Symmetric forward osmosis membrane coupled with dendritic draw solute: New insights into sustainable properties

The development of current forward osmosis (FO) technology has experienced a significant challenge because of the ineliminable internal concentration polarization effect in conventional asymmetric FO membranes as well as the extremely energy-intensive recovery process of the common draw solutes (e.g., NaCl). Here, we report, for the first time, a coupling system comprising a symmetric FO (SFO) membrane and a series of macromolecular draw solutes (MDS). The lack of a support layer in the SFO membrane facilitates free MDS diffusion, thus completely eliminating the ICP effect. As a result, the obtained reverse flux selectivity (Jw FO/JFO s , ratio of water flux to reverse salt flux) of the SFO/MDS system was approximately 5000, 20000, and 40000 L mol-1, which were 2-3 orders of magnitude higher than that of the conventional salt-based FO system. Moreover, due to the low rejections to inorganic salts, the SFO membrane exhibited the unique ability for allowing most NaCl to pass through while retained most MDS simultaneously, which endowed a great utility of the SFO/MDS system for desalination of textile wastewater. Subsequently, the MDS with large molecular weights could be readily recovered by a facile nanofiltration membrane process with a much higher water flux than that of the conventional reverse osmosis process at the same operating pressure, indicating the high energy-saving capacity of the SFO/MDS system. Given the significant compatibility of SFO and MDS, our study provides a new coupling strategy for the development of sustainable FO technologies.

Automated summary

The coupling system of symmetric FO membrane and macromolecular draw solutes effectively eliminates the internal concentration polarization effect in conventional FO systems, resulting in significantly higher water flux selectivity. Additionally, the SFO/MDS system shows high efficiency in allowing NaCl to pass through while retaining large molecular weight draw solutes during desalination processes.