Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

CH 4 EM IS SI ONS FROM SO LID WA S TE
D ISP OSA L
ACKNOWLEDGEMENTS
This paper was written by Jens E. Frøiland Jensen (Norconsult) and R. Pipatti (VTT Energy, Finland). It has beenreviewed by: Pascal Boeckx (University of Gent, Belgium), S.A. Bhide (NEERI, India), Keith A. Brown (AEA
Technology Environment, UK), Katarzyna Steczko (Poland), Gerd Mauschitz (Austria), Hao Jiming (China),
Prof. Hackl (Austria), T. Kleffegaard (The Netherlands), Dina Krueger (USEPA), and Thomas Martinsen(IPCC/OECD/IEA).

ABSTRACTThe purpose of this paper is to support the development of so-called good practice guidelines for the estimation of
methane (CH4) emissions from solid waste (SW) disposal for national greenhouse gas inventories. The paper
reviews and discusses the emission estimation methods given in the IPCC 1996 Revised Guidelines (IPCC
Guidelines), and uncertainty and quality management issues related to the emission estimation.
At solid waste disposal sites (SWDS) the degradable organic carbon in waste is decomposed by bacteria underanaerobic conditions into methane (CH4) and other compounds. The CH4 emissions from SWDS are important
contributors of global anthropogenic CH4 emissions.
The IPCC Guidelines give two methods for estimation CH4 emissions from solid waste disposal. The IPCC default
method is a simple mass balance calculation which estimates the amount of CH4 emitted from the SWDS assumingthat all CH4 is released the same year the waste is disposed of. The other method outlined in the IPCC Guidelines is
the so-called First Order Decay (FOD) method. The FOD method takes the time factors of the degradation process
into account, and produces annual emission estimates that reflect this process, which can take years, even decades.
The estimates on annual emissions produced by the two methods are therefore not comparable. The FOD method
produces better estimates on annual emissions, whereas the IPCC default method has merits e.g. in studies
comparing the potential to reduce the CH4 emissions by alternative waste treatment methods.
The use of the IPCC default method and FOD method require as input annual SW disposal data including
information on the composition of the waste and on the conditions at the SWDS. The IPCC default method
requires this data only for the inventory years, whereas the FOD method requires data for also the past 20-25 ormore years. In addition, the rate of degradation for waste disposed at SWDS needs to be determined in the FOD
method. The IPCC Guidelines contain default values for most of the data needed in the use of the default method,whereas the guidance and default values needed in the use of the FOD method are insufficient.
The uncertainties in the emission estimates produced by both the IPCC method and the FOD method are large inmost countries. Even few industrialised countries have good SW disposal data based on weighing of amounts
disposed and frequent sampling to determine the composition of waste at the SWDS. The SW disposal data inmany developing countries is especially poor and some concern is expressed also on the suitability of some of thedefault parameters in their conditions. More frequent aerobic decomposition, scavenging and fires in theconditions prevailing in many developing countries may cause much lower emissions from SW disposal than inindustrialised countries. Improvements in activity data collection and emission factors (parameters used in thecalculation) are needed in many countries. Also some of the IPCC default values should be reviewed and updated.

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Background Paper

1

INTRODUCTION

When solid waste (SW) is disposed in waste dumps and landfills, most of the organic material will be degradedover a longer or shorter period, ranging in a wide span from less than one year to 100 years or more. The majorityof this process will be bio-degradation. Strongly depending on conditions in the site where the SW is disposed, thisbiodegradation will be aerobic or anaerobic. The main degradation products are carbon dioxide (CO2), water andheat for the aerobic process and methane (CH4) and CO2 for the anaerobic process. The CH4 produced and released
to the atmosphere contributes to global warming and the emissions need to be estimated and reported in national
greenhouse gas inventories under the United Nations’ Framework Convention of Climate Change (UNFCCC).
The CO2 produced originates from biogenic sources (e.g., food, garden, paper and wood waste) and the emissions
need therefore not be considered in national inventories.
The estimated global annual emissions from solid waste disposal sites (SWDS) are in the range of 20 - 40 million
tonnes of CH4, of which the most comes from industrialised countries (so-called Annex I countries of the
UNFCCC). This contribution is estimated to be approximately 5-20 percent of the global anthropogenic CH4,
which is equal to about 1 to 4 percent of the total anthropogenic greenhouse gas (GHG) emissions. The emissions
from developing countries and countries with economies-in-transition will increase in the near future due toincreased urban population, increased specific (pro capita) municipal solid waste (MSW) generation due toimproved economy and improved SW management practices. From the Annex I countries, the emissions are
estimated to remain stable or decline over the next 10 - 20 years. A recent compilation of reported emissions to the
UNFCCC (UNFCC, 2000) indicate emissions of 24 million tonnes CH4 from Annex I countries in 1990. In theyear 1998 these emissions had been reduced to about 20 million tonnes. The reduction is due to increased recycling
and alternative treatments and increasing implementation of landfill gas extraction and recovery systems.
This document is prepared for the IPCC National Greenhouse Gas Inventories Programme to support the developmentof good practice guidelines for estimation of greenhouse gas emissions from the Waste sector and to manage
associated uncertainties. The document is a background paper for the IPCC expert meeting on Waste in Sao Paulo. The
document concentrates on the anaerobic degradation process generating landfill gas (LFG). The existing IPCC
Guidelines for national Greenhouse Gas Inventories are reviewed, and an upgraded basis for a worldwide goodpractice framework to carry out as accurately as possible national inventories of emissions of CH4 is proposed.

2

METHODOLOGICAL ISSUES

2.1

Choice of method

The IPCC Guidelines describe two main methods:(A): The default IPCC methodology that is based on the theoretical gas yield (a mass balance equation).
(B): Theoretical first order kinetic methodologies, through which the IPCC Guidelines introduces the “First orderdecay model” (FOD).
The main difference between the two methods is that method A does not reflect the time variation in SW disposal
and the degradation process as it assumes that all potential methane is released the year the SW is disposed. The
timing of the actual emissions is reflected in method B. Only if the yearly amounts and composition of waste
disposed as well as disposal practices have been nearly constant for long periods, the method A will produce fairly
good estimates of the yearly emissions. Increasing amounts of waste disposed will lead to an overestimation, anddecreasing amounts correspondingly to underestimation, of yearly emissions.
Method B gives a more accurate estimate of the yearly emissions. Many countries may, however, have problems
getting the necessary data and information (historical data on SW disposal, rate constant for the decay) to establish
the proper basis for emission inventories with acceptable accuracy.
The two methods are explained in further detail below.

