated that German N20 emissions from activated sludge WWT are about
850 Mg/yr or 0.2 percent of total German N20 emissions. Debruyn et al., (1994) estimated
that N20 emissions from Belgian wastewater are 0.6 percent of total Belgian emissions,
but provides no absolute figures. As the emission factor for conventional WWT that was
used in this report is based on data from the aforementioned authors, no relative U.S.
data are provided. The combined N20 emission estimates from anaerobic industrial and
domestic WWT, based on the emission factor from the field tests are 0.17 Tg/yr.
TABLE 20. SUMMARY OF GLOBAL GHG ESTIMATES FOR DOMESTIC AND
INDUSTRIAL WWT.
GHG
SOURCE
LOWER
BOUND
(Tg/yr)
AVERAGE
(Tg/yr)
; UPPER
BOUND
(Tg/yr)
REMARKS
ch4
Industrial WWT
0.6
2.4
6.1
ch4
Domestic WWT
0.6
1.3
2.1
n2o
Domestic Activated
Sludge WWT
0.004
These are rough
estimates.
No lower and upper
bounds are
available.
n2o
Domestic Anaerobic
WWT
0.5
n2o
Anaerobic WWT at
meat, poultry, fish, and
dairy processing
industries
0.24
57
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UNCERTAINTIES
Uncertainties Associated With the CHj Emission Factor
The specific uncertainties associated with the development of the field test emission
factors, such as the representativeness of the test sites and suitability of the test
procedures, are discussed in the field test report (Eklund and LaCosse, 1997). It is
believed that the field test emission factors reflect an upper-end estimate because part of
the CH4 may not come from the wastewater but from sludge at the bottom of the lagoons
that had been deposited in previous years (see Appendix C).
The CH4 emission factor used in this report is expressed as 0.3 ± 0.1 g CH4/g
CODramoved. The emission factor reflects a value that is based on theoretical and digester
data, as well as, the lower-end of the range of the emission factors derived from the field
test results. The emission factor expresses CH4 emissions per mass of CODremoved and is
used for all types of organic wastewater. CODremoved is a surrogate for the amount of
degradable organic carbon in the wastewater that can be turned into CH4. The ratio of
COD to actual degradable organic carbon may vary for different types of wastewater.
Inorganic components in wastewater will also contribute to the COD. As this report only
examines wastewater that is basically organic in nature, errors associated with inorganic
COD cannot be examined but are thought to be relatively minor. Nevertheless, the
correlation between COD and emissions of specific GHGs warrants more research.
The range for the emission factor (i.e., ±0.1 g CH4/g CODremoved) is based on expert
judgement and accounts for the aforementioned 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 reason is that both the theoretical
and digester emission factors reflect upper-end estimates. Also, the field test emission
factors reflect emissions that may be relatively high.
Uncertainties Associated With Industrial Wastewater Activity Data
Equation 11 expresses the methodology used to estimate emissions from industrial
wastewater. The uncertainties associated with each activity parameter in the equation
are addressed below.
Country-specific annual industrial output data (Pfc) are compiled by the United
Nations and published in the Industrial Statistical Yearbook or UNISY. Pk numbers were
multiplied by average industry-specific wastewater outflow (Q, in m3/Mg of product) and
CODi values (g/1) to obtain total COD in wastewater (Tg/yr). The UNISY data base
contains over 100 countries and includes output data for each country for up to
22 industrial categories. It may be presumed that some reporting errors are made and
the data reduction that was necessary to make the data base manageable may also have
lead to inaccuracy. Compared to the uncertainties that are expected to be associated with
average Q, and CODL values, uncertainties in Pic are expected to be relatively minor.
Qi and CODi values depend on the product that is being produced, the production
process, and the efficiency of the process. The type and efficiency of the industrial process
58
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are likely to be dependent on plant scale, availability and cost of water, local water and
wastewater regulations and the degree of enforcement. Ultimately, it is expected that
errors are associated with the extrapolation of data across industries, even within the
same category. It is likely that there is a certain inverse correlation between Qi and
CODt, and possibly Pt .13 Because of this likely correlation, it was decided to assign ranges
to reflect the inaccuracies of the total COD numbers and not to the individual
constituents Pk, Qi} and CODTable 12 includes average and CODi values, as well as
ranges for Qi and CODt. If only one data set was available, the range was assumed to be
a factor of two (i.e., 60 percent, +100 percent). For most industries, the variability in
CODt values are considerably wider than the ranges for Qt. Therefore, the ranges in CODt
values were also used to reflect the uncertainty in the total COD output.
Assignment of values for the industry- and country-specific fraction of COD in
wastewater that is treated anaerobically at the industrial site (TAtc) is based on anecdotal
information and on engineering judgement. Anecdotal information addresses the limited
degree of WWT in many parts of the world. Engineering judgement includes knowledge
on restrictions in aerobic or anaerobic WWT for certain industries.
Apart from treatment of meat and poultry processing wastewater, anaerobic
treatment is uncommon. Nevertheless, average values for TAk in Table 13 are higher
than zero. For OECD countries, TAk values are typically between 1 and 4 percent, and
for developing and Eastern European countries TAk values may be as high as 20 percent
(e.g., the Russian pulp and paper industry). For OECD countries it was assumed that
some anaerobic conditions may exist, for instance as a result of poorly aerated sections of
lagoons or tertiary sedimentation basins. Also, temporary sludge storage on site may be a
source of CH4 emissions. For developing and Eastern European countries the same
assumptions were made, but it also was assumed that under-aeration and/or overloading
of aerobic WWT system may easily result in anaerobic conditions. Significant
uncertainties are associated with these assumptions.
A sensitivity analysis was conducted to quantify and compare the uncertainties
associated with the different parameters used to develop CH4 emissions from industrial
WWT. Different parameters were varied and the percent change in total global CH4
emissions was recorded. As pulp and paper, meat and poultry, organic chemicals, and
alcohol and starch are expected to be the prime sources for CH4 emissions from industrial
WWT, the sensitivity analysis is limited to these groups.
As is indicated by Table 21, relatively large uncertainties are associated with the
quantification of the degree of wastewater that may decompose under anaerobic
conditions in WWT plants that are designed to be aerobic.
13 This correlation is based on economies of scale and on the understanding that the wastewater stream is an
indicator of process efficiency. For a large plant, the combination of per unit wastewater outflow and
wastewater loading is likely to be lower than for a smaller plant. A certain plant may have a relatively small
flow of highly concentrated wastewater or it may have a relatively larger flow of diluted wastewater.
59
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TABLE 21. SENSITIVITY ANALYSIS OF INDUSTRIAL CH4 ESTIMATES
INDUSTRY
GROUP
OLD ASSUMPTION
(STATUS QUO)
NEW ASSUMPTION
CHANGE IN
GLOBAL CH4
EMISSIONS
Pulp and Paper
Some anaerobic
decomposition likely (e.g.,
overloading, underaeration)
WWT is 100% aerobic
-27%
Pulp and Paper
WWT in OECD countries is
1% anaerobic
WWT in OECD countries is 4%
anaerobic
+ 8%
Organic Chemicals,
et al.
Raw discharge in developing
countries is 60% and in
OECD countries 0 to 10%
Raw discharge more
widespread: 80% in developing
countries. 10% in OECD
countries.
-3%
Organic Chemicals,
et al.
