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The first biogas plant was established in 1984 and at the present there are around 20 communal plants in Denmark, as well as 50 – 55 plants operating on farms. In 2002, 1.4 million tonnes of animal manure were treated, equivalent to approximately 4 percent of the total animal ma-nure, supplemented with around 200,000 tonnes organic waste from industry, wastewater treatment works and households (Biogas Branch Association 2003). The total energy production is shown in Table form in Appendix D.
Using slurry in biogas plants reduces the emission of both methane and nitrous oxide. No descriptions on how to include this reduction in the inventories are provided in the IPCC guidelines. Therefore, the Danish inventory uses data based on Danish studies (Sommer et al. 2001). It is expected that the CH4 emission from biogas treated slurry can be re-duced by 30 percent in relation to cattle slurry and 50 percent from pig slurry (Table 38).
In evaluation of the effect of biogas plants on the emission of green-house gases, the frequent addition of animal fat to increase productivity in the process should also be taken into account. Moreover, that biogas substitutes the burning of fossil fuels is not taken into account in the calculation. Under the assumption that the 1,703 TJ (Terra Joule = 1012 Joule) of energy produced at slurry-based biogas plants in 2002 substi-tuted natural gas, a reduction in CO2 emissions of 0.097 million tonnes results (1,703 TJ * 57,25 tonnes CO2 per TJ).
The reduction in the CH4 emission is based on the amount of organic matter VS(Volatile Solids). The amount of VS in treated slurry is calcu-lated as shown in Equation 5. It is assumed that slurry from cattle stems from dairy cattle and that slurry from pigs stems from slaughter pigs.
The Danish Energy Authority (Søren Tafdrup, pers. comm. 2003) esti-mates that cattle slurry represents 45 percent and that pig slurry repre-sents 55 percent of the total amount of biogas treated slurry.
Equation 7
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CH4 = ∗ ∗ −
7DEOH Contribution of straw burning to the CH4 emission, 1985 – 1989
1985 1986 1987 1988 1989
Straw burning, M tonnes straw 1.094 0.938 0.901 0.708 1.065 CH4-emission, 1,000 tons CH4 2.9 2.5 2.4 1.9 2.8
7DEOH Reduction of CH4 emission from treatment in a large communal biogas plant. Capacity:
550 m3 per day-1 (Source: Nielsen et al. 2002 based on Sommer et al. 2001) Reduction of methane Untreated Biogas
treatment
Reduction following biogas treatment
Reduction in emission (RN2O,potential)
tonne CH4 tonne CH4 tonne CH4 Pct Cattle slurry
Pig slurry
263.1 197.7
183.6 97.2
-79.5 -100.5
30 50
where CH4 reduction is the reduction in the amount of methane from live-stock type L, VS treated slurry is the amount of treated slurry, B0 is the maximum methane forming capacity, MCF is the methane conversion factor and RCH4-potential is the reduction potential – i.e. 30 percent for cat-tle slurry and 50 percent for pig slurry. Table 39 provides the back-ground data employed for the calculation of the methane reduction re-sulting from biogas production.
a after Poulsen et al. 2001
b after Henrik.B. Møller, DIAS (pers. comm. 2003), Husted 1994 and Massé et al. 2003
In 2002, the total effect of biogas plants was calculated at a reduction of 0.82 Gg CH4, which corresponds to 0.5 percent of the total CH4 emission from the agricultural sector. The extent of the reduction is expected to rise in coming years due to increased focus on biogas production as a potential approach in relation to reducing the greenhouse emission from agricultural activities.
The effect of the biogas treatment of slurry is subtracted from the emis-sion from dairy cows and slaughter pigs in the emisemis-sions inventory.
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IPCC guidelines recommend that national production Figures are used as far as possible. In earlier emissions inventories, emission factors were based on Danish standard values, but aligned with production condi-tions in 1995. This means that the same emission factor was used for all years and that this was calculated on the basis of feed intake and hous-ing type, correspondhous-ing to conditions in 1995. Recalculation of the CH4
emission is based on further development of the methodology previ-ously used. The recalculations now take into account that a change in feed intake and housing type distribution has taken place over the years, which is reflected as changes in emission factors.
