Limitations and quality upgrading techniques for utilization of MSW incineration bottom ash in engineering applications – A review

Municipal solid waste (MSW) is being considered as a renewable resource for producing energy in Waste-to-Energy (WtE) incineration plants. However, a considerable amount of MSW incineration bottom ash (MSWIBA) is generated in the process of MSW incineration (MSWI). Disposal of MSWIBA in landfills poses a threat to the environment due to leaching of pollutants (e.g. heavy metals and soluble salts). Over the last decade, with increasing awareness of sustainable development, many researchers carried out studies on pre-treatment techniques to upgrade the quality of MSWIBA as construction materials. Moreover, its utilization as an alternative recycled construction resource to replace natural materials has been promoted, but various limitations for its engineering applications still exist due to the potential environmental risks as well as its relatively inferior properties compared to natural aggregates (e.g. high porosity and alkali-silica reaction). This paper presents an overview of the environmental and engineering issues facing the utilization of MSWIBA to replace natural aggregates in different applications, as well as the current pre-treatment techniques for upgrading the quality of MSWIBA. In the literature, most of the past research studies focused on the leaching of pollutants from MSWIBA. However, techniques for improving the properties of MSWIBA as aggregates for engineering applications have been relatively less studied. Moreover, the pre-treatment methods had been reported in individual case studies, but there was no comprehensive review for large-scale operation. To provide scientific and technical ways for utilization of MSWIBA, it is suggested to develop integrated pre-treatment processes of MSWIBA combining with two or more techniques in association with each targeted application, which not only reduces the environmental risk of MSWIBA, but also improves its engineering properties in applications.