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

全氟辛烷磺酸是一组人造化学品，自20世纪50年代以来已被用于数百种不同的应用。它们最重要和最拯救生命的应用之一是生产消防泡沫。全氟辛烷磺酸分子的极端稳定性使它们在环境中高度持久，这使得它们被称为“永远的”化学品。全氟辛烷磺酸在人类和动物中都与许多健康影响有关。全氟辛烷磺酸也广泛存在于环境中，包括饮用水、地下水和垃圾渗滤液中。不幸的是，常用的水处理工艺并不能有效地去除全氟辛烷磺酸。该项目的目标是表征PFAS独特的类似洗涤剂的特性，并利用这些信息开发一种气泡辅助PFAS水处理工艺。像洗涤剂一样，全氟辛烷磺酸会在气泡表面积聚。然后，可以去除水面上浓缩的PFAS层，留下不含PFAS的处理水。为实现该项目的目标而设计的具体目标是：i)表征控制气泡表面全氟辛烷磺酸相互作用的机制，ii)确定导致全氟辛烷磺酸积累增加的条件，以及iii)利用结果来开发优化的实验室规模的反应器，该反应器使用精确控制的气泡和常用的水处理化学品来加强全氟辛烷磺酸的去除。该方法的简单性和可扩展性是与饮用水处理厂使用的传统单元工艺相结合的理想应用。这项研究的成功完成为开发节约成本的水处理技术带来了希望，以帮助自来水公司和其他利益攸关方解决与PFAS相关的法规。对社会的其他好处来自教育和对服务不足的人群的外联，以提高科学素养和使国家的STEM工作多样化。全氟辛烷磺酸具有疏油和疏水特性，因此由于表面张力相互作用，容易在空气-水界面积聚。关于全氟辛烷磺酸与气泡相互作用的机制研究相对较少，我们对这些过程的认识存在很大差距。拟议的研究旨在解决这一重要的知识差距，以提供对全氟辛烷磺酸在空气-水界面积累的机理的了解。这些结果将被用来开发一种气泡辅助水处理工艺，以有效地从受污染的水中捕获和去除全氟辛烷磺酸。这项研究的主要假设是：1)在水中引入纳米到微米尺寸的气泡可以有效地捕获和浓缩空气-水界面的PFAS分子；以及H2)在空气-水界面积累的PFAS的稳定性和寿命取决于单个PFAS的表面张力、阳离子修饰剂的存在以及低于其临界胶束浓度(CMC)的浓度时的自组装行为。为检验这些假设而设计的具体研究目标是：i)使用常规和同步辐射X射线散射技术确定选定的全氟辛烷磺酸的表面张力、空气-水界面的自组装结构和CMC，作为水质组成的函数；ii)评估可以增加短链全氟辛烷磺酸在空气-水界面的累积以改善与水源水的分离的条件；iii)阐明气泡大小对从水中累积和随后提取全氟辛烷磺酸的影响；以及iv)开发与常规混凝剂相结合的优化的空气鼓泡系统，以有效地从水中去除全氟辛烷磺酸。这种方法的成功开发可能导致有效和可扩展的处理技术，用于从饮用水、地下水和垃圾渗滤液等各种来源去除全氟辛烷磺酸，并有可能去除水成膜泡沫(AFFF)。更广泛地说，关于全氟辛烷磺酸界面积累的知识可能揭示以前未知的全氟辛烷磺酸在环境中的命运和传输机制。通过与西蒙斯夏季研究和女性科学与工程项目的外联活动，让高中生和女本科生参与实践研究，增加对社会的参与，社会将获得更多好处。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.