Fast humification of biomass via hydrothermal conversion: A Review

Abstract

Humic acid (HA), a crucial substance for maintaining soil fertility and health, plays a vital role in sustainable agricultural development and environmental remediation. Hydrothermal humification (HTH), offers the advantage of generating HA analogues from biomass in a much shorter timeframe than the natural process, which enhances carbon efficiency and aligns with green chemistry principles by promoting sustainable resource utilization and minimizing environmental impact. However, research on the hydrothermal production of HA is still in its early stages, with the conditions, influencing factors, and conversion mechanisms remaining unclear, and the potential applications of hydrothermal HA not yet well understood. Drawing from nearly a decade of research, this article addresses the mechanism of hydrothermal conversion of biomass into HA and discusses the impacts of diverse HTH operating parameters such as reaction time, biomass composition, reaction solvent, and reaction temperature on the humification process. Due to the current lack of research on the applications of hydrothermal HA, we have demonstrated the potential applications and challenges of hydrothermal HA by exploring the use of HA from various other sources in different scenarios including agriculture, environmental protection, function material preparation and animal husbandry. Furthermore, the challenges and research directions for the commercial application of hydrothermal HA are discussed, aiming to provide a reference for the study of HA from biomass via hydrothermal conversion.