Aluminum Sulfate as an Innovative Draw Solute for Forward Osmosis Desalination

Abstract

Forward osmosis (FO) is a membrane technology which has attracted attention for water treatment and desalination. However, selecting an appropriate draw solute is vital to optimize its performance. This study seeks the efficiency of aluminum sulfate as an alternative draw solute in FO desalination with a cellulose triacetate (CTA) membrane. The effects of operating parameters on the performance of the FO were studied such as feed and draw temperatures, concentrations and flow. The experiments revealed that the permeate flux was improved by monitoring draw temperature, with a maximum of 2.5 L/m2 h was obtained at 53 °C. Also, the permeate flux was found to decrease with feed concentration. A maximum permeate flux of 2 L/m2 h was obtained at a draw flow rate of 35 L/h and draw concentration of 1 mol/L. On the other hand, using deionized water as feed solution yielded a reverse aluminum sulfate flux of 1.46 g/m2 h. The plots of the experimental and the modeling water flux displayed analogous trends in all tests, but the results showed a large deviation which was attributed to reverse solute flux, internal polarization concentration (ICP), external polarization concentration (ECP) and membrane fouling. Precipitation reaction using calcium hydroxide served to recover product water from the diluted draw solution. This operation was carried out via a precipitation reaction of aluminum sulfate with calcium hydroxide to eliminate the soluble chemicals like insoluble aluminum hydroxide and calcium sulfate. Eventually, aluminum sulfate draw solution was recovered by the reaction of aluminum hydroxide with sulfuric acid.