A transient model for predicting concentration polarization in commercial spiral-wound membranes

This dissertation investigates concentration polarization and resulting permeate flux decline in commercial spiral wound membranes. Concentration polarization refers to the accumulation of contaminants (solutes) near the membrane surface that offer additional resistance to separation. It is a serious problem that decreases permeate throughput and quality, increases operating costs and results in frequent membrane cleaning and replacement.; Previous studies on concentration polarization provided an understanding of the process at a fundamental level but were limited to simplified membrane systems such as the one-dimensional batch cell or flow in porous pipes. This study focuses on predicting concentration polarization in commercial spiral wound membranes operating at high solvent recoveries.; A transient finite difference model is developed and presented to explain concentration polarization in spiral wound membranes that operate at moderate to high solvent recoveries. The solute mass transport equation is solved in axial and transverse directions along with appropriate fluid flow equations that describe flow in spiral wound membranes. In addition, a model for membrane transport based on osmotic theory is used to describe solvent (water) flow across the membrane surface.; The model was tested for numerical stability and accuracy, and compared with existing steady state models that predict concentration polarization for low solvent recoveries. The model was also verified with experimental data collected from a pilot-scale spiral wound reverse osmosis system. This included specific tests conducted to collect initial flux decline data during separation of NaCl solutions under various operating conditions. Finally, transient and steady state concentration polarization and permeate flux decline data are presented for a wide range of feed and operating conditions including different feed flow rates, recycle rates, temperatures and membrane permeabilities. This information is expected to be especially useful during design and operation of membrane facilities for both water and wastewater treatment, and desalination applications.