Sustainable operation of membrane distillation for hypersaline applications: Roles of brine salinity, membrane permeability and hydrodynamics

This study aims to explore the role of brine salinity in achieving sustainable operation of membrane distillation (MD), particularly in hypersaline applications where highly concentrated or saturated solutions are treated. Given the state-of-the-art MD modeling work mainly focused on the mass and heat transfer phenomena for dilute systems, our simulation work predicts the trends of permeation flux in direct contact MD (DCMD) with elevated feed concentrations up to saturation, by a newly-developed exponential decay function. Also, a semi-empirical equation of the solute transport coefficient Sherwood number (Sh) is derived as Sh = (alpha(1)omega(F) + alpha(2)) Re-beta Sc-0.33, which for the first time incorporates the influence of feed concentration into the concentration polarization calculation in MD. Numerical analysis on the supersaturation ratio, concentration factor and concentration polarization effect showed that low to modest membrane permeability, reasonably high feed temperature and modest hydrodynamics (500 < Re < 2000) may help to prevent supersaturation and potentially reduce membrane scaling in hypersaline applications.