Circular Management of Lavandula stoechas L. Post-Phytoremediation of Contaminated Soils: From Essential Oil to Biochar for Supercapacitors

This study proposes a circular economy model to manage plant residues derived from the phytoremediation of soils contaminated with heavy metals (Pb, Zn and Tl) by means of Lavandula stoechas L. Under greenhouse conditions, its effectiveness for phytostabilization was confirmed, as it retains most of the metals in its roots (65%) with bioconcentration factors less than one, confirming the suitability of the species for phytostabilization. The research focuses on the transformation of this waste into high value-added resources for various industries. In pharmaceutical and cosmetic applications, as essential oil and hydrosol were obtained through distillation with a yield of more than 0.4%. These products, rich in therapeutic terpenoids, are safe for public health as they are free of metal contaminants. Or in the energy sector, since the post-distillation residual biomass, which contains the metals retained in its tissues, was processed by pyrolysis to obtain biochar. This material achieved an electrical conductivity of 35 S/cm, demonstrating great potential for fabricating supercapacitor electrodes. In conclusion, this work validates the transition from hazardous waste to valuable industrial by-products, laying the foundations for its future implementation on an industrial scale under environmental safety criteria.