In order to be able to compare the emission factors with the IPCC rec-ommended standard values, the Danish emission factors are calculated in Table 40 as the average methane emission per year for each livestock category. I.e. the calculated emission factor corresponds to the emission per livestock unit, which in turn corresponds with the number pro-vided in Statistics Denmark’s agricultural statistics.
7DEOHData used in the calculation of VS in biogas treated slurry and the reduction in the CH4 emission i 2002 2002 Amount of slurry used in
biogas production
Dry matter (Ts)a
VS of Tsb VS in treated slurry
Reduced CH4 emission as result of biogas treatment M tonne slurry pct pct 106 kg VS Gg CH4
Cattle slurry 0.63 10.3 80 15.69 0.25
Pig slurry 0.78 6.1 80 18.92 0.57
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7DEOH Comparison of IPCC standard values against the emission factors calculated in earlier emis-sions inventories and in the revised inventory
For dairy cows, the emission factor arrived at in the recalculation agrees more closely with the emission from other lands with comparable pro-duction conditions (USA and Holland). The emission factor for dairy cows is higher than the IPCC standard value due to Danish agricultural conditions with high lactating dairy cows and their associated higher feed consumption. Feed consumption for dairy cows, large breed, has increased from 5,700 FE in 1985 to 6,100 in 2002.
The emission factor calculated for other cattle types is somewhat lower than that stated in the IPCC guidelines. Among other things, this can be due to the relatively low number of sucklers, a large proportion of food intake taking place in the stable and the relatively high productivity le-vel in Danish agriculture.
In the recalculation of the CH4 emission for pigs, distinction is drawn between sows, weaners and slaughter pigs, as opposed to previously, where the emission associated with digestive processes did not distin-guish between the various sub-categories. The same value, as that rec-ommended by the IPCC is, therefore, used in the calculation – i.e. 1.5 kg CH4 per year per animal.
The emission factor for sheep and goats is almost twice as high com-pared with the IPCC standard values. This can be seen in the light of the inclusion of the emission from lambs and kids in the Danish values.
The emission factor calculated for horses is, similarly, higher than the values stated by the IPCC.
IPCC Earlier calculation Recalculation
Tier 1 Tier 2 Tier 2 Tier 2 kg CH4/animal/yr kg CH4/ animal/yr kg CH4/ animal/yr kg CH4/ animal/yr
1985 2002
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Dairy cattle 100.00 104.14 109.31 117.95 Other cattle 48.00 37.77 32.81 35.80 Sheep (incl. lambs) 8.00 8.00 17.17 17.17 Slaughter pigs + weaners 1.50 1.50 0.92 0.94
Horses 18.00 18.00 23.90 23.90
Goats (incl. kids) 5.00 Not calculated 13.15 13.15
Sows 1.50 1.50 2.40 2.53
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Dairy cattle 14.00 21.80 13.57 17.26
Other cattle 6.00 1.60 2.47 1.62
Slaughter pigs + weaners 3.00 2.10 1.65 2.35
Sows 3.00 6.00 4.00 5.05
Sheep (incl. lambs) 0.19 0.46 0.32 0.32
Horses 1.60 1.10 1.74 1.74
Hens + pullets 0.08 0.07 0.03 0.02
Broilers 0.08 0.02 0.01 0.01
Ducks, geese and tur-keys
0.08 0.06 0.02 0.03 Animals bred for skins Not calculated Not calculated 0.23 0.44
Goats (incl. kids) 0.12 Not calculated 0.26 0.26
The IPCC has not prepared guidelines for the methane emission associ-ated with animals bred for their skins. In consideration of that Denmark is the world’s largest producer of mink, it has been decided that the emission from this type of livestock should be included in the inven-tory. It is not expected that a significant methane emission stems here from digestive processes, so the emission stems exclusively from the handling of the manure for this category of livestock.