Fouling mitigation and enhanced dye rejection in UF and NF membranes via layer-by-layer (LBL) assembly and altering PVP percentage as pore former

Abstract

In this study, ultrafiltration (UF) and nanofiltration (NF) membranes with different polyvinylpyrrolidone (PVP) percentages were firstly synthesized to explore membranes with the highest flux and flux recovery ratio (FRR). From the membranes fabricated, the UF membrane containing 1 and 2% PVP, and NF membrane containing 2% PVP were selected as the optimal membranes. In the following step, the selected membranes were modified using a layer-by-layer assembly with poly 4-styrenesulfonic acid-co-maleic acid (PSSMA) (negatively charged) and poly allylamine hydrochloride (PAH) (positively charged). The positively charged membranes were prepared by placing 3 bilayers of the polymers with an extra PAH positive layer [(PAH/PSSMA)3+PAH], while the negatively charged membranes were prepared with only 3 bilayers of the polymers [PAH-PSSMA]3. To investigate the effect of electrostatic attraction and repulsion and their effect on the removal of dye, two anionic (direct red 16) and cationic (methylene blue) dyes were used. Having relatively high flux close to the UF and high color removal efficiency almost similar to the NF was the main achievement of this study with the modified UF membrane (1 wt% PVP). The characterization of the selected membrane was elucidated in detail. The stability of the filtration process for the selected membrane (UF 1 wt%) was confirmed through removing algal color from a stabilization pond effluent (turbidity reduction from 58 to 1 NTU) in a cross-flow filtration setup.