| 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.
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