2.1.1

IPCC default method

The default method is based on the main equation 1:
EQUATION 1
Methane emissions (Gg/yr) = (MSWT ● MSWF ● MCF ● DOC ● DOCF ● F ● 16/12-R) ● (1-OX)
Where:

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Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

MSWT :

total MSW generated (Gg/yr)

MSWF :

fraction of MSW disposed to solid waste disposal sites

MCF :methane correction factor (fraction)

DOC :degradable organic carbon (fraction) (kg C/ kg SW)

DOCF :

fraction DOC dissimilatedF:

fraction of CH4 in landfill gas (IPCC default is 0.5)

16/12 :

conversion of C to CH4

R:

recovered CH4 (Gg/yr)OX :oxidation factor (fraction – IPCC default is 0)

The method assumes that all the potential CH4 emissions are released during the same year the waste is disposedof. The method is simple and emission calculations require only input of a limited set of parameters, for which the
IPCC Guidelines provide default values, where country-specific quantities and data are not available.
The IPCC Guidelines introduce various specific default values and recommendations, (particularly for use incountries with lack of SW statistics):
MSWT :

A selection of national specific MSW generation (in kg/capita/day) figures are provided, but
information appropriate for many low and medium income countries and regions is missing

MSWF :

A selection of national specific MSW disposal figures (in kg/capita/day) are provided (to be usedinstead of MSWT )MCF :Three default values ranging from 1.0 to 0.4 are included, depending on the site management andwith 0.6 as general default value

DOC :A selection of national values for DOC in MSW are provided, although a more limited selection
than for MSWT and MSWF. In addition, an equation is provided together with default values
related to MSW fractions to estimate country specific figures based on national MSW
composition.

DOCF :

Tabasaran’s (1981) theoretical equation DOCF = 0.014T + 0.28, where T = temperature is used todetermine the value. The IPCC default value is 0.77 as suggested by Bingemer and Crutzen(1987).

F:

0.5 is the IPCC default value

OX :0 is the IPCC default value

The minimum national figures required are:•National MSW quantities ending up at SWDS, eventually (in lack of SW statistics) based on the number ofurban inhabitants in the country multiplied with a specific national MSW disposal rate figure, and• National quantities of landfill gas recovered.
In most developing countries there is no gas extraction and recovery; hence the only figure needed in thecalculation is the number of inhabitants in the country, with clear focus on the urban population.

2.1.2

Theoretical first order decay methodologies

IPCC Guidelines
This model is presented through three equations. The first equation is applicable for one or a selection of specificlandfills:
EQUATION 2
Q = Lo ● R ● (e-kc - e-kt)
Where:
Q : methane generated in current year (m3/yr) Lo : methane generation potential (m3/Mg of refuse)

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R : average annual waste acceptance rate during active life (Mg/yr)
k : methane generation rate constant (l/yr)
c : time since SWDS closure (yr)t : time since SWDS opened (yr)When estimating regional or national figures, the following equation for CH4 generation in year T from all solid
waste landfilled in one specific year x (Rx) may be used:
EQUATION 3
QT,x = k ● Rx ● Lo ● e-k(T-x)
Where:
QT,x : the amount of methane generated in year T by the waste Rx (Mg)x:the year of waste input

Rx :the amount of waste disposed in year x (Mg)T:current year

In order to estimate all emissions in the year T from waste disposed of in previous years, Equation 3 can be solved
for all values of Rx and the results summed using the following equation:
EQUATION 4
QT = ∑QT,x
for x = initial year to T
Where:
QT :total emissions in year T from waste disposed of in previous years (including year T)

No specific recommendations of default values for variable factors like Lo and k are given, only a very wide rangeof values: Lo <100 - >200 Nm3/Mg; k = 0,005 – 0,4. Limited information of units involved is provided in theguidelines. Furthermore, no reduction due to recovery of gas or oxidation factor is introduced. Although the IPCC
encourages the use of this model (equations 3 and 4) it does not supply sufficient material for use of this method
directly in national inventories.
Nationally Adjusted FOD-model
Several countries have made adjustments to the presented FOD-model by including supplementary information of
the factors Lo and k, and are in the process of using these in their national inventories.
A model implemented in Norway in 1998 (Bartness, et al, no date) is proposed as follows:
EQUATION 5
QT,x = k ● MSWT(x) ● MSWF(x) ● MCF(X) ● Lo(X) ● e-k(T-x) ● F
Where:
QT,x : the amount of methane generated in the current year from waste disposed in the year xT:the current year (year of the emission estimate) (Gg/yr)x:

the historical year of the disposal of the relevant national MSW quantities

Lo(X) : DOC x DOCF for the year x (Gg CH4/Gg waste)k:ln (2)/t½. (1/yr)

t ½:

half-life period for the degradation process (yr)MSWT(x), MSWF(x) and MCF(x) and F are the same factors as in the default method (equation 1), but estimated forthe year x.
This is for the year x and when doing the same calculation for each year back in time from T until a point of time
when the majority of the MSW is degraded in year T; total emissions in year T will be the result (equations 4
applies). From this total figure (QT), LFG extracted and flared and/or recovered in year T (RT) must be subtracted
together with the oxidation effect to obtain the total net emission in the year T (QNet,T):

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Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

EQUATION 6
QNet,T = (QT - RT) ● (1 - OX)
In addition to the necessary input to the IPCC default model, this model will require information on:•

historical MSWT(x), MSWF (x), MCF(x) values or assumptions of the rates of changes over time;•

historical DOC or assumptions of the rates of changes over time, and•a choice of half-life period for bio-degradation in the country.

Guidelines for estimating historical figures and/or default values may be established. The mathematical
calculation and data input is simple when set up in a spreadsheet.

2.1.3

Comparisons between the Methods

The IPCC default method (A) and first order decay model (B) do not provide comparable estimates of yearly
emissions. The IPCC default methodology provides estimates on potential CH4 emissions without incorporating
any time factors. The first order decay model on the other hand estimates actual yearly emissions. The differencesin the results provided by the two models are illustrated in Figure1, where emission estimates for MSW disposal in
Finland are given (Pipatti et al. 1996). Method A predicts up to approximately 60 % (in 1990) more methane
emissions than method B.
Emissions with the default (A) and FOD (B) models withgrowth and then reduction in SW disposal

Gg CH4/a

Figure 1

200
180
160
Mass balance model
140
without time factors
120
100
80
First order decay model
60
40
20
0
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Year
Source: Pipatte et al., 1996

The curves given in Figure 1 are based on the following assumptions:•

MSW disposal in Finland is assumed to have grown steadily since the beginning of the century. Since1990’s
waste reduction, recycling and alternative waste treatment methods have been utilised increasingly, and•More stringent restriction in SW disposal will take place in the coming years. The changes in the amount of
MSW disposal are reflected immediately in the emissions calculated with the IPCC default method whereas
the first order decay model responds more slowly to the changes.

Figure 2 presents an illustration of a simulation with the default and FOD method of emission estimates from thesame SW amounts disposed of during 1970 to 2010 with a continuous annual growth of 2 percent in the quantities.
The parameters used in the calculations differ from those used in Figure 1. As indicated, the difference between themethods will be reduced as the simulation period increases.
Box 1 presents some test calculations with the Norwegian national model (Barrett et al, no date) of the effect fromvarying factors like SW quantities and composition (DOC) and disposal practices over time in the FOD method
and compares these to results with the default method.

