Heterogeneous Catalytic Ozonation Treatment Of Refractory Organic Wastewater

Refractory organic wastewater exhibits high toxic, long-term residual and biological accumulation both in environment and organism. Conventional biological processes are not effective for it due to its characteristics of complicated components, high quantity organic compounds and low biodegradability. Accordingly, it is necessary to develop new advanced wastewater treatment technology. Ozone, as a strong oxidant has been widely applied in wastewater treatment. New Cu-Mn/γ-Al2O3 catalyst supported on γ-Al2O3 was first prepared by impregnation method, and then used in heterogeneous catalytic ozonation system for the treatment of refractory organic wastewater. With acid red B and terephthalic acid simulated wastewater as the research object, the effects of catalyst dosage, initial pH value and ozone rate on the removal efficiencies were investigated. The kinetics and mechanisms for degradation of acid red B and terephthalic acid were also studied. Meanwhile, cephalosporin synthesis wastewater was used to study the degradation efficiency of Cu-Mn/γ-Al2O3-O3 system toward refractory organics present in actual wastewater. The main experimental conclusions were as follows:1) A novel Cu-Mn/γ-Al2O3 catalyst was developed, of which the best preparation conditions was γ-Al2O3 as carrier, 0.5mol/L Cu(NO3)2 and 0.5mol/L Mn(NO3)2 mixing solution as impregnation liquid, calcination temperature 550℃ and roasting time 3h. The property of the catalyst was examined by XRD, SEM and FTIR. Results showed that the main active groups of the catalyst were CuO and CuMn2O4. They were coordinated into the central metal ions of γ-Al2O3 and highly dispersed on its surface. The pH vaule was 8.3. The catalyst showed good catalytic performance and stability through the experiment.2) There was a good removal effect in Cu-Mn/γ-Al2O3 catalytic ozonation of acid red B. Under the conditions of acid red B of 250mg/L, ozone rate of 4.26mg/min, initial solution pH value of 8.3, catalyst dosing quantity of 4g/L and reacting time of 20 min, the removal efficiency of acid red B was up to 99.36%. Total organic carbon(TOC) of the solution decreased from 48.50mg/L to 22.13mg/L. Comparing with ozonation alone process, the removal efficiency of acid red B and TOC was improved by 20.43% and 35.03%, respectively. The degradation of acid red B fitted the pseudo-first-order reaction kinetics. The equation was ln(c0/ct)=0.2498t+0.1370 and the correlation coefficient R2 was 0.9974.3) The removal efficiency of terephthalic acid was 99.26% when terephthalic acid of 100mg/L under the condition of ozone rate of 3.18mg/min, initial solution pH value of 8.3, catalyst dosing quantity of 3g/L and reaction time of 20 min, respectively. TOC of the solution decreased from 35.15mg/L to 15.04mg/L. The removal efficiency of terephthalic acid and TOC was improved by 23.34% and 22.76% compared to ozonation alone process, respectively. The degradation of terephthalic acid fitted the pseudo-first-order reaction. The equation was ln(c0/ct)=0.2455t-0.1354 and the correlation coefficient R2 was 0.9959.4) Cu-Mn/γ-Al2O3 catalytic ozonation process had good effect on the treatment of synthetic cephalosporin wastewater. The COD, BOD5, NH3-N and color decreased form 250mg/L, 10mg/L, 12mg/L and 70 times to 114mg/L, 6mg/L, 5mg/L, and 5 times, respectively, under the condition of ozone rate of 5.64mg/min, initial solution pH value of 8.3, catalyst dosing quantity of 5g/L and reaction time of 20 min, respectively. The quality of the effluent water meet the “chemical synthetic pharmaceutical industrial water pollutant emission standards”(GB 21904-21904) requirements.5) Hydroxyl free radical(·OH) inhibition test proved that the Cu-Mn/γ-Al2O3 catalyst can promote the decomposition of ozone to produce hydroxyl radicals and improve the efficiency of the ozone oxidation.