Direct Blue 71 Degradation in the Presence of ZVI and H<sub>2</sub>O<sub>2</sub> Advanced Fenton Process: Determination of Optimum Conditions and Kinetics

This study investigated color and COD removal of azo dye Direct Blue 71 (DB71) by a Fenton-like process in zero-valent iron (Fe 0 = ZVI).The UV-vis spectra of DB71 exhibit three main absorption bands -two in the UV region and one in the visible region.UV-vis spectra showed that the azo linkages in the molecule structure of the dyes were destroyed during the decolorization.The influence of various operational parameters such as pH, ZVI dosages, hydrogen peroxide (H 2 O 2 ) concentrations and temperature are studied to determine the optimum conditions for color and COD removal.pH is highly effective parameter of decolorization and COD destruction in this work.However, H 2 O 2 concentration and ZVI dosages were not only effective in the removal of COD for 100 mgL -1 initial DB71 concentration.Therefore, the optimum ZVI:H 2 O 2 ratio is based on determining the value of COD removal.Optimum conditions were accepted to be pH of 2.5, ZVI:H 2 O 2 ratio 4:1 and 20ºC temperature.The result indicated that 100% of decolorization efficiency was achieved within 20 min in the range of 150-400 mg/L initial DB71 concentrations by using optimal conditions.Residual COD values were 15.38, 22.35, 22.58, 27.04, 31.86 mg/L for 150, 200, 250, 300, 400 mg/L initial DB71 concentrations at the end of reaction time, respectively.Additionally, increasing the reaction temperature from 20 to 40ºC negatively affected the decolorization and degradation rate DB71.The experimental kinetic data are fitted very well the Behnajady-Modirshahla-Ghanbery model for color removal of DB71 dye.