Enhanced adsorption of natural organic matter on calcium carbonate particles through surface charge modification

In this research, means to increase the removal of natural organic matter (NOM) during drinking water treatment were investigated. Specifically, the modification of calcium carbonate surfaces by cationic polyelectrolytes was tested as a way to improve humic acid adsorption to floc surfaces during lime softening. Results demonstrated that under high pH conditions (pH 9.5), coating the particles with high charge density cationic polyacrylamide (CPAM) significantly increased the adsorption of humic acid, while coating the particles with low charge density CPAM had no positive effect. The amount of humic acid adsorbed also depended on the molecular weight of CPAM, with high molecular weight coatings being more effective at enhancing adsorption than low molecular weight coatings. Electrophoretic mobility measurements demonstrated that the cationic polymer reduced repulsive electrostatic interactions between humic acid and the particle surface. Under low pH conditions (pH 7.5), adsorption of polyacrylamide was low, and coating the particles had less effect on the amount of humic acid adsorbed. The results presented here suggest that the modification of calcium carbonate floc surfaces using cationic polymers with high charge density may enhance natural organic matter removal during drinking water treatment. (C) 2001 Elsevier Science B.V. All rights reserved.