Composting-based degradation of poly (ethylene terephthalate) microplastics and its enhancement with exogenous PET hydrolase supplementation

Poly (ethylene terephthalate) (PET) constitutes an important composition of environmental microplastics (MPs). This study was to explore the degradation of PET MPs in high-temperature composting and also to make an attempt for an enhanced degradation by exogenous addition of thermophilic PET hydrolase. Herein, six 220 L composters were applied to perform the composting, with half designated enhanced group with PET hydrolase added. After 20 days, PET MPs exhibited a notable reduction (21.1%) in weight and the addition of PET hydrolase resulted in 32.8% reduction of PET MPs. This is also corroborated by the increase of terephthalic acid (one of PET degradation products) from 2.0μg/g sample in initial mixture to 3.7μg/g sample in composting group and 9.3μg/g sample in enhanced group. Besides, the particle size distribution of PET MPs shifted toward smaller sizes after composting, with the supplementation of PET hydrolase further accentuating this shift. After composting, the surface of PET MPs in both treatments exhibited conspicuous corrosion and oxidation. An analysis of publicly available compost metagenomes indicated the wide distribution of potential PET hydrolase and TPA 1,2-dioxygenase genes. These findings suggest that composting exhibited a noticeable performance in the degradation of PET MPs and enzyme-assisted composting enhanced the degradation, providing a new approach for addressing environmental microplastics pollution.