Study On Degradation Mechanism Of Printing And Dyeing Wastwater By Ozone Oxidation And Its Aplication

Printing and dyeing wastewater is one of the important industrialwastewater, due to its complex composition, high content of COD_Cr,refractory and other characteristics, it is difficult for the traditional treatmentprocess to achieve the emission standards. Therefore, exploring and seekingnew and efficient treatment method of printing and dyeing wastewater havereality significance.In recent years, ozonation as an advanced oxidation technology, has beenwidely used to remove the chromaticity and refractory organic matter inprinting and dyeing wastewater. The reaction mechanism is:“·OH” reactswith organic substance, which breaks the unsaturated bond of the dyechromophore to attain the purpose of decolorization and degradation.In this thesis, accordingly to the characteristics of printing and dyeingwastewater, decolorization of commen dyes with ozonation was investigated.Changes of reaction kinetics of the solution and the effect of pH ondegradation rate were examined. In addition, the acute toxicity of dye solutionin the ozonation process was measured by the method of luminescent bacteria,the variation of the acute toxicity was discussed. Meanwhile, treatment effectof printing and dyeing wastewater was observed by ozone/coagulation. Themain contents of this paper were as follows:The decolorization reaction kinetics of20anthraquinone, azo and otherdyes were investigated in the present study and the effect of pH on thedecolorization effect of dye solution by ozonation was discussed. Theapparent reaction rate constants and half-life of20kinds of dyes weredetermined. The results showed that degradation effect of refractorybiodegradation of20dyes with ozonation was higher than other treatmentmethod. When t_1/2moved from15.2676s to72.9629s, the decolorization rateof dyes generally reached90%after3min. The ozonation decolorizationprocess of20dyes solution was found to be first-order kinetic reaction, ofwhich the squared correlation coefficients（R2） were all larger than0.9500,which indicated that relationship between ln（Ct/C0） and reaction time had agood correlation. In the acidic conditions at pH=2.0maybe suitable for decolorization.The toxicity, pH, decolorization rate and conductivity of20dyes withozone oxidation were investigated. The results showed that the ozonationconductivity of solution increased gradually with time while the ozonation pHof the solution decreased with time, and ozone was suitable for decolorization.The toxicity of dye intermediates was bigger than others through the ozonedegradation, the toxicity of acid dyes was the maximum, followed by directdyes, and that of reactive dyes was the minimum.The treatment effect and influencing factors of printing and dyeingwastewater were investigated by the individual ozonation and coagulation,and the treatment effect of printing and dyeing wastewater was discussed byozone/coagulation. The results showed that under optimal conditions ofpH=7.0, the dosage of coagulantion was100mg/L and stirring speed was120r/min, the removal efficiency of colority and COD_Crwere60.48%and46.36%respectively. When the ozone concentration was constant, pH=5.0, theozonation time was8min, temperature was30℃, color and COD_Crremovalrates were65.28%and36.18%respectively. Treatment of printing and dyeingwastewater by coagulation/ozonation were better than single coagulation,color and COD_Crremoval rates reached90.57%and78.03%respectively. Andreduced indicators of pollutants in wastewater significantly, were up to thedyeing wastewater emission standards for three levels.