ERASE-PFAS: Understanding the surface-active properties of PFAS for enhanced removal by bubbling-assisted water treatment processes

PFAS are a group of manufactured chemicals that have been used in hundreds of different applications since the 1950s. One of their most important and life-saving applications is in the production of firefighting foams. The extreme stability of PFAS molecules makes them highly persistent in the environment, which has led to them being referred to as ‘forever’ chemicals. PFAS have been associated with numerous health effects in both humans and animals. PFAS are also widely detected in the environment, including in drinking water, groundwater, and landfill leachate. Unfortunately, commonly used water treatment processes do not remove PFAS efficiently. The goal of this project is to characterize the unique detergent-like properties of PFAS and use that information to develop an air bubble-assisted PFAS water treatment process. Like detergents, PFAS can accumulate at the surface of air-bubbles. The enriched PFAS layer at the water surface can then be removed leaving behind PFAS-free treated water. The specific objectives designed to achieve the goal of this project are to: i) characterize the mechanisms controlling PFAS interactions at air bubble surfaces, ii) identify conditions leading to increased accumulation of PFAS, and iii) use the results to develop an optimized bench-scale reactor using precision-controlled bubbles with commonly used water treatment chemicals to enhance PFAS removal. The simplicity and scalability of the proposed approach are ideal for application in combination with conventional unit processes used in drinking water treatment plants. Successful completion of this research holds promise for the development of cost-saving water treatment technology to help water utilities and other stakeholders address PFAS-related regulations. Additional benefits to society result from education and outreach to underserved populations to increase scientific literacy and diversify the Nation’s STEM workforce.PFAS exhibit both lipophobic and hydrophobic properties, and thus tend to accumulate at air-water interfaces due to surface tension interactions. The mechanisms governing the interaction of PFAS with air-bubbles are relatively understudied, and there are significant gaps in our knowledge of these processes. The proposed research is designed to address this important knowledge gap to provide a mechanistic understanding of air-water interfacial accumulation of PFAS. These results will be used to develop a bubble-assisted water treatment process to efficiently capture and remove PFAS from contaminated water. The governing hypotheses of this study are that: H1) introduction of nano- to micro-sized air bubbles in water can effectively capture and concentrate PFAS molecules at the air-water interface; and H2) the stability and lifetime of the accumulated PFAS at the air-water interface is dependent on the individual PFAS surface tension, presence of cationic modifiers, and self-assembly behavior at concentrations below their critical micelle concentration (CMC). The specific research objectives designed to test these hypotheses are to: i) determine the surface tension, self-assembly structure at the air-water interface, and CMC of selected PFAS using conventional and synchrotron X-ray scattering techniques as a function of water quality composition; ii) assess conditions that can increase air-water interface accumulation of short-chain PFAS to improve separation from source water; iii) elucidate the impact of bubble size on accumulation and subsequent extraction of PFAS from water; and iv) develop an optimized air-bubbling system in combination with conventional coagulants for effective removal of PFAS from water. Successful development of this approach may lead to effective and scalable treatment technology for removal of PFAS and, potentially, aqueous film forming foam (AFFF) from various sources such as drinking water, groundwater, and landfill leachate. More generally, knowledge on the interfacial accumulation of PFAS may reveal previously unrecognized fate and transport mechanisms of PFAS in the environment. Additional benefits to society result from increasing participation in STEM through outreach activities with the Simons Summer Research and Women in Science and Engineering programs to involve high school students and female undergraduates in hands-on research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.