Seawater Desalination and Industrial Wastewater Recovery Using Hybrid Forward and Reverse Osmosis at the Pilot System Level

Forward osmosis (FO) is an emerging membrane technology that offers certain advantages over currently implemented forms of water treatment, reuse, and desalination. When coupled with reverse osmosis (RO), an economically viable technology solution can unfold as a hybrid FO-RO system. In this, FO acts as a pretreatment to RO while RO regenerates the spent draw solution and produces fresh water. For several years now, bench-scale tests have been done on this type of configuration, but information on module scale performance, system scale-up, system dynamics, effects of operating conditions, and recovery rate is lacking. In order to evaluate these parameters, a pilot-scale system with commercial FO and RO membrane modules is assessed. Performance was assessed for each system (RO and FO) individually and while run in tandem using similar operating conditions. From initial tests, we find no significant difference between the two setups in terms of osmotic performance, rejection, and recovery. From FORO operation, it has been found that feed volumes for both FO and RO systems need to be replenished quickly at high recovery rates. It was also seen that operating the RO system at low pressure self regulates overall dynamics of the system. Further, it was observed that high permeation of solute in either the feed (in FO) or permeate (in RO) limits long time closed loop operation. Future work will focus on the self-regulating nature of FORO, the effect of recovery on overall system performance in terms of rejection in RO and solute flux in FO, the effect of draw solute type, concentration, flowrate etc., the effect of module type, and a side by side comparison with pilot scale to bench scale systems.