【作者】 崔英杰；

【导师】 贾永刚； 杨世迎；

【作者基本信息】 中国海洋大学 ， 环境工程， 2008， 硕士

【摘要】 由于对有机化合物尤其是四氯乙烯(PCE)和三氯乙烯(TCE)等含氯有机污染物的广泛使用和不适当的处理,导致有机物成为土壤和地下水的主要污染物之一。含氯有机污染物十分稳定并具有生物拮抗特性,在环境中不易被分解而受到关注。Fenton氧化法作为一种高级氧化技术,在废水处理领域已经得到深入的研究,而最近在土壤和地下水有机污染修复中也受到越来越多的重视。本论文针对目前仍备受争议的Fenton试剂对非水相有机污染物降解的反应机理,包括反应活性粒子(羟基自由基和超氧自由基)的贡献、反应的位点等关键问题进行了探讨,并系统地考察了温度、催化剂浓度和氧化剂浓度对降解反应的影响,及在Fenton试剂中添加非离子表面活性剂曲拉通TX100和阴离子表面活性剂十二烷基苯磺酸钠(SDBS),形成表面活性剂-Fenton系统,并初步研究了该系统对非水相有机污染物的降解。本论文采用硫酸铁和乙二胺四乙酸二钠(EDTA)配制的铁螯合剂(Fe(III)-EDTA)作催化剂,在对土壤和地下水中的微生态系统生长有利的中性环境条件下进行研究。研究的主要内容包括三部分:第一,在降解的反应机理方面,反应中是否产生还原性活性粒子超氧自由基;降解反应是以羟基自由基还是以超氧自由基起决定作用;反应发生在重非水相流体DNAPLs(dense non-aqueous phase liquids)的水溶液中,还是可以直接在DNAPLs的非水相降解等问题,目前还存在很大争议。本研究以四氯乙烯(PCE)和三氯乙烯(TCE)为目标有机污染物,采用异丙醇和氯仿分别作为羟基自由基和超氧自由基的俘获剂,来验证降解反应中是否产生超氧自由基以及何种活性粒子起决定作用。结果发现:在Fenton试剂降解PCE/TCE DNAPLs的反应中,不仅产生羟基自由基,还产生超氧自由基,并以羟基自由基的贡献为主,羟基自由基的产生与否与氧化剂量的多少没有必然联系;采用气相色谱法,分析比较反应30 min时降解反应与挥发溶解实验中PCE剩余量,计算得出,除催化剂与氧化剂浓度皆很低及与PCE的配比很小的情况外,Fenton试剂可以直接降解非水相的PCE。第二,研究了温度、催化剂浓度、氧化剂浓度对Fenton试剂降解PCE DNAPL的影响,优化了反应条件。实验表明:1、同一反应时间时,20、40和60℃的环境温度中,从降解效果和经济上考虑,40℃时为最佳反应温度。2、在有机物、氧化剂浓度一定时,0.5、5和10 mM催化剂浓度中,5mM催化剂浓度为最佳反应浓度;而在有机物、催化剂浓度一定时,50、100和200 mM氧化剂浓度中,100 mM氧化剂浓度为最佳反应浓度。浓度过高或过低都不利于降解反应的进行。第三,首次在反应体系中添加非离子表面活性剂曲拉通(TX100)或阴离子表面活性剂十二烷基苯磺酸钠(SDBS),构成表面活性剂-Fenton体系,对PCE DNAPL的降解进行了探讨。结果发现:1、添加TX100或SDBS,都能显著促进Fenton试剂对PCE DNAPL的降解效果,且TX100对降解反应的促进性要高于SDBS。2、表面活性剂的添加量及反应初始浓度与该体系的降解效果成反向关系,在表面活性剂少量且反应初始浓度较低时,该体系的降解效果更好。3、系统温度在0~60℃时,与非离子表面活性剂-Fenton体系的降解效果成反比关系;系统温度在4~38℃时,与阴离子表面活性剂-Fenton体系的降解效果成反比关系。4、表面活性剂-Fenton体系降解PCE DNAPL的反应中羟基自由基起主要作用,且在降解反应过程中有超氧自由基生成。更多还原

【Abstract】 The widespread use and improper of disposal of organic chemicals, especially non-aqueous phase pollutants such as Trichloroethylene (TCE) and Perchloroethylene (PCE), has led to significant contaminant of soils and groundwater throughout much of the world. As one of the advanced oxidation technologies, Fenton oxidation has been deeply researched in wastewater treatment. Recently, the technology attracts more and more attention in organic polluted groundwater remediation. However, there are still open questions concerning on mechanicms of non-aqueous phase organic degradation by Fenton reagent, such as the contribution of active species and the site that the reaction takes place. In this paper, we had focused our attention on the concerning questions, systemically studied the factors on degradated reactions by modified Fenton’s reagent with iron(III)-ethylenediaminetetraacetic (Fe(III)-EDTA) chelator at neutral pH. The studies are such as follows:(1) There are different viewpoints of the degradation mechanism whether the organic phase can be directly degradated by modified Fenton’s reagent, and which active species plays a major role in the reactions. In this study, PCE and TCE are present as dense non-aqueous phase liquids (DNAPLs) in solution system at neutral pH. The experiments were carried out with isopropyl alcohol as hydroxyl radical scavenger and trichloromethane as superoxide radical scavenger. These results showed that both hydroxyl radicals and superoxide radicals were generated in degradation reactions, and hydroxyl radical played a major role. There were no necessary relation between the concentration of the oxidant and the generation of hydroxyl radicals, and the directly degradation of non-aqueous phase PCE by modified Fenton’s reagent.(2) Effect of operational parameters such as temperature, the concentration of chelator or oxidant, on PCE degradated reactions by Fenton’s reagent were systemically studied. The results showed that the optimal reaction temperature was 40 centigrade, the optimal concentration of chelator was 5 mM, and the optimal concentration of H2O2 was 100 mM.(3) Surfactant was added to Fenton’s reagent, and studied the DNAPL degradation by surfactant-Fenton system. Results were founded that the PCE DNAPL degradation by surfactant -Fenton was better than that only by Fenton reagent with the same conditions of reactions. There were inverse proportion between the concentration of surfactant and the effect of degradation.That is to say, the higher of the temperature when controlled in 20~60℃, the lower of the rate of degradation. And both hydroxyl radical and superoxide radical were possibly generated in reactions of PCE DNAPL degradated by surfactant -Fenton reagent.It’s important of the paper to improve the efficiency of organic degradation by Fenton’s reagent. And the paper can provide scientific gist for practical project of organic degradation by Fenton’s achnology at home and abroad.更多还原