Abstract
This research evaluated how to minimize calcium (Ca) loading onto granular activated carbon (GAC) by adjusting pH and/or adding coagulants. Batch tests used raw water samples from New Castle, Pa. Total organic carbon (TOC) ranged from 4.0 to 5.3 mg/L. Variations in Ca loading reflected variability in natural organic matter composition between samples. For most samples, 5 mg/L of iron coagulant (as Fe) diminished Ca loading by 200–600 mg Ca/kg GAC—an 18–75% drop. In batch tests at constant pH with no coagulant and variable GAC doses, Ca loading increased linearly with TOC loading indicating that Ca and TOC adsorbed into GAC together. The ratio of Ca to TOC loaded onto GAC decreased with decreasing pH or increasing Fe. This showed that H+ or Fe(III) could displace the Ca that loaded with TOC and that utilities could diminish Ca loading by slightly depressing pH and/or by using moderate coagulant dosages.
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