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Figure 2

Emissions with default and FOD models with continuous
growth in SW disposal

Meth an e em issio n
160
140

G g CH4120
100

F O Dm ethod

80
60

IP CC
defaultm ethod

40
20
0
1970

1980

1990

2000

2010

Ye a rIn the long run the total emissions calculated with the two models should be similar even though yearly estimates
may differ substantially. A test calculation was made for a very long period (60 years) for the FOD model, and thetotal amount of CH4 estimated with the IPCC Default method was only approximately 5 percent higher than theemissions estimated with the FOD model, being within an acceptable margin.
BOX 1

Test calculations made using the IPCC default method and the first order decay model (FOD)
indicate that the IPCC default method may give inaccurate estimates of actual annual emissions
when the input factors like SW quantities, composition and/or disposal site practices change overtime (1.5 percent growth, 7 years as t½ , increased paper content etc.). Assuming changes in thesefactors for the last 25 years, a situation realistic for many developing countries, calculations indicatethat up to 66 percent higher emissions are estimated for the present year with the default method.
This is in correspondence with the main conclusions of the paper that the IPCC default method canbe used only to estimate potential emissions caused by SW disposal in the inventory years.
Estimation of actual annual emissions would require the use of a kinetic model (e.g. FOD model) or
introducing/proposing a time correction factor to the default method. The FOD model or a timecorrection factor may give emission estimates which are lower than 50 percent of the figures basedon the default model in cases with steadily increasing waste disposal.
Calculations have also been made to check the contribution to this difference from various changes
assumed. They indicate that:by keeping the other historical factors similar to existing and assuming approximately 1.5 percent
growth in MSW quantities, the IPCC default method gave 30 percent higher figures (the IPCC
Guidelines indicate 20-25 percent higher estimates using 2 percent growth in SW quantities)
by keeping the other historical factors similar to existing and assuming a substantial change in MSW
composition, the IPCC default method gave 21 percent higher figuresby keeping the other historical factors similar to existing and assuming change in SWDS conditions
through the MCF of 0.7 on average compared to 0.8 as default, the IPCC default method gave 30
percent higher figures

2.1.4

Recommendations - future methods

The IPCC default method can produce relatively good estimates of the potential future emissions. It is simple,
transparent and easy to use. The use of the method could therefore be recommended as a reference methodology in424

Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

national inventories. It is also suitable for simple and illustrative calculations of the effect of various policies andmeasures to reduce the emissions from SW disposal (Pipatti and Wihersaari, 1998)
The calculation of the actual yearly emissions from SW disposal is, however, the target in the national inventories.
The actual yearly emissions can be estimated with the FOD method. More information on the use of the methodand default values for the input data would, however, need to be included in the IPCC Guidelines.
Other possibilities for the estimation of the actual yearly emissions put forward are the use of correction factorsthat account for changes in the SW disposal to the IPCC default methodology with the aim of achieving results
based on a simplified first order decay model. (See p.11 “correction factor for SW changes over time).

2.2
2.2.1

Choice of emission factors
Emission factors in the default method (mass balance)

The default method introduces the following emission factors:
MCF-Methane correction factor
MSW can be disposed of in a wide range of site conditions. Modern sanitary landfills are characterised byconditions favourable for anaerobic degradation:•

sufficient depth (minimum 10 m, preferably more);•high compaction with suitable equipment;•

properly designed and well-operated leachate and storm water systems;•

proper site management with no scavenging at the operational area;•

control of incoming waste types and quantities and environmental monitoring schemes established;•frequent surface covering;•

prevention of landfill fires, litter and scavenging animals, and•gas control and extraction/recovery.

Open dumps are more favourable for aerobic degradation and are characterised by conditions like:•shallow sites (<5 m) (favourable for aerobic degradation);•poor and light operational equipment, for instance bulldozers (being in widespread use) have in general a low
area pressure, resulting in limited compaction effect (favourable for aerobic degradation);•no or limited coverage (favourable for aerobic degradation);•scavenging by people and animals;•

aerobic degradation conditions in substantial or all parts of the sites,and•frequent fires, often used deliberately and systematically mainly to reduce volumes and to “get rid of ” theSW.

Most sites will have conditions between these two extremes. The IPCC Guidelines present the following default
values for the site conditions factor:•

Managed sites

MCF = 1.0;•

Unmanaged, deep sites (≥ 5m)

MCF = 0.8;•

Unmanaged, shallow sites (<5m)

MCF = 0.4, and•Unspecified SWDS – default value: MCF = 0.6

To estimate a country-specific MCF, the national SW quantities should be divided in these SWDS categories to
end up with a weighted average. However, probably even countries with relatively good data on SW disposal may
have problems splitting the SW quantities in these site groups. For countries without sufficient data andinformation to do this split, the default value of 0.6 is proposed.
The reduction implied by the MCF is normally caused by two conditions:•

SWDS conditions allowing aerobic degradation resulting in other emissions than CH4. This may be caused byloose compacting, shallow site or lack of cover material, normally a combination of all these ,and

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Fires in the landfill instantly reduce the organic matter with very limited emissions of CH4.

Thus the MCF may be split in sub-factors. As an illustration, Table 1 presents proposals for sub-factors for
Norwegian site conditions, which probably to some extent are similar to many other western countries.

TABLE 1ESTIMATES OF NORWEGIAN MCF HISTORICAL SUB-FACTORS
PeriodReduction caused by
Loose/inpropercompactinG

Shallow SWDS
areas

Inproper top coverage(aerobic top zones)

Fires

Summarised
MCF

2000-2009

0.99

0.97

0.98

1.0

0.94

1990-1999

0.98

0.96

0.96

1.0

0.90

1980-1989

0.96

0.93

0.94

0.97

0.82

1970-1979

0.92

0.88

0.90

0.90

0.66

1960-1969

0.85

0.82

0.87

0.80

0.49

1945-1959

0.80

0.78

0.85

0.72

0.38

According to this, questions may be raised if a MCF factor equals 1 is correct even for managed, modern sites andif perhaps 0.95 as MCF would be a more realistic figure. Even a managed site will have brink zones, top layers etc.,
where aerobic conditions occur.
A more substantial concern is, however, which MCF to use for many developing countries in the tropical andsub-tropical climatic zone. Numerous site observations from countries like Thailand, Philippines, China andJamaica indicate that almost all the organic material in an unmanaged or poorly-managed SWDS under tropical or
sub-tropical conditions is more or less degraded in 2 up to 7 years after disposal. When excavated, the remaining
material is soil, plastics, metals and inert material. The speed of the process and registered site conditions indicatethat most of the process probably is aerobic. Thus, the MCF for such site conditions may be 0.3 and even lower.
Site observations show also that burning is a widespread practice in many countries. Normally, this can be
explained by accidental fires or fires started by scavengers. Some of the fires may also be set by the operational
staff to reduce the volume of waste and problems with smell, rodents, etc. Whatever causes the fires, reduces theCH4 emission potential to almost nothing in the areas/zones, and the MCF for the whole site may be low.
One consequence of this is that the default value of 0.6 may be too high for many developing countries. Default
values for the MCF in the range between 0.3 and 0.8 could therefore be more relevant.
In general, the choice of MCF values and the given default values should be further assessed and adjusted in the
proposed guidelines, based on agreed decisions at the expert meeting.
DOC - Content (fraction) of degradable organic carbon
The IPCC Guidelines provide the following equation:
EQUATION 7
DOC = 0.4 ● (A) + 0.17 ● (B) + 0.15 ● (C) + 0.30 ● (D)426

Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

Where default values for DOC related to A, B, C and D are as presented in Table 2:
TABLE 2DEFAULT DOC VALUES FOR MAJOR WASTE STREAMS
A.
B.
C.
D.

Waste Stream
Paper and textiles ( % portion in SW)
Garden and park waste, and other (non-food) organic
putrescibles ( % portion in SW)
Food waste ( % portion in SW)
aWood and straw waste ( % portion in SW)

Per cent DOC (by weight) in wet (fresh) SW
40
17
15
30

a

excluding lignin C
Source: IPCC Guidelines

This provides a good basis for estimating a DOC value for the specific country. However, some elements should becommented on:•

A+B+C+D should not sum to 1.0 (100 %), as other materials like metals, plastics, rock/dust etc. are also
included in the indicated MSW generation figures listed in the guidelines;•

In many countries, the composition figures are not related to mixed MSW but to, for example, household
waste and non-household waste, for example. A supplementary calculation of weighted DOC for mixed MSW
should be carried out, and•Questions may be raised if some plastics should be included. Plastics are usually considered non-degradable
in SWDS. Some, especially new types of plastics may behave differently, for instance polyethylene (PE)plastics have a high content of organic carbon and may bio-degrade, though over a very long period. As
plastics are of fossil origin (oil), the CO2 emissions produced should in theory also be accounted for, although
their importance in the national inventories is probably negligible. In some countries, plastics have been
included to some extent in the estimated DOC value.

The default values for DOC in various countries show some variations within rather similar regions that may seem
strange. In general, a developing country normally should have a higher total DOC, because of higher content of
paper, textile and wood with relatively high DOC. The variations may be caused by different definitions of waste
included in the inventory.
The emissions from disposal of industrial, construction and demolition waste and sludge should also be included in
the inventory. The DOC content of these wastes differ much from that of average MSW and guidance how toestimate this is needed.
DOCF - fraction of DOC dissimilatedThis factor is based on a theoretical model where the variation depends on the temperature in the anaerobic zone of
the landfill: DOCF = 0.014 ● T + 0.28 where T is the temperature. This factor may vary from 0.42 for 10oC to 0.98
for 50oC. In fact, in many deep landfills (>20 m) temperatures of more than 50oC have been registered in gas
streams from highly productive (thus clearly anaerobic) gas wells.
This theoretical factor is currently under review. An IPCC workshop in Washington in 1995 recommended the useof 0.5 as a new default factor on the basis of several experimental studies. It is, however, unclear to what extent thetemperature in the strictly anaerobic zone influences the fraction of the total DOC being converted to CH4 during
the degradation process. The temperature clearly influences the speed of the process, which in the FOD model ismainly reflected in the choice of half-life period for the degradation (t½ ).
For the default mass balance model, it must be further discussed how realistic this substantial influence oftemperature is. If only 56 percent of the DOC is converted to CH4 and CO2 during the process (under e.g. 20oC
conditions), then 44 percent should be stored in the SWDS (as stable organic matter), or be degraded through otherunspecified and probably non-biological processes, or be degraded over a longer period than reflected in the DOCF
equation.
F - fraction of CH4 in landfill gas (LFG)
LFG from undisturbed SWDS zones in the main anaerobic phase has a composition of mainly CH4, CO2 and alarge number of trace components, normally accounting for less than 1 percent of volume. As indicated in the
Figures 3 and 4, the composition of the gas produced and emitted may vary during the bio-degradation process.

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Figure 3

Composition of landfill gas in different phases of thedegradation process

Source: Tasaran, 1981
Phase I :Phase II:
Phase III:
Phase IV:
Phase V:TOTAL

Oxygen- and nitrate-reducing phase – Duration range: Hours – 1 week
Acidic phase – Duration range: 1 – 6 months
Instable methane generating phase – Duration range: 3 months – 3 years
Long term stable methane generating phase – Duration range: 5 – 50 years
Humus-generating and/or sulphide oxidation phase – Duration: 1 – min. 40 years
Duration range: 10 – min. 90 years

Figure 4428

Schematic presentation of the degradation process at
landfills

Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

Various sources operate with a CH4-content in LFG between 50 and 60 percent, and the default value in the IPCC
Guidelines is 50 percent. Experiences from a number of pumping tests are indicating that composition ofundisturbed LFG very often is in the order 55 percent CH4 and 45 percent CO2. The adjustment of the default value
to e.g., 55 percent CH4 for F may be relevant and may be discussed further.
OX – oxidation factor
The default value for this is 0, although an increasing focus is being put on this factor. Numerous field tests
including flux measurements clearly indicate that there is an oxidation effect, but the results are not systematic or
consistent. It is, though, registered that the oxidation effect increases with rising temperature. The oxidation effectis also highly dependent on the type and thickness of cover at the SWDS.
At the IPCC workshop in Washington in 1995 and at an international seminar in Chicago in 1997 there was anagreement of using 10 percent as a standard value, which later on has been subsequently implemented in several
national inventories. More recent studies on oxidation have not changed the basis for this value substantially, and it
is proposed to introduce this as a default value in the IPCC Guidelines. The possibility to have a variable range
depending on the temperature/climate may be discussed.Correction factor for SW changes over time
The emissions estimated with the default mass balance method do not reflect the changes over time in SW
composition and quantities or disposal practices. A recent paper (Irwing et al., 1999) proposes to add a correction
factor, aiming to include changes over time of disposed SW quantities and to introduce effects of degradation time
for the process.
The mathematical expression for the factor introduced is:

CORRECTION FACTOR

EQUATION 8= [1 / (1 + R)T] ● {1- 1/[T ● ln(1 + R)]}

Where:
R: national annual growth rate of waste to disposal for a certain period
T: duration of methane generation
For a high growth rate for SW disposal, this correction factor may be down to 0.4, changing the emissions
estimates dramatically compared to estimates by using the default model.
A comparison of estimates of US emissions (an increasing trend in the emissions) based on the FOD model
indicate figures approximately 10-12 percent higher for the default IPCC model with added correction factor
compared to the FOD model. This is a promising similarity in light of the simplicity in adding this factor.
Two sub-factors for potential changes over time are still not included in the correction factor: changes in MSW
composition and changes in SWDS management and practices. The possibility to incorporate these in the factor
may be assessed. The use of the correction factors in situations where the amounts of SW disposal fluctuate fromyear to year may, however, not apply.

