Clean cotton dyeing in circulated dyebath of waste cooking oil: A feasible industrialization strategy for pollution minimization

Abstract

To circumvent wastewater concern of textile industry and cost-effectively utilize waste cooking oil, this study replaced water with waste cooking oil (WCO) in reactive dyeing, and enabled circulated utilization of WCO without jeopardizing dyeing quality, as well as value addition to WCO industry. Current textile dyeing process discharges tremendous amount of wastewater comprised of high concentrations of salts and hydrolyzed dyes. However, none of the existing remediation methods, such as optimization of dyeing processes, chemical modifications of fibers and post-dyeing treatments, showed effectiveness or efficiency. In a dual-phase reactive dyeing, oil and water were used to disperse dye particles and swell cotton fibers. Dyes could be quickly dissolved in water phase and adsorbed into cotton fibers from the interface of water and oil. Though non-edible WCO could be used as a medium for salt-free reactive dyeing, WCO degraded during dyeing and showed gradually deteriorated dyeing quality if repeatedly used. For the first time, this work quantified influence of glycerol and sodium fatty acid, two main WCO hydrolysates, on dyeing results, and revealed the influencing mechanism. As a solution, alkaline refinement was applied after each dyeing cycle to revive functionality of the WCO medium, and could effectively enable WCO reusable in reactive dyeing. Effluent from conventional reactive dyeing could contain up to 100 g/L electrolytes and 50% of initially added dyes, while effluent from WCO reactive dyeing contained no electrolytes and minimal amount of dyes, and could be discharged after simple treatment. Regarding value addition to WCO, textile route might also be economically favorable than biodiesel route. Overall, the WCO reactive dyeing system could have good industrialization potential as a cleaner textile wet process.