Fate and removal rates of microplastics in multiple WWTP’s utilizing different Biological Active filters (BAF)

, Iordachescu Lucian, Papacharalampos Konstantinos, Denieul Marie-Pierre, Barritaud Lauriane, Baratto Gilles, Ingrand Valerie, Plessis Emmanuel, Vollertsen Jes.

In recent years, wastewater treatment plants have been in focus as potential sources of microplastic (MP) pollution in receiving waters. However, several studies show that WWTPs remove between 80-99 % of synthetic particles from the influent. Due to discrepancies between sampling methods, sample preparation and characterization of MP, comparison between MP studies on WWTP's is though challenging. In this study, the distribution of MP in four WWTPs, three discharging into the Mediterranean Sea, is investigated applying identical sampling strategies and analytical methods, allowing direct comparison of the obtained results. The key features of the four WWTPs are: WWTP1 - Downflow BAF (Media 1) WWTP2 - Upflow BAF (Media 2) WWTP3 - Upflow BAF (Media 3) WWTP4 - Activated sludge/clarifier Samples were taken in duplicates of the plant inlet, sludge, outlet and before the biofilters. Treated wastewater, was sampled by a filtration system where large amounts of water – typically some 1000 L – were filtered on 10 µm steel filters and the retentate then processed in the lab. Concentrated matrices, e.g. raw wastewater, were taken with an autosampler over 24 hours. The results represent samples collected during dry weather. Prior to analysis, the samples underwent extensive treatment. Subsequently, the concentrated samples were analyzed with a state-of-the-art FPA-µFTIR instrument in transmission mode, where MP's were quantified in terms of particle number and mass, polymer composition, size distribution in size range from 10 – 500 µm. This technology was combined with an automated analysis of the vast amounts of data that such analysis produces, removing much of the human bias otherwise occurring during data analysis. Particles of 500 – 5000 µm were quantified by ATR-FTIR. The investigated WWTP's showed overall MP removal rates of 91-99.93 %, while the removal rates of the biofilters varied between 29.69 and 68.5 %.

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