EAGER: Water Continuity on the Performance of Osmotically Driven Membrane Processes

渗透驱动膜过程(ODMP)利用被半透膜(即渗透压)隔开的两种溶液之间的化学势的差异，将水从低溶质浓度侧(进水侧)转移到高溶质浓度侧(拉料液)。这种通过渗透压力通过膜输送水的能力，无需施加外部液压驱动力，即可用于供应清洁水，并直接从咸水中生产可再生能源。然而，膜上的低水通量限制了ODMP的性能及其满足全球水和能源需求的潜力。一种被称为内部浓差极化(ICP)的现象被认为是仅在渗透压力驱动力下的低水通量的主要原因。流行的理论是，在膜的多孔性支撑层中形成较强的ICP，并且相对于膜抽拉溶液的总渗透压，降低了驱使水通过活性(皮肤)层的有效渗透压。然而，旨在最大限度地减少或消除ICP从而提高水通量的膜几乎没有产生技术突破。这个项目将考虑一个有争议的观点，即渗透压下的低水通量主要是由于跨膜的水连续性的崩溃，而不是ICP。成功地证明了膜内水的连续性是ODMP性能的关键因素，这可能会改变膜基水处理和净化领域。该项目还将通过奇卡诺人和美洲原住民科学促进会的德克萨斯理工大学分会，为研究生培训和STEM外联提供机会。该项目的目的是证明ODMP膜内水的连续性的丧失是造成低水通量的主要因素。将构建一个定制的膜系统，以便可以在给水和出液两端独立控制液压，并且可以在进水室密封和从进水箱拆卸时测量进料室中的压力。膜系统将被用来观察渗透压力下密封进料室中的负压积聚。在典型的ODMP操作条件下，系统预计将呈现负压积累和突然消散的过程，其中负压通过水连续性的崩溃(即空化)来解除。除了证明水的连续性被打破外，这项研究还将系统地研究ODMP中的水通量与水的连续性状态之间的关系，作为操作条件和膜材料的函数。还将评估施加到给水和出水液侧的液压的独立性。这项研究有望对渗透压力驱动的跨膜水传输机制产生新的见解。这一奖项反映了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。

Osmotically-driven membrane processes (ODMPs) leverage the difference in chemical potentials between two solutions that are separated by a semipermeable membrane (i.e., osmotic pressure) to move water from the low solute concentration side (feed water) to the high solute concentration side (draw solution). This ability to transport water through a membrane via osmotic pressure, without applying an external hydraulic pressure driving force, can be used to supply clean water and produce renewable energy directly from saline waters. However, low water flux across the membrane limits the performance of ODMPs and their potential to meet global water and energy needs. A phenomenon called internal concentration polarization (ICP) has received much of the blame for the low water flux under an osmotic pressure-driving force alone. The prevailing theory is that a strong ICP develops in the membrane’s porous support layer and diminishes the effective osmotic pressure driving water across the active (skin) layer relative to the total osmotic pressure of the membrane draw solution. Yet, membranes designed to minimize or eliminate ICP and, thus, improve water flux have yielded few technological breakthroughs. This project will consider the controversial idea that the collapse of water continuity across the membrane, instead of ICP, is mainly responsible for the low water flux under osmotic pressure. Successfully demonstrating that water continuity within the membrane is a key factor in ODMP performance has the potential to transform the field of membrane-based water treatment and purification. The project will also provide opportunities for graduate student training and STEM outreach through the Texas Tech University Chapter of the Society for the Advancement of Chicanos and Native Americans in Science. The goal of this project is to demonstrate that the loss of water continuity inside the membrane of an ODMP is a principal factor contributing to low water flux. A custom membrane system will be constructed such that hydraulic pressure can be independently manipulated on both the feed water and draw solution sides and that the pressure in the feed chamber can be measured when it is sealed and detached from the feed water tank. The membrane system will be used to observe the buildup of negative pressure in the sealed feed chamber under osmotic pressure. Under typical ODMP operating conditions, the system is expected to exhibit a process of negative pressure buildup and abrupt dissipation, wherein the negative pressure is relieved by the collapse of water continuity (i.e., cavitation). In addition to demonstrating the breakup of water continuity, the study will systematically examine the relationship between water flux in ODMPs and the status of water continuity as a function of operating conditions and membrane material. The independence of the hydraulic pressures applied to the feed water and draw solution sides will also be evaluated. The research is expected to generate new insights into osmotic pressure-driven water transport mechanisms across membranes.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.