Aging microplastics in wastewater pipeline networks and treatment processes: Physicochemical characteristics and Cd adsorption

Despite a wealth of information on removal of the microplastics (MPs) in wastewater treatment plants (WWTPs), little attention has been paid to how wastewater treatment process affect the MP physicochemical and adsorption characteristics. In this study, changes in physicochemical property of three MPs, i.e. polyamide (PA), polyethylene (PE) and polystyrene (PS) through the wastewater pipeline, grit and biological aeration tanks were investigated. The results show that compared with virgin MPs, the treated MPs have higher specific surface area and O content, and lower C and H contents, and glass transition temperature, implying that the three treatments cause the chain scission and oxidation of the MPs. Cd adsorption capacities of the MPs are higher than the corresponding virgin MPs after sulfidation in the pipeline (SWPN) and biological treatment in aeration tank (BTAT). Pearson correlation analysis shows that the increase is mainly resulted from the enhancement of the O-containing groups on the MPs. However, Cd adsorption capacities of the MPs decrease after mechanical abrasion in grit tank (MAGT), corresponding to the decrease in carbonyl index. Two dimensional FTIR correlation spectroscopy demonstrates that the N\\H bond in the PA plays a more important role than C\\H bond in the adsorption of Cd, but only change of the C\\H bond is found in the PE and PS. The findings provide new insights into the effect of WWTPs on the MP aging and physicochemical characteristics. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the effects of wastewater treatment process on the physicochemical properties of three types of microplastics. The treated microplastics showed higher specific surface area and oxygen content, leading to increased Cd adsorption capacities in certain stages of the treatment process. Additionally, the study found that different treatments resulted in distinct changes in the microplastics' characteristics, providing new insights into microplastic aging in wastewater treatment plants.