Due to the widespread use of plastic products and low biodegradability microplastics (MP) have become an ubiquitous environmental pollutant. These are small particles (1–1000 µm) formed from larger plastics through abrasion and degradation. Given their small size and density, MP particles are easily transported between different ecosystems. One of the major sources of MP are wastewater treatment plants (WWTPs), where the majority of MP is captured in activated sludge, while the remaining MP passes through treatment processes. Recently, advanced oxidation processes (AOPs) have emerged as promising methods for removing persistent pollutants, relying on the formation of reactive oxygen species to oxidize contaminants. The use of ozonation in wastewater treatment processes can contribute to the degradation of MP and the leaching of various substances, which reduce wastewater quality and simultaneously affect further treatment options for excess sludge (composting, biogas production).
In this master's thesis, we assessed the potential of wastewater ozonation for the leaching of organic substances from MP. For this purpose, we compared polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polypropylene (PP) MP (< 1 mm), as these are among the most commonly detected types of microplastic in wastewater and sludge samples. The experiments were conducted in a batch reactor, specifically a bubble column, with an initial MP concentration of 1 g∙ L−1. We varied the type of MP (PET, PP, PVC), the ozone dose (3,5–4,5 g∙h−1), and the ozonation time (1, 2, 3, 4, 5, 6 hours) while monitoring pH levels. The effectiveness of ozonation was determined by measuring total organic carbon (TOC) and chemical oxygen demand (COD). For the characterization of MP, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used. The results showed that MP degradation during ozonation increases, with PET reaching the highest TOC and COD values. FTIR analysis revealed a new absorption band (1713 cm−1), associated with the presence of carbonyl groups C=O on ozonated PP. On SEM images, we observed numerous particle agglomerates and newly formed microcracks on the surface of ozonated PET and PP, ranging in size from 5 m to 15 m.
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