Research On Decolorization Technology Of Dyeing And Printing Wastewater

The textile industry of our country is developed, produces plenty of wastewater containing high concentrations of dyes and auxiliaries, and is one of industrial pollution sources which seriously threaten water environment. Among textile industry wastewater, dyeing and printing wasteater is most serious. The treatment of dyeing and printing wastewater has been one of key topics in our country and even in the world. Wastewater treatment techiniques mainly include physical method, chemical method, physical and chemical combination method, biochemistry method and so on. With the development of science and technology, the variety of dyes shows an increasing tendency, their component is becoming complex, and the wastewater of many dyes has the characteristic of oxidation resistance, anti-photolysis, high color degree and high concentration. So these lead to the high requires for the techniques of wastewater treatment.With the improvement of environmental protection requirements and the shortage of resources day by day, the reasonable recycling and reuse of water resources and non-renewable resources have also become the important content of environmental protection. Under such background, many advanced engineering techniques have been applied to wastewater treatment, and the decolorization techniques of dyeing and printing wastewater have become the research focus in recent years. For example, the highly effective flocculation decolorants should be developed and the flocculation pretreatment ability should be improved. In addition, to use origin pulverized coal to treat the waste water, which is low cost and easy to avail, not only reduces the color degree of wastewater greatly, but also eliminates suspension SS, and CODcr effectively, and thus achieve the aim of comprehensive utilization.The pulverized coal ash is the solid waste of coal-burning power plant. The slag is the solid waste from power plant boilers, civil and industrial boilers and kilns. Both have a large surface area, strong adsorption ability and low price, which results in their wide application prospects in wastewater treatment. In this paper, the research situation of the application of pulverized coal ash and slag to the treatment of dyeing and printing wastewater was reviewed as well as their decolorization mechanism. On this basis, some experiments were performed in the aspects of the structure of pulverized coal ash and slag, and their decolorization mechanism. The optimum decolorization condition of pulverized coal ash and slag with and without modification was determined according to decolorization percent. Finally, the main existing problem of the application of pulverized coal ash and slag to wastewater treatment and the future research directions were put forward. The research and discussion were valueable for the treatment of dyeing and printing wastewater. From the experiments, the following conclusions were concluded:(a) The pulverized coal ash has certain adsorption capacity, and is especially suitable to treat low concentrations of wastewater.At the presence of enough pulverized coal ash, the decolorization percent can reach to 58%~78%. The pulverized coal ash without activation treatment has no high adsorption capacity, for this reason, the pulverized coal ash should be modified by physical or/and chemical methods to obviously increase its adsorption capacity.(b) The adsorption of dyes on the original pulverized coal ash and the ash modified by hydrogen peroxide follows the Freundlich equation. The modified pulverized coal ash exhibited high adsorption capacity. The adsorption equilibrium time of the modified ash is 40min, which is slightly longer than that of of the original ash.(c) The adsorption capacity and decolorization effect of the ash modified by hydrogen peroxide are better than those of original ash, and not greatly affected by pH. Under the the same condition, the lowest decolorization percent is 86.6% at pH 7 while the highest value is 96.32% at pH 9. The modified ash exhibits not only the high decolorization percent, but also the good removal effect of CODcr and SS.(d) If pulverized coal ash and excess sludge are combined to treat dyeing and printing wastewater, the best removal effect of suspension SS, CODcr and color is achieved when the volume ratio of wastewater, sludge and pulverized coal ash is 60:1:4. (e) When the volume ratio of wastewater, sludge and pulverized coal ash is 60:1:4, the most suitable sedimentation time of the mixture liquid is 10~25 min.(f) If pulverized coal ash and excess sludge are used to the treatment of dyeing and printing wastewater, this treatment can be regared as one of pretreatment methods, and should be used before bio-chemical processing. After this treatment, the elimination percent of SS, CODcr and color can reach to 50%, 20% and 80%, respectively.(g) In the case of slag application, the economic and practical disposal conditions are obtained through the experimental studies on the decolorization of Acid Red GR and Reactive Red X-3B dye wastewater.