How nutrients, pH and element concentration shape the biosorption of classical and emerging contaminants by living Gracilaria gracilis

Marine and freshwater ecosystems are not only exposed to metals but to increasing macronutrient enrichment, causing environmental and health consequences. Macroalgae can bind contaminants and use nutrients in their growth. The influence of nutrients in the biosorption of Rare Earth Elements (REEs) and Classical contaminants, in complex mixtures, has not been fully covered. Response Surface Methodology (RSM) with Box-Behnken Design was applied to study the influence of biosorbent mass, element concentration and nutrient concentration on the removal response. Batch sorption experiments were performed for 48 h at salinity (10) and pH (6 and 8). Living biomass exhibited high removal rates ('80%) for REEs, Hg, and Pb, while As and Cd showed less affinity. Biosorbent dosage showed to be an influential parameter, while nutrients were not significant. Quadratic models exhibited the best fit after 48 h of exposure for all elements, except Hg. Despite the negligible effect of nutrients, in different optimisation scenarios, it was possible to improve the removal response in their presence. To better understand the environmental impact of adding nutrients or the need for high doses of biosorbent, LCA methodology would give further insights into the cost and environmental impacts of a macroalgae cultivation step.