| 摘要: | 本研究主要是探討使用”雙重性還原氧化系統”去除三氯乙烯(TCE)之反應行為。本系統可分為兩個階段，第一階段主要是藉由批式實驗控制在pH = 4、攪拌轉速為300 rpm、三氯乙烯初始濃度為52 mg/L時，改變元素鐵劑量及UV照光條件，對三氯乙烯進行還原脫氯反應。當再繼續添加過氧化氫(過量或少量)於反應系統中，可與第一階段所產生之二價鐵產生Fenton反應，此為第二階段之氧化脫氯反應。探討之操作參數為過氧化氫、元素鐵劑量及UV照光強度對三氯乙烯殘餘量及水質參數溶氧、氧化還原電位、二價鐵及氯離子濃度等之影響。
結果顯示，當三氯乙烯在不同照光條件(未照光、64 watt、128 watt)下進行揮發及光解試驗時，得到在未照光條件下，三氯乙烯會因為攪拌作用造成的揮發量為52 %；於照光條件為64、128 watt時之光解效率為及68%。在元素鐵溶出試驗中，元素鐵劑量為0.5及1.0 g/L時，二價鐵溶出量及溶氧及氧化還原電位降低之變化量分別為：UV(64 watt)＞UV(128 watt)＞未照光。元素鐵劑量為2.0 g/L時，二價鐵溶出量為UV(128 watt)＞UV(64 watt)＞未照光。而溶氧及氧化還原電位亦隨二價鐵濃度上升而下降，但下降量並無顯著差異。
在Fe0/H2O系統中，當元素鐵劑量增加時二價鐵累積濃度隨之上升。但氯離子濃度並未隨二價鐵濃度上升而增加，可能原因為光解之效率大於元素鐵還原脫氯效率及水中溶氧亦會消耗電子，故亦會導致二價鐵濃度增加，但氯離子生成量仍以照光強度為128 watt為佳。
於過量之Fe0/H2O2系統中，反應第一小時，為還原及揮發效應；反應第二小時，主要由Fenton之氧化脫氯反應去除，形成自由氯離子；反應第三小時，則主要是由Fenton-Like程序所引起之氧化脫氯反應，亦會產生自由氯離子。少量之Fe0/H2O2系統時，反應第一小時，三氯乙烯亦為還原脫氯及攪拌揮發所去除；反應第二、三小時下，則是Fenton之氧化脫氯反應所去除之。Fe0/H2O2/UV系統中(相對過量及少量添加H2O2者)，於反應三小時後，添加相對過量H2O2者之系統的氯離子累積量在照光條件為64 watts下較佳，且會隨著元素鐵添加劑量增加而增加。添加相對少量H2O2者，亦在照光強度為64 watts下之氯離子生成量較高；但卻與元素鐵之添加劑量成反比。
另外，並以多功能掃描式電子顯微鏡(SEM)觀察經Fe0/H2O2/UV系統處理後，沉降顆粒有明顯增大之變化情形。由能量散射X-ray光譜儀(EDS)數據指出，三氯乙烯降解所產生之氯離子濃度並不會受到混凝沉降作用所影響。
The purpose of this study was aimed to investigate the reaction behavior of trichloroethylene (TCE) by “ Dual Redox System “ of Fe0/UV/H2O2. The first stage controlled operational conditions:pH values at 4, stripping reading about 300 rpm, TCE initial concentration was 52 mg/L. In addition, the emphasis of this study was placed on the effects of zero-valent iron dosage and UV intensity on dechlorination of TCE. The second stage was removing TCE by Fenton (Fe2+/H2O2) and photo-Fenton (Fe2+/H2O2/UV) processes. There operational parameters including Fe0, H2O2 dosage and UV intensity were explored for their impacts on TCE removal, Cl- build-up, DO (dissolved oxygen) and ORP (oxidation and reduction potential) changes.
Stripping efficiency of TCE without UV was 52%. At UV intensities of 64 and 128 watts, the efficiency of TCE degradation were 50% and 68%, respectively. Using the Fe0 dosages of 0.5 and 1.0 g/L, Fe2+ accumulation concentrations were in the order of UV(64 watts) > UV(128 watts) > without UV. As the Fe0 dosage was 2.0 g/L, Fe2+ accumulation concentration was in the order of UV(128 watts) > UV(64 watts) > without UV.
In the Fe0/H2O system, the TCE removal increased with increasing Fe0 dosages. In the Fe0/UV system, the Fe2+ accumulation concentration increased with increasing Fe0 dosages. But the Cl- build-up does not increase accordingly due to photodegradation pathway being more significant than reductive pathway.
In the Fe0/H2O2 system (H2O2 in excess), reductive reaction and stripping occurred in the first hour, and this were followed by Fenton and Fenton-like reactions in the second and third hours, respectively. In the Fe0/H2O2 system (deficient H2O2 dosage), reductive reaction and stripping occurred in the first hour, while the Fenton was induced in the second and third hours. In the Fe0/H2O2/UV system, UV intensity of 64 watts presents the best removal efficiency with H2O2 either in excessive or deficient dosage.
The SEM configuration shows a significant growth in particle size after Feo/H2O2/UV treatment. The EDS data indicated that the Cl- dechlorinated from TCE was not affected by possible ferric coagulation. |
