The role of graft-modified chitosan-based coagulants in pharmaceutically combined polluted water: Performance and mechanism

The extensive use of ibuprofen (IBU) and acetaminophen (APAP) has led to their accumulation in surface water, resulting in combined pollution with natural organic matter (NOM). In this study, a novel modified chitosan-based coagulant (CTS-DMDAAC) was successfully synthesized by adding ceric ammonium nitrate (CAN) to make chitosan (CTS) and dimethyldiallylammonium chloride (DMDAAC) produce free radicals for graft copolymerization. The study investigated the effects of pH, initial NOM concentration, and suspended particulates on the performance of contaminant removal and the characteristics of flocs. Through analysis of the Zeta potential and floc characteristics, the primary flocculation mechanisms were identified as: net capture and sweep, charge neutralization, and bridging effect. CTS-DMDAAC demonstrated effective removal of NOM, particularly humus, but encountered challenges in removing small-molecule pharmaceuticals such as IBU and APAP, with removal rates below 15 %. To enhance the removal rate of small organic molecules, powdered activated carbon (PAC) was incorporated into the coagulation system, resulting in increased removal rates of IBU and APAP to 71.44 % and 79.9 %, respectively. Additionally, PAC improved the bridging capacity during coagulation, resulting in a 1.25-fold increase in the strength factor and a 2.34-fold increase in the recovery factor of the flocs. These findings suggest that the combined use of PAC and CTS-DMDAAC presents a novel approach for treating water bodies contaminated with NOM and pharmaceutical complexes.