Treatment on site is 50 to
90%
Treatment on site is 25 to 45%
-7%
Organic Chemicals,
et al., and Alcohol
and Sugar Refining
Some anaerobic
decomposition likely (e.g.,
overloading, underaeration,
sludge storage)
Anaerobic WWT/decomposition
is twice of what was assumed
before.
+ 17%
Meat and Poultry
70 to 95% of wastewater
assumed to be treated on
site.
100% of wastewater is treated
on site (as opposed to some
discharge into sewers)
+ 5%
Uncertainties Associated With Domestic Wastewater Activity Data
The emission factor used for estimating CH4 emission from anaerobic domestic WWT
is the same as for industrial wastewater. Uncertainties associated with the emission
factor are discussed there. The country populations are believed to be relatively accurate
and no ranges were defined for this parameter. Country-specific per capita COD
generation rates (g/day) are also believed to be well known. Values and ranges are
included in Table 15. These ranges are propagated in the ultimate emission estimates.
Table 17 includes information on the country-specific fraction of COD that is treated
anaerobically (TAC). Assumptions were made to quantify the extent to which sewage is
discharged into a city sewer to be treated at a municipal WWT plant. Only for OECD
countries is domestic sewage typically treated at municipal WWT plants, whereas for
other countries sewage is mostly discharged without treatment or treated in latrines.
(Latrines and septic tanks as a source for GHG emissions are not included in this
research.) In OECD countries WWT is expected to be almost fully aerobic (90 to
95 percent). The remaining 5 to 10 percent reflect probable anaerobic conditions in
sections of the process, such as sedimentation tanks, and sludge storage. For other
countries it was assumed that 50 percent of WWT is anaerobic. This number reflects the
use of anaerobic lagoons, as well as, mismanagement or overloading of aerobic systems
and/or facultative lagoons.
60
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Compared to industrial WWT, the uncertainties associated with the extent of
domestic WWT are not expected to be as large. More information is available in the
literature, for example on sanitation issues, and this information can also be used to
define the extent of sewerage and types of WWT. Table 22 includes a sensitivity analysis
to quantify and compare the uncertainties associated with TAC. Different components of
TAC were varied and the percent change in total global CH4 emissions was recorded.
TABLE 22. SENSITIVITY ANALYSIS OF DOMESTIC CH< ESTIMATES
OLD ASSUMPTION
(STATUS QUO)
NEW ASSUMPTION
CHANGE IN
GLOBAL
ch4
EMISSIONS
In developing countries about 50% of
WWT is anaerobic.
In developing countries about 25% of
WWT is anaerobic. (Improve WWT
plant management)
-30%
In developing countries there is little
WWT
Amount of WWT is twice as high (see
Table 17)
+ 69%
In developing countries 10 to 15% of
population has a sewer connection (Latin
America 40%)
Number of sewer connections is twice
as high (see Table 17)
+ 43%
Eastern and Southern Europe does not
have adequate WWT
Brought to North European standards
-8%
China has very little WWT
Number of plants is twice as high.
+ 33%
In China about 50% of WWT is
anaerobic.
Ensured all WWT plants are aerobic.
(Optimize WWT plant management)
-11%
Table 22 indicates that there is a large uncertainty associated with the estimates of
the extent of WWT in developing countries. Also, significant uncertainties stem from the
assumptions that estimate the degree of anaerobicity in WWT plants in developing
countries and eastern Europe.
Uncertainties Associated With the N2Q Emission Estimates
N20 is generated, as well as, absorbed during nitrification and denitrification and
many uncertainties are associated with the development of reliable N20 emission factors.
Schon et al. (1993) summarizes the reasons for the uncertainties as follows:
• Emissions show strong variations over daily, as well as over longer, time
frames. The reasons for these variations are not yet known;
• The influences caused by different WWT methods have not yet been quantified;
and
• Development of a nitrogen mass balance to assist in quantifying emissions from
specific sources in the WWT is very difficult.
61
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The field tests detected N20 emissions only from the anaerobic waste lagoons at the
chicken processing plant; consequently, only one set of N20 emissions data was obtained.
No emissions were detected from the anaerobic waste lagoons at the two beef processing
plants or the facultative lagoons at the two POTWs.
The field test emission factor, as well as, the emission factor developed from the
literature must be used cautiously. The uncertainties associated with the activity data
have been addressed earlier. The industrial activity data used in the U.S. estimate are
believed to be relatively accurate. Also the activity value for conventional domestic WWT
is believed to be fairly accurate, as it is based on population. The estimate for anaerobic
domestic WWT includes an assumption on the degree in which COD decomposes under
anaerobic circumstances. This assumption is based on expert judgement and may have
large uncertainties associated with it.
TRENDS
Trends that affect CH4 emissions from WWT are directly related to the amount of
organics that degrade in wastewater under anaerobic conditions. Trends that affect N20
emissions are related to anaerobic, as well as anoxic wastewater conditions associated
with denitrification. On a global scale, only a small fraction of all wastewater is treated.
Most wastewater is discharged into gutters or sewers where it may remain stagnant or
through which it may flow into rivers or other surface water. Changes in the amount of
wastewater that is treated are, of course inversely proportional to changes in the amount
of wastewater that is not treated. Untreated wastewater may rapidly turn septic and
may be a major source of GHG emissions. Therefore, trends in wastewater treatment as
they affect GHG emissions, can best be discussed when adequate background knowledge
on untreated wastewater, such as sanitation issues and open sewers, is included in the
evaluation. As issues regarding untreated wastewater were not included in this study,
this section on trends in WWT is necessarily generic.
Ongoing global industrialization, population growth, and also urbanization are likely
to increase the annual industrial and domestic wastewater outflow. In many urbanized
areas in developing countries, inadequate disposal of wastewater has become a major
health issue. Although significant gains have been made in the provision of sanitation
services, the influx of migrants into cities has nullified most efforts. In addition, the
extended sewer line coverage has intensified the problems associated with the lack of
WWT. As mentioned before, industrial and domestic wastewater is typically discharged
raw into surface water, and rivers in developing countries are often little more than open
sewers, making them unsuitable as a source for drinking or even irrigation water for
down stream users. (Bartone 1990; Bartone 1994.) In some areas the inadequate
disposal of pollutants has resulted in widespread ground water contamination, thus
further reducing the availability of clean water (World Resources Institute, 1994).
The problems associated with the lack of WWT extend throughout the developing
world including the countries of the former Soviet Union and most Eastern European
countries. As far as domestic WWT, no significant improvements are expected for most of
these countries in the near future (Draaijer, 1994). There are few exceptions such as the
62
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former German Democratic Republic which has had access to West German financial and
technical support. It should be noted that in some areas, problems associated with WWT
and water availability have become so demanding that the implementation of
improvements cannot be put off much longer. For example several arid countries, such as
Tunisia, Turkey, and Bahrain are actively contemplating improved WWT with the main
objective to recycle the effluent as crop irrigation water.
In regard to industrial WWT the situation may be a little better. Large industries
are more easily regulated and monitored than indeterminate groups of urbanites. Also,
such industries may be financed or managed by multinational companies that are more
inclined to an integrated approach to WWT. Also, in some developing countries including
countries such as Chile, Taiwan, Indonesia, and Singapore, notable economical growth has
lead to a degree of prosperity making WWT affordable. Also, to sustain their high
economical growth rates industries in these countries may be encouraged to implement
source reduction and conservation programs which will impact wastewater generation. It
is expected that these countries will increase efforts to clean their wastewater in the near
future (Doppenberg, 1994).
