Coagulation performance and floc characteristics of aluminum sulfate with cationic polyamidine as coagulant aid for kaolin-humic acid treatment

In this study, novel cationic polyamidine (Pa) was synthesized and used as coagulant aid with aluminum sulfate (AS) for kaolin-humic acid simulated water treatment. The effects of Pa on coagulation performance and floc properties were investigated. Results showed that Pa addition significantly enhanced the removal of turbidity, ultraviolet absorbance at 254   nm wavelength (UV 254 ) and dissolved organic carbon (DOC). AS–Pa exhibited high coagulation efficiency at border pH range and increased floc size and growth rate significantly. Floc recovery ability was also improved, while floc fractal dimension was lower with Pa addition. This would be attributed to high cationic charge density and long chain of Pa, which could enhance the effect of charge neutralization and adsorption bridging.