【作者】 王蕾；

【导师】 姜玄珍；

【作者基本信息】 浙江大学 ， 化学， 2008， 博士

【摘要】 辉光放电等离子体水处理技术是近十余年发展起来的具有工艺灵活,放电电压低,适合处理高含盐量废水和无二次污染的新型水处理高级氧化技术。目前辉光放电等离子体降解水中有机污染物尚存在能量利用率较低的缺点。本论文利用加入铁盐催化放电过程中产生的过氧比氢生成羟基自由基来加速有机物的降解,以提高等离子体的能量利用效率。实验结果发现铁离子的催化效果优于亚铁离子,本研究为Fenton试剂处理有机废水提供了新的思路。铬化合物广泛应用于电镀,制革,冶金等行业。这些工业在生产过程中排放出大量的含铬废水,其中含有强致癌性的六价铬。常规含铬废水的治理方法需要大量的还原剂并产生二次污染。本论文首次运用辉光放电等离子体诱导还原模拟含铬废水中六价铬,发现辉光放电等离子体能有效地将六价铬还原为三价铬,为等离子体在水中有毒重金属的还原去除开拓了新领域。本论文分为两部分共五章:第一章介绍了典型等离子体水处理工艺及基本原理,比较了各种等离子体水处理技术的优缺点;并讨论了含铬废水的治理方法现状和未来的发展趋势。第二章以硝基苯水溶液为模拟废水,考察了污染物初始浓度、电流、电压和溶液体积等实验参数对硝基苯辉光放电等离子体降解的影响;比较了高压脉冲放电和辉光放电在硝基苯的去除和过氧化氢的生成方面的能量效率;探讨了硝基苯的降解机理。结果表明无催化剂条件下硝基苯降解遵守一级反应动力学规律,在450-550V之间,一级反应速率常数与放电电流成正比,与溶液体积成反比。当电压低于450 V时,速率常数急剧降低;pH值对降解没有明显的影响;主要中间产物为硝基苯酚,苯酚,1,3-二硝基苯、羧酸、硝酸根和亚硝酸根,最终产物是硝酸根离子、水和二氧化碳。降解过程中有过氧化氢生成,铁盐对硝基苯降解有明显的催化作用。第三章考察了电解质种类、自由基清除剂、催化剂等条件对双酚A降解及过氧化氢生成的影响。结果表明在氯化钠电解质溶液中双酚A降解速率最大,但过氧化氢生成速率最低。自由基清除剂对双酚A的降解和过氧化氢的生成有抑制作用,三价铁离子的催化作用优于亚铁离子。铁盐存在时双酚A降解的中间产物量比较高,无铁盐存在时降解中间产物主要为羧酸。研究发现辉光放电等离了体降解双酚A的能量效率高于光催化。第四章系统地研究了铁盐对辉光放电等离子体降解苯酚的催化作用,结果表明在放电过程中有大量过氧化氢生成,三价铁离子的催化效果优于二价铁离子。原因是辉光放电等离子体产生了羟基自由基和过氧化氢,羟基自由基与苯酚反应生成二羟基环己二烯自由基,该自由基有还原性,能将铁离子还原成亚铁离子,亚铁离子与过氧化氢反应生成更多的羟基自由基,如此循环。在铁盐存在下,中间产物主要为对苯二酚,邻苯二酚和对苯醌。第五章尝试运用辉光放电等离子体还原模拟含铬废水中的六价铬,考察了电压、pH值和自由基清除剂对六价铬还原的影响并对其机理进行了初步的解释。结果发现辉光放电等离子体能有效地诱导还原模拟废水中的六价铬为三价铬,降低pH值和加入羟基自由基清除剂有利于还原。在溶液初始pH值为2,和100 mg/L苯酚存在的条件下,100 mg/L的六价铬可以在10分钟内被完全还原去除。研究发现辉光放电等离子体诱导还原六价铬的能量效率高于光催化。更多还原

