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

Abstract

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.