| Printing and dyeing wastewater account for a large proportion of the total industrial wastewater in China, and it is charateristic of strong alkaline, high chroma, high concentrations of organic matter, with complex composition, nonbiodegradable and so on, which is difficult to deal with. So the research on techniques of dyeing wastewater treatment has a great value and practical significance. In this work, an efficient technique of advanced oxidation process (AOP), catalytic ozonation is used for degradation of the azo dye of reactive red X-3B and anthraquinone dye of disperse blue 56 (DB-56). The degradation ability of catalytic ozonation, the catalyst preparation conditions, the rational optimization of reactor, the influencing factors on the catalytic reaction and the reaction mechanism of the catalytic ozonation are investigated.In the process of the preparation of heterogeneous catalysts, Mn-Fe-ceramic honeycomb catalyst is prepared by impregnation. Experiments on the X-3B degradation show that the catalytic effects are influenced by the catalyst preparation conditions significantly, such as soaping time, calcinating temperature and calcinating time. The optimal preparation conditions are:soaping for 6 hrs, calcinating at 480℃for 4 hrs.99% of X-3B and 75% of DB-56 can be degradated during this process.In the study of catalytic ozonation of X-3B, we find the optimal reaction conditions: initial concentration of X-3B is 200mg/L, reaction time is 60min, the reaction temperature is 40℃, pH= 7, circulation flow is 0.3L/min. Under these conditions, this study is focused on the pressure and ozone flow rate of the reaction, the results show that:(1) The raise of pressure (0～0.04Mpa) will increase the degradation efficiency of X-3B, the best effect of catalytic ozonation is under the pressure of 0.02Mpa. The investigation of the mechanism proves that catalytic ozonation by Mn-Fe-ceramic honeycomb catalyst follows the radical mechanism and the raise of pressure enhances the formation ability of hydroxyl radical (·OH). (2) With the raise of ozone flow rate, the degradation efficiency of X-3B increase. In order to cut the cost,1.5g/h is chosen as the best conditions for ozone flow rate. Investigation of the mechanism also find that the raise of the ozone flow rate conducive to the degradation due to promotion of hydroxyl radicals in the reaction system.During the study of catalytic ozonation of DB-56, we follow the same reaction conditions including the target concentration, reaction time, pH and circulation flow rate. Pressure, temperature and ozone flow rate of the catalytic reaction are discussed as influencing factors. The reaction mechanism is also investigated. The results show that:(1) The raise of pressure will promote the degradation efficiency of DB-56 significantly under the stable ozone flow rate. The research of the mechanism of catalytic ozonation of DB-56 proves that catalytic ozonation by Mn-Fe-ceramic honeycomb catalyst also follows the radical mechanism and the raise of pressure enhances the formation ability of hydroxyl radical (·OH). (2) Under 0.02Mpa, the best reaction temperature is 50℃. DB-56 degradation rate will increase when reaction temperature raise from 0-50℃, and decline when reaction temperature raise above 50℃. The catalytic ozonation still mainly follows the radical mechanism at the changde temperature. The raise of temperature is conducive to catalytic reaction mainly due to the increase of hydroxyl radicals in the system. (3) With the raise of ozone flow rate, the degradation efficiency of DB-56 increase. The ozone flow rate was set at 1.5g/h as the best conditions for cost reducing, Investigation of the mechanism has found that the raise of the ozone flow rate promotes the catalytic reaction to DB-56 due to the increase of hydroxyl radicals'formation in the reaction system.
|
PDF Full Text Request