Treatability of PFOA, PFOS, & other Perflouroalkyl Substances: Utility’s Response to Health Advisory
Last Modified: Oct 02, 2018
- David Briley - Hazen and Sawyer
The health effects and occurrence of perfluoroalkyl substances (PFAS) as well as other emerging contaminants of concern in drinking water supplies has received significant attention lately. In May 2016, the U.S. Environmental Protection Agency (EPA) issued health advisory levels (HALs) for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) at a level of 70 ppt. US EPA is considering adding other PFAS compounds to the Health Advisory. UCMR data as well as additional sampling by utilities is providing additional information on the occurrence of PFAS, 1,4-dioxane, and other emerging contaminants in our water supplies. The available database on the treatability of these merging contaminants, particularly in surface water supplies, is fairly limited.
A case study for PFOA, PFOS, and other PFAS compounds in a water supply in Alabama will be presented. The water treatment facility utilizes conventional treatment facility and added a MIEX system in recent years for disinfection byproduct precursor removal. Monitoring has shown that the MIEX process does not provide sufficient removal of PFAS to maintain finished water levels below the HALs. Post-filter Granular Activated Carbon (GAC) adsorption was implemented to ensure finished water is within the EPA HALs based on available performance data. Whereas the short-term goal is to ensure finished water is within the EPA HALs, removal efficiencies for short chain PFAS was also a consideration. The initial capacity of the GAC Contactor Facility will be less than the full WTP capacity and will rely on blending of GAC treated water with filtered water from the WTP to meet the HALs. The initial capacity of this Phase 1 GAC Facility is 6 mgd and is designed for an empty bed contact time (EBCT) of 20 minutes. The Phase 1 project allows for reduction of PFOA and PFOS in the finished water while further assessment can be performed on removal efficiencies for short chain PFAS to assess potential long-term needs.
This paper focuses on a utility’s fast-track treatment design of a GAC adsorption process to address concerns with exceeding the recent health advisory levels issued for PFOA and PFOS. Design considerations were also given to the removal of short chain PFAS, providing an example of a utility’s proactive effort to address both current and potential, future regulated contaminants.
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