well understood today and in most cases appropriate technologies exist already. These technologies include in principal thermal processes (vitrification, sintering) or chemical transformation methods for solidification/stabilization of fly ash and transformation to a material with reduced release of contaminants. The costs of these processes are similar in most industrialised counties, whereas the disposal fees will change from country to country. In general, all processes intended for quality improvement have carefully to be analysed whether they result in real ecological benefits, whether all potential impacts upon the environment are taken into consideration, and whether these benefits pay in view of effort and expenses.