Bioaugmentation mechanism on humic acid formation during composting of food waste

In this study, microbes were added to food waste compost in order to investigate the bioaugmentation mechanism of Humic acid (HA) formation. Thermogravimetric analysis, structural equation model, Fourier transform infrared spectroscopy and statistical analysis were utilized to explain the bioaugmentation mechanism. The results showed that bioaugmentation increased humification rate and degree. Bioaugmentation not only promoted the formation of aromatic structures and CC bonds but also brought different change orders of functional groups in HA. The HA obtained in bioaugmentation group (BA, 7.51 g/kg) was significantly higher compared to the control group (CK, 2.37 g/kg). Similarly, the HA/FA of BA (1.90) was also higher than that of CK (0.62), and peaked at 2.34 on day 40. The polyphenol humification pathway played a major role regardless of the addition of inoculant. However, the exogenous microbes promoted protein and carbohydrate degradation in the initial stage, and the abundance of precursors (amino acids and reducing sugars) enhanced both Maillard and polyphenol humification pathways. When polyphenol was insufficient in later stage, bioaugmentation mainly embodied in the strengthening of Maillard humification pathway. This finding benefited the practice of directional humification process of food waste composting.