Evaluating the Dual Role of Municipal Wastewater Treatment Plants in the Removal Efficiency and Environmental Emission of Microplastics

This thesis investigates the occurrence, fate, and environmental implications of microplastics (MPs) in municipal wastewater treatment plants (WWTPs), highlighting their dual role as pollutants and vectors for hazardous contaminants. The research develops and applies a comprehensive analytical framework that integrates spectroscopic and chromatographic techniques—including Focal Plane Array Micro-Fourier Transform Infrared Spectroscopy (FPA micro-FTIR), Laser Direct Infrared Spectroscopy (LDIR), and Thermal Desorption Gas Chromatography-Mass Spectrometry (TD-GC/MS)—to characterize and quantify MPs across various WWTP stages. Sampling methods, combined with pre-treatment protocols such as Fenton oxidation and density separation, ensured the effective recovery and analysis of particles ranging from a few µm to several mm in size. Results indicate that while wastewater treatments, such as tertiary filtration and membrane bioreactors, achieve removal efficiencies of up to 99 %, significant quantities of MPs still persist in treated effluent and accumulate in sewage sludge. Notably, sludge dewatering processes were identified as a critical point of reintroduction into the wastewater treatment line. The study also reveals that plastic particles exhibit a pronounced capacity to adsorb and transport a variety of micropollutants, including metal(loid)s, synthetic musk fragrances, sunscreens, pharmaceuticals, organophosphate flame retardants, and pesticides. Different polymer types, such as polyethylene, polypropylene, and polystyrene, were evaluated for their pollutant retention capacities, with polystyrene demonstrating particularly high affinity. These findings underscore the environmental and human health risks associated with residual MPs in the discharged effluent and in the land application of sewage sludge, calling for improved removal technologies and more effective sludge management strategies. This thesis contributes valuable material for analysing MPs in WWTPs, offering data that enable comparisons across diverse territorial contexts. In addition, the study elucidates the interactions between plastic particles and organic and inorganic micropollutants, providing critical insights for the development of next-generation wastewater treatment processes and continuous monitoring strategies aimed at minimizing the ecological footprint of urban wastewater.