Study of the potential valorization of metal contaminated Salix via phytoextraction by combustion
Résumé
Phytoextraction is an emerging technology to remediate soils and sediments contaminated with trace elements. In the particular case of dredged sediment landfill sites contaminated with metals, phytoextraction may contribute to the management scheme of sediments and to the revaluation of certain land-disposed contaminated sediments. In this study, rapidly growing trees (willows) were cultivated in short rotation coppice (SRC) on a metal contaminated dredged sediment landfill site to produce biomass for heat and financial return. Three willow clones were planted on 4.5 hectares of this disposal site to assess phytoextraction efficiency and biomass production. Two combustion assays were performed in a biomass boiler of 30 KW, the first one with Salix Zn and Cd enriched wood harvested from the SRC and the second one with Salix wood bought at a wood producer (control). Combustibles, ashes and gases were analyzed to study trace element behaviour during the combustion process. For phytoextraction efficiency, best results are obtained when exportation of both stems and leaves are carried out. The most optimistic scenario led to a reduction of the total Cd content of the sediment from 3.16 to 2 mg kg -1 in 23 years. Due to boiling points, Cd and Zn were more found in fumes than in ashes. According to current regulation, Salix wood issued from phytoextraction should be used for non-domestic purpose, in industrial or collective boilers equipped with efficient filters.
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