Chapter 4: Biological Treatment of Solid Waste

CHAPTER 4

BIOLOGICAL TREATMENT OF SOLIDWASTE

2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Volume 5: WasteAuthors
Riitta Pipatti (Finland)
Joao Wagner Silva Alves (Brazil), Qingxian Gao (China), Carlos López Cabrera (Cuba), Katarina Mareckova(Slovakia), Hans Oonk (Netherlands), Elizabeth Scheehle (USA), Chhemendra Sharma (India), Alison Smith(UK), Per Svardal (Norway), and Masato Yamada (Japan)

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Chapter 4: Biological Treatment of Solid Waste

Contents
4Biological Treatment of Solid Waste
4.1

Methodological issues .................................................................................................................... 4.4

4.1.1

Choice of method ................................................................................................................... 4.5

4.1.2

Choice of activity data ............................................................................................................ 4.6

4.1.3

Choice of emission factors ...................................................................................................... 4.6

4.2

Completeness ................................................................................................................................. 4.7

4.3

Developing a consistent time series ................................................................................................ 4.7

4.4

Uncertainty assessment .................................................................................................................. 4.7

4.5

QA/QC .......................................................................................................................................... 4.7

4.6

Reporting and Documentation ........................................................................................................ 4.7

References .................................................................................................................................................... 4.8

Equations
Equation 4.1

CH4 emissions from biological treatment ......................................................................... 4.5

Equation 4.2

N2O emissions from biological treatment ........................................................................ 4.5

TablesTable 4.1

Default emission factors for CH4 and N2O emissions
from biological treatment of waste .................................................................................. 4.6

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4 BIOLOGICAL TREATMENT OF SOLID
WASTE
4.1

METHODOLOGICAL ISSUES

Composting and anaerobic digestion of organic waste, such as food waste, garden (yard) and park waste andsludge, is common both in developed and developing countries. Advantages of the biological treatment include:
reduced volume in the waste material, stabilisation of the waste, destruction of pathogens in the waste material,and production of biogas for energy use. The end products of the biological treatment can, depending on its
quality, be recycled as fertiliser and soil amendment, or be disposed in SWDS.
Anaerobic treatment is usually linked with methane (CH4) recovery and combustion for energy, and thus thegreenhouse gas emissions from the process should be reported in the Energy Sector. Anaerobic sludge treatment
at wastewater treatment facilities is addressed in Chapter 6, Wastewater Treatment and Discharge, and emissions
should be reported under the categories of Wastewater. However, when sludge from wastewater treatment istransferred to an anaerobic facility which is co-digesting sludge with solid municipal or other waste, any related
CH4 and nitrous oxide (N2O) emissions should be reported under this category, biological treatment of solidwaste. Where these gases are used for energy, then associated emissions should be reported in the Energy Sector.
Composting is an aerobic process and a large fraction of the degradable organic carbon (DOC) in the wastematerial is converted into carbon dioxide (CO2). CH4 is formed in anaerobic sections of the compost, but it isoxidised to a large extent in the aerobic sections of the compost. The estimated CH4 released into the atmosphereranges from less than 1 percent to a few per cent of the initial carbon content in the material (Beck-Friis, 2001;
Detzel et al., 2003; Arnold, 2005).
Composting can also produce emissions of N2O. The range of the estimated emissions varies from less than 0.5
percent to 5 percent of the initial nitrogen content of the material (Petersen et al., 1998; Hellebrand 1998;Vesterinen, 1996; Beck-Friis, 2001; Detzel et al., 2003). Poorly working composts are likely to produce moreboth of CH4 and N2O (e.g., Vesterinen, 1996).
Anaerobic digestion of organic waste expedites the natural decomposition of organic material without oxygenby maintaining the temperature, moisture content and pH close to their optimum values. Generated CH4 can beused to produce heat and/or electricity, wherefore reporting of emissions from the process is usually done in theEnergy Sector. The CO2 emissions are of biogenic origin, and should be reported only as an information item in
the Energy Sector. Emissions of CH4 from such facilities due to unintentional leakages during process
disturbances or other unexpected events will generally be between 0 and 10 percent of the amount of CH4generated. In the absence of further information, use 5 percent as a default value for the CH4 emissions. Where
technical standards for biogas plants ensure that unintentional CH4 emissions are flared, CH4 emissions are likely
to be close to zero. N2O emissions from the process are assumed to be negligible, however, the data on theseemissions are very scarce.
Mechanical-biological (MB) treatment of waste is becoming popular in Europe. In MB treatment, the wastematerial undergoes a series of mechanical and biological operations that aim to reduce the volume of the waste
as well as stabilise it to reduce emissions from final disposal. The operations vary by application. Typically, themechanical operations separate the waste material into fractions that will under go further treatment (composting,anaerobic digestion, combustion, recycling). These may include separation, shredding and crushing of thematerial. The biological operations include composting and anaerobic digestion. The composting can take placein heaps or in composting facilities with optimisation of the conditions of the process as well as filtering of theproduced gas. The possibilities to reduce the amount of organic material to be disposed at landfills are large, 40 60 percent (Kaartinen, 2004). Due to the reduced amount in material, organic content and biological activity, theMB-treated waste will produce up to 95 percent less CH4 than untreated waste when disposed in SWDS. The
practical reductions have been smaller and depend on the type and duration of MB treatments in question (seee.g., Binner, 2002). CH4 and N2O emissions during the different phases of the MB treatment depend on thespecific operations and the duration of the biological treatment.
Overall, biological treatment of waste affects the amount and composition of waste that will be deposited inSWDS. Waste stream analyses (see example in Box 2.1) are recommended methodologies for estimating theimpact of the biological treatment on emissions from SWDS.
The estimation of CH4 and N2O emissions from biological treatment of solid waste involves following steps:

