Recently, the Innovation Team of Clean Conversion and High-value Utilization of Farming Waste at the Institute of Environment and Sustainable Development in Agriculture (IEDA), Chinese Academy of Agricultural Sciences (CAAS), has made significant progress in the directional conversion of biogas residue through hydrothermal humification and in nitrogen fixation. The related findings have been published in Biochar.

To address the challenges of massive biogas slurry production, difficult resource utilization, and high risk of nitrogen loss, hydrothermal humification technology can efficiently upgrade organic wastes under subcritical conditions. This process converts nutrient components—including lignin, cellulose, and nitrogen—into nitrogen-rich humic acid within a few hours, achieving efficient value-added conversion of organic wastes.

This study highlights the synergistic role in promoting the formation and structural evolution of humic acid during the hydrothermal humification of biogas slurry and residue. The study reveals that biogas slurry promotes lignin depolymerization and nitrogen-containing Maillard reactions, driving the aromatization and condensation of carbon-nitrogen components. This facilitates efficient nitrogen enrichment, ultimately boosting humic acid yield and optimizing its molecular structure. The resulting product features high aromaticity along with abundant oxygen- and nitrogen-containing functional groups. With a carbon-to-nitrogen (C/N) ratio below 24:1, it is well-suited for use as a nitrogen-enriched soil amendment. This study provides a novel technical pathway for the synergistic resource utilization of biogas slurry and residue, highly efficient nitrogen recovery, and the high-value conversion of agricultural organic waste.

This study was supported by the Agricultural Science and Technology Innovation Program (ASTIP) of the Chinese Academy of Agricultural Sciences and the National Key Research and Development Program of China.

Linkage: https://link.springer.com/article/10.1007/s42773-026-00662-4