Significant improvements in regard to WWT can currently only be expected from
developed countries that have not had comprehensive WWT before. Examples of these
countries are Belgium, Spain, Greece, and Turkey. Also, some east European countries,
including Czechia, Slovenia, Hungary, and possibly Poland are experiencing significant
economical growth that may enable them to finance improved WWT. Furthermore, the
European Union in principal enforces uniform water and effluent quality regulations for
its members, as well as its candidate members. For example, pressure to meet such
regulations (in this case 90 percent reduction of load) has forced Spain to clean up its act.
(WWEE, 1992.)
As mentioned before, preferred WWT throughout the world typically is aerobic
(activated sludge) for large scale applications and facultative lagoons for small scale
applications. Therefore, increased levels of WWT could lead to a reduction in GHG
emissions. However, if WWT is favored over, for instance an ocean outfall, GHG
emissions may increase. Without incorporating the contributions of untreated
wastewater, it is not possible to properly estimate the effect of increased WWT on GHG
emissions from this source category.
63
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APPENDIX A: SUMMARIES OF FIVE INTERVIEWS WITH WWT EXPERTS
In 1993, the state of knowledge, as reflected in the Report to Congress (EPA, 1994) was
considered too limited to be a basis for improved emissions estimates. To obtain additional
international WWT activity data, a data quest was undertaken in 1994 in Western Europe.
Efforts focussed on the Netherlands, a German technical library and Belgium. The
Netherlands is an international leader in environmental technology development, particularly
in the fields of biotechnology and WWT. Data from a Belgian N20 study have been included
in the report and are not repeated here. Below are summaries of interviews with six Dutch
wastewater experts.
INTERVIEW 1 (5/27/94)
Mr. Hans Draaijer, Advisor
GRONTMIJ
de Bilt, Netherlands
Grontmij is an environmental engineering firm and contractor (2,300 people). The majority of
their activities are executed in the Netherlands. However, they also do work in Poland,
Hungary, Russia, Japan, India, Taiwan, and China.
General
Draaijer expects that untreated wastewater is a significant global methane source since there
is very little WWT worldwide. Draaijer suggests that statistics on the percentage of people
with sewer hookup may be a useful activity indicator. In the Netherlands and West Germany,
this number is 95 percent. In Belgium, it is less than 50 percent. Also, the fraction of
wastewater that is treated per country might be very low. For instance, Belgium does not
treat significant portions of their wastewater. Countries with tourism (e.g., Greece, Portugal,
and Spain) usually are inclined to do a little more toward WWT, for public relations reasons.
Outside of the OECD, the fraction of the wastewater treated is negligible.
India and Sri Lanka
Draaijer has spent extensive time in India. Grontmij works on two UASB projects in
Mirzapur and Kanpur, India. The two UASB plants in India (on line April 94 and December
94) are funded with Dutch Government development aid. There is practically no sewerage in
India. Usually sewage runs in a ditch to a river or lake. According to Draaijer, even a
shallow ditch (30 cm) would quickly become anaerobic. This may be concluded from the black
slime on top and the emanating bubbles. Anaerobic conditions are facilitated by high ambient
temperatures. Also, wastewater in these ditches may have a very long residence time. The
gradient might be very low and the gutter or canal may be filled with debris. The residence
time would be an important parameter, according to Draaijer.
Draaijer points out that in municipal sewage, methanogens are already present in the liquid,
as well as in deposits in pipe bends, etc. In sewer pipes, he expects the water to become
anaerobic very rapidly, because the deposits will be a continuous source of methanogens.
Eventually the sewage may make it to a larger body of water, typically a river. Draaijer
thinks that rivers will become oxygen poor, but never totally anaerobic. He does not know
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how much methane could be generated in semi-anaerobic rivers. (Note: rivers would have an
aerobic facultative layer that breaks down any methane.)
In Sri Lanka, Draaijer also witnessed small channels into which sewage was discharged.
They were almost completely clogged up and completely anaerobic.
Policy in India and Sri Lanka is to promote standardized aerated lagoons. Construction is
simple, so proper operation will depend on maintenance (and energy cost for aeration). In Sri
Lanka, Draaijer visited an industrial park with mainly large exporting or foreign owned
companies. Such a cluster of wealthy companies would typically have WWT. In India, there
are a few showcase WWT installations. In Varanasi, a brand new aerobic WWT plant was
installed but it never ran, because of high energy cost. Draaijer said it had a large by-pass.
Like many developing countries, India has modern regulations copied from a country such as
the USA or Britain. However, there is no enforcement and some institutions or certain states
may conduct a little monitoring.
What can be done in India (and similar countries) regarding the municipal sewage situation:
1. The awareness level of the population should be raised.
2. Build latrines or biogas vaults or tanks.
3. The retention time of the sewage in the ditches of pipes should be reduced. Build
concrete ditches and make sure sludge deposits containing methanogen seeds
cannot form.
4. Implement new technologies. UASB is interesting for developing countries. The
technology is very simple. There are only two moving parts. The reactor can be
built out of concrete blocks. It is recommended that the generated gas be burned in
a direct user (such as a boiler), since electricity generation requires high technology
expertise to operate, which is not always available.
Eastern Europe
In Eastern Europe, engineering development stopped 40 years ago. There are many
antiquated WWT plants, most of which are not running. Almost all of the projects in Eastern
Europe are being financed with West European funds. Firms like Grontmij are hired for
studies and not to actually perform or assist with construction.
Case study from East Germany. A Dutch company bought a slaughter house in Nohra, near
Weimar. Before, wastewater from the slaughter house simply drained into a forest. Grontmij
was hired to build a new WWT plant. This plant was laid out with a capacity to treat all
slaughter house waste (70 percent of capacity) and an additional 30 percent of sewage from a
nearby town. Now the plant is finished but only the slaughter house waste is being treated.
The sewers still have to be built (consider sewers part of infra-structure).
Within a very short period of time, East Germany will have to start applying West German
regulations; therefore, a high level of activity may be expected in East Germany, funded for
100 percent by the Western part. All other Eastern European countries really have no money
at all. Draaijer expects that the environmental situation in most countries is going to get
worse before it gets better. Poland is a little less poor and may be somewhat of an exception.
Draaijer does not know how many lagoons there are in Eastern Germany.
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If a WWT plant would be built, it typically would consist of aerobic pretreatment (activated
sludge reactor) which can remove 35 percent of the COD, and an anaerobic sludge digester.
Sludge digesters may be a considerable methane source (Lexmond mentioned this also). In
the Netherlands, methane leaks from the sludge digesters are estimated at 30 percent (?). In
India, at sites inspected by Grontmij, 100 percent of the methane was emitted. In Eastern
European countries, methane leakage from sludge digesters could well be 50 percent.
Methane Indicator
BOD is an aerobic test. Anaerobic organisms are more sensitive than aerobic. COD is better.
Grontmij knows from experience what part of COD gets turned into methane: (1) Municipal
wastewater: 80 percent of COD will turn into methane and 5 percent into sludge; (2)
Industrial wastewater: low concentrations, 80 percent of COD will turn into methane and for
high concentrations this number is 90-95 percent.
INTERVIEW 2 (5/31/94)
Mr. Doppenberg, Senior Advisor
Hoofdweg 490
IWACO
Rotterdam, The Netherlands
IWACO is an environmental engineering firm with 350 employees with a focus on water and
wastewater technology.
