Occurrence and Seasonal Variation of Microplastics in the Effluent from Wastewater Treatment Plants in Qingdao, China

Wastewater treatment plants (WWTPs) are considered as one of the important sources of microplastics (MPs) in the marine environment. In this paper, the characteristics of MPs in the effluent discharged from five WWTPs in Qingdao, China, in winter and summer were analyzed. The results showed that only fibers and fragments were observed, with fibers as a dominant part. Rayon was the most domain polymer type, followed by Polyethylene terephthalate (PET) and chlorinated polyethylene (CPE). The average sizes of fiber MPs were 1010 ± 924 µm and 610 ± 691 µm in winter and summer, respectively. The contents of rayon were higher in summer than in winter. More small and transparent MPs were observed in summer. Rayon abundances ranged from 4.1 to 19.9 items/L and 33.3 to 116.7 items/L, with 12.3 ± 5.6 items/L and 67.6 ± 30.6 items/L as the average value in winter and in summer, respectively. The abundances of other polymer type MPs were 7.23~19.65 items/L with average value of 12.7 ± 4.7 items/L in winter and 12.0~20.0 items/L with 16.8 ± 4.7 items/L in summer. The daily emissions were estimated as 8.38 × 109~4.25 × 1010 items (9.2~27.8 kg) for rayon and 8.0 × 109~1.2 × 1010 items (7.6~5.3 kg) discharged for the other polymer type MPs from the five WWTPs. The results indicated that the seasonal variation of characteristics and emission of MPs in the effluent from WWTPs was mainly caused by increasing discharge of rayon, which may relate to people’s living habits and tourism activities.