| Summary: | 博士 === 國立臺灣大學 === 環境工程學研究所 === 101 === Microwave oxidation process (MOP) was evaluated for treatment of landfill leachate. The experimental parameters include pH, temperature, oxidant doses, microwave power setting, and irradiation time. The study explored the microwave-specific effects of the MOP. The contributions of pure thermal, persulfate oxidation and microwave irradiation on TOC removal were quantified. It was then found the combinations of them were usually synergistic in MOP except two of them were antagonistic (128W/85℃/1M Na2S2O8 and 128W/85℃/2M Na2S2O8) due to the difference in the heating mechanisms between conventional heating oxidation (CHO) and MOP. At the highest temperature tested (85℃) in this study, microwave irradiation may cause generation and termination of oxidizing radicals at adverse rates. The study also found that persulfate decayed rapidly in either MOP or CHO treatment of landfill leachate. Besides, this study compared formation and degradation behaviors of organic acids in landfill leachate under MOP and CHO and explored derivative mechanisms of organic acids in MOP. The results showed that formation and degradation behaviors of oxalic acid (OA) were very similar under CHO and MOP, in which its concentrations decreased in the temperature-raising period, then increased due to decomposition of TOC from 10 to 70 min, decreased due to persulfate oxidation from 70 to 130 min, and stayed the same afterwards. The pH values of the leachate solution dropped 0.51 and 0.65 pH units after MOP and CHO treatment, respectively. OA was the dominant organic acid formed in MOP. The derivative mechanisms of organic acids were developed using the experimental results. Lactic acid (LA) was generated from decomposition of malic acid (MA), and OA was formed from oxidation of its precursors. Acetic acid (AA) was formed and soon decomposed. LA had its maximum concentration with a persulfate dose of 2381 mg/L, while lower or higher persulfate doses yielded few or no LA in MOP. The study also evaluated the feasibility of MOP and the cost, the results showed MOP 550W/85℃/1M had color removals of 80% to 90% within 5 minutes, TOC removals of 70% to 80% within 30 minutes, UV254 removals of 65% to 70% within 30 minutes, and COD removals of 45% to 55% within 40 minutes. Within the same heating time, electric cost of MOP (181 NTD/m3) was slightly lower than that of CHO (183 NTD/m3). Besides, MOP was suit to use in wide pH range and more cost saving without pH-controlled, so MOP was an alternative of pre-treatment.
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