Chapter 6: Wastewater Treatment and Discharge

CHAPTER 6

WASTEWATER TREATMENT AND
DISCHARGE

2006 IPCC Guidelines for National Greenhouse Gas Inventories

6.1

Volume 5: Waste

Authors
Michiel R. J. Doorn (Netherlands), Sirintornthep Towprayoon (Thailand), Sonia Maria Manso Vieira (Brazil),
William Irving (USA), Craig Palmer (Canada), Riitta Pipatti (Finland), and Can Wang (China)

6.2

2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

Contents
6

Wastewater Treatment and Discharge
6.1

Introduction ......................................................................................................................................... 6.6

6.1.1
6.2

Changes compared to 1996 Guidelines and Good Practice Guidance ......................................... 6.9Methane emissions from wastewater ................................................................................................... 6.9

6.2.1

Methodological issues ................................................................................................................. 6.9

6.2.2

Domestic wastewater ................................................................................................................. 6.10

6.2.2.1

Choice of method ................................................................................................................. 6.10

6.2.2.2

Choice of emission factors ................................................................................................... 6.12

6.2.2.3

Choice of activity data ......................................................................................................... 6.13

6.2.2.4

Time series consistency ....................................................................................................... 6.16

6.2.2.5

Uncertainties ........................................................................................................................ 6.16

6.2.2.6

QA/QC, Completeness, Reporting and Documentation ....................................................... 6.17

6.2.3

6.3

Industrial wastewater ................................................................................................................. 6.18

6.2.3.1

Choice of method ................................................................................................................. 6.19

6.2.3.2

Choice of emission factors ................................................................................................... 6.20

6.2.3.3

Choice of activity data ......................................................................................................... 6.21

6.2.3.4

Time series consistency ....................................................................................................... 6.22

6.2.3.5

Uncertainties ........................................................................................................................ 6.23

6.2.3.6

QA/QC, Completeness, Reporting and Documentation ....................................................... 6.23

Nitrous oxide emissions from wastewater ......................................................................................... 6.24

6.3.1

Methodological issues ............................................................................................................... 6.24

6.3.1.1

Choice of method ................................................................................................................. 6.24

6.3.1.2

Choice of emission factors ................................................................................................... 6.25

6.3.1.3

Choice of activity data ......................................................................................................... 6.25

6.3.2

Time series consistency ............................................................................................................. 6.26

6.3.3

Uncertainties .............................................................................................................................. 6.26

6.3.4

QA/QC, Completeness, Reporting and Documentation ............................................................ 6.27

References ......................................................................................................................................................... 6.28

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Volume 5: Waste

Equations
Equation 6.1

Total CH4 emissions from domestic wastewater ............................................................... 6.11

Equation 6.2

CH4 emission factor for each domestic wastewater
treatment/discharge pathway or system ............................................................................. 6.12

Equation 6.3

Total organically degradable material in domestic wastewater ......................................... 6.13

Equation 6.4

Total CH4 emissions from industrial wastewater ............................................................... 6.20

Equation 6.5

CH4 emission factor for industrial wastewater .................................................................. 6.21

Equation 6.6

Organically degradable material in industrial wastewater ................................................. 6.22

Equation 6.7

N2O emissions from wastewater effluent .......................................................................... 6.25

Equation 6.8

Total nitrogen in the effluent ............................................................................................. 6.25

Equation 6.9

N2O emission from centralized wastewater treatment processes ....................................... 6.25

Figures

6.4

Figure 6.1

Wastewater treatment systems and discharge pathways ...................................................... 6.7

Figure 6.2

Decision Tree for CH4 emissions from domestic wastewater ............................................ 6.10

Figure 6.3

Decision Tree for CH4 emissions from industrial wastewater treatment ........................... 6.19

2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

TablesTable 6.1

CH4 and N2O emission potentials for wastewater and sludge treatment
and discharge systems ......................................................................................................... 6.8

Table 6.2

Default maximum CH4 producing capacity (Bo) for domestic wastewater ....................... 6.12

Table 6.3

Default MCF values for domestic wastewater ................................................................... 6.13

Table 6.4

Estimated BOD5 values in domestic wastewater for selected regions and countries ......... 6.14

Table 6.5

Suggested values for urbanisation (U) and degree of utilisation of treatment,
discharge pathway or method (Ti,j) for each income group for selected countries ............ 6.15

Table 6.6

Example of the application of default values for degrees of treatment utilization (T)by income groups .............................................................................................................. 6.16

Table 6.7

Default uncertainty ranges for domestic wastewater ......................................................... 6.17

Table 6.8

Default MCF values for industrial wastewater .................................................................. 6.21

Table 6.9

Examples of industrial wastewater data ............................................................................. 6.22

Table 6.10

Default uncertainty ranges for industrial wastewater ........................................................ 6.23

Table 6.11

N2O methodology default data .......................................................................................... 6.27

Boxes
Box 6.1

Subcategory - Emissions from advanced centralised wastewater treatment plants ........... 6.26

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Volume 5: Waste

6 WASTEWATER TREATMENT AND
DISCHARGE
6.1

INTRODUCTION

Wastewater can be a source of methane (CH4) when treated or disposed anaerobically. It can also be a source ofnitrous oxide (N2O) emissions. Carbon dioxide (CO2) emissions from wastewater are not considered in the IPCC
Guidelines because these are of biogenic origin and should not be included in national total emissions.
Wastewater originates from a variety of domestic, commercial and industrial sources and may be treated on site
(uncollected), sewered to a centralized plant (collected) or disposed untreated nearby or via an outfall. Domestic
wastewater is defined as wastewater from household water use, while industrial wastewater is from industrial
practices only. 1 Treatment and discharge systems can sharply differ between countries. Also, treatment anddischarge systems can differ for rural and urban users, and for urban high income and urban low-income users.
Sewers may be open or closed. In urban areas in developing countries and some developed countries, sewer
systems may consist of networks of open canals, gutters, and ditches, which are referred to as open sewers. In
most developed countries and in high-income urban areas in other countries, sewers are usually closed andunderground. Wastewater in closed underground sewers is not believed to be a significant source of CH4. The
situation is different for wastewater in open sewers, because it is subject to heating from the sun and the sewers
may be stagnant allowing for anaerobic conditions to emit CH4. (Doorn et al., 1997).
The most common wastewater treatment methods in developed countries are centralized aerobic wastewater
treatment plants and lagoons for both domestic and industrial wastewater. To avoid high discharge fees or tomeet regulatory standards, many large industrial facilities pre-treat their wastewater before releasing it into thesewage system. Domestic wastewater may also be treated in on-site septic systems. These are advanced systems
that may treat wastewater from one or several households. They consist of an anaerobic underground tank and adrainage field for the treatment of effluent from the tank. Some developed countries continue to dispose of
untreated domestic wastewater via an outfall or pipeline into a water body, such as the ocean.
The degree of wastewater treatment varies in most developing countries. In some cases industrial wastewater isdischarged directly into bodies of water, while major industrial facilities may have comprehensive in-plant
treatment. Domestic wastewater is treated in centralized plants, pit latrines, septic systems or disposed of in
unmanaged lagoons or waterways, via open or closed sewers. In some coastal cities domestic wastewater isdischarged directly into the ocean. Pit latrines are lined or unlined holes of up to several meters deep, which may befitted with a toilet for convenience. Figure 6.1 shows different pathways for wastewater treatment and discharge.
Centralized wastewater treatment methods can be classified as primary, secondary, and tertiary treatment. In
primary treatment, physical barriers remove larger solids from the wastewater. Remaining particulates are thenallowed to settle. Secondary treatment consists of a combination of biological processes that promotebiodegradation by micro-organisms. These may include aerobic stabilisation ponds, trickling filters, and activatedsludge processes, as well as anaerobic reactors and lagoons. Tertiary treatment processes are used to further purify
the wastewater of pathogens, contaminants, and remaining nutrients such as nitrogen and phosphorus compounds.
This is achieved using one or a combination of processes that can include maturation/polishing ponds, biologicalprocesses, advanced filtration, carbon adsorption, ion exchange, and disinfection.
Sludge is produced in all of the primary, secondary and tertiary stages of treatment. Sludge that is produced inprimary treatment consists of solids that are removed from the wastewater and is not accounted for in thiscategory. Sludge produced in secondary and tertiary treatment results from biological growth in the biomass, aswell as the collection of small particles. This sludge must be treated further before it can be safely disposed of.
Methods of sludge treatment include aerobic and anaerobic stabilisation (digestion), conditioning, centrifugation,
composting, and drying. Land disposal, composting, and incineration of sludge is considered in Volume 5,
Section 2.3.2 in Chapter 2, Waste Generation, Composition, and Management Data, Section 3.2 in Chapter 3,
Solid Waste Disposal, Section 4.1 in Chapter 4, Biological Treatment and Disposal, and Chapter 5, Incineration
and Open Burning of Waste, respectively. Some sludge is incinerated before land disposal. N2O emissions fromsludge and wastewater spread on agricultural land are considered in Section 11.2, N2O emissions from managed
1

Because the methodology is on a per person basis, emissions from commercial wastewater are estimated as part ofdomestic wastewater. To avoid confusion, the term municipal wastewater is not used in this text. Municipal wastewater is a
mix of household, commercial and non-hazardous industrial wastewater, treated at wastewater treatment plants.

