Efficient Bioprocess for Mixed PET Waste Depolymerization Using Crude Cutinase

In recent years, several plastic-degrading enzymes with efficient depolymerization abilities for PET have been reported. Here, we report a bioprocess for mixed PET waste depolymerization using crude extracellularly expressed enzymes in E. coli. The enzymes, namely FastPETase, LCC, and LCC^ICCG, were screened to depolymerize amorphous PET powder and films of different sizes and crystallinity. FastPETase, LCC, and LCC^ICCG achieved approximately 25, 34, and 70% depolymerization, respectively, when applied to 13 g L^-1 of PET film, powder, or mixed waste in optimized enzyme conditions without any pH control. The yield of terephthalic acid in the hydrolytic process was maximum for LCC^ICCG followed by LCC and FastPETase. Finally, extracellular LCC^ICCG-producing E. coli cells were cultivated using minimal media supplemented with 0.1% ammonium chloride and 1% glycerol as nitrogen and carbon sources in a bioreactor with a final protein content and specific activity of 119 ± 5 mg L^-1 and 1232 ± 18 U mg^-1, respectively. Nearly complete depolymerization of 13 g L^-1 PET and 23.8 g L^-1 post-consumer PET was achieved in 50 h using crude LCC^ICCG supernatant, without enzyme purification, at 62 °C. A bioprocess was thus developed to depolymerize 100 g L^-1 mixed PET trays and bottle waste (MW1 and MW2), reaching 78% and 50% yield at 62 °C with a crude enzyme loading of 2.32 mg g^-1 PET in 60 h. The results demonstrate an easy PET depolymerization strategy that could be exploited in large-scale facilities for efficient plastic waste treatment.