The use of rare earth elements is a growing trend in diverse industrial activities, leading to the need for eco-friendly approaches to their efficient recovery and reuse. The aim of this work is the development of an environmentally friendly and competitive technology for the recovery of those elements from wastewater. Kinetic and equilibria batch assays were performed with zeolite, with and without bacterial biofilm, to entrap rare earth ions from aqueous solution. Continuous assays were also performed in column setups. Over 90% removal of lanthanum and cerium was achieved using zeolite as sorbent, with and without biofilm, decreasing to 70% and 80%, respectively, when suspended Bacillus cereus was used. Desorption from the zeolite reached over 60%, regardless of the tested conditions. When in continuous flow in columns, the removal yield was similar for all of the rare earth elements tested. Lanthanum and cerium were the elements most easily removed by all tested sorbents when tested in single- or multi-solute solutions, in batch and column assays. Rare earth removal from wastewater in open setups is possible, as well as their recovery by desorption processes, allowing a continuous mode of operation.

Two fungi (Alternaria sp. and Penicillium sp.) and one gram-positive bacterium (Streptococcus equisimilis) were used to remove Ni and Cd from aqueous solutions in the presence of diethylketone. Individual toxicity assays were performed at an initial stage to evaluate the xenobiotic impact of the initial concentration of those metals on the growth of the microorganisms and allowed to infer that the growth of S. equisimilis is negatively affected by both metals, whereas the growth of both fungi is positively stimulated by the presence of Ni and inhibited by Cd (>40 mg/L). Within the group of microorganisms tested, S. equisimilis presented higher removal efficiency (%) and uptake. In a second stage, biosorption assays were performed using aqueous solutions containing Ni, Cd and diethylketone (mixed solutions) and aimed to infer about the overall effect of the initial metal concentrations on the growth and on the sorption capacity of the microorganisms, as well as to evaluate the interaction between the sorbent matrices. It was demonstrated that despite the mixed solution exert a negative effect on the removal process and on the growth of the three microbial cultures, the system is able to decontaminate aqueous solutions with high concentrations of Ni, Cd and diethylketone.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by gs3:European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. Filomena Costa thanks FCT for a PhD Grant (SFRH/BD/77666/2011)