Efficient removal of microplastics through a combined treatment process: Pre-filtration and adsorption

Microplastics (MPs) pollution necessitates efficient removal technologies. This study developed a novel combined filtration-adsorption process using coal-based modified activated carbon (CMAC) synthesized from low-ash anthracite via carbonization, KOH activation, and chitosan dip-coating. Characterization revealed CMAC's positive surface charge under acidic conditions (pH < 7) enhances electrostatic adsorption of negatively charged MPs, while chitosan coating provides additional active sites. Orthogonal experiments identified bed loading as the most influential parameter, followed by flow velocity, initial concentration, and pH value. Under optimal conditions, the combined process achieved 95.48 % MP removal rate, surpassing pure filtration by 52.59 %. This improvement stems from dual mechanisms: (1) Filtration stage physically intercepts coarse MPs (>0.125 mm) via quartz sand's "pseudo-filter" structure; (2) Adsorption stage combines chemical interactions (electron donor-acceptor interactions, electrostatic forces) with physical adsorption (chitosan-mediated bridging). This synergistic approach effectively removes MPs of varying sizes and properties, demonstrating superior performance for practical wastewater treatment applications. The study provides a sustainable, scalable solution for MPs pollution control through waste-derived adsorbents and mechanistic insights for process optimization.