【Abstract】 Water treatment with glow discharge plasma (GDP) is a novel kind of advanced oxidation processes that is developed in recent years. Compared with other electrical processes, GDP offers advantages of lower voltage needed and being able to operate at highly conducting solutions. One of the major problems associated with GDP is its relatively lower energy efficiency in degradation of organic pollutants. The present study will focuse on improving the energy efficiency by adding the iron salts to the solution to catalyze the hydrogen peroxide formed to produce the reactive hydroxyl radicals. Experimental resuts indicated that the catalytic action of ferric ion was better than that of ferrous ion. The findings will provide new insight in Fenton’s study.Chromium compounds are widely used in electroplating, leather tanning and other industrial processes. Consequently, a huge quantity of aqueous chromium wastes are produced, which would greatly pollute the environment without proper disposal. Hexavalent chromium is extremely toxic and has demonstrated to be carcinogenic. Conventional treatment of Cr(VI) suffers the shortcomings of process complexity and producing second contamination. This paper investigated the efficient reduction of Cr(VI) by GDP for the first time. It was demonstrated that GDP is very efficient in Cr(VI) reduction. The findings woud provide an alternative to the treatment of chromium wastewater.The thesis includes 5 chapters:Chapter 1 reviewed the application of low temperature plasma technology in the treatment of water and wastewater and the present status of chromium wastewater treatment.Chapter 2 systemetically investigated the liquid-phase degradation of nitrobenzene (NB) by GDP under various reaction conditions, such as, the initial solution pH, current intensity, volume of solution and iron salts. Experimental results indicated that, in the absence of catalysts, the depletion of NB followed first-order kinetics, where the observed value of the first-order rate constant ’k’ is directly proportional to the applied current intensity and inversely proportional to the solution volume. Initial solution pH had little effect on the value of k. HPLC and IC analyses showed that the major intermediate products were nitrophenols, phenol, 1,3-dinitrobenzene, organic acids and nitrate ions. The eventral products were carbon dioxide and nitrate ions. During the treatment, a lot of hydrogen peroxide was formed and the role of Fenton’s reaction was examined. A reaction pathway is proposed based on the degradation kinetics and the distribution of intermediate products.In Chapter 3, degradation of bisphenol A (BPA) and simultaneous formation of hydrogen peroxide induced by GDP were investigated. Experimental results indicated that the BPA degradation rate was higher in sodium chloride solution than in sodium sulfate or phosphate solutions. However, the formation rates of hydrogen peroxide were on the opposite case. Both the BPA removal and the hydrogen peroxide production rates decreased in the presence of hydroxyl radical scavengers, indicating that hydroxyl radicals are the most probable oxidants responsible for BPA degradation and the precursors of hydrogen peroxide. Ferric ion showed better catalytic effect than that of ferrous ion, suggesting that the ferric ion was reduced by the intermediates formed during BPA degradation, which was confirmed by following the production of ferrous ion in the system. TOC of the solution gradually reduced with discharge time; however, without catalysts, the solution COD increased with discharge time and sharply decreased in the presence of iron salts. The major intermediate products were identified by LC/MS and the possible degradation mechanism was discussed.In Chapter 4, unusual catalytic effects of iron salts on phenol degradation induced by GDP were examined. It was found that ferric ions showed much better catalytic effect than that of ferrous ions. The reason was that GDP could produce hydroxyl radicals and hydrogen peroxide simultaneously; the hydroxyl radicals reacted with phenol to produce dihydroxylcyclohecyldinel radicals which reduced the ferric ions to ferrous ions and the newly formed ferrous ions catalyzed the hydrogen peroxide to produce more hydroxyl radicals. Without iron salts, TOC of the solution gradually decreased with treatment time while COD of the solution increased due to the accumulation of the hydrogen peroxide. Without iron salts, catechol, hydroquinone, and hydroxylhydroquinone were major byproducts. However, large amounts of catechol, hydroquinone and benzoquinone yielded in the presence of iron salts. The present study presents some new information related to Fenton’s reaction.In Chapter 5, an efficient reduction of hexavalent chromium [Cr(VI)] induced by GDP has been achieved for the first time. Experimental results show that Cr(VI) can be smoothly reduced to trivalent state [Cr(III)] by means of GPD. The rates of Cr(VI) reduction can be enhanced either by decreasing the solution pH or by addition of radical scavengers to the solution. At initial pH 2.0, 100 mg/L of Cr(VI) can be completely reduced with 10 minutes of GDP treatment in the presence of 100 mg/L phenol. Possible reaction mechanism was proposed based on the reduction kinetics. The energy efficiency of Cr(VI) reduction in GDP has been compared with those in semiconductor photo-catalytic reduction.更多还原