2.2.2

Emission factors connected to IPCC’s FOD method

There are two factors in IPCC FOD model (see equation 3) that have not been discussed yet: the methane
generation potential Lo and methane generation rate constant k.
Lo- methane generation potential
A range between less than 100 m3/Mg SW and more than 200 m3/Mg SW is presented in the IPCC Guidelines. No
basis for this range is presented, no default values given or the conditions that influence the factor mentioned.
However, this factor depends on the DOC and DOCF and the conditions at the SWDS as in the default method (Locorresponds to MCF ● DOC ● DOCF ● F ● 16/12 in the default method).
k - methane generation rate constantThis factor is depending on waste composition and site conditions, and describes the rate of the degradation
process. A very wide range of values between 0.005 and 0.4 is given for k in the IPCC Guidelines.

2.2.3

Emission factors connected to an adjusted FOD model

The main equations of the Adjusted FOD model are given in 2.1.2.
k – methane generation rate constant
The formula for k = ln(2)/t ½, where t ½ is the average time for 50 percent degradation. The half life t ½ ranges
usually between 4 and 10 years for MSW disposal, where warmer climate results in shorter time. The degradation
time is different for various types of waste. Organic material like food waste degrades rapidly, whereas material inpaper and wood degrades slowly. Thus household waste normally has a shorter degradation time thanCH4 Emissions from Solid Waste Disposal

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non-household waste and industrial waste. Furthermore, the choice of degradation time also may reflect how
optimised the physical and chemical conditions are inside the landfill (chemical composition, humidity etc.). If for
instance the landfill is partly filled with water, this will increase the degradation time substantially.
When sufficient data material is available, a weighted average for t ½ for mixed MSW may be calculated.
Alternatively, a set of default values depending on climate and MSW composition may be provided.
Test calculations with various t½ values have been carried out and the results have been compared to results basedon the default IPCC method. The results are presented in Figure 5 and the main conclusion is that the difference
between the two methods is at a minimum when assuming approximately 4.5 years as an average t½ for the SW. At
this point the difference is approx. 12 percent. Both through increasing and decreasing the t½ from this value, thedifference will increase.
A default value in the range between 4 and 7 years could be realistic for most developing countries (in a tropical or
sub-tropical climate) and countries with economies-in-transition. Values for k should be further discussed.
To estimate total emissions in year T from all historically disposed MSW, the equation QT = ∑ QTx, is used. The
relevant total time (ttot) that includes all historical years that have an impact on the emissions in year T can beindicated by ttot = 5 x t½. Mathematically, when repeating the 50 percent reduction 5 times, only approx. 3 percent
is left for degradation. This ttot is typically in the range of 20-25 years in a tropical climate, and 50 years or more fora cold climate. The historical assumptions may be based on data registered over time or trends, growth rates etc.,
either specific for the country or the region. The net emissions of CH4 can be established by the equation 6:
Figure 5Comparison of emissions estimated with the IPCC
Default and the FOD method

Maximal CH 4- emission after 25 year of disposal of
the same SW quantity each year
120

kg methane

100

FODmethod

80
60

IPCC
default
method

40
20
0
0

2

4

6

8

10

12

T1/2

2.2.4

Emission factors with associated uncertainties

The guidelines mention potential uncertainty, in factors like DOC, MCF and OX, but without any further
instructions or guidance. Uncertainty related to DOCF or any factors related to the FOD-model are not mentioned.
The use of the factor DOCF introduces uncertainty particularly for lower temperatures. Questions can be raised
whether this factor should be fully implemented, for example the DOC available for degradation is reduced by 0.56
when the temperature is 20oC. A substantial portion of the DOC is excluded without a proper basis.
The IPCC Guidelines indicate that the uncertainties in the various factors in equation 1 will partly overlap, andthus must not be summarised directly, but by using the equation 9:
EQUATION 9
UT = ± √(UE+UA)
Where:
UT: total uncertainty

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UE: uncertainty connected to source E
UA: uncertainty connected to source A
Equation 9 is applicable only when UE and UA both are less than 60 percent.
For instance, if uncertainty is + 10 percent for two factors, the total uncertainty would be + 14 percent. The
equation may be similarly extended, if more uncertainty factors are included.
In Table 3, default values and ranges from the IPCC Guidelines and ranges estimated by the authors of this paper
are summarised. The actual uncertainty ranges can differ much by country depending on the level of information
available. Table 4 presents how the uncertainties in the Norwegian inventory were broken down and summarised.

TABLE 3
DEFAULT UNCERTAINTIES GIVEN IN IPCC GUIDELINES AND ESTIMATED BY THE AUTHORS
MethodDefault EF

Default range

Estimated range

Cause of uncertainty andcomments

Default IPCC massbalance method

MCF

Default range
1 - 0.4
Default value 0.6

0.3 – 0.95 (or 1?)

Normally not 100% optimal
Real average condition may
vary.

DOCF

0.77

10 oC - 0.42
50 oC - 0.98

Unclear what happens to the
DOC in low temperatures(alternative degradation
processes or carbon storage in
SWDS).

F

50% default value

40 - 60%

Not sufficient in situ testing.
LFG analysis world-wideOX

0 - default value
10% recommended

0 - 30%No systematic and reliable
survey has been presented.

FOD method
introduced in the
IPCC GuidelinesLo< 100 m3/Mg > 200 m3/Mg

Same uncertainty as for DOC
and DOCF above.

k0.005 - 0.4

No further explanation of thebasis for k is provided.

Adjusted FOD
method(k) with t½

t½ : 4-10 yrs
7 yrs realistic as default
value for tropical and 10
years for tempered
climateSee Table 4(Note: In the EPA model therange 14-17 years waschosen)Historical
DOCF andMCF

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Lack of information on portion of organic
material in industrial waste. Inaccurate historic
data

Cause

Quantities of organic
industrial waste
outside MSW
Substantial uncertainty in the extent of anaerobic
conditions in disposed industrial waste

Component

LFG production fromorganic industrial
waste

Half-life times are based on estimate
composition and adjusted to Norwegian climate

Quantities ofUncertainty in the extent of anaerobic conditions
construction/demolitio and the portion of organic material in disposedn waste not included in construction/demolition waste
MSW
Half-life time (t½) for
various waste types

Composition of MSW

MCF

Oxidation effectInsufficient information on estimates and trends

Lack of data on composition of non- household
waste in MSW

Incorrect estimates of effects of site conditions
not favourable for CH4 production. No fieldsurveys referred toRelatively newly reported aspect. International
agreement of using 10%

Content of CH4 in LFG Based on review of various sources and on
undisturbed LFG samples

