Comparing the efficiency of living and non-living macroalgae biomass in removing classical and emergent contaminants from complex multi-element mixtures

Although macroalgae are promising biosorbents for the removal of various contaminants, their effectiveness in complex mixtures requires comprehensive comparative evaluation under multi-contaminant conditions. The ability of living and non-living Ulva lactuca and Gracilaria gracilis to simultaneously uptake Rare Earth Elements (REEs) (Y, La, Nd, Eu, Gd, Dy) and classical contaminants (Hg, Cd, Pb, As) from equimolar mixtures was compared. Batch sorption experiments were conducted for 72 h under optimised conditions of salinity (10) and pH (7.8), in which 5 g of living biomass and an equivalent non-living biomass (0.60-0.85 g) were exposed to contaminated seawater (1 L) under constant stirring (800 rpm). The living biomass exhibited high removal rates (> 80%) for REEs, Hg, and Pb, while for As and Cd, lower removals were achieved. Non-living biomass showed significantly lower removal ability for REE (generally < 40%). These findings suggest a two-step approach, exploiting, first, non-living biomass to remove common contaminants and, after, living biomass for bioaccumulating REEs, which could later be recovered for reuse.