Monday, September 9, 2024
10:30 AM - 11:00 AM
Location Name
How a Focus on PFAS can Lead to the Removal of DBP Precursors and Taste & Odor Compounds
Drinking Water Quality

Out of abundance of caution to protect the public health and in anticipation of PFAS becoming regulated to very low concentrations, CDM Smith’s client initiated an investigation into PFAS in their source water. If PFAS was found in the client’s source water, they wanted to know how they could effectively treat it. The client currently treats their water with PAC for the removal of taste and odor compounds. The effectiveness of the Plant’s existing PAC treatment with respect to PFAS removal was unknown prior to this study and was one of the key factors to the experiment. The study also investigated the effectiveness of GAC treatment after the existing filtration process. The potential for pH excursion, arsenic mobilization, and disinfection byproduct formation because of treatment were evaluated to ensure adverse impacts on water quality are fully characterized and mitigated. This presentation will discuss the results of the bench-scale PFAS treatability study. Investigations into treatment with multiple available PAC and GAC products and how those treatments affect DBP formation potential and taste & odor compounds. Recommendations for limiting arsenic mobilization and pH excursion during GAC treatment startup will also be discussed. The method to test the GAC treatment was a bench-scale test with rapid, small-scale column testing (RSSCT) using two commercially available GACs for the filtered water. The sorptive media was ground to reduce the particle size, thereby enhancing mass transfer and allowing shorter empty bed contact times (EBCTs) to reduce the duration of the bench-scale study. RSSCTs have been widely applied for testing the removal of trace organic contaminants by GAC using small-scale columns operated at low EBCTs and have been demonstrated by our team to be appropriate for PFAS. PFAS removal effectiveness will be evaluated as a function of time, perfluorinated chain length, and functional head group. In addition, the effectiveness of two commercially available GAC products in removing PFAS will be compared. Media longevity will also be interrogated to facilitate media selection and develop CAPEX and OPEX costs for future design/implementation. In addition, the effectiveness of three PAC products including the product currently used at the Plant and two others recommended for removing PFAAs and taste and odor compounds from the raw water will be evaluated with respect to PAC type, dosage, and contact time. Simulated Distribution System (SDS) testing was performed on GAC- and PAC-treated raw and filter effluent water, respectively. The SDS test involved chlorinating to a target dose of 2.0 mg/L after a contact time of two hours. The samples were then stored in amber jars with Teflon coated lids in the dark at 25°C for six days prior to being tested for THM and HAA9. This Study’s investigation into potential pH excursion, arsenic mobilization, and disinfection byproduct formation because of PFAS treatment will inform the design of any future treatment processes. This more complete look at the water quality will allow for a more fully integrated and optimized water treatment design if a PFAS treatment program is implemented.