以微波氧化程序降解掩埋場滲出水有機物之研究

本研究係以微波氧化程序(MOP)來進行掩埋場滲出水之研究，主要探討的因子有酸鹼值、溫度、氧化劑濃度、微波功率及微波照射時間。研究中以熱效應、過硫酸鹽氧化、微波照射之總有機碳移除量來探討MOP的微波特殊效應(Microwave - Specific effects)，實驗結果發現MOP相較於傳統加熱氧化(CHO)效果提升10%，除了在微波低功率(128W/85℃/1M Na2S2O8 和128W/85℃/2M Na2S2O8) 效果不如CHO外，其餘MOP大多呈現加乘效果，且隨著溫度上升，加乘效果更明顯，這是因為MOP與CHO加熱機制不同的緣故。在整個加熱過程，不論是MOP或CHO過程，過硫酸根離子皆呈現快速的消耗，並轉換成硫酸根離子，造成其殘留之過硫酸根離子濃度不足，難以持續降解TOC及COD。本研究也針對MOP及CHO過程，其有機酸的生成降解曲線進行探討，並著重於MOP之衍生有機酸生成機制。實驗結果表示，草酸的生成降解曲線在MOP及CHO過程非常類似，由25℃上升至85℃過程，滲出水中之草酸皆因過硫酸鹽的熱催化產生的氧化作用而降解；草酸於10至70分鐘期間，因部分有機物降解生成新草酸；該草酸又於70至130分鐘期間，再度因微波氧化而持續降解，隨後，草酸曲線因殘留氧化力不足呈現草酸濃度停滯情形。觀測MOP及CHO實驗過程，該酸鹼值因衍生有機酸的生成分別下降了0.51及0.65 pH單位，於MOP實驗中，草酸是主要的有機酸衍生物，依實驗結果推斷，乳酸的生成似由蘋果酸的降解；草酸則由草酸前驅物質或其他有機酸降解而成；醋酸於MOP過程，呈現快速降解及快速生成的特性，為一種短暫存留的中間型產物；乳酸在過硫酸鹽濃度過低(952 mg/L)或過高(4762 mg/L)劑量下，僅生成少量或無乳酸形成，於本研究，僅在適當過硫酸鹽濃度2381 mg/L，方能利於乳酸的累積。本研究最後也針對MOP的可行性及成本進行分析，結果顯示MOP 550W/85℃/1M在5分鐘內可完成80%到90%色度移除率；30分鐘內可完成80%到90% TOC移除率；30分鐘內可完成65%到70% UV254移除率；40分鐘內可完成45%到55% COD移除率。在相同的加溫時間下，MOP成本約為181 NTD/m3 ，略低於CHO為183 NTD/m3。此外，MOP不用調整處理水的酸鹼值，所以可省下pH值控制的成本，經評估MOP具有成為前處理程序之潛力。

關鍵字

滲出水；微波氧化；過硫酸鹽；傳統加熱；草酸；乳酸；醋酸

並列摘要

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.

並列關鍵字

leachate ； microwave oxidation ； persulfate ； conventional heating ； oxalic acid ； lactic acid ； acetic acid

參考文獻

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[4] X. Bi, P. Wang, C. Jiao, H. Cao, Degradation of remazol golden yellow dye wastewater in microwave enhanced ClO2 catalytic oxidation process, J. Hazard. Mater., 168 (2009) 895-900.

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以微波氧化程序降解掩埋場滲出水有機物之研究

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