Comparison of reverse osmosis and nanofiltration membranes in the treatment of biologically treated textile effluent for water reuse Original Research Article

This study aimed to evaluate and compare the effectiveness of reverse osmosis (RO) and nanofiltration (NF) membranes in the treatment of biologically treated textile effluent in terms of COD removal, salinity reduction as well as permeate flux. Cross-flow filtration tests of the textile effluent were conducted under various hydrodynamic conditions employing BW30 reverse osmosis and NF90 nanofiltration flat-sheet membranes. The experimental results showed that, under the same operating pressure, the nanofiltration membrane NF90 exhibited higher water permeability and more severe flux decline than membrane BW30 because of its higher porosity and more serious concentration polarization and membrane fouling; while under the same initial flux, the reverse osmosis membrane BW30 experienced more serious flux decline than membrane NF90 due to its tendency towards fouling. Both the membranes could reduce COD to a desirable level of less than 10.0 mg/L. However, the nanofiltration membrane showed better COD removal efficiency compared to the reverse osmosis membrane, possibly due to its sieving removal mechanism. Additionally, the reverse osmosis membrane BW30 reduced salinity to a greater extent than the nanofiltration membrane NF90. The treated water could be recycled back into the process, thereby offering economical benefits by reducing the water consumption and wastewater treatment cost.