O_3与O_3/H_2O_2两个体系降解除草剂2,4-D反应特性研究

分别采用O3、O3/H2O2体系降解苯氧羧酸类除草剂2,4-D,探讨了降解过程中反应温度、pH值、O3混合气流量、有机物初始浓度等操作条件的变化对降解动力学的影响。结果发现,温度和pH值的影响较大,O3流量影响最小,温度升高、pH值增大、臭氧流量增加、2,4-D初始浓度降低均有助于降解速率的提高。O3/H2O2体系中,H2O2能促进O3分解产生大量自由基,导致2,4-D反应活化能降低。和O3相比,O3/H2O2体系降解效果好,降解时间短,反应条件温和,操作费用低,是很有发展前景的高级氧化技术。

Degradation of 2,4-Dichlorophenoxyacetic Acid by O3 and O3/H2O2

Degradation of 2,4-dichlorophenoxyacetic acid using O3 and O3/H2O2 has been investigated. Both treatments have been compared in terms of dependence on several experimental parameters including temperature, pH, ozone dose and organic initial concentration on reaction efficiency. The results showed that temperature was key factor of removal rate, while pH strongly affected degradation process, and gas flow had very little influence on the efficiency of processes. Elevated reaction temperature was easily over the energy barrier of 2,4-D removal. More hydroxyl radicals were produced during higher temperature process. Hydroxyl radical was more reactive and nonselective than ozone, and was dominating oxidant during 2,4-D degradation. pH was an important parameter of O3 stability in solution, and hydroxyl ion was the initiator of ozone decomposition chain reaction to generate hydroxyl radical. The higher the pH level was, the more hydroxyl radicals were formed. Furthermore, the solution pH affected dissociation of 2,4-D, and the anion species was more reactive than its non-dissociate state. The degradation efficiency was enhanced when 2,4-D initial concentration decreased. Ozone flow rate had both positive and negative influence on reaction, thereby, its overall effect was not evident. Compared with O3 process, O3/H2O2 greatly increased the removal efficiency of 2,4-D. Greater amounts of hydroxyl radicals were generated by the O3/H2O2 system than ozonation alone. O3/H2O2 had more advantages such as excellent degradation effectiveness, faster removal rate, more moderate conditions and lower operating cost than O3 system. O3/H2O2 technology was an excellent advanced oxidation process in removal of 2,4-dichlorophenoxyacetic acid.