General
According to Doppenberg, when dealing with developing countries, it is important to realize
that people in developing countries have no influence. The system is rather feudal. People
put up with bad circumstances, such as stench. They don't know any better.
In Africa, facultative lagoons have been in use since the late seventies, especially near smaller
cities. In Asia, there would be few lagoons. The population density is too high. No
quantifiable data are available.
Europe
In Eastern Europe, most cities have sewer lines; however, there is very little WWT. In rural
areas septic tanks are being used. Money invested in WWT in Eastern Europe, it usually
comes from the European Community and the European Bank for Reconstruction and
Development based in London. Just like the World Bank, this bank might have information
on the level of sanitation in Eastern European countries. If WWT systems are installed in
Eastern Europe, they would typically be activated sludge systems with anaerobic sludge
digestion. (Doppenberg mentions that sludge digestion installations are known to leak.)
Doppenberg confirms that Belgium has no WWT. Wastewater flows' straight into rivers.
France is better.
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Newlv Industrialized Countries
Newly industrialized countries include countries such as Singapore, Korea, and Taiwan.
Urbanization rates in these countries are between 4-6 percent per year. The result is that
infrastructure cannot keep up with the urban growth. For instance, due to high freshwater
demand, there may easily occur a water shortage in the region. This would not only reduce
freshwater supply, but also reduce water flows in rivers. Yet the quantity of waste disposed of
by water is on the rise. Taiwan is investing a lot of money in sewerage. Together with the
World Bank, master plans have been developed.
Doppenberg expects that newly industrialized countries may start to purify in 10 to 20 years.
He also believes that the wastewater problem caused by domestic sources is greater than that
caused by industrial sources. Industrial sources can be pinned down and isolated more easily.
Also, they have more financial resources. Environmental law enforcement usually has no
teeth. Economic considerations prevail.
Indonesia
Indonesia has started an active program to get industry to clean up its wastewater.
Doppenberg calls it: "a reasonably consequent approach." Currently, in Djakarta and also in
the rest of Indonesia there is no sewerage and no WWT. Sewage is collected in gutters which
discharge into larger canals. The water appears to be stagnant. From observation it may be
judged to be completely anaerobic. When it rains the system is somewhat flushed out.
Eventually it runs into a river or the ocean.
Recently, there was a study conducted at a laboratory in Delft which specializes in water
engineering problems (contact Eelco van Beek or Jos Dijkman, 015-569353). The objective
was to calculate the amount of water to flush the open sewers in Djakarta and to see if rain
would provide this amount. The conclusion was negative. Rainwater cannot provide enough
flow for the open sewers to do the job. Relief can only come from reduction at the source
(sanitation programs). Issues relating to developing the mass balance include, the amount of
sewage that seeps away through the soil, the water evaporation rates, and "fast run off'
losses.
Mr. Doppenberg related his experience from a boat ride off the Djakarta coast towards an
archipelago called the Thousand Islands. The speed boat ride was about an hour. Coming
back, half an hour off shore, there is an obvious and sudden change in the water quality.
Clean seawater changes into brown/black water, which apparently is not aerobic.
Methodology proposed bv Doppenberg
In order to develop CH4 emission estimates from domestic wastewater in developing countries,
Doppenberg's suggests to eliminate the rural population contributions, collect sanitation data
from the World Bank and the European Bank for Reconstruction and Development, calculate
how much methane can be formed in open sewers.
For industrial wastewater he suggests to eliminate cooling water contributions, see which part
of industry is located on rivers and assess if wastewater from these sources can be excluded as
a methane source, assess if the conditions and retention time are sufficient for industrial
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wastewater to turn anaerobic before it reaches the river, develop emission factors for these
situations, estimate emissions from WWT.
Innovative Methodologies
Suitable Technologies (for newly industrialized countries and Developing Countries).
Population density or urbanization determines the type of WWT that is most suitable.
• Large scale would be aerobic. Large city, high density: sewerage and treatment
plant. (If something breaks down in aerobic WWT, it will be the aerator, since that
is the mechanical part.)
• Medium size might actually be lagoons. Smaller cities, less urban: introduce
sewerage in phases, build WWT plant which can be expanded easily.
• Small scale projects: anaerobic WWT is suitable. Even smaller, just a
neighborhood: UASB. Eventually you can switch to centralized WWT.
• Individual housing, low population density: septic tanks and basic latrines.
An issue with anaerobic WWT is that there is typically no natural gas piping network, so the
gas cannot be sold or transported by existing pipeline. An option would be to store the
biomethane in bottles. Doppenberg points out that it is all a matter of economics. If other
types of energy are cheap, you can forget selling the digester methane. For instance,
Indonesia has a lot of oil. A market is slowly being created for natural gas. If natural gas is
available, nobody will want the digester gas. On the other hand, wood is getting scarce in
many countries.
INTERVIEW 3 (6/1/94)
Mr. W.M. Wiegant and Ms. A.T.J.J. Kalker,
HASKONING, Royal Dutch Consulting Engineers
Nijmegen
The Netherlands
Haskoning is a large international civil and environmental consulting/engineering firm with
wastewater related projects in many countries, including India, Japan, South America, and
Africa. Recently Haskoning was commissioned a project to assess needs to clean up the
Danube river. As part of this project they will produce estimates of wastewater discharges
into the river.
General
Wiegant believes that on a global scale domestic sewage is a larger methane source than
industrial wastewater. Significant industrial sources are the food processing and agricultural
industries; a large plant may produce wastewater quantities equivalent to that of a city of a
million inhabitants. Industrial WWT, if any, would typically be a lagoon. Exceptions are
plants that have been built by the British. For some reason they favor trickling filters.
Either method requires sludge treatment. Wiegant stressed the importance of sludge
formation. In a sewer, half of the dry solids may become sludge. Only the remaining half
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then would be the potential methane source. Wiegant says that for domestic sewage, dry-
solids is a good parameter for estimating methane potential.
Wiegant believes there are many lagoons in South America.
According to Wiegant, rivers or lakes may indeed become facultative with excessive BOD
inflow. Wiegant does not know how to assess the fraction of methane that still might be
emitted from facultative rivers. Wiegant confirms that seas or oceans can indeed turn
anaerobic. However they will not emit methane. The reason is that there are sulfates in the
sea water. "H2S-ogens" are dominant compared to methanogens.
South America. Colombia
Ms. Kalker spent several years in Colombia in the late eighties. At that time, there was
practically no WWT in the country. There are WWT laws, but there is no enforcement. Only
recently the Government Department of the Environment was established. If Kalker had to
give a number, she would say that currently (1988?) no more than 2 percent of wastewater is
treated in Colombia.
In South America the alcohol industry is a large polluter. The production of one liter of
alcohol produces five kg of COD. The palm oil industry seems to be somewhat of an exception,
and has historically received more than average attention, possibly because the palm oil
process is highly polluting. Kalker believes they are using lagoons.
The city of Cali, Colombia, population 2,000,000, has recently developed a master plan to treat
its wastewater. There was already a sewage system in place. (Note: there is anecdotal
evidence that other South American countries, such as Brazil, also have extended sewer
systems). In the early 1990's, a UASB WWT plant became operational. This plant takes care
of sewage from 200,000 people or 10 percent of the population of Cali.
India
The fraction of wastewater treated in India is negligible. Typical WWT (if existent) would be
aerobic (activated sludge reactor). Nevertheless, Wiegant would recommend anaerobic WWT
for warm countries. Experience has been positive. It requires practically no energy or
maintenance. You can avoid pumping by using natural gradients. Then the only remaining
piece of mechanical equipment is the rake mechanism at the top. The methane is usually
flared off.
