A pilot-scale fertiliser drawn forward osmosis and nanofiltration hybrid system for desalination

The usage of fresh water for both non-potable and potable purposes will increase with the surging growth in water demand. Rapid increases in population contribute to the significant consumption of fresh water resources and massive increase in food demand. Water consumption in the agricultural sector is more than 70% of the total water usage worldwide. Water scarcity is one of the greatest issues confronting people everywhere and almost one-fifth of the world’s population lives in areas of physical water scarcity. Sustainable fresh water resources have to be created and developed to solve this water problem; however, 97.5% of the earth’s water is seawater. Nevertheless, it is an abundant and unlimited source of saline water, and the desalination of seawater or brackish groundwater for both non-potable and potable water supply is therefore increasingly being considered as one of the solutions to water scarcity. A drawback is that the significant energy consumption of current desalination technologies mostly contributes to the cost of desalination. Cost-effective desalination technology for non-potable water, particularly for irrigation use, would contribute to a significant reduction in freshwater consumption and would make more freshwater available for other potable uses. One of the most promising technologies is the forward osmosis (FO) process in which the driving force is generated by the concentration gradient, unlike the reverse osmosis (RO) process where the driving force is hydraulic pressure, which leads to significant energy consumption. In the FO process, freshwater is extracted from saline water and flows to a concentrated draw solution (DS) using a special FO membrane. However, the FO process still has issues such as the lack of a suitable DS and FO membrane, resulting in it is having limited application for drinking water supply purposes. In addition, an additional process to separate DS solutes and pure water is required which could lead to increased energy consumption. Considering the challenges of the FO process for potable water, a novel concept of fertiliser drawn forward osmosis (FDFO) has recently been introduced. In this process, a highly concentrated fertiliser solution is used as the DS to extract water from saline water sources using a semi-permeable membrane by natural osmosis. The main concept and advantages of the FDFO desalination process is that the final product water, the diluted fertiliser DS, can be used for direct fertigation and thus the separation of draw solutes is not necessary. The FDFO process requires significantly less energy because there is almost zero hydraulic pressure. However, because of a number of intrinsic process limitations with FO, the diluted fertiliser DS does not usually meet the water quality standards for direct fertigation especially when a high salt concentration of feed water is used. The final diluted DS may require dilution to several orders of magnitude before it is suitable for direct application. To reduce the concentration of the diluted DS, the…