Predicting the removal of soluble organic contaminants by lime softening

The removal of organic contaminants by lime softening and molecular characteristics influencing removal were experimentally and theoretically examined. Coprecipitation appeared to be the major removal mechanism for organic substances in low concentrations, and only those substances able to adsorb onto CaCO3 were able to be removed by lime softening. All of the removable anionic compounds were able to coordinate with Ca2+ to form relatively insoluble complexes. Fatty acids, which form relatively soluble complexes with Ca2+, and hydrophobic chemicals unable to coordinate with Ca2+ were not removed. Molecular characteristics influencing removal included molecular charge, functionality, degree of polymerization, molecular geometry and affinity for water. In general, softening is effective in removing polymeric electrolytes possessing acidic oxygen-containing residues, such as carboxyl, phenol, enol, phosphoryl, phosphonyl, sulfuryl and sulfonyl groups. Simple monomeric molecules are not expected to be effectively removed unless they polymerize or possess phosphorus-containing functional groups such as phosphoryl and phosphonyl.