Impacts of Wastewater Treatment Processes on the Occurrence Characteristics of Microplastics—Taking Four Wastewater Treatment Plants in Northern Henan Province as Examples

Vollständiger Abstract

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As emerging persistent contaminants, microplastics (MPs) are ubiquitous in aquatic environments. Wastewater treatment plants (WWTPs) act as critical sinks and sources of MPs, and their MPs removal efficiency can strongly influence aquatic ecological safety. To investigate how different process configurations affect MPs occurrence and removal performance, four municipal WWTPs equipped with diverse biological and advanced treatment processes were sampled and analyzed. MPs were extracted via density flotation combined with H2O2 digestion, and their morphological and polymeric features were identified using stereomicroscopy and Fourier-transform infrared (FTIR) spectroscopy. The results revealed that MPs removal efficiencies differed significantly across treatment processes: WWTP4 exhibited the highest comprehensive removal efficiency of 63.89% in the operational situations, followed by WWTP1 of 56.25% and WWTP3 of 51.61%, while WWTP2 exhibited the weakest elimination capacity of 28.12%. It could also be concluded that the differences were primarily governed by biological adsorption and advanced filtration units. Meanwhile, Fragmented and pellet MPs showed higher removal efficiencies than fibrous and film-shaped MPs, while Polymers including PVC, PS, PTFE and PP were more resistant to removal. Longer hydraulic retention time (HRT) and a stable and sufficiently long sludge retention time (SRT) promoted the association of MPs with activated sludge, whereas excessive aeration induced MPs fragmentation and resuspension. Optimizing operational parameters and upgrading advanced filtration facilities could facilitate the regulation and management of MPs. This study provides a theoretical basis for mitigating MPs emissions from municipal WWTPs.