| 摘要: | 本研究係以生物淋溶法來探討底泥中重金屬溶出之可能性。藉由二仁溪底泥中所馴養出之原生硫氧化菌作為生物淋溶所需之微生物，在各種控制條件下(包括基質與接種體的添加、接種百分比、基質濃度、總固體物濃度、溫度)，將底泥中硫化物或額外添加還原態硫化物氧化，以形成硫酸進而溶出底泥中重金屬。此外，本研究也以逐步萃取法(sequential extraction procedure, SEP)分析並探討底泥中重金屬各鍵結型態組成(包括可交換態，與碳酸鹽鍵結態，與錳氧化物鍵結態，與鐵氧化物鍵結態以及與有機物鍵結態)，在生物淋溶前後之變化。本研究結果顯示，在生物淋溶過程中，底泥溶液pH值逐漸下降，氧化還原電位則逐漸上升，底泥中硫化物及添加之硫代硫酸鈉逐漸氧化成硫酸鹽，而總可萃取重金屬之溶出效率也隨之增加。在基質與接種體的添加的試驗中，發現接種體對底泥溶液pH值降低之影響比硫添加的影響為高。在不同接種百分比的淋溶試驗中則顯示，高接種百分比能使pH值的下降較快。經生物淋溶後，總可萃取重金屬的平均溶出效率之次序為鋅、銅、鎳＞鉻＞鈷＞鉛。除了鈷與鎳以外，鉻、鋅、銅和鉛鍵結型態之分佈在淋溶前後皆較有一致性的分佈變化。在不同基質濃度的生物淋溶試驗中，發現當基質濃度小於4.80 g S/L時，隨著基質濃度含量增加時，其底泥溶液最終pH值也隨之下降。當基質濃度大於4.80 g S/L時，硫氧化菌之生物氧化作用可能受到抑制，因而使得底泥溶液pH值無法下降。總可萃取重金屬之溶出效率以基質濃度含量為4.80 g S/L時最佳，其中以鋅的溶出效率為最高，鉛之溶出率則最低。
總固體物之含量(TS)可表示為底泥的緩衝能力。結果發現，此值明顯影響底泥溶液中pH值之下降速率。當總固體物含量愈低時，底泥溶液pH值之下降速率愈大。經生物淋溶後，不同重金屬在不同的總固體物含量下，有不同的鍵結行為。在不同控制溫度的淋溶試驗中顯示，硫氧化菌氧化活性在37.0 ℃時最為明顯。除了鉛以外，其他重金屬從各鍵結位置之溶出率在37.0 ℃時最高，25.0 ℃時溶出率稍差，而在55.0℃時之溶出效率則明顯最差。溫度變化對生物淋溶前後各種重金屬鍵結型態之變化有顯著性的影響。在55.0 ℃時，六種重金屬各鍵結型態間之重新分佈現象最為明顯。
The aim of this study is to explore the mobility of heavy metals from contaminated river sediments by using bioleaching process. Indigenous sulfur-oxidizing bacteria (SOB) enriched from the sediments of Ell-Ren river were used to oxidize the reduced sulfur originally existed in sediments or added to sulfuric acid under controlled operational conditions (including percentage of inoculum, percentage of substrate added, total solid content and temperature), which resulted in the mobilization of heavy metals from contaminated sediments. In addition, the changes in metal binding characteristics that occur during bioleaching will be explored by using sequential extraction procedure. Due to the production of sulfuric acid from the oxidation of reduced sulfur, the accompanying increase of sulfates, decrease of pH and increase of mobility of total extractable heavy metals were found. Results show that the effect of inoculum adding on pH decrease was more than that of sulfur adding. Higher inoculum percentage could speed up the decrease of pH more during bioleaching. The order of mobilization of total extractable heavy metals (TEHMS) could be shown as following: Zn, Cu, Ni＞Cr ＞Co＞Pb. Except for Co and Ni, the binding fractions of other heavy metals had a consistent variation after bioleaching. It was found that the sediment pH decreased with the increase of substrate concentration while it was lower than 4.80 gS/L. When the concentration of substrate was higher than 4.80 gS/L, the sediment pH could not drop down, which might be due to the inhibition of biochemical reaction. The optimum dosage of substrate for mobilizing TEHM was found at 4.80 gS/L. The total sediment solids (TS) represent the buffer capacity of sediment. Consequently, a lower TS leads to a easier likelihood of overcoming the sediment buffer, and hence a lower sediment pH. Different heavy metals showed different binding behavior at the various TS concentrations. Of three temperatures tested (25.0℃, 37.0℃ and 55.0℃), pH decrease was greatest at 37.0℃, indicating that, after acclimation, bacterial oxidizing activity is greatest at this temperature. Except for Pb, the optimal temperature for solubilization of total extractable heavy metal was 37.0℃. The temperature of bioleaching had a significant impact on changes in partitioning of heavy metals. Transfer of heavy metals between binding fractions was most apparent at 55.0℃ before and after bioleaching. |
