Application of molasses as draw solution in forward osmosis desalination for fertigation purposes

Certain challenges exist in forward osmosis (FO) separation technique that has to be studied yet such as a selection of a proper draw solution (DS) to supply the required driving force for separation. In this work, the performance of molasses DS in terms of water flux (Jw) was evaluated using a commercial FO membrane. Deionized water (DIW), an oilfield brackish wastewater (BWW) and seawater (SW) were used as three different feed solutions (FS). Effects of molasses concentration (CDS) and solutions cross-flow velocities on Jw were investigated. The results indicated that the relationship between Jw and CDS is non-linear that may be attributed to internal concentration polarization in the membrane support layer. Jw was improved slightly by increasing the FS velocity and enhanced moderately by increasing the DS velocity from 6 to 11.5 cm/s. Fluxes of 16.7, 13.3 and 7.5 LMH were obtained during 30 min against the feeds of DIW, BWW and SW, respectively. After 12 h, the osmotic pressure of molasses is reduced from an initial value of 79.8 bar to 54.5, 62.8 and 66.3 bar for the FSs, respectively. Reverse solute flux is increased by decreasing Jw and is more significant at values lower than 10.67 LMH for DIW feed. Based on the results, Molasses has a good performance ratio in comparison to other fertilizers and diluted molasses can potentially be used for fertigation purposes.