Detection and evaluation of microbeads and other microplastics in wastewater treatment plant samples

Microplastics (MPs) are ubiquitously spread in water environment and have raised global concerns due to their adverse effect to biological and ecological systems. Wastewater treatment plants have been reported to be an important route of releasing MPs into the environment. As a great source of MPs in number in wastewater, the characteristics of microbeads have hardly been studied. In this study, the variation of the characteristics of microbeads prior to and after incubating in wastewater samples has been identified. Reported digestion methods of acid, alkaline, enzymatic, and wet preoxidation digestion were subsequently applied to assess their efficacy for digesting microbeads from the wastewater, and enzymatic digestion has shown the optimal efficacy. Finally, enzymatic digestion was applied to evaluate microbeads and other MPs in real wastewater treatment plant samples. It is shown that the sequential treatment of fine screen, grit chamber, and improved sequencing batch reactor activated sludge processes were able to remove 72% pellets in number and 43% MPs in total, while a large portion was still remaining after the secondary treatment. This study set a base for understanding the characteristics and occurrence of MPs, especially microbeads in wastewater samples.