6.6

2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Dischargesoils, in Chapter 11, N2O Emissions from Managed Soils, and CO2 Emissions from Lime and Urea Application,
in Volume 4 of the Agriculture, Forestry, and Other Land Use (AFOLU) Sector.
Figure 6.1

Wastewater treatment systems and discharge pathways

Domestic/industrial wastewater

Collected

Uncollected

Untreated

Rivers, lakes,
estuaries, sea

TreatedSewered toplant

Stagnant
sewer

Treated on site
Domestic: latrine, septic tankIndustrial: on site plant

Wetland
Aerobic treatment

SludgeAnaerobic
Digestion

Land
Disposal

Untreated

Rivers, lakes,
estuaries, sea

TogroundAnaerobic treatment

Reactor

LagoonLandfill orIncineration

Note: Emissions from boxes with bold frames are accounted for in this chapter.

Methane(CH 4 )Wastewater as well as its sludge components can produce CH4 if it degrades anaerobically. The extent of CH4
production depends primarily on the quantity of degradable organic material in the wastewater, the temperature,and the type of treatment system. With increases in temperature, the rate of CH4 production increases. This isespecially important in uncontrolled systems and in warm climates. Below 15°C, significant CH4 production isunlikely because methanogens are not active and the lagoon will serve principally as a sedimentation tank.
However, when the temperature rises above 15°C, CH4 production is likely to resume.
The principal factor in determining the CH4 generation potential of wastewater is the amount of degradableorganic material in the wastewater. Common parameters used to measure the organic component of thewastewater are the Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Under thesame conditions, wastewater with higher COD, or BOD concentrations will generally yield more CH4 thanwastewater with lower COD (or BOD) concentrations.
The BOD concentration indicates only the amount of carbon that is aerobically biodegradable. The standard
measurement for BOD is a 5-day test, denoted as BOD5. The term ‘BOD’ in this chapter refers to BOD5. The
COD measures the total material available for chemical oxidation (both biodegradable and non-biodegradable). 2
Since the BOD is an aerobic parameter, it may be less appropriate for determining the organic components inanaerobic environments. Also, both the type of wastewater and the type of bacteria present in the wastewater
influence the BOD concentration of the wastewater. Usually, BOD is more frequently reported for domestic
wastewater, while COD is predominantly used for industrial wastewater.

2

In these guidelines, COD refers to chemical oxygen demand measured using the dichromate method. (American Public
Health Association, American Water Works Association and Water Environment Federation, 1998)

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Volume 5: Waste

Nitrous Oxide (N 2 O)

Nitrous oxide (N2O) is associated with the degradation of nitrogen components in the wastewater, e.g., urea,
nitrate and protein. Domestic wastewater includes human sewage mixed with other household wastewater, which
can include effluent from shower drains, sink drains, washing machines, etc. Centralized wastewater treatment
systems may include a variety of processes, ranging from lagooning to advanced tertiary treatment technology
for removing nitrogen compounds. After being processed, treated effluent is typically discharged to a receiving
water environment (e.g., river, lake, estuary, etc.). Direct emissions of N2O may be generated during both
nitrification and denitrification of the nitrogen present. Both processes can occur in the plant and in the water
body that is receiving the effluent. Nitrification is an aerobic process converting ammonia and other nitrogencompounds into nitrate (NO3-), while denitrification occurs under anoxic conditions (without free oxygen), andinvolves the biological conversion of nitrate into dinitrogen gas (N2). Nitrous oxide can be an intermediate
product of both processes, but is more often associated with denitrification.

Treatment and Discharge Systems and CH 4 and N 2 O Generation Potential

Treatment systems or discharge pathways that provide anaerobic environments will generally produce CH4
whereas systems that provide aerobic environments will normally produce little or no CH4. For example, forlagoons without mixing or aeration, their depth is a critical factor in CH4 production. Shallow lagoons, less than
1 metre in depth, generally provide aerobic conditions and little or no CH4 is likely to be produced. Lagoons
deeper than about 2-3 metres will generally provide anaerobic environments and significant CH4 production canbe expected.
Table 6.1 presents the main wastewater treatment and discharge systems in developed and developing countries,
and their potentials to emit CH4 and N2O.

TABLE 6.1
CH4 AND N2O EMISSION POTENTIALS FOR WASTEWATER AND SLUDGE TREATMENT AND DISCHARGE SYSTEMS
Types of treatment and disposal

Untreated

River discharge
Sewers (closed and underground)Not a source of CH4/N2O.

Sewers (open)

Stagnant, overloaded open collection sewers or ditches/canals arelikely significant sources of CH4.

Aerobic treatment
Anaerobic
treatment

TreatedCollected
Uncollected

Stagnant, oxygen-deficient rivers and lakes may allow for
anaerobic decomposition to produce CH4.
Rivers, lakes and estuaries are likely sources of N2O.

Centralized aerobic
wastewater treatment
plants6.8

CH4 and N2O emission potentials

May produce limited CH4 from anaerobic pockets.
Poorly designed or managed aerobic treatment systems produce
CH4.
Advanced plants with nutrient removal (nitrification anddenitrification) are small but distinct sources of N2O.

Sludge anaerobic
treatment in centralized
aerobic wastewater
treatment plant

Sludge may be a significant source of CH4 if emitted CH4 is notrecovered and flared.

Aerobic shallow ponds

Unlikely source of CH4/N2O.
Poorly designed or managed aerobic systems produce CH4.

Anaerobic lagoons

Likely source of CH4.
Not a source of N2O.

Anaerobic reactors

May be a significant source of CH4 if emitted CH4 is notrecovered and flared.

Septic tanks

Frequent solids removal reduces CH4 production.

Open pits/Latrines

Pits/latrines are likely to produce CH4 when temperature andretention time are favourable.

River discharge

See above.

2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

6.1.1

Changes compared to 1996 Guidelines and Good
Practice Guidance

The Revised 1996 IPCC Guidelines (1996 Guidelines, IPCC, 1997) included separate equations to estimate
emissions from wastewater and from sludge removed from the wastewater. The distinction has been removed
because the CH4 generation capacities for sludge and wastewater with dissolved organics are generally the same,and separated equations are not necessary. The 2006 Guidelines include a new section to estimate CH4 emissions
from uncollected wastewater. Also, guidance has been included to estimate N2O emissions from advanced
wastewater treatment plants. Furthermore, the industrial wastewater section has been simplified by suggestingthat only the most significant industrial sources need to be addressed. See Section 6.2.3.

6.2

METHANE EMISSIONS FROM WASTEWATER

6.2.1

Methodological issues

Emissions are a function of the amount of organic waste generated and an emission factor that characterises theextent to which this waste generates CH4.
Three tier methods for CH4 from this category are summarised below:
The Tier 1 method applies default values for the emission factor and activity parameters. This method is
considered good practice for countries with limited data.
The Tier 2 method follows the same method as Tier 1 but allows for incorporation of a country specific emission
factor and country specific activity data. For example, a specific emission factor for a prominent treatment
system based on field measurements could be incorporated under this method. The amount of sludge removed
for incineration, landfills, and agricultural land should be taken into consideration.
For a country with good data and advanced methodologies, a country specific method could be applied as a Tier
3 method. A more advanced country-specific method could be based on plant-specific data from large
wastewater treatment facilities.
Wastewater treatment facilities can include anaerobic process steps. CH4 generated at such facilities can berecovered and combusted in a flare or energy device. The amount of CH4 that is flared or recovered for energy
use should be subtracted from total emissions through the use of a separate CH4 recovery parameter. The amountof CH4 which is recovered is expressed as R in Equation 6.1.
Note that only a few countries may have sludge removal data and CH4 recovery data. The default for sludge
removal is zero. The default for CH4 recovery is zero. If a country selects to report CH4 recovery, it is goodpractice to distinguish between flaring and CH4 recovery for energy generation, which should be reported in the
Energy Sector taking into account the avoidance of double counting emissions from flaring and energy used.
Emissions from flaring are not significant, as the CO2 emissions are of biogenic origin, and the CH4 and N2Oemissions are very small so good practice in the Waste Sector does not require their estimation. However, if it iswished to do so these emissions should be reported under the Waste Sector. A discussion of emissions fromflares and more detailed information are given in Volume 2, Energy, Chapter 4.2. Emission from flaring is nottreated at Tier 1.

