The Potential of Methane Production and Humus Fluorescence Characteristics During Anaerobic Co-Digestion of Food Waste

To explore the methane production potential and mechanism of anaerobic co-digestion using organic solid residues and residual liquid derived from food waste pretreatment, batch experiments were conducted at 37 ± 0.5°C with varying mass ratios of the substrates. Analytical methods such as detection analysis, gas chromatography, and three-dimensional fluorescence characterization were adopted to study the influence mechanism of key indicators such as total solids, volatile solids (VS), ammonia nitrogen, volatile fatty acids (VFAs), and humus on anaerobic co-digestion. The results showed that when the mass ratio of organic solid residues to residual liquid was 2:1, the methane production efficiency of anaerobic co-digestion was the highest, and the methane production per unit VS was 483.71 mL/g VS. The VFAs in hydrolyzed products were predominantly acetic, propionic, and butyric acids, with trace valeric acid (n-pentanoic acid). Methanogenic activity was significantly inhibited during later stages due to the influence of VFAs and free ammonia. Fluorescence spectral analysis revealed the fluorescence peak of humus shifts from the protein-like peak to the fulvic acid and humic acid peaks during the methane production process; the fluorescence intensity of fulvic acid increased markedly compared with humic acid in the middle stage of digestion, and the fluorescence change of humus reflected the degree of organic matter mineralization. As a characteristic fluorescence substance, humus can be used to characterize the anaerobic digestion process. These findings provide theoretical foundations for food waste resource utilization.