Optimization and Enhancement of PAN Ultrafiltration Membrane for Separation of Lignin from Waste Water of Paper Mill Using Response Surface Methodology

Hypothesis: Wastewater from paper industries is one the most polluting effluents. Due to presence of polymeric compounds such as lignin, this effluent is harmful for environment and public health. In this study, ordinary and electrospun (ES) polyacrylonitrile (PAN) ultrafiltration membranes were used to separate the lignin from paper mill effluent. Methods: To improve the ultrafiltration process, response surface methodology (RSM) was employed to model and optimize the effective factors including effluent concentration, pressure and PVP concentration against rejection and flux. In addition, ‎the electrospun membranes were used to separate lignin, moreover the electrospun membranes ‎were modified by DMF vapor. Finally, the fouling effect was evaluated on all 3 types of membranes (ordinary, ES, and modied ES). Findings: The results showed that, the performance of PAN ultrafiltration membrane was acceptable to separate the lignin from the wastewater. In fact, by increasing the waste concentration the flux decreased, but the rejection first increased and then decreased gradually. Pressure increment increased the flux and decreased the rejection linearly, however, this behavior at high pressures was taken place gradually. To improve the hydrophilic effect of PAN membranes, PVP was added to the ultrafiltration membranes. So, the flux increased significantly but PVP had a negative effect on the rejection. At optimum condition, the flux and rejection of ultrafiltration membrane reached 14.76 L/m2.h and 93.91%, respectively. In electrospun membranes the flux increased at least by twice in comparison with the optimized ultrafiltration membrane, though the rejection was lower. To increase the rejection, the electrospun membrane was modified by DMF vapor. For this study, exposing of electrospun membrane to DMF vapor for 20 min gave the best results. Finally, the fouling test was accomplished on all 3 types of membrane. The electrospun membrane displayed the longest fouling time of about 210 min, however, the ultrafiltration and modified electrospun membranes were blocked after 190 and 110 min, respectively.