Causes and analysis of failures in in-situ microscopy observation for the characterization of scaling in membrane distillation membranes

Abstract

In membrane technology at large, fouling limits membrane performance and membrane lifespan. In the case of reverse osmosis membrane distillation (MD) involving fluid mixtures of inorganic elements, inorganic foulants build up on membrane surfaces, and reduce the flux of fluids across a membrane. Inorganic fouling can degrade the quality of water produced by membrane distillation. In order to counteract the effects of membrane fouling, potentially costly procedures like intense chemical cleaning or membrane replacement are necessary. Some theory suggests that, instead of reacting and adhering to membrane surfaces, salts tend to bulk nucleate in solution, and then deposit on high energy surfaces, like metal heat exchangers and hydrophilic reverse osmosis membranes. This is in contrast to the theory that crystals first deposit on the membrane surface to cause fouling. A solution of Na2SO4. and CaCl, was pumped across a membrane at 70°C at 2.6 GPM (9.8 LPM) to observe membrane fouling. Using an in-situ camera, fouling on a membrane distillation surface was captured to characterize the nature of MD fouling. Due to failures in heat distribution across the solution and system leaking, no fouling on the membrane surface was observed.