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Chapter 4: Biological Treatment of Solid Waste

Step 1:

Collect data on the amount and type of solid waste which is treated biologically. Data on composting
and anaerobic treatment should be collected separately, where possible. Regional default data on
composting are provided in Table 2.1 in Chapter 2, and country-specific data for some countries canbe found in Annex 2A.1 of this Volume. Anaerobic digestion of solid waste can be assumed to be
zero where no data are available. The default data should be used only when country-specific data are
not available (see also Section 4.1.2).

Step 2:Estimate the CH4 and N2O emissions from biological treatment of solid waste using Equations 4.1
and 4.2. Use default or country-specific emission factors in accordance with the guidance as provided
in Sections 4.1.1, 4.1.2 and 4.1.3.

Step 3:

Subtract the amount of recovered gas from the amount of CH4 generated to estimate net annual CH4emissions, when CH4 emissions from anaerobic digestion are recovered.

Consistency between CH4 and N2O emissions from composting or anaerobic treatment of sludge and emissions
from treatment of sludge reported in the Wastewater Treatment and Discharge category should be checked. Also,
if emissions from anaerobic digestion are reported under Biological Treatment of Solid Waste, the inventory
compilers should check that these emissions are not also included under the Energy Sector.
Relevant information on activity data collection, choice of emission factor and method used in estimating theemissions should be documented following the guidance in Section 4.6.

4.1.1

Choice of method

The CH4 and N2O emissions of biological treatment can be estimated using the default method given inEquations 4.1 and 4.2 shown below:

EQUATION 4.1
CH4 EMISSIONS FROM BIOLOGICAL TREATMENT
CH 4 Emissions = ∑ (M i • EFi ) • 10 −3 − Ri

Where:
CH4 Emissions=

total CH4 emissions in inventory year, Gg CH4Mi=mass of organic waste treated by biological treatment type i, GgEF=emission factor for treatment i, g CH4/kg waste treatedi=composting or anaerobic digestionR=

total amount of CH4 recovered in inventory year, Gg CH4When CH4 emissions from anaerobic digestion are reported, the amount of recovered gas should be subtracted
from the amount CH4 generated. The recovered gas can be combusted in a flare or energy device. The amount ofCH4 which is recovered is expressed as R in Equation 4.1. If the recovered gas is used for energy, then also theresulting greenhouse gas emissions from the combustion of the gas should be reported under Energy Sector. Theemissions from combustion of the recovered gas are however not significant, as the CO2 emissions are ofbiogenic origin, and the CH4 and N2O emissions are very small so good practice in the Waste Sector does not
require their estimation. However, if it is wished to estimate such emissions, the emissions from flaring should
be reported under the Waste Sector. A discussion of emissions from flaring and more detailed information are
given in Volume 2, Energy, Chapter 4.2. Emissions from flaring are not treated at Tier 1.