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Volume 5: Waste

6.2.2

Domestic wastewater

6.2.2.1

C HOICE OF METHOD

A decision tree for domestic wastewater is included in Figure 6.2.
Figure 6.2 Decision Tree for CH 4 emissions from domestic wastewater
Start

Are
wastewater
treatment pathways
characterised?

No

Collect data on theshare of wastewater
treatment in eachpathway.

YesAremeasurements orother bottom-up data available
from the most important
pathways?

Yes

Is a
countryspecific method
available?

Yes

Estimateemissions using
bottom-up data.
Box 3: Tier 3

No
No

Are
country-specificemission factors available
for the key
pathways?

Yes

Estimate emissions
using country-specificemission factors.
(Bo, MCF, etc.)
Box 2: Tier 2

No

Is this a
key category1?

Yes

No

Estimate country-specific
Bo and MCFs for the key
pathways.

Estimate emissions
using default emission
factors. (Bo, MCF, etc.)
Box 1: Tier 1

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for
discussion of key categories and use of decision trees.

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2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

The steps for good practice in inventory preparation for CH4 from domestic wastewater are as follows:
Step 1:Use Equation 6.3 to estimate total organically degradable carbon in wastewater (TOW).

Step 2:

Select the pathway and systems (See Figure 6.1) according to country activity data. Use Equation 6.2
to obtain the emission factor for each domestic wastewater treatment/discharge pathway or system.

Step 3:Use Equation 6.1 to estimate emissions, adjust for possible sludge removal and/or CH4 recovery andsum the results for each pathway/system.

As described earlier, the wastewater characterisation will determine the fraction of wastewater treated or
disposed of by a particular system. To determine the use of each type of treatment or discharge system, it is goodpractice to refer to national statistics (e.g., from regulatory authorities). If these data are not available,
wastewater associations or international organisations such as the World Health Organization (WHO) may havedata on the system usage.
Otherwise, consultation with sanitation experts can help, and expert judgement can also be applied (see Chapter
2, Approaches to Data Collection, in Volume 1). Urbanisation statistics may provide a useful tool, e.g., city sizes
and income distribution.
If sludge separation is practised and appropriate statistics are available, then this category should be separated
out as a subcategory. If default factors are being used, emissions from wastewater and sludge should be
estimated together. Regardless of how sludge is treated, it is important that CH4 emissions from sludge sent tolandfills, incinerated or used in agriculture are not included in the wastewater treatment and discharge category.
If sludge removal data are available, the data should be consistent across the sectors, and categories, amountdisposed at SWDS, applied to agricultural land, incinerated or used elsewhere should be equal to the amountorganic component removed as sludge in Equation 6.1. Wastewater and sludge that is applied on agriculturalland should be considered in Volume 4 for AFOLU Sector, Section 11.2, N2O emissions from managed soils, in
Chapter 11, N2O Emissions from Managed Soils, and CO2 Emissions from Lime and Urea Application.
Wastewater treatment system/pathway usage often differs for rural and urban residents. Also, in developing
countries, there are likely to be differences between urban high-income and urban low-income residents. Hence,a factor U is introduced to express each income group fraction. It is good practice to treat the three categories:
rural population, urban high income population, and urban low income population separately. It is suggested touse a spreadsheet, as shown in Table 6.5 below.
The general equation to estimate CH4 emissions from domestic wastewater is as follows:
EQUATION 6.1
TOTAL CH4 EMISSIONS FROM DOMESTIC WASTEWATER⎡
CH 4 Emissions = ⎢∑ U i • Ti. j • EF j⎢⎣ i , j()⎤⎥ ( TOW − S ) − R⎥⎦

Where:
CH4 Emissions =TOW

CH4 emissions in inventory year, kg CH4/yr= total organics in wastewater in inventory year, kg BOD/yr

S=

organic component removed as sludge in inventory year, kg BOD/yrUi=fraction of population in income group i in inventory year, See Table 6.5.

Ti,j

=

degree of utilisation of treatment/discharge pathway or system, j, for each income group
fraction i in inventory year, See Table 6.5.

i=income group: rural, urban high income and urban low incomej=each treatment/discharge pathway or system

EFj =emission factor, kg CH4 / kg BOD

Ramount of CH4 recovered in inventory year, kg CH4/yr=

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6.2.2.2

C HOICE OF EMISSION FACTORSThe emission factor for a wastewater treatment and discharge pathway and system (terminal blocks with bold
frames in Figure 6.1) is a function of the maximum CH4 producing potential (Bo) and the methane correction
factor (MCF) for the wastewater treatment and discharge system, as shown in Equation 6.2. The Bo is the
maximum amount of CH4 that can be produced from a given quantity of organics (as expressed in BOD or COD)
in the wastewater. The MCF indicates the extent to which the CH4 producing capacity (Bo) is realised in eachtype of treatment and discharge pathway and system. Thus, it is an indication of the degree to which the system
is anaerobic.

EQUATION 6.2
CH4 EMISSION FACTOR FOR
EACH DOMESTIC WASTEWATER TREATMENT/DISCHARGE PATHWAY OR SYSTEM
EF j = Bo • MCF j

Where:
EFj =emission factor, kg CH4/kg BOD

j=each treatment/discharge pathway or systemBo=maximum CH4 producing capacity, kg CH4/kg BOD

MCFj= methane correction factor (fraction), See Table 6.3.

Good practice is to use country-specific data for Bo, where available, expressed in terms of kg CH4/kg BOD
removed to be consistent with the activity data. If country-specific data are not available, a default value, 0.6 kg
CH4/kg BOD can be used. For domestic wastewater, a COD-based value of Bo can be converted into a BODbased value by multiplying with a factor of 2.4. Table 6.2 includes default maximum CH4 producing capacity (Bo)for domestic wastewater.

TABLE 6.2
DEFAULT MAXIMUM CH4 PRODUCING CAPACITY (BO) FOR DOMESTIC WASTEWATER
0.6 kg CH4/kg BOD
0.25 kg CH4/kg COD
Based on expert judgment by lead authors and on Doorn et al., (1997)

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Chapter 6: Wastewater Treatment and Discharge

Table 6.3 includes default MCF values.
TABLE 6.3
DEFAULT MCF VALUES FOR DOMESTIC WASTEWATER
Type of treatment anddischarge pathway orsystemComments

MCF 1

Range

Sea, river and lake
discharge

Rivers with high organics loadings can turnanaerobic.

0.1

0 – 0.2

Stagnant sewer

Open and warm

0.5

0.4 – 0.8

Flowing sewer(open or closed)

Fast moving, clean. (Insignificant amountsof CH4 from pump stations, etc)

00Centralized, aerobic
treatment plantMust be well managed. Some CH4 can beemitted from settling basins and otherpockets.

0

0 – 0.1

Centralized, aerobic
treatment plant

Not well managed. Overloaded.

0.3

0.2 – 0.4

Anaerobic digester forsludgeCH4 recovery is not considered here.

0.8

0.8 – 1.0

Anaerobic reactor

CH4 recovery is not considered here.

0.8

0.8 – 1.0

Anaerobic shallow lagoon

Depth less than 2 metres, use expert
judgment.

0.2

0 – 0.3

Anaerobic deep lagoon

Depth more than 2 metres

0.8

0.8 – 1.0

Septic system

Half of BOD settles in anaerobic tank.

0.5

0.5

LatrineDry climate, ground water table lower thanlatrine, small family (3-5 persons)0.1

0.05 – 0.15

LatrineDry climate, ground water table lower thanlatrine, communal (many users)

0.5

0.4 – 0.6

LatrineWet climate/flush water use, ground watertable higher than latrine

0.7

0.7 – 1.0

LatrineRegular sediment removal for fertilizer

0.1

0.1

Untreated system

Treated system

1

Based on expert judgment by lead authors of this section.

