Atomization of brine for zero liquid discharge

Solar thermal evaporation of brine is one of the most energetically-efficient approaches for achieving zero liquid discharge, which can solve the environmental problems associated with various desalination technologies. To accelerate the evaporation process, brine can be atomized to microdroplets (i.e., fog) by ultrasonic atomization. In this study, brine with systematically varying concentrations of salt and surfactants is atomized to investigate the effects of salinity and surfactants on the rate of fog generation and the size of generated fog droplets. The fog-generation rate is calculated by measuring the decrease in brine mass on a microbalance and the droplet size is directly visualized using a high-speed camera with a microscopic lens. At a fixed atomization condition, results show that the rate of fog generation decreases and the size of generated fog droplets increases with the increase in the brine salinity. With the addition of surfactants to the brine, the fog generation rate is enhanced and the fog droplet size is reduced. The physico-chemical properties of brine such as surface tension are found to be the main factors that determine the generation rate and the size of droplets.