Toward a universal framework for evaluating transport resistances and driving forces in membrane-based desalination processes

Desalination technologies using salt-rejecting membranes are a highly efficient tool to provide fresh water and augment existing water supplies. In recent years, numerous studies have worked to advance a variety of mem-brane processes with different membrane types and driving forces, but direct quantitative comparisons of these different technologies have led to confusing and contradictory conclusions in the literature. In this Review, we critically assess different membrane-based desalination technologies and provide a universal framework for comparing various driving forces and membrane types. To accomplish this, we first quantify the thermodynamic driving forces resulting from pressure, concentration, and temperature gradients. We then examine the resis-tances experienced by water molecules as they traverse liquid-and air-filled membranes. Last, we quantify water fluxes in each process for differing desalination scenarios. We conclude by synthesizing results from the litera-ture and our quantitative analyses to compare desalination processes, identifying specific scenarios where each process has fundamental advantages.