Effects of aeration rates on the structural changes in humic substance during co-composting of digestates and chicken manure

High humidity and potential threat of pathogen of anaerobic digestates are unfavorable to the environment by direct utilization. To achieve the sustainable utilization of digestates, composting might be a good choice. Meanwhile, the aeration rate of composting has been optimized. Co-composting of digestates and chicken manure was performed under different aeration conditions (0.05, 0.1 and 0.15 L·min⁻¹·kg⁻¹·organic matter (OM)). During composting, internal transformation of humic substance (HS) has been studied for obtaining the potential application value of the co-composting products. Results suggested that the HS concentration was increased by 21.1%, 26.4% and 22.4% with the aeration rates were 0.05, 0.1 and 0.15 L·min⁻¹·kg⁻¹·OM, respectively. The aeration rate of 0.15 L·min⁻¹·kg⁻¹·OM was more conducive to germination. Parallel factor analysis and dimensional correlation spectra (2DCOS) have been combined to reveal the conversion relationships of HS components for understanding the compost application pattern. Hetero-2DCOS indicated that aeration of 0.05 min⁻¹·kg⁻¹·OM and 0.1 L·min⁻¹·kg⁻¹·OM contributed to the formation of complex compounds at long wavelength, and aeration of 0.15 L·min⁻¹·kg⁻¹·OM was beneficial for labile compounds formation at short wavelength. In views of the aeration of 0.1 L·min⁻¹·kg⁻¹·OM was more beneficial to improve HS concentration than 0.05 L·min⁻¹·kg⁻¹·OM, 0.1 L·min⁻¹·kg⁻¹·OM and 0.15 L·min⁻¹·kg⁻¹·OM were consider as the most important aeration rate to conduct digestates composting. Overall, the aeration affected the HS composition which, in turn, might affect the application ways of composting products. This study could provide a reference for industrial composting production and applications.