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We report on the effectiveness of a combined reduction-biological treatment system for the decolourization of non-biodegradable textile dyeing wastewater. In this treatment system a bisulfite-catalyzed sodium borohydride reduction followed by activated sludge technique was used in order to remove the colours at ambient temperature and pressure. This experimental investigation consisted of two major parts: reduction treatment and biological oxidation. Both synthetic and actual wastewaters were used in this research. Synthetic wastewaters were made by several groups of dyes such as direct, basic and reactive colours. Actual wastewaters were 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 ASTM-E450-82 method was used to measure the colour. The results of this study demonstrated that this biological treatment technique decreased colour, BOD, COD and TSS by 74 to 88%, 97 to 100%, 76 to 83% and 92 to 97%, respectively. The IR and UV analyses showed that nonbiodegradable dyes are converted to biodegradable organic compounds such as alkyl and alkens. Another major advantage of this method with respect to other methods, namely, adsorption and coagulation, was that it removes colour without causing any disposal problem. The optimum dosage for treatment of actual wastewaters was found to be 50 to 60 mg/L for catalyst bisulfite and 200 to 250 mg/L for sodium borohydride. Finally, a benchscale experimental comparison of this technique with other combined chemical and biological methods currently used showed higher efficiency and lower cost for the newly developed technique.

A Combined Chemical Reduction and Biological Oxidation Process for the Treatment of Textile Wastewater