PFAS and Our Water Supplies
By Craig Nowak, PE – As a nation, we’re learning more and more about substances that are impacting both water and wastewater systems. PFAS, or per- and polyfluoroalkyl substances, caught my attention a few months ago, which led to an article on what we know – or more importantly, what we don’t know – about them.
Several Google searches will show you that PFAS are of concern because of their potential human health risks, which are now being studied, and their widespread use dating back to the 1940s. While we address many other issues in water supply and wastewater treatment design, our industry is now also taking PFAS into account.
Many national organizations such as The American Water Works Association (AWWA) have issued PFAS briefings to help guide our future design projects. Details from this 2019 report are the source of much of the information provided here.
The Connection to Our Water Supplies
Common depositories of PFAS are industrial sites, landfills, and sites where firefighting foams are used (both training and actual fires). Unfortunately, PFAS are not always contained at these sites and can leach into groundwater or be carried away with storm runoff. In addition, PFAS are found in products we use every day including packaging materials, non-stick coatings, water-repellant coatings, apparel, and carpets.
Regarding water supplies, PFAS can enter our drinking water sources and, if not removed during treatment, continue into potable water systems. After the water is used, PFAS may also enter our wastewater collection and treatment systems. Most wastewater treatment removes some portion of PFAS from the water and traps it in the biosolids or sludge. The effluent containing the remaining PFAS may be discharged to rivers, lakes, and groundwater, while sludge is typically sent to a landfill or applied to agricultural land. As the cycle continues, PFAS can spread and build up throughout every aspect of the environment, including our own bodies.
EPA and the US Centers for Disease Control and Prevention characterize PFAS human health effects as uncertain. There are studies of laboratory animals that indicate PFAS compounds could impact growth and development, reproduction, thyroid function, the immune system, and the liver. More studies are necessary to determine the human health effects and what reasonable PFAS limits should be with respect to potable water. For more information and a closer look at what’s being done on the federal level, an EPA publication that was released in February 2020, EPA PFAS Action Plan: Program Update, addresses the development of PFAS drinking water standards. For those interested in the regulation process, please see page 7 of this document.
Three Ways to Treat Water Systems
At this time, there are three filtration treatment methods identified to reduce PFAS levels in the water treatment industry. These include activated carbon, anion (ion) exchange, and membrane filtration. As with any treatment technology, there are advantages and disadvantages specific to each water system. Each of these methods brings with them capital costs, operation and maintenance costs, and the need to manage the residuals which include the PFAS compounds.
Granular Activated Carbon
Granular activated carbon (GAC) is widely used for PFAS removal and offers potential high removal rates. The carbon requires regeneration for reuse but regenerated carbon may not be as effective as virgin carbon. Exhausted GAC is a waste when disposed of – which in turn leads to another potential pollutant source.
Anion exchange can be more effective than GAC treatment when using adsorption resin targeting specific PFAS compounds. Exchange rates are dependent upon many factors such as the resin and the treatment system itself, as well as the PFAS levels. Adsorption media will be exhausted and need to be replaced periodically similar to GAC.
Membrane filtration is applicable for groundwater sources or following pre-treatment in a surface water treatment process with broad-spectrum treatment capabilities. Membrane filtration brings with it the need to dispose of rejected water containing high concentrations of the removed compounds. In addition, a considerable volume of the supply water is lost in the process, rejected as brine, and not provided to users. Reverse osmosis and nanofiltration are common methods of membrane filtration. Each type requires expensive equipment and has high energy requirements related to pumping.
Costs Still in Question
AWWA has estimated capital costs for the treatment of PFOA and PFOS, the two PFAS compounds, in the US. These costs vary widely, dependent on treatment associated with meeting potential MCLs. EPA’s lifetime health advisory level is 70 ng/l; AWWA estimates US capital costs would exceed $3 billion to treat to this level. Some states have established a lower level of 20 ng/l, for which AWWA estimates a capital cost of $38 billion. Should a potential treatment technique standard be established, this capital cost estimate balloons to $370 billion. As you can see, the toxicity and potential regulation unknowns produce a wide range of treatment costs that should be tracked closely in the next few years in order for funding discussions to begin.
It’s Time to Learn More About PFAS
Much is to be determined and much is to be learned because much is unknown in this PFAS arena. The saying, “taking a drink from a fire hydrant” certainly applies here. Regardless, as professionals working to ensure safe and reliable drinking water, we must become familiar with PFAS, their presence in our state and our locality, and the actions our state and local regulators are taking to monitor, mitigate, and regulate them.
Craig Nowak, PE is a Senior Water-Wastewater Engineer and the Great Falls Office Operations Manager. He was recently honored with the 2019 American Water Works Association, Montana Section, George Warren Fuller Award. This is the highest award an engineer can receive in the field of water engineering.
Technical reviews of this article provided by Rika Lashley, PE, and Eric Blanskma PE.