Permeable pavement blocks as a sustainable solution for managing microplastic pollution in urban stormwater

Permeable pavement systems (PPS) designed to store stormwater and facilitate its drainage into pipeline networks also provide the added advantage of retaining particulate pollutants in the stormwater runoff. Among these pollutants, microplastics (MPs), are increasingly being detected in the atmosphere and can be deposited in the environment via rainfall. Consequently, mitigating the transport of airborne MPs through rainfall is crucial for preventing water and soil contamination, thereby reducing the potential risks to human health and ecosystems. To achieve effective pollution control, an experimental study was conducted to assess MPs removal efficiencies and permeability performance of various permeable pavement blocks. The pore structure, which is a critical factor influencing permeability, was analyzed using porosity measurements and X-ray computed tomography imaging. Additionally, computational fluid dynamics (CFD) simulations were utilized to investigate the MPs removal mechanisms within the PPS, modeling the flow of MPs through blocks with distinct pore structures and varying permeability levels. Notably, Block A, with the highest permeability (1.7 mm/s), achieved removal efficiencies exceeding 90 % for polyethylene (PE) and polyethylene terephthalate (PET). CFD analysis revealed that low-density PE particles were retained more effectively, while high-density PET particles displayed greater mobility through the pavement blocks. Furthermore, as rainfall intensity increased, the removal efficiencies of PE and PET gradually decreased. This study highlights the critical role of material design and CFD-optimised pore structures in enhancing the efficacy of permeable pavement systems for urban stormwater management. By elucidating the MPs removal mechanisms driven by distinct transport behaviors of PE and PET particles based on density differences, these systems offer a promising solution for mitigating urban stormwater contamination and advancing sustainable water resource management.