Direct and Indirect Seawater Desalination by Forward Osmosis

Abstract Forward osmosis (FO) is an emerging membrane technology with a range of possible water treatment applications including desalination. The FO process itself can directly desalt seawater as a feed solution by employing a draw solution with higher osmotic pressure than seawater. However, the energetics of product water recovery and draw solution reuse is not favorable. Alternatively, the FO process using seawater as a natural draw solution and quality-impaired water as the feed can potentially couple with low-pressure reverse osmosis as a hybrid to be a lower-energy desalination process, in which indirect desalination is achieved. Most organic fouling in FO desalination process is reversible. However, the mechanism of scaling formation in FO desalination is more complicated than the conventional RO process. Both feed and draw solution can influence the scaling formation and its reversibility. The economic feasibility of FO desalination process depends on the operational mode (direct and indirect) as well as the plant scale and level of commercialization. Although there are still some choke points in the current deployment of FO desalination, the future development of efficient draw solution and novel FO membrane will significantly promote FO desalination technology.