Membrane Technologies for Fractionation of Dye/Salt Mixture and Resource Reuse in Textile Industry

Textile wastewater is generated during the dye production and textile dyeing process and typically has a high salinity (>6.0% NaCl or >5.0% Na2SO4). A typical 200-350 m3 of pure water is required for producing one ton of dye products, which in turn leads to the generation of a huge amount of textile wastewater. This kind of wastewater contains high concentrations of dyes, with a detrimental toxicity for the environment and for humans through e.g., azo functional groups. Furthermore, upon exposure to light, the chromophore structure of the dyes absorbs the light. This phenomenon hinders the photosynthetic activity of aquatic organisms. Therefore, these severely polluted streams should be appropriately treated before disposal. In the current concept of sustainability for wastewater treatment, wastewater is to be considered a resource rather than a waste, in view of resource production and water reclamation. The reuse of dyes from textile wastewater not only remarkably reduces the expenditure of dyes, but also tremendously lowers the toxicity to the aqueous environment. However, conventional approaches (i.e., adsorption, coagulation, biological treatment and advanced oxidation processes) mainly focus on dye removal or destruction, reducing the possibility for dye recovery and salt reuse from textile wastewater. Therefore, state-of-the-art treatment technologies focusing on recovery of valuable resources from textile wastewater are on the research agenda. In this thesis, the novel membrane technologies are put forward to treat the textile wastewater. The general aim of the thesis is to investigate the feasibility of fractionate dye/salt binary mixtures in view of dye and salt recovery. The main contents of the thesis are: (1) To investigate the potential of loose nanofiltration membrane in the fractionation of dye/NaCl mixture; (2) To study the hybrid nanofiltration and bipolar membrane electrodialysis process for textile wastewater treatment, in view of resource recovery and zero liquid discharge; (3) To test the application of tight ultrafiltration membrane in the separation of dye/Na2SO4 binary mixtures; (4) The feasibility of modification of ultrafiltration membrane by nanoparticle incorporation for enhanced performance.nrpages: 220status: publishe