With our world waking up to the realization some everyday products contain forever chemicals known as PFAS, per- and polyfluoroalkyl substances, scientists and engineers are working to find the most cost-effective, efficient, and environmentally responsible way to remediate them. The financial and technical challenges of remediating PFAS are cause for serious concern. With over 2,300 contaminated sites across the United States to clean-up, we need an efficient method for removing these toxic chemicals from our water, soil, and biota. But remediation efforts currently face two enormous hurdles: who will pay, and how will we clean up the environmental mess we are just beginning to uncover?
Part of the difficulty with PFAS remediation stems from the chemistry. PFAS contain carbon-fluorine bonds—some of the strongest bonds found in nature. This resiliency makes PFAS ideal for heat-resistant products like firefighting gear, water, oil, and grease repellent products like food wrappers, carpets, water-proof clothing, and non-stick cookware. The widespread usefulness and commercial profitability of PFAS has kept them in production since the 1940s and facilitated the development of over 3,000 different compounds. But the same chemical stability that makes PFAS useful also makes them resistant to the natural processes that break down other pollutants. Once released into the environment, these toxic chemicals bioaccumulate in the tissues of plants and animals and can disseminate far beyond the original point of exposure. In many ways, PFAS are a remediation nightmare: they are difficult to destroy, they are everywhere, and there is often no clear point of contamination.
Given the prevalence, variety, and resiliency of PFAS, remediation technologies face severe implementation challenges. The ideal technology would filter for thousands of different PFAS compounds; efficiently separate PFAS molecules from other elements and contaminants; destroy PFAS without creating hazardous byproducts; and treat large volumes of water with minimal overhead and maintenance costs. Unfortunately, no “silver bullet” remediation technology can check off every item on the list. Instead, most PFAS experts believe that using available techniques in concert together is the best way forward for our environment and our wallets.
Many large-scale PFAS operations already use a divide-and-conquer approach towards cleaning up contaminated sites. The remediation process is usually split between separation and destruction techniques. During separation, on-site facilities isolate PFAS from the contaminated water, capture PFAS in a solid or liquid state, and then transfer the toxic waste off-site for storage or destruction. Although properly stored PFAS waste does not pose an environmental threat, there are concerns about long-term sustainability; transferring, storing, and monitoring toxic waste requires extra equipment and incurs additional expenses. Given the fiscal and sustainability issues stemming from storing PFAS waste, many experts are working on creating compatible destruction techniques. These experimental technologies could theoretically destroy PFAS molecules without releasing hazardous byproducts or breaking PFAS down into ever-smaller parts. While most destruction technologies are not ready for large-scale commercial use, each successful laboratory pilot study offers another tantalizing glimpse into a PFAS-free future.
Of the PFAS treatments currently available and employed, the most effective methods combine separation and destruction technologies. The three main separation technologies--Granted Activated Carbon (GAC), ion exchange resin, and high-pressure membranes--use adsorption to isolate and capture PFAS molecules. The adsorption process accumulates a substance, like PFAS, at the interface between liquid and solid phases. The accumulated substance must then be disposed of, usually via heat treatment. GAC is typically combined with incineration because the two methods are relatively cheap, able to filter large quantities of water, and effectively catch certain types of PFAS. During the GAC process, water is trickled over beds of carbon that are “activated”, or made porous, with heated oxygen or steam. Organic compounds like PFAS are attracted to the porous carbon particles and latch onto the carbon beds until the carbon is “spent” and can no longer absorb contaminants. Spent carbon is then either disposed of at a landfill or treated in an incinerator and topped with fresh carbon for reuse. Incineration theoretically destroys PFAS chemicals and renders them harmless, but some studies question the environmental impacts of burning PFAS. Unfortunately, potential environmental damage is not the only drawback to GAC. Although activated carbon can effectively remove long-chain PFAS like perfluorooctanesulfonic acids and perfluorooctanoic acids, the treatment usually fails to catch short-chain PFAS like perfluorobutane sulfonate. The incineration process only exacerbates the problem by enlarging the pores in the carbon and decreasing small molecule absorption. Considering that short-chain PFAS were used to replace their long-chain counterparts in manufacturing years ago, this limitation severely hampers GAC’s future efficacy.
Similar to GAC, ion exchange resin can only efficiently filter long-chain PFAS compounds. The resin is usually made of tiny hydrocarbon beads that are installed in packed beds. The positively charged anion exchange resin attracts and binds to negatively charged PFAS contaminants. The beds can then be incinerated or cleaned with a chemical flush and reused. Unfortunately, because the flush does not destroy PFAS molecules, it creates a toxic liquid byproduct that must be stored or otherwise destroyed.
The other primary adsorption technology, high-pressure membranes, can remove both long and short-chain PFAS. But the technology is exorbitantly expensive, especially when compared to GAC, and extremely delicate. The cost of replacing the membranes far exceeds the cost of replacing carbon sheets or resin beds, making membranes unsuitable as a primary filtration method. Much like GAC and ion exchange resin, membranes also produce a highly toxic concentrate that must be stored or disposed of separately.
All three of these separation methods can utilize incineration as a complimentary destruction technology. But concerns over the environmental impact and efficiency of the incineration process have promoted researchers to explore other, greener destruction methods.
One of the more promising methods utilizes high voltage to oxidize and defluorinate PFAS molecules. The electrochemical process is ideal partially because it leaves no toxic waste; the PFAS compounds are mineralized and produce only harmless fluoride ions, carbon dioxide, and water. Unfortunately, electrochemical destruction requires too much energy to work for large-scale operations. But for small, acute points of contamination, researchers are hopeful that electrochemical destruction could be an effective remediation technique.
Another breakthrough process called sonolysis uses soundwaves to degrade PFAS chemicals in the water. Electric current is converted into sound frequencies that create microbubbles. When these bubbles burst, they release significant levels of heat and energy--blasting PFAS molecules apart and breaking the water down into free radicals. One major benefit of sonolysis is convenience; treating groundwater is extremely difficult for most PFAS remediation technologies. The water is usually pumped out of the ground, treated, and pumped back--an expensive and inefficient solution. If sonolysis can effectively destroy PFAS molecules in groundwater without needing to move the water itself, the method could be far more environmentally friendly and cost-efficient than any current treatment process.
While these emerging technologies show a lot of promise inside laboratory settings, there is still one overarching consideration—the price. The cheapest method available, GAC, cost one facility around 46 million dollars to install and required an additional 2.6 million dollars annually for maintenance costs. Experimental methods like electrochemical and sonolysis remediation carry an unknown price tag but are undoubtedly not cheap. Furthermore, depending on state budgets and legislation, there may be limited funds for remediation efforts. Although some PFAS polluters have paid for remediation efforts in the past, more legislative framework must be set in place before the “polluter pays” rule can truly apply.
PFAS remediation technologies face significant barriers before they can become widely available. The good news is more politicians and researchers are spotlighting PFAS as a substantial environmental issue. A responsible combination of legislative and budgetary influence combined with scientific innovation could soon overcome these technological and financial hurdles. As more information breaks about PFAS remediation, regulations, and testing, Babcock Laboratories will continue to provide our clients with the latest news. For more information about PFAS or to arrange for PFAS testing, contact Babcock Labs.