Sweco Environment was commissioned by the Swedish Environmental Protection Agency to do a screening study of metals and brominated and chlorinated dioxins and furans in ashes from incineration of waste and biofuels. The study has two primary objectives:
a. to assess whether the composition of incineration ashes can serve as indicator for the monitoring of the change of use of environmentally harmful substances in society.
b. to provide a basis for evaluation of risks in connection to the use of ashes Eleven metals (arsenic, cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, vanadium, and zinc) as well as chlorinated and brominated dioxins and furans were analysed in the ashes.
The study included 25 samples from the following matrices: · 8 samples of municipal solid waste incineration (MSWI) bottom ash
· 5 samples of MSWI fly ash
· 6 samples of biofuel incineration bottom ash
· 6 samples of biofuel incineration fly ash
Samples from biofuel incineration ashes included two samples of each fly and bottom ashes from plants that include recycled wood in their fuel mix.
Sampling was undertaken in accordance with a simplified method based on NT Envir 004. A minimum of three samples were collected over a period of one to two weeks.
Samples collected within this project were complemented with saved samples from a previous project on critical metals in waste incineration ashes (Johansson et al 2013). All sampling was undertaken by participating incineration plants.
Metal concentrations detected in this study were broadly similar to concentrations shown in previous studies (WSP 2012, Johansson et al 2013), though the variation was large (which is in agreement with results in other studies).
Metal concentrations in ashes from incineration of biofuels containing recycled wood are generally higher than in ashes from plants using pure biofuels. However, the mean mercury concentration is slightly higher in fly ash from incineration of pure biofuels.
Chlorinated dioxins and furans were detected in all samples. The total concentrations varied between 12.9 and 340,000 ng/kg dw corresponding to between 0.88 and 4,300 ng WHO-TEQ/kg dw (upper bound). Concentrations of chlorinated dioxins and furans were generally higher in fly ashes than in bottom ashes. Results are presented in Table A.
The results from analyses of municipal waste incineration ashes showed similar results as in the study performed in 2006 by Avfall Sverige (Avfall Sverige 2009). However, the analyses of biofuel ashes showed higher concentrations in this study than in previously reported studies (WSP 2012, Bjurström 2006).
There was no difference in the concentrations of dioxins and furans in the ashes from ecycled wood and pure biofuels.
Brominated dioxins and furans were detected in all samples. The total concentrations varied between 12 and 29,600 ng/kg dw. There are no toxic equivalency factors (TEFs) for brominated dioxins and furans. To calculate WHO-TEQ sums for the brominated species in the samples, the TEFs for the corresponding chlorinated species were used.
WHO-TEQ sums for the brominated species varied between 0.3 and 140 ng/kg dw (upper bound). Results are presented in Table B.
Table B. Results from analyses of brominated dioxins and furans in incineration ashes.
Results from the analyses of brominated dioxins and furans indicated similar levels in MSWI bottom ash as in a Taiwanese study (Wang et al 2010), however the distribution was larger in this study. Concentrations in MSWI fly ash was slightly higher in this study compared to the Taiwanese study. Similar to the Taiwanese study, results from this study indicated higher concentrations in MSWI bottom ash than in MSWI fly ash.
No previous studies of brominated dioxins and furans in biofuel ashes were found. The results from this study indicate lower concentrations in biofuel ashes than in MSWI ashes.
As opposed to MSWI ashes, concentrations are higher in fly ash from incineration of biofuels than in bottom ash. No effects could be seen from the use of recycled wood in the fuel mix in biofuel incineration plants on the concentrations of brominated dioxins and furans.
For the purpose of describing risks in connection with use of ashes, a simplified assessment has been made by comparing the concentrations in this study with concentrations deemed to be of negligible risk to human health and the environment (Swedish: mindre än ringa risk) for aggregates from recycled materials, as described in a guidance document from Swedish Environmental Protection Agency (Naturvårdsverket 2010). The comparison shows that these concentrations were exceeded in all samples.
This does not mean that the ashes are not suitable for use in aggregates, but that the use is subject to an individual assessment in each case.
Only total concentrations has been analysed within the scope of this study, and no speciated analyses were undertaken. Risks associated with unwanted compounds in the ashes are not only connected to the total concentrations in the ashes, but to a large extent also to the leachability of those compounds. In order to decide whether an ash is suitable for recycling for a certain purpose, additional characterisation is required.
Furthermore, the risk associated with potential exposure or contamination in relation to that specific usage should be highlighted.
Also, positive environmental effects from the use of ashes should be taken into account when evaluating the suitability of its use. Recycling of ashes as aggregate may substitute virgin materials, thereby saving natural resources.
Overall, the results obtained in this study, correlate well with results from previous studies. Brominated dioxins and furans, which are not as extensively studied previously, were detected in all samples in this study. The contribution to WHO-TEQ is small in most samples, compared to the contribution from chlorinated dioxins and furans. In MSWI bottom ash, the contribution to WHO-TEQ is larger from brominated than from chlorinated dioxins and furans. However, the sum of WHO-TEQ in MSWI bottom ash is low compared to the concentrations in fly ash.
In conclusion, the study showed that incinerator ashes are not suitable as indicator for the monitoring of the change of use of environmentally harmful substances in society.
Municipal and industrial wastes are often incinerated together and since municipal waste is imported for incineration in Sweden, the ashes will not reflect changes in consumption patterns in Sweden.
2015. , 101 p.