THE EFFECT OF OPERATING CONDITIONS ON THE PERFORMANCE OF A VACUUM MEMBRANE DISTILLATION UNIT USING PES FLAT SHEET MEMBRANE

Abstract

Vacuum Membrane Distillation (VMD) is a new separation technology based on the evaporation of saline water through hydrophobic porous membranes by applying vacuum pressure on the permeate side of the membrane to desalinate seawater. A lab scale experimental model was constructed and operated using hydrophobic polyethersulfone flat sheet membrane (PES), modified PES membrane, and PVDF membrane to study the effect of operating conditions on the performance of the VMD unit. Resultant permeate flux and salt rejection were measured for the following operating conditions: feed flow temperature (25-40-50-60-70°C), flow rate (1-1.2-1.3-1.4-1.5-1.6 L/min), salt concentration (5000, 10000, 15000 and 30000 ppm), and vacuum pressure (-0.2,-0.3,-0.4,-0.5 Bar). Results showed an increase in permeate flux due to increased temperature, flow rate and vacuum pressure, while it decreased with the increase in salt concentration. An increase in salt rejection was observed due to increased temperature, feed flow rate and vacuum pressure, while it decreased with the increase in salt concentration. An increase in salt rejection was observed due to increased membrane contact angle (membrane hydrophobicity). The system can be used at room temperature and low pressure (decrease energy cost), the system satisfy the allowable values for treated water for drinking water.