Possible changes of pore size during nanofiltration

The textile industry plays an important role in the world economy as well as our daily life. However, the industry consuming a large quantity of water and generating huge amount of wastewater are unsustainable to the conservation of our precious resources and environment and need improvement. The wastewater, especially the one from spent cotton reactive dyebaths, contains high salt content, various dyes and high alkalinity. This study was carried out to investigate the feasibility of membrane filtration treating spent cotton reactive dye baths. A stirred cell with nanofiltration membrane was used aiming at reusing the reclaimed water. Spent dyebath solutions were synthesized containing hydrolyzed C. I. Reactive Black 5 and sodium chloride. When a piece of membrane was used repeatedly it was expected the flux would decrease after each usage due to fouling of impurities. However, it was found that the water flux increased while dye rejection decreased after each run. At pH 10, the dye rejection decreased significantly. It was proposed that the pore sizes of membrane might have changed during membrane filtration. An equation was derived calculating the possible changes of pore sizes.