Pretreatment of the textile dye wastewater was accomplished using reducing agents. The reducing agents studied were sodium hydrosulfite, thiourea dioxide, and sodium borohydride. Preliminary tests were conducted using just the reducing agents. Although there was color reduction, the reduced wastewater was inhibitory to biological degradation. Additional tests were conducted with sodium hydrosulfite. These included reductions followed by pH adjustment, nutrient addition, pH adjustment and nutrient addition, and lime addition. These tests were also successful in reducing the color but were not biologically degradable.

Reduction of the dye wastewater followed by oxidation, however, provided positive results (color reduction and biodegradation). A series of reduction/oxidation experiments on the textile wastewater were performed: treatment of 17 percent, 33 percent, 67 percent, and 100 percent of the textile wastewater stream. The wastewater is composed of 75 percent textile and 25 percent municipal wastewater. For the 17, 33, and 67 percent of the textile wastewater pretreated with reduction/oxidation, untreated textile and municipal wastewater were added before transfer into sequencing batch reactors for biological treatment. For the 100 percent textile wastewater stream, the initial, untreated parameters were: 2650 American Dye Manufactures Institute (ADMI) color; 780 mg/L COD; 211 mg/L TOC; and 182 mg/L BOD. The reduction/oxidation pretreatment followed by biological treatment resulted in effluent values of 615 ADMI color (77 percent reduction), 310 mg/L COD (60 percent reduction), 82 mg/L TOC (61 percent reduction), and 62 mg/L BOD (66 percent reduction).