【作者】 林莉；

【导师】 陆晓华；

【作者基本信息】 华中科技大学 ， 环境工程， 2010， 博士

【摘要】 随着我国工业化和城市化发展及《斯德哥尔摩国际公约》的履约进程,近几年出现了一大批关闭搬迁或即将退役的化工企业。废弃的化工污染场地被开发作商用和民用,污染场地中大量有毒物质的存在严重影响着生态环境和人居环境安全,因此亟需对化工污染场地进行高效、快速的修复。在污染场地修复工程中,热修复技术作为一种最主要的场地修复技术得到广泛应用。土壤热修复技术中,由于常规加热的传热机制导致能量传递速度慢,处理效率低下；另外由于需要将土壤进行整体加热,消耗的能量较大。近年来有研究采用微波(Microwave, MW)来替代常规加热的热源,利用MW的特殊加热方式来迅速提高土壤温度,促进污染物的解吸、分解或固定化过程并实现土壤修复；同时MW加热具有选择性,直接作用于土壤中的极性污染物和水分子等吸波物质,可大大节省能量。MW技术具有对污染物的种类和性质无选择性、处理时间短等优点,对于化工场地土壤中种类繁多、毒性大、浓度高的污染物是一种非常合适的治理技术。本文分别以制药业的抗生素、有机化工的硝基化合物和无机化工的重金属三类不同污染物为研究对象,研究了污染土壤MW修复技术的影响因素和机理,在小试研究的基础上对MW土壤修复设备进行了研究开发。本文的主要研究内容与结论有：(1)研究了氯霉素(Chloramphenicol, CAP)污染土壤的MW修复条件及机理,结果表明：MW敏化剂对MW修复CAP污染土壤的效果依次为颗粒活性炭(GAC)>铁粉>水>二氧化锰；GAC作MW敏化剂时,MW功率和GAC剂量对修复效率影响最大；在一定范围内,土壤修复效果随土壤量的增加而显著增大,对于3 g土壤,CAP的去除率在辐射5 min时可达到93%,而对于0.5 g土壤,MW辐射20 min后去除率仅为80%；污染物的初始浓度对修复效果影响较小;MW辐射下CAP经历了C-C键的断裂和氧化反应,部分裂解碎片与土壤有机质发生反应,生成了新的大分子产物,但产物的浓度极低,辐射时没有脱氯过程的发生。(2)研究了4-硝基酚(4-nitrophenol,4-NP)模拟污染土壤的MW修复条件及机理,并对实际污染土壤的修复效果进行了考察,结果表明：几种MW敏化剂中GAC的敏化效果最好,向土壤中添加一定水分可使4-NP的去除率有所提高,但提高率不足10%；MW功率越高去除效果越好,4-NP初始浓度对去除率无显著影响。加入GAC作MW敏化剂时可显著促进MW修复4-NP污染实际土壤的效果,以1 g污染土为处理对象并加入0.3 g GAC,采用700 w的MW功率辐射20 min后4-NP去除率达70%；保持土壤量和GAC剂量的比值一定,增加土壤量可以显著促进4-NP的去除率,当土壤量大于2 g时4-NP去除率达96%以上；4-NP在MW辐射下的去除无挥发作用的发生,其机理很可能为在高温下直接矿化为CO2和H2O,或者本身和分解的中间产物直接同土壤产生化学结合而被固定,因而从土壤中无法被萃取出来。(3)研究了土壤中Cr(Ⅵ)的MW强化还原技术,结果发现：土壤有机质的存在本身会使土壤中的Cr(Ⅵ)还原,初期还原速率较快,初始浓度为100 mg·kg-1的Cr(Ⅵ)污染土壤,放置3天后Cr(Ⅵ)还原率接近70%,后期还原速率显著降低,Cr(Ⅵ)的浓度趋于平稳；当有机质含量一定时,Cr(Ⅵ)初始浓度越高,还原率越低,但实际还原量增大。以GAC作为还原剂,采用MW辐射对土壤中的Cr(Ⅵ)进行强化还原,MW辐射在1-3 min内就可将土壤中85%以上的Cr(Ⅵ)还原成Cr(Ⅲ),其中GAC的剂量是影响还原效果的重要因素,辐射时间和MW功率对Cr(Ⅵ)的还原率影响不大；Cr(Ⅵ)初始浓度对还原率无显著影响,MW辐射处理3 min对浓度范围为7.34-610.48 mg·kg-1的Cr(Ⅵ)污染土壤还原率都能达到75%以上；若仅依靠土壤有机质对Cr(Ⅵ)的还原作用,将土壤中85%的Cr(Ⅵ)还原成Cr(Ⅲ)需数十天的时间,而采用MW辐射技术仅需1-3 min就可获得同样的还原效果；对于土壤中Cr(Ⅵ)的还原,MW强化还原技术具有高效、快速的特点。(4)在小试研究基础上,设计加工了MW原位土壤修复和MW脱氮中试设备。土壤修复中试设备对污染土壤有着较好的修复效果,对200 g初始浓度为100mg·kg-1的4-NP污染硅藻土,600W的MW功率下辐射处理50min时4-NP的去除率为68-82%,且设备运行稳定、操作方便,也无MW泄漏现象的发生,但MW敏化剂的回收和循环使用问题还需要解决。MW脱氮中试设备的日处理量为5吨,MW功率为4.8 kW,该设备对实际焦化废水的脱氮率可达74-84%；较低的环境温度和较高的废水流速会降低脱氮效率,废水的初始氨氮浓度对脱氮效果影响不大,曝气能使脱氮率增加9-10%；该设备比常规蒸氨工艺所需成本稍低。更多还原

