High-efficiency enzymatic biodegradation of polypropylene-based melt-blown fabric debris

The coronavirus pandemic (COVID-19) has led to a dramatic increase in the usage and disposal of disposable masks worldwide, most of which are manufactured from melt-blown fabric composed of polypropylene (PP). Biodegradation of PP is considered to be extremely challenging because of its saturated chemical structure and high stability. In this study, we discovered that PP-based melt-blown fabric debris (MBFD; <i>M</i> _w, ∼157 kDa; crystallinity, 40-60%) and PP industrial particles (<i>M</i> _w, 100 kDa; crystallinity, 40-50%) can be degraded by the natural metabolizing enzyme glutathione <i>S</i>-transferase (GST) and digestive enzyme trypsin. The degradation efficiency of MBFD reached 86.7% (trypsin) and 99.2% (GST) with degradation rates of 1.57 and 3.98 g L^-1 h^-1, respectively, under physiological conditions at 1 atm. Chemical multi-fingerprinting analysis revealed that the mechanisms of MBFD degradation included oxidation and unreported nitridation pathways. Molecular dynamics simulations demonstrated the stability of the enzyme-PP complex system, primarily attributed to hydrophobic interactions. This enzymatic method was also successfully applied to degrade MBFD from disposable activated carbon masks, PP industrial particles, and polyethylene (PE) industrial particles. Finally, we demonstrated the potential of this enzymatic method in biodegradation of MBFD and PP industrial particles in real environmental wastewaters and human serum.