Biotransformation of microplastics from three-layer face masks by nitrifying-denitrifying consortia

COVID-19 increased microplastics (MP) contamination due to the extensive use of single-use personal protective equipment, particularly three-layer face masks. MP from face masks enter wastewater treatment plants (WWTPs), which were not designed to remove them. We utilized nitrifying-denitrifying microbial consortia and synthetic urban wastewater to evaluate the biotransformation of MP from each layer of three-layer face masks made of polypropylene (PP). The biotransformation carried out by the nitrifying-denitrifying consortia altered the surface of the outer, middle, and inner layers, as a consequence of the chemical modification of the PP-MP structure. Abiotic controls did not show changes on the physicochemical and thermal properties of PP-MP. Biotic tests showed increments in both the carbonyl and hydroxyl indices of the three layers in 42 days. The outer layer showed the greatest degree of biotransformation, which was consistent with morphological changes detected by scanning electron microscopy and in physicochemical properties such as crystallinity, evaporation, and fusion temperature. The nitrifying-denitrifying consortia, which removed 99 % of the total nitrogen from the synthetic urban wastewater, had several genera with proven capacity to biotransform MP such as Cephaloticoccus and Pseudomonas.