Removal Or Degradation Of Azo Dye From Aqueous Solution

The azo dye wastewater is characterized with high value of CODcr, complication of organic components, more difficult remediation, and high colority. Increasing attention has been focused on the economic and efficient procedure for the decolorization or degradation of azo dyes aqueous solution. The methods used for treating azo dye wastewater are described. Progress in treatment of azo dye pollutants in water by using ultrasound technology (including ultrasound irradiation individually and ultrasonic waves in conjunction with other techniques) is reviewed.Decolorization or degradation of azo dyes aqueous solution by ultrasound/exfoliated graphite, ultrasound/Fenton, ultrasound/Fly ash/H2O2 and kaolinite was studied. The results showed that the processes are effective in removing azo dyes from aqueous solution.A combination of ultrasound and exfoliated graphite was used to treat Acid Brown 348 and Direct Blue 78 aqueous solutions, respectively. The influence of various affecting factors, such as irradiation time, reaction temperature, pH value and the initial concentration were systematically evaluated. The model of azo dye adsorption on exfoliated graphite under ultrasound irradiation was investigated. It can achieve better results than either exfoliated graphite or ultrasound only. Low pH value is conducive to the removal of the dye. The Langmuir and Freundlich isotherms were used to observe sorption phenomena of exfoliated graphite under ultrasound irradiation. The results have shown that the Langmuir isotherm and Freundlich isotherm were well fitted into the experimental data. In the optimum conditions, the removal ratio of Acid Brown 348 from industrial wastewater was 85.0%.Fenton process is one of the advanced oxidation technology, and it combined with ultrasound is effective to degrade the organic contaminations. In the combination of ultrasound and Fenton reagent, the degradation efficiency of 98.6%(Acid Red 88) and 99.9%(Acid Red 97) was achieved respectively. Based on the degradation compounds identified from UV-Vis, FT-IR and LC-MS, reaction scheme of the degradation of Acid Red 88 in the US/Fenton system is proposed. The kinetics of ultrasound/Fenton oxidation of Acid Red 97 can be described by pseudo-first-order kinetic model. Degradation of Direct Black 168 from aqueous solution using US/Fenton-like system was investigated. The effect of the heterogeneous catalysts, such as fly ash, kaolinite or diatomaceous earth on the degradation of Direct Black 168 was observed under ultrasound. The fly ash was the most efficient catalyst and the 99.0% removal ratio was achieved. In the US/Fenton, the degradation of Acid Red 88 from industrial wastewater was 97.2%.Kaolinite is a kind of common, cheap mineral clay. The adsorption of Acid Brown 75 onto kaolinite in aqueous solution was studied with respect to the pH, adsorbent dosage, contact time, initial concentration and operating temperature. Experimental data indicated that pH value plays an important role, the adsorption capacity of kaolinite for the dye was higher in acidic rather than in basic solution. At the optimal adsorption condition, the dye removal ratio was 95.5%. The linear Langmuir and Freundlich isotherm models were well fitting to represent the experimental data. The removal of Acid Brown 75 from industrial wastewater was 66.2%.The use of heterogeneous photodegradation for wastewater treatment is emerging as an effective treatment technique. TiO2 assisted photodegradation of azo dyes in aqueous solution in sunlight was observed. The degradations of ten experimental azo dyes were almost 100.0% except Acid Orange 74 which was 47.8%; the various affecting factors about the photodegradation of azo dye Direct Blue 78 in aqueous solution was investigated. The possible intermediates during degradation process were monitored with UV-Vis spectrum and LC-MS. Based on the degradation compounds, a possible pathway for the photocatalytic degradation of Direct Blue 78 is proposed.