By-product synergy in the textile industry: Indigo waste recovery in the denim finishing process
Textile dyeing effluents present a substantial environmental problem, primarily because such wastewaters contain high concentrations of waste dyes, dye by-products, and variable salt concentrations originating from printing or dyeing processes. Such wastewater streams often do not meet regulatory standards for wastewater discharge even after undergoing treatment by conventional means. The decolorization of textile wastewaters is a worldwide problem. Various processes have been utilized to remove the colored colloidal bodies and suspended solids and to reduce the associated high Biological Oxygen Demand (BOD). ^ Currently, no single treatment system is adequate to degrade the dye structures in wastewaters. A significant disadvantage of the current processes is their high capital and operating expenditures. Oxidation methods for example, are only effective in wastewater with a very low concentration of organic color while the adsorption process by active polymer resin is expensive and it is difficult to regenerate the adsorbent. ^ Palygorskite is a crystalloid hydrous magnesium-aluminum silicate mineral with very good colloidal properties such as specific features in dispersion high temperature endurance, salt and alkali resistance, and a high adsorbing and de-coloring capability. The structure of palygorskite was first proposed by Bradley (1940), who described a theoretical formula of [Si8Mg 5O20(OH)2] (H2O)4.4H 2O. Due to its sorptive properties, Palygorskite has been effectively applied in decolorizing and clarifying mineral oils and fats, as a carrier in pesticides, in the filtration of special products, as a sorbent on factory floors, and in the pharmaceutical industry. Its ability to adsorb indigo waste and other contaminants from textile effluents however has not been studied. Palygorskite is one of the two constituents of Maya Blue, a material of unprecedented stability with potential application in paints and coatings. The properties and quality of the pigments synthesized from the recovery products compares favorably to pigments synthesized from pure products. ^ The primary objective of this research was to demonstrate the ability of palygorskite to recover waste indigo dye from blue denim wastewater and to use the recovery products as a substrate for the synthesis Maya-blue pigment, a by-product with potential commercial applications. A secondary objective was to demonstrate the simultaneous removal of salts from the wastewater without substantially compromising the quality of the synthesized pigment. Salt reductions of up to over 60 per cent were achieved. Removal of the color and salts from the wastewater essentially opens up opportunities for possible reuse of the wastewater. ^ We demonstrate the effectiveness of palygorskite to concurrently remove indigo dye and salts from the wastewater without significantly compromising the quality of the synthesized by-product. Given that over a billion pairs of blue jeans are manufactured every year and the inordinate quantities of indigo dye used and released as effluent in the stonewash process, the possibility to apply the process on a commercial scale would have substantial economic and environmental implications.^
Engineering, Environmental|Textile Technology
Wambuguh, Dennis, "By-product synergy in the textile industry: Indigo waste recovery in the denim finishing process" (2009). ETD Collection for University of Texas, El Paso. AAI3358861.