Composting
At a WWT plant, the remaining solids left after sludge digestion may be composted. A
compost heap is anaerobic (according to Wiegant). The inside is anaerobic, but the outside
layer is aerobic and will break down the methane again. Even if the compost is turned over,
the fresh oxygen is depleted rapidly and anaerobic conditions will be recreated within the
hour.
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INTERVIEW 4 (5/24/94)
Mr. Karel Jansen,
Wastewater Expert Netherlands
Heineken Breweries, Zoeterwoude, The Netherlands.
In 1993, Heineken produced 1,480 million gallons of beer with operations in 50 countries.
For every gallon of beer, 5 to 9 liters of wastewater are generated. Typically, wastewater from
a brewery has BOD = 1,400 and COD = 2,400 (rule of thumb: COD = 1.8 x BOD). The
wastewater also contains significant amounts of nitrogen. Wastewater from one hundred
liters of beer will require 540 grams of 02. In aerated lagoons 35 percent of the COD and
50 percent of the BOD can be removed daily.
Worldwide Heineken policy is to treat wastewater in aerated lagoons. Mr. Jansen pointed out
that aeration requires energy and therefore, costs money. As such, there may be an
inclination to under-aerate.
Heineken is constructing new anaerobic WWT systems at breweries in the Netherlands and in
Spain, and in the future, possibly in other European countries. These plants are UASB
reactors and are meant for pretreatment and can remove 80 to 90 percent of all pollutants.
The main reason for switching to anaerobic treatment would be space constraints. Also,
Heineken actively uses the biogas as fuel in on-site boilers or, for instance in space heating or
electricity generation for offices.
INTERVIEW 5 (5/24/94)
Ms. Dr. Ir. G. Zeeman
Department of Environmental Technology
Wageningen Agricultural University
Wageningen, Netherlands
Anaerobic treatment is of particular interest to Wageningen Agricultural University and
ongoing research is conducted to study and improve anaerobic WWT systems, in particular the
upflow anaerobic sludge blanket digester (UASB), which was invented here. The UASB is a
mechanically simple pretreatment technique that requires little space and maintenance. It is
suitable for small to medium size wastewater flows and has been employed for treatment of
sewage, as well as, wastewater from the following processes: alcohol, sugar, most food and
beverages, fermentation, and petrochemicals. The key to the process is the formation and
maintenance of a suspended granular anaerobic sludge which allows high upflow wastewater
velocities and as a consequence high COD loading rates (up to 20 kg COD/m3.d). Gas, water
and return sludge are separated in the top of the vessel by a system of fixed baffles.
Disadvantage of the system is that methanogens are very sensitive to changing environmental
conditions, such as pH, temperature, presence of toxins and/or nutrients. (Information from
Biothane International, phone 011.31.15.700111. and Paques, phone 011.31.5140.8500.)
Dr. Zeeman and Ms. Lexmond (not present) have worked on a global inventory of waste and
wastewater flows for specific industries that emit methane and thus may be suitable for
anaerobic WWT (Lexmond and Zeeman, 1994; Lexmond and Zeeman, 1995). Activity data
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were collected in part by interviewing environmental professionals from developing countries.
These people were in the Netherlands for training. The 1994 and 1995 reports of Lexmond
and zeeman are quoted extensively throughout this report and are not discussed here again.
Also, Zeeman and Lexmond hope to get funding for a new project. The aim of this project is to
categorize global non-C02 greenhouse gas control technologies. Information will be provided
with respect to: state-of-the-art technologies, emission reduction potentials, costs of controls,
prospects for further development and (nontechnological) constraints, all per type of
wastewater. The lead contractor will be Ecofys in Utrecht, the Netherlands (drs. de Jager,
phone 011.31.30.732144).
Zeeman disapproves of using BOD as a parameter for methane emissions because BOD
determination is an aerobic test. The relationship between BOD and produced methane will
depend on the type of wastewater. To compensate for this effect Lexmond introduced a factor
which is specific for different types of wastewater.
REFERENCES
Biothane Systems International, P.O. Box 5068, 2600 GB Delft, The Netherlands.
(Not Dated.) Commercial data.
Lexmond, M.J., and G. Zeeman. 1994. Potential of Uncontrolled Anaerobic Wastewater
Treatment in Order to Reduce the Global Emissions of Methane and Carbon Dioxide.
From "Non-C02 Greenhouse Gases." Ham, J. van et al. (Eds.), pp. 411-419. Kluwer
Academic Publishers, the Netherlands. 1994.
Lexmond, M.J., and G. Zeeman. 1995. Potential of Controlled Anaerobic Wastewater
Treatment in Order to Reduce the Global Emissions of the Greenhouse Gases Methane
and Carbon Dioxide. Department of Environmental Technology, Agricultural University
of Wageningen, Wageningen, the Netherlands. Report nr. 95-1. May 1995.
U.S. EPA. 1994. International Anthropogenic Methane Emissions: Estimates for 1990.
Report to Congress. EPA/230-R-93-010. 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. 1994.
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APPENDIX B: WASTEWATER TREATMENT METHODS
Removal of contaminants from wastewater is done by physical, chemical, or
biological means or a combination thereof. Simple treatment methods in which the
application of physical forces predominates are screening, mixing, and sedimentation.
Filtration, flocculation, and flotation are more complicated physical treatment methods.
Precipitation, adsorption, and disinfection are examples of common chemical treatment
methods. Biological treatment is used to remove the biodegradable organic substances
from the wastewater. Basically, these substances are converted into gases (including
GHGs) that can escape to the atmosphere and into biological cell tissue that can be
removed by settling (sludge). Biological treatment is also used to remove nutrients (such
as dissolved nitrogen and phosphorus compounds) from the wastewater. (Metcalf & Eddy,
Inc., 1991.)
Another common classification of WWT methods is in primary treatment (or
pretreatment), secondary treatment, and tertiary (or advanced) treatment. In primary
treatment, physical operations are used to remove floating and settleable solids from the
wastewater. In secondary treatment biological and, to a lesser extent, chemical processes
are used to remove most of the organic matter. Subsequently, in tertiary treatment
combinations of processes are used to remove the remaining constituents and pathogens
in order to upgrade the quality of the treated wastewater. Tertiary treatment processes
include: maturation/polishing ponds, filtration, carbon adsorption, ion exchange,
disinfection, and phosphorus and nitrogen removal (nitrification/denitrification).
Denitrification may be a source of N20. Otherwise, tertiary treatment processes are not
considered to have potential for GHG emissions.
The text below gives an overview of the processes that are typically found in a
standard municipal WWT plant or POTW treating domestic sewage and possibly some
industrial wastewater. Particular industries that (pre)treat their liquid waste may
employ different treatment processes, which are not included in the text below. Standard
municipal WWT plant systems are only economical if they have a certain minimum size.
Small community WWT systems may include processes that are principally similar to that
of large municipal WWT plants, or they may use processes that are entirely different,
such as land treatment. Also, domestic wastewater may be treated in septic tanks or pit
latrines. The description of small scale systems is not included in this report. Future
research will be aimed at estimating GHG emissions from such systems and from
untreated wastewater.
