Hyperthermophilic composting accelerates the humification process of sewage sludge: Molecular characterization of dissolved organic matter using EEM-PARAFAC and two-dimensional correlation spectroscopy.

The aim of this work was to study the chemical and structural changes of dissolved organic matter (DOM) at the molecular level during hyperthermophilic composting (HTC) of sewage sludge using excitation-emission matrix-parallel factor (EEM-PARAFAC) combined with two-dimensional correlation spectroscopy (2DCOS) analyses. Results showed that HTC accelerated the humification process by decreasing protein-like and increasing humus substances more quickly compared to conventional thermophilic composting. The rapid humification process of HTC was related to the structural changes of DOM, in which the C-O stretching within polysaccharides could be the main factor responsible for the formation of humus substances. Redundancy analysis enabled the relationship between spectral indices and composting parameters to be explained, demonstrating that these indices can be used for assessing the degree of humification. This work has contributed to resolving the humification mechanism of HTC and expanding the application of EEM-PARAFAC and 2DCOS.