活性污泥降解鄰苯二甲酸酯類之研究

Abstract

摘要 由於塑化工業上對鄰苯二甲酸酯類 (phthalate esters, PAEs) 之需求日漸升高，鄰苯二甲酸酯類於都市污水處理廠之檢出濃度有持續上升之趨勢，都市污水處理廠中鄰苯二甲酸酯類之來源來自塑膠製品中所含之鄰苯二甲酸酯類鄰苯二甲酸酯類，由於鄰苯二甲酸酯類與塑膠分子間並非以化學型態鍵結，因此，極易從塑膠製品中滲漏而出，隨著污水下水管道進入都市污水廠中，因此，若於都市污水處理廠中無法有效予以去除，則將隨著放流水或污泥排放至自然承受水體。鄰苯二甲酸酯類中之六種已被美國環保署公告為 129 種優先列管物質之一，日本環境廳亦公告其中之 8 種為環境荷爾蒙之一，鄰苯二甲酸酯類已被證實對於生物體的內分泌系統，具有擾亂之作用，並具致癌性、致畸胎性、極易累積於生物體之脂肪層中，因此對於居於生物鏈最高層之人類而言，其長期累積之慢毒性危害是不容忽視的。因此，鄰苯二甲酸酯類之管制與處理已經成為未來的趨勢。 都市污水處理廠中之最常被檢測出之鄰苯二甲酸酯類為鄰苯二甲酸-2-乙基己基酯 (DEHP) 與鄰苯二甲酸二丁酯 (DBP)，不論污水與污泥樣品，其檢出濃度皆高於其他種類之鄰苯二甲酸酯類，且存在於污泥固相中之濃度高於丹麥環保署 (Danish EPA) 所規定之法規限值，本研究針對都市污水處理廠中最常見之兩種鄰苯二甲酸酯類之處理，利用半連續式反應槽，反應槽之工作體積 15 升，控制條件，水力停留時間 4 天、溶氧 2 mg/L以上、食微比 (F/M) 維持 0.2 kg-COD/kg-MLVSS-day，DEHP 與 DBP進流濃度由 10 至 180 mg/L，漸進式馴養之方式模擬 DEHP 與 DBP 進流至污水處理單元之後，污水與污泥整體之濃度變化，及討探 DEHP 與 DBP 由進流水進流至活性污水處理單元之後，DEHP 與 DBP 於污泥固相、污水及污泥混合液三者之濃度分佈關係，以瞭解 DEHP 與 DBP 於活性污泥系統之分解與吸附之效應。 結果顯示污水中之 DEHP 與 DBP 去除率維持 90% 以上；活性污泥去除鄰苯二甲酸酯類之機制除了生物分解之外，吸附現象亦扮演相當重要之角色，吸附實驗結果顯示 DEHP 累積於污泥固相之趨勢相當地明顯，且隨著進流鄰苯二甲酸酯類濃度增加而增加。污泥混合液相方面，污泥經過 DEHP 與 DBP 馴養與污泥未經 DEHP 與 DBP 馴養對於 DEHP 之代謝率有 60 % 以上效率之差距，顯示污泥經過鄰苯二甲酸酯類馴養，可活化活性污泥對於鄰苯二甲酸酯類之分解能力。馴養之活性污泥對於鄰苯二甲酸酯類之處理濃度並非可無限制地被提升，當鄰苯二甲酸酯類進流濃度超過 140 mg/L 時，活性污泥系統代謝 DEHP 能力明顯地受抑制，此時之系統代謝 DEHP、DBP 與 SCOD 之效率受固相 DEHP 濃度影響相當大。進流濃度 10-180 mg/L 期間，本研究之 DBP 基質利用模式型態為 Monod 非抑制型態；DEHP 基質濃度與 SOUR 之關係為 Haldane 抑制型態，PAEs顯示 DEHP 對於系統具抑制之效應，而 DBP 對系統不具抑制之效應。

Abstract The demand of phthalate acid esters on industrious manufactory are increasing, the more high PAEs concentration detected in municipal wastewater treatment plant (MWTP). The resource of PAEs in MWTP is from various plastics. PAEs in the plastics are not bounded chemically, they are easily leakage from the plastics and enter the MWTP by means of transportation in the sewerage. If they can’t be effectively removed from MWTP, they will discharge into the water system by means of secondary effluent or sludge. Among all kinds of PAEs, six kinds of PAEs had been listed of the 129 prior pollutants by US EPA; eight kinds of PAEs had been listed of the environmental hormones by Japanese EPA. PAEs had been proved to be interrupt on the endocrine of organism. They are carcinogenic, mutagenic and accumulate to organism. For human being, the top of the food chain, the risk of accumulation must be taken care. For the future, the restriction and the treatment of PAEs must be a crosscurrent. DBP and DEHP are two kinds of most common PAEs in MWTP. The concentrations of PAEs in the sewage or the sludge, DBP and DEHP concentrations are much higher than other kinds of PAEs. The concentrations of DBP and DEHP in MWTP are excess the law restriction of Danish EPA. Thus, we focus on the step by step acclimated treatment of DBP and DEHP to simulate the behavior of DEHP and DBP in the activated sludge secondary process by means of semi-continuous activated sludge process. The volume of reaction tank is 15 liter. Stationary controlled condition was HRT equal to 4 days, dissolved oxygen above 2 mg/L, F/M equal to 0.2 kg-COD/kg-MLVSS-day. The transit condition was that PAEs influent concentrations from 10 to 180 mg/L. The items we discuss include the concentration distribution of DEHP and DBP in the supernatant, solid, and mix liquor phases of acclimated activated sludge to realize the biodegradation and adsorbtion effect of this system. The result showed that the DEHP and DBP removal rate in supernantant was higher than 90 % of biological process in this study. The mechanisms of PAEs removed from the supernatant in this study were biological effect and adsorption effect. The accumulation phenomenon of DEHP in solid phase of activated sludge was quite obvious and it increased with higher influent PAEs concentrations. In the mixed liquor phase, it had a quite large difference above 60 % between acclimated and un-acclimated activated sludge, it telled us a fact that the acclimation could enhance the biodegradability of DEHP. The biodegradability of DEHP in this system could not be unrestrictly enhanced. If the DEHP influent concentration was over the concentration of 140 mg/L, the DEHP, DBP and SCOD biodegradability of this biological system was inhibited. The DBP utilization model in this study was the form of Monod. The DEHP and SOUR utilization model in this study was the form of Haldane. The biological activated sludge system in this study was inhibited by the DEHP, but we could not had seen the inhibition effect of DBP when PAEs influent concentration ranged from 10-180 mg/L.