Preparation, morphology and performance evaluation of polyvinylalcohol (PVA)/polyethersulfone (PES) composite nanofiltration membranes for pulp and paper wastewater treatment

In this study, thin film composite PVA/PES nanofiltration membranes were fabricated for the treatment of pulp and paper industrial wastewater. Phase separation induced by immersion precipitation was used to prepare the PES support membrane. PVA/PES composite nanofiltration membranes were prepared by dipping the support PES membrane in the PVA and cross-linking solutions at different conditions. Maleic acid (MA) was used as cross-linking agent. PVA and MA have concentrations of 0.5-2 and 0.05-1 wt%, respectively. Morphological studies were carried out by means of scanning electron microscopy (SEM) as well as atomic force microscopy (AFM) techniques. In addition, the hydrophilicity of membranes was examined by contact angle measurements. Permeability and ability of PVA/PES composite nanofiltration membranes to reduce COD of the wastewater were evaluated by a cross flow filtration system. SEM images indicated that the PVA layer was uniformly formed on the PES support membrane. AFM images showed that the surface roughness, porosity and pore sizes of PES support membrane were reduced after formation of PVA layer on the support surface. Moreover, the hydrophilicity of the membranes was significantly increased. Experimental results demonstrated that the PVA/PES composite nanofiltration membranes were able to reduce the COD of wastewater. Optimum conditions for preparation of PVA/PES composite membrane are consisted of PVA concentration: 1 wt%, MA concentration: 0.5 wt%, cross-linking time: 3 min and curing time: 3 min.