| In recent years, as a kind of advanced oxidation process, light degradation is often used to study the degradation of pollutant treatment,.due to its advantages such as strong oxidation ability, non-selectivity, non-subsequent pollution, etc. Electrodeless lamp, being a new light source, has become a research hotspot, because of its long life, good light efficiency and convenient structure. At present, in the field of pollution control, the electrodeless lamps used in the reports are of high frequency irradiated by the microwave(>2GHz). To achieve the purpose of changing spectra and improving process efficiency, the parameters which could be changed just include the gas composition and pressure. Thus, the energy efficiency is very low, since no improvement in energy conversion and energy consumption structure. This study selected a low frequency electrodeless lamp (LFEL) induced by an external electromagnetic field as a new type of light source. Without addition of any catalytic material, the ability of degradation of organic pollutants Acid Orange 7 (AO7) and tetracycline in water was investigated, and the main influence factors and mechanism of degradation were also discussed.In this thesis, a novel reactor was designed and fabricated by ourselves, in which electrodeless lamp was the light source, and the aeration introduction was an assistive technique. Azo-dye Acid Orange 7 and antibiotic tetracycline were used as objective compounds of the degradation. The main influence factors are discussed, particularly the new type of photochemical light source of LFEL and the practical feasibility of the new treatment process for organic wastewater. The main contents are summarized as follows:(1)By employing the 40W low frequency electrodeless lamp as the light source for photochemistry, the main body of the reactor was designed and made from organic glass by ourselves. In the reactor, the aerator is supported with the adjustable aeration flow, and the height of lamp position can be adjusted. The submerged reaction was designed, i.e. the electrodeless lamp completely contacts with the reaction solution. A common UV mercury lamp with similar power was also placed at the reactor for the purpose of comparison. The aeration tubes were uniformly distributed at the bottom of the reactor to supplying microporous aeration (0.02-0.05mm), which also act as stirring, oxygen filling and scouring at the same time. The LEEL irradiates a continuous spectral light, which includes full band spectra from ultraviolet to visible light with UV intensity peaks at 246,310,361.7,401.6,432.2nm. These characters result from the internal LFEL parameters such as gas filled, gas pressure, trace metal material of the.lamp and frequency converter and the electrical parameters.(2) When aeration was 2 m3/min, reaction volume was 7L, pH was 7.0±0.5, AO7 was 20mg/L, the degradation efficiency was up to 94.1%, TOC removal rate reached 71.9% after 240 min LFEL irradiation.2.67mg/L ozone concentration was found in water after 60min LFEL irradiation. Ozone provides the main carrier of active oxygen in the reaction of indirect degradation process. In comparison, the mercury UV lamp was employed as light source under the same conditions, the same time and aeration conditions, the degradation rate of AO7 was 21%, the removal rate of TOC was 16.3%only, indicating that LFEL light source has a unique effect on the degradation of dye, far more than common UV lamp. GC-MS detection showed that a lot of small molecular fragments were found. The effect of quenching found that,1O2 and ·O2-were the main active oxygen substances in the reaction, and the hydroxyl radical had little effect.(3) The reactor with LFEL light source can also degraded tetracycline very well. When aeration was 2 m3/min, reaction volume was 7L, pH was 7.0±0.5 and tetracycline was 20mg/L, the degradation efficiency was up to 91.3% after 240 min irradiation. The alkaline condition has a promoting effect on the reaction, e.g. the degradation rate could be up to 95.2% with pH 11 solution. The addition of H2O2 could further improve the reaction rate. When the concentration of H2O2 reached 5.28 mmol/L, degradation efficiency could reach 98.3% at 120min.(4) Using of LFEL as light source to treat organic pollutants, if tetracycline concentration reached above 15 mg/L, insoluble matter would be produced in the reactor. These insoluble matter could be floated to the surface to form scum as the flotation. Taking 50mg/L tetracycline as an example, the final precipitation of scum dry weight reached 38.4% of the total mass of tetracycline, so the TOC removal was up to 76.6%. |
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