Forward Osmosis for irrigation Water Supply Using Hybrid Membrane System for Draw Solution Regeneration

Forward Osmosis (FO) process was applied for irrigation water supply using fertilizers and seawater as the draw and feed solutions. Four agents, KNO3, Na2SO4, CaNO3, and MgCl2, plus 35 g/L seawater were used as the draw and feed solutions of the FO process. Net Driving Pressure (NDP) in FO process was manipulated either by increasing the concentration of draw solution (FO process) or by increasing feed pressure (Pressure Assisted FO; PAFO process). Series of NF and RO membranes were used for the regeneration of draw solution. The results showed that PAFO was more energy efficient than FO provided using the low energy of brine flow from the NF/RO membrane for pressurizing the feed solution of PAFO process. Furthermore, the study suggested using a mixture of a primary draw solution, MgCl2, and a secondary draw solution, KNO3, for NO3 supply into the irrigation water. As such, MgCl2 provided the driving force for fresh water extraction while KNO3 is the source of fertilizer for irrigation water. Results showed that water quality provided by MgCl2+KNO3 mixture draw solution was better than that from KNO3 or Ca(NO3)2. The concentrations of NO3 and SO4 in irrigation water were within the recommended level when the diluted draw solution was regenerated by a dual stage low pressure RO process.