Evaluation of the Efficiency of Biological Treatment in Activated Sludge from a WWTP at Laboratory Scale for the Elimination of Biomicroplastics and Related Products

Nowadays, bioplastics are increasingly being used as an alternative to single-use fossil-based plastics. However, a major challenge associated with bioplastics is the need for higher amounts of plastic additives to achieve material properties comparable to those of conventional plastics, which raises concerns regarding their potential ecological impact. In this study, we evaluated the capacity of mixed liquor sludge from a wastewater treatment plant (WWTP) to eliminate bioplastics and their associated plastic additives compared to fossil-based materials. To this end, we exposed three items under controlled laboratory conditions: pure polylactic acid (PLA) pellets, a PLA garbage bag and a conventional fossil-based polyethylene (PE) bag. The study of plastic degradation was carried out by pyrolysis coupled with gas chromatography high-resolution mass spectrometry (Pyr-GC-HRMS). The results show a higher degree of degradation of biobased bags (96.8 ± 4.0%) and PLA pellets (91.3 ± 9.0%), whereas fossil-based bags of PE exhibited negligible degradation (18.3 ± 25.8%). Furthermore, leaching compounds generated during the treatment process were monitored using a suspect screening strategy by means of liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). The main results showed that the concentration of several tentatively identified compounds increased after treatment because of the leaching process or because they were degradation products of other previously leached additives. The evaluation of the associated toxicity of these compounds using predicted no-effect concentrations (PNECs) disclosed that these compounds may pose a risk to organisms in receiving waters.