Numerical Study of Microplastic Dispersal in Simulated Coastal Waters Using CFD Approach

Abstract

Microplastics are accumulated in coastal regions due to human activity. Although limited data from beach surveys show an increase in microplastics in marine habitats, continuous monitoring is required on microplastics loading and distribution in the marine environment. In this study, CFD numerical simulations using VOF and Airy wave models coupled with DPM were carried out to investigate the effects of various variables on microplastics motion and distribution in a simulated coastal marine environment. PET, PU, and PP microplastic particles were released from the oceanside to investigate the effects of microplastic type, size, and shape with two different ocean–water flow velocities and temperature conditions. Particle position data from their tracking were used to determine the effect of each variable on the spatial distribution of particles. The quantitative analysis of vertical and horizontal distribution of microplastics particles revealed that, with low water velocity, most of the large denser spherical PET and PU microplastics would sink towards the bottom and settle at the ocean floor, while most of the small non-spherical particles would float near the surface and travel towards the shoreline. For lighter PP microplastics, larger spherical particles would float more readily than denser spherical ones. Large spherical and smaller non-spherical PP particles travel farthest reporting to the shoreline. Increasing the oceanwater velocity altered the distribution patterns in which lighter PP particles, almost independent of shape and size, travel swiftly to the shoreline together with smaller non-spherical denser microplastics. Lastly, the simulation results revealed that the oceanwater temperature did not play any significant role in the spatial distribution of microplastic particles.

A study on transboundary governance of marine plastic debris—the case of an adjacent waters between China and Taiwan

“…Over the past few decades, the global increase in the use of plastics and its high durability has resulted in the accumulation of large amounts of MPD in the marine environment (Fatahi et al, 2021). Microplastics are ubiquitous, and they have been found in the world's rivers, oceans and their adjacent waters, in coastal areas and offshore (Gewert et al, 2017).…”

“…Microplastics are ubiquitous, and they have been found in the world's rivers, oceans and their adjacent waters, in coastal areas and offshore (Gewert et al, 2017). In the sea surface of the coastal areas, the water column, and seabed plastics have been exposed to different environmental conditions, resulting in physical and chemical degradation to produce micro-plastics (Fatahi et al, 2021). The degradation of microplastics is mainly due to the oxidation of light through the ultraviolet radiation of the sun in the environment, such as on the surface of sea and on the beaches, and though the colonization of biofouling may promote the transport and deposition of small particles to the seabed (Andrady et al, 2015).…”

“…Therefore, when considering the outcome of microplastics, buoyancy is important as a major factor. Medium buoyancy particles are found on the ocean surface and in the upper part of the water column, while less buoyancy particles sink to the ocean oor over time, leading to ingestion of marine life and seabirds (Fatahi et al ., 2021).…”

“…Its distribution and motion are affected by its physical properties, such as shape, density, size, and buoyanc (Pita & Castilho, 2017), and ocean dynamics, such as the transport dynamics of waves, wind and tides and the sedimentation and growth of organisms on plastic debris, have an impact on benthic sediments (Zhang, 2017). Microplastic particles are exposed to different physical transport processes, including vertical mixing, surface drift, biofouling, and being carried ashore until they reach their nal destination (Fatahi et al, 2021). Moreover, entanglement and ingestion are the key issues associated with large plastic fragments.…”

“…As a result of human activities, microplastics are accumulated in coastal areas. Limited data from beach surveys show an increase in microplastics in marine habitats (Fatahi et al, 2021). Therefore, there is still a need for sustained attention to the loading and distribution of microplastics in the marine environment.…”