Chemical catalytic reaction and biological oxidation for treatment of non-biodegradable textile effluent

The effectiveness of a combined reduction–biological treatment system for the decolorization of non-biodegradable textile dyeing wastewater was investigated. In this treatment system, a bisulfite-catalyzed sodium borohydride reduction followed by activated sludge technique was used in order to remove the color at ambient temperature and pressure. This experimental study consisted of two major parts: reduction treatment and biological oxidation. Both synthetic and actual wastewater was used in this research. Synthetic wastewater was made by several groups of dyes such as direct, basic and reactive colors. Actual wastewater was collected from two different textile industries in the city of Isfahan, Iran. The characterization of raw and treated wastewater was carried out by infrared and ultraviolet spectrometers. The results of this study demonstrated that the newly developed treatment technique decreased color, biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) by 74–88, 76–83 and 92–97%, respectively. The IR and UV analyses showed that non-biodegradable dyes are converted to biodegradable organic compounds such as alkyl and alkenes. Another major advantage of this method with respect to other methods, namely, adsorption and coagulation, was that it removes color without causing any disposal problem. The optimum dosage for treatment of actual wastewater was found to be 50–60 mg/l for catalyst bisulfite and 200–250 mg/l for sodium borohydride. Finally, a bench-scale experimental comparison of this technique with other reported combined chemical–biological methods showed higher efficiency and lower cost for the new technique.