Forward osmosis: understanding the hype

Abstract

AbstractThe scientific interest in forward osmosis has increased dramatically over the last decade. The hype has resulted in a high scientific production, but research activities seem to go in all directions, and the real benefits of the process are not always well understood. This paper aims to give some directions based on the current state of the art. Without going into details about the process itself, the current research lines and their background are described. While some of these are important, others – notably the search for alternative draw solutions – have become the Holy Grail of forward osmosis. The further analysis of the process is based on suggested applications and uses the observations made on contemporary research topics in the field. At first, direct application of forward osmosis for potable water production is considered. This leads back to the research challenges of the reverse draw solute flux, concentration polarization, and the regeneration of the draw solution. Special attention is given to desalination, as forward osmosis is often incorrectly denoted as a desalination technology. It can be used in the context of desalination; however, the question remains in which applications this is of interest. Combining desalination and wastewater treatment is one such interesting application, which is further described in this paper for some types of wastewater found in the literature. In the last part, the paper emphasizes the need to develop processes in which the challenge of the draw solution is intrinsically solved. The foremost example of such application is the one for which forward osmosis was developed four decades ago: the use of impaired water sources diluted through a forward osmosis membrane by using a concentrated fertilizer solution to provide osmotic pressure. This application was suggested four decades ago but was never applied on any scale. Process economics and an insufficiently developed technology may have been the basis of this failure. However, a renewed focus on such applications would allow forward osmosis to come to its real potential and contribute to solving the global water challenge.