Rapid and efficient biosorption of Pb(II) by microalgae cultivated in high nitrate medium

Heavy metal pollution, particularly lead (Pb(II)), poses a significant threat to ecosystems and human health, necessitating sustainable remediation strategies. Microalgae offer an eco-friendly solution due to their rapid biosorption kinetics and high biosorption capacity. Nitrate, as an essential element in microalgal cultivation, plays a critical role in microalgal growth, biochemical composition, and surface functional groups, all of which can impact Pb(II) biosorption. This study optimized green microalga Neochloris oleoabundans cultivation in nitrate-rich media (125-800 mg NaNO₃ L^-1) to enhance biomass production and Pb(II) removal. Cultures with 800 mg L^-1 NaNO₃ achieved the highest biosorption capacity (60 mg g^-1), 3.3 times greater than cultures with 125 mg L^-1 (18 mg g^-1) within 5 min. Biosorption increased with pH (2.0-6.0) due to functional group deprotonation. X-ray photoelectron spectroscopy revealed elevated protein (95 %) and carboxyl group (53 %) content in high-nitrate cultures, enhancing Pb(II) biosorption. Competitive tests showed Cu(II) had the highest inhibitory effect (72 % reduction). This feature, combined with the self-propagating nature of microalgae, offers a rapid, environmentally friendly, and potentially cost-effective solution to the heavy metal ion contamination in aquatic ecosystem.