Comb-Like Cationic Chitosan-Based Flocculant with Enhanced H‑Bond Hydration for Effectively Treating Saline Colored Effluents with High Salinity

Quaternized chitosan flocculants exhibit excellent removal efficiencies for anionic contaminants, while the treatment efficacy is greatly impeded for colored effluents with high salinity due to their lower hydration ability in saline solutions. In this work, we developed a new kind of comb-like cationic chitosan-based flocculants with hydrogen-bond (H-bond) enhanced hydration ability, CS-g-p­(DMC-co-HEMA) (CPDH), by grafting copolymerization of 2-hydroxyethyl methacrylate (HEMA) and methacrylatoethyl trimethylammonium chloride (DMC) onto chitosan skeletons. The hydroxyl groups from HEMA could improve the hydration ability of the developed CPDHs in a saline environment, while the abundant quaternary ammonium groups from DMC endow CPDHs with satisfactory antibacterial ability against both Staphylococcus aureus and Escherichia coli. Three CPDHs with different H-bond components were synthesized by tuning the molar ratio of DMC and HEMA and applied to treat different types of pollutants in saline solution using kaolin and anionic dyes as the model pollutants. Experiments showed that the developed CPDH1 with H-bond components exhibited excellent salinity tolerance and achieved more than 96% removal efficiency to methyl blue in both deionized water and saline conditions. In contrast, the removal efficiency of CPDH0 without the H-bond component in saline media was greatly undermined, showing more than a 12.5% decrease when compared to that in deionized water. Furthermore, CPDH1 demonstrated universal flocculation performance to effectively remove different pollutants including different anionic dyes and kaolin particles from different water sources with wide pH and salinity ranges, demonstrating a good tolerance of CPDH1 in diverse saline environments and providing a new approach to develop qualified biopolymer-based flocculants for treating saline dyeing wastewaters.