| Summary: | 碩士 === 中臺科技大學 === 環境與安全衛生工程系碩士班 === 106 === Semiconductor and some petrochemical industries generate high ammonia-containing wastewater, and their discharge into water body can cause eutrophication and threats to aquatic lives. Conventional biological treatment is limited to low concentration wastewater with slow reaction rate as compared to chemical oxidation. However, the end product of oxidized ammonia is nitrate, which also causes eutrophication. In this study, a three-phase fluidized bed reactor was used to treat ammonia-containing wastewater with ozone and goethite as the catalyst. The effects of pH, weights of catalyst, and addition of Br- were examined. Results indicate part of the ammonia was converted toN2. Effect of pH influences the reaction rate dramatically. The second order reaction rate constant at pH 9 and 6 were 20.6 and 0.13 M-1s-1, respectively. This result is consistent with the molar fraction of molecular ammonia, the only reactive species with ozone or hydroxyl radical instead of ammonium, at corresponding pHs. The conversion to nitrogen gas was higher with the increasing amount of catalyst applied. The conversion to nitrogen gas with 0.75 and 2.3 kg catalyst at pH 9 were 14 and 55%, respectively. Ozone demands with catalyst were about 10% lower than without using catalyst at pH 6 and 9. Though the use of catalyst can convert ammonia to N2, the ammonia reaction rates were not was not enhanced. The addition of Br- enhanced the conversion to N2. The mechanism for converting ammonia to N2 is proposed. The generated HO‧ reacts with Cl- or Br- to form Cl‧ or Br -, which in turn converted to form HOCl or HOBr, and proceeds the so-called “break-point dechlorination” to form N2. A batch experiment was conducted by controlling different amount of Cl-, and results confirmed the N2 formation is propotional to the amount of Cl- applied in the system.
Keyword：catalytic ozonation ; three-phase fluidized bed; ammonia
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