Historical quantities
before 1970
Summarised effect

432

TABLE 4

Variation range

Uncertainty incomponent÷ 10 % - +5%

Effect of uncertainty
in total emissions in
1995

UNCERTAINTY ASSESSMENT IN THE NORWEGIAN CH4 INVENTORY
Used value

÷ 100 - +50%

Comments

Substantial uncertainty in how large
portion have been disposed in larger
SWDS

1998 and onwards:
0-150.000

Summarised:∼ 100.000 ton in 1995 andonwards

÷ 5 % - +10 %÷5%-0%

÷ 25 % - +15 %∼ 200 - 425 Nm3/ton

0 - 200.000 ton/yr
generating LFG

÷ 10 % - +20 %Mainly loose compacted landfills for
waste from wood/tree processing andworking0

Household waste:
7-11yrs

÷ 10 % - +35 %50 - 60%

÷ 50 % - +300 %÷ 10 % - +10 %÷ 15 % - +5 %

÷ 20 % - +5 %± 10 %

Recent research indicate higher values,
particularly when proper top cover

Employed values in other sources in therange 50% to 62%

0 % - +10 %Household waste: 9,5 years

Non- household waste
in MSW: 10-13 yrs

Non- household waste in
MSW: 11 years

55%

5-30 %

÷ 25 % - +10 %Industrial waste 11 years

10%

From 0.95 – 0.8 in
1995

Industrial waste: 10-15
yrs

0.9 i 1995

Mainly uncertainty related to
non-household waste in MSW± 10 %

Limited effect due to high degree ofdegradation today

For non- household waste
in MSW± 10 - 15%± 2-3%

Many of the uncertainty factors willinternally even± 20-30% for several
fractions

± 30%

± 30%

Waste Sector

Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

2.3

Choice of activity data

2.3.1

The default method

MSWT - Total MSW quantities
The default model only requires figures for the inventory years. Developed countries often have statistics on MSW
generation and disposal quantities. Such figures may for many developing countries and countries with economies
in transition be based on sample surveys being scaled up through multiplying specific figures (kg/capita/day) withthe assumed urban population. Full-scale and full-time weighing of MSW is very often not implemented on anational basis in large regions of the world, not even in the developed countries. This clearly introduces asubstantial uncertainty.
The World Bank has presented a comparison of the average MSW generation related to average GNP per capita. In
Table 5 and Figure 6 this relationship is indicated. Many SW surveys have confirmed the validity of this. This may
also be an indicative basis for assuming historical changes.

TABLE 5CORRELATION BETWEEN INCOME LEVEL AND SPECIFIC WASTE GENERATION RATE FOR MUNICIPAL SOLID WASTE
Average GNP per capita 1)

Average MSW generation 2)

No. of countries in statistics 1)

US$/yrkg/cap./day

Low income

360

0.53

51

Lower-middle income

1,590

0.63

39

Jamaica

1,540

0.65

1

Upper-middle income

4,640

0.71

16

High income

23,4201.20

24World average

4,470

0.67

133

Sources:1) World Development Report 1996. The World Bank 2) The Economics of MSW. The World Bank Research Observer vol. 2, 1995

Figure 6

Waste generation rates for municipal solid waste vs. GNP
in various countries

kg/cap/day
1.3
1.2

y = 0.027x + 0.5695
R2 = 0.9826

1.1
1.0
0.9
0.8
0.7
0.6
0.5
0

5

10

15

20

25

GNP/capita, 1,000 US$

There is also a major concern of what types of waste to be included in these emission inventories. The IPCC
workbook focuses on industrial waste as a potential LFG emission source in addition to MSW. The national
inventories should, however, include all waste types, for example:

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agricultural waste (note: double counting with the CH4 estimates from manure management in the agricultural
sector must be avoided);•building and demolition waste;•

ship/harbour waste;•sludge;•institutional waste (hospitals, municipal activities etc.), and•other, not specified waste.

A presentation of SW types that may be included in the national inventories is in Figure 7.
Figure 7

Breakdown of major waste types in MSW

The waste types in dotted frames only partly enter the municipal waste stream.
Large objects/bulky waste
Household waste (HHW)

Yard waste
Daily collected waste
Light waste (similar to HHW)

Commercial waste

Food waste (from markets etc.)
Packaging waste
Light waste (similar to HHW)

Industrial waste

Heavy/bulky waste
Industry-specific wase
Light waste (similar to HHW)

Institutional waste

Medical waste
Infectious waste

Municipal
solid waste

Light waste (similar to HHW)
Hotel and restaurant waste

Food waste
Light waste (similar to HHW)

Construction and demolition waste

Wood waste
Inert materials
Light waste (similar to HHW)

Ship, harbour and airport waste

Special waste (from customs etc)
Cargo spills
Light waste (similar to HHW)

Agricultural waste

Organic waste
Street sweeping

Street waste and municipal cleansing waste

Park waste
Gully and drainage cleaning
Manholes and fat-trap sludge

The default values in the IPCC Guidelines do not include all these types, and national inventories must focus onestablishing complete figures for the SW disposed in their country.
Another element with a substantial influence on the MSWT figures is the split between urban and rural population,and if and to what degree the rural population should be included. Even in many developing countries, MSW fromvillages and townships is collected to some extent and brought to SWDS although their population is not includedin the urban figures. Furthermore, many countries have limited updated information of their urban population.

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Consequently, the figures for population to be used must be assessed and selected based on experience of theconditions in the country.
MSWF - fraction to disposal
This fraction differs from MSWT through:
EQUATION 10
MSWF = (MSWT ● CC) - MSWTREAT - MSWREC
Where:CC:

Collection Coverage (this figure may range from near 100 percent in many developed countries
to 40-50 percent even in urban areas in many developing countries)

MSWTreat: Registered or estimated MSW quantities to other treatment like incineration or composting
MSWRec: Registered or estimated MSW quantities to recycling
For many developing countries and countries with economies-in-transition the two last figures are relatively low,
although an extensive recycling activity may be observed through scavenging and sorting both in the collection
areas and in the SWDS.
R - Recovered LFG
Many countries have operative LFG extraction and recovery plants at present. The global number of plants is notknown, but in 1995 some 270 plants with LFG recovery were reported worldwide (Doom and Barlaz, 1995). At
present, the Scandinavian countries alone with a population of approximately 23 million have a total of more than
120 plants in operation, and UK have over 100 LFG recovery schemes, so the present world-wide figures should behigher than estimated by Doom and Barlaz for 1995.
Most modern LFG plants have a flare in operation when recovery for energy use is not in place, and normally acentral flow meter with a counter would be installed. A flare will convert most of the CH4 to CO2. Thus the total
extracted LFG quantities must be included in the figures for R under the condition that either flaring or recovery forenergy use is implemented.