6.2.2.3

C HOICE OF ACTIVITY DATA

The activity data for this source category is the total amount of organically degradable material in the wastewater(TOW). This parameter is a function of human population and BOD generation per person. It is expressed interms of biochemical oxygen demand (kg BOD/year). The equation for TOW is:

EQUATION 6.3
TOTAL ORGANICALLY DEGRADABLE MATERIAL IN DOMESTIC WASTEWATERTOW = P • BOD • 0.001 • I • 365

Where:
TOW=

total organics in wastewater in inventory year, kg BOD/yr

P=

country population in inventory year, (person)

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Volume 5: Waste

BOD=

country-specific per capita BOD in inventory year, g/person/day, See Table 6.4.

0.001

=

conversion from grams BOD to kg BOD

I=

correction factor for additional industrial BOD discharged into sewers(for collected the default is 1.25, for uncollected the default is 1.00.)

The factor I values in Equation 6.3 are based on expert judgment by the authors. It expresses the BOD fromindustries and establishments (e.g., restaurants, butchers or grocery stores) that is co-discharged with domestic
wastewater. In some countries, information from industrial discharge permits may be available to improve I.
Otherwise, expert judgment is recommended. Total population statistics should be readily available fromnational statistics agencies or international agencies (e.g., United Nations Statistics, see http://esa.un.org/unpp/).
Table 6.4 includes BOD default values for selected countries. It is good practice to select a BOD default value
from a nearby comparable country when country-specific data are not available. The degree of urbanization for acountry can be retrieved from various sources, (e.g., Global Environment Outlook, United Nations Environment
Programme and World Development Indicators, World Health Organization). The urban high-income and urbanlow income fractions can be determined by expert judgment when statistical or other comparable information is
not available. Table 6.5 includes default values of Ui and Ti,j for selected countries.

TABLE 6.4
ESTIMATED BOD5 VALUES IN DOMESTIC WASTEWATER FOR SELECTED REGIONS AND COUNTRIES
BOD5(g/person/day)

Range

Reference

Africa37

35 – 45

1

Egypt

34

27 – 411

Asia, Middle East, Latin America

40

35 – 45

1

India

34

27 – 411West Bank and Gaza Strip (Palestine)

50

32 – 68

1

Japan

42

40 – 45

1

Brazil50

45 – 55

2

Canada, Europe, Russia, Oceania

60

50 – 701

Denmark62

55 – 681

Germany

62

55 – 68

1

Greece57

55 – 60

1

Italy

60

49 – 60

3

Sweden75

68 – 82

1

Turkey38

27 – 50

1

United States

85

50 – 120

4Country/Region

Note: These values are based on an assessment of the literature. Please use national values, if available.
Reference:
1. Doorn and Liles (1999).
2. Feachem et al. (1983).
3. Masotti (1996).
4. Metcalf and Eddy (2003).

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2006 IPCC Guidelines for National Greenhouse Gas Inventories

0.10
0.09
0.08
0.12

0.12
0.06
0.12
0.07
0.06
0.80

0.73
0.94
0.90
0.76
0.68

0.78
0.80

0.25
0.19

0.92

0.52
0.57
0.62
0.39

0.59
0.71
0.54
0.65
0.72
0.20

0.27
0.06
0.10
0.24
0.32

0.22
0.20

0.16
0.25

0.08

0.00

0.59
0.56

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.29
0.23
0.34
0.28
0.22
0.00

0.38
0.34
0.30
0.49

Rural urban-high2 urban-low2

0.90

0.00
0.00

0.90
0.90

0.30
0.20
0.11
0.37
0.42

0.00
0.00
0.00
0.00
0.00
0.20

0.02
0.02
0.02
0.10

Septic
Tank

0.02

0.45
0.45

0.02
0.02

0.10
0.00
0.00
0.00
0.00

0.47
0.47
0.47
0.47
0.47
0.00

0.28
0.28
0.28
0.28

0.00

0.00
0.00

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.50
0.10
0.00
0.00
0.00
0.50

0.04
0.04
0.04
0.04

0.08

0.10
0.10

0.08
0.08

0.60
0.80
0.89
0.63
0.58

0.00
0.10
0.10
0.10
0.10
0.30

0.10
0.10
0.10
0.10

0.00

0.45
0.45

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.03
0.33
0.43
0.43
0.43
0.00

0.56
0.56
0.56
0.48

0.05

0.00
0.00

0.05
0.05

0.10
0.05
0.00
0.00
0.04

0.18
0.18
0.18
0.18
0.18
0.00

0.32
0.15
0.32
0.15

0.00

0.20
0.20

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.08
0.08
0.08
0.08
0.08
0.00

0.31
0.05
0.31
0.15

2006 IPCC Guidelines for National Greenhouse Gas Inventories

0.00

0.00
0.00

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.07
0.07
0.00
0.00
0.00
0.10

0.00
0.10
0.00
0.00

0.95

0.80
0.80

0.95
0.95

0.90
0.95
1.00
1.00
0.96

0.67
0.67
0.74
0.74
0.74
0.90

0.37
0.70
0.37
0.70

0.00

0.00
0.00

0.00
0.00

0.00
0.00
0.00
0.00
0.00

0.00
0.00
0.00
0.00
0.00
0.00

0.00
0.00
0.00
0.00

NA

0.00
0.00

NA
NA

NA
NA
NA
NA
NA

0.14
0.14
0.14
0.14
0.14
0.10

0.17
0.17
0.17
0.17

NA

0.40
0.40

NA
NA

NA
NA
NA
NA
NA

0.10
0.10
0.10
0.10
0.10
0

0.24
0.24
0.24
0.24

NA

0.00
0.00

NA
NA

NA
NA
NA
NA
NA

0.03
0.03
0.03
0.03
0.03
0

0.05
0.05
0.05
0.05

NA

0.40
0.40

NA
NA

NA
NA
NA
NA
NA

0.68
0.53
0.53
0.53
0.53
0.90

0.34
0.34
0.34
0.34

6.15

NA

0.20
0.20

NA
NA

NA
NA
NA
NA
NA

0.05
0.20
0.20
0.20
0.20
0

0.20
0.20
0.20
0.20

Degree of utilisation of treatment or discharge pathway or method for each income group (Ti,j )3
U=ruralU= urban high income
U=urban low income
Septic
Septic4 None4 NoneLatrine Other Sewer
Latrine Other Sewer
Latrine Other Sewer4 None
Tank
Tank

Notes:
1.
Urbanization projections for 2005 (United Nations, 2002).
2.
Suggested urban-high income and urban low income division. Countries are encouraged to use their own data or best judgment.
3.
Ti.j values based on expert judgment, (Doorn and Liles, 1999).
4.
Sewers may be open or closed, which will govern the choice of MCF, see Table 3.3
5.
Destatis, 2001.
Note: These values are from the literature or based on expert judgment. Please use national values, if available.

AfricaNigeria
Egypt
Kenya
South Africa
Asia
China
India
Indonesia
Pakistan
Bangladesh
Japan
EuropeRussiaGermany5
United Kingdom
FranceItaly
North America
United States
CanadaLatin America
and Caribbean
BrazilMexicoOceania
Australia and
New ZealandCountry

Urbanization(U) 1
Fraction of Population

TABLE 6.5
SUGGESTED VALUES FOR URBANISATION (U) AND DEGREE OF UTILISATION OF TREATMENT, DISCHARGE PATHWAY OR METHOD (Ti,j) FOR EACH INCOME GROUP FOR SELECTED COUNTRIES

Chapter 6: Wastewater Treatment and Discharge

Volume 5: Waste

ExampleTable 6.6 includes an example. Categories with negligible contributions are not shown. Note that the table caneasily be expanded with a column for MCF for each category. The degree of urbanization for this country is 65
percent.
TABLE 6.6
EXAMPLE OF THE APPLICATION OF DEFAULT VALUESFOR DEGREES OF TREATMENT UTILIZATION (T) BY INCOME GROUPS
Treatment or discharge system or pathway

T (%)

Notes

Urban high-income

To sea10

No CH4

To aerobic plant20

Add industrial component

To septic systems

10

Uncollected

To sea10

Collected

To pit latrines

15

Uncollected

To rivers, lakes, sea

15

To pit latrines

15

To septic tanks

5

Urban low-income

Rural

Total

100%

UncollectedMust add up to 100 %Reference: Doorn and Liles (1999)

6.2.2.4

T IME SERIES CONSISTENCY

The same method and data sets should be used for estimating CH4 emissions from wastewater for each year. The
MCF for different treatment systems should not change from year to year, unless such a change is justifiable anddocumented. If the share of wastewater treated in different treatment systems changes over the time period, thereasons for these changes should be documented.
Sludge removal and CH4 recovery should be estimated consistently across years in the time series. Methane
recovery should be included only if there are sufficient facility-specific data. The quantity of recovered methane
should be subtracted from the methane produced as shown in Equation 6.1.
Because activity data are derived from population data, which is available for all countries and all years,
countries should be able to construct an entire time series for uncollected and collected wastewater. If data on theshare of uncollected wastewater treated onsite vs. untreated are missing for one or more years, the surrogate dataand extrapolation/interpolation splicing techniques described in Chapter 5, Time Series Consistency, of Volume
1, General Guidance and Reporting, can be used to estimate emissions. Emissions from wastewater typically do
not fluctuate significantly from year to year.

