Distribution of microplastics in rainfall and their control by a permeable pavement in low-impact development facility

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.

Removal and fate of microplastics in permeable pavements: An experimental layer-by-layer analysis

The increasing prevalence of microplastics (MP) in urban environments has raised concerns over their negative effects on ecosystems and human health. Stormwater runoff, and road dust and sediment, act as major vectors of these pollutants into natural water bodies. Sustainable urban drainage systems, such as permeable pavements, are considered as potential tools to retain particulate pollutants. This research evaluates at laboratory scale the efficiency of permeable interlocking concrete pavements (PICP) and porous concrete pavements (PCP) for controlling microplastics, including tire wear particles (TWP) which constitute a large fraction of microplastics in urban environments, simulating surface pollution accumulation and Mediterranean rainfall conditions. Microplastic levels in road dust and sediments and stormwater runoff inputs were 4762 ± 974 MP/kg (dry weight) and 23.90 ± 17.40 MP/L. In infiltrated effluents, microplastic levels ranged from 2.20 ± 0.61 to 5.17 ± 1.05 MP/L; while tire wear particle levels ranged between 0.28 ± 0.28 and 3.30 ± 0.89 TWP/L. Distribution of microplastics within the layers of PICP and PCP were also studied and quantified. Microplastics tend to accumulate on the pavements surface and in geotextile layers, allowing microplastic retention efficiencies from 89 % to 99.6 %. Small sized (< 0.1 mm) fragment shaped microplastics are the most common in effluent samples. The results indicate that permeable pavements are a powerful tool to capture microplastics and tire wear particles, especially by surface and geotextile layers. The study aims to shed light on the complex mobilisation mechanisms of microplastics, providing valuable insights for addressing the growing environmental concern of microplastic pollution in urban areas.