Harnessing buoyancy-driven instabilities for enhanced membrane desalination

美国的工业活动产生了大量复杂的废水，因为它们含有高浓度的溶解盐，很难处理。这些废水通常被排放到当地的地表水、下水道、水井和地表，污染资源和生态系统。本项目采用计算机模拟和实验室实验相结合的方法，开发一种称为膜蒸馏的高级水处理工艺，可以对复杂的废水进行脱盐和循环利用。具体来说，我们表明重力可以用来改善膜蒸馏中的混合，并使可再生太阳能的使用能够减少能源消耗。综合教育活动包括高中生暑期实习、本科生研究活动、开发免费教科书、组织学生研究专题讨论会等。膜蒸馏是一种热脱盐过程，其中水蒸发并通过去除盐的多孔膜。所提出的工作解决了膜蒸馏长期存在的两个技术难题。首先是冷却膜附近的水，这可以减缓蒸发和淡水的恢复。第二种是溶解的盐在膜附近积聚，在那里它们沉淀并堵塞膜。我们通过调整膜的方向来解决这些问题，这样重力就会使冷的、富含盐的水从膜上沉降下来，在废水中产生浮力混合。我们还表明，这种混合可以通过通过膜对面的表面主动加热废水来加强。为此，提出的工作使用计算流体动力学和实验尺度来(1)阐明浮力混合的物理特性；(2)探索利用电力或可再生太阳能主动加热废水的最佳方法；(3)对日益受到关注的现实城市和工业废水进行验证。我们期望这项工作通过缓解水资源短缺和提高海水淡化过程的环境可持续性，以及能源-水-气候关系的关键应用，对社会产生广泛影响。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。

Industrial activities in the United States generate large volumes of complex wastewaters that are challenging to treat, because they have a high concentration of dissolved salts. These wastewaters are often discharged to local surface waters, sewers, wells, and land surfaces, where they contaminate resources and ecosystems. This project uses a combination of computer simulations and laboratory experiments to develop an advanced water treatment process called membrane distillation, which can desalinate and recycle complex wastewaters. Specifically, we show that gravity can be harnessed to improve mixing within membrane distillation, and enable the use of renewable solar energy to reduce energy consumption. Integrated educational activities include summer internships for high-school students, undergraduate research activities, the development of free textbooks, and the organization of student research symposia.Membrane distillation is a thermal desalination process in which water evaporates and travels through a porous membrane that removes salts. The proposed work solves two long-standing technical challenges of membrane distillation. The first is cooling of the water near the membrane, which slows evaporation and the recovery of freshwater. The second is the accumulation of dissolved salts near the membrane, where they precipitate and clog the membrane. We address these issues by orienting the membrane so that gravity causes cool, salt-rich, water to sink away from the membrane, generating buoyant mixing within the wastewater. We also show that this mixing can be strengthened by actively heating the wastewater through a surface opposite the membrane. To that end, the proposed work uses computational fluid dynamics and bench-scale experiments to (1) elucidate the physics of the buoyant mixing; (2) explore optimal methods of actively heating the wastewater using electricity or renewable solar energy; and (3) validate the process against real-world municipal and industrial wastewaters of growing concern. We expect the work to broadly impact society by mitigating water scarcity and improving the environmental sustainability of desalination processes with critical applications to the energy-water-climate nexus.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.