6.2.2.5

U NCERTAINTIES

Chapter 3, Uncertainties, in Volume 1 provides advice on quantifying uncertainties in practice. It includes
guidance on eliciting and using expert judgements which in combination with empirical data can provide overall
uncertainty estimates. Table 6.7 provides default uncertainty ranges for emission factor and activity data ofdomestic wastewater. The following parameters are believed to be very uncertain:•

The degrees to which wastewater in developing countries is treated in latrines, septic tanks, or removed bysewer, for urban high, urban low income groups and rural population (Ti,,j).

•The fraction of sewers that are ‘open’, as well as the degree to which open sewers in developing countries
are anaerobic and will emit CH4. This will depend on retention time and temperature, and on other factors
including the presence of a facultative layer and possibly components that are toxic to anaerobic bacteria(e.g., certain industrial wastewater discharges).

•

The amount of industrial TOW that is discharged into open or closed domestic sewers for each country isvery difficult to quantify.

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2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

TABLE 6.7
DEFAULT UNCERTAINTY RANGES FOR DOMESTIC WASTEWATER
Parameter

Uncertainty Range

Emission Factor
Maximum CH4 producing capacity (Bo)± 30%

Fraction treated anaerobically (MCF)

The MCF is technology dependent. See Table 6.3. Thus the uncertainty
range is also technology dependent. The uncertainty range should bedetermined by expert judgement, bearing in mind that MCF is a fraction
and must be between 0 and 1. Suggested ranges are provided below.
Untreated systems and latrines, ± 50%
Lagoons, poorly managed treatment plants± 30%
Centralized well managed plant, digester, reactor, ± 10%

Activity Data
Human population (P)± 5%

BOD per person± 30%

Fraction of population income group (U)Good data on urbanization are available, however, the distinction
between urban high income and urban low income may have to be
based on expert judgment. ± 15%

Degree of utilization of treatment/
discharge pathway or system for each
income group (Ti,j)Can be as low as ± 3% for countries that have good records and only
one or two systems. Can be ± 50% for an individual method/pathway.
Verify that total Ti,j = 100%

Correction factor for additional industrial
BOD discharged into sewers (I)For uncollected, the uncertainty is zero %. For collected theuncertainty is ± 20%

Source: Judgement by Expert Group (Authors of this section).

6.2.2.6

QA/QC, C OMPLETENESS , R EPORTING AND
D OCUMENTATION

It is good practice to conduct quality control checks and quality assurance procedures as outlined in Chapter 6,
Volume 1. Below, some fundamental QA/QC procedures are included.

Activity Data•

Characterize all wastewater according to the percentages flowing to different treatment systems (aerobic andanaerobic), and the percentage of untreated wastewater. Make sure that all wastewater is characterized sothat the wastewater flows sum to 100 percent of the wastewater generated in the country.

•

Inventory compilers should compare country-specific data on BOD in domestic wastewater to IPCC default
values. If inventory compilers use country-specific values they should provide documented justification why
their country-specific values are more appropriate for their national circumstances.

Emission Factors•

For domestic wastewater, inventory compilers can compare country-specific values for Bo with the IPCC
default value (0.25 kg CH4/kg COD or 0.6 kg CH4/kg BOD). Although there are no IPCC default values forthe fraction of wastewater treated anaerobically, inventory compilers are encouraged to compare values for
MCFs against those from other countries with similar wastewater handling practices.

•

Inventory compilers should confirm the agreement between the units used for degradable carbon in thewaste (TOW) with the units for Bo. Both parameters should be based on the same units (either BOD or COD)
in order to calculate emissions. This same consideration should be taken into account when comparing theemissions.

2006 IPCC Guidelines for National Greenhouse Gas Inventories

6.17

Volume 5: Waste

CH 4 Recovery and Sludge Removal•

A carbon balance check can be used to ensure that the carbon contained in the inflow and outflow (effluent
BOD, methane emission and methane recovery) are comparable.

•

If sludge removal is reported in the wastewater inventory, check for consistency with the estimates for
sludge applied to agriculture soils, sludge incinerated, and sludge deposited in solid waste disposal.

Comparison of emissions estimates using different approaches•

For countries that use country-specific parameters, or Tier 2 or higher methods, inventory compilers cancross-check the national estimate with emissions using the IPCC default method and parameters.

COMPLETENESS
Completeness can be verified on the basis of the degree of utilization of a treatment or discharge system orpathway (T). The sum of T should equal 100 percent. It is a good practice to draw a diagram similar to Figure
6.1 for the country to consider all potential anaerobic treatment and discharge systems and pathways, includingcollected and uncollected, as well as treated and untreated. Any industrial wastewater treated in domestic
wastewater treatment facilities should be included in the collected category. If sludge is removed for the purposeof incineration, disposal in landfills or as fertilizer on agricultural lands, the amount of organic material removed
as sludge should be consistent with data used in the relevant sectors (see text under Section 6.2.2).

REPORTING AND DOCUMENTATION
It is good practice to document and report a summary of the methods used, activity data and emission factors.
Worksheets are provided at the end of this volume. When country-specific methods and/or emission factors areused, the reasoning for the choices as well as references to how the country-specific data (measurements, literature,expert judgement, etc.) have been derived (measurements, literature, expert judgement, etc.) should be documented
and included in the reporting.
If sludge is incinerated, landfilled, or spread on agricultural lands, the quantities of sludge, and associatedemissions, should be reported in the waste incineration, SWDS, or agricultural categories, respectively.
Where CH4 is recovered for energy use, then the resulting greenhouse gas emissions should be reported under
Energy Sector. As discussed in Section 6.2.1, good practice in the Waste Sector does not require the estimationof CH4 and N2O from CH4 recovery and flaring. However, if it is wished to do so emissions from flaring should
be reported under the Waste Sector.
More information on reporting and documentation can be found in Volume 1, Chapter 6, Section 6.11
Documentation, archiving and reporting.

6.2.3

Industrial wastewaterIndustrial wastewater may be treated on site or released into domestic sewer systems. If it is released into thedomestic sewer system, the emissions are to be included with the domestic wastewater emissions. This section
deals with estimating CH4 emissions from on-site industrial wastewater treatment. Only industrial wastewaterwith significant carbon loading that is treated under intended or unintended anaerobic conditions will produce
CH4. Organics in industrial wastewater are often expressed in terms of COD, which is used here.

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2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

6.2.3.1

C HOICE OF METHOD

A decision tree for industrial wastewater is included in Figure 6.3.
Figure 6.3

Decision Tree for CH 4 emissions from industrial wastewater treatment
Start

Identify major industrial
sectors with large potentials
for CH4 emission.

Forthese industrial
sectors, is a country-specificmethod from individual
facilities or companies
available?

Estimateemissions using
bottom-up data.

Yes

Box 3: Tier 3

No

For these
industrial sectors, are
COD and wastewater outflow
data available?

Yes

Are
country-specificemission factors forselected industrial
sectors
available?

No

Estimate emission
factors using areview of industry
wastewater
treatment practices.

No
Is
industrial
wastewater a key
category1?

Yes

Collect COD
and outflow
for eachindustrial
sector.

Yes

Estimate CH4
emissions using
country-specificemission factors.
Box 2: Tier 2

No
Estimate outflow
using industrial
production data.

Estimateemissions using
default data.
Box 1: Tier 1

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources),for discussion of key categories and use of decision trees.

