Modifications of ultraviolet irradiation and chlorination on microplastics: Effect of sterilization pattern

Chlorination and ultraviolet disinfection in drinking water treatment plants (DWTPs) may be highly destructive for microplastics (MPs). Investigating the effect of sterilization patterns on MPs behavior modifications can provide useful information to evaluate their potential risk to drinking water safety. In this study, aged polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS) and polyvinyl chloride (PVC) were applied, and five well-designed sterilization patterns with low and high doses disinfection were performed. Especially, a combining sterilization pattern including ultraviolet disinfection, low-dose chlorination and high-dose chlorination was designed to simulate the actual disinfection processes in environmental engineering systems. Different sterilization patterns contributed various chlorinated and oxidized modifications on the MPs surface, resulting in distinct effects on their sinking and adsorption performance. After combining sterilization (180 mJ cm^-2 UV-C irradiation +9675 mg min L^-1 chlorination), the adsorption capacities of ciprofloxacin by PET and PVC were slightly improved, and the one by PS was inhibited. Yet, PET, PVC and PS tend to sink (>95%) after this combining sterilization, implying that these MPs would be retained in DWTPs or water supply pipes. For PE, even though it maintained floating on water, its adsorption of ciprofloxacin was inhibited by combining sterilization (K_f reduced from 0.142 L g^-1 to 0.069 L g^-1). In general, multiple sterilization patterns can enhance the sinking and inhibit the adsorption performance of MPs, reducing their potential to become vectors of organic contaminants and risk to drinking water users.