Research Decolorization Of Direct Dye Wastewater By Electrochemical

Water pollution from industrial effluents has become a serious problem in Viet Nam in recent years. Noticeably, wastewater from textile dyeing industry is supposed to be the most polluted sources. Though the textile dyeing factories in Viet Nam have applied treatment technologies for dyeing wastewater process, the two major problems involving instability of treatment technology and high residue of dyes in treated water have still existed. Besides that, bleach chemicals added during production also make dye wastewater treatment process more difficult.The methods of dye wastewater treatment have not been effectively applied in Viet Nam in recently. Some of them require high costs that are not economic for treatment. In addition, since dyes are intentionally designed to resist color degradation, the conventional treatment methods are ineffective in removing the dyes. Electrochemical treatment process is believed to be a feasible treatment method which may achieve both treatment efficiency and costs. This method may decrease COD in water and does not affect biodiversity. Moreover, electrochemical treatment method saves investment cost because of low costs for equipments and infrastructure as well as energy consumption. In addition, a simple operation principle may be highly appreciated for widely applications. A remark advantage of this method is reported that it limits secondary pollutants and sediment from treatment process. Therefore, the electrochemical process is a promising method for dye waste water treatment.The present study focuses on electrochemical treatment of three types of dyes including Direct Yellow R, Direct Red 4BE and Direct Green BE which have been commonly known as basic dyes used in Viet Nam currently. The electrochemical experiments were carried out with the iron/aluminum anode and the stainless steel cathode, respectively. The effects of factors consist of current density, initial pH, initial dye concentration, electrolyte time and electrolyte kind and electrolyte concentration on decolorization efficiency and electrical energy consumption of the three direct dye wastewater. At the same time, this study analyses the before and after treatment direct dyes simulated wastewater treatment by UV-visible absorption spectroscopy, examine the decolorization and COD removal relationship and conduct the decolorization velocity constant of study.The obtained results from the present research show that for direct yellow R dye simulated wastewater, the initial dye concentration of 50 mg/L, electrolyte concentration of 0.1 mol/L, temperature of 20?, stirring speed of 600 rpm, electrolyte time of 60 minutes are optimal conditions for dye decolorization. Using iron anode to treat under conditions of current density of 2.083 mA/cm2, initial pH value of 7.11 and Na2SO4 electrolyte, achieved decolorization efficiency to 92.2%, electrical energy consumption of 1.709 kWh/kg dye and COD removal efficiency reached of 62.9%. When NaCl electrolyte was replaced to Na2SO4 electrolyte and the same experimental conditions were remained, decolorization efficiency reached to 92.9%, electrical energy consumption was 2.334 kWh/kg dye. A little change in results was observed when using aluminum anode. The experiments conducted at current density of 2.5 mA/cm2, initial pH value of 6.76 and Na2SO4 electrolyte reached decolorization efficiency of 96.1%, electrical energy consumption of 2.399 kWh/kg dye and COD removal efficiency of 83.6%. With the same experimental conditions, but replacing NaCl electrolyte to Na2SO4 electrolyte were applied, decolorization efficiency was 97.2%, electrical energy consumption was 2.797 kWh/kg dye and COD removal efficiency was little changed compared to that of the use of Na2SO4 electrolyte.For direct red 4BE dye simulated wastewater, the initial dye concentration of 50 mg/L, electrolyte concentration of 0.1 mol/L, temperature of 20?, stirring speed of 600 rpm, electrolyte time of 60 minutes were optimal conditions for dye decolorization. Using iron anode to treat under conditions of current density of 1.667 mA/cm2, initial pH value of 6.54, Na2SO4 electrolyte, decolorization efficiency reached to 92.1%, electrical energy consumption was 1.298 kWh/kg dye and COD removal efficiency was 33.9%. Replacing NaCl electrolyte to Na2SO4 electrolyte but not change other experimental conditions, codecolorization efficiency achieved 88.7%, electrical energy consumption was 3.146 kWh/kg dye. Using aluminum anode at conditions of current density of 1.25 mA/cm2, initial pH value of 6.83, Na2SO4 electrolyte were implemented, decolorization efficiency was 94.3%, electrical energy consumption was 1.014 kWh/kg dye, COD removal efficiency reached to 79.3%. NaCl electrolyte was replaced to Na2SO4 electrolyte, decolorization efficiency reached to 92.8%, electrical energy consumption was 0.966 kWh/kg dye.For direct green BE dye simulated wastewater, the initial dye concentration of 50 mg/L, electrolyte concentration of 0.1 mol/L, temperature of 20?, stirring speed of 600 rpm, electrolyte time of 60 minutes were optimal conditions for dye decolorization. The iron anode used at current density of 3.333 mA/cm2, initial pH value of 6.65, Na2SO4 electrolyte, reached decolorization efficiency of 90.3%, electrical energy consumption of 4.073 kWh/kg dye, COD removal efficiency of 33.9%. When NaCl electrolyte was replaced to Na2SO4 electrolyte, decolorization efficiency was 88.9% and electrical energy consumption was 5.373 kWh/kg dye. Using aluminum anode at current density of 2.083 mA/cm2, initial pH value of 6.54 and electrolyte achieved decolorization efficiency of 92.2%, electrical energy consumption of 1.844 kWh/kg dye, COD removal efficiency of 71.0%. The use NaCl electrolyte at the same other conditions obtained decolorization efficiency of 92.6%, electrical energy consumption of 2.16 kWh/kg dye.Using iron and aluminum as the anode, the obtained results indicates that influence of factors on decolorization velocity constant was different at impact level for all three simulated wastewater types. The decolorization velocity constant of direct green BE dye simulated wastewater was not much be affected. The pH effects on decolorization velocity constant of all three direct dye simulated wastewater types when using iron anode was more obvious than using aluminum anode. In addition, the influence of initial dye concentration on the decolorization velocity constant of the direct R dye simulated wastewater was obvious effect. The decolorization velocity constant of three direct dyes simulated wastewater by two electrolytes Na2SO4 and NaCl concentration has little effect.