Innovative Approaches to PFAS Control in Stormwater and Industrial Discharges

Introduction
As PFAS abatement strategies are contemplated, impacts to NPDES permits raise questions of the financial and performance responsibility to remove them from wastewater effluents. While the US EPA seeks to hold polluters accountable, the onus is on utilities to identify contamination levels and search upstream for the source. Technologies such as GAC and IX used in treated effluent to remove low-level PFAS may not be suited for the higher-strength contaminants found upstream. This paper presents a novel approach to remove high-strength PFAS at the source which can be used as a tool for utilities to work with polluters to develop a sustainable strategy to prevent PFAS from entering drinking source waters and wastewater collections systems from industry.

Background
The Environmental Security Technology Certification Program (ESTCP) is research initiative managed by the DoD to promote innovative technologies to improve environmental sustainability. Under this program, testing of a novel, micro-adsorbent and separations technology was conducted to remove high-PFAS levels from contaminated stormwater. The 2-year program validated the technology's ability to meet the US EPA Regional Screening Limits (RSLs) from influent PFAS levels of up to 10,000 ng/L. The PFAS removal system (AquaPRS) was able to adsorb the six priority compounds identified in the USEPA's UCMR3 at levels 275 times greater than observed for GAC. Lifecycle cost comparisons performed with GAC and IX were favorable for the AquaPRS, revealing payback periods of < 24 months. High unit adsorption rates resulted in reduced waste product volumes that are amenable to treatment with destructive technologies. Work continues with the modification of the existing AquaPRS process to utilize Pile Cloth Media Filtration (PCMF) for the separation process, which has been already demonstrated to handle wet weather flows.

Methods
Initial development testing involved both bench top and field pilot trials were conducted using production level sorbent media and separation technologies. The sorbent is carbon-based with a mean particle diameter below 1 µm and held in a concentrated suspension. The sorbent slurry is rejected by a robust, ceramic separator with 0.1 µm aperture. The AquaPRS system (Figure 1) is operated in cross-flow, which enhances contact between the contaminant and the sorbent material. Reaction times from 5 to 20 minutes were evaluated alongside sorbent levels from 1 to 40 g/L. A key element of cross-flow operation is the scouring effect of the sorbent. In lieu of periodic wasting, a brief back-pulse dislodges solids buildup in the separator feed channels using treated filtrate and returned to the sorbent reactor for contact with the influent. The sorbent is held usually 1 to 2 weeks between replacements. The high adsorption capacity reduces the sorbent mass compared to GAC and the slurry matrix can be replaced automatically in less than 1 hour. The wasted media represents less than 40 gals per 1 MGD treated resulting in lower disposal costs compared to other adsorptive technologies. Many tests were conducted over a 9-month period at the Horsham Air Guard Station (HAGS) using a dual-train pilot system on surface water.

The continued development involves both bench top and field pilot trials using production level the modified AquaPRS system is operated with PCMF for separation of the sorbent and turbidity. Contact is achieved with high energy flocculation, which enhances contact between the contaminant and the sorbent material. Reaction times from 5 to 20 minutes were evaluated alongside sorbent levels from .2 to 1 g/L.

Findings
HAGS testing proved challenging due to high sediment loading during wet weather events. Use of PCMF for pre-treatment effectively reduced turbidity (Figure 4) and permitted sustained operation of the AquaPRS. Single-stage AquaPRS reduced the combined UCMR3 compounds from 8,000 ng/L to 40 ng/L at a specific adsorption rate (SAR) of 146 µg PFAS removed per gram of sorbent (Figure 5). In comparison, rapid small-scale testing (RSST) with GAC yielded a 2.1 µg PFAS/g carbon SAR, and only 90% removal of the UCMR3 compounds exceed the 40 ng/L target. Dual-stage treatment was able to reduce UCMR3 compounds further, with all compounds below their limit of quantitation except for PFBS (13 ng/L) and PFHpA (12 ng/L). Despite the higher initial capital cost, the substantially higher SAR exhibited by the AquaPRS resulted in an 8-month payback period when compared to GAC. The preliminary bench scale testing has been completed for the testing with PCMF. The field tests will be completed by June 2025 as part of an ESTCP project. The modified AquaPRS process reduced the combined regulated compounds from 100 ng/L to 4.6 ng/.

Significance
Access to effective, economical and sustainable technologies that are designed for higher concentrations will be required. The AquaPRS process concepts offers a viable alternative that can augment a utility's toolbox. Significantly reduced sorbent requirements will reduce disposal costs and facilitate ultimate PFAS destruction. The adsorptive technology can be coupled with pre-treatment technologies, such as biological treatment or filtration depending on the nature of the waste. The continued development of the modified AquaPRS could lead to the implementation in tertiary part of a wastewater facility due to the proven experience with PCMF in the facility.