Analysis of Volatile and Semivolatile Organic Compound Transport in Membrane Distillation Modules

Membrane distillation (MD) is an emerging water treatment process that offers near-complete removal of nonvolatile contaminants. However, the transport of volatile compounds in the process is highly varied and poorly understood. In this work, we investigate the transport of a wide range of semivolatile and volatile compounds in membrane distillation (55 compounds total) allowing us to gain broad insights into the compound properties, system designs, and operating conditions that impact transport rates in direct-contact MD. We first use experimentally verified simulations to study the effects of different molecular properties on transport and show that the Henry's constant and diffusion coefficient are the most important molecular properties in determining solute flux. We then study the transport resistances across distillation membranes and find distinct transport regimes dominated by resistances associated with either diffusion through the membrane or boundary layers on either side of the membrane. Simulations of large-scale MD modules reveal the impact of membrane area, operating temperature, and crossflow velocity on the removal of contaminants. Finally, we comprehensively compare the removal of different classes of contaminants between MD and RO, finding that MD is more effective in removing small neutral compounds with low volatility. Overall, the results of this work demonstrate important compound properties and operating conditions that control volatile mass transport in MD.