Biodegradation and Carbon Resource Recovery of Poly(butylene adipate-co-terephthalate) (PBAT) by Mealworms: Removal Efficiency, Depolymerization Pattern, and Microplastic Residue

Poly(butylene adipate-co-terephthalate) (PBAT) waste biodegrades slowly under ambient conditions and typically ends up in incineration plants and landfills with great carbon emissions, and little is known about recovering carbon resources from PBAT waste in environmentally friendly ways. Here, we tested the biodegradation and resource recovery of PBAT using it as a supplementary feedstock for mealworms (Tenebrio molitor larvae). Over the 36-day test period, the PBAT removal was 49.2–54.9% depending on the ratio of PBAT in PBAT-containing feedstocks (100, 80, 60, 40, 20, and 10% PBAT). A low ratio of PBAT (10% PBAT content) in the PBAT–bran mixture feedstock was favorable for the growth and development of mealworms due to the highest final survival rate (96.3 ± 1.5%) and greatest larval weight growth (39.5 ± 1.5%). The biodegradation and depolymerization of PBAT were confirmed by chemical and thermal modifications as well as changes in molecular-weight distribution (MWD). Notably, the bran addition altered the depolymerization pattern of the ingested PBAT from broad depolymerization (a decrease in molecular weights) to limited-extent depolymerization (an increase in molecular weights) due to competitive digestion. Digestive biodegradation and removal resulted in a particle size reduction of the ingested PBAT material and generated residual PBAT particles within the range of microplastics (>9 μm). Based on the results, we provide a conceptual approach for management and resource recovery from PBAT waste via insect-mediated biodegradation.