Biosurfactant-mediated water depollution: efficiency assessment

Pollution of water bodies is a major environmental problem driven by industrialization and urban development. To protect human health and aquatic ecosystems, new water treatment techniques are needed since traditional methods often show limitations related to cost, scalability, or removal efficiency. Biosurfactants are non-toxic, bio-based molecules that can remove organic pollutants through micelles formation. Moreover, ionic forms can remove inorganic contaminants via complexation. This thesis investigated the potential of four anionic biosurfactants (G-C181, surfactin, RhaC10C10 and SL-C18:1) as water depolluting molecules. The approach was to induce a phase separation between a biosurfactant-rich phase, which entrapped or interacted with the pollutants, and an aqueous cleaner phase. Tested contaminants included four heavy metals (Pb²⁺, Ni²⁺, Cr³⁺, Cd²⁺), two organic dyes (methyl orange and rhodamine B), naphthalene, and PFOA (perfluorooctanoic acid). Removal efficiency and residual concentrations were assessed by using AAS, ICP, UV-Vis and NMR spectroscopy. The results demonstrated that most biosurfactants were able to remove each heavy metal individually. Phase separation was induced in the form of a flocculate, a precipitate or a metallogel by controlling parameters such as pollutant-to-biosurfactant molar ratio, pH or kinetics. Moreover, biosurfactants were tested for organic pollutant removal, often requiring calcium to induce aggregation. Among them, G-C18:1 ranked as the best depolluting molecule reaching efficiencies up to 99% for Cr3+, 65% for Ni2+ and 72-92% across all organic contaminants. In contrast, SL-C18:1 was the least effective biosurfactant. Whereas surfactin and RhaC10C10 displayed moderate efficiencies that varied depending on the type of pollutant remediated. Lastly, in multi-polluted systems (containing both one heavy metal and one organic pollutant), G-C18:1 emerged again as the most effective and versatile biosurfactant.