AWWA JAW70294

Finished water hardness is not regulated, but many utilities target residual hardness levels at 50-100 mg/L as calcium carbonate in order to minimize such adverse effects as scale formation, deposition in hot water pipes, and inhibition of the cleansing action of soap and detergents. Operational data from a Florida utility that had implemented a full-scale magnetic ion exchange (MIEX®) process upstream of its lime-softening facilities demonstrated improved calcium removal after implementation of this treatment. However, the effects of natural organic matter (NOM) in the lime-softening process were not well understood. To bridge this information gap, the authors undertook a systematic study of anion exchange removal of NOM and lime-softening. Analysis of simulated natural waters with varying concentrations of dissolved organic carbon (DOC) provided evidence that NOM interferes with lime-softening by inhibiting calcium carbonate nucleation and crystal growth. In this research, when model water and real waters were pretreated with anion exchange resin, DOC concentrations were reduced and the result was improved calcium removal by lime-softening. Includes 19 references, table, figures.