【作者】 彭立君；

【导师】 刘云国；

【作者基本信息】 湖南大学 ， 环境科学与工程， 2008， 硕士

【摘要】 随着科技的不断发展,人们逐渐认识到土壤环境中很少存在着单一污染物,无机物和有机物的复合污染对人类的健康和生态的安全造成了一定的威胁,已经引起人们的关注。重金属和多环芳烃(PAHs)作为常见的无机污染物和有机污染物的典型代表,是当前土壤修复研究的热门物质。土壤淋洗作为常见的应用广泛的土壤修复技术,通过选择有效的淋洗剂,可以有效修复复合污染的土壤。本文以生物表面活性剂鼠李糖脂作为淋洗剂去除土壤环境中的重金属和PAHs。鼠李糖脂可以通过降低表面张力和促进污染物的移动从而增溶污染物,它对环境无毒害,可完全生物降解不产生二次污染。由于重金属PAHs种类繁多,选取土壤环境中浓度最高的三种重金属(Pb、Zn、Cu)和美国环保局推荐的16种优先污染物PAHs做为研究对象。在批次实验中,研究了不同浓度(0.1%、0.5%、2%和4%)和不同pH值(6.5, 8.0. 10.0)的鼠李糖脂溶液对污染物的去除效率。结果表明,随着浓度的提高鼠李糖脂对污染物的去除效率逐渐增加。在鼠李糖脂溶液浓度为4%时,∑PAHs的去除率达到66.8%, Pb、Zn、Cu的去除率分别为66.7%、50.5%、48.5%;在鼠李糖脂溶液浓度为0.5%时,∑PAHs的去除率仅为20.5%,Pb、Zn、Cu的去除率分别为23.2%、12.5%、10%。pH值不断变化,污染物的去除效率液也在不断改变。在pH值为10时, Pb和Cu达到最大去除率为79.5%和35.5%,PAHs也达到最大去除率60.3%;Zn在pH值为8时达到最大去除率20.5%。同时,批次实验还将鼠李糖脂与羟丙基环糊精HPCD、十二烷基硫酸钠(SDS)+乙二胺四乙酸(EDTA)对比去除污染物。结果表明, HPCD对重金属和PAHs的去除能力不如鼠李糖脂, SDS+EDTA对重金属的去除效率高于鼠李糖脂,但是对PAHs的去除能力较鼠李糖脂弱。依据批次实验的结论,在土柱实验中,以2%的鼠李糖脂(pH=8)淋洗污染土壤。经过三轮淋洗, Pb、Zn、Cu的去除率分别达到85.6%、74%和63.7%,第一轮与第二轮之间Pb、Zn、Cu淋洗去除率增幅分别为25.4%、36.6%、18%;第二轮与第三轮之间Pb、Zn、Cu淋洗去除率增幅分别为16.7%、22%、20.1%,表明随着淋洗次数增加,每阶段能去除的污染物逐渐减少。经过三轮淋洗, PAHs的去除率非常高,如萘的去除率高达98%,对于难去除的6环PAHs的去除率也达到70%。随着苯环数的增加,第一轮的解吸率逐渐降低,第二轮和第三轮的淋洗对4环、5环和6环的PAHs作用更为显著。随着环数增加,辛醇-水分配系数(Kow)逐渐增加,化合物疏水性增强,去除难度增加,即PAHs淋溶率与其lgKow之间存在相关性。虽然原理上土柱法与批次实验法都是利用鼠李糖脂去除PAHs和重金属,但是二者在运行过程中会有很大的差别,故研究了上述两种运行模式。总体而言,鼠李糖脂可有效去除自然界土壤中的复合污染物,对实际污染土壤的修复具有重要的参考价值。更多还原

【Abstract】 Contamination of soil environment by toxic metals and organic compounds is widely recognized as one of the major concern because of the potential health hazard they may pose for humans. The presence of these contaminants can destroy the balance in the natural habitat. Therefore, there is a need for remediation to mitigate these effects on humans and the environment at large. This paper presented laboratory batch and column experiments to evaluate the ability of tipical biosurfactant rhamnolipid to simultaneously remove heavy metals and low-polarity organic compounds US EPA’s 16 priority-pollutant PAHs (polycyclic aromatic hydrocarbon) from contaminated soil.The contaminated soil was obtained from the outlet of Jingzhu highway contained 86% sand, 8% fines, 0.42% organic matter and high concentrations of total PAHs (1573mg/kg), lead (395.2 mg/kg), zinc (282.6 mg/kg) and copper (98.5mg/kg).Batch leaching tests were conducted at different concentrations and pH to determine the mechanisms controlling heavy metals and PAHs release and optimize the conditions of removing pollutants. The combination of SDS (sodium dodecyl sulfate) and EDTA(ethylenediamine tetra acetic acid), HPCD (hydroxypropyl-β-cyclodextrin ) were investigated to compare with rhamnolipid. The results showed that different concentrations were significantly influenced removal efficiencies. The maxium tatal PAHs remval efficiency (66.8%) was obtained with 4% rhamnolipid; in addition, the maxium removal efficiency on lead (66.7%), zinc (50.5%) and copper (48.5%) was also obtained with 4% rhamnolipid. The maxium zinc remival (20.5%) was obtained with 2%rhamnolipid at pH 8.0; highest lead (79.5%) and copper (35.5%) and total PAHs ( 60.3%) removal was obtained with 2% rhamnolipid at pH 10.0. It was observed that HPCD was less effective than rhamnolipid; the combination SDS (sodium dodecyl sulfate) with EDTA was found to be more effective than rhamnolipid in removing of heavy metals.According to batch leaching tests, column experiments carried out with 2% rhamnolipid at pH 8.0. The results showed that after a series of three washings of the soil using biosurfactant; the highest removal of lead, zinc and copper was 85.6%, 74% and 63.7%, respectively. As for PAHs, from 70% to 98% of PAHs were removed in three-stage solvent washing. The desorption effiency of high rings of PAHs was higher than the lower rings. Desorption ratio in the first stage was increased and the desorption ratio in the second; third stages were decreased with the increasing of the rings of PAHs. PAHs desorption ratio associated with octanol-water partition coefficient (Kow).The results of the experiments showed that rhamnolipid could greatly enhance the simultaneous desorption and elution of the model organic compound (PAHs) and the model heavy metal (lead, zinc and copper) from the soil examined.更多还原