Valorization of Municipal Solid Waste Incinerator Bottom Ash by Microwave Irradiation and Alkali Activation

Municipal solid waste incinerator bottom ash (BA) is a waste that results from the incineration of municipal solid waste, for which valorization has proved to be challenging. In the current research, BA was subjected to a purification technique through microwave vitrification, in order to be used as a precursor for alkali activated materials. Prior to realising a microwave process, the ability of the material to absorb microwave energy was the principal aim. Thus, BA dielectric properties were measured, so that its behavior when subjected to microwave irradiation is unreaveled. Fundamental research on BA response to the microwave field succeeded the realization of microwave vitrification of BA, using a single-mode cavity. The designed process was assessed in terms of power input, treatment time, energy and vitrified BA (VBA) yield rate. Low energy consumption was achieved, although with a limited VBA yield. The observations from the dielectric properties measurements were underpinned with the experimental and simulation results performed for BA microwave vitrification process.

In order to establish a closed-loop process , VBA was valorized in porous glass-ceramics and porous inoganic polymers. The sustainability of the two proposed valorization routes for BA was evaluated based on a life-cycle impact study, which compared the porous glass-ceramics to the porous inorganic polymers. The results of this study showed increased impact of porous glass-ceramics arising from the high energy consumption of the microwave vitrification process and the firing processes their manufacture entails. The production of porous inorganic polymers appears to be a sustainable upgrade path for BA, while the high energy consumption associated with the microwave process should be thoroughly considered in case of a potential scale-up.