| With the rapid development of industrialization in the world,the demand for phenol is increasing year by year,resulting in the massive discharge of phenol wastewater has become an important environmental problem.Heterogeneous catalytic ozonation technology has received much attention in water treatment due to its advantages of easy separation of supported catalysts from water,high catalytic activity,reusability and no secondary pollution to the environment.However,ozone is difficult to dissolve in water,resulting in low mass transfer efficiency between gas-liquid-solid phases,thus affecting the mineralization effect of organics.As a new process intensification technology,high gravity technology relies on a rotating packed bed?RPB?to generate centrifugal force.The liquid can be sheared into micro elements in the form of liquid droplets,thinner liquid filament,and liquid film,which can increase the contact area between the gas-liquid-solid phases,so as to increase interphase mass transfer rate of ozone.In this paper,the first innovative proposal is to establish Cat/O3-RPB system to degrade phenol wastewater by coupling high gravity technology and heterogeneous catalytic ozonation technology,using RPB as a reactor and Fe-Mn-CuOx/?-Al2O3 catalyst?Cat?as a packing.In Cat/O3-RPB system,the effects of different parameters on the overall decomposition rate constant?Kc?and the overall volumetric mass transfer coefficient?KLa?were studied in detail.The degradation efficiency of phenol and the interaction between factors were studied by factor analysis and response surface methodology?RSM?.The reaction mechanism and degradation process of phenol wastewater were also studied.The specific research results are as follows:?1?The effects of different operating parameters on the overall decomposition and mass transfer of catalytic ozone were studied in Cat/O3-RPB system.The results showed that the initial pH,the high gravity factor???,the concentration of ozone in the gas phase(CO3?g?)and the water temperature?T?all agreed with the pseudo first order kinetic equation for the overall decomposition rate of ozone.The Kc and KLa were 4.28×10-3 s-11 and 11.6×10-3 s-1,respectively,under the following conditions,a high gravity factor of 40,an initial pH value of 6,a gaseous ozone concentration of 60 mg/L and a water temperature of 20?.Moreover,under similar experimental conditions,the decomposition and mass transfer of ozone in Cat/O3-RPB system and traditional agitated bubbling reactor?Cat/O3-BR system?were compared.It was found that the Kc and KLa values in Cat/O3-RPB system were 1.81 times and 1.9 times of Cat/O3-BR system,respectively.The results show that the high gravity technology can effectively promote the decomposition and mass transfer of ozone,which also provides a theoretical basis for the high gravity enhanced heterogeneous catalytic ozonation technology to degrade organic wastewater.?2?In Cat/O3-RPB system,the heterogeneous catalytic ozonation of phenol wastewater with an initial concentration of 100 mg/L was studied.The results showed that as high gravity factor increases from 10 to 40,the interphase interface was rapidly updated,causing more gas-phase ozone to enter the liquid phase,thereby accelerating the decomposition of ozone on the catalyst surface to produce more·OH,which is beneficial to the mineralization of phenol wastewater.Under the conditions of a high gravity factor of 40,an initial pH value of 6,a gaseous ozone concentration of 60 mg/L and a liquid flow rate of 85 L/h,the phenol removal rate was 99.99%at 7 min,and the mineralization rate of phenol was 96.42%at 30 min.In addition,compared with Cat/O3-BR and RPB-O3 system,the mineralization rate of phenol wastewater in Cat/O3-RPB system was increased by 21%and 57.27%,respectively,which indicated that the high gravity technology strengthens the mass transfer and reaction process between gas-liquid-solid phases,and has a good effect on the advanced degradation of phenol wastewater.?3?Using the BBD?Box Benhnken Design?principle of RSM to design the experiment.The result showed that the significant order of the factors in mineralized phenol wastewater was CO3?g?>QL>?>initial pH value.Meanwhile,there was an extremely significant interaction between?and initial pH,and a significant interaction between?and QL.By establishing a mathematical model,the R2 of the quadratic regression equation was found to be 0.9861,which was greater than 0.9,indicating that the established mathematical model had a higher fitting accuracy.The predicted value of phenol mineralization rate by RSM is 91.54%,which is 0.97%?<2%?higher than the measured value.It can be seen that this model is reliable for optimizing the process conditions of high gravity enhanced heterogeneous catalytic ozonization of phenol wastewater.?4?The reaction mechanism and degradation process of phenol wastewater with heterogeneous catalytic ozonation enhanced by high gravity were studied.Adding an excess of tert butyl alcohol?TBA?to the Cat/O3-RPB system,the phenol mineralization rate decreased by 59.7%,which played a significant inhibitory effect,indicating that the reaction was mainly dominated by·OH oxidation.An obvious 1:2:2:1 hydroxyl radical?·OH?peak and the change of the·OH content during the degradation of phenol wastewater were detected by an electronic paramagnetic resonance spectrometer?EPR?.The main intermediate products of phenol degradation were analyzed by GC-MS,and the degradation pathway of phenol was concluded as follows:phenol?catechol,hydroquinone,p-benzoquinone?malonic acid,acetic acid?CO2 and H2O.In addition,compared with Cat/O3-BR system,the ozone utilization rate?Ru?of Cat/O3-RPB system is 20.64%higher than that of Cat/O3-BR system,indicating that high gravity technology can enhance the mass transfer of ozone,thereby improving the ozone utilization rate and reducing the cost of treating phenol wastewater. |
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