高溫好氧消化降解污泥中鄰苯二甲酸酯類之研究

Abstract

台灣素有塑膠王國之稱，塑膠製品廣泛使用與散佈於環境中，而普遍使用於塑膠增塑劑之鄰苯二甲酸酯類化合物，亦因此大量散佈與累積於環境當中。鄰苯二甲酸酯類為一具有烷基側鏈之苯環結構物質，由於具有疏水特性使其大量地累積於底泥與污泥當中，對於人體之危害主要為致癌性與致突變性，且鄰苯二甲酸酯類對於人體荷爾蒙運作具有干擾之作用，因此，其已被日本環境廳列為環境荷爾蒙之一。 台灣廢水處理系統漸趨完備與衛生下水道接管率逐年增加，對於污水處理廠而言，無可避免的將導致有機物負荷大量增加，亦使得污泥產量大幅提升。面對日益增加的污泥產量，污泥處理與處置即成為備受矚目之焦點，故將污泥予以資源化乃潮流之所趨。然而，廢水經處理後所產生之污泥中已被證實含有鄰苯二甲酸酯類，在污泥資源化之原則下，污泥處理妥善與否實為其再利用之關鍵。因此，本研究使用高溫好氧消化的方式，針對污泥中存在對於人體具有危害性之鄰苯二甲酸酯類進行生物降解，以期利用本文之方式，將污泥中鄰苯二甲酸酯類降低至法規限值以下。 本研究採集民生污水處理廠之喜氣消化污泥作為樣品來源，並以水力停留時間為主要討論因子。在不同水力停留時間下，首先活化樣品中高溫菌群，並利用添加鄰苯二甲酸酯類方式作污泥馴養，再利用經活化之高溫菌進行鄰苯二甲酸酯類之降解實驗。實驗結果顯示使用高溫好氧處理技術，高溫菌活化與鄰苯二甲酸酯類之降解，可於實驗起始後一週內達擬平衡狀態，而添加之鄰苯二甲酸酯類，總鄰苯二甲酸二(2-乙基己基)酯 (di- (2-ethyl hexyl) phthalate, DEHP) 降解89%至93%間，總鄰苯二甲酸二丁酯 (di-n-butyl phthalate, DBP) 降解82%至94%間。馴養完成之高溫菌，對固相中DEHP之降解模式符合一階動力模式，反應常數介於0.11d-1至0.49d-1間，得到最大反應常數之水力停留時間為20天，而固相中DBP皆於一天內降解殆盡。除此之外，由於本研究主要目標為污泥資源化再利用，因此亦相當重視污泥消化後營養鹽含量與脫水性，結果發現經高溫好氧消化之污泥脫水性變差，此將不利於後續污泥脫水程序進行，而氨氮濃度有些微上升，總磷則有些微下降之情況。 由以上之實驗結果得知，高溫好氧處理對降解鄰苯二甲酸酯類優於常溫與厭氧處理方式，而缺點為污