2.3.2

The FOD-model with supplements

In addition to the required input to the default model, the FOD-model requires historical figures or assumptions ofchange rates over time. Preferably these figures or assumptions should cover both quantities and composition of
SW and disposal conditions.
There are international statistics and sources that may provide some of this information, presented in various
publications from organisations such as United Nations (UN), International Monetary Organisation (IMF), WorldBank (WB). These may be information on economic growth, urban population growth rates or MSW generation
rates. Most countries have also available local surveys and supplementary information enabling estimates and/or
assumptions of historical changes. As earlier mentioned, a historical period of 20-25 years would be appropriate
for most countries in the tropical and sub-tropical zones, and relevant specific figures should be available based on
various studies and surveys either in the country or in similar countries in the region.

2.3.3

Accuracy of activity data

The accuracy of activity data will vary fundamentally between the countries. For some developed countries, MSW
quantities and composition are normally well documented and registered since the last 20-30 years, although the figuresfrom the 1970’s and earlier have more errors included. Probably the data on MSW generation and composition incountries with good data collection systems may have an uncertainty range of ±10-20 percent. In other countries, theuncertainties associated with MSW quantities and composition may be more than twice as large.
Even for most of the industrialised countries the figures on MSWF and other SW disposal are more uncertain. Thisis especially true for data on industrial and other waste than MSW. The composition of other SW than MSW is alsoless well known and hence also the uncertainties associated with emission potentials larger. For instance, the waste
emissions in the Norwegian inventory have been estimated to have an uncertainty of –80 to +50 percent., and thatthese emission figures have had an effect of –8 to +5 percent over time on the total national emission figures.
For many developing countries and countries with economies in transition, the inaccuracy will be substantial
higher, with a multiple set of causes like:•lack of weighing statistics;•

lack of updated figures for urban population;

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lack of information of collection coverage;•

lack of information of disposal conditions, and• lack of information of management of SW outside the MSW.
Summarised, this may lead to inaccuracy in some countries of up to ±50% in the activity data.

2.4

Input to uncertainty workshop

Uncertainties associated with the emission factors (see text and Tables 3 and 4 in 2.2.4) and activity data (2.3.3) areaddressed in the above chapters and ranges for the values are suggested. When assessing the total uncertainties ofthe emission inventories the uncertainties need to be combined. When using the FOD model the ability of themodel to describe the timing of the emissions need also to be considered in the estimation of the uncertainties of theannual emissions. The uncertainties are, however, very dependent on quality of the country-specific data on thevarious input parameters needed in the calculations. The possibilities to produce figures on global and regional
uncertainties in emission estimates will be explored at the Sao Paulo expert meeting.

2.5

CompletenessCompleteness means that estimates should cover all sources and sinks, as well as all gases (included in the IPCC
Guidelines) and other existing relevant source/sink categories which are specific to individual Parties, andtherefore may not be included in the IPCC Guidelines. Completeness means also full coverage of sources and sinksof a Party to the UNFCCC (FCCC/SBSTA/1999/l.5).
Some factors that may, in addition to introducing uncertainty and inaccuracy, also result in the lack ofcompleteness in the inventories, are identified:•

Rural population contributing to LFG and CH4 emissions. The IPCC Guidelines assume that this population
does not contribute to the emissions, while to some (though limited) extent they do, and•Emissions caused by other SW types than MSW, particularly for countries using the specific generation figures andindicated default values given in IPCC Guidelines, might be missing entirely from the inventories. Although the
Guidelines’ workbook mention organic industrial waste as a source, no information on how to estimate emissions
from this waste type is provided. For instance, Norway has a relatively wide definition of MSW, but still
approximately 15 percent of the national emissions come from other SW types apart from MSW. In Finland thewaste categories used in the calculation are MSW, industrial SW, construction/demolition waste, community andindustrial sludge. MSW contributes 60 – 70 percent to the total emissions.

In the preparation of the inventories on GHG emissions from SWDS, Parties could use the following checklist to
ascertain the completeness of their inventory:•

Activity data should cover all types of SW disposal (see Annex 7); if information on only MSW is used, thisshould be stated in the inventory;•

SW disposal may produce GHG emissions apart from CH4, for example CO2 from fossil waste, N2O andNMVOCs. If information on these emissions is available, countries are encouraged to report them withdescriptions and documentation on the emission estimation methods and emission factors, and•Information on LFG recovery.

2.6

Baseline determination

The activity data available on SW disposal has improved considerably in many countries during the last decade andwill continue to do so in the coming years. As activity data on 1990 cannot be improved afterwards, the consistencyof the time series from 1990 onwards may suffer. Transparent reporting on how these issues are dealt with in theinventories is therefore very important.

3
3.1

REPORTING AND DOCUMENTATION
Existing reporting and documentation guidelines

IPCC Guidelines contain a sectoral table where emissions are to be reported and worksheets where all relevant
information concerning the estimation of the emissions may be included. Documentation is required to enable review
and comparison of the inventories (major assumptions, methodology, etc.) and to provide a basis for reconstruction of
the inventories by a third party. The instructions also include an annex explaining how to manage uncertainties.

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The UNFCCC Secretariat has prepared, in co-operation with the IPCC, new “Common Reporting Format” tables.
The draft table for waste is very similar to the IPCC table on emissions from waste. The draft table on backgrounddata contains information on input values (activity data, emissions factors and other relevant information) used in
the calculation. This new table clearly adds to the transparency of the reporting, but could still be improved.
Furthermore, information on the quality of the data used in the calculation is needed. The accuracy of theinventories is dependent on the collection systems for activity data being used, and the basis for the emission
factors used. Information on how the activity data has been collected or estimated and the basis of the emissions
factors and other variables used in the calculation is needed. This information will also enhance the transparency of
the inventories.
When country-specific values are used they should be well documented and justified. As the factors influencing
the emissions are very country-specific, determination of such values should, however, be encouraged.

3.2

Potential improvements

Some potential improvements on the current IPCC Guidelines are listed here. Some of them are already included
in proposed Common Reporting Format – tables prepared by the UNFCCC Secretariat.
As the minimum supplementary information, the choice of method (default or FOD or other) should be presented.
The tables should be modified accordingly.
For the method chosen, the selected type of data (default or country-specific or other) and emission factors should
be presented, either in the national inventory or in attachments or cited documents.
For added transparency, as much as possible the following information should be attached:•

MSWT and MSWF and their basis (whether statistical data or default values are used, how the statistical data iscollected and preferably a division in MSW and other SW types);•

Chosen DOC (data on waste composition) and DOCF;•

Chosen OX;•

R-figures (LFG extracted/recovered, number of plants, etc.) and how the data is collected, and•k value chosen if FOD-model used and how it is obtained (e.g. t½ for different waste types).

