Acoustically activated trapping for colloidal filtration: a multiscale experimental investigation using laser-based optical diagnostics

胶体过滤广泛用于水和废水处理，以去除固体，微观颗粒（称为胶体），包括饮用水水源和废水中存在的无机颗粒，细菌和其他聚集体。该工艺利用压力驱动含有胶体的流体（如受污染的水）通过微滤/超滤膜，该膜由一系列微观通道组成，允许流体通过，但阻止胶体通过。随着时间的推移，通道被胶体堵塞，直到驱动流体通过膜所需的压力变得太大，膜必须更换。膜更换成本占过滤系统总运行成本的50%。操作膜式过滤器所需的费用是造成用水不平等的一个重要因素。为了解决这些挑战，该项目的首席研究员（pi）建议探索使用声波（声音）来打破堵塞并在胶体到达膜界面之前捕获胶体，以延长膜的使用寿命并降低总体操作成本。这个项目的成功完成将通过产生关于膜污染的基本知识和可能降低运营成本来造福社会，这可能会增加农村地区或基础设施不足的社区获得清洁水的机会。通过学生教育和培训，包括爱荷华州立大学（ISU）的一名研究生的指导，将为社会带来额外的好处。膜被广泛应用于从水和废物流中分离固体颗粒（胶体）。胶体过滤过程中的污垢是由于胶体颗粒在膜界面积聚而形成的，形成了所谓的饼层。驱动流体通过滤饼层所需的压力随着时间的推移而增加，因此需要显著增加泵送功率输入。本提案的总体目标是开发经过实验验证的二维和三维模型，这些模型是由于声场相互作用而在膜界面上形成和破裂的。为了实现这一目标，首席研究员（pi）提出测试假设，即声场的应用会在膜界面产生一个体力，从而改变饼层内的颗粒分布。具体的研究目标是：(1)在没有声场的情况下测量饼层的生长情况，以了解膜的表面力；(2)研究和模拟声场与膜的相互作用；(3)光学询问三维膜中的声混合。这项研究的成功完成，通过产生与外部声场驱动的膜饼层形成相关的界面现象的基本知识，具有变革性影响的潜力。为了实现该项目的教育和培训目标，pi计划与西班牙裔专业工程师协会（SHPE）的ISU分会和卓越学术计划（APEX）计划合作，为STEM中代表性不足的高中生和本科生开发和提供学习经验。此外，pi计划利用ISU现有的项目，如科学与工程领域的女性项目，介绍、招募和指导科学与工程领域的女性。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。

Colloidal filtration is widely used in water and wastewater treatment to remove solid, microscopic particles (known as colloids) including inorganic particles, bacteria, and other aggregates present in drinking water sources and wastewater. This process uses pressure to drive a colloid-bearing fluid (e.g., contaminated water) through a microfiltration/ultrafiltration membrane that consists of a series of microscopic channels that allows the fluid to pass through but blocks the passage of colloids. Over time, the channels become clogged with colloids until the pressure required to drive the fluid through the membrane becomes too great and the membrane must be replaced. Membrane replacement costs represent 50% of the total operational cost of a filtration system. The expense required to operate membrane-type filters is a significant contribution to water access inequality. To address these challenges, the Principal Investigators (PIs) of this project propose to explore the use of acoustic waves (sound) as a to break up clogs and capture colloids before they reach the membrane interface with the goal of extending the operational lifetime of the membrane and reduce the overall operating costs. The successful completion of this project will benefit society through the generation of fundamental knowledge on membrane fouling and a potential reduction in operating costs which could increase access to clean water in rural areas or communities with inadequate infrastructure. Additional benefits to society will be achieved through student education and training including the mentoring of one graduate student at Iowa State University (ISU). Membranes are used in a wide variety of applications to separate solid particles (colloids) from water and waste streams. Fouling during colloidal filtration processes results from the build-up of colloidal particles at a membrane interface, forming what is known as a cake layer. The pressure required to drive fluid through a cake layer increases with time, thus requiring a significant increase in pumping power input. The overarching goal of this proposal is to develop experimentally validated 2D and 3D models of cake layer formation and break-up at membrane interfaces due to acoustic field interactions. To advance this goal, the Principal Investigators (PIs) propose to test the hypothesis that the application of an acoustic field generates a body force at the membrane interface that modifies the particle distribution within the cake layer. The specific research objectives are to (1) measure cake layer growth without an acoustic field to understand membrane surface forces; (2) investigate and model acoustic field interactions with the membrane; and (3) optically interrogate acoustic mixing in 3D membranes. The successful completion of this research has the potential for transformative impact through the generation of fundamental knowledge of interfacial phenomena related to external, acoustic field-actuated formation of cake layers in membranes. To implement the education and training goals of the project, the PIs plan to engage with the ISU chapter of the Society of Hispanic Professional Engineers (SHPE) and the Academic Program for Excellence (APEX) program to develop and deliver learning experiences to high school and undergraduate students underrepresented in STEM. In addition, the PIs plan to leverage existing programs at ISU, such as the Women in Science and Engineering program to introduce, recruit, and mentor women in science and engineering.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.