Large quantities of microplastics
are thought to be emitted to
freshwater environments via wastewater treatment plants (WWTPs). To
evaluate the occurrence of microplastics in Korean WWTPs, a nationwide
study was conducted for the first time in 50 representative WWTPs
with large treatment capacities. Grab sampling and laboratory filtration
were used for influents, whereas in situ filtration using a custom-made
sampling device was used for effluents. The filtrates were pretreated
using wet peroxidation and density separation prior to the identification
of microplastics with a dissection microscope and Fourier-transform
infrared spectroscopy. Pooled analyses of the microplastics revealed
that they were predominantly fragment-shaped, and thermoplastics and
synthetic fibers were the dominant microplastic materials in WWTPs.
The concentration ranged from 10 to 470 L–1 in influents
and 0.004 to 0.51 L–1 in effluents. The removal
efficiency of microplastics during wastewater treatment was calculated
to be 98.7–99.99% in 31 WWTPs. Additionally, WWTPs using advanced
phosphorus removal processes exhibited higher removal efficiency than
those not implementing such processes. Power-law distribution was
successful in describing microplastic particle sizes down to 100 μm,
although it was not applicable for smaller particles. This comprehensive
monitoring study provides information on the current level and characteristics
of microplastics in WWTPs in Korea.
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