A Study On Decoloration Behaviour Of Reactive Dye Wastewater With Electrochemical Method

Dyeing and printing industry is one of the highest water-consuming industries, which is characteristic of enormous water demand quantity, strong color, high concentration of COD, low biodegradability, widely varied quantity, and serious damage to environment, etc.Thus the treatment of dye wastewater has been a hotspot and a difficult point all through. Electrochemical method has some significant advantages, such as no additional chemicals and little sludge produced, amenability to automation, small floor space for its equipment etc.The purpose of this paper is to investigate the decoloration behavior of treating reactive dye wastewater by electrochemical method with sacrified anode. The three kinds of reactive dyes(Reactive red M-3BE、 Reactive yellow M-3RE and Reactive black KN-B) are selected as experimental objectives, which are characteristic of representative molecular structures and great outputs. Absorbance at characteristic wavelength of the three kinds of reactive dyes in UV and visibility are measured to follow the decolorization of the dye wastewater. The electrolysis for the simulated waster is conducted under galvanostatic model in a self-regulating undivided cell, using iron or aluminum as sacrificial anode and stainless steel as cathode. The decolorization efficiency, kinetics and energy consumption of dye wastewater are comparatively analyzed and the decolorization behavior is discussed.The decloration mechanism of dye effuluent with sacrified anodes is enriched, which makes the foundation for the application of electrochemical method in the treatment of practice dye wastwater with sacrified anodes.Experimental results have shown that the electrochemical methods with iron or aluminum anode take significant effects on the decolorization of the three kinds of reactive dyes wastewater. Decolorization efficiency is various under different current density, initial pH, species and concentration of electrolyte, initial concentration of dye, electrolysis time, water temperature and structure of dye. When NaCl is added, higher decolorization efficiency is achieved than when Na2SO4electrolyte is added.Experimental data are achieved under these same experimental conditions:50mg/L dye, T=25℃,0.0lmol/L Na2SO4,600r/min-stirring speed,60-min electrolysis. For Reactive Red M-3BE,92%decolorization of the dye and30.8%COD removal efficiency are achieved and energy consumption is1.53kWh/kg under current density of1.25mA/cm2, pH=7.53, iron anode. When electrolyte is changed into NaCl, maximal decolorization is98%.59%decolorization of the dye and17.1%COD removal efficiency are achieved and energy consumption is71.7kWh/kg under current density of10.42mA/cm2, pH=6.87, aluminum anode. When electrolyte is changed into NaCl, maximal decolorization is98.2%. For Reactive Yellow M-3RE,30%decolorization of the dye and18.9%COD removal efficiency are achieved and energy consumption is82.6kWh/kg under current density of4.17mA/cm2, pH=7.26, iron anode. When electrolyte is changed into NaCl, maximal decolorization is99%.54.5%decolorization of the dye and25.3%COD removal efficiency are achieved and energy consumption is85.7kWh/kg under current density of8.33mA/cm2, pH=7.39, aluminum anode. When electrolyte is changed into NaCl, maximal decolorization is98%. For Reactive Black KN-B,93%decolorization of the dye and36.6%COD removal efficiency are achieved and energy consumption is4.14kWh/kg under current density of4.17mA/cm2, pH=7.26, iron anode. When electrolyte is changed into NaCl, maximal decolorization is93%.51%decolorization of the dye and30.4%COD removal efficiency are achieved and energy consumption is236.9kWh/kg under current density of8.33mA/cm2, pH=7.39, aluminum anode. When electrolyte is changed into NaCl, maximal decolorization is88.6%.Coagulation and redox of the dye cooperate in the decolorization process. The results show that the structures of dyes are broken and transform into new substances. The reactive dye structure take a important role in the decolorization process.For Reactive Yellow M-3RE, hydrogenation redox is dominant when the color removal is higher.When the pH is low, for Reactive Red M-3BE and Reactive Black KN-B, hydrogenation redox and complexation of ferrous ion and dye cooperate in the decorization process with iron as sacrified anode, while hydrogenation redox is dominant by aluminum; Between pH4-9, coagulation is dominant by iron or alunimun anode, and precipitation and entrapment adsorption prevail in the process.The decolorization of three kinds of dye wastewater is in accordance with the first order reaction. The decolorization rate contant is directly affected by current density, initial pH and concentrations of the dye. The effects of current density, initial pH, concentrations of the dye and electrolyte on the energy consumption are distinctive.For the practice textile wastewater, clear treatment results are obtained with iron and aluminum anodes. When20.54%of COD ramoval ratio,52.3%color removel ratio is achieved with iron anodes, the energy consume is1.482kwh/kg; when using aluminum anodes,47.57%of COD ramovel ratio,62.7%color removel ratio are achieved and the energy consume is2.84kWh/kg COD. Under the same experimental conditions, color removal ratio is always higher than COD removal ratio.