Degradation of nano-sized polystyrene plastics by ozonation or chlorination in drinking water disinfection processes

The presence of nanoplastics in drinking water inducing inevitable exposure to human beings has aroused considerable attention. It is worth evaluating the degradation and even mineralization of nanoplastics in drinking water treatment plants designed for guaranteeing drinking water safety. Herein we mainly focus on the decomposition of nano-sized polystyrene plastics by two commonly used disinfection techniques, namely ozonation and chlorination. At recommended dosage for disinfection, ozonation achieves 99.9% molecular weight (MW) degradation and 42.7% mineralization of nano-sized polystyrene plastics in 240 min, while chlorination only attains 7.1% MW degradation and 4.3% mineralization. The overwhelming MW degradation is concentrated in first 30 min with 96.3% for ozonation and 4.2% for chlorination. With the proceeding of ozonation, the surface of nano-sized polystyrene plastics becomes rough and the particle size is decreased, during which the introduction of oxygen-containing groups on the surface of nano-sized polystyrene plastics increases the hydrophilicity of plastics, thus contributing to the further oxidative degradation to produce formic acid, phenol, acetophenone, hydroquinone and other products. However chlorination cannot roughen the surface of nano-sized polystyrene plastics, and only destroys a small amount of C-C bonds in main chain to form shorter chains polymers. This finding shows ozonation other than chlorination is available and effective for degradation of nano-sized polystyrene plastics, indicating that ozonation could be employed as a potential technique to tackle nanoplastics pollution in drinking water treatment plants.