Assessment of CH4 production potential from industrial wastewater streams is based on the concentration of
degradable organic matter in the wastewater, the volume of wastewater, and the propensity of the industrial
sector to treat their wastewater in anaerobic systems. Using these criteria, major industrial wastewater sources
with high CH4 gas production potential can be identified as follows:•

pulp and paper manufacture,•meat and poultry processing (slaughterhouses),

2006 IPCC Guidelines for National Greenhouse Gas Inventories

6.19

Volume 5: Waste•

alcohol, beer, starch production,•organic chemicals production,•other food and drink processing (dairy products, vegetable oil, fruits and vegetables, canneries, juice making,etc.).

Both the pulp and paper industry and the meat and poultry processing industries produce large volumes ofwastewater that contain high levels of degradable organics. The meat and poultry processing facilities typically
employ anaerobic lagoons to treat their wastewater, while the paper and pulp industry also use lagoons andanaerobic reactors. The non-animal food and beverage industries produce considerable amounts of wastewaterwith significant organic carbon levels and are also known to use anaerobic processes such as lagoons andanaerobic reactors. Anaerobic reactors treating industrial effluents with biogas facilities are usually linked withrecovery of the generated CH4 for energy. Emissions from the combustion process for energy should be reported
in the Energy Sector.
The method for estimating emissions from industrial wastewater is similar to the one used for domestic
wastewater. See the decision tree in Figure 6.3. The development of emission factors and activity data is more
complex because there are many types of wastewater, and many different industries to track. The most accurate
estimates of emissions for this source category would be based on measured data from point sources. Due to thehigh costs of measurements and the potentially large number of point sources, collecting comprehensive
measurement data is very difficult. It is suggested that inventory compilers use a top-down approach that
includes the following general steps:
Step 1:Use Equation 6.6 to estimate total organically degradable carbon in wastewater (TOW) for industrial
sector i

Step 2:

Select the pathway and systems (Figure 6.1) according to country activity data. Use Equation 6.5 toobtain emission factor. For each industrial sector estimate the emission factor using maximum
methane producing capacity and the average industry-specific methane correction factor.

Step 3:Use Equation 6.4 to estimate emissions, adjust for possible sludge removal and or CH4 recovery andsum the results.

The general equation to estimate CH4 emissions from industrial wastewater is as follows:
EQUATION 6.4
TOTAL CH4 EMISSIONS FROM INDUSTRIAL WASTEWATER

CH 4 Emissions = ∑ [( TOWi − S i ) EFi − Ri ]i

Where:
CH4 Emissions =CH4 emissions in inventory year, kg CH4/yr

TOWi =

total organically degradable material in wastewater from industry iin inventory year, kg COD/yri=industrial sector

Si=

organic component removed as sludge in inventory year, kg COD/yr

EFi=emission factor for industry i, kg CH4/kg COD
for treatment/discharge pathway or system(s) used in inventory year
If more than one treatment practice is used in an industry this factor would need to bea weighted average.

Ri=amount of CH4 recovered in inventory year, kg CH4/yr

The amount of CH4 which is recovered is expressed as R in Equation 6.4. The recovered gas should be treated as
described in Section 6.2.1.

6.2.3.2

C HOICE OF EMISSION FACTORS

There are significant differences in the CH4 emitting potential of different types of industrial wastewater. To theextent possible, data should be collected to determine the maximum CH4 producing capacity (Bo) in eachindustry. As mentioned before, the MCF indicates the extent to which the CH4 producing potential (Bo) is

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2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

realised in each type of treatment method. Thus, it is an indication of the degree to which the system is anaerobic.
See Equation 6.5.
EQUATION 6.5
CH4 EMISSION FACTOR FOR INDUSTRIAL WASTEWATER
EF j = Bo • MCF j

Where:
EFj=

emission factor for each treatment/discharge pathway or system, kg CH4/kg COD,
(See Table 6.8.)

j=each treatment/discharge pathway or systemBo=maximum CH4 producing capacity, kg CH4/kg COD

MCFj

=

methane correction factor (fraction) (See Table 6.8.)

Good practice is to use country and industry sector specific data that may be available from government
authorities, industrial organisations, or industrial experts. However, most inventory compilers will find detailed
industry sector-specific data unavailable or incomplete. If no country-specific data are available, it is goodpractice to use the IPCC COD-default factor for Bo (0.25 kg CH4/kg COD).
In determining the Methane correction factor (MCF), which is the fraction of waste treated anaerobically, expert
judgement is recommended. A peer-reviewed survey of industry wastewater treatment practices is one usefultechnique for estimating these data. Surveys should be conducted frequently enough to account for major trends
in industry practices (i.e., every 3-5 years). Chapter 2, Approaches to Data Collection, in Volume 1, describes
how to elicit expert judgement for uncertainty ranges. Similar expert elicitation protocols can be used to obtainthe necessary information for other types of data if published data and statistics are not available. Table 6.8
includes default MCF values, which are based on expert judgment.
TABLE 6.8
DEFAULT MCF VALUES FOR INDUSTRIAL WASTEWATER
Type of treatment and discharge
pathway or system

Comments

MCF 1

Range

Rivers with high organics loadings may turnanaerobic, however this is not considered here.

0.1

0 – 0.2

Aerobic treatment plantMust be well managed. Some CH4 can beemitted from settling basins and other pockets.

0

0 – 0.1

Aerobic treatment plant

Not well managed. Overloaded

0.3

0.2 – 0.4

Anaerobic digester for sludge

CH4 recovery not considered here

0.8

0.8 – 1.0

Anaerobic reactor(e.g., UASB, Fixed Film Reactor)

CH4 recovery not considered here

0.8

0.8 – 1.0

Anaerobic shallow lagoon

Depth less than 2 metres, use expert judgment

0.2

0 – 0.3

Anaerobic deep lagoon

Depth more than 2 metres

0.8

0.8 – 1.0

Untreated
Sea, river and lake discharge
Treated1

Based on expert judgment by lead authors of this section

6.2.3.3

C HOICE OF ACTIVITY DATA

The activity data for this source category is the amount of organically degradable material in the wastewater(TOW). This parameter is a function of industrial output (product) P (tons/yr), wastewater generation W (m3/tonof product), and degradable organics concentration in the wastewater COD (kg COD/m3). See Equation 6.6. The
following steps are required for determination of TOW:(i)

Identify the industrial sectors that generate wastewater with large quantities of organic carbon, by
evaluating total industrial product, degradable organics in the wastewater, and wastewater produced.

2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 5: Waste(ii)

Identify industrial sectors that use anaerobic treatment. Include those that may have unintended
anaerobic treatment as a result of overloading of the treatment system. Experience has shown thatusually three or four industrial sectors are key.

For each selected sector estimate total organically degradable carbon (TOW).
EQUATION 6.6
ORGANICALLY DEGRADABLE MATERIAL IN INDUSTRIAL WASTEWATER
TOWi = Pi • Wi • CODi

Where:
TOWi=

total organically degradable material in wastewater for industry i, kg COD/yri=industrial sector

Pi=

total industrial product for industrial sector i, t/yrWi=

wastewater generated, m3/t product

CODi

=

chemical oxygen demand (industrial degradable organic component in wastewater),kg COD/m3

Industrial production data and wastewater outflows may be obtained from national statistics, regulatory agencies,
wastewater treatment associations or industry associations. In some cases quantification of the COD loading in
the wastewater may require expert judgement. In some countries, COD and total water usage per sector data may
be available directly from a regulatory agency. An alternative is to obtain data on industrial output and tonnes
COD produced per tonne of product from the literature. Table 6.9 provides examples that could be used as
default values. These should be used with caution, because they are industry-, process- and country-specific.
TABLE 6.9
EXAMPLES OF INDUSTRIAL WASTEWATER DATA
Industry Type

Wastewater Generation W

Range for W

33(m /ton)(m /ton)

COD
3

COD Range(kg/m )

(kg/m3)

Alcohol Refining

24

16 – 32

11

5 – 22

Beer & Malt

6.3

5.0 – 9.0

2.9

2 – 7

Coffee

NA

NA –

9

3 – 15

Dairy Products7

3 – 102.7

1.5 – 5.2

Fish ProcessingNA

8 – 182.5

Meat & Poultry

13

8 – 184.1

2 – 7

Organic Chemicals

67

0 – 400

3

0.8 – 5

Petroleum Refineries

0.6

0.3 – 1.2

1.0

0.4 – 1.6

Plastics & Resins

0.6

0.3 – 1.2

3.7

0.8 – 5

Pulp & Paper (combined)

162

85 – 2409

1 – 15

Soap & DetergentsNA

1.0 – 5.0NA

0.5 – 1.2

Starch Production

9

4 – 1810

1.5 – 42

Sugar RefiningNA

4 – 183.2

1 – 6

Vegetable Oils
Vegetables, Fruits &JuicesWine & Vinegar

3.1

1.0 – 5.0NA

0.5 – 1.2

20

7 – 355.0

2 – 1023

11 – 46

1.5

0.7 – 3.0

Notes: NA = Not Available.
Source: Doorn et al. (1997).

