Effect of Biofilm Formation on the Sedimentation Rate of Microplastics in Freshwater and Seawater

Microplastics (MPs) are plastic pieces smaller than 5 mm. They find their way into freshwater, sea, or wastewater treatment plants during their life cycle, and eventually, they have adverse impacts on ecosystems. Since they have a high surface area/volume ratio and are a good carbon source, they provide a suitable attachment surface for microorganisms. As a result, biofilm formation appears on the surface of microplastics. This formation increases the weight and volume of the microplastics. For this reason, their settling velocity in the water columns, and therefore their transport behaviour in the vertical direction in water bodies, changes. In this study, biofilm formation by Escherichia coli, Enterococcus faecalis, and Pseudomonas aeruginosa cultures on common MPs, polystyrene (PS), polypropylene (PP), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET), polyethylene (PE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and its effects on the settling velocity of the MPs in freshwater and seawater are investigated. The settling velocity measurements were carried out by using MATLAB Image Processing Algorithm. Thus far, this is the very first study measuring settling velocities of biologically weathered MPs using image processing algorithm. Initially buoyant MPs did not settle down after biofilm formation in