Decolorization and cod removal from synthetic and real textile dye bath wastewater containing reactive black 5

Abstract

Treatment of textile wastewater containing reactive dyes is highly important as dyes and their breakdown products are toxic. The application of chemical coagulation and Fenton oxidation on the color and the chemical oxygen demand (COD) reduction of Reactive Black 5 (RB 5) dye solu-tion, the synthetic textile wastewater (STW), and the real dye bath real textile wastewater (RTW), was investigated. Among three coagulants used, polyaluminium chloride (PAC) decolorized more than 98% of RB 5 dye at a dosage of 200 ppm and pH = 5, while most common coagulants, alum, and FeSO4, removed only 11% and 6% of RB 5 dye, respectively. PAC removed also 80% of the COD at 300 ppm dosage. All the three coagulants failed to decolorize highly saline STW containing RB 5 dye, but 80% decolorization was successfully achieved for the real textile dye bath wastewater by the polyaluminium coagulant dosage of 400 ppm while alum and FeSO4 of the same dosage reduced only about 66% and 75%, respectively. Fenton oxidation reduced 98% of the color and 61% of the COD in 100 ppm RB 5 dye at pH = 3 and dosage of 0.2 mM Fe2+ and 2.0 mM H2 O2 . The COD was reduced by 90% when Fe2+ dose was increased to 0.5 mM keeping the Fe2+:H2 O2 ratio 1:10. When pH was increased from 3 to 7, the color reduction decreased from 91% to 78%. STW was decolorized to 87% by 0.25 mM Fe2+ and 2.0 mM H2 O2 at pH = 3. For the discoloration of RTW, the optimum Fenton condition was 0.1 mM Fe2+ and 0.5 mM H2 O2 at the same acidic condition. The current study reveals that the coagulation with PAC and Fenton oxidation can be successfully used to treat the real textile dye bath wastewater containing reactive dyes.