A dual-layer, nanofibrous styrene-acrylonitrile membrane with hydrophobic/hydrophilic composite structure for treating the hot dyeing effluent by direct contact membrane distillation

Abstract

A robust, nanofibrous membrane with dual-layer composite structure and remarkable features has been developed in this work. The new membrane is based on the affordable styrene-acrylonitrile (SAN) polymer and a commercial hydrophilic nonwoven for the support layer. This can help to step forward the industrialization of the direct contact membrane distillation (DCMD) process for treating the hot dyeing effluent in the textile industry. The modified electrospinning with a gas-jet surrounding the Taylor cone was used for fabricating the membrane samples. Using the gas-assisted electrospinning, a nanofibrous nonwoven structure embedded with micro-cups and micro-spheres can be achieved in a one-step, gas-assisted electrospinning. The hydrophilic substrate was used for enhancing the permeate flux of the resultant composite membrane. The fabricated membrane showed remarkable features in comparison with a commercial polytetrafluoroethylene (PTFE) membrane, including high surface hydrophobicity (≥148°), higher porosity (≥81%), and smaller tortuosity factor (1.71). The unique properties of the membrane with the best performance provided a promising permeate flux (28.31 kg.m−2.h−1) and contaminant rejection (RCOD: 98.15%) compared to the commercial membrane (flux: 18.50 kg.m−2.h−1 and RCOD: 97.10%), without considerable pore wetting. However, the new membrane possessed lower liquid entry pressure (LEP) owing to its higher porosity, larger maximum pore size (0.76 μm), and thinner structure (150 μm). Results indicated that the decline in the permeate flux was mainly caused by the cake layer formation on the surface of the membrane rather than the partial pore wetting during the long-term operation for 48 h. Therefore, the newly developed nanofibrous SAN membrane with hydrophobic/hydrophilic composite structure is a promising, robust candidate for DCMD application in the textile wastewater treatment.