Influence of ionic surfactant contaminants on polystyrene-air bubble interactions for microplastics removal from wastewater

Microplastics are pervasive environmental pollutant, creating an urgent need for effective removal from aquatic systems. Froth flotation has recently gained attention as a promising, cost-effective, and environmentally friendly technique for microplastic (MP) removal. However, flotation performance depends on bubble-particle interactions, which can be profoundly altered by surfactants which are widespread in municipal and industrial wastewaters. Despite their constant presence, no systematic studies have examined how surfactant adsorption onto MPs and air bubbles affects these interactions. In this work, we assess how two ionic wastewater surfactants: anionic sodium dodecylbenzenesulfonate (SDBS) and cationic cetyltrimethylammonium bromide (CTAB) affect the surface characteristics of virgin and photo-aged polystyrene (PS) microplastics, and how they impact the efficacy of sodium oleate (NaOL) as a flotation collector. We demonstrate that MP aging and surfactant adsorption strongly change surface wettability and thereby bubble-particle attachment. Although NaOL effectively can restore the hydrophobicity of aged MPs in clean systems, its effectiveness declines markedly with increasing SDBS or CTAB concentration. These results reveal a complex interplay among MP surface properties, surfactant contamination, and collector performance, highlighting the need to consider the adverse impacts of wastewater surfactants when developing flotation-based MP removal strategies.