Insight to maturity during biogas residue from food waste composting in terms of multivariable interaction

This study used biogas residue produced by anaerobic fermentation of food waste as the raw material in large-scale windrow composting. The effects of the addition of a microbial consortium on the physical and chemical properties and stability of composting of biogas residue were studied. The maturity of food waste biogas residue during composting was investigated by multivariate interaction of environmental, maturity, and nutrient parameters, using structural equation modeling (SEM). Results showed that the temperature of T2 compost with the microbial consortium increased more rapidly. The pH ranges of T1 (without the microbial consortium) and T2 were 8.75-9.15 and 8.42-9.27, respectively; the electrical conductivity (EC) ranges of T1 and T2 were 2.74-3.95 mS/cm and 2.81-3.85 mS/cm, respectively; the degradation rates of organic matter (OM) in T1 and T2 were 21.74% and 33.62%, respectively; and the total nitrogen (TN) ranges of T1 and T2 were 1.93-3.10% and 1.80-3.21%, respectively. By the end of composting, the germination indices (GI) of T1 and T2 were 20.57% and 64.24%, respectively. The total oxygen consumption after 4 days (AT₄) was 1.88 mg-O₂/g and 1.2 mg-O₂/g in T1 and T2, respectively. SEM of T1 showed that compost temperature and EC were important factors affecting compost maturity. These factors highly significantly affected OM, which in turn affected AT₄ of the biogas residue composting. SEM of T2 showed that compost temperature, pH, and EC affected OM, which in turn affected compost maturity. Temperature affected compost maturity by affecting AT₄ and GI. Principal component analysis (PCA) showed that the overall score of T2 was higher than that of T1, indicating that the addition of the microbial consortium was beneficial for industrial-scale composting of biogas residue produced by anaerobic digestion of food waste.