Stabilization of Fly Ash Dioxin Using Solidification/Stabilization Method

[[abstract]]台灣地區現今的垃圾處理以焚化為主，但垃圾經由焚化處理後所排放出之煙道氣及飛灰中均可發現戴奧辛(PCDD/Fs)存在，依據日本經驗，焚化廠產生之PCDD/Fs 有20%以氣相存在，其餘80%則附著在飛灰和吸附於活性碳吸附劑。傳統之飛灰固化/穩定化處理程序主要著眼於抑制飛灰中之重金屬溶出，但對飛灰中PCDD/Fs 溶出特性之了解甚為缺乏，若其經由雨水或滲出水溶出，則可能污染地下水體並且對環境造成重大衝擊。本研究主要針對國內某大型垃圾焚化爐所採集的飛灰為研究對象，探究飛灰固化後重金屬與PCDD/Fs 之溶出行為特性。研究結果顯示，飛灰經固化/穩定化處理後，重金屬Cr、Cu、Zn、As、Se、Cd 及Hg 之毒性特性溶出試驗(TCLP)溶出值均符合法規標準；在PCDD/Fs 溶出之結果顯示，飛灰經由TCLP 後，僅極少量之高氯數PCDD/Fs 被溶出，抽樣檢測經TCLP 後飛灰中所含之PCDD/Fs 顯示，大約有80％以上之PCDD/Fs 還存在於飛灰中，因此可知現行之TCLP 無法將飛灰中之PCDD/Fs 有效的溶出，固化/穩定化處理對於降低PCDD/Fs 長期溶出潛勢尚待探討。[[abstract]]In Taiwan, a major portion of municipal solid wastes is treated by combustion.The flue gases and fly ash released from the gas streams of municipal wasteincinerators (MWIs), however, contain Dioxin and Furan (PCDD/Fs) that are highlyconcerned due to their severe health effects. In Japan, 20% of the PCDD/Fs generatedfrom MWIs is in the gas phase, the other 80% is adsorbed by the fly ash and injectedactivated carbon adsorbents. The conventional fly ash solidification/stabilizationprocesses are mainly focused on exhibiting the leaching of toxic heavy metal insteadof PCDD/Fs. No attention has been designed to attenuate PCDD/Fs in fly ash. Thus,the main objective of this study is to investigate the leaching behaviors of fly ashdioxin and trace heavy metals before and after solidification/stabilization processes.The results showed that the TCLP (toxic characteristic leaching procedure) values ofCr, Cu, Zn, As, Se, Cd, Hg and PCDD/Fs were, in general, in compliance with theregulation after solidification/stabilization processes. Only certain high-chlorinePCDD/Fs were observed in the TCLP leachate. Based on the mass balance results,more than 80% of PCDD/Fs was still remained on the surface of fly ash, indicatingthat TCLP cannot effectively leach the PCDD/Fs out of the fly ash structure. As aresult, the effectiveness of conventional fly ash solidification/stabilization processeson exhibiting the release of PCDD/Fs from long-term leaching is still unclear. Furtherstudies are needed to better understand the low-term leaching potential andmechanisms of fly ash dioxins.[[note]]NSC91-2211-E327-01