Quantification and Characterization of Microplastics in Seven Urban Wastewater Treatment Plants

Microplastics (MPs) are routinely detected throughout wastewater treatment plants (WWTPs), yet current treatment trains were not designed specifically to remove them. This study quantified and characterized visually identified MPs in influent and effluent waters from seven urban WWTPs in Andalusia (southern Spain) during a six-month monitoring period (July–December 2020). The targeted analytical size range was 45–5000 µm, and a subset of particles was further characterized by FTIR. MPs were detected in all sampling campaigns. Concentrations ranged from 6 to 78 items/L in influent and from 12 to 65 items/L in effluent. Fibers were the dominant morphology, and the 100–500 µm size class was the most represented fraction. Among the subset analyzed by FTIR, PA, PP, PVC and LDPE were the most frequent polymer assignments, with PA predominating in the fiber-rich fraction. However, because influent and effluent 24 h time-composite samples were not hydraulic retention time (HRT)-paired and FTIR interpretation was based on a selected subset of particles, the dataset is best interpreted as describing spatiotemporal variability during the study period rather than robust process-specific removal efficiency. Overall, the results support WWTPs as an ongoing pathway for MP release to receiving environments.