有机污染土壤的低温等离子体修复方法及机理研究
发布时间：2018-11-18 15:34
【摘要】：我国由于工业化和城市化进程的加快,污染物大量排放,造成了严重的土壤污染,其中土壤场地的有机污染是除重金属污染之外的另一种土壤污染的主要形式。针对有机污染土壤,尤其是高浓度有机污染土壤,传统的物理、化学、生物及植物土壤修复技术由于其分别具有产生二次污染、需要投加化学药剂、处理有机物种类有限及修复周期长等局限性而难以满足绿色、高效、快速的土壤修复目的。低温等离子体(Non-thermal plasma,NTP)技术被越来越多地应用到环境领域并被认为是一种有前途的污染物治理技术。低温等离子体又被称为非平衡等离子体,是指在由气体或液体放电产生的含有电子、带正电的重离子、UV、O3、强电场、冲击波及各种自由基(·O、·O2、·OH等)的等离子体系中,温度高的电子密度较低,与重粒子碰撞机会较少,使对系统温度起决定作用的重粒子动能与高温电子差别较大,整个体系温度较低。这种技术因不需要另外投加化学药剂即可原位产生各种活性粒子而被称为“绿色处理技术”,并逐渐成为污染物治理领域研究的热点。本文采用介质阻挡放电(Dielectric Barrier Discharge,DBD)和脉冲电晕放电(Pulsed Corona Discharge,PCD)等离子体对PNP(P-nitrophenol,PNP)和菲(Phenanthrene,PHE)污染土壤进行了修复,探讨了降解过程中土壤特性对降解效率的影响,分析了污染物的降解机理,并对比了 DBD和PCD放电方式对污染土壤的处理效能差异,以考察低温等离子体技术在难降解、重污染土壤修复方面的可行性。主要研究内容和结果如下:(1)以PNP为目标污染物,系统地考察了 DBD体系的电压、土壤污染的初始浓度、土壤pH值、气体流速等实验参数对DBD等离子体降解PNP效果的影响。结果表明,DBD等离子体能够有效去除土壤中的PNP,在50 min内污染物的去除率为63.6%,能量效率为0.0067 mg/kJ。DBD等离子体反应系统可以矿化20%的PNP。通过对比等离子体法和臭氧法发现,臭氧在PNP降解过程中起到的作用约为25%。此外,对处理前后的土壤进行了 FTIR、GC-MS、IC和HPLC分析,检测到了邻苯二酚、对苯二酚、富马酸、马来酸、草酸,甲酸、乙酸、硝酸根等产物,推测出了PNP在降解过程中发生了脱氮反应、羟基化反应、替代反应和苯环破裂等反应,并对其降解途径进行了推导。(2)以典型的多环芳烃(Polycyclic Aromatic Hydrocarbons,PAHs)PHE 为目标污染物,考察该DBD反应器对其降解效果和机理。结果表明,在频率为150 Hz,电压为110 V,放电间隙为1.5 cm,占空比为20%,空气流速为0.6 L/min时,系统的输入功率为64 W,PHE的去除率为98%。采用DBD等离子体技术修复PHE污染土壤取得了良好的效果,证明了该技术对不同结构的有机污染均有理想的处理效果。通过GC-MS、FTIR、IC的色谱分析检测到了 9,10-菲醌和2,2'-联苯甲酸等主要降解产物。利用密度泛函理论(Density Functional Theory,DFT)对PHE的分子轨道进行了计算和结构优化。通过实际检测与模拟计算对PHE的降解途径进行推导与验证。采用光学发射光谱(Optical Emission Spectra,OES)鉴定了含氧活性粒子、含氮活性粒子以及羟基自由基,并推导了其产生方式。(3)采用PCD等离子反应器对PHE污染土壤进行修复研究。结果表明,PCD等离子体反应系统对PHE污染土壤有良好的降解效果,在初始浓度160 mg/kg,放电电压30 kV、脉冲频率50 Hz、放电间隙20 cm、放电气氛空气的条件下,PHE的去除率能达到93%,反应遵循一级反应动力学,反应速率常数为0.032 min-1。此外,通过脉冲波形、处理效果、降解产物等多方面对比分析了正脉冲电晕放电、负脉冲电晕放电和双脉冲电晕放电。通过对比处理前后的FTIR光谱图可知PHE的分子结构遭到破坏并生成了带有C=O、N-H、羧基和羟基等基团的中间产物。最后,通过DBD等离子体和PCD等离子体处理PHE污染土壤的对比研究可知,两种不同的等离子技术均对PHE污染土壤产生了很好的修复效果。然而,两者对PHE污染土壤的修复也存在一定的差异,主要体现在放电波形、能源效率、动力学反应系数以及主要降解中间产物等方面。DBD等离子体反应快,污染物的去除率高。然而,PCD等离子体的能源效率高。
[Abstract]:As a result of the accelerated industrialization and the process of urbanization, the large amount of pollutant is discharged, which causes serious soil pollution, in which the organic pollution of the soil site is the main form of another kind of soil pollution other than the heavy metal pollution. in the light of the organic pollution soil, in particular the high-concentration organic pollution soil, the traditional physical, chemical, biological and plant soil remediation technology has the advantages of secondary pollution generation, It is difficult to meet the needs of green, high-efficiency and fast soil remediation by the limitation of limited organic species and long repair cycle. Low-temperature plasma (NTP) technology is increasingly applied in the field of environment and is considered a promising pollutant treatment technology. the low-temperature plasma is also referred to as a non-equilibrium plasma, which means that in a plasma system containing electrons, positively charged heavy ions, uv, o3, strong electric fields, shock waves, and various free radicals (路 o, 路 o2,. oh, etc.) generated by gas or liquid discharge, the electron density with high temperature is lower, and the collision chance of the heavy particles is less, so that the kinetic energy of the heavy particles acting on the temperature of the system and the high-temperature electronic difference are large, and the temperature of the whole system is lower. This technique is known as a 鈥済reen treatment technology鈥，
本文编号：2340431
[Abstract]:As a result of the accelerated industrialization and the process of urbanization, the large amount of pollutant is discharged, which causes serious soil pollution, in which the organic pollution of the soil site is the main form of another kind of soil pollution other than the heavy metal pollution. in the light of the organic pollution soil, in particular the high-concentration organic pollution soil, the traditional physical, chemical, biological and plant soil remediation technology has the advantages of secondary pollution generation, It is difficult to meet the needs of green, high-efficiency and fast soil remediation by the limitation of limited organic species and long repair cycle. Low-temperature plasma (NTP) technology is increasingly applied in the field of environment and is considered a promising pollutant treatment technology. the low-temperature plasma is also referred to as a non-equilibrium plasma, which means that in a plasma system containing electrons, positively charged heavy ions, uv, o3, strong electric fields, shock waves, and various free radicals (路 o, 路 o2,. oh, etc.) generated by gas or liquid discharge, the electron density with high temperature is lower, and the collision chance of the heavy particles is less, so that the kinetic energy of the heavy particles acting on the temperature of the system and the high-temperature electronic difference are large, and the temperature of the whole system is lower. This technique is known as a 鈥済reen treatment technology鈥，
本文编号：2340431
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