氣提式生物溶出反應系統處理重金屬污染底泥之研究

Abstract

採礦工業中，生物溶出法 (bioleaching) 已被廣泛的使用。硫氧化菌可代謝元素硫或是金屬硫化物，藉由氧化硫化物的過程，獲得生長所需的能量，因此伴隨著重金屬離子的釋出，使重金屬自固相轉移至液相，在生物溶出法中最具代表性的細菌是 thiobacili屬，可將重金屬自固相的金屬硫化物溶出，但為了達到高效率的金屬溶出效果，往往需添加較多的硫粉，可是當實驗終了，硫粉往往殘留於底泥中並無法回收。這些殘留的硫粉易使處理之後的污泥或底泥產生酸化的現象，若往後需將處理過後的污泥或底泥使用於農地改良劑上，將會造成土壤酸化。因此為了避免過量的硫粉殘留於底泥中，將生物溶出程序中未利用的硫加以回收，是有其必要性、並可降低元素硫的總使用量。 本研究於氣提式反應系統中進行生物溶出程序，主要是利用回收之片狀硫顆粒來進行生物溶出的程序，並以片狀硫顆粒作為硫氧化菌的擔體，增加生物溶出反應系統內的生物濃度，結果發現，隨著片狀硫顆粒的回收次數增加，比起以全新硫片進行生物溶出程序加快許多，並使用回收之硫片來進行生物溶出實驗，探討底泥固體物含量及添加質種量對系統中硫氧化菌之氧化產酸能力及重金屬去除效率之影響。結果顯示當系統中底泥固體物含量為1-10% (w/v) 時，經過 14 天之反應後，底泥 pH 值自 8 分別下降至 2.10、2.15、2.25、2.35及2；當底泥固體物含量愈高時，因其具有較高之緩衝能力，所以底泥 pH 值下降速率有變慢之現象，pH 變化曲線較平緩，且底泥中氧化還原電位之上升速率亦有相同之趨勢。底泥固體物含量較大時，其緩衝能力較大，需產生較多之產酸量以使pH達到重金屬溶出之界限值 (threshold)。當底泥固體物含量為1-10% (w/v)，經過 14 天之處理時間後，底泥中重金屬溶出效率分別為鎳：34-74%，錳：40-84%，銅：56-99%，鋅：62-99%，鉛：21-38%，鉻：14-49%。根據底泥酸化速率、硫酸根的產生與重金屬溶出效率並考慮經濟效益，以添加底泥固體物含量為 2%之生物溶出程序的效果為最佳。 於生物溶出程序中添加不同植種量 (0-15% (v/v) ) 對底泥中重金屬生物溶出之影響，以瞭解所添加之植種量於生物溶出反應之成效。結果顯示，當植種添加量低於 10% (v/v) 時，其對底泥酸化與重金屬溶出速率並無促進效果。而當添加量為10% (v/v)時，底泥酸化速率與重金屬溶出效率皆有明顯之促進效果，然而當添加量為15% (v/v)則溶出發生抑制現象。整體而言，考慮底泥酸化速率、硫酸根的產生與重金屬溶出效率以添加植種量為10% (v/v)之生物溶出程序之結果為最佳。且硫片回收率高達 90-95%，可大幅降低底泥裡硫的殘留量，減少底泥再酸化之現象。 由以上結果得知，雖然固體物含量及植種量會對底泥酸化及重金屬溶出速率產生影響，但藉本研究之氣提式生物溶出反應系統可有效地處理受重金屬污染底泥，以達底泥去污染及無害化之目的。

Because riverbed sediments act as potential sources of contaminants in aquatic environment, and most of pollutant were polluted by human, industrial and urban waste discharge into river system. The present study in bioleaching costs low of treatment and ease of operation. In order to enhance the sulfur oxidation rate. Sulfur powder, which provides larger surface area for the adsorption of sulfur-oxidizing bacteria. However, sulfur-oxidizing bacteria used only 30-40% of sulfur powder during bioleaching process. The unrecoverable sulfur powder remaining in treated sediments increases the operational costs and causes acidification of the disposal land. Therefore, it is necessary to use recoverable forms of sulfur as substrates for sulfur-oxidizing bacteria in the bioleaching. In this study, the recovered of sulfur pellets on bioleaching of heavy metal from contaminated sediment were investigated. Adding recovered sulfur pellets at the beginning of bioleaching process, in order to increase bioconcentraion in an air-lifting reactor. With times of recovery increased, could accelerate the rates of acidification, sulfate production and metal solubilization. One was change sediment solid content. The results showed that the rate of pH reduction decreased with increasing sediment solid content because of the buffering capacity of sediment solid content. For different solid contents (1-10% (w/w)), 34-74% (w/w) of Ni; 40-84% (w/w) of Mn; 56-99% of Cu; 62-99% of Zn; 21-38% of Pb; 14-49% of Cr were leached from sediments in the bioleaching process. The optimal sediment solid content in the bioleaching was 2% (w/w). Another was change inoculum concentration (0-15% (v/v)), the optimal concentration of inoculum concentration added in the bioleaching was 10% (v/v). When adding 15% (v/v) of inoculum concentration to the bioleaching, inhibition of acidification, sulfate production and metal solubilization were fond. And the recovery of sulfur pellets could reach 90-95%, the results decrease sulfur in the treated sediments.