Navigating PFAS: Treatment Strategies for Achieving 2029 Compliance

From absorption systems to high-pressure membrane solutions, water process engineers leverage several technologies for removing PFAS from drinking water, each with varying degrees of effectiveness.

Granular activated carbon (GAC) is one of the most common methods of PFAS removal. This technology adsorbs PFAS compounds into carbon media, effectively trapping them. With an empty bed contact time (EBCT) of 10 minutes per vessel, GAC can effectively remove PFAS, although its efficiency may vary based on water quality and the specific PFAS compounds present. One advantage of GAC is its ability to remove additional contaminants, such as chlorine, making it a multi-functional solution. However, GAC requires periodic backwashing to maintain performance and regular replacement when it reaches the in-pressure differential.

Ion exchange (IX) technology uses resin to target and remove PFAS by exchanging ions in the water with ions in the resin. Unlike GAC, IX does not require frequent backwashing. However, it is not chlorine-tolerant. IX systems typically have shorter EBCTs than GAC (2.5 to 5 minutes), making them more effective for certain applications. Still, IX systems require careful water chemistry monitoring, particularly for compounds like sulfates and nitrates and particular elements like iron and manganese, which may affect treatment performance.

While clay media is less common, it is still a viable option for removing PFAS from water. Like GAC, clay media adsorbs PFAS compounds onto its surface, requires backwashing, and is chlorine-tolerant up to one part per million. However, there are currently limited potable water installations using clay media, and its long-term effectiveness is still being evaluated.

Reverse osmosis (RO) and nanofiltration (NF) are high-pressure, membrane-based filtration technologies that remove PFAS based on the size of the molecules. Both methods force water through a semi-permeable membrane, trapping larger PFAS molecules. However, RO has tighter membranes and can remove up to 99% of PFAS, while NF typically removes 70-90%. Both technologies produce a concentrated effluent that requires proper disposal to prevent PFAS from re-entering surface waters and the environment. However, RO is more energy intensive and may also remove beneficial minerals like fluoride and iron from the water.

Every water source has a unique profile, including varying levels of PFAS and other contaminants. That’s why pilot testing is a great option for water suppliers before committing to a full-scale PFAS treatment solution. Pilot testing allows organizations to evaluate different treatment technologies under local water conditions, which may significantly impact the treatment outcomes. It allows for: 

• Tailored treatment solutions that help utilities assess how each technology performs with their specific water quality. 
• Treatment efficacy evaluation to determine how well specific treatment media or methods remove various PFAS compounds and how they may affect other emerging contaminants.  
• Cost optimization, including operating costs like energy use and efficiency, media replacement, and waste management. 
• Performance monitoring, which can highlight issues like media fouling, pressure reduction, or contaminant breakthrough, and enable adjustments before full-scale implementation. 
• Regulatory compliance can be demonstrated on a smaller scale, allowing water suppliers to refine their treatment processes and reduce the likelihood of regulatory violation.

In the City of Eau Claire, Wisconsin, we recently conducted a pilot test comparing GAC and IX at a water treatment plant with 16 wells operating at 18 million gallons per day. The current water treatment process involves pre-chlorination, flocculation, advanced settling, gravity filters, clearwell distribution, and chlorination disinfection. Chemical treatment includes lime for softening, sodium hypochlorite for disinfection, potassium permanganate for water purification, and fluoride and ammonia to improve disinfection. Our experience with this facility demonstrates how pilot testing revealed insights into essential water quality and treatment efficacy.

In this case, GAC was initially expected to be the most cost-effective treatment solution, especially given the treatment plant’s use of well water. However, pilot testing revealed that high levels of total organic carbon (TOC) in the water significantly reduced GAC’s effectiveness. The TOC compounds, which are larger than PFAS molecules, saturated the media, preventing it from effectively removing PFAS. In fact, the GAC columns showed PFAS breakthrough at around 12,000 bed volumes, far earlier than expected. By contrast, IX resins, which specifically target PFAS, were not affected by high TOC levels. Some columns showed no detectable PFAS breakthrough even after 130,000-bed volumes, leading to the recommendation that the water treatment plant switch to IX for PFAS removal.

Following the initial water quality testing, we performed additional testing for chloride and sulfates since they may affect the media efficacy. In summary, the pilot involved: 

• 16 wells, separated into six north and 10 south. 
• GAC and IX media columns.  
• Two influent supplies. 
• Daily, weekly, and bi-weekly testing frequency. 
• 10-month timeframe.

• Thorough Pilot Testing: Conducting pilot tests on multiple water sources is essential to understanding the impact of water quality on treatment performance. Factors like TOC levels can significantly affect the lifespan and effectiveness of GAC media.  
• Data Collection and Monitoring: Routine sampling and monitoring during pilot testing are critical for accurate analysis. Though you may analyze every two to three weeks, weekly samples can provide a failsafe in case of laboratory issues or equipment malfunctions. 
• Consider Multiple Treatment Options: While GAC may be the most familiar solution to destroy PFAS, other technologies, such as IX and clay media, may offer better performance, depending on specific water quality and regulatory requirements.  

Cost is always an important factor when selecting a PFAS treatment technology. Although GAC is typically more affordable when it comes to media costs ($2 per pound vs. $4 to $12 for IX resins), it often requires more frequent replacement. In contrast, IX has a longer media lifespan, but higher costs may offset the reduced maintenance savings. 

Energy costs are also a consideration for membrane-based technologies like RO and NF, as these systems are more energy-intensive compared to GAC and ion exchange. Ultimately, the best choice will depend on the specific water quality conditions, regulatory requirements, and available budget.