Geotechnical Performance and Microplastics Interception in PMACZ Permeable Barriers Under Groundwater Flow

Microplastic transport through subsurface porous media poses a growing risk to groundwater resources because most conventional barrier systems are not designed to limit long term particle migration under sustained hydraulic gradients. From a geotechnical perspective, microplastic mobility is strongly influenced by interactions between particles and granular barrier media, including pore structure, surface chemistry and packing characteristics. This study evaluates a polymer coated magnetic activated carbon zeolite (PMACZ) permeable reactive barrier for microplastic removal under controlled upward flow conditions. Two identical 3 ft acrylic columns were packed with PMACZ and silica sand, respectively, using nine saturated lifts to ensure uniform packing and minimize preferential flow. Fluorescent 15 µm polystyrene microplastics were injected at 100 mg L⁻¹, and columns were operated for 100 pore volumes (approximately 2400 h). Microplastic concentrations were monitored longitudinally and during a 90 min flow reversal, yielding 390 samples. Concentrations were quantified by UV–Vis spectrophotometry at 465 nm (R² = 0.9925) in triplicate. The sand column exhibited rapid breakthrough, with normalized concentrations (C/C₀) exceeding 0.9 within about 40 days. In contrast, the PMACZ column maintained C/C₀ below 0.1 for nearly 90 days and remained below 0.2 at 100 days. Longitudinal profiles demonstrated sustained, distance dependent attenuation across the PMACZ bed.