Granular Activated Carbon Treatment May Result in Higher Predicted Genotoxicity in the Presence of Bromide

Abstract

Certain unregulated disinfection byproducts (DBPs) are more of a health concern than regulated DBPs. Brominated species are typically more cytotoxic and genotoxic than their chlorinated analogs. The impact of granular activated carbon (GAC) on controlling the formation of regulated and selected unregulated DBPs following chlorine disinfection was evaluated. The predicted cyto- and genotoxicity of DBPs was calculated using published potencies based on the comet assay for Chinese hamster ovary cells (assesses the level of DNA strand breaks). Additionally, genotoxicity was measured using the SOS-Chromotest (detects DNA-damaging agents). The class sum concentrations of trihalomethanes, haloacetic acids, and unregulated DBPs, and the SOS genotoxicity followed the breakthrough of dissolved organic carbon (DOC), however the formation of brominated species did not. The bromide/DOC ratio was higher than the influent through much of the breakthrough curve (GAC does not remove bromide), which resulted in elevated brominated DBP concentrations in the effluent. Based on the potency of the haloacetonitriles and halonitromethanes, these nitrogen-containing DBPs were the driving agents of the predicted genotoxicity. GAC treatment of drinking or reclaimed waters with appreciable levels of bromide and dissolved organic nitrogen may not control the formation of unregulated DBPs with higher genotoxicity potencies.

Chlorine addition prior to granular activated carbon contactors improves trihalomethane control

“…Bromide is a DBP precursor and was measured using ion chromatography (USEPA, ). Bromine incorporation factors (BIFs) for THMs were calculated as follows: where CHCl 3 , CHCl 2 Br, CHClBr 2 , and CHBr 3 are their corresponding THM molar concentrations (μmol/L) (Krasner et al, ). BIF indicates the average THM species in a given water source.…”

“…Bromide is a DBP precursor and was measured using ion chromatography (USEPA, 1993 where CHCl 3 , CHCl 2 Br, CHClBr 2 , and CHBr 3 are their corresponding THM molar concentrations (μmol/L) (Krasner et al, 2016). BIF indicates the average THM species in a given water source.…”

“…After a 24-h contact time in the SDS tests, maximum chloroform formation was 8 μg/L in the column run with virgin GAC and without prechlorination (B1) effluent and 5 μg/L in the columns run with virgin Figure 9 shows similar trends for virgin GAC after 72 h chlorine contact time, indicating that longer chlorine reaction times (e.g., within the distribution system) would not significantly alter the TTHM speciation in finished water. Reducing bromoform concentrations is beneficial from a health perspective as bromoform presents higher toxicity than other THMs (Krasner et al, 2016;Richardson, Plewa, Wagner, Schoeny, & DeMarini, 2007). Figure 9 also shows the SDS tests for the water treated using reactivated GAC.…”

Re‐assessing effects of bromide and granular activated carbon on disinfection byproduct formation

“…As a result, the Br/TOC ratio in GAC effluent is higher than its influent, thus causing a shift toward formation of more brominated species. Previous studies have shown that GAC adsorption resulted in higher bromine incorporation into DBPs and an increased formation of some Br-DBP species, such as bromoform (Symons et al, 1993) and dibromoacetonitrile (Krasner et al, 2016). In a recent study, GAC has been shown to effectively remove precursors for THM4, HAA5, HAA9, and nitrosamines in the presence of elevated bromide (Stanford, 2017).…”

“…Extensive research has been conducted on the effect of GAC on DBP formation in the presence of bromide in water (Amy, Tan, & Davis, 1991;Chiu et al, 2012;Jiang, Li, Zhang, Liu, & Zhu, 2018;Krasner et al, 2016;Stanford, 2017;Summers, Benz, Shukairy, & Cummings, 1993;Symons, Krasner, Simms, & Sclimenti, 1993). GAC removes dissolved organic matter (often measured as total organic carbon, TOC) but has little effect on bromide.…”