3. Nanofiltration of Dye Bath Towards Zero Liquid Discharge: A Technical and Economic Evaluation

A dye bath effluent is the most resource-rich stream in a dye house in the textile industry with almost all salts used and 0–40% of unfixed dyes, and 10% of water in a wet process. A lot of effort has been made to breakdown dyes physically, chemically and biologically and mainly for meeting the local government discharge standard, however, salts in the dye bath are unchanged and are simply diluted and discharged to the environment. Both salts and dyes are valuable commodities. If they are recovered, less resources will be wasted and less damage will be done to the environment. This is beneficial to both the industries and the environment. Membrane filtration is an effective tool to separate chemicals according to their sizes and surface charges without altering their properties. In this chapter, we reviewed the development of Nanofiltration membrane technology (NF) in terms of lower salt rejection and membrane fouling and proposed the mechanisms of membrane pore enlargement during separating salts from dye in a dyebath for recovery, recycling and reuse. We also mentioned the industries that use dyes and pigments in their daily operations. We have concluded that membrane swelling/pore enlargement remains a challenge on NF application.