Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7b. Ex Situ PFAS Treatment Approaches

Formatted Title:

Treatment Train for Removing PFAS from High Concentration Stormwater

Background/Objectives:

Historic fire training activities using aqueous film forming foam (AFFF) have resulted in PFAS releases to soil and groundwater which has migrated to a county stormwater drainage system (SDS) via stormwater runoff and venting groundwater impacted with high (part per billion [ppb]) concentrations of PFAS. The SDS discharges to a municipal sanitary sewer and the effluent of the wastewater treatment plant (WWTP) discharges to a river which is considered a drinking water source. Perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and PFHxS are the primary focus of regulatory concern. Concentrations of PFOS, PFOA, and PFHxS in the SDS near the site boundary are generally 1,500, 100, and 400 parts per trillion (ppt), respectively. Identification of PFAS impact in sediment and stormwater has become more common due to regulatory agency sampling requirements and permit renewal requiring PFAS analysis. Treating impacted stormwater presents significant challenges including the need for pre-treatment and the likelihood of high flow volumes from heavy storm events. This presentation is a case study of an ex situ treatment system that captures stormwater from the SDS and utilizes a robust pre-treatment approach followed by ion exchange (IX) resin treatment before discharging back to the SDS.

Approach/Activities:

IX resin was selected as the PFAS removal technology due to its smaller footprint for higher flowrates. However, PFAS removal by IX resin is more sensitive to influent water quality than granular activated carbon and requires robust pre-treatment. The treatment train for the site includes an18,000-gallon weir tank to settle out solids, a three-vessel sand filter system, a 3,000-gallon backwash tank, a bag filter assembly, and three 1,000-pound vessels of single-use IX resin. The entire system is winterized (including insulation and heat tracing) to allow year-round operation. The stormwater collection system includes installation of a sump and downstream weir in the SDS, submersible pumps, and piping. Prior to startup of the full treatment train, stormwater was pumped through the pre-treatment portion of the system alone and sampling confirmed that water quality was suitable for the IX resin vessels. The current system is designed to handle approximately 100-gallons per minute of stormwater, which is expected to treat the SDS flow during dry conditions (venting groundwater) as well as small storm events. There are already plans to expand the system to accommodate treatment of larger storm events. Operation of the system began in April 2023 with weekly O&M visits, biweekly performance sampling, and biweekly resin sampling.

Results/Lessons Learned:

Based on the first 5 months of data, the system is achieving PFAS discharge criteria (PFOS < 65 ppt), with the PFOS concentration in the system effluent generally non-detect (less than 1 ppt). However, high differential pressure (DP) across the lead IX bed is being observed and breakthrough of the lead IX vessel was sooner than expected. Results from performance monitoring, resin sampling, and particle-size analysis indicated that additional pre-treatment for colloidal particles, organics, and iron/manganese may be necessary to reduce DP across the first IX vessel and increase longevity of the resin. Efforts are currently underway to evaluate pre-treatment optimization options and select an approach for implementation in February/March. At the time of the conference, we will have more than 1 year of system operating and performance data to share and can discuss lessons learned for operating, maintaining, and evaluating performance of a stormwater PFAS treatment system. In addition, design, implementation, and results of additional pre-treatment will be shared.

Menu

Matt McCloskey