本研究係以批次和管柱試驗探討商用微米級及自行合成之奈米級零價金屬對水中五氯酚之去氯還原處理之效果、中間產物、可能反應途徑及動力研究。研究結果發現，Fe0顆粒(10-40mesh)對PCP似乎沒有去氯還原的效果，而Zn0顆粒(20mesh)對水溶液中PCP之去氯還原的效果則非常顯著且PCP減少的動力學曲線若以一階反應速率模式來逼近時(r2＝0.98)，可得出反應半衰期(t1/2)為43.3 hrs，擬一階反應速率常數為1.6×10-2 h-1。此外，以雙金屬組合(Zn0顆粒/Pd0粉末)來探討對PCP之去氯還原的效果時，水溶液中氯酚類化合物依序去氯之變化則更為明顯，PCP減少的動力學曲線若以一次反應速率模式來逼近時(r2＝0.93)，可得出反應半衰期(t1/2)為33.6 hrs，擬一階反應速率常數(95%信賴區間)為2.06×10-2 h-1。此反應速率常數比僅添加Zn0顆粒之試驗時高出約28.75%，半衰期也縮短，顯示出Zn0顆粒與PCP溶液反應中，再加入Pd0粉末做催化劑時，PCP的減少速率將加快。
而在自行合成奈米級零價鐵(Fe0)和零價雙金屬(Fe0/Ni0)對水溶液中PCP之去氯還原反應中發現，PCP減少的動力學曲線若以一階反應速率模式來逼近時(r2＝0.93)，可得出反應半衰期(t1/2)分別為20.8 hrs和16.3 hrs，此擬一階反應速率常數(95%信賴區間)分別為3.32×10-2h-1和4.24×10-2 h-1，其中又以自行合成奈米級Fe0/Ni0效果最佳，其反應速率常數比起自行合成奈米級零價鐵約高出27.71%。由動力學試驗結果可看出其去氯之反應途徑依序為PCP→TeCP→TCP→DCP→MCP。
在管柱試驗過程中，結果發現進流初期，水中溶氧及還原態硫化物將阻礙零價鐵對五氯酚之去氯還原效果。隨著進流量增加，即孔隙容積(pore volumes, PV)增加時，無論溶氧高低，零價鐵去氯還原五氯酚之效果均逐漸提升，但仍以低溶氧時之效果較高。隨著進流量增加，不含還原態硫化物時去氯還原五氯酚之效果仍然顯著大於含還原態硫化物時之效果。此外，於進流初期，鐵鎳雙金屬組合對五氯酚之去氯還原效果比單獨零價鐵之效果稍高，但隨著進流量增加，鐵鎳雙金屬組合對五氯酚之去氯還原效果比單獨零價鐵之效果差異已很小，甚至當進流量增加至6.10倍PV時，單獨零價鐵之效果已稍微超越鐵鎳雙金屬組合。 The aim of this study is to find the effectiveness, intermediates, reaction paths and kinetics of pentachlorophenol (PCP) dechlorination by using commercial microscale and nanoscale zero-valent iron during batchand column tests.
Results indicate that Fe0 particles (10-40mesh) had no effects on the dechlorination of PCP, whereas Zn0 particles (20mesh) had significant effects on the dechlorination of PCP with a pseudo first order reaction (rate constant of 1.6×10-2 h-1).
The serial dechlorination of chlorophenols using bimetals (Zn0/Pd0) showed more significant. The reaction rate constant of PCP dechlorination by Zn0/Pd0 (2.06×10-2 h-1) was 28.75% higher than that by Zn0, which indicates that the addition of Pd0 could catalyze the dechlorination rate.
The kinetics of PCP dechlorination of either nanoscale zero-valent iron or bimetals (Fe0/Ni0) showed a pseudo first order reaction. The reaction rate constant of PCP dechlorination by nanoscale zero-valen Fe0/Ni0 (4.24×10-2 h-1) was 27.71% higher than that by nanoscale zero-valent iron.
Reduced sulfur and dissolved oxygen lowered the effect of dechlorination of PCP by zero-valent metal or bimetallics via column tests in the low-pore-volume inflowing period.
The effect of dechlorination of PCP by Fe0 or Fe0/Ni0 via column tests increased with the increase of pore-volume inflowing, especially for the condition of lower DO content.
In addition, the effect of dechlorination of PCP by Fe0 or Fe0/Ni0 was better when the reduced sulfur existed. The effect of Fe0/Ni0 bimetals on dechlorination of PCP was more than that of Fe0 in the lower pore-volume inflowing period. However, the effect of Fe0/Ni0 bimetals on dechlorination of PCP was nearly the same as that of Fe0 in the higher pore-volume inflowing period.
