Effects of Pretreatment with Proteinase K at Different Concentrations on Methane Production and Microbial Community Structure in Anaerobic Co-digestion of Food Waste and Bioplastics

The integration of bioplastic bags in China’s food waste (FW) management has introduced challenges for anaerobic digestion due to asynchronous degradation of FW and bioplastics. This study assesses the effects of proteinase K pretreatment at concentrations ranging from 0.03–0.20 g/L on methane production, bioplastic degradation, and microbial community dynamics during anaerobic co-digestion at 35 and 55°C. Optimal methane outputs of 320 mL/g VS at 35°C (0.10 g/L) and 380 mL/g VS at 55°C (0.15 g/L) were achieved, with production peaks advanced by 4–6 days compared to controls. Scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed significant structural (pore density increased by 40–60%) and chemical (carbonyl bond reduction at 1700 cm–1) modifications in bioplastics. Microbial analyses indicated an enhanced abundance (25–30%) of methane-producing archaea (Methanosaeta), along with bacterial community shifts (Bacteroidota increased to 40–45%) that facilitated bioplastic hydrolysis. The results demonstrate that proteinase K pretreatment effectively enhances digestion efficiency while accelerating bioplastic degradation, providing a practical approach for co-digestion systems.