Toward Using Membrane Distillation for Brine Treatment: Understanding Energy Efficiency and the Challenge of Mineral Scaling

Abstract

Membrane distillation (MD) is an emerging technology that carries potential for brine treatment. Energy efficiency analysis and mineral scaling, which are the most critical challenges in MD, remain unresolved and poorly understood. Energy efficiency analysis of MD thus far has been unintuitive and difficult to draw conclusions from, especially when the MD process is coupled with latent heat recovery or driven by waste heat. Scaling is problematic because it directly hinders vapor transport across the membrane, which leads to inefficiency in the production of pure water, and eventually leads to pore wetting, which can allow for contamination of the produced water. In this work, I 1) develop intuitive metrics for the evaluation of energy efficiency in MD in varying contexts, and 2) evaluate scaling-related failure in the MD process when operated with highly saline and complex feed waters composed of sparingly soluble salts. Specifically, I explore the thermodynamics of an MD system coupled with heat exchangers for waste heat delivery and/or the delivery of latent heat stored within the distillate solution. Also, I investigate how operating parameters and feed solution composition contribute to the precipitation of minerals onto the surface of an MD membrane. This work informs the necessary discussion surrounding the optimization of MD for the cheap and efficient treatment of high-salinity brine.