•

Major historical assumptions (how historical waste amounts are obtained (e.g. percent growth), change in
MCF due to disposal practices, etc.) when using the FOD-model

3.3

Lack of Information

Many countries probably may lack established reporting requirements and routines, hence information may beavailable but is not automatically presented to the authorities or the inventory agency. This may be information of
SW quantities in some regions in the country or information from LFG recovery plants, etc.
Thus, for all countries, improved reporting schemes should be encouraged and supported. As a minimum, allavailable information that may be available in the country should be collected. Normally, there should be nolimitations in information availability due to commercial concerns or other private or official obstructions.

44.1

INVENTORY QA/QC
Introduction

Quality Assurance (QA) and Quality Control (QC) should be an integrated part of the inventory process. This will
ensure a confidence in the inventory results among relevant parties.
The QA/QC process may be divided into an internal process and an external process. The internal procedure
should ensure the accuracy, check for calculation errors and assure that the best available activity data and otherinformation is used in the inventory. Inventory producers are encouraged to consult waste experts within the
country. Externally, unbiased review and audit will enable identification of preparation errors and sources ofincorrect inherent bias. Comparisons of emission factors with countries with similar conditions are encouraged.

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4.2

Internal QA/QC items

Since the IPCC Guidelines introduce two methods for estimating emissions, national figures could be based on anyof these. The reporting instructions may require countries to always report the potential emissions calculated with
the IPCC default methodology and should encourage reporting of actual emissions also. The method used in thecalculation should naturally always be reported.

4.2.1

Emission factors

The emission factors should be based on IPCC Guidelines and default values, or preferably on evaluations of andadjustments to local conditions. If the inventory agency does not have sufficient knowledge of the conditions,information may be collected from environmental authorities, institutes, consulting companies, etc. Some
information may be collected from national statistics, for instance the status and number of SWDS.
Documentation of the factors, including both present and historical values, used in the calculation must be presented.
QA systems should be implemented in these decisions and a QC-form for verification and later review may beestablished.

4.2.2

Collection of activity data

When activity data is based on national statistics, it is important to use a QA system throughout the relevant
reporting agencies. Information must be reported in a standardised form to enable transparency, and the reported
figures should be checked by the inventory agency or others for completeness and correctness. When more
simplified methods are used (like using specific figures multiplied with relevant population figures), the chosen
values must be selected or verified by agencies with sufficient professional knowledge.

4.3

External QA/QC systems

This may include external reviews and audits, both during the inventory execution and after the draft figures havebeen presented. Some aspects to be reviewed are:•Quality and appropriateness of emission factors in use;•

The use of the relevant equations, depending on the method;•

The correctness and validity of the resulting figures, and•

The QA/QC systems implemented in the inventory process

The external review should be implemented within certain intervals, not necessarily each year. As a minimum,
initial review should be carried out when estimation method is changed.
External review may be carried through:•Expert (peer) review by local or international experts;•

Third party audit; review by selected third parties;•

Review by stakeholders (government, official pollution agency, SW companies associations, etc.), and•Public review (NGOs, etc.).

5

CONCLUSIONSSW disposal is a significant source of CH4 emissions in many countries. The CH4 emissions from SW disposal haveshown a declining trend in many industrialised countries lately, whereas the emissions from developing countries are
expected to grow in the near future due to improved economy and improved landfill management practices.
The IPCC Guidelines give two methodologies for estimation of CH4 from SW disposal – the IPCC default (a massbalance method) and the FOD (a first order decay method) methods. The emission estimates calculated with thetwo methods are not comparable. The mass balance method gives an estimate of the potential CH4 emissions ofsolid waste disposed on land without consideration of the timing of the emissions. The FOD method takes thetiming of the emissions into consideration and gives a more realistic picture of the actual emissions during for theinventory year in question.

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Both the IPCC default method and FOD method have advantages depending on how the results are used. The IPCC
default method gives an estimate of the total potential CH4 emissions caused by disposal of a certain amount ofSW, and the FOD method gives an estimate on how these emissions are realised in time. Changes in the amount of
SW disposal are reflected immediately in the results of IPCC default method, whereas the FOD method responds
corresponding to reality more slowly to the changes. The IPCC default method is easy to apply and the result arevery transparent. The FOD method is more complicated and its use requires more input data and knowledge of the
decay process at SWDS. As the emission estimates of the methods are very different, especially when changes in
SW disposal are taking place, clear guidance on how the methodologies should be used in the preparation ofnational greenhouse gas inventories should be given.
The FOD is inadequately described in the IPCC Guidelines and default values for all parameters needed in its use
are not given. Wider use of the method would require more information on how the necessary national input data
can be estimated, as well as default values for the method parameters.
The uncertainties in the estimates on CH4 emissions from waste are large, regardless of the method used. The dataon composition and amount of waste disposed of at landfills is still often based on rough estimates and, whenlooking at past values, the lack of data is even greater. Statistics on both municipal and industrial waste
management are currently improving in many countries, and future emissions will be based on more reliable data.
Waste management and SW disposal practices, as well as the composition of waste, varies much from country tocountry. Data collection and choice of emission factors should therefore to the extent possible take national
circumstance into account. Transparent and comparable reporting of the emissions is also important, as well as
systematic evaluation and improvement of the accuracy and quality of the emission estimates.

REFERENCES
Bartnes, J., J.E. Frøiland-Jensen, T. Williksen, Norconsult: “Development of a national inter-active calculation
model and estimation of CH4 emissions from Norwegian SW landfills”. Report prepared by Norconsult for
Norwegian State Pollution Control (SFT).
Bingemer, H.G. and P.J. Crutzen (1987): “The production of methane from solid wastes”. Journal of GeophysicalResearch, 92 (D2): 2181-2187.
Doorn, M. and M.A. Barlaz (1995):“ Estimate of Global Methane Emissions from Landfills and Open Dumps.”
Prepared for US-EPA Office of Research and Development, February 1995, EPA-600/R-95-019.
Irving, W.; Woodbury, J.; Gibbs, M.; Pape, D.; Bakshi, V. (1999): “Applying a Correction Factor to the IPCC
Default Methodology for Estimating National Methane Emissions from Solid Waste Disposal Sites”. Waste
Management & Research: 16: 1-8.
Pipatti, R. and Wihersaari, M. (1998): “Cost-effectiveness of alternative strategies in mitigating the greenhouse
impact of waste management in three communities of different size”. Mitigation and Adaption Strategies for
Global Change 2: 337 – 358.
Pipatti, R., Savolainen, I. and Sinisalo, J. (1996): “Greenhouse impacts of anthropogenic CH4 and N2O emission in
Finland. Environmental Management”, Vol. 20, No. 2, pp. 219-233.
Tabasaran, O. (1981): “Gas production from landfill”. In: Household Waste Management in Europe, Economics
and Techniques, A.V. Bridgewater and Lidgren, K. (eds.), Van Nostrand Reinhold Co., New York, USA, pp.
159-175.
UNFCCC (2000): “National Communications from Parties included in Annex I to the Convention: Greenhouse
Gas Inventory Data from 1990 to 1999. “ FCCC/SBI/2000/11. 92 p.

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