Effective Treatment Methods of PFAS
In the water industry, PFAS has become a common topic. PFAS is a categorization for a range of over four thousand substances with various physical and chemical properties. PFAS is the abbreviation for Perfluoroalkyl and Polyfluoroalkyl Substances which are man-made chemicals that are difficult to break down due to the carbon and fluorine bond. These substances can be found in common household items such as pizza boxes, cookware coating, cosmetics and dental floss. There are also utilized for industrial activities like foam used in fire-fighting, paints and metal plating.
PFAS is categorized in two sections; long chain and short chain. Long chain PFAS is more highly regulated as it is more common. Long-chain PFAS has also been found to bioaccumulate meaning it can compound in the human body. Long-chain PFAS has been found to be toxic for wildlife and harmful to humans. Short-chain PFAS is less regulated as it does not stay in the human body and therefore is less likely to have long-term effects. PFOA (perfluorooctanoic acid) and PFOS (perfluoro octane sulfonic acid) are both types of PFAS identified because of their potential health effects. These classifications have garnered additional attention beyond that of the category as a whole. PFOA chemicals are used to create coatings and products that resist heat, oil, stains, grease and water. PFOS has been deemed a global pollutant and is no longer produced in the United States, it was most often used in non-stick and stain resistant products.
Recently, a national, legally enforceable standard has been released surrounding allowable levels of PFAS in water. Released April 10th, 2024, public water systems have three years to monitor practices and inform the public of the measured PFAS chemicals in their drinking water. If the levels found are not within the standards, these systems have five years to correct and upgrade facilities as needed. The new standards include various classifications of the chemicals: PFOA, PFOS, PFNA, PFHxS, PFBS and Gen X., limiting amounts to 4 parts per trillion for some chemicals.
PFAS have been produced since the 1940s and are still used today due to their wide applicability. The strong bond obstructs them from being removed from water via typical water treatment, creating a need for stronger removal methods. Several methods have been found, and the EPA is continuing research to find more efficient and effective processes. Water samples should always be collected before large scale treatment as current PFAS removal methods do not remove all other contaminants from water.
The most popular options for PFAS removal include granular activated carbon, anion exchange and reverse osmosis. Each process has benefits and is chosen for the amount of water needed to be treated and other compounds present in the water. Feed water quality is essential to choosing the correct PFAS removal method. Organic compounds, hardness and metals can all effect PFAS treatment.
PFAS treatment often occurs at water treatment facilities but can also be found at point of use systems inside buildings and homes in more rural areas. The EPA has released lifetime advisory levels for PFAS exposure from drinking water. The level is set at a concentration that protects against all effects of PFAS in humans.
One method of PFAS removal uses activated carbon to adsorb contaminates. Granular activated carbon (GAC) or powder activated carbon (PAC) methods utilize large tanks with layers of carbon called beds that the water filters through with the help of gravity. PFAS is contained in the granulated carbon as the water passes through. This process is measured by empty bed contact time (EBCT) the ratio of the volume of the bed divided by the flow rate of the system. EBCT for activated carbon is around 10-20 minutes. Like all methods of PFAS removal, it is important to be aware of other contaminants present in the water. Various types of activated carbon may be better suited depending on the quality of the water and will result in different EBCT. This method is more cost effective, but facilities must compromise as the treatment time is longer than others and the equipment required demands extensive space for the tanks. GAC is proven to remove between 80-99% of PFAS depending on the substances present.
The GAC material becomes exhausted after multiple treatments and must be regenerated. GAC regeneration requires high heat to destroy the components that were adsorbed in the carbon. Most PFAS removal techniques produce waste. The EPA is researching multiple methods of PFAS waste elimination including incineration
Another option for removing PFAS from water is through using ion exchange (IX). This process utilizes resin to produce negatively charged ions to separate the bonded carbon and fluorine by replacing the undesirable ions. IX is the optimal choice for short-chain PFAS as carbon cannot eliminate short-chain PFAS. IX also utilizes smaller equipment than the large tanks required for GAC. The treatment rate for PFAS is also measured by EBCT; IX EBCT ranges from 2-5 minutes. It is important to remove suspended solids and organic matter from the water before the IX process, as the presence of these materials will disrupt the removal of PFAS. IX is proven to remove 94-99% of PFAS from water, working most effectively against short-chain. The resin chosen for IX is the driving force for the cost of the process.
Filtration with high-pressure membranes, most commonly, reverse osmosis is another option for removing PFAS from water. This option is most practical for small scale treatment like single households. Contaminated water is pushed through a semi-permeable membrane that removes the PFAS. Membrane filtration is the most effective choice for removing PFAS from water ranging from 93-99.9% effective but is also the costliest. A large portion of the water initially treated, about 20%, is discarded as waste. Making this option inefficient for large scale treatment.
All of these methods also produce waste that needs to be discarded. As we learn more about PFAS, more effective treatment methods will emerge. PFAS is actively regulated and researched by the EPA. The United States has developed and published various methods to support the analysis of PFAS in water and how to properly dispose of the waste. Read more about disposal options released by the EPA here.
If you are interested in learning more about PFAS treatment and other contaminants of emerging concern, watch our on-demand webcasts from the 2023 Sustainable Water Compliance Summit. And tune in to the Addressing Emerging Contaminants in the Water Industry Panel at our 2024 Sustainable Water Compliance Summit, April 24th 2024.