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

PFAS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。它们最重要和拯救生命的应用之一是生产消防泡沫。PFAS分子的极端稳定性使它们在环境中具有高度持久性，这导致它们被称为“永远”的化学物质。PFAS与人类和动物的许多健康影响有关。PFAS也广泛存在于环境中，包括饮用水、地下水和垃圾填埋场渗滤液中。不幸的是，常用的水处理工艺不能有效地去除PFAS。该项目的目标是表征PFAS独特的洗涤剂性质，并利用该信息开发气泡辅助PFAS水处理工艺。和清洁剂一样，PFAS也会积聚在气泡表面。然后可以去除水面上富集的PFAS层，留下不含PFAS的处理水。为实现该项目的具体目标是：i)表征控制PFAS在气泡表面相互作用的机制，ii)确定导致PFAS积累增加的条件，以及iii)利用结果开发优化的实验规模反应器，使用精确控制的气泡和常用的水处理化学品来增强PFAS的去除。所提出的方法的简单性和可扩展性非常适合与饮用水处理厂使用的传统单元工艺相结合。这项研究的成功完成为开发节约成本的水处理技术提供了希望，以帮助水务公司和其他利益相关者解决与pfas相关的法规。通过教育和向服务不足的人群推广，提高科学素养，使国家的STEM劳动力多样化，从而为社会带来额外的好处。PFAS表现出疏脂和疏水的特性，因此由于表面张力相互作用，PFAS倾向于在空气-水界面积聚。控制PFAS与气泡相互作用的机制研究相对不足，并且我们对这些过程的了解存在显着差距。提出的研究旨在解决这一重要的知识差距，以提供对PFAS的空气-水界面积累的机制理解。这些结果将用于开发气泡辅助水处理工艺，以有效地捕获和去除污染水中的PFAS。本研究的主要假设是：H1)在水中引入纳米至微尺度的气泡，可以有效地在空气-水界面捕获和浓缩PFAS分子；和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、阳离子改性剂的存在以及浓度低于其临界胶束浓度（CMC）时的自组装行为。测试这些假设的具体研究目标是：i)使用常规和同步x射线散射技术确定选定PFAS的表面张力，空气-水界面的自组装结构和CMC作为水质成分的函数；ii)评估可以增加短链PFAS在空气-水界面积聚的条件，以改善与水源的分离；iii)阐明气泡大小对PFAS在水中的积累和随后的提取的影响；iv)开发一种优化的气泡系统，结合传统的混凝剂，有效地去除水中的PFAS。这种方法的成功开发可能会带来有效的、可扩展的处理技术，用于去除PFAS，并可能从各种来源（如饮用水、地下水和垃圾填埋场渗滤液）中去除水膜形成泡沫（AFFF）。更一般地说，对PFAS界面积累的了解可能揭示PFAS在环境中的命运和运输机制。通过西蒙斯暑期研究和女性参与科学与工程项目的外展活动，让高中生和女本科生参与动手研究，增加了对STEM的参与，为社会带来了额外的好处。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.