6.2.3.4

T IME SERIES CONSISTENCY

Once an industrial sector is included in the inventory calculation, it should be included for each subsequent year.
If the inventory compiler adds a new industrial sector to the calculation, then he or she should re-calculate the

6.22

2006 IPCC Guidelines for National Greenhouse Gas Inventories

Chapter 6: Wastewater Treatment and Discharge

entire time series so that the method is consistent from year to year. General guidance on recalculation of
estimates through time series is provided in Volume 1, Chapter 5, Time Series Consistency.
As with domestic wastewater, sludge removal and CH4 recovery should be treated consistently across years in
the time series. CH4 recovery should be included only if there are facility-specific data. The quantity ofrecovered CH4 should be subtracted from the CH4 produced as shown in Equation 6.4.

6.2.3.5

U NCERTAINTIES

Uncertainty estimates for Bo, MCF, P, W and COD are provided in Table 6.10. The estimates are based on
expert judgement.
TABLE 6.10
DEFAULT UNCERTAINTY RANGES FOR INDUSTRIAL WASTEWATER
Parameter

Uncertainty Range

Emission Factor
Maximum CH4 producing capacity (Bo)± 30%

Methane correction factor (MCF)

The uncertainty range should be determined by expert judgement, bearing
in mind that this is a fraction and uncertainties cannot take it outside therange of 0 to 1.

Activity Data
Industrial production (P)± 25% Use expert judgement regarding the quality of data source toassign more accurate uncertainty range.

Wastewater/unit production (W)These data can be very uncertain as the same sector might use different
waste handling procedures at different plants and in different countries.
The product of the parameters (W•COD) is expected to have lessuncertainty. An uncertainty value can be attributed directly to kg
COD/tonne of product. –50 %, +100% is suggested (i.e., a factor of 2).

COD/unit wastewater (COD)

Source: Judgement by Expert Group (Co-chairs, Editors and Authors of this sector).

6.2.3.6

QA/QC, C OMPLETENESS , R EPORTING AND
D OCUMENTATION

It is good practice to conduct quality control checks and quality assurance procedures as outlined in Chapter 6,
QA/QC and Verification, of Volume 1. Below, some fundamental QA/QC procedures include:•

For industrial wastewater, inventory compilers may review the secondary data sets (e.g., from national
statistics, regulatory agencies, wastewater treatment associations or industry associations) , that are used toestimate and rank industrial COD waste output. Some countries may have regulatory control over industrial
discharges, in which cases significant QA/QC protocols may already be in place for the development of thewastewater characteristics on an industry basis.

•

For industrial wastewater, inventory compilers should cross-check values for MCFs against those from othernational inventories with similar wastewater characteristics.

•

The inventory compilers should review facility-specific data on CH4 recovery to ensure that it was reported
according to criteria on measurements outlined in Chapter 2, Approaches to Data Collection, in Volume 1.

•

Use a carbon balance check to ensure that the carbon contained in CH4 recovery is less than the carbon
contained in BOD entering the facility that reports CH4 recovery.

•

If sludge removal is reported in the wastewater inventory, check for consistency with the estimates for
sludge applied to agriculture soils, sludge incinerated, and sludge deposited in solid waste disposal.

•

For countries that use country-specific parameters or higher tier methods, inventory compilers should crosscheck the national estimates with emissions using the IPCC default method and parameters.

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COMPLETENESS
Completeness for estimating emissions from industrial wastewater depends on an accurate characterization ofindustrial sectors that produce organic wastewater. In most countries, approximately 3-4 industrial sectors willaccount for the majority of the organic wastewater volume, so the inventory compilers should ensure that these
sectors are covered. Periodically, the inventory compilers should re-survey industrial sources, particularly ifsome industries are growing rapidly.
This category should only cover industrial wastewater treated onsite. Emissions from industrial wastewater
released into domestic sewer systems should be addressed and included with domestic wastewater.
Some sludge from industrial wastewater treatment may be incinerated or deposited in landfills or on agriculturallands. This constitutes an amount of organic waste that should be subtracted from available TOW. It is goodpractice to be consistent across sectors: the amount of sludge that is removed from TOW should be equal to theamount of sludge disposed at landfills, applied to agricultural soils, incinerated or treated elsewhere.

REPORTING AND DOCUMENTATION
It is good practice to document and report a summary of the methods used, activity data and emission factors.
Worksheets are provided at the end of this volume. When country-specific methods and/or emission factors areused, the reasoning for the choices as well as references to how the country-specific data (measurements,
literature, expert judgement, etc.) have been derived (measurements, literature, expert judgement, etc.) should be
documented and included in the reporting.
If sludge is incinerated, landfilled, or spread on agricultural lands, the quantities of sludge and associated emissions
should be reported in the waste incineration, SWDS, or agricultural categories, respectively.
If CH4 recovery data are available for industrial wastewater treatment, these should be documented for flaring
and energy recovery separately. The treatment of recovered CH4 and how to report emissions from flaring shouldbe the same as the guidance for domestic wastewater in Section 6.2.2.6.
More information on reporting and documentation can be found in Volume 1, Chapter 6, Section 6.11
Documentation, archiving and reporting.

6.3

NITROUS OXIDE EMISSIONS FROMWASTEWATER

6.3.1

Methodological issues

6.3.1.1

C HOICE OF METHOD

Nitrous oxide (N2O) emissions can occur as direct emissions from treatment plants or from indirect emissions
from wastewater after disposal of effluent into waterways, lakes or the sea. Direct emissions from nitrificationand denitrification at wastewater treatment plants may be considered as a minor source and guidance is offeredin Box 6.1 to estimate these emissions. Typically, these emissions are much smaller than those from effluent andmay only be of interest to countries that predominantly have advanced centralized wastewater treatment plants
with nitrification and denitrification steps.
No higher tiers are given, so it is Good practice to estimate N2O from domestic wastewater effluent using themethod given here, No decision tree is provided. Direct emissions need to be estimated only for countries thathave predominantly advanced centralized wastewater treatment plants with nitrification and denitrification steps.
Accordingly, this section addresses indirect N2O emissions from wastewater treatment effluent that is discharged
into aquatic environments. The methodology for emissions from effluent is similar to that of indirect N2Oemissions explained in Volume 4, Section 11.2.2, in Chapter 11, N2O Emissions from Managed Soils, and CO2
Emissions from Lime and Urea Application. The simplified general equation is as follows:

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EQUATION 6.7
N2O EMISSIONS FROM WASTEWATER EFFLUENT
N 2 O Emissions = N EFFLUENT • EFEFFLUENT • 44 / 28

Where:
N2O emissions= N2O emissions in inventory year, kg N2O/yr

N EFFLUENT=

nitrogen in the effluent discharged to aquatic environments, kg N/yr

EFEFFLUENT=

emission factor for N2O emissions from discharged to wastewater, kg N2O-N/kg N

The factor 44/28 is the conversion of kg N2O-N into kg N2O.

6.3.1.2

C HOICE OF EMISSION FACTORSThe default IPCC emission factor for N2O emissions from domestic wastewater nitrogen effluent is 0.005(0.0005 - 0.25) kg N2O-N/kg N. This emission factor is based on limited field data and on specific assumptions
regarding the occurrence of nitrification and denitrification in rivers and in estuaries. The first assumption is that
all nitrogen is discharged with the effluent. The second assumption is that N2O production in rivers and estuaries
is directly related to nitrification and denitrification and, thus, to the nitrogen that is discharged into the river.
(See Volume 4, Table 11.3 of Section 11.2.2 in Chapter 11, N2O Emissions from Managed Soils, and CO2
Emissions from Lime and Urea Application.)

