Sustainable Cotton Dyeing Using Reused Textile Effluent Treated by Cobalt-Oxide-Activated Sulfate Radical Oxidation

Textile wastewater generated from the dyeing of cotton fabrics with reactive dyes is considered one of the most challenging types of industrial effluent to treat due to its complex chemical composition and high concentrations of residual dyes and auxiliary chemicals. Therefore, treatment methods that could lead to the reuse of treated textile effluents in the dyeing process must be explored in addressing water sustainability issues, as the dyeing process consumes a large amount of water. Previous studies have reported the efficiency of the cobalt-oxide-mediated sulfate-radical-based advanced oxidation process in reducing color by reusing the treated effluent. This work aims to study the reusability of a treated textile effluent using peroxymonosulfate (Oxone®) activated by a cobalt oxide (Co3O4) catalyst in the dyeing process for at least three reuse cycles. A novel continuous-flow reactor system with the catalyst immobilized in a permeable reaction barrier was used to treat the effluent. The effects of Oxone® concentration, dye concentration, and the number of reuse cycles at low, high, and medium levels have been evaluated on the color fastness of the dyed cotton fabrics using a Box–Behnken design. From the results, a useful, predicted model for color fastness of the dyed fabrics treated by cobalt-oxide-mediated sulfate radicals are reported. The optimization process shows that the treated effluent can be reused in three successful dyeing processes with a good (4) rating of color fastness at the predicted optimum process conditions of 4.4% dye concentration during the dyeing process and the waste-obtained effluent treated with 1.3 g/L of Oxone®. The highest chemical oxygen demand (COD) removal efficiency was achieved at a 2% dye concentration. The adjusted coefficient of determination between the experimental and model predicted values obtained from the color fastness response was 0.8352, and the model was significant at 5% (p = 0.0025). This study provides evidence that the cobalt-oxide-mediated sulfate-radical advanced oxidation process can be used for wastewater recovery and reuse in three successful dyeing processes without altering the quality of the dyed fabrics, thereby taking a step forward in addressing sustainability issues in effluent treatment.