脉冲放电等离子体对有机污染土壤的修复研究

发布时间：2018-08-17 10:52

【摘要】：近年来,土壤污染逐渐加重,成为人类健康的潜在威胁以及农业可持续发展的重大隐患,因此,土壤修复已成为环保工作的紧迫任务和重要内容。针对有机污染土壤的修复,现有的物理法、化学法和生物法等很难同时满足快速、高效、清洁的修复要求。而低温等离子体技术作为一种高效、快速、无二次污染的高级氧化技术,为有机污染土壤的修复提供了新的方向。本文以多环芳烃芴以及农药阿特拉津两种有机污染物作为研究对象,采用高压脉冲电源和针板反应器,通过电晕放电产生的等离子体降解土壤中的有机物。主要研究包括芴的检测条件的优化、反应系统的放电特性、系统参数对芴降解率的影响、芴和阿特拉津降解机理分析。主要研究结果如下:(1)明确了芴分别溶于乙酸、丙酮、乙醇和甲醇四种溶剂后的HPLC检测条件,在0~60mg/L浓度范围内可以得到相关性较好的标准曲线;制备污染土样时,样品在摇床中附着的最佳震荡时间为10h,提取土壤中的芴时,只需震荡1h即可使之溶出;离心和震荡对芴的提取效果相同,虽然离心提取过程较为复杂,但耗时较短,而震荡提取过程相对简单,但耗时较长;四种溶剂对芴的提取率大小顺序为乙酸丙酮乙醇甲醇,综合考虑四种溶剂的物化性质、HPLC检测时长及提取率,选择甲醇作为芴的溶剂。(2)电源的负极输入功率大于正极,放电电压和放电频率升高则输入功率随之增大,电极间距在20~50mm之间输入功率随着间距的增加而减小,同一间距下输入功率随着电压的升高而增大,而电极间距为10mm时输入功率随着电压的升高而减小,土壤厚度的增加会削弱放电效果,从而输入功率随着土壤厚度的增加而减小,空气流量对输入功率无显著影响。(3)高压正极脉冲的能量效率高出负极0.035mg/kJ,选择正极作为连接反应器的电极;土壤中芴的降解率随着放电电压和放电频率值的增加而增大,综合考虑污染物的降解效果以及能量消耗值,选择最佳电压值为30kV,最佳频率值为50Hz;放电效果最佳的电极间距是20mm;0L/min~6L/min范围内的空气流量对芴的降解率没有明显的影响,只需自然通气即可;等离子体对土壤中不同初始浓度的芴的实际降解量大小顺序为:1000mg/kg200mg/kg100 mg/kg;等离子体对含水率分别为0%、10%和20%的芴污染土壤的降解率大小顺序为:0%10%20%,此外,等离子体对pH值分别为3.0、6.8和9.0的土壤中芴的降解率大小顺序为:9.06.83.0,土壤pH值为9时的降解率比pH为6.8时只提高了0.23%,故该技术在处理典型PAHs污染土壤时无需进行pH调节。对等离子体降解芴的过程进行动力学拟合,发现该过程符合准一级动力学。(4)等离子体对芴的降解效果明显优于单独臭氧对芴的降解效果,放电60min后,O3所起的作用占等离子的46.94%。通过定期洗脱土壤表层被氧化的产物可以改善等离子体在土壤表层的传质效果,能够较大幅度地提高芴的降解率;通过芴在放电前后的FTIR图谱结合相关文献推断出了芴的可能降解途径,副产物主要为酚、醇和酸。此外,等离子体对阿特拉津的降解率为23%,而O3对阿特拉津的降解率只占2.19%,这表明对于均三氮苯类农药污染的土壤,采用低温等离子体技术可能比采用臭氧技术有优势;此外,洗脱土壤氧化层的方法对对阿特拉津的降解率同样有促进作用,通过红外检测结合相关文献对阿特拉津的降解途径进行了分析,最后的产物为三聚氰酸。
[Abstract]:In recent years, soil pollution has become a potential threat to human health and a major hidden danger to the sustainable development of agriculture. Therefore, soil remediation has become an urgent task and an important content of environmental protection work. Low temperature plasma technology, as an advanced oxidation technology with high efficiency, high speed and no secondary pollution, provides a new direction for the remediation of organic contaminated soils. The main results are as follows: (1) Fluorene is soluble in acetic acid, acetone, ethanol and methanol, respectively. The standard curve with good correlation can be obtained in the concentration range of 0-60 mg/L under the conditions of HPLC after extraction. When preparing the contaminated soil sample, the optimum oscillation time for the sample to adhere to the shaking table is 10 hours, and when extracting fluorene from the soil, it can dissolve after only one hour of oscillation. The extraction rate of fluorene by the four solvents is acetone ethanol methanol, considering the physicochemical properties of the four solvents, the detection time and extraction rate by HPLC, and the methanol is selected as the solvent of fluorene. (2) The input power of the negative electrode of the power supply is greater than that of the positive electrode, and the discharge voltage is higher. The input power increases with the increase of discharge frequency, the input power decreases with the increase of electrode spacing between 20 mm and 50 mm, the input power increases with the increase of voltage at the same spacing, while the input power decreases with the increase of voltage when the electrode spacing is 10 mm, and the increase of soil thickness will weaken the discharge effect and thus transmit. The input power decreases with the increase of soil thickness, but the air flow rate has no significant effect on the input power. (3) The energy efficiency of high voltage positive pulse is 0.035mg/kJ higher than that of negative electrode, and the positive electrode is chosen as the electrode connecting the reactor. The degradation rate of fluorene in soil increases with the increase of discharge voltage and discharge frequency. The best voltage value is 30kV and the best frequency value is 50Hz; the best spacing of electrodes is 20mm; the air flow rate in the range of 0L/min~6L/min has no obvious effect on the degradation rate of fluorene, only natural ventilation is needed; the actual degradation amount of fluorene in different initial concentration of soil by plasma is small. The degradation rate of fluorene in soil contaminated by 0%, 10% and 20% fluorene by plasma was 0% 10% 20%, and the degradation rate of fluorene in soil with pH 3.0, 6.8 and 9.0 was 9.06.83.0. The degradation rate of fluorene in soil with pH 9 was only 0.23% higher than that in soil with pH 6.8. (4) The degradation of fluorene by plasma was better than that by ozone alone. After 60 minutes of discharge, the effect of O3 accounted for 46.94% of the plasma. By periodically eluting the oxidized products from the soil surface layer, the mass transfer efficiency of plasma in the soil surface layer can be improved, and the degradation rate of fluorene can be greatly increased. The possible degradation pathway of fluorene can be deduced from the FTIR spectra of fluorene before and after discharge, and the by-products are mainly phenol, alcohol and acid. The degradation rate of Razine was 23%, whereas that of Atrazine by O3 was only 2.19%. This indicated that the low temperature plasma technology might be superior to ozone technology in the treatment of soil contaminated by triazobenzene pesticides. The degradation pathway of atrazine was analyzed in conjunction with relevant literature, and the final product was cyanuric acid.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53

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