Brackish water desalination for agriculture: Assessing the performance of inorganic fertilizer draw solutions

Abstract

Fertilizer drawn forward osmosis (FDFO) is a cost-effective technology for brackish water desalination. The diluted fertilizer draw solution can be used to supply nutrients to crops instead of separating it from the desalinated water. This work evaluates the performance of the FDFO using four fertilizer draw solutions with various concentrations (1.0, 1.5, 2.0 mol/L) and a polyamide thin film composite (TFC) FO membrane for brackish water desalination. The results revealed that KCl fertilizer draw solution achieved the highest water flux and adequate reverse salt flux as compared to other fertilizer draw solution. The mixture KCl + KNO3 and KH2PO4 fertilizer draw solution generated the lowest water permeation and reverse salt flux. KH2PO4 draw solute promoted the growth of salt scaling which affected the membrane productivity in terms of water flux. The negatively charge of the membrane surface was responsible for precipitation of salt on the selective layer. This influenced the performance and resulted in low water permeation and minimum loss of nutrients in the fertilizer draw solution. The advantage of FDFO is in not needing a recovery step to reconcentrate the draw solution, instead using diluted draw solution as a supplement to irrigation water via fertigation.