Synthesis of humic-like acid from biomass pretreatment liquor: Quantitative appraisal of electron transferring capacity and metal-binding potential

The treatment of alkaline pretreatment liquor is critical for the clean production of biomass refinery industry. There is a compelling need to develop a simple technology for reuse of organic matter in the pretreatment liquor to achieve a more value-added product with high application potential in agriculture and benefit environmental sustainability. The objective of this study is to examine a strategy for synthesizing humic-like acid under H₂O₂ oxidation by using biomass pretreatment liquor as a precursor and evaluate their electron transferring capacity and metal-binding potential. The results show that 8% H₂O₂, a temperature of 40 °C, and a reaction time of 2 h yielded humic-like acid up to 2.9 g L−1. Meanwhile, the recovery of total phenols, total sugars, proteins, and amino acids in the pretreatment liquor was 82.8, 56.2, 78.1, and 64.2%, respectively. Compared to the commercial humic acid, humic-like acid has a more uniform particle size and higher C (22.5%), N (2.3%), O (33.8%), K (4.5%), and P (11.2%) contents. The hydroxyl and carboxyl group contents were 3.3 and 2.0 times higher in humic-like acid than that in humic acid, respectively. Moreover, humic-like acid has more electron transferring capacity as well as metal-binding potential than commercial humic acid, suggesting the great application potential for remediation of heavy metal polluted soils. The reported strategy of synthesizing humic-like acid from pretreatment liquor in this study would promote the process of cleaner production of biorefinery industry as well as circular economy in agriculture. [Display omitted] •New strategy for humic-like acids synthesis from pretreatment liquor was evaluated.•H2O2 oxidation efficiently synthesized HLA with higher recovery of components.•HLAs contain higher contents of functional groups than commercial humic acids.•HLA has more electron transferring capacity as well as metal-binding potential.