Primary Treatment
Upon entering a municipal WWT plant, wastewater will typically first encounter a
coarse screen to remove large size solids, such as rags and wood. At this location, the
velocity of the wastewater will be relatively high to prevent settling of solids and the
screen itself will cause additional turbulence in the wastewater. This turbulence is
conducive to stripping a significant fraction of the gases that may have been dissolved in
the wastewater. Such gases may include VOCs from industrial facilities or
biodegradation products, such as C02, CH4, or H2S that were generated in closed sewers.
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The ensuing primary treatment step typically incorporates a reduction of the
wastewater velocity to bring about settling of TSS (sedimentation). Settling tanks for
coarse particulates are often called "grit chambers," whereas finer solids are separated
from the wastewater in a "clarifier." (Clarifiers may also be included as intermittent
steps in secondary treatment.) Other primary WWT may consist of oil and grease
removal by skimming the surface of, for instance the clarifier.
Secondary Treatment
Secondary treatment is a combination of biological processes in which organic matter
is biodegraded in an aerobic environment, sometimes in combination with an anaerobic
phase. The oxidized TSS fraction will settle as sludge. Secondary biological treatment
processes may be divided into:
• Stabilization lagoons (also referred to as aerated/aerobic lagoons, oxidation
ponds, anaerobic lagoons, facultative lagoons);
• Trickling filters; and
• Activated sludge processes.
Stabilization Lagoons—
Treatment in stabilization lagoons is the most natural, effective and economically
viable process, especially in regions with plenty of sunshine and available land.
Depending on the secondary treatment process, the removal efficiency may be between
75 to 95 percent of BOD and 80 to 95 percent of TSS. To obtain optimal results, several
lagoons may be employed in series (e.g., an anaerobic primary pond followed by one or
more facultative or aerobic lagoons, followed by oxidation ponds). (Oxidation ponds are
also called maturation or polishing ponds and are considered tertiary treatment.)
Facultative lagoons are those in which the upper layer is maintained as an aerobic
zone and the lower one as an anaerobic zone. The upper layer can retain an aerobic
status, due to algal photosynthesis, as well as weather influences, such as wind and rain.
The depth of facultative lagoons ranges from 1 to 2.5 m depending on the temperature
and the type of wastewater to be treated. These lagoons are normally used as primary or
secondary units to anaerobic or aerated lagoons for industrial wastewater.
In oxidation ponds aerobic conditions are also maintained by the natural
photosynthetic process by algae and by surface aeration. Unaerated lagoons are usually
very shallow (e.g., 0.6 m), whereas the depth in aerated lagoons may be around
1.5 meters, reducing the area requirements for lagoon construction significantly. Aerobic
lagoons are typically used for treating domestic sewage that has had some form of
pretreatment.
Anaerobic lagoons can be compared to a digester and are routinely used for the
treatment of very strong wastewater, such as from slaughterhouses. Their primary
function is to reduce the initial high demand of oxygen which otherwise would be required
for oxidation of the organics. The effluent from anaerobic lagoons requires additional
aerobic treatment to meet most quality standards. The anaerobic degradation process of
organic matter involves two types of bacteria. Facultative organisms break down large
B-2
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organic molecules into smaller molecules, such as organic acids, while other bacteria
transform the organic acids into CH4 and C02. Simultaneously, other bacteria convert
organic nitrogen into NH3 and H2S may also be formed.
Design criteria for different types of lagoons are summarized in Table B-l.
Anaerobic lagoons may have depths that exceed 5 m. The effect of retention time on BOD
removal in anaerobic lagoons is relatively minor. The storage of deposited solids seems to
be of primary importance and the actual liquid retention time should be such that the
CH4 producing bacteria are not washed out of the system. The optimum retention time is
5 days (Mullick, 1987). Anaerobic lagoons operated with higher hydraulic retention times
(HRTs) have been found to be facultative rather than anaerobic. Unlike for aerobic and
facultative lagoons, design criteria for anaerobic lagoons are not based on area
considerations, as the processes in the pond do not depend on insolation. Recommended
loading rates vary between 0.1 to 0.4 kg BOD/m3/day, depending on the type of waste and
water temperature. BOD removal efficiencies may be around 65 to 80 percent. (Mullick,
1987.)
TABLE B-1. DESIGN CRITERIA FOR LAGOONS
Aerobic
Facultative
Aerated
Anaerobic
Organic loading
85-170 kg
BOD /ha/day
17-55 kg
BOD /ha/day
25-400 kg
BOD /ha/day
0.1-0.4 kg
BOD/m3/day
Depth (m)
0.6
0.9-2.5
1-3
2-5
Retention time (days)
5-20
10-100
3-20
2-30
pH range
6.5-10.5
6.5-9
6.5-8
6.8-7.2
Temp. Range (*C)
0-40
0-40
0-40
7-40
Temp. Optimum («C)
20
20
20
30-35
BOD (%)
80-95
75-95
80-95
50-80
Based on Mullick (1987) and Metcalf & Eddy (1991).
Trickling Filters—
Trickling filters are large circular tanks filled with porous elements, such as crushed
rock, slag, or molded plastic. The wastewater is mixed with air by spraying it onto the
elements after which it trickles down to the bottom of the tank to be removed or
recirculated. The microorganisms that are responsible for breaking down the dissolved
and suspended organics live in a slimy layer on the surface of the elements. Trickling
filters are considered to be entirely aerobic and will, therefore, be a source of C02
emissions to the air. Also, due to the agitation of the wastewater during the spraying
action, gases that are dissolved in the wastewater will easily be stripped. A high rate
trickling filter may have a loading rate of 0.75 kg BOD/m3/day. The BOD removal
efficiency is approximately 80 percent.
B-3
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Activated Sludge Process—
The activated sludge process is a continuous-flow aerobic biological process for the
treatment of domestic and biodegradable industrial wastewater. The process provides a
high-quality effluent and is characterized by the thorough mixing of microorganisms,
oxygen, and wastewater induced by the aeration system. The mixture is referred to as
"mixed liquor." During the aeration phase bacteria convert organic matter into cell
matter, energy, C02, NH3, water (H20), and other end products. The mixed liquor is
usually recirculated. Excess sludge is removed from the process and effluent from the
aeration basins will typically be discharged into a clarifier where the microorganisms
settle out and are recycled to the aeration basin.
There are many varieties to the activated sludge process, some of which comprise
two or more separate aeration steps. Therefore, it is difficult to produce overall
characteristic data; however, the following design data from Standard Handbook of
Environmental Engineering (1990), applicable to a "conventional" activated sludge system,
may provide an indication:
• volumetric loading
• detention time
• mixed liquor recycle
• sludge retention time
• sludge production
Nitrification and Denitrification
Nitrification and denitrification are an integral part of WWT. Nitrification is the
oxidation of NH3 to nitrate and water and takes place in aerobic reactors such as trickling
filters or rotating biological contactors, either separately or in combination with
carbonaceous matter removal. Denitrification is the reduction of nitrate and nitrite to
N20 and nitrogen (N2). It may be classified as advanced treatment and takes place under
absence of oxygen. The presence of dissolved oxygen will inhibit the process. Also, the
denitrification organisms are sensitive to changes in temperature and pH. Usually an
extra carbon source (i.e., methanol) is required for cell growth. Separate stage
denitrification may take place in plug-flow type reactors or in column reactors. To avoid
the cost of carbon addition, processes have been developed that combine nitrification/
denitrification processes with other treatment steps. These combined systems are
characterized by an aerobic and an anoxic zone and recirculation of part of a stream that
is rich in organic carbon (Metcalf & Eddy, 1991). N20 emission models are discussed
separately in the section entitled "Additional Information on Greenhouse Gas Emissions
from WWT."
