Novelty three stages for humification of sewage sludge during hyperthermophilic aerobic fermentation

Compared with conventional aerobic fermentation (CAF), there is limited knowledge of how hyperthermophilic aerobic fermentation (HAF) enhances the humification of sewage sludge. This study compared three novel stages of organic degradation, precursors, functional groups, bacterial community, and humus synthesis mechanism in HAF with CAF. The results showed that organic matter (OM) degraded rapidly, and 68% of the degradation could be completed of stage I in HAF. Compared with the initial stage, ammonium nitrogen (NH₄⁺-N), water-soluble organic carbon, and water-soluble total nitrogen increased by 2.83 times, 40.5 times, and 33.5 times, respectively. Cellulose and hemicellulose decreased by 29.22% and 21.85%, respectively. These results suggested that temperature (>80 °C) and Bacillus dominated accelerate the humification process by rapidly improving OM degradation. Compared with the initial value of HAF, the maximum increment of reducing sugar at stage II was 297%, and the degradation rate of cellulose was effectively increased by 21.03% compared with that of CAF. The precursors such as reducing sugars and amino acids formed humus at stage II. The content of Aryl C increased significantly during the HAF process, the degree of polymerization of humus and the aromatization degree of HA and FA increased significantly, and complex organic macromolecular material polymers were formed at stage III. The sugar-amine condensation was the mechanism of humification in the sludge HAF process. This investigation provided three new stages of insights into the synthesis of humification during the HAF process and extended the current mechanism of humification in the HAF process.