Occurrence, Characteristics and Removal Efficiencies of Microplastics in Urban Water Cycles : Normalized Protocol Proposal for Sampling and Analytical Procedures

This study supported the development of possible practical and normalized protocol for the representative assessment of the abundance and the typologies of microplastics in the urban water cycle. A prototype for automatic sampling of microplastics in water matrices was implemented and tested with long term campaigns. The proposed protocol was applied to three drinking water plants and two wastewater treatment plants. Specific roles of chemical and physical conventional processes for the microplastics (MPs) removals were investigated. The influent flows of wastewater treatment plants generally contained more than 200 particles per m3, mostly fibers and with a limited contribution of films and particle shaped MPs'. Instead, drinking water treatment plants influents are characterized by less than 15 MPs/m3. For both the cases, the initial concentrations greatly depend on influent fluctuations and different external environmental conditions. Along the conventional water lines a significative reduction in microplastics concentrations occurred, depending on the treatment units. Different roles and removal percentages of MPs were found in case of physical or chemical processes both in wastewater and in drinking water treatment plants. In the sludge flows, when fibers predominated in samples, larger microplastics (0.5-5 mm) and high frequencies of polyester were recorded, whereas in presence of other shapes, small-medium particles (0.02-0.5 mm) and more heterogeneous polymeric composition, with the prevalence of resins and polypropylene, were detected. Data on the occurrence of cellulose-based microfibers was also provided highlighting the importance of considering them as problem of environmental interest