In the sensitivity analysis of this work factors that are assumed to have a significant impact on the overall results are tested. In the life cycle inventory phase typical deviations of these factors were identified. The sensitivity analysis is conducted by calculating results with these identified minimum and maximum values and results are calculated for both options. The sensitivity analysis is conducted only for the substitution approach to ensure consistency as presented in chapter 4.1.7. The sensitivity analysis is conducted for the climate change im-pact category, except that the sensitivity analysis on wastewater effluent emissions of recy-cling processes is conducted for the freshwater eutrophication impact category. Factors are tested one by one without simultaneously testing their overlapping effects.
Figure 28 presents the results of the sensitivity analysis for the climate change impact cate-gory. In the figure is also a comparison on the contribution of different significant factors and EOL approach selection on the results of the net climate change impact of the studied product. Results presented in figure 28 are the total net impacts in which credits and impacts are summed. The reference result is the result calculated with substitution approach without any changes, which was presented first time on figure 23. Percentages shown in figure 28 represent difference to the reference result. In this figure blue color represents results of the sensitivity analysis, calculated with the substitution approach. Results calculated with other allocation methods are presented to illustrate what is the impact of EOL approach selection compared to deviation caused by the sensitivity analysis. Results calculated with allocation methods are presented with grey color to be distinguished from results calculated with the substitution approach. Grey color illustrates that as methodologies differentiate, the results
are not consistent between each other and cannot be directly compared correspondingly to other results presented.
Figure 28. Illustration of how different factors and EOL approach selection have effect on the overall net results calculated for the studied product. Results calculated with the substitution approach are presented with blue color. Results calculated with allocation methods are presented with grey color.
In general, from the results of this sensitivity analysis indicate that current system is rela-tively sensitive to changes in studied factors. This increases the importance of defining the EOL phase as accurately as possible. One reason for high deviation on the results of this sensitivity analysis is that the used reference net overall impact is rather low compared to impacts of single processes. As an example, it can be seen from earlier presented figure 23 that the impact of recycling processes is almost two times higher, than the overall net impact for the whole product, of which recycling credits are already reduced.
Figure 28 illustrates clearly that selection of EOL treatment option has a significant effect on the overall net results. Change from the reference case to a situation in which the product
195 % 199 %
is fully directed to the testliner production increases the overall impact by 244 %. Change is mainly related to a fact that the substitution of the kraftliner that is produced in Sweden gives significantly less credit to the studied system than substitution of the newsprint that is pro-duced in Germany. In addition to that processes are significantly different, also differences between background processes, as grid mix energy production, increase the difference of these credit processes. The incineration EOL treatment option increases the net impact by 144 % compared to the reference case. The difference is highly significant, even though difference between the reference result and the incineration option are not as huge as they are for the testliner option.
From the results can be concluded that by increasing amount of material directed to news-print manufacturing, it is possible to decrease the overall environmental impact of the studied product, when results are calculated with the substitution approach. Based on the results of the sensitivity analysis on EOL treatment options, it could be also presumed that recycling in newsprint manufacturing is more beneficial than directing material to the incineration or to the testliner production. However, from results of attributional LCA, we can only con-clude that the environmental impact calculated to the studied product is lower when the product is recycled in newsprint manufacturing, but attributional LCA does not provide in-formation does environmental impact in wider context decrease. If these EOL options should be more comprehensively compared to each other, a consequential LCA should be assessed instead of an attributional LCA.
Energy consumption and yield have also a significant, but not as high impact as EOL treat-ment option selection has. Energy intensive recycling process increases the overall impact up to 59 % and energy efficient recycling process can decrease the overall impact by 8 %.
Yield has slightly less impact on the overall results, up to 22 % increase or decrease.
Figure 28 also shows that variation caused by different variables in processes can have as significant impact as EOL approach selection.
Table 19 presents the sensitivity analysis on wastewater effluent emissions in recycling pro-cesses. This sensitivity analysis is conducted on the freshwater eutrophication impact cate-gory. It can be seen from the results that either high or low amount of wastewater effluents from recycling processes do not have a significant impact on the overall freshwater eutroph-ication results.
Table 19. The results of the sensitivity analysis on the freshwater eutrophication impact category.
Analysed factor Net impact Change in result
Reference result: Substitution approach 0,083 kg P eq. -
Wastewater effluent emissions in recycling process: Max 0,085 kg P eq. 3 % Wastewater effluent emissions in recycling process: Min 0,080 kg P eq. -3 %
From results can be concluded that EOL approach selection, EOL treatment option, energy efficiency of recycling process and yield of recycling process have a significant impact on results. This verifies the findings from literature review. However, based on literature review it was assumed that wastewater effluents from the recycling processes would have had a notable impact on the overall results, but in the sensitivity analysis it was found that effect is not significant. Effluents of recycling process did not have assumed effect, as primary production had significantly more contribution on category and effluents are only single source of eutrophicating emission from recycling processes.