A relevant LCA methodology adapted to biomass-based products

Jul 2008

The Life Cycle Assessment (LCA) methodology is commonly employed to assess the performances of the different uses of biomass. The range of LCA results is however very wide and prevents from having reliable and accurate results for policymaking.
In order to better understand such discrepancies in results, this work reviews the LCA methodology and issues, and carries a sensitivity analysis on every LCA parameter, either assumption or data. Nonspecific methodological elements appear to be of major importance for LCA results: allocation rule influence is quantified to range from 48 to 82%, and system boundaries one from 0 to 93%. Input data play also an important role in results discrepancy, especially for GHG emissions. Local specificities can influence the final results by 53 to 118% and N2O uncertainties by 31 to 67%. This calls for agreements about LCA methodology depending on its application, limitations of geographical coverages and integration of the best scientific knowledge about N2O dynamics.
Finally the soil integration shortcoming is pointed out. Variations of soil carbon quantities due to land use changes can be very important and overwhelm GHG savings induced by biofuels use. This parameter is however lacking in LCA methodology applied to biomass-based products.
LCA methodology appears in this work as the major source of discrepancy in the assessments of biofuels environmental performances. Agreements have to be found about typical methodological issue such as allocation rule, whose influence on results can reach 80%, depending on LCA goal and application. In particular the proposal of the 23rd January 2008 for the European directive on the promotion of the use of energy on renewable sources pointed that allocation issues should be managed with the system expansion approach for ‘policy analysis purposes’ and with allocation based on energy content ‘for regulatory purposes’ (Commission of the European communities, 2008). Specific recommendations for application of LCA methodology to biomass-based products can however be made from this work in order to improve the reliability and accuracy of available results: limiting the geographical coverage to more homogeneous agricultural areas, and integrating the most WS 5: GHG emission reduction and energy production in agriculture, forestry, aquaculture and mariculture: potentials and impact 8th European IFSA Symposium, 6 - 10 July 2008, Clermont-Ferrand (France) 665 accurate data available on N2O fluxes. Indeed, according to this work, local specificity influence can go past 100% in specific cases and N2O uncertainties represent 30 to 70%. Finally new elements of the LCA methodology itself have to be developed. Soil integration is especially a key element to obtain a reliable assessment of land use and land use change.

By: A. Benoist, D. Dron, A. Zoughaib (ENSMP)

 
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