0.4-0.8 kg BOD/day/m3;
4-8 hrs;
50-100 percent;
5-10 days;
0.5 kg/kg BOD.
B-4
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Sludge Treatment and Disposal
Sludge withdrawn from various stages of a WWT plant normally needs to be treated
further to ensure its safe and most cost-effective disposal. Economic considerations play
an important role, because the cost of sludge treatment and disposal may represent up to
half the cost of the preceding liquid treatment facilities. Aerobic bacteria produce
considerably more sludge than anaerobic bacteria, given similar loadings and efficiencies.
The volume of sludge produced usually ranges from 0.3 to 0.7 percent of the volume
of wastewater treated and depends on the BOD or TSS loading. In conventional plants
(primary treatment followed by activated sludge treatment) approximately 0.6 to 1.0 kg
sludge (dry solids) are produced per kg BOD. Sometimes a value of 0.025 to 0.03 kg (dry
solids)/person/day is used. For pond systems a rate of sludge accumulation of 0.03 to
0.08 m3/person/yr is used. This implies that pond sludge removal would be necessary
every 2 to 5 years (Mullick, 1987). Sludge generation in lagoons will vary widely. In cold
climates sludge will accumulate faster than in warm climates due to sedimentation of
unbiodegraded matter. Fresh sludge typically has a moisture content of up to 99 percent
and is difficult to consolidate. Methods for sludge treatment are:
• Aerobic and anaerobic digestion (also referred to as stabilization);
• Conditioning (e.g., use of flocculants);
• Concentration and dewatering (e.g., centrifugation or filter press);
• Composting; and
• Drying.
These sludge treatment processes are often used in combination with each other. Aerobic
and anaerobic digestion are the only sludge treatment processes that involve significant
breakdown of the sludge to produce C02 and/or CH4 and other end products. Therefore,
they will be discussed in some detail below.
Aerobic Digestion—
Stabilization of sludge by aerobic digestion is usually employed for secondary
activated sludges. The operating costs are relatively high, because the aeration necessary
for proper mixing of the sludge is energy intensive. On the other hand, capital costs are
lower and operation and maintenance is easier compared to anaerobic digestion. Because
of the energy requirements aerobic digestion is best suited for smaller treatment facilities.
Performance is strongly affected by temperature and below 10°C sludge stabilization may
be insufficient (Mullick, 1987; Standard Handbook of Environmental Engineering, 1990.)
The reduction of volatile solids is about 30-50 percent, depending on the temperature and
sludge retention time may vary between 12 to 30 days.
Anaerobic Digestion—
Anaerobic digestion of sewage sludge results in conversion of readily degradable
organic matter into CH4 (60 to 70 vol. percent), C02 (20-30 vol. percent), H2S, other gases,
and water, leaving a biologically stable residue. Volatile solids are reduced by 40 to
60 percent. In addition a significant reduction in pathogenic bacteria occurs. Anaerobic
digestion takes place in cylindrical tanks with a conical bottom. The tank cover is usually
floating and auxiliary equipment is required for gas collection, mixing and heating.
B-5
-------
Digester gas, which has a heating value of around 600 British thermal units (Btu)/ft3 can
be a valuable resource. Even though the gas produced by anaerobic digesters is meant to
be collected, digesters should be considered as potential GHG sources, because significant
amounts of gas may leak to the air (Lexmond and Zeeman, 1994).
REFERENCES
Lexmond, M.J., and G. Zeeman. 1994. Potential of Uncontrolled Anaerobic Wastewater
Treatment in Order to Reduce the Global Emissions of Methane and Carbon Dioxide.
From "Non-C02 Greenhouse Gases." Ham, J. van et al. (Eds.), pp. 411-419. Kluwer
Academic Publishers, the Netherlands. 1994.
Metcalf & Eddy, Inc. 1991. Wastewater Engineering': Treatment Disposal and Reuse.
3rd Edition. McGraw-Hill Book Company, New York. ISBN 0-07-041690-7. p. 109.
Mullick, M.A. 1987. Wastewater Treatment Processes in the Middle East. The Book
Guild Lt. Lewes, Sussex, Great Britain. ISBN 0-86-332-336.
Standard Handbook of Environmental Engineering. 1990. Edited by R. A. Corbitt,
McGraw-Hill Publishers. ISBN 0-07-013158-9.
B-6
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APPENDIX C: EFFECT OF WATER AND AMBIENT AIR TEMPERATURE ON
CH4 EMISSIONS AND COD REMOVAL RATES IN ANAEROBIC LAGOONS
The temperature of wastewater in an anaerobic lagoon is expected to have a
significant effect on the decomposition of organics in wastewater and on biogas
generation. Lettinga et al. (1983) studied domestic sewage treatment in a 120 1 pilot
upflow anaerobic sludge blanket (UASB) reactor and collected numerous influent and
effluent data over a period of almost a year. COD removal efficiency and biogas
production data from this study are plotted against temperature in Figure C-l.
350
300
250
200
150
100
50
~
~
~
A A
~
k
Biogas P
oduction
A
~
i
k
A
J
k
~
I
A
\
/
*
< X
X ;
X
, x
X
px
X
COD R<
smoval E
ficiency
>»
O
c.
o
100%
50%
10 12 14 16
Water Temperature (deg. C)
20
;igure C-1. Biogas Production and COD Removal Efficiency as
a Function of Temperature in a Pilot UASB Reactor Treating
Domestic Sewage.
According to Figure C-l the COD removal efficiency does not vary significantly with
temperature. The biogas production, however, decreases significantly and drops to about
one third of the 20°C value. Lettinga does not provide data on the composition of the
biogas, but as the reactor is anaerobic, it may be assumed that the gas is predominantly
CH4. A comparable study was conducted by Viraraghavan and Kikkeri (1990) who
monitored the effect of temperature on anaerobic filter treatment of dairy wastewater for
various retention times at three set temperatures: 12.5, 21, and 30°C. For a 6-day
retention time, they observed a slight drop (about 10 percent) in COD removal efficiency
from 82 percent to 74 percent over the 30 to 12.5°C temperature range. The CH4
production rate however, dropped from 0.29 to 0.08 m3/kg COD (72 percent) for that
temperature range (Figure C-2).
C-l
-------
The COD removal efficiency curves in Figure C-2 indicate a non-linear relationship
with temperature. Toprak (1993) also summarizes findings that manifest a non-linear
curve for CH4 emission rates versus lagoon temperatures. From Figure C-2, it is unclear
if the accelerated drop in CH4 generation occurs at 21°C or at lower temperatures
(because the lines consist of only three points). But according to Draaijer (1994) the 20 to
21°C zone is significant. Draaijer relates the following experience concerning a full scale
UASB system in India: "The treatment efficiency remained constant irrespective of the
decrease in temperature during winter time; even though there was a clear decline in gas
production during about four weeks in January, when the sewage temperature decreased
to 20°C, the biogas production increased rapidly again when the sewage temperature went
up." All studies cannot be quantitatively compared, because each uses different output
data. Nevertheless, it may be concluded in general that CH4 emission rates in an
anaerobic wastewater treatment system begin to drop at about 21°C and that below about
12 to 15°C CH4 emissions are insignificant.
