PFAS, or Per-and Polyfluoroalkyl Substances, are a group of man-made chemicals that have been in use since the mid-20th century. They are used in a wide array of consumer products, from non-stick cookware to water-repellent clothing. However, these chemicals have a dark side - they are incredibly persistent in the environment and in the human body, earning them the nickname "forever chemicals."

One of the most significant challenges in treating aqueous PFAS is their extreme resistance to degradation. The carbon-fluorine bond at the heart of these compounds is one of the strongest in nature, making them highly stable and resistant to ordinary treatment processes.

Another challenge is the low concentrations at which these compounds are typically found in water. This makes it difficult to accurately detect and quantify them, let alone remove them. Furthermore, the sheer number of individual compounds that make up the PFAS family (over 4,700) complicates treatment efforts.

Research and development into effective PFAS treatment technologies are ongoing, with potential solutions ranging from advanced oxidation processes to nanofiltration. However, these technologies are still in the early stages of development and have yet to be proven on a large scale.