Impacts of lignin nanoparticles as antibacterial agents on the composition of biofilms in water treatment.

The development of green, high-efficiency biocides is critical for the effective control of microbial biofilms in water treatment processes. In this study, lignin nanoparticles (NPs), with an average size of around 30 nm, were synthesized via a 'green' process and applied as biocides. A gravity-driven ultrafiltration membrane system was employed to investigate their effects on biofilm composition. The results showed that when the dosage of lignin NPs was only 1 mg C/L, the abundances of bacteria and fungi in the membrane biofilms were reduced by >98%, and the total protein and polysaccharide contents in the extracellular polymeric substance (EPS) decreased significantly, demonstrating remarkable advantages. The core antimicrobial mechanism involves two synergistic effects: (1) Hydrogen bonds are formed between the hydrophilic carboxyl groups on lignin nanoparticles (NPs) and EPS-components of microbial cell walls, directly inhibiting microbial viability and proliferation while reducing EPS secretion; (2) Lignin NPs are oxidized to aromatic derivatives, with benzene rings converted into hydroxyl‑enriched phenolic structures, and the concurrent elevation of carbonyl (C=O) groups in extracellular proteins enhances hydrophobicity. The oxidized lignin NPs then amplify antimicrobial efficacy via hydrophobic associations with these modified aromatic compounds and proteins. This work provides a novel approach and new insights into the rational design of green biocides and the regulation of membrane biofilms.