| Volatile organic compounds（VOC）gas treatment is one of the research focuses inthe field of air pollution control.Ozonation is an effective technology for VOC gas treatment,including adsorption ozonation and catalytic ozonation.The microbubble ozonation technology was used to treat high concentration toluene gas with water medium by absorption-oxidation process in this study.The enhanced absorption and oxidation in the microbubble ozonation treatment for high concentration toluene gas were investigated.The effects of water medium pH,the ratio of ozone to toluene and the catalyst on oxidation removal performance of toluene gas in the microbubble ozonation treatment were also investigated.Then the oxidation removal mechanism of toluene gas was analyzed.The results were as follows:1)The microbubble technology could enhance absorption process of toluene gas in water medium.The toluene removal efficiency was 95.62%in nitrogen/toluene microbubble treatment.In addition,·OH oxidation occurred in nitrogen/toluene microbubble treatment,which resulted in an average toluene oxidation mineralization efficiency of 40.97%.The toluene removal efficiency and absorption amount in nitrogen/toluene conventional bubble treatment were much lower than those in nitrogen/toluene microbubble treatment and there was no oxidation removal.2)The efficient removal performance of toluene gas was achieved in ozone/toluene microbubble treatment in water medium.In this case,the average toluene removal efficiency was 97.08%,the average toluene oxidation mineralization efficiency was88.56%and the average ozone utilization efficiency was 82.54%.The ratio of ozone dosage to mineralization removal of toluene was 1.26 mg·mg-1.The removal performance of toluene gas in ozone/toluene microbubble treatment was much better than that in ozone/toluene conventional bubble treatment.Its oxidation and mineralization capacity for toluene gas was 3.6 times of ozone/toluene conventional bubble treatment.The·OH oxidation reaction played a key role in oxidation removal of toluene gas.At the same time,GC-MS analysis showed that toluene could be oxidized and mineralized completely,and there was almost no accumulation of oxidative degradation intermediates.3)The water medium pH affected toluene gas treatment in microbubble ozonation to some extent.The toluene removal efficiency was nearly same at different water medium pH.However,the toluene oxidation mineralization efficiency was maximum under neutral condition,and decreased a little under alkaline and acid conditions.The toluene removal efficiency varied little when decreasing the ratio of ozone to toluene,but the toluene oxidation mineralization efficiency decreased and ozone utilization efficiency increased.4)When activated carbon was used as ozone catalyst,the oxidation and mineralization ability of microbubble catalytic ozonation treatment of toluene gas was significantly improved.The nitric acid modified and supported iron activated carbon showed stronger catalytic ability.At the same time,the oxidation and mineralization ability of microbubble catalytic ozonation treatment of toluene gas was stronger in alkaline condition. |
