氯代硝基苯类废水臭氧化动力学和机理

Kinetics and mechanism of chloronitrobenzenes wastewater ozonation

采用半连续臭氧化工艺处理氯代硝基苯类废水,对氯代硝基苯(ClNBs)臭氧化过程反应动力学、臭氧分子与自由基氧化反应的贡献、过程降解机理等方面进行了研究。结果表明,ClNBs降解遵循准一级反应动力学,降解速率顺序为o-CNB<m-CNB<p-CNB,同时反应速率常数随反应体系pH的升高、目标污染物和自由基猝灭剂浓度降低而增大。但ClNBs的矿化速率远低于其降解速率,表明臭氧化不能彻底矿化ClNBs。HPLC和GC-MS结果表明,ClNBs主要被转化为氯酚、硝基酚、氯代硝基酚、硝基苯、氯苯和低分子的羧酸等物质。通过评估臭氧分子和自由基在反应中的贡献发现,自由基起决定性作用。因此,强化自由基产生的高级氧化工艺可对氯代硝基苯污染环境进行有效的修复和治理。

The kinetics and mechanism of ozonation degradation of chloronitrobenzenes（ClNBs）in aqueous solution were investigated in a semi-continuous reactor,and the molecular and free radical contribution of ozone to the degradation of ClNBs was also evaluated.The results of kinetic studies showed that the decomposition of ClNBs was a pseudo-first-order reaction with respect to pollutant concentration and the degradation rate was in the order o-CNB 〈m-CNB〈p-CNB. The overall rate constant increased with increasing pH, however decreased with increasing pollutant and free radical scavenger concentration. Furthermore, the TOC removal rate was significantly lower than the degradation rate. Ozonation could not reduce TOC completely, the results of HPLC and GC-MS showed that p-CNB was mainly transformed into p-chlorophenol, p nitrophenol, 2 chloro-5-nitrophenol, etc. , and carboxylic acids with low molecular weight. Finally, it was found through evaluating the contribution of ozone molecule and hydroxyl radical that hydroxyl radical played a decisive role in the removal of CINBs. Therefore, advanced oxidation processes （AOPs） which enhance the generation of free radicals in eliminating this kind of pollutants from environment may be a preferred choice.