A Study of Treating Textile Wastewater after Reactive Dye Printing by using Nanofiltration

Abstract

A synthetically-prepared reactive dye printing wastewater was subjected to nanofiltration. Except for the dye type, the basic composition of the synthetic wastewater was similar to wastewater obtained from a local textile factory in Slovenia. The dyes used were: C.I. Reactive Red 24 and C.I. Reactive Black 5. The filtrations were carried out with two nanofiltration membranes (NFT- 50 and DL), which were evaluated for membrane fouling tendency, permeate flux, and their suitability in removing salt, colour and COD. All filtration experiments were conducted in a plate and frame module. For both the NFT-50 and DL membrane the permeate flux did not increase linearly with pressure due to concentration polarization. However, at all pressures the permeate flux obtained with the DL membrane were higher than with the NFT-50 membrane. The retentions, observed at transmembrane pressures ranging from 2-15 bar, showed that the highest retention values were achieved at 10 bar. The best separation efficiency was achieved with NFT-50 membrane where permeate samples were practically colourless. The low retention of COD for both membranes was explained by the fact that smaller organic molecules such as urea, rapidoprint (nitrobenzene sulphonate) are not retained by the membrane and therefore contributes to high COD values in the permeate.