Composite membranes with multifunctionalities for processing textile wastewater: Simultaneous oil/water separation and dye adsorption/degradation

In this work, we report on a novel membrane design with both photocatalysis and electrocatalysis for simultaneous oil/water separation and dye adsorption/degradation to treat oily wastewater from textile dyeing and finishing. The membrane (designated as PAN-CF/MWCNT/FeOOH) comprised a cotton fabric (CF) dopped with carbon nanotubes (MWCNT) and FeOOH and a microporous polyacrylonitrile (PAN) top layer. Under a flow-through dynamic filtration mode, the membrane allowed for separation of oil-in-water emulsions by the PAN layer via wettability sieving and coalescence demulsification, while hydrosoluble dyes were captured and degraded by the CF/MWCNT/FeOOH via adsorption and in situ electro-degradation. The kinetics of adsorptive capture and electro-induced degradation of hydrosoluble dyes on the PAN-CF/MWCNT/FeOOH membrane was determined, which confirmed that the flux decline during flow-through filtration caused by the accumulated foulant in the membrane was alleviated effectively. A flow-through filtration test with methylene blue (MB) dyed petroleum ether-in-water emulsion showed that a high removal rate of oil (99.9 %) and dyes (97.6 %) was achieved simultaneously in a single pass at a high water permeability (17.2 m3/m2.h.bar) under an operating pressure of 6.5 kPa and a DC current of 10 mA. In addition, the fouled membrane could be cleaned easily via photo-Fenton degradation under light irradiation. This novel approach to the design and fabrication of membranes with multifunctionalities is expected to offer numerous advantages for treating complex oily wastewater from textile processing.