The effectiveness of humic acid coagulation with the use of cationic polyacrylamides

The chemical coagulation process is a popular method for eliminating the precursors of disinfection by-products. This study presents the results of a laboratory experiment which investigates the use of cationic polyacrylamide copolymers (CPAMs) as primary coagulants in the purification of solutions containing humic acids (HA). A number of polymers with various molecular weight and charge density were tested. The optimal doses were determined by colloidal titration. The effectiveness of coagulation-flocculation was determined by jar test method. The post-coagulation suspension was separated by filtration through cellulose filter paper. The experiment showed that charge neutralization destabilizes organic colloidal particles. An inversely proportional relationship was observed between the optimal dose and polymer charge density. The effectiveness of UV₂₅₄ reduction (52–81%) and colour removal (51–88%) was determined by the effectiveness of filtration in removing post-coagulation turbidity, as well as by the type of applied polymer. The results of the study suggest that the use of CPAMs with high charge density and low molecular weight enables effective removal of humic acids from water in the coagulation and filtration process.