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Kvalitet af slagge fra forbrændingsanlæg Summary and ConclusionsThe Danish Environmental Protection Agency is aiming at maintaining the rate of recycling of bottom ash from municipal waste incineration plants at the same high level as previously. Intensification of the requirements for leaching tests means that the quality of bottom ash must be improved if it is to be used for construction work as category 1[2] or category 2 bottom ash. The aim of the present study was to identify the design and process parameters which may influence the quality of bottom ash from municipal waste incineration plants. The overall method for the study was as follows:
Twenty-three municipal waste incineration plants chose to participate in the study. The analyses of the bottom ashes collected showed that there is no obvious correlation between the concentration of salt and heavy metals in bottom ash and in the leachate. The majority of the samples of bottom ashes do not comply with the category 1 requirements on the content inbottom ashes. Thus, the concentration in the leachate will determine the classification of the bottom ashes. None of the municipal waste incineration plants can fulfil the category 2 requirements on leaching of salts. Almost all of the incineration plants are capable of fulfilling the temporary category 2 requirements on leaching of the salts. The majority of the samples of bottom ash do not comply with the category 2 requirements on leaching of chrome and copper. Therefore, it was decided to define the quality of the bottom ash as the concentration of chrome and copper in the leachate. In 2001, one of the participating incineration plants generated significantly better quality bottom ash than the other municipal waste incineration plants. The plant is Reno-Nord. The analyses of the bottom ashes from Reno-Nord complied with the category 2 requirements on chrome in the leachate and it complied with the category 3 requirements on copper in the leachate. Leaching of the remaining heavy metals from the bottom ash samples from Reno-Nord fulfilled all the category 2 requirements. Similarly, none of the bottom ash samples exceeded the category 3 requirements. On the basis of the design and process data collected from the municipal waste incineration plants, it has been possible to identify one design parameter which influences the quality of the bottom ash (leaching of chrome), and this is the presence of a rotary kiln. The data collected shows that leaching of chrome from bottom ash from incineration plants equipped with a rotary kiln is much lower than leaching from incineration plants with other types of kiln. Municipal waste incineration plants with rotary kilns in Denmark are only at Vestforbrænding (plant 1-4) and at Reno-Nord. Thus, the statistical data are rather limited. Kolding generates the best bottom ash in Denmark in relation to leaching of copper from the bottom ash. Unfortunately, several of the samples of bottom ash from Kolding exceed the category 3 requirements regarding leaching of other heavy metals (lead and chrome). Leaching of copper from the majority of the samples of bottom ash from Reno-Nord and Vestforbrænding are amongst the best 50 per cent of the bottom ashes. Therefore it is concluded that the rotary kiln has a positive influence on the leaching of copper from the bottom ashes as well. The result of the study cannot exclude the possibility that the temperature in the kiln may have an influence on the quality of the bottom ash. Unfortunately, it has not been possible to prove such a correlation with the data material collected. Fodnoter[2] According to the Danish Order on recycling of waste residues and soil for construction works, Order No. 655, 27th June 2000
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