【Abstract】 With the industrialization and urbanization and the performance of "Stockholm International Convention", a large number of chemical enterprises to be closed or retired are presented in our country. The abandoned chemical industry sites will be developed for commercial and residential use. The residues of the multi-type, high load, high toxic pollutants in contaminated sites pose potential risk to ecological environment and public health. Thus, it is necessary to remediate the contaminated sites effectively.Thermal remediation technology was widely used in contaminated sites remediation. In conventional heating method, heat transfers by thermal conduction, convection and radiation, which leads to slow heat transfer velocity and low remediation efficiency. Besides, conventional heating is an integral heating process, which consumes more energy. In recent years, microwave (MW) heating was used to instead of the conventional heating method for soil remediation. Soil can be heated rapidly and selectively by MW, and the pollutants in the soil were desorbed, degraded or stabilized. MW technology has shown great potential for the remediation of contaminated site of chemical industry due to its non-selective for the pollutants, high heating rates and great control of the treatment process.In this paper, three typical contaminants, antibiotic of pharmaceutical industry, nitro-compound of organic chemical industry and heavy metal of inorganic chemical industry, were selected as the treatment targets by MW technology. The operation conditions were optimized and the removal mechanisms were investigated. Then pilot-scale MW equipments were designed and used to explore the prospect of industrial application of MW technology. The main conclusions are drawn as follows:(1) Chloramphenicol (CAP), a typical antibiotic, was treated by MW radiation. The catalytic effect of the MW absorbents followed granular activated carbon (GAC)>Fe>H2O>MnO2. When GAC was used as MW absorbent, large MW power and GAC dosage should be used for a completed decomposition of CAP. The remediation efficiencies increased with the soil mass in the range from 0.5 g to 3.0 g. For 3 g soil, 93% of CAP remediation efficiency was reached in 5 min, whereas for 0.5 g soil, it was only 80% even in 20 min MW radiation. The effect of initial CAP concentration was minute. CAP experienced carbon-carbon bond rupture and oxidation reactions in MW radiation, and a part of CAP fragment reacted with the soil organic matter and formed new compounds, but the concentration of each product was extremely low. No dechlorination process occurred during this process.(2) MW technology was used to treat simulated 4-nitrophenol (4-NP) contaminated soil. GAC shows the best catalysis effect among the MW absorbents. Degradation efficiency of 4-NP increased when water was added into the soil, but the increment was less than 10%. The addition of GAC obviously increased the degradation efficiency of 4-NP in real soil. For 1 g real soil mixed with 0.3 g GAC,70% of 4-NP remediation efficiency was reached in 20 min at the MW power of 700 W. The 4-NP remediation efficiency was above 96% for 2 g soil mixed with 0.6 g GAC. The degradation efficiency increased with the MW power, the 4-NP initial concentrations had minute effect on the degradation efficiency.4-NP did not evaporate from the simulated soil by MW radiation, it was probably thermally decomposed to CO2 and H2O, or decomposed to fragments, which were further tightly bound to the soil.(3) Cr (Ⅵ) could be reduced by soil organic matter (SOM), Cr (Ⅵ) was reduced fastly at the beginning state, its concentration in soil decreased from 100 mg·kg-1 to 31.73 mg·kg-1 in the first 3 days. Then the reduction rate decreased. At a certain SOM concentration, the reduction rate of Cr (Ⅵ) decreased with the initial Cr (Ⅵ) concentration, but the reduction amount was increased. MW radiation posed a great reduction effect for Cr (Ⅵ) in the soil, and about 85% of the Cr (Ⅵ) could be reduced in 1-3 min at the MW power of 700 W. GAC dosage was the most important impact factor for the reduction process, the effects of radiation time and MW power were minute. When the initial concentration ranged from 7.34-610.48 mg kg-1, more than 75% of Cr (Ⅵ) could be reduced in 3 min. Several ten days was needed to reduce 85% of Cr (Ⅵ) by SOM in the soil, but only 3 min was needed by MW radiation. MW enhanced reduction of Cr (Ⅵ) showed great efficiency, which is of fleetness and high performance.(4) The pilot-scale MW soil remediation equipment showed great effect for the contaminated soil. For 200 g 4-NP contaminated diatomite with initial concentration of 100 mg kg-1, the removal of 4-NP reached 68-82% in 50 min MW radiation. The equipment was run stable and convenient to operate, and no MW leakage was detected. Nevertheless, the problem of recovery and utilization of the MW absorbent needs to be solved. Summarily, MW radiation can be considered as a promising technology for the site remediation of chemical industry. A pilot-scale MW reactor was developed to remove ammonia nitrogen in coke-plant wastewater, the output power of the reactor was 4.8 kW and the handling capacity was about 5 tons per day. Low ambient temperature and higher flow rate reduced the effectiveness of the MW reactor, initial concentration had minute influence on ammonia removal, and the removal could be enhanced about 9-10% with aeration. Ammonia removal efficiency of the MW pilot-scale system could reach 74-84% for real coke-plant wastewater. The cost of the MW equipment was a litter lower than conventional steam-stripping method.更多还原