Normalmall

Measurements Show
Less Global Warming from Waste
Incineration
than Previously Believed
Lia Detterfelt, Renova AB
Lia Detterfelt, Renova AB
Box 156, SE-401 22 Göteborg
Phone +46 31 618772

Executive summary
Measurements of the content of fossil carbon in waste incinerated at the Renova
plant in Sweden. The measurements were done using 14C-analysis in six waste
samples taken out in a standardized manner and representing a large amount of
waste incinerated in about 6 months in 2008. The measurements indicate that the
contribution to the global warming from waste incineration in Sweden may be highly
overrated.

Introduction
Global warming is the most important environmental challenge of the world today.
Taxes and support systems have are used to help fulfill the targets of lowering fossil
CO2-emissions set by governments. These taxes highly affect the waste incineration
industry. There is also an on-going debate whether to consider waste incineration as
a green source of electricity and district heating, or not.
Waste consists both of biogenic carbon from e.g. paper, food and textiles as well as
fossil carbon from e.g. plastics. The carbon in waste is transformed into CO2 in the
incineration process and that originating from fossil carbon is contributing to the
global warming. A common way to describe the global warming from incineration is
by using emission factors. The emission factors for fossil CO2 from waste
incineration used when reporting the countries´ contribution to global warming vary
much between countries and are often based on general assumptions. For example,
the emission factors used when reporting within Europe may vary from 18-104 kg
CO2/GJ, depending on country and type of waste incinerated.
The emission factor used by Swedish authorities is 25kg CO2/GJ and is based on
assumptions of the presence of fossil carbon in various materials and the amount of
the specific material in the general waste mixture determined in so called pick-
analyses.
Renova study
To get a better knowledge of the contribution from waste incineration to the global
warming the waste management company Renova, situated in Göteborg on the West
Coast of Sweden, analyzed the fossil content in the incoming waste to the plant using
carbon-14-analysis.
Samples were taken from the waste bunker in a standardized manner to represent
the entire volume coming in to the plant during approximately one week’s time. The
method is described by Johansson et al. About 5 tonnes of waste was taken out of
the bunker and crushed. After crushing it was spread and divided in two parts, using
a wheel loader. One part was removed, the remaining part was spread and divided
again. The procedure was continued until only a small amount remained. About 40
kg of waste then taken out and sent to a chemical laboratory, which milled the
sample and analyzed it for e.g. chemical composition and heating value. A part of the
sample, now in the form of a powder, was sent for 14C-analysis.
Waste sampling was done at four different occasions in a time period of about six
months in 2008. At two of the occasions a double-sample was sent for 14C-analysis.
Fig. 1 Waste crushing and partitioning at one of the sampling dates at Renova, and the
resulting powder of the waste to be analyzed with 14C
The 14C analysis was done at the Lund University Radiocarbon Dating Laboratory
using Acceleration Mass Spectroscopy (AMS) on the gases formed during
combustion. The pretreatment of samples by dissolution in an inorganic acid which is
normally done before analyzing archeological samples, was excluded to avoid the
possibility of bringing carbonates into solution.
Since Swedish legislation differ in responsibilities between “hushållsavfall”
(≈Municipal Solid Waste, MSW) and “verksamhetsavfall” (≈Industrial Waste) the
amount of incoming waste of the two types was noted from the Renova registration
system of incoming waste trucks.
Results and conclusion

Content of fossil carbon out of total carbon in waste
at Renova incineration plant in 2008
fossil of total c
%
Approx. MSW content out of total waste (%-wt)
Fig. 2 Content of fossil carbon in waste at the Renova incineration plant in Göteborg, Sweden
in 2008.
During the incineration process almost all carbon in the waste is turned into CO2. The fossil part of the carbon in waste is therefore equal to the fossil part of CO2 of the total amount of CO2 in flue gas to the atmosphere. Since fossil CO2-emissions are often described in emission factors, this was also determined by using the analyzed heat values in the samples. Emission factors
Approx. part of industrial waste in waste (%-wt)
Fig. 3 Emission factors for various waste mixtures at the Renova plant in 2008. The emission
factor used by Swedish authorities is 25 kg/GJ.
The result implies that the effect on global warming from waste incineration may be highly overrated in Sweden and possibly also in other countries. The fossil carbon content in the six samples varied between 1-12% of the total carbon with a mean value of 7 %. The amount of fossil carbon increased with increasing amounts of industrial waste in the waste mixtures. The mean value corresponds to a fossil CO2 1 The remaining carbon content in fly ash is less than 3% and the amount of CO and other not completely oxidized C is less than 1%. The fossil part in ash and non-oxidized gaseous C is assumed to be equal to that in the waste. release of 6 kg/GJ (LHV, wet samples) which is significantly lower than that used by
Swedish authorities and the waste industry which is 25 kg/GJ. (Naturvårdsverket)
Assumptions on the atmospheric concentration
One factor that has been proven to be important when determining the fossil carbon
content in a sample is the atmospheric concentration of 14C used in the calculations.
Because of nuclear bomb testing, the concentration of 14C in the atmosphere
drastically increased in the 1960s and thereafter decline to a concentration of less
than 106% today.
In the Renova study the concentration of 14C in the atmosphere in the year the
analysis was performed, was used. This is the standard procedure when dating
archeological objects. However, it can be argued that a mean value of the
atmospheric content during a number of years when the plant or animal were still
alive to absorb carbon should be used. Concentrations between 105-113% have
been mentioned by laboratories and other studies. When assuming the highest of
these values the result is as follows:
Content of fossil carbon out of total carbon in waste
at Renova incineration plant in 2008
fossil of total c
Approx. MSW content out of total waste (%-wt)
Fig. 4 Content of fossil carbon out of the total carbon in waste at the Renova plant Göteborg,
Sweden. Calculated from the atmospheric concentration of 14C the year the analysis was
performed and as an assumed mean value of 113%
The graph shows that also when using a much higher assumed concentration of 14C
in the atmosphere (113% ) than in the Renova study, the fossil content in waste is
still much lower than previously thought.
How to use the results

2 The total emission factor from waste incineration should also include all greenhouse gases released to the atmosphere. The most important at the Renova plant is N2O (Miljörapport 2009). The contribution of N2O, when using the equivalence factor of 310, shows that the contribution is in the range of 1 mg/GJ, which means it is negligible. The results suggest that waste incineration should be considered to be a more
biogenic energy source than it is today and that the contribution to the global
warming may be much lower than earlier estimated.
However, the study only covers one plant in a limited range of time and from a limited
set of samples. The study may therefore be seen as a first attempt of measuring the
fossil release of CO2 into the atmosphere during waste incineration and for creating a
model for how to measure.
To get a better understanding, there is a need to perform a larger study with a deeper
discussion on for example sampling techniques in flue gas, what atmospheric
concentration is the appropriate to assume and so forth. A study like this was started
in September 2010 in Sweden.
References
Johansson, Ingvar et al, Karaktärisering av fasta inhomogena avfallsbränslen -
inverkan av metoder för provtagning och provberedning, Avfall Sverige Rapport
F2008:05, ISSN 1103-4092
Miljörapport 2008 för avfallskraftvärmeverket och sorteringsanläggningen, inklusive
återvinningscentralen vid Sävenäs, Renova 2009
Naturvårdsverket, Beräkna utsläpp av växthusgaser, www.naturvårdsverket.se

Appendix
Table 1. Description of samples and result of calculations in the Renova study
3 Crushed industrial waste sampled before delivery to waste bunker

Source: http://www.iswa.org/uploads/tx_iswaknowledgebase/Detterfelt.pdf