| The heterogeneous catalytic ozonation,one of the advanced oxidation process(AOPs),can be used in the pretreatment system to break the persistent organic compounds to biodegradable organic matter.Meanwhile,this technology also can be used in converting oxide organic matters to CO2 and H2O in the advanced treatment and realize to resuse the wastewater.The problems,such as the high cost,the catalyst loss and the low utilization of ozone,have seriously restricted the application of catalytic ozonation technology.In addition,there are organic matters and ammonia nitrogen in the water,and it is difficult to removal them under room temperature and atmospheric pressure by catalytic ozonation at the same time.The challenge is how to develop new catalyst that can both removal organic matters and ammonia nitrogen at the same time,and be running steady and efficiency on a large scale application.Based on this situation,the following contents are mainly carried out in this research:The mesoporous ?-Al2O3 supported manganese-cerium mixed oxides(Mn-CeOx/?-Al2O3)catalyst was facilely prepared by an incipient wetness impregnation-calcination method.The best performance of the catalyst has achieved at the conditions that immersion time was 24 h,the concentration of the Mn(NO3)2 and Ce(N03)3 were 150 mmol/L and 30 mmol/L,calcination temperature was 500 ? and the calcination time was 4 h.The mass of loaded Mn and Ce were 1.37 wt.%and 1.17 wt.%.Characterization results demonstrated that the as-synthesized catalyst retained the mesoporous structure of ?-Al2O3,possessed large pore volume,and existed in multi-valence redox couples of Mn4+/Mn3+ and Ce4+/Ce3+.The bromaminic acid(BAA)was selected as a target pollutant to evaluate the activity of the Mn-CeOx/?-Al2O3 catalyst.Results showed that TOC removal was 9.4%by single ozone,64%removal of TOC was achieved by Mn-CeOx/?-Al2O3-catalyzed ozonation.The presence of Mn-CeOx/?-Al2O3 led to the decrease in residual ozone and the consumed ozone amount per unit mass of TOC removal as well as the increase of ozone utilization efficiency in catalytic ozonation process.BAA degradation by the catalytic ozonation was in accrodance with the combined pseudo-first-order kinetic model.The TOC removal was above 57%during repeated experiments and there are no significant differences in the crystallinity,textural properties and surface morphology of Mn-CeOx/?-Al2O3 before and after catalytic ozonation.18 intermediates were detected by LC-MS and IC during the Mn-CeOx/?-Al2O3 catalyzed ozonation process,and the final products were COZ and H2O.The reactions were dominated through surface reaction,and ·OH and O2·-were the main reactive oxygen species contributed to BAA degradation in terms of TOC removal.In the meantime,the reaction conditions of catalytic ozonation were optimized by the response surface method,and the maximum COD removal rate 94.35%was obtained when the concentration of O3 was 33.58 mg/L,pH was 8.53,and the amount of catalyst was 197.92 g/L.NH4+-and organic compounds are the most common pollutants in the wastewater.In order to removal the NH4+ and organic compounds at the same time,the catalyst of Co3O4/?-Al2O3 was used to remove NH4+-N from wastewater and preferably decomposed into harmless compounds at the room temperature and pressure.The catalyst Co3O4/?-Al2O3 achieved 100%conversion of NH4+-N(100 mg/L)by catalytic ozonation,the main products were N2(90%)and small amount of NO3-(10%)after 360 min.The kinetics of NH4+-N removal was modeled using a zero-order kinetic model and the Ea for catalytic ozonation of NH4+-Nwas 12.2 kJ/mol.Compared with two catalysts Co3O4/?-Al2O3 and Mn-CeOx/?-Al2O3,the better result of NH4+-N removal was achieved by Co3O4/?-Al2O3,but the result of COD removal was on the contrary.Co3O4/?-Al2O3 can remove organic matters and ammonia nitrogen by catalytic ozonation at the same time,the COD removal was more than 90%and NH4+,N removal was 100%.At the same time,the effects of reaction factors on the catalytic ozonation,such as reaction temperature,pH value and coexisting anion were investigated.Raising the temperature and pH will have a positive effect on the reaction.The degradation of NH4+-N was improved in the presence of the halogen ions Cl-and Br-,but PO43-inhibited the activity of the catalyst.The active groups of·NH2 and N2H4 play an important role in the degradation of ammonia nitrogen.In order to investigate the activity of the catalyst in the treatment of wastewater,and considering the characteristics of the high temperature in the DAF wastewater.An integrated process of catalytic ozonation-persulfate oxidation was investigated for DAF wastewater of pretreatment in pilot scale.In terms of investment and operating costs,Box-Behnken design and response surface methodology(RSM)were used for the design and optimization of the integrated process to remove the COD and TN as more as possible.Reaction time,temperature,the addition of ozone and persulfate were used as reaction variables.Results showed that the maximum COD and TN removal efficiency of 42.36%and 28.51%were achieved for DAF wastewater when reaction time,reaction temperature,the addition of ozone and the addition of persulfate was 4.44 h,61.82?,40 g/h and 1.3 kg/t,respectively.Furthermore,the biodegradability of raw and treated DAF wastewater was compared,and(BOD5)/CODcr(B/C)ratio increased from 0.078 to 0.315,indicating a significant biodegradability improvement.The GC-MS was also employed to detected the composition of the wastewater before and after catalytic ozonation-persulfate oxidation treatment.The results showed that nitrile materials were effectively degraded,and the decomposition of organic compounds containing N heterocyclic were converted into ammonia nitrogen,eventually oxidized to nitrate nitrogen and N2.Aiming at the disadvantages of the old process of the TDI wasterwater pretreatment in the chemical plant,the technology of catalytic ozonation with Mn-CeOx/?-Al2O3 was provided instead of old system as an upgrade process.At the first step,the laboratory experiments demonstrated the feasibility of the catalytic ozonation technology,and then the parameters of the reacting time 10 h,the ratio of the ozone and COD 1.7:1 were given as a reference in the pilot scale experiments.At last,the design of the project has been introduced that the designed wastewater volume was 720 m3/d,3 ozone generator(50 kg/h)worked and 300 m3 catalyst,the cost of the investment and running was carried out.The results showed that the COD of the TDI wastewater degraded from 2500 mg/L to 200 mg/L by catalytic ozonation with Mn-CeOx/?-Al2O3,the cost of wastewater per ton was 21.8 RMB.The feasibility of the application values of the catalyst in practical application were verified. |
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