A combined chemical reduction and biological oxidation process for the treatment of textile wastewater

We report on the effectiveness of a combined reduction-biological treatment system for the decolourization of non-biodegradable textile dyeing wastewa ter. In this treatment system a bisulfite-catalyzed sodium borohydride redu ction followed by activated sludge technique was used in order to remove th e colours at ambient temperature and pressure. This experimental investigat ion consisted of two major parts: reduction treatment and biological oxidat ion. Both synthetic and actual wastewaters were used in this research. synt hetic 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 r aw and treated wastewater was carried out by infrared and ultraviolet spect rometers. The ASTM-E450-82 method was used to measure the colour. The resul ts of this study demonstrated that this biological treatment technique decr eased colour, BOD, Coo and TSS by 74 to 88%, 97 to 100%, 76 to 83% and 92 P o 97%, respectively. The IR and UV analyses showed that nonbiodegradable dy es are converted to biodegradable organic compounds such as alkyl and alken s. Another major advantage of this method with respect to other methods, na mely, adsorption and coagulation, was that it removes colour without causin g any disposal problem. The optimum dosage for treatment of actual wastewat ers was found to be 50 to 60 mg/L for catalyst bisulfite and 200 to 250 mg/ L for sodium borohydride. Finally; a bench-scale experimental comparison of this technique with other combined chemical and biological methods current ly used showed higher efficiency and lower cost for the newly developed tec hnique.