Photocatalytic oxidation of a reactive azo dye and evaluation of the biodegradability of photocatalytically treated and untreated dye

The purpose of this study was to investigate the photocatalytic oxidation of a reactive azo dye and determine the improvement in the biodegradability when photocatalytic oxidation was used as a pretreatment step prior to biological treatment. The results obtained from the experiments adding H2O2/TiO2 show that the highest decolorisation rate is provided by the combination of (UV+TiO2+H2O2). The decolorisation efficiencies were 18%, 22%, 34% and 52% in the runs UV, UV+H2O2, UV+TiO2 and (UV+TiO2+H2O2) after approximately 100 min illumination periods, respectively. The decolorisation rate was increased significantly by initially increasing the concentration of TiO2 in the dye solution; however, it was decreased due to the reduced light transmission when the concentration of TiO2 was in excess. The decolorisation rate constant was 0.018 ± 0.002·min -1 in the presence of 1 g·l-1 TiO2 while it was 0.004 ± 0.001·min -1 in the presence of 0.125 g·l-1 TiO2. The results of the obtained oxygen uptake rate measurements in biological activated sludge have shown that the photocatalytically treated dye was easier to degrade than untreated dye. The ability of the activated sludge to degrade glucose was not inhibited in the presence of photocatalytically treated and untreated dye. Also, the biodegradability of photocatalytically treated and untreated dye was investigated via the biological oxygen demand (BOD) test. The results indicated that further degradation of the treated dye may take place by activated sludge in aerobic conditions.