Enhancing Escherichia coli removal mechanism using quaternary phosphine group–modified chitosan flocculant

To overcome the low removal efficiency of common flocculants for bacterial pollutants, herein, a series of quaternary phosphine groups (QPGs)–modified chitosan (CTS)-based flocculants (CTS-P) was proposed. The removal efficiency of CTS-P for Escherichia coli (E. coli) and other coexisted pollutants was evaluated. The binding mode and interaction mechanism between CTS-P and E. coli were elucidated using theoretical calculations. Results showed that flocculation performance of CTS-P was the most efficient in near-neutral water (pH = 6–8). The removal efficiencies of CTS-P (10 mg/L) for humic acid and E. coli is 71 % and 1.82 1og, respectively, and the removal process was dominated by charge neutralization and adsorption bridging effects. The QPGs increased the charge density of the coagulation system and promoted the formation of large particle flocs. During the collision and growth processes of flocs, E. coli was quickly flocculated onto their surface and encapsulated within them. The binding of the QPGs to the cell membrane leads to E. coli cell death and structural rupture. Theoretical calculations show that the interfacial interaction energy of CTS-P for capturing E. coli is dominated by intermolecular interaction energy and polar interaction energy. The CTS-P flocculant proposed in this study provides a new pharmaceutical product and a theoretical basis for removing bacterial pollutants from drinking water sources.