Investigating fertilizer drawn forward osmosis process for groundwater desalination for irrigation in Egypt

Abstract

Groundwater desalination could be a possible solution to Egypt’s water scarcity problem through applying state-of-the-art desalination technologies. This work investigated a recently developed sustainable desalination technology which is fertilizer drawn forward osmosis (FDFO). In this work, ammonium sulfate was selected as a draw solution being a commercial, inexpensive, and efficient Egyptian fertilizer. Three commercially available Forward Osmosis (FO) membranes were tested for baseline flux. The best membrane was selected for further experimentation. A real Egyptian brackish groundwater sample from El Tor in Sinai was used as the feed solution. Performance has been assessed by the water flux, reverse permeation, and the forward rejection of the feed solutes. Porifera’s commercial FO membrane proved to be the best membrane with respect to baseline flux. It was chosen for further experimentation. Water flux and ammonium sulfate concentration can be correlated logarithmically. Further increase in ammonium sulfate concentration decreases water flux gradually due to increased severity of concentration polarization effects that take place at high draw solution concentration. Specific Reverse Solute Flux (SRSF) values did not exceed 0.18 g/l for both NH4+ and SO42- ions, indicating high membrane selectivity. At flux exceeding 20 Lm−2 h−1, NH4+ ion reported higher SRSF values than that of SO42- ion, a phenomenon that could be attributed to thermodynamic influence. SRSF is almost constant irrespective of ammonium sulfate concentration. While increasing draw solution concentration lead to increasing Na+ ion rejection, it caused a significant decline in Cl– ion rejection. This phenomenon could be probably associated to an ion exchange mechanism and the membrane surface charge. In conclusion, the scheme studied showed that ammonium sulfate is an efficient draw solution for FDFO process using Porifera’s commercial FO membrane exhibiting high osmotic pressure, low reverse solute permeation, and remarkable rejection of feed solute.