Pro K-Enhanced Mesophilic Anaerobic Co-Digestion of Food Waste and Pla/Pbat/Starch Plastics: Key Gene and Pathway Activation for Methane and L-Lactate Production

Abstract

Due to the limitations of hydrolysis, numerous biodegradable plastics (BPs) have extended degradation cycles and reduced biodegradation rates under anaerobic conditions. To improve the anaerobic co-degradation efficacy of food waste mixed with commercial biodegradable plastics (PLA/PBAT/starch), porcine pancreatic lipase (PPL) and protease K (Pro K) were embedded in the plastics, and the reaction process was analyzed through metagenomics. Biomarkers at each stage of the anaerobic co-digestion process were measured to verify the accuracy of the pathway analysis. After Pro K enzyme embedding, according to the kinetic equations, the hydrolysis kinetic constant of the co-digestion system increased by 18.42%, accompanied by an increase in the degradation rate of plastics from 7.3% to 19.3%. In the hydrolysis phase, the pathways producing pyruvate and lactate from food waste and plastic hydrolysis were enhanced, respectively, according to the functional gene analysis. Interestingly, enzyme modification significantly enhanced the conversion pathway from D-lactate to L-lactate, raising the L/D ratio from 1:1 in control to a peak of 20:1 in PKBP. During the acidogenesis phase, the enrichment of L-lactate, led to an increase in acetate concentration, strengthening the pathways of converting L-lactate directly into acetate and via acetyl-CoA. In the methanogenesis phase, the genes for the acetoclastic and hydrogenotrophic methanogenesis pathways were both enhanced, resulting in methane production increases of 17.59%. This study attempts to verify the impact of enzyme modification on gene pathways in BP anaerobic co-digestion from the perspective of metagenomic analysis, thereby improving asynchronous multi-substrate degradation.

Keywords: Metagenomic analysis, Proteinase K, Commercial biodegradable plastics, Anaerobic co-digestion, enzyme immobilization