以厭氧生物法處理高濃度四氯乙烯之研究

Abstract

四氯乙烯(tetrachloroethylene, PCE)為工廠常用之去脂溶劑及乾洗業之乾洗油劑，土壤與地下水中最常發現的氯化有機污染物之一。過去研究證實，厭氧生物反應可以脫氯降解PCE，但鮮有直接利用厭氧消化污泥分解PCE者。因此，本研究乃以都市污水處理廠及養豬廢水處理廠厭氧消化污泥，直接進行生物代謝PCE試驗，以探討消化污泥全程分解PCE之能力，及是否可完全轉化PCE至無毒且環境可接受之產物 - 乙烯。 結果顯示，養豬廢水處理廠之消化污泥僅可將PCE脫氯降解至三氯乙烯(trichloroethylene, TCE)及1,2-cis-二氯乙烯(dichloroethylene, DCE) 。都市污水處理廠之新鮮污泥則可將PCE，經由TCE、cis-DCE、氯乙烯(vinyl chloride, VC)之代謝途徑，最後生成乙烯；濃縮新鮮污泥更可快速分解PCE至乙烯。由此證實，某些特殊厭氧消化污泥具有直接分解PCE至環境無毒產物乙烯之能力，且當污泥濃度越高及以半連續式(10μmol/ 3 days)的加藥方式，均會加速PCE生物分解。但全部研究過程，所有厭氧消化污泥均無法將四氯乙烯完全(100%)轉化成乙烯。其中分解效果最佳者為都市污水處理廠之新鮮污泥加入50、110μmol之PCE，反應時間38天，可分別產生43.1 (86.2%)及83.56μmol (76%)之乙烯。

Perchloroethylene (PCE) is one of the most frequently identified contaminants in soils and groundwaters because it has been widely used for degreasing in industry and as a solvent for dry cleaning. Many previous studies have shown that anaerobic biological treatments are capable of converting the heavily chlorinated compound into harmless metabolites. However, anaerobic digested sludge is seldomly applied directly to the treatment of PCE contamination. In this research, perchloroethylene-dechlorinating ability and feasibility of completely converting PCE to non-toxic metabolites were examined directly in anaerobic digested sludge from swine wastewater and domestic wastewater treatment plant. According to the results of this study, digested sludge of swine waterwaste treatment plant can dechlorinate PCE into trichloroethylene (TCE) and dichloroethylene (DCE) but no further. In contract, digested sludge of domestic wastewater treatment plant can dechlorinate PCE through TCE, DCE, vinyl chloride (VC), and finally result in the nontoxic ethylene. This proves that certain kinds of anaerobic digested sludge are capable of directly breaking down PCE into the nontoxic ethylene. Besides, it has been found that the higher the sludge concentration and adding PCE by semi-continuous method (10 μmol/3 days) can speed up the detoxification processes.