Cytotoxicity Comparison between Drinking Water Treated by Chlorination with Postchloramination versus Granular Activated Carbon (GAC) with Postchlorination.

Granular activated carbon treatment with postchlorination (GAC/Cl 2 ) and chlorination followed by chloramination (Cl 2 /NH 2 Cl) represent two options for utilities to reduce DBP formation in drinking water. To compare the total cytotoxicity of waters treated by a pilot-scale GAC treatment system with postchlorination (and in some instances with prechlorination upstream of GAC (i.e., (Cl 2 )/GAC/Cl 2 )) and chlorination/chloramination (Cl 2 /NH 2 Cl) at ambient and elevated Br - and I - levels and at three different GAC ages, we applied the Chinese hamster ovary (CHO) cell cytotoxicity assay to whole-water extracts in conjunction with calculations of the cytotoxicity contributed by the 33 (semi)volatile DBPs lost during extractions. At both ambient and elevated Br - and I - levels, GAC/Cl 2 and Cl 2 /NH 2 Cl achieved comparable reductions in the formation of regulated trihalomethanes (THMs) and haloacetic acids (HAAs). Nonetheless, GAC/Cl 2 always resulted in lower total cytotoxicity than Cl 2 /NH 2 Cl, even at up to 65% total organic carbon breakthrough. Prechlorination formed (semi)volatile DBPs that were removed by the GAC, yet there was no substantial difference in total cytotoxicity between Cl 2 /GAC/Cl 2 and GAC/Cl 2 . The poorly characterized fraction of DBPs captured by the bioassay dominated the total cytotoxicity when the source water contained ambient levels of Br - and I - . When the water was spiked with Br - and I - , the known, unregulated (semi)volatile DBPs and the uncharacterized fraction of DBPs were comparable contributors to total cytotoxicity; the contributions of regulated THMs and HAAs were comparatively minor.