Critical performance assessment of a submerged hybrid forward osmosis - membrane distillation system

FO and MD have their drawbacks when employed as independent systems. To establish substantial superiority over single membrane process, an innovative FO and MD integration in a hybrid submerged module was introduced in this study. Initially, FO and MD were evaluated individually, using a conventional side-stream module. The stable-operation conditions of the hybrid module were estimated based on the results of the sidestream module: feed, DS, and distillate temperatures at 20, 40, and 20 degrees C, respectively. Sequentially, the actual stable-operation of the hybrid module was determined. The DS temperature found was higher than the one estimated by using the side-stream module (45 degrees C). This was related to lower fluxes in the submerged configuration, explained by significant polarization effects. Despite that, the hybrid is less energy-intensive compared to the side-stream since it is not necessary to pump the feed solution to an external compartment. The hybrid showed high rejection of TOC, TN, NH4, and TrOCs, which were 94.9%, 93.8%, 99.8%, and > 97.5%, respectively. The results showed the potential of hybrid configuration in water treatment systems. The use of a single module allows the re-concentration of the DS and the production of distillate continuously, reducing the foot-print of the processes.