Environmental Systems Analysis for utilisation of bottom ash in ground constructions

Abstract: To decrease the disposal of waste and to save natural resources, several political initiatives have been initiated both in Sweden and at a European level. Therefore an urgent task is to find suitable utilisation areas for residuals, such as construction materials. For residual products to be an interesting alternative to conventional aggregates, such as sand, gravel or crushed rock, it is important that the material is environmentally acceptable. So far, environmental evaluations of residuals mainly have focused on measurements of total chemical content and leaching behaviour. The result has been that the positive effects, like for example less disposal of material and reduced extraction of natural aggregates, not have been considered in the evaluations. At the Royal Institute of Technology (KTH) in Stockholm, a method that uses a broader system perspective has been developed. The method is based on an Environmental Systems Analysis (ESA) approach and can act as a complement to the current leaching test. The method has been used for studying the difference in environmental impacts that can be expected if bottom ash from municipal solid waste incineration (MSWI) is used in road construction or is disposed of. This study contributes with an expanded set of scenarios for application of the MSWI bottom ash and with an improvement of data quality for disposal of material. The new application of MSWI bottom ash is its use as a drainage material in covering structures in a landfill. The thesis showed that leaching of metals, resource use and emissions to air were the environmental flows that were of most importance for assessing the environmental impact of the studied scenarios. The use of MSWI bottom ash in road construction was found to be the most environmentally preferable alternative, compared to utilisation of the MSWI bottom ash as drainage material in a landfill structure or disposal of the ash. None of the applications were free from negative environmental impact and different categories of impact were dominating in the different applications. However, these results are strongly dependent on the chosen system boundaries. The results are sensitive to changes in parameters such as transport distance and the conditions affecting leaching, for example the amount of precipitation. Besides these results, new life cycle data for disposal of material is presented in the study. Previous data for the environmental impact from disposal of material were old and lacked important information, such as the environmental impact related to covering structure in the landfill. The ESA approach allowed both resource use and emissions to be considered and can therefore be seen as valuable complement to other studies that use a narrower system perspective. The results can be used to improve information for decision support concerning waste management.