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Impacts of Wastewater Treatment Processes on the Occurrence Characteristics and Morphologies of Microplastics
Summary
Wastewater treatment plants don't fully filter out microplastics before sending water back into rivers and lakes, tiny fragments (under half a millimeter), fibers, and certain plastic types like PVC and PS are especially likely to slip through. The good news: this study found that tweaking plant operations, like extending how long wastewater and sludge stay in treatment, and upgrading filtration equipment, could significantly cut microplastic pollution, which matters since these particles can end up in drinking water and food sources, potentially affecting long-term human exposure.
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, which were primarily governed by biological adsorption and advanced filtration units. MPs removal rates rose with increasing particle size, and MPs sized 0–0.5 mm were most likely to penetrate the treatment system. Fragmented and pellet MPs showed higher removal efficiencies than fibrous and film-shaped MPs. Polymers including PVC, PS, PTFE and PP, as well as dark-colored MPs, 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 enable targeted MPs control. This study provide a theoretical basis for mitigating MPs emissions from municipal WWTPs.