100
80
>-
60
40
20
0.3
0.2
RETENTION
TIMES
-O- 6 days
•A- 3 days
-O- 1 day
en 0-1
CO
12.5
21
30
Water temperature (deqr. C)
Figure C-2. COD Removal Efficiencies and CH4 Production
as a Function of Temperature
As mentioned earlier, Lettinga's data in Figure C-l show no apparent drop in COD
removal with falling temperatures, whereas Viraraghavan and Kikkeri (Figure C-2) found
only a slight decline. Both studies describe systems (an UASB reactor and anaerobic
filter) that are believed to be more efficient than ordinary anaerobic lagoons and, hence,
COD removal efficiencies for lagoons may be lower. Also, removal efficiencies for lagoons
will depend on many other factors, including retention time (see Figure C-2), type of
C-2
-------
wastewater, and the lagoon layout. Merker (1996) gave the following generic numbers for
anaerobic U.S. poultry processing waste lagoons: BOD removal efficiency in summer is
about 70 percent and in winter about 40 percent.14 In spite of lower removal efficiencies
in winter, it is apparent that in an anaerobic lagoon in a country such as the United
States, significant amounts of undegraded COD stay behind in winter. When in spring
the water temperature increases again to around 15°C partial anaerobic degradation of
this stored COD may again start up, whereas, at 21°C optimum degradation temperatures
will again have been reached. Accordingly, in late spring and summer, CH4 emissions
may be expected to be significantly higher than predicted using theoretical estimates,
whereas, in winter they may be expected to be near zero. It is unclear if degradation and
thus, gas emissions peak as soon as the 21°C mark is reached, or if there is a certain lag
time.
Lagoon water temperatures may be related to average ambient air temperatures.
Metcalf and Eddy (1991, p. 606) include an equation (Equation 7) for a completely mixed
lagoon and state that the complete mixing assumption is acceptable as long as the depth
of the lagoon does not exceed 12 ft (3.7 m).
T...
AfTa + QT,
Af + Q
(14)
where: Tw =
Ta =
Tt =
A
Q =
f =
The factor f incorporates the appropriate heat transfer coefficients and includes the
effect of surface area change due to aeration, wind, and humidity. For the Southeastern
United States f = 0.5. No values for /"for other areas are given so this number was also
used for the Southern United States. Anaerobic lagoons usually have fairly standard
areas and depths, governed by the flow and required retention time. Hence,
representative values for Q and A can be obtained fairly easily from actual data or from
design criteria. Th however, is difficult to determine by methods other than direct
measurement. Before it reaches the lagoon, wastewater may travel a considerable
distance through an underground sewer line, or it may travel through an above ground
pipeline, as is often the case with industrial wastewater. In addition, it may pass through
weirs, screens or settling tanks, where it is subject to short- and long-term climatic
influences, such as solar radiation, wind, humidity, and ambient air temperature (Ta)
variations. Here, it is assumed that Tt is equal to Ta, which, in turn, implies that Tw is
lagoon water temperature (°C);
ambient air temperature (°C);
influent water temperature (°C);
lagoon surface area (m2);
flow rate (m3/day); and
proportionality factor of 0.5.
14 The removal rate for the poultry plant in the field test report is considerably higher (92 percent). The
retention time at the field test plant was 16 days.
C-3
-------
equal to Ta. As long as Ta is an average value, not reflecting short term swings, this
approach appears reasonable.
Figure C-3, shows approximations of monthly water temperatures for two lagoons in
Texas. One curve is for a hypothetical lagoon in Amarillo, Texas, and was developed
using Equation 7 and the assumption discussed above. Ambient air temperatures came
from The National Atlas (Department of the Interior, 1970). The second curve represents
actual effluent water temperatures for a facultative municipal wastewater lagoon in the
Southwestern United States, provided by the plant operator during the field tests
(Eklund, 1996). Effluent temperatures are used here as a surrogate for actual water
temperatures. Figure C-3 is divided into three temperature zones which reflect intensity
of anaerobic degradation (and thus, CH4 emissions). The approximate duration of each
zone in months may be determined from Figure C-2 and is included below.
Zone: Optimum Degradation Partial Degradation Zero Degradation
Facultative lagoon 4% months 31/2 - 5 months 2Vz - 4 months
Hypothetical lagoon 31/2 months 2 - 5 months 5Vz - 6V2 months
Based on the information above it may be concluded that in the Southern United
States optimum temperatures for organics (COD) degradation exist only for a relatively
short time of the year (i.e., ZV2 to AV2 months). During 2V2 to 6V2 months, no degradation
of organics takes place and during the remainder of the year only partial degradation is
likely to occur. During the Partial and Zero Degradation phases, undegraded COD
logically must accumulate in the lagoon. As Draaijer indicated, when the water
temperature rises above 21°C during the 3lA to AV2 months, Optimum Degradation period
(summer), this COD will yet be degraded. During this period, fresh COD will also be
degraded and consequently, CH4 emissions are likely to be significantly higher compared
to emissions from an identical lagoon in a climate with a temperature that is constantly
above the 21°C mark. Without further tests it is unclear if CH4 generation from "old"
COD happens evenly or peak-wise. For example, there may be a peak in microbial
activity shortly after the Optimum Degradation phase is reached, and CH4 emissions
during this peak time may be many times higher than what would be expected as a
yearly average. If CH4 generation from "old" COD is more gradual, it may be expected
that overall summer emissions are at least twice as high as what would be expected at an
ideal lagoon.
C-4
-------
Actual effluent data
for facultative lagoon
in SW U.S., 94/95
OPTIMUM
DEGRADATION
ZONE
24
O) 20
PARTIAL
DEGRADATION
ZONE
Q. 14
F 12
ZERO
DEGRADATION
ZONE
Lagoon temperature data
based on average Amarillo
ambient air temperatures
Mid-Month Values
Figure C-3. Monthly Water Temperatures for Two Lagoons in the Southern
United States
C-5
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REFERENCES
Draaijer, H. 1994. Personal communication between M. Doom, E.H. Pechan &
Associates, Inc., Durham, NC and H. Draaijer, Engineer, GRONTMIJ, de Bilt, the
Netherlands. May 27, 1994.
Eklund, B. 1996. Personal communication between M. Doom, E.H. Pechan & Associates,
Inc., Durham, NC and B. Eklund, Radian Corporation, Austin, TX. 1996.
Lettinga, G., R. Roersma, and P. Grin. 1983. Anaerobic Treatment of Raw Domestic
Sewage at Ambient Temperatures Using a Granular Bed UASB Reactor. Biotechnology
and Bioengineering, Vol, XXV, pp 1701-1723 (1983), John Wiley & Sons, Inc.
Merker B. 1996. Extension Poultry Science Specialist, University of Georgia. Phone:
(910) 519-5610. Teleconference with Michiel Doom.
Metcalf & Eddy, Inc. 1991. Wastewater Engineering: Treatment Disposal and Reuse.
3rd Edition. McGraw-Hill Book Company, New York. ISBN 0-07-041690-7. p. 109.
Toprak, H. 1993. Methane Emissions from the Anaerobic Waste Stabilization Ponds
Case Studv: Izmir Wastewater Treatment System. Dokuz Eyliil University, Turkey.
PhD dissertation.
U.S. Department of the Interior. 1970. The National Atlas.
Viraraghavan, T. and S.R. Kikkeri. 1990. Effect of Temperature on Anaerobic Filter
Treatment of Dairy Wastewater. Water Science and Technology, Vol. 22, No. 9,
pp 191-198.
C-6
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