Electrochemical Treatment Of Anthraquinone Dye With In Situ Electrogenerated Active Chlorine

Dye wastewater is characterized by complicated components,strong color,highly fluctuating pH, high concentration of COD, TOC and suspend solids, low biodegradability, widely varied quality and quantity, etc, so it has been rather difficult to treat dye wastewater. As an eco-friendly technology, electrochemical method has some significant advantages, such as little or no additional chemicals and no sludge produced, versatility, higher energy efficiency, amenability to automation, cost effectiveness, etc.In recent years, there has been increasing interest in the use of electrochemical method for the treatment of dye wastewater. Nowly, decolourization and degradation of many azo dyes have been studied by electrochemical method. However, few anthraquinone dyes, which is the second dye in the synthetic dyes, are studied with this method.The purpose of this paper is to investigate the possibility of treating C.I. Reactive Blue 19 wastewater by electrochemical oxidation via electro generated active chlorine. Absorbance at 592nm and 255nm are measured to follow the decolorization of the dye and the degradatin of its aromatic ring. The electrolysis for the simulated wastewater is conducted under potentiostatic model and galvanostatic model in a divided cell and an undivided cell, using metallic oxide coatings(DSA^?) as anode and graphite as cathod, respectively. The effect of anode potential, current density, NaCl concentration, dye concentration, initial pH, temperature and supporting electrolyte concentration,on the decolorization of the dye and the degradatin of its aromatic ring, are surveied. At the same time the effect of anode on the decolorization of the dye and the degradatin of its aromatic ring is emphatically reaserched, the effect of cathode is also analysed.Experimental results have shown that, in divided cell, 100% decolorization of the dye and about 40% degradation of its aromatic ring are achieved and the energy consumption is 0.12 (kWh/m³) after a 4-hour electrolysis under the experimental conditionsranodic potential of 1.13V, 0.5 mol/L NaCl, 0.1 mol/L Na₂SO₄, 0.1 mmol/L dye, initial pH=6.4 and T=30°C;in a divided cell, 100% decolorization of the dye and about 45% degradation of its aromatic ring are achieved and the energy consumption is 0.19 (kWh/m³) after a 4-hour electrolysis under the experimental conditions:current density of 15 A/m , 0.2 mol/L NaCl, 0.1 mol/L Na₂SO₄, 0.1 mmol/L dye, initial pH=6.4 and T=30°C; in an undivided cell, 90% decolorization of the dye and about 32% degradation of its aromatic ring are achieved and the energy consumption is 0.27 (kWh/m³) after a 6-hour electrolysis under the experimental conditions:current density of 15 A/m², 0.2 mol/L NaCl, 0.1 mol/L Na₂SO₄, 0.1 mmol/L dye, initial pH=6.4 and T=30°C.Experimental results have also suggested that no obvious change of TOC is observed in the oxidative degradation of the dye;that the decolorization of the dyeand degradation of its aromatic ring are pseudo-first-order reaction, and the decolorization rate contant is higher than degradation rate contant; that indirect electrooxidation, using electrogenerated active chlorine, is predominately in the electrochemical oxidation, while direct electrooxidation is inconspicuousness.In a divided cell and under potentiostatic model, the decolorization of the dye and degradation of its aromatic ring are directly affected by anodic potential, initial pH, concentrations of the dye and NaCl, while slightly affected by temperature and Na2SO4 concentration; in a divided cell and under galvanostatic model, directly affected by current density, temperature, concentrations of the dye and NaCl, while slightly affected by Na2SO4 concentration and initial pH; in an undivided cell and under galvanostatic model, directly affected by current density, temperature, concentrations of the dye and NaCl, and initial pH, while slightly affected by Na2SO4 concentration.Effect of cathodic reaction on the decolorization of the dye and degradation of its aromatic ring is indistinctive under the experim...