6.3.1.3

C HOICE OF ACTIVITY DATA

The activity data that are needed for estimating N2O emissions are nitrogen content in the wastewater effluent,country population and average annual per capita protein generation (kg/person/yr). Per capita protein generationconsists of intake (consumption) which is available from the Food and Agriculture Organization (FAO, 2004),
multiplied by factors to account for additional ‘non-consumed’ protein and for industrial protein discharged into
the sewer system. Food (waste) that is not consumed may be washed down the drain (e.g., as result of the use of
garbage disposals in some developed countries) and also, bath and laundry water can be expected to contribute tonitrogen loadings. For developed countries using garbage disposals, the default for non-consumed protein
discharged to wastewater pathways is 1.4, while for developing countries this fraction is 1.1. Wastewater fromindustrial or commercial sources that is discharged into the sewer may contain protein (e.g., from grocery storesand butchers). The default for this fraction is 1.25. The total nitrogen in the effluent is estimated as follows:

EQUATION 6.8
TOTAL NITROGEN IN THE EFFLUENTN EFFLUENT = ( P • Protein • FNPR • FNON − CON • FIND − COM ) − N SLUDGE

Where:NEFFLUENT =total annual amount of nitrogen in the wastewater effluent, kg N/yrP=

human population

Protein=annual per capita protein consumption, kg/person/yr

FNPR

=

fraction of nitrogen in protein, default = 0.16, kg N/kg protein

FNON-CON =factor for non-consumed protein added to the wastewater

FIND-COM =factor for industrial and commercial co-discharged protein into the sewer system

NSLUDGE =nitrogen removed with sludge (default = zero), kg N/yr

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BOX 6.1
SUBCATEGORY - EMISSIONS FROM ADVANCED CENTRALISED WASTEWATER TREATMENT PLANTS

Emissions from advanced centralised wastewater treatment plants are typically much smaller thanthose from effluent and may only be of interest for countries that have predominantly advanced
centralized wastewater treatment plants with controlled nitrification and denitrification steps. The
overall emission factor to estimate N2O emissions from such plants is 3.2 g N2O/person/year. Thisemission factor was determined during field testing at a domestic wastewater treatment plant in the
Northern United States (Czepiel et al., 1995). The emission data were obtained at a plant thatreceived only domestic wastewater. This wastewater already included non-consumption protein,
but did not include any co-discharged industrial and commercial wastewater. No other countryspecific emission factors are available. The emissions from N2O from centralized wastewater
treatment processes are calculated as follows:

EQUATION 6.9
N2O EMISION FROMCENTRALIZED WASTEWATER TREATMENT PROCESSESN 2 O PLANTS = P • T PLANT • FIND −COM • EFPLANT

Where:N2OPLANTS = total N2O emissions from plants in inventory year, kg N2O/yr
P= human population

TPLANT= degree of utilization of modern, centralized WWT plants, %FIND-COMM= fraction of industrial and commercial co-discharged protein (default = 1.25,
based on data in Metcalf & Eddy (2003) and expert judgment)

EFPLANT= emission factor, 3.2 g N2O/person/year

Note: When a country chooses to include N2O emissions from plants, the amount of nitrogenassociated with these emissions (NWWT) must be back calculated and subtracted from the
NEFFLUENT. The NWWT can be calculated by multiplying N2OPLANTS by 28/44, using themolecular weights.

6.3.2

Time series consistency

If a country decides to incorporate plant emissions into the estimate, this change must be made for the entire timeseries. Potential sludge removal should be treated consistently across years in the time series.

6.3.3

Uncertainties

Large uncertainties are associated with the IPCC default emission factors for N2O from effluent. Currently
insufficient field data exist to improve this factor. Also, the N2O emission factor for plants is uncertain, because
it is based on one field test. Table 6.11 below includes uncertainty ranges based on expert judgment.

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TABLE 6.11
N2O METHODOLOGY DEFAULT DATA
Definition

Default Value

Range

Emission Factor
EFEFFLUENTEmission factor, (kg N2O-N/kg –N)

0.005

0.0005 – 0.25

EFPLANTS

Emission factor, (g N2O/person/year)

3.2

2–8

Activity DataP

Number of people in country

Country-specific± 10 %

Protein

Annual per capita protein consumption
Fraction of nitrogen in protein(kg N/kg protein)
Degree of utilization of large WWT plants

Country-specific± 10 %

0.16

0.15 – 0.17

FNPR
TplantFNON-CON

Factor to adjust for non-consumed protein

FIND-COM

Factor to allow for co-discharge of industrial
nitrogen into sewers. For countries with significant
fish processing plants, this factor may be higher.
Expert judgment is recommended.

6.3.4

Country-specific± 20 %

1.1 for countries with nogarbage disposals,
1.4 for countries withgarbage disposals

1.0 – 1.5

1.25

1.0 – 1.5

QA/QC, Completeness, Reporting andDocumentation

This method makes use of several default parameters. It is recommended to solicit experts’ advice in evaluating
the appropriateness of the proposed default factors.

COMPLETENESS
Unless sludge removal data are available, the methodology for estimating emissions from effluent is based on
population and on the assumption that all nitrogen associated with consumption and domestic use, as well as
nitrogen from co-discharged industrial wastewater, will eventually enter a waterway. As such, this estimate canbe seen as conservative estimate and covers the entire source associated with domestic wastewater use.
The methodology does not include N2O emissions from industrial sources, except for industrial wastewater thatis co-discharged with domestic wastewater into the sewer system. The N2O emissions from industrial sources are
believed to be insignificant compared to emissions from domestic wastewater.
Very few countries collect data on wastewater sludge handling. If these data exist, it is suggested to make themavailable to the appropriate inventory teams.
The emission factor used for N2O emissions from effluent is the same as the emission factor used for indirect
N2O emissions in the AFOLU Sector.

REPORTING AND DOCUMENTATION
It is good practice to document and report a summary of the methods used, activity data and emission factors.
Worksheets are provided at the end of this volume. When country-specific methods and/or emission factors areused, the reasoning for the choices as well as references to how the country-specific data (measurements, literature,expert judgement, etc.) have been derived (measurements, literature, expert judgement, etc.) should be documented
and included in the reporting.
If sludge is incinerated, landfilled, or spread on agricultural lands, the associated quantities of sludge should bereported in the waste incineration, SWDS, or agricultural categories, respectively.
More information on reporting and documentation can be found in Volume 1, Chapter 6, Section 6.11
Documentation, archiving and reporting.

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References
American Public Health Association and American Water Works Association (1998). Standard Methods for the
Examination of Water and Wastewater, 20th edition, Water Environment Federation, ISBN 0-87553-2357.
Czepiel, P., Crill, P. and Harriss, R. (1995). ‘Nitrous oxide emissions from domestic wastewater treatment’
Environmental Science and Technology, vol. 29, no. 9, pp. 2352-2356.
Destatis (2001). "Öffentliche Wasserversorgung und Abwasserbeseitigung 2001, Tabelle 1 "Übersichtstabelle
Anschlussgrade" (Statistical Office Germany (http://www.destatis.de/)
Doorn, M.R.J., Strait, R., Barnard, W. and Eklund, B. (1997). Estimate of Global Greenhouse Gas Emissions
from Industrial and Domestic Wastewater Treatment, Final Report, EPA-600/R-97-091, Prepared forUnited States Environmental Protection Agency, Research Triangle Park, NC, USA.
Doorn, M.R.J. and Liles, D. (1999). Global Methane, Quantification of Methane Emissions and Discussion of
Nitrous Oxide, and Ammonia Emissions from Septic Tanks, Latrines, and Stagnant Open Sewers in theWorld. EPA-600/R-99-089, Prepared for U.S. EPA, Research Triangle Park, NC, USA.
FAO (2004). FAOSTAT Statistical Database, United Nations Food and Agriculture Organization. Available on
the Internet at <http://faostat.fao.org/>
Feachem, R.G., Bradley, D.J., Gareleck H. and Mara D.D. (1983). Sanitation and Disease – Health Aspects of
Excreta and Wastewater Management, World Bank, John Wiley & Sons, USA.
IPCC (1997). Houghton, J.T., Meira Filho, L.G., Lim, B., Tréanton, K., Mamaty, I., Bonduki, Y., Griggs, D.J.
and Callander, B.A. (Eds). Revised 1996 IPCC Guidelines for National Greenhouse Inventories.
Intergovernmental Panel on Climate Change (IPCC), IPCC/OECD/IEA, Paris, France.
Masotti, L. (1996). "Depurazione delle acque. Tecniche ed impianti per il tratatmento delle acque di rifiuto".
Eds Calderini. pp. 29-30
Metcalf & Eddy, Inc. (2003) Wastewater Engineering: Treatment, Disposal, Reuse. McGraw-Hill: New York,ISBN 0-07-041878-0.
United Nations (2002). World Urbanization Prospects, The 2001 Revision Data Tables and Highlights.
Population Division, Department of Economic and Social Affairs, United Nations Secretariat.
ESA/P/WP.173. March 2002.

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