Abstract
Simulated natural waters with various concentrations of natural organic matter (NOM) were softened using lime precipitation to determine the effects of dissolved organic carbon (DOC) on calcium removal. Water with 8.3 mg/L of DOC showed reduced calcium removal compared with waters with 0 and 1.5 mg/L of DOC and exhibited high degrees of oversaturation before precipitation commenced, providing evidence that NOM interferes with lime softening by inhibiting calcium carbonate nucleation and crystal growth. In 2005, the utility serving the Village of Palm Springs, Fla., implemented a full‐scale magnetic ion exchange (MIEX®) process upstream of its lime‐softening facilities. In this research, anion exchange treatment of simulated natural water and raw water from Palm Springs reduced DOC concentrations from 8.1 to 3.5 mg/L and from 7.7 to 2.1 mg/L, respectively, and therefore was expected to improve the performance of downstream softening. Both waters showed improvement in softening performance after anion exchange treatment with the resin. Analysis of raw and finished water quality at Palm Springs found improved hardness removal after implementation of the MIEX process, even at reduced lime doses.
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