5 years ago



156 7 Annex

156 7 Annex Eutrophication potential for wood is larger because of the higher NH3 emissions at combustion. Slurry from the biogas plant contains a bit more nitrogen in the mineral form, which increases the risk of NH3 emissions and NO3 - leaching and consequently causes a worse result for the biogas system. Summer smog (photochemical ozone creation potential POCP) – Switzerland POCP not only depends on hydrocarbons, included as NMVOC emissions, but also on methane. This is important for the biogas system in which no methane is emitted during slurry storage, resulting in a lower score than that of its reference system (see result table below). For the two other investigated biofuels systems, the differences of the NMVOC emissions explain the results. Impact category RME Diesel Wood Light oil Natural gas Summer smog g ethen eq./MJ Eutrophication g NO3 - eq. /MJ Ozone depletion by nitrous oxide in g N2O /MJ MJ refers to MJ of useful energy Ozone depletion by nitrous oxide – Switzerland Biogas Natural gas 0.11 0.12 0.02 0.01 0.02 0.05 0.1 4.1 7.6 0.2 0.1 0.1 0.5 0.1 0.437 0.020 0.001 0.001 0.001 0.003 0.001 For this impact category only the N2O emissions are included. RME has a considerably higher potential than its fossil alternative because of the possible denitrification of the fertiliser used (see result table above). Human toxicity – Switzerland The impact on human toxicity depends mainly on heavy metals, pesticides, NOx, SO2 and particles. Biogas has a higher score than CHP from natural gas because of higher SO2 emissions. In spite the fact that wood burning causes more particles, the toxicity potential for heating oil is higher due to more heavy metals emitted in different processes (see result diagram below). 40000 35000 30000 25000 20000 15000 10000 5000 0 Summary and conclusion Humantoxicity (m3/MJ useful energy) Processing & utilisation Agriculture/forestry part Fossil fuel life cycle Agricultural reference system RME Diesel Wood Heating oil Natural Gas Biogas Natural Gas In the result table below there is an overview of the advantages and disadvantages from the biofuels compared to their fossil counterparts. The scheme for determining and assessing the significance of the results for each impact category was published in Wolfensberger and Dinkel (1997).

7.1 Country specific life cycle comparisons 157 Impact category RME Wood vs. oil Wood vs. gas Biogas Use of fossil fuels Very favourable Very favourable Very favourable Very favourable Greenhouse effect Favourable Very favourable Very favourable Very favourable Acidification Unfavourable Comparable Unfavourable Unfavourable Eutrophication Favourable Unfavourable Unfavourable Comparable Human toxicity Comparable Favourable Very unfavourable Unfavourable Summer smog Comparable Favourable Unfavourable Favourable Regarding the major reasons of the authorities for promoting biofuels (saving of fossil fuels and reduction of global warming), all three investigated biofuels are highly recommendable. But one has to be aware of the fact that for biogas these advantages have to be partly paid with higher potentials in acidification and human toxicity. Moreover, the outcome for RME, which is more favourable as it was the case in previous studies (the results are unfavourable here only for acidification), partly depends on the procedure applied for taking into account the contribution of rape seed meal (this comment is valid first of all for eutrophication and the use of fossil fuels). Research is needed concerning the real relevance of these negative environmental aspects in the whole assessment. The results indicate that the probably best biofuel is wood compared to oil heating, because there only the impact potential eutrophication is unfavourable and the result does not depend on a methodological choice.

Bioenergy Update 10-02 - General*Bioenergy