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Removal of Volatile Organic Contaminants (VOCs) from the Groundwater Sources of Drinking Water via Granular Activated Carbon Treatment (WaterRF Report 4440)
Citation:
Summers, R., D. Kempisty, T. Dougherty, AND D. Knappe. Removal of Volatile Organic Contaminants (VOCs) from the Groundwater Sources of Drinking Water via Granular Activated Carbon Treatment (WaterRF Report 4440). Water Research Foundation, Denver, CO, 2015.
Impact/Purpose:
The U.S. Environmental Protection Agency (EPA) is considering setting or lowering the maximum contaminant level (MCL) for several carcinogenic volatile organic contaminants (cVOCs) from their current MCL of 5 μg/L or 2 μg/L, and a sub-μg/L range is being considered. While current MCLs for organics are commonly attained using granular activated carbon (GAC), an order-of-magnitude reduction in MCLs may present a challenge to water treatment facilities using GAC. This is especially true when considering the adsorption complications presented by dissolved organic matter (DOM) and co-solutes in the background matrix of the water being treated. DOM has been shown to decrease both GAC uptake rates and overall capacity for contaminants. The overall objective of this research is to determine if GAC can remove cVOCs to the sub-μg/L level in groundwaters (GW) with environmentally relevant DOM concentrations. Demonstrating GAC’s potential as a viable cVOC treatment technology is both environmentally relevant and timely. Many stakeholders benefit from this research: the EPA for regulatory purposes; municipalities for economic reasons; and environmental restoration site managers for implications to future cleanup criteria. Regarding Superfund sites, both the National Contingency Plan and Superfund (i.e. CERCLA) have language stating that in certain cases, remedial action must attain federal standards (MCLs or nonzero health goals) established under the Safe Drinking Water Act (SDWA). A common metric used to determine efficiency of GAC treatment for various constituents is the carbon use rate (CUR). The CUR, expressed in mass of carbon required to treat a volume of water to a specified treatment objective, is one metric used to estimate carbon performance. The rapid small scale column test (RSSCT) is a fast way to assess full-scale carbon performance, but often over-predicts the performance for specific organic compounds like cVOCs. RSSCTs use the principles of similitude to replicate adsorption phenomena, but do so in a fraction of the time required by pilot-scale columns. It has been estimated that less than 10% of the time and water is required for RSSCT experiments to produce comparable full-scale column data. Adjustments to the empty bed contact time (EBCT), the volume of the adsorber column divided by the volumetric flow rate, can also produce changes in GAC adsorber efficiency. Designed appropriately, the RSSCT allows multiple EBCTs to be quickly evaluated, thus allowing the effects of different EBCTs on GAC performance to be determined.
Description:
The overall goal of this project was to assess the feasibility of granular activated carbon (GAC) for the treatment of selected carcinogenic volatile organic compounds (cVOC) to sub-μg/L levels. The project consisted of three tasks. The task objectives are: Task I - determine carbon usage rates (CUR) at empty bed contact times (EBCT) of 7.5 min and 15 min for the cVOCs in a groundwater (GW), Task II - address: (a) a threshold where cVOC breakthrough normalized to the influent cVOC concentration is independent of the influent cVOC concentration for one cVOC, (b) the effects of GW dissolved organic matter (DOM) type and concentration on breakthrough of three cVOCs, and (c) competitive effects between two commonly co-occurring cVOCs in GW on cVOC breakthrough, and Task III - review scale-up method analysis, addressing the current understanding and procedures associated with accurate scale-up. The specific cVOCs evaluated were: • carbon tetrachloride (CT) • 1,2-dichloroethane (1,2 DCA) • 1,2-dichloropropane (1,2 DCP) • tetrachloroethylene (PCE) • trichloroethylene (TCE) • 1,1-dichloroethane (1,1 DCA) • 1,1,2,2-tetrachloroethane (1,1,2,2 TCA) • 1,1,1,2-tetrachloroethane (1,1,1,2 TCA) • 1,2,3-trichloropropane (1,2,3 TCP)A baseline influent concentration of 5 μg/L was used. The evaluation of benzene, dichloromethane (DCM), and 1,3- butadiene (1,3 BD) was initially proposed, but spiking issues precluded their use and evaluation.
