Performance regulation of lignin-based flocculant at the practical molecular level by fractionation

Lignin, an inedible yet sustainable aromatic resource, has great commercial prospects as raw material to prepare flocculants with efficient flocculation coupled with sterilization. However, the troublesome heterogeneity of lignin is the bottleneck for the large-scale production of highly efficient flocculants. In this study, an easy to operate organic solvent fractionation approach was first applied to separate industrial lignin and generate several homogeneous fractions, and the polydispersity of lignin improved from 2.80 to 1.30-1.85. Subsequently, a series of lignin-based flocculants were synthesized in a UV-induced biphasic polymerization system using different lignin fractions (F0-F4). Surprisingly, the lignin-based flocculants L-F1 and L-F2, which were prepared from lignin F1 and lignin F2 fractionated by ethyl acetate and ethanol, respectively, exhibited over 99% removal rate and excellent sterilization efficiency on E. coli suspensions. The improved efficiency could be attribute to the more homogeneous structure of the fractionated lignin. Moreover, more G units and phenolic hydroxyl groups in lignin contributed to the increase of its copolymerization activity, while the low molecular weight and excellent hydrophilicity led to superior dispersibility and reactivity accessibility in biphasic polymerization. The purification test of E. coli suspensions showed that the flocculation performance of lignin-based flocculants was not only affected by charge density and molecular weight, but also by the balance of amphiphilicity, and its sterilization ability was mainly determined by charge density. The effect of lignin structure on the preparation and performance of lignin-based flocculants was fully explored at the actual molecular level, which has important enlightening significance for the application of lignin in wastewater recycling.

Automated summary

In this study, the heterogeneity of lignin was improved by an organic solvent fractionation method, which resulted in the synthesis of efficient flocculants. The homogeneity of the fractionated lignin contributed to the improved efficiency, while the low molecular weight and hydrophilicity enhanced the dispersibility and reactivity of the flocculants in polymerization reactions.