Microplastic (MP) pollution poses a significant environmental challenge, underscoring the need for improved water treatment methods. This study investigates the effectiveness of coagulation, flocculation, and sedimentation processes for removing microbeads, focusing on key factors that influence removal efficiency. Among the coagulants tested, polyaluminium chloride (PAC) demonstrated superior performance by enhancing the aggregation of microplastics with flocs. Optimal treatment conditions were determined to be 0.4 mmol/L PAC and 3 mg/L polyacrylamide (PAM) at pH 8 (before adding PAC), with rapid stirring at 240 rpm for 1 min, followed by slow stirring at 35 rpm for 13 min, and a sedimentation period of 25 min. Under these conditions, removal efficiencies exceeded 95 % for a range of microbeads (10-1000 μm: Polystyrene (PS), Polypropylene (PP), Polyvinyl chloride (PVC), Polyamide (PA), Polyethylene (PE), and Polyurethane (PU)) from natural water samples. Without PAM, PAC alone achieved a 97 % removal rate for PS microbeads. The addition of PAM maintained high removal efficiency, while aluminium sulphate and ferric chloride were less effective, with removal rates of 67 % and 48 % for PS microbeads, respectively. PAM enhanced MP removal across various coagulants and microbead types, with maximum efficiency observed at PAM concentrations of ≥3 mg/L. The treatment also demonstrated that organic matter in Regent's Park pond water could further improve MP removal. Size significantly impacts removal efficiency: larger microbeads (1 mm to >250 μm) were removed more effectively (95 %) compared to smaller ones (10 to <250 μm), which had a lower removal rate of 49 %. Denser microbeads like PVC (density 1.38 g/cm³) settled more efficiently than lighter microbeads such as PE (density 0.97 g/cm³). These findings suggest a need for advanced technologies to better remove lighter, smaller MPs from water.

With the widespread use of plastic products globally, the issue of microplastics as environmental pollutants has become increasingly severe. Due to their small size, large surface area, and hydrophobic properties, microplastics are capable of adsorbing various pollutants, particularly radionuclides, which, in turn, can impact the stability of ecosystems. This laboratory study investigates the adsorption capacity of microplastics (PVC) for radionuclides (Ra-226, Cs-137, and K-40) under controlled conditions, examining the effects of spatial distribution and particle size. The laboratory experiment results indicate that the adsorption of Ra-226 by microplastics was significantly higher in the bottom water compared to the surface layer, with concentrations of 13.29 mBq/kg on microplastics mixed with the bottom water and 1.65 mBq/kg in the surface layer. The concentration of Cs-137 on microplastics mixed with the bottom water was 6.99 mBq/kg, while on microplastics mixed with the surface water, the concentration was 1.31 mBq/kg. In contrast, the adsorption of K-40 was lower, with concentrations of 2.1 mBq/kg and 0.35 mBq/kg on microplastics mixed with the bottom and surface water, respectively. Furthermore, microplastics with smaller particle sizes exhibited stronger adsorption capacities. The adsorption concentrations of Ra-226 and Cs-137 by 50 µm microplastics were 13.29 mBq/kg and 6.99 mBq/kg, respectively, while the concentrations for 100 µm and 150 µm particles decreased to 3.14 mBq/kg and 1.39 mBq/kg, and 2.2 mBq/kg and 0.35 mBq/kg, respectively. These findings suggest that the adsorption capacity of microplastics is significantly influenced by particle size and sediment depth, highlighting the potential risk of exacerbating the spread of radioactive pollutants in marine ecosystems.