- Mechanical Engineering
Top 3 Areas of Expertise:
Expected date of graduation:
Energy-efficient desalination and water reuse play an important role in ensuring universal access to clean water. Reverse osmosis (RO) is the most efficient desalination process for almost any water source, but it is susceptible to membrane fouling, which can lead to declining water production, increasing solute permeation, and higher energy consumption and water cost. Fouling can be reduced through (energy-intensive) pretreatment, delayed by membrane coatings, and partially reversed by cleaning. However, poor understanding of fouling physics hinders our ability to design for fouling resistance, and inefficient desalination processes continue to be used because of their superior resistance to fouling. Better models of fouling are needed to improve the RO process, replace energy-intensive alternative processes, and provide sustainable sources of desalinated or recycled water to water-scarce communities.
This thesis approaches this problem from several angles, including quantifying fouling, isolating the effect of pressure, and elucidating fouling and cleaning mechanisms. The effect of foulant accumulation on flux decline in RO and forward osmosis (FO) is modeled to enable calculation of foulant accumulation from flux measurement. This quantification method shows that, although flux decline was less significant in FO than in RO for the same initial flux, the higher average flux caused the rate of foulant accumulation to be higher in FO. In addition, although high pressure is often considered the cause of RO's susceptibility to fouling, FO trials at elevated pressure show that high pressure alone does not adversely affect fouling. Once formed, foulant layers in FO and RO can be removed through osmotic backwashing, which causes isotropic swelling of the foulant layer followed by wrinkling and detachment from the membrane. These results guide process selection, membrane design, and cleaning protocol development to reduce the cost associated with membrane fouling in desalination.
Top 5 Awards and honors (name of award, date received):
5 Recent Papers:
Tow, E. W. and Lienhard V, J. H. (2016), “Quantifying osmotic membrane fouling to enable comparisons across diverse processes,” Journal of Membrane Science, 511, 92-107.
Tow, E. W., et al. (2015), “Raising forward osmosis brine concentration efficiency through flow rate optimization,” Desalination, 366, 71-79.
Tow, E. W. and Lienhard V, J. H. (2014), “Heat transfer to a horizontal cylinder in a shallow bubble column,” International Journal of Heat and Mass Transfer, 79, 353-361.
Tow, E. W. and Lienhard V, J. H. (2014), “Experiments and modeling of bubble column dehumidifier performance,” International Journal of Thermal Sciences, 80, 65-75.
Tow, E. W. (2014), "The antireflective potential of dropwise condensation," Journal of the Optical Society of America A, 31(3), 493-499.