Formation of Nano- and Microplastics and Dissolved Chemicals During Photodegradation of Polyester Base Fabrics with Polyurethane Coating.

Polyurethane (PU) synthetic leathers possess an intricate plastic composition, including polyester (PET) base fabrics and upper PU resin, but the release of fragments from the complexes is unclear. Therefore, we investigated the photodegradation trends of PET base fabrics with PU coating (PET-U) as a representative of composite plastics. Attention was paid to the comparison of the photoaging process of PET-U with that of pure PET base fabric (PET-P). To reveal the potential for chain scission, physical and chemical changes (e.g., surface morphology, molecular weight, and crystallinity) of the two fabrics were explored. The generation of microplastic fibers (MPFs) and microplastic particles (MPPs) was distinguished. Compared with PET-P, PET-U showed a similar but delayed trend in various characteristics and debris release rate as the photoaging time prolonged. Even so, after 360 h of illumination, the generated number of MPs (including MPFs and MPPs) rose considerably to 9.32 × 107 MPs/g, and the amount of released nanoplastics (NPs) increased to 2.70 × 1011 NPs/g from PET-U. The suppression of MP formation from PET-U was potentially directed by the physical shielding of the upper PU layer and the dropped MPs, which resisted the photochemical radical effect. The components of dissolved organic matter derived from plastics (P-DOM) were separated by molecular weight using a size-exclusion chromatography-diode array detector-organic carbon detector/organic nitrogen detector (SEC-DAD-OCD/OND), and the results showed that a larger amount of carbon- and nitrogen-containing chemical substances were generated in PET-U, accompanied by more aromatic and fluorescent compounds. The results provided theoretical bases and insights for future research on the risks of plastic debris from PU synthetic leathers on aquatic organisms and indicated feasible directions for exploring combined pollution studies of plastics.

Elucidating the production and inhibition of melanoidins products on anaerobic digestion after thermal-alkaline pretreatment.

The refractory organics released from waste activated sludge (WAS) are unwanted produced in thermal-alkaline pretreatment, which are not well documented. In this study, we refer to them as melanoidins products (MPs) with characteristics of high molecular weight and inhibition to microbes. The results showed that these MPs from thermal-alkaline (80 °C and pH 10) pretreatment of WAS were identified with a broad molecular weight (>1000 Da). Dark-colored MPs were further verified from glucose and tryptophan as the model components, with values of UV280 and UV420 increasing. The produced MPs with a molecular weight of 1220, 6835, and even 21,200,000 Da were confirmed by SEC-HPLC. Unexpectedly, MPs were found to be electroactive with higher redox peak values than that of humic acids, which were almost not degraded by anaerobes as revealed by SEC-HPLC and 3D-EEM spectra. For the first time, the results demonstrated that MPs delayed volatile fatty acids production and reduced the methane yield (22-26% lower), which was likely attributed to the toxicity and/or electrons competition with anaerobes such as Methanosaeta. Thus, it is clear that MPs negatively impact anaerobic digestion after thermal-alkaline pretreatment, which shall be re-evaluated to minimize MPs when producing biochemicals from WAS.