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Quantification and Characterization of Microplastics in Seven Urban Wastewater Treatment Plants
Summary
Wastewater treatment plants are a key pathway through which microplastics enter rivers and coastal waters, and this six-month study across seven Spanish treatment plants found that conventional processes offer inconsistent and often inadequate protection. Microplastics were present in all samples, and in some cases effluent concentrations were nearly as high as influent concentrations — meaning the plants were adding little removal value for plastic particles. The dominance of synthetic fibers and the seasonal variation observed point to the need for better tertiary treatment steps to capture microplastics before discharge.
Microplastics (MPs) are routinely present throughout wastewater treatment plants (WWTPs) due to their widespread occurrence, while current treatment technologies achieve only partial removal. Therefore, WWTP effluents can still discharge a substantial fraction of MPs to receiving water bodies leading to environmental contamination. Most previous studies reported MP concentrations at specific time points, precluding a long-term monitoring and may result in over- or underestimation. The aim of this study is to examine the concentration, size, and polymer composition of MPs at inlet and outflow waters over a six-month period, from July to December, to assess the temporal variability of MPs across seven conventional urban WWTPs located in the Andalusia region, southern Spain. MPs were found in all sampling campaigns. In influent samples, concentrations were found to reach 6 – 78 MP/L, while the WWTP effluents contained a range of 12 – 65 MP/L. Fibers were the most abundant shape across all the WWTPs. The average size in the influent was 848 ± 1427 μm and effluent 918 ± 1221 μm. Polymers such as PA, PP, PVC and LDPE were the most abundant, reflecting the domestic origin of water samples.
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