Assessing the Mass Concentration of Microplastics and Nanoplastics in Wastewater Treatment Plants by Pyrolysis Gas Chromatography-Mass Spectrometry

The level of microplastics (MPs) in wastewater treatment plants (WWTPs) has been well evaluated by the particle number, while the mass concentration of MPs and especially nanoplastics (NPs) remains unclear. In this study, pyrolysis gas chromatography-mass spectrometry was used to determine the mass concentrations of MPs and NPs with different size ranges (0.01-1, 1-50, and 50-1000 mu m) across the whole treatment schemes in two WWTPs. The mass concentrations of total MPs and NPs decreased from 26.23 and 11.28 mu g/L in the influent to 1.75 and 0.71 mu g/L in the effluent, with removal rates of 93.3 and 93.7% in plants A and B, respectively. The proportions of NPs (0.01-1 mu m) were 12.0-17.9 and 5.6-19.5% in plants A and B, respectively, and the removal efficiency of NPs was lower than that of MPs (> 1 mu m). Based on annual wastewater effluent discharge, it is estimated that about 0.321 and 0.052 tons of MPs and NPs were released into the river each year. Overall, this study investigated the mass concentration of MPs and NPs with a wide size range of 0.01-1000 mu m in wastewater, which provided valuable information regarding the pollution level and distribution characteristics of MPs, especially NPs, in WWTPs.

Automated summary

This study used pyrolysis gas chromatography-mass spectrometry to determine the mass concentrations of microplastics (MPs) and nanoplastics (NPs) in two wastewater treatment plants (WWTPs). The results showed that the mass concentrations of total MPs and NPs decreased during the treatment process, with NPs having a lower removal efficiency than MPs. It was estimated that approximately 0.321 and 0.052 tons of MPs and NPs were released into the river each year based on the annual wastewater effluent discharge. Overall, this study provided valuable information about the pollution level and distribution characteristics of MPs, especially NPs, in WWTPs.