Complete enzymatic degradation and microbial upcycling of agricultural PBAT mulching films

Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) mulching films are increasingly used in agriculture as alternatives to conventional plastics, however their persistence in soils and slow environmental degradation still require effective depolymerization and upcycling strategies. Here, an integrated enzymatic–microbial cascade was developed for the degradation and valorization of commercial PBAT-based mulching films. Initial screening of benchmark and novel polyester hydrolases for degradation of virgin PBAT and poly(butylene terephthalate) (PBT), identified LCCICCG as the most effective catalyst, while PBAT depolymerization released product concentrations two orders of magnitude higher than PBT. Building on these results, LCCICCG was applied in a 2 L stirred-tank reactor for the breakdown of PBAT-based mulching film at 5% (w/w) polymer loading (100 g material), resulting in extensive degradation and release of approximately 75 g water-soluble monomers after 76 h. The hydrolysate contained adipic acid (AA: 13.1 g L⁻¹), 1,4-butanediol (BDO: 13.0 g L⁻¹) and terephthalic acid (TPA: 12.9 g L⁻¹). Downstream processing enabled recovery of 24 g TPA ('90% purity), while the remaining hydrolysate retained about 85% of aliphatic monomers that was directly utilized for microbial upcycling. Under nitrogen-limited conditions, Cupriavidus necator H16 predominantly assimilated AA and accumulated high-molecular-weight (7.5 ×105 g mol−1) polyhydroxyalkanoates (PHAs) at 86% of cell dry weight, corresponding to 0.24 gPHAs gAA−1. Importantly, BDO remained unconsumed, enabling its potential recovery as a co-product (0.21 gBDO gfilm−1 in hydrolysate). Overall, this work demonstrates coupling enzymatic depolymerization at high material loading with microbial bioconversion to transform PBAT agricultural waste into monomers and value-added biopolymers.