Superior microplastic removal and gravity-driven membrane filtration optimization: The role of octadecyl-quaternium hybrid coagulant and molecular dynamics insights

Microplastics (MPs) contamination in surface water poses significant environmental and health threats, particularly in rural areas without centralized water treatment systems. Although pre-coagulated gravity-driven membrane (GDM) is a promising decentralized drinking water treatment technology, the impact of MPs on its performance has not been clearly understood yet. In this study, octadecyl-quaternium hybrid coagulant (OQHC) is proposed as an innovative solution for the efficient removal of MPs. Specifically, the effectiveness and mechanisms of OQHC in removing MPs are investigated, and the performance of a GDM pre-coagulated with OQHC is comprehensively evaluated. The findings reveal that OQHC achieves a superior MPs removal efficiency of 93.45% in surface water, outperforming conventional coagulants such as PACl and AlCl3. 3 . Molecular dynamics simulations suggest that OQHC primarily removes MPs through hydrophobic interactions facilitated by its long octadecyl carbon (C18) 18 ) chains, with humic acid (HA) enhancing the electrostatic interactions. Furthermore, the stability and permeability of GDM filtration pre-coagulated with OQHC are influenced by the cake layer's zeta potential in the initial stage (0-90 h) and porosity in the late stage (90-120 h). Moreover, the presence of MPs increases the quantity of particles smaller than 6 mu m, resulting in lower porosity of the cake layer and steeper flux decline rates during prolonged filtration. Overall, this study establishes OQHC pre-coagulated GDM filtration as a promising approach for addressing MPs contamination in surface water, offering an efficient solution for ensuring safe drinking water in rural areas.