Treatment Of Printing And Dyeing Wastewater With Catalytic Wet Oxidation Technology

With the development of fine chemicals and printing and dyeing technologies, PVA dyestuffs, new-style doping agents and other hard-biodegradable organic matter in printing and dyeing wastewater have been increasing with each passing day, therefore, the wastewater treatment has become more and more difficult, and the conventional treatment technologies of printing and dyeing wastewater have been faced with challenges. Wet Oxidation (WO) is regarded as the second era technology for treating organic wastewater, and it has been used to treat wastewater that is nocuous and hard-biodegradable for the first era technology of wastewater treatment. It is important for the treatment of organic wastewater and for the protection of water resource that the WO technologies on printing and dyeing wastewater treatment are developed and the new-style, high-effect, low-cost and steady catalysts are prepared.Methylene blue (MB) watery solution with the COD value of2000mg/L was selected as printing and dyeing simulant wastewater, and COD removal rate, color removal rate, effluent pH and Cu concentration in solution of nonhomogeneous CWO were selected as evaluation standards. Printing and dyeing simulant and actual wastewater was treated with the technologies of WO, homogeneous catalytic wet oxidation (HCWO) and nonhomogeneous catalytic wet oxidation (NHCWO), then some important conclusions have been acquired.The results on the treatment of printing and dyeing simulant wastewater with WO technology showed that COD removal rates of MB increased with the increase of oxygen pressure, reaction temperature and influent pH values. The best value of stirring speed was880rpm, and the reaction comprised quick reaction course and slow reaction course. MB degradation mechanism was investigated by the FT-IR spectra of different moments, and the results showed that:firstly,-C-S-、-C=S-secondly,-C-N-、-C=N-in heterocyclic broke off, then the-C-N-of the carbon in benzene ring and the nitrogen in (CH3)2N-broke off, so xylidine was degraded,1,4-benzoquinone and (CH3)2NH were come into being. Printing and dyeing simulant wastewater was treated with HCWO technology, and18dissolvable metals were filtrated, according to their catalytic activity, the better catalysts of them were Cu(NO3)2, CuSO4, Fe(NO3)3, FeSO4, Zr(NO3)4, Cr(NO3)3. CuSO4and FeSO4were selected to compound CulFe3, CulFel and Cu3Fel according to the mass proportion of metal ion. The results indicated that Cu1Fel took on the most excellent catalytic activity. With the catalyst dosage of50mg/L, and the reaction temperature of120℃, COD removal rate enhanced about50percents than that of the course without any catalyst. Then the application of Cu1Fel was investigated in the course of MB oxidation. The results indicated that the COD and color removal rates increased with the increase of the catalyst dosage, the oxygen pressure and the reaction temperature. With the following conditions, the influent pH of5.25, the catalyst dosage of150mg/L, the oxygen pressure of1.0MPa, the reaction temperature of180℃, and reaction time of60minutes, the water sample COD dropped to130mg/L from2000mg/L, and COD removal rate was93.5%; The water sample chromaticity dropped to20from300thousands, and color removal rate was99.99%. The effect mechanism of Cu1Fe1in the course of MB wet oxidation was researched:For one thing, Cu and Fe behaved dominant catalysis, and puissant oxidant radicle induced organic matter to oxidize. For another, Fe(Ⅱ) was oxidized to Fe(Ⅲ), so Fe(Ⅲ) and its polymers agglomerated water sample.Printing and dyeing simulant wastewater was treated with NHCWO technology. Among4types of support materials:FSC, AC, FSD and FSE, FSC was selected as the support material of the catalysts,and the analysis of XRD spectra showed that the central ingredient of FSC was γ-Al2O3. Based on the research of homogeneous CWO, Cu(NO3)2was selected as active component. The impregnating state, the impregnating temperature, the impregnating time, the impregnating concentration, the calcination temperature and time were researched systematically, by atom absorption, SEM, XRD, and so on. Considering the activity and stability of catalyst, the preparation process of Cu/FSC were optimized:the impregnating temperature of35℃, the impregnating state of dynamic, the impregnating time of8hours, the impregnating liquid concentration of6wt%Cu, the calcination temperature and time were650℃and5hours, respectively. With the Cu/FSC dosage of2g/L, and the reaction temperature of150℃, COD removal rate of simulant wastewater enhanced about20percents than that of WO course. The effect mechanism of Cu/FSC as a catalyst of oxidation reaction could be explained by redox mechanism.In order to decrease the leaching of Cu and promote the catalytic activity and stability of Cu/FSC, Ce(NO3)3was selected as doping agent. The preparation conditions of Cu-Ce/FSC catalyst were as follows:Cu(NO3)2and Ce(NO3)3were impregnated together, the total metal ions concentration of6wt%, the Cu:Ce ratio of1:1, the impregnating temperature of35℃, the impregnating time of8hours, the impregnating state of dynamic, the dryness temperature and time of110℃and10hours, respectively, the calcination temperature and time of550℃and5hours, respectively. Compared with Cu/FSC, the catalyst activity of Cu-Ce/FSC improved slightly, but its stability promoted greatly. The mechanism research indicated that CeO2behaved the function of configuration doping agent and electron doping agent in Cu-Ce/FSC catalyst. Cu-Ce/FSC catalyst was applied to treat simulant wastewater, the operational conditions were as follows:the influent pH of5.25, the oxygen pressure of1.0MPa, the reaction temperature of180℃, the catalyst dosage of10g/L, and the reaction time of60minutes. With these conditions, the water sample COD dropped to176mg/L from2000mg/L, and COD removal rate was91.2%; The water sample chromaticity dropped to20from300thousands, and color removal rate was99.99%. Effluent pH value promoted from5.25to7.5, and Cu concentration in solution was1.92mg/L.Printing and dyeing actual wastewater was treated with CWO technology. With these conditions:Cu1Fel dosage of150mg/L, Cu-Ce/FSC dosage of10g/L, the reaction temperature of200℃, the oxygen pressure of1.0MPa, and the reaction time of90minutes, COD and BOD5could make third grade standard of "sewerage synthesis letting standard"(GB8978-1996), chromaticity and pH made first grade standard, and Cu concentration in effluent water made third grade standard. The biodegradability of actual printing and dyeing improved greatly, its BOD5/COD increased to0.423(HCWO) and0.307(NHCWO) after treatment from original0.021.