5 years ago



38 3 Life cycle

38 3 Life cycle assessment of biofuels: methods and tools Inhabitant equivalents These data were largely obtained from the literature or previous projects funded by the various ministries. Due to the small number of sources – which meant little scope for subsequent improvements – only one validation round was carried out. For several parameters, particularly with regard to toxicity, data are missing completely. Furthermore, the reliability of available figures for inhabitant equivalents tends to be lower than those for life cycle specific data. Sensitivity analysis Three types of sensitivity analysis were carried out, which are described in further detail in Chapter 4.1.3: • Data uncertainty analysis: The uncertainties of the results of the individual life cycles were estimated from the mean as well as extreme values of the results of all the countries involved in the respective comparisons. The ratios minimum to mean and maximum to mean respectively were considered representative of the life cycles for the respective countries. • Different system boundaries: The influence of various credits and agricultural reference systems was investigated through their inclusion or exclusion in the calculations. • Different life cycle comparisons: A further type of sensitivity analysis consisted of the comparison of four biofuels (firewood, Miscanthus, willow and straw) with light oil as well as natural gas, showing the influence of the choice of comparison on the environmental performance of those biofuels. 3.4 Impact assessment 3.4.1 Selection of the impact assessment categories After the collection of data describing the energy systems, it can now be assessed to what extent the processes contribute to environmental problems. For this project, focus is set on the following impact categories (for detailed descriptions see Chapter 3.4.2): • Use of fossil fuels • Greenhouse effect • Acidification • Eutrophication • Summer smog • Ozone depletion by nitrous oxide • Human toxicity The following impact categories have partly been investigated to a certain extent: • Depletion of abiotic resources • Ecotoxicity • Persistent toxicity • Biodiversity and soil quality The following sections explain to what extent these four categories have been investigated, which methods were used and to what extent they have been included in the impact assessment. Depletion of abiotic resources Different methodologies exist for assessing the use of abiotic resources in LCA, but in this study, besides the use of the energy content of finite energy carriers, the only depletion of abiotic resources with special relevance for energy supply and agriculture might be the use of water in countries where it is limited. The reason for this is that experience from previous projects (Reinhardt et al. 1999) has shown that with regard to the biofuels investigated here no scarce resources are utilised to a significant extent. In this study, ground water consumption for irrigation is only included in the inventory in areas where water is depleted. Evaporation of water from plants, which could possibly lead to increased ground water consumption, was not considered. However for the countries concerned (Italy and Greece)

3.4 Impact assessment 39 energy crops are likely to be cultivated on non-irrigated marginal land, therefore for all countries, only the depletion of energy resources as explained in Chapter 3.4.2 is considered. Ecotoxicity and persistent toxicity Toxic substances emitted to the atmosphere, aquatic recipients or soil potentially contribute to ecotoxicity and/or human toxicity (Wenzel et al. 1997 and Hauschild and Wenzel 1998). The health of an ecosystem may be affected in different sectors: the air, the soil or in the aquatic environment, where the impact may be acute or chronic. The toxic properties of each individual substance depend on a large number of different factors concerning the substance itself, the quantity emitted and the circumstances under which it is emitted and converted in the environment. In contrast to the situation pertaining to many of the other impact categories, there are no common internationally accepted equivalence factors for toxic substances. However, there is general agreement that the developed methodology shall be based on an integrated quantification of the environmental fate and the inherent toxicity potential of the substance (Udo de Haes 1996). These criteria are fulfilled by the EDIP-method (Wenzel et al. 1997) and this method is advantageous because a large amount of effect factors were available and new factors could be calculated within the expertise in the project. Since the number of toxicity potentials is larger than the number of the rest of the environmental potentials there is a risk of focusing too much on toxicity compared to the other potentials. Thus it has been decided to aggregate the potentials into three impacts (human toxicity, persistent toxicity and ecotoxicity), representing different geographical scales and time horizons. Persistent toxicity is an aggregated parameter of ecotoxicity and human toxicity on a regional scale. It also represents the longterm effects. The toxicological impact of a substance is measured in relation to how many m 3 of the environmental medium (air, water or soil) will bring the emission to a level with no toxic effect. Generally the PNEC (predicted no effect concentration) value is used. For humans a similar value is used: HRC (human reference concentration) which is the highest concentration of the substance in the inhaled air expected to give no effect on humans on life-long inhalation under standard conditions. For the water and soil compartment, HRD (human reference dose) is used. This is based on no effect on humans on daily digestion. Ecotoxicity and persistent toxicity were calculated within this project but due to high uncertainty it was decided not to show the results in the graphs presented in Chapter 4. The reason for the uncertainty was mainly due to lack of information and the uncertainty inherent in the method. Biodiversity and soil quality The issues of biodiversity and soil quality are extremely difficult to assess quantitatively and so far no standardised methodology has been developed for LCA. There are many possible approaches to choose from and parameters to consider. Within this project, four of these have been investigated: • Ecosystem occupation as an indicator of loss of biodiversity • Ecosystem occupation as a measure for life support functions of the soil • Harmful rainfall as an indicator of erosion • Soil compaction Ecosystem occupation as an indicator of loss of biodiversity: only few quantitative methodological approaches for the assessment of biodiversity are available. They must still be validated and are often not practicable because of the data requirement. However, it is important to determine the impact on biodiversity in the overall evaluation of chains and crops for bioenergy, if one aims for sustainable agricultural and forest production. Therefore biodiversity has to be taken into account, even if it appears not to be quantifiable. Biodiversity, or biological diversity, according to UNEP (1998) means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. The methodology in this study is based on Lindeijer et al. (1998) and looks at the impact on the number of species in the area that is used for energy production (see Annex 7.5). Unfortunately, most data required were not available for many countries under concern. Therefore this parameter could not be assessed successfully.

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