Granular activated carbon (GAC) treatment is currently the most common approach to remove per- and polyfluoroalkyl substances (PFAS) from water, especially perfluorooctane sulfonic acid (PFOS) and perfluorooctanic acid (PFOA). Recent studies have shown relatively short breakthrough times for certain PFAS when using GAC and there is a significant need to develop more cost-effective treatment solutions for the removal of a broad-range of PFAS (e.g., short-chain perfluoroalkyl acids [PFAAs] and precursors). As a result, a recent collaboration between Aqua-Aerobic Systems, Inc. (AASI) and the Colorado School of Mines evaluated the use of sub-micron powdered activated carbon (SPAC) in conjunction with ceramic microfiltration (CMF) to remove PFAS from various impacted water sources during a laboratory study. These laboratory studies indicated that SPAC had a significantly higher sorption capacity (> 2,000 times) for certain PFAS compared to conventional GAC. The objective of the project was to demonstrate and validate the application of the SPAC-CMF treatment approach to reduce the total life-cycle cost of treating groundwater impacted with PFAS. This demonstration was conducted at Horsham Air Guard Station (AGS) and former Naval Air Station (NAS) at Willow Grove in Horsham, Pennsylvania.
The approach focused on a combination of proven CMF and SPAC technologies into a new configuration specifically designed to treat water resources highly impacted with PFAS (> 1 microgram per liter [µg/L]) with a prototypical system at a fidelity level that could be replicated at other sites. This AquaPRS technology provides an alternative to GAC and ion exchange (IX) systems based on treatment efficacy and cost performance using life cycle cost analyses. The SPAC-CMF system consisted of cloth media filters to remove particulates, a sorbent reactor in which SPAC is mixed with influent surface water, followed by a CMF filter to separate PFAS-sorbed SPAC from the water matrix to obtain PFAS-free water. The SPAC is recirculated back into the sorbent reactor to continue the treatment cycle.
The first study conducted at Horsham AGS demonstrated and validated the SPAC-CMF treatment approach using a mobile pilot system, while the second study (conducted at the former NAS at Willow Grove) provided further optimization of cost, performance, and scalability. At Horsham AGS, 13 tests were conducted over nine months using a dual-train pilot, with 10 tests conducted with treatment systems in parallel and the remaining three conducted in series. At Willow Grove, 10 tests were conducted over a six-month period.
The technology was validated by measuring the specific adsorption rate (SAR) of various PFAS on SPAC, followed by its comparison to GAC and IX. Costs of the three treatment systems were compared to estimate a payback period for the SPAC-CMF system compared to GAC and IX. At 10 percent breakthrough, the SAR of SPAC-CMF for the combined concentration of the U.S. Environmental Protection Agency’s Third Unregulated Contaminant Monitoring Rule (UCMR3) compounds was nearly 1,000 times higher compared to those treated with GAC. At 40 nanograms per liter (ng/L) breakthrough for combined UCMR3 compounds, a single-stage SPAC-CMF system at Horsham achieved 146 µg PFAS/g sorbent SAR, while a dual stage SPAC-CMF system at Willow Grove achieved 2,128 µg PFAS/g sorbent. The SPAC-CMF system showed a payback period of three months compared to a comparable GAC system, while with an IX system, the payback period ranged from 24 to 36 months.
The benefits of the SPAC-CMF system are its effective performance in the presence of co-occurring chemicals, adaptability to changing conditions, limited downtime for sorbent replacement, resistance to biofouling, small footprint, and reduced disposal requirements. The reduced disposal requirements are due to the ability of the SPAC-CMF system to dewater the sorbent resulting in a waste generation of just 0.002 percent of the total volume of water treated. Based on the treatment efficacy and cost performance, the SPAC-CMF system is positioned as an alternative to GAC and IX systems. (Project Completion - 2023)
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