The Effect of Groundwater Temperature and DOM on Adsorption of cVOCs by GAC Adsorption.

摘要

The Environmental Protection Agency is investigating modification of drinking water regulations regarding carcinogenic volatile organic compounds (cVOCs). Changes may include reducing maximum contaminant levels (MCLs) and creating standards for unregulated cVOCs. Granular activated carbon (GAC) adsorbers are effective for GAC treatment, though research hasn't focused on lower concentrations, and other unregulated cVOCs have not been extensively evaluated. When multiple cVOCs co-occur, competition for adsorption sites may impact adsorption. GAC adsorbers also remove naturally occurring dissolved organic matter (DOM), fouling adsorption sites, and decreasing cVOC adsorption capacity. The temperature effect on GAC adsorption has not been extensively studied, but could be important. Finally, GAC produced from alternate sources may increase cVOC adsorption.;Using rapid small-scale column tests, GAC adsorption of 1,1 dichloroethane, 1,2 dichloropropane, 1,2,3 trichloropropane, 1,2 dichloroethane, carbon tetrachloride, trichloroethelene, 1,1,2,2 tetrachloroethane, 1,1,1,2 tetrachloroethane, and perchloroethylene was studied using natural groundwaters with DOM concentrations of 1.6 and 3.5 mg/L at temperatures of 7 and 20 °C.;To evaluate DOM fouling, cVOC adsorption capacity at different empty bed contact times (EBCTs) was observed. Decreased adsorption capacity at longer EBCTs indicated DOM fouling, and up to 23% decreases occurred. Competition was studied by running each adsorber with one strongly, moderately, and weakly adsorbing cVOC. Minimal cVOC competition was observed, and results showed increased adsorption capacity with increasing cVOC adsorption strength. Groundwaters with higher DOM concentration had 9 to 41% less adsorption capacity. When both groundwaters had the same DOM concentration, the more reactive groundwater had 38 to 64% less capacity, indicating DOM fouling. Compared to the baseline bituminous GAC, coconut-based GAC showed increased cVOC capacity, between 22 and 40%, yet less DOM capacity, likely due to pore structure. The 7 °C GAC column had increased cVOC adsorption capacity, between 3 and 52%, and exhibited breakthrough behavior different than the 20 °C columns, potentially indicating temperature's effect on adsorption.