Comparative life cycle assessment of MSWI fly ash treatment and disposal

Municipal solid waste incineration (MSWI) fly ash constitutes a hazardous waste. The possibilities for managing this waste comprise disposal at underground deposits or at above-ground landfills after cement stabilisation, application of the FLUREC process, thermal treatment in a dedicated furnace or thermal co-treatment together with combustible hazardous waste. A comparative life cycle assessment (LCA) study was conducted in order to assess the environmental impact of these five MSWI fly ash disposal options with regard to two different time horizons (100years, indefinite). The uncertainties of the input parameters were propagated by Monte Carlo simulations (MCS). As could be shown by the discernibility analysis, the FLUREC process has the lowest impact in more than 90% of the MCS results. In case long-term emissions (beyond 100years) are neglected, the second lowest impact is caused by thermal co-treatment in more than 90% of the MCS results. Consideration of long-term emissions indicates the disposal at underground deposits as second best option. Furthermore, it is shown that stabilisation with cement has the second highest and thermal treatment in a dedicated furnace has the highest environmental impact, mostly due to high CO₂ emissions. Therefore these two treatment options should be avoided in the future. Besides the comparative evaluation of the different options, it could be shown that uncertainty analysis is useful to determine the relevance of long-term emissions for the ranking of different systems.