Two-step hydrothermal conversion of biomass waste to humic acid using hydrochar as intermediate

Yuchao Shao, Jun Zhao*, Yuyang Long, Wenjing Lu*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

4 Citations (Scopus)


Converting biomass materials to humic acid is a sustainable method for humic acid production and achieve biomass valorization. A two-step hydrothermal treatment method was adopted in this study to produce humic acid from corn stalks. In the first step of the process, hydrochar was prepared at different hydrothermal temperatures and pH values. Their chemical properties were then analyzed, and the hydrochar-derived humic acids were produced under alkaline hydrothermal conditions (denoted as HHAalk). The hydrochar, prepared under high temperature (200 °C) and strong acidic (pH 0) conditions, achieved high HHAalk yields (i.e., 67.9 wt% and 68.8 wt% calculated based on weight of hydrochar). The sources of HHAalk formation were as follows: 1) production in the hydrochar preparation stage, and 2) increment under the alkaline hydrothermal treatment of hydrochar. The degree of hydrochar unsaturation was suggested as an indicator for evaluating the hydrochar humification potential under alkaline hydrothermal conditions. This study provides an important reference for the preparation of suitable hydrochar with high hydrothermal humification potential.

Original languageEnglish
Article number119
JournalFrontiers of Environmental Science and Engineering
Issue number10
Early online date20 Apr 2023
Publication statusPublished - Oct 2023

Scopus Subject Areas

  • Environmental Science(all)

User-Defined Keywords

  • Biowaste
  • Humic acid
  • Hydrochar
  • Hydrothermal parameter
  • Unsaturation


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