PFAS (per- and polyfluoroalkyl substances) have established themselves among the most scrutinized contaminants in drinking water. Commonly referred to as “forever chemicals” because of their extraordinary persistence, they resist breakdown in both the environment as well as the human body. The U.S. EPA’s newly implemented maximum contaminant levels (MCLs) for several PFAS compounds are putting pressure on utilities to act fast to meet these new requirements.

While much of the focus is on removal technology (i.e. granular activated carbon — GAC, ion exchange, membranes, etc.), flow control is crucial in ensuring these systems can operate to their maximum effectiveness. Key factors such as maintaining contact time for adsorption media, preventing channeling in treatment beds and controlling residence time in destruction systems are dependent on precise hydraulic management to ensure PFAS treatment success.

The importance of flow in PFAS removal

PFAS are generally categorized as long-chain or short-chain, each form behaving differently in treatment systems. Long-chain PFAS are more readily adsorbed onto media like GAC, while short-chain versions are more mobile and harder to capture. In both forms, system design considerations such as empty bed contact time (EBCT), flow rate and pressure directly influence treatment efficiency.

PFAS removal across technologies such as GAC, ion exchange and membranes depend on effective flow management. This will help prevent channeling in adsorption systems, maintain optimal EBCT, regulate feed pressures in membrane processes and control residence time in destructive treatments. When managed effectively, these factors ensure that all treatment stages operate at full capacity, and the risk of breakthrough is minimized.

Meeting the latest regulations

The latest U.S. drinking water regulations require utilities to meet low parts-per-trillion limits for certain PFAS. Compliance depends on both the employment of appropriate removal technology and ensuring that effective flow control measures are put in place to achieve the necessary capture or destruction performance. In many cases, this will require retrofitting existing plants to enable better flow balancing and monitoring.

Core PFAS capture technologies and flow control requirements

Granular activated carbon (GAC)

GAC treatment requires a precisely calculated EBCT — typically in the range of 10 minutes to 20 minutes — to optimize adsorption. If EBCT is too fast, PFAS slip through will occur; and if it is too slow, costs will increase unnecessarily. In addition, ensuring even distribution across the bed will help prevent channeling, which can leave untreated “streaks” of water.

To maintain consistent feed rates and ensure proper EBCT across GAC beds, solenoid valves are often used. These electromechanical devices precisely control liquid flow through an electrically actuated plunger, which facilitates rapid adjustment and accurate flow distribution.

Ion exchange

Treatment through ion exchange involves the use of resins to exchange PFAS ions with harmless ones. Flow distribution and velocity are also critical here. Uneven or excessive flow reduces contact efficiency and can allow shorter-chain PFAS to bypass the resin.

Preventing uneven distribution among multiple resin beds can be achieved using balancing valves, such as butterfly valves, which regulate flow by rotating a disc within the fluid path to control flow rate evenly. These valves help maintain uniform contact across resin vessels.

High-pressure membranes

In these applications, membranes act as physical barriers, removing a wide range of PFAS molecules. Pressure control is essential to prevent fouling, while recovery rate and concentrate management depend on accurate flow balancing.

High-pressure pumps with precise flow characteristics, such diaphragm metering pumps, are essential for regulating feed pressure and volume in membrane systems. These electronically actuated pumps operate reliably across variable pressures to stabilize performance.

From capture to destruction

While most systems focus on capturing PFAS, there is growing interest in destruction technologies such as electrochemical oxidation, plasma treatment, supercritical water oxidation and advanced oxidation/reduction. These methods require highly controlled feed rates and residence times to ensure complete molecular breakdown without generating harmful byproducts.

Designing PFAS treatment trains

Many utilities now use treatment trains that combine methods, for example, ion exchange resins followed by nanofiltration membranes, or GAC followed by an electrochemical polishing step. The choice depends on source water chemistry, the types of PFAS forms present and cost constraints. Flow replication from pilot to full scale is critical to ensure that the system meets MCL targets consistently.

Smart monitoring for continuous optimization

Advances in smart water technology, real-time flow and pressure sensors, automated EBCT control and breakthrough alarms are helping utilities run PFAS systems more efficiently. By combining continuous monitoring with predictive analytics, operators can anticipate media exhaustion, schedule replacements and fine-tune flows to minimize cost and environmental impact.

Cost, risk and lifecycle decisions

Flow rates influence every part of the cost equation, from energy consumption in membrane systems to waste disposal volumes in GAC and ion exchange processes. Designing for optimal hydraulics not only improves PFAS removal, but it also reduces lifecycle costs and environmental footprint.

Conclusion

As PFAS regulations become increasingly stringent and detection technologies improve, there is a growing push toward standardized, flow-optimized treatment trains within the water industry. Future developments will likely include better solutions for short-chain PFAS, real-time contaminant sensors and more full-scale data to guide designs.