Field demonstration of polymer stabilized activated carbon for in situ treatment of per- and polyfluoroalkyl substances (PFAS)-impacted groundwater.

 

 

This study focuses on per- and polyfluoroalkyl substances (PFAS), a class of emerging contaminants of concern in the environmental field in recent years, with particular emphasis on the efficient and cost-effective remediation of PFAS-contaminated groundwater. Although the traditional Pump-and-Treat (P&T) technology is widely used, it suffers from drawbacks such as long operational cycles and high costs. This study proposes and validates an in-situ remediation technology involving the injection of Colloidal Carbon Product (CCP, a polymer-stabilized activated carbon), evaluating its feasibility and effectiveness in treating PFAS-contaminated groundwater through laboratory and field Push-Pull tests.

In the laboratory-scale aquifer model, researchers used PFAS-spiked synthetic groundwater and sediment collected from the field to observe PFAS removal efficiency after injecting CCP suspension. Results showed that the technology achieved a removal rate of 90.9% to 99.9% for six PFAS compounds, verifying its strong adsorption performance. Subsequent field Push-Pull tests were conducted at a U.S. Navy fire training area (a site with significant PFAS contamination), where approximately 1,900 liters of CCP suspension was injected into the underlying aquifer. Sampling and analysis were performed at 3 months and 10 months post-injection, revealing that the total PFAS concentration in groundwater decreased from >50,000 ng/L to below the detection limit, achieving a removal efficiency of up to four orders of magnitude.

Furthermore, an economic assessment was conducted, indicating that the total cost of this technology over a 20-year operational period is approximately $1.47 million, with long-term operational costs less than half of those associated with traditional P&T systems. The study also investigated the potential formation risk of the byproduct N-nitrosodimethylamine (NDMA) and proposed preventive recommendations.

Overall, this study is the first to validate the effectiveness of polymer-stabilized activated carbon (CCP) injection for remediating PFAS-contaminated groundwater under field conditions, demonstrating its practical potential for widespread application.
 

 

 

Figure 1. Panel A shows the concentrations (ng/L) of six perfluoroalkyl substances (PFBS, PFHxS, PFOS, PFHxA, PFHpA, and PFOA) in groundwater samples extracted from Port 7 of the aquifer unit during the "pull" phase of the push-pull feasibility test. A total volume of 200 mL of groundwater was extracted, accounting for 15.7% of the aquifer unit volume (1275 mL). PFAS concentrations in the samples were measured at 10 mL intervals.

 

Figure B shows the average PFAS concentrations in the groundwater of the aquifer unit before the push-pull test, the average PFAS concentrations in the groundwater extracted from Port 7 during the "pull" phase of the test, and the average PFAS removal efficiency of the CCP push-pull test (%;right vertical axis).





Figure 2. Target PFAS concentrations in groundwater samples collected during the "pull" phase of the push-pull field demonstration. The point labeled "0 L Extracted" represents the PFAS concentrations in the area prior to the push-pull test. Two "pull" operations were conducted after the injection of 1,900 liters of CCP (5,000 mg/L polyDADMAC + 5,000 mg/L PAC): the first operation was performed 3 months post-injection, with 2,850 liters of groundwater extracted; the second operation was conducted 10 months post-injection, with 1,900 liters of groundwater extracted. Note: Only PFAS detected before and after the push-pull test are plotted in the figure.


 

 

The innovation of this study is reflected in three aspects: technical concept, experimental design, and practical validation.

Firstly, the authors propose the idea of using a polycationic polymer (polyDADMAC) to stabilize powdered activated carbon (PAC) for forming an injectable CCP system, addressing the limitations of traditional activated carbon in subsurface media such as excessive particle size, proneness to clogging, and uneven distribution. This system not only maintains a stable particle size (average 225 nm) but also forms a Permeable Adsorptive Barrier (PAB) in the aquifer, enabling long-term in-situ capture and immobilization of PFAS.

Secondly, in terms of experimental method innovation, the study combines laboratory simulation with field "push-pull" testing. The former is used to optimize the formulation, control particle size and concentration, while the latter conducts large-scale validation at a real contaminated site (a U.S. Navy fire training area), establishing a closed loop from experiment to application. Results show that the technology achieves a significant four-order-of-magnitude reduction in PFAS concentrations in the field, and maintains extremely low concentrations 10 months after injection, demonstrating excellent durability and system stability.

Thirdly, the study conducts a systematic assessment of costs and byproduct risks, revealing that the long-term operational cost of the CCP in-situ remediation technology is more than 50% lower than that of P&T, offering economic advantages. Meanwhile, the authors note that polyDADMAC may generate NDMA under specific conditions, proposing that chlorine-containing or chloramine-containing water sources should be avoided for preparing CCP suspensions, and NDMA precursor testing should be performed prior to field application. This safety discussion expands the research from mere pollution remediation to the level of sustainability and risk control.

In summary, this study is the first to validate the feasibility and high efficiency of the polymer-stabilized activated carbon in-situ injection method under field conditions. It provides a replicable, low-cost, and sustainable new technical pathway for PFAS-contaminated groundwater remediation, laying a scientific foundation for future promotion and application in complex geological formations and broader pollution scenarios.