Environmental Science and Engineering Seminar

Membrane distillation (MD), a hybrid thermal-membrane desalination technology, has recently received tremendous interest as a sustainable technology for the treatment of hypersaline brines. MD is tolerant to higher salinity than reverse osmosis (RO) and capable of leveraging low-grade thermal energy such as waste heat and geothermal energy. However, several fundamental aspects need to be addressed to achieve resilient MD systems for industrial applications. In this seminar, I will present and discuss two of such aspects from the perspectives of process optimization. First MD performance is constrained by inorganic fouling from mineral growth, or scaling, due to the increased concentration over time of sparingly-soluble feed water constituents. Accordingly, careful control of the driving force for feed water concentration (i.e., the vapor pressure gradient across the hydrophobic membrane) has been used to improve the robustness of MD performance. Recently we discovered that an equivalent trans-membrane vapor flux (i.e., the rate of vapor transferred through the membrane per unit area) can be achieved at varying feed water temperatures by separately controlling the vapor pressure on the opposite side of the membrane. Such control has enabled the investigation of the thermodynamic state of the nucleating minerals at the interface between the feed water and the membrane. Second, MD is highly competitive to RO when low-grade thermal energy is applied efficiently. I will present findings that elucidate the nuanced variations in energy efficiency definitions when varying heat sources and operational configurations are applied. Our work highlights the importance of determining whether the integration of low-grade thermal energy will minimize the costly high-grade energy to maintain the process or maximize the usage of the greatest amount of latent heat upon feed recycling. At the conclusion of the seminar, I will also discuss the prospects and research needs associated with MD to improve environmental sustainability at the water-energy nexus.