It remains challenging yet of great importance to develop a qualified biopolymer-derived flocculant in treating complex high-salinity wastewaters polluted by suspended solids and refractory soluble organic substances such as organic dyes. The key to this success is to endow the developed flocculants with versatile intermolecular and interfacial interactions in high salinity to trigger effective flocculation. Herein, inspired by mussel's powerful wet adhesion in a salted marine environment to diverse interfaces, we develop a mussel-inspired chitosan-based flocculant (CQ-CS) by simultaneously grafting catechol and cationic trimethylammonium groups to chitosan backbones. Compared with its cationic compartment, the optimal dosage of CQ-CS is decreased greatly after introducing catechol groups. Moreover, CQ-CS works in a wide pH range from 2 to 7 and can achieve more than 95% removal efficiency of soluble organic dyes and suspended particles such as anionic dyes and kaolin clay at the optimal dosages. More importantly, the flocculation performance of CQ-CS exhibits excellent tolerance to the salinity. As NaCl concentration increases from 0 to 2000 mg/L, CQ-CS maintained similar removal efficiencies for organic dyes, while the removal efficiency of quaternized chitosan (Q-CS) for organic dyes decreased by approximately 8% at this salinity. Finally, CQ-CS exhibits excellent flocculation performance to industrial dyeing wastewaters.

Biomass-based flocculants have been widely studied and applied to wastewater treatment due to their environmental friendliness. However, these flocculants tend to generate flocs with small size and lead to difficult solid-liquid separation after the flocculation. The key to solving the floc size problem is enhancing intermolecular or intramolecular interaction forces by changing the molecular structure and functional groups of flocculants. Herein, we developed a mussel-inspired cationic biomass flocculant by functionalizing chitosan (CS) with cation component acryloyloxyethyltrimethyl ammonium chloride (DAC) and mussel-inspired monomer N-2-(3, 4-dihydroxyphenethyl) acrylamide (DAA) through free radical polymerization. The prepared flocculant could provide multiple interaction forces such as electrostatic interaction, cation-π interaction, π −π stacking, and hydrogen bonding to pollutants. As a result, the spent CS-g-p (DAC-co-DAA) flocculant generate dye-containing flocs with dramatically increased size when compared with its counterpart CS-g-pDAC without catechol groups and are capable to realize more than 95% removal efficiency towards organic dyes such as MB and CR over a broad pH range from 3 to 9. This study provides some insights in how to apply this mussel-inspired strategy to develop environmentally friendly biomass-derived flocculants with floc enlarging capacity to treat organic wastewaters in wide pH range.