EQUATION 4.2
N2O EMISSIONS FROM BIOLOGICAL TREATMENT
N 2 O Emissions = ∑ (M i • EFi ) • 10 −3i

2006 IPCC Guidelines for National Greenhouse Gas Inventories

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Where:N2O Emissions=

total N2O emissions in inventory year, Gg N2O

Mi=mass of organic waste treated by biological treatment type i, GgEF=emission factor for treatment i, g N2O/kg waste treatedi=

composting or anaerobic digestion

Three tiers for this category are summarised below.
Tier 1:

Tier 1 uses the IPCC default emission factors.

Tier 2:

Country-specific emission factors based on representative measurements are used for Tier 2.

Tier 3:Tier 3 methods would be based on facility or site-specific measurements (on-line or periodic).

4.1.2

Choice of activity data

Activity data on biological treatment can be based on national statistics. Data on biological treatment can becollected from municipal or regional authorities responsible for waste management, or from waste managementcompanies. Table 2.1 in Chapter 2, Waste Generation, Composition and Management Data, gives regional
default values on biological treatment. Country-specific default values for some countries can be found in Annex
2A.1 of this Volume. These data can be used as a starting point. It is good practice that countries use national,
annually or periodically collected data, where available.

4.1.3

Choice of emission factors

4.1.3.1

T IER 1The emissions from composting, and anaerobic digestion in biogas facilities, will depend on factors such as typeof waste composted, amount and type of supporting material (such as wood chips and peat) used, temperature,moisture content and aeration during the process.
Table 4.1 gives default factors for CH4 and N2O emissions from biological treatment for Tier 1 method.

TABLE 4.1
DEFAULT EMISSION FACTORS FOR CH4 AND N2O EMISSIONS FROM BIOLOGICAL TREATMENT OF WASTE
CH4 Emission Factors(g CH4/kg waste treated)

N2O Emission Factors(g N2O/kg waste treated)on adry weight
basis

on a
wet weight
basis

on a
dry weight
basis

on a
wet weightbasis

Composting10(0.08 - 20)

4(0.03 - 8)

0.6
(0.2 - 1.6)

0.24
(0.06 - 0.6)

Anaerobic
digestion atbiogas
facilities

2(0 - 20)0.8(0 - 8)

Assumednegligible

Assumednegligible

Type ofbiologicaltreatment

Remarks

Assumptions on the waste treated:
25-50% DOC in dry matter,
2% N in dry matter,moisture content 60%.
The emission factors for dry waste
are estimated from those for wet
waste assuming a moisture contentof 60% in wet waste.

Sources: Arnold, M.(2005) Personal communication; Beck-Friis (2002); Detzel et al. (2003); Petersen et al. 1998; Hellebrand 1998;
Hogg, D. (2002); Vesterinen (1996).
Note: Default emission factors for CH4 for anaerobic digestion already account for CH4 recovery.

Emission from MB treatment can be estimated using the default values in Table 4.1 for the biological treatment.
Emissions during mechanical operations can be assumed negligible.

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Chapter 4: Biological Treatment of Solid Waste

4.1.3.2

T IER 2 AND T IER 3

In Tier 2, the emissions factors should be based on representative measurements that cover relevant biologicaltreatment options applied in the country. In Tier 3, emission factors would be based on facility/site-specificmeasurements (on-line or periodic).

4.2

COMPLETENESS

Reporting on CH4 and N2O emissions from biological treatment, where present, will complement the reportingof emissions from SWDS and burning of waste and contribute to full coverage of all sources in the Waste Sector.
This will be particularly important in countries for which biological treatment is, or is becoming, significant.

