A pilot plant study was conducted in Newport News, Virginia to investigate the effectiveness
of powdered activated carbon [PAC] and granular activated carbon [GAC], with and without
preoxidation, for reducing trihalomethane [THM] precursor concentrations in Harwood's Mill
Reservoir water. Preoxidation with ozone followed by GAC is referred to as the "biological
activated carbon” [BAC] process. This study showed that the GAC and BAC processes
obtained the same level of organic removal; however, BAC would provide longer bed life and
require less carbon than the GAC process. PAC treatment of alum coagulated water provided
significantly higher TOC and THMFP removals than alum coagulation alone. The use of a
preoxidant (ozone) with PAC slightly improved the organic removal efticiency. While
treatment by PAC increased THMFP removals, it was not as efficient as the GAC and BAC
processes. UV absorbance measured at 254 nm and TOC were found to be good surrogates
for THMFP in the GAC column, but not in the BAC column.
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