Fouling control in a forward osmosis process integrating seawater desalination and wastewater reclamation

A hybrid system that combines forward osmosis with a reverse osmosis seawater desalination process could reduce both energy requirements and environmental impacts by osmotic dilution of the seawater and concentrated brine with an impaired low salinity stream, such as treated wastewater effluent. In this study, we investigate the membrane fouling behavior in forward osmosis under conditions simulating the osmotic dilution process and the use of hydrodynamic methods without the use of cleaning chemicals, to control membrane fouling. Fouling runs with seawater or SWRO brine draw solution and deionized (DI) water feed solution showed insignificant water flux decline, which implies negligible effect of particulate and organic matter in the seawater/brine on fouling of the FO membrane support layer. Fouling of the membrane active layer was evaluated by using an enriched synthetic wastewater effluent containing a mixture of inorganic and organic foulants, focusing on the impact of permeate drag force on fouling layer formation. Our results demonstrate that higher permeate water flux causes an increase in concentration build-up of foulants at the membrane surface, thereby forming a dense inorganic/organic combined fouling layer during FO fouling runs. We also examined three hydrodynamic methods for minimizing FO membrane fouling in the osmotic dilution process: (1) applying shear force on the membrane surface by increasing the cross-flow velocity, (2) using a feed-channel spacer to induce turbulence, and (3) employing pulsed flow to remove foulants from the membrane surface. Our results show that these hydrodynamic methods substantially reduce fouling and flux decline rate.