Evaluating the potential of phytoextraction on waste-to-energy bottom ash-a review

Waste-to-energy produces district heating and electricity and generates bottom ash. This ash contains valuable chemically bound metals and current methods for extracting them face significant challenges, prompting the need for alternative methods such as phytoextraction. This review evaluates the potential of using phytoextraction on sorted and aged bottom ash to recover metals and enhance the usability of the MIBA residue in new applications. The focus is on the minor elements Cu, Zn, Pb, Ni and Co. A list of suitable terrestrial plants is suggested based on their ability to grow in the Nordic climate and the presence of the metals of interest. A further evaluation using qualitative multicriteria analysis (MCA) based on selected criteria, i.e. biomass, extraction capacity, metal diversity, perennial or annual growth, and accumulation above ground or in roots was performed. More than 100 different plants were reviewed for their suitability for MIBA phytoextraction, with 13 plants identified as the most promising. Among the selected plants, Sesbania drummondii scored the highest, followed by Salix alba and Salix viminalis. All these plants are perennial and can extract multiple metals; Salix exhibits lower to moderate extraction efficiency but compensates for this with high biomass and rapid growth compared to other plants with higher extraction capacity. In conclusion, the study shows the potential use of phytoextraction as a method to treat MIBA. However, further cultivation experiments are necessary to evaluate its efficiency. This review provides valuable information for designing such research.