Occurrence and migration of microplastics and plasticizers in different wastewater and sludge treatment units in municipal wastewater treatment plant

Highlights

● Reduce the quantifying MPs time by using Nile red staining.

● The removal rate of MPs and PAEs in wastewater and sludge were investigated.

● MPs and PAEs were firstly analyzed during thermal hydrolysis treatment.

● The removal of PAEs from wastewater and sludge was mainly biodegradation.

Abstract

Microplastics (MPs) and plasticizers, such as phthalate esters (PAEs), were frequently detected in municipal wastewater treatment plants (MWTP). Previous research mainly studied the removal of MPs and PAEs in wastewater. However, the occurrence of MPs and PAEs in the sludge was generally ignored. To comprehensively investigate the occurrence and the migration behaviors of MPs and PAEs in MWTP, a series of representative parameters including the number, size, color, shape of MPs, and the concentrations of PAEs in wastewater and sludge were systematically investigated. In this study, the concentrations of MPs in the influent and effluent were 15.46±0.37 and 0.30±0.14 particles/L. The MP removal efficiency of 98.1% was achieved and about 73.8% of MPs were accumulated in the sludge in the MWTP. The numbers of MPs in the sludge before and after digestion were 4.40±0.14 and 0.31±0.01 particles/g (dry sludge), respectively. Fourier Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that the main types of MPs were polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS). Six PAEs, including phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DIBP), ortho dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), and bis(2-ethyl) hexyl phthalate (DEHP), were detected in the MWTP. The concentrations of total PAEs (ΣPAEs) in the influent and effluent were 76.66 and 6.28 µg/L, respectively. The concentrations of ΣPAEs in the sludge before and after digestion were 152.64 and 31.70 µg/g, respectively. In the process of thermal hydrolysis, the number and size of MPs decreased accompanied by the increase of the plasticizer concentration.

Graphical abstract

Keywords

Microplastics / Municipal wastewater treatment plant / Phthalate esters / Thermal hydrolysis

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Acknowledgements

This research was supported by the National Natural Science Foundation of China (Nos. 42177051 and 52170021).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-022-1577-9 and is accessible for authorized users.

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