4.3

DEVELOPING A CONSISTENT TIME SERIESAs the methodological guidance for estimating and reporting of emissions from biological treatment was notincluded in the previous IPCC Guidelines, it is recommended that the whole time series is estimated using thesame methodology. The activity data for earlier years may not be available in all countries. Also current data on
biological treatment may not be collected on an annual basis. The methods for obtaining missing data aredescribed in Volume 1, Chapter 5, Time Series Consistency.
The default emission factors are based on limited amount of studies. The data availability is expected to improvein coming years. It is good practice to use updated scientific information to improve emission factors when it
becomes available. Then, the estimates for the whole times series should be recalculated accordingly.

4.4

UNCERTAINTY ASSESSMENT

The uncertainty in activity data will depend on how the data are collected. The uncertainty estimates for waste
generation and the fraction of waste treated biologically can be estimated in the same manner as for MSW
disposed at SWDS (see Table 3.5). The uncertainties will depend on the quality of data collection in the country.
Uncertainties in the default emission factors can be estimated using the ranges given in Table 4.1. Uncertainties
in country-specific emission factors will depend on the sampling design and measurement techniques used todetermine the emission factors.

4.5

QA/QC

The requirements on QA/QC addressed in Section 3. 8 in Chapter 3, Solid Waste Disposal, are also applicable forbiological treatment of waste.

4.6

REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national greenhouse gas
inventory as outlined in Section 6.11 of Chapter 6, QA/QC and Verification, in Volume 1 of these Guidelines. Afew examples of specific documentation and reporting relevant to this category are outlined in the following
paragraphs.
•The sources of activity data should be described and referenced. The information on the collection
frequency and coverage (e.g., whether composting at households is included or not) should be given.

•Information on types of waste (e.g., food waste, garden and park waste) composted or treated anaerobicallyshould be provided, if available.

•Country-specific emission factors should be justified and referenced.

•In cases where reporting of biological treatment will be split under several sectors and/or categories, thereporting should be clarified under all relevant sectors/categories, to avoid double counting or omissions.

The worksheets developed for the estimation of the greenhouse gas emissions from biological treatment areincluded at the end of this Volume. These worksheets include information on activity data and emission factors
used to calculate the estimates.

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References
Arnold, M. (2005). Espoo: VTT Processes: Unpublished material from measurements from biowaste composts.
(Personal communication).
Beck-Friis, B.G. (2001). Emissions of ammonia, nitrous oxide and methane during composting of organic
household waste. Uppsala: Swedish University of Agricultural Sciences. 331 p. (Doctoral Thesis).
Binner, E. (2002). The impact of Mechanical-Biological Pretreatment on the Landfill Behaviour of Solid Wastes.
Workshop Biowaste. Brussels, 8-10.04.2002. 16 p.
Detzel, A., Vogt, R., Fehrenbach, H., Knappe, F. and Gromke, U. (2003). Anpassung der deutschen Methodik
zur rechnerischen Emissionsermittlung und internationale Richtlinien: Teilbericht Abfall/Abwasser.
IFEU Institut - Öko-Institut e.V. 77 p.
Hellebrand, H.J. (1998). ‘Emissions of nitrous oxide and other trace gases during composting of grass and greenwaste’, J. agric, Engng Res., 69:365-375.
Hogg, D., Favoino, E., Nielsen, N.,Thompson, J., Wood, K., Penschke, A., Economides, D. and Papageorgiou,S., (2002). Economic analysis of options for managing biodegradable municipal waste, Final Report tothe European Commission, Eunomia Research & Consulting, Bristol, UK.
Kaartinen, T. (2004). Sustainable disposal of residual fractions of MSW to future landfills. Espoo: TechnicalUniversity of Helsinki. (Master of Science Thesis). In Finnish.
Petersen, S.O., Lind, A.M. and sommer, S.G. (1998). ‘Nitrogen and organic matter losses during storage of cattle
and pig manure’, J. Agric. Sci., 130: 69-79.
Vesterinen, R. (1996): Impact of waste management alternatives on greenhouse gas emissions: Greenhouse gas
emissions from composting. Jyväskylä: VTT Energy. Research report ENE38/T0018/96. (In Finnish). 30p.

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