Feasibility evaluation of element scale forward osmosis for direct connection with reverse osmosis

Forward osmosis (FO) and reverse osmosis (RO) hybrid process is taking center stage under the international spotlight in water treatment and desalination industries. Nevertheless, most existing researches are on the lab-scale and only few researches have been done on the element-scale. Currently, two types of elements are available, spiral wound FO (SWFO) and flat sheet FO (FSFO). However their performances have not yet been clearly addressed or compared. In addition, there is no research of which type of FO element is suitable for FO-RO hybrid process for wastewater treatment and desalination. Therefore, this paper investigated to find the main factors that need to be considered for scale-up with lab-scale and element-scale experiments under different operational conditions (draw solution (DS) concentration, and flow rates of feed and draw side). For SWFO, it is limited in the changing operating conditions due to its structural characteristic. However, FSFO is relatively free to change operating conditions and the flow rate difference also show a positive effect on the FO performance (water fluxes at 20 and 30 L/min with 0.5 M of DS were around 6.0 and 13.7 L/m2h, respectively). Through the scenario of serial stage for scale-up, the volume of DS, it was found that the final concentration of DS, and the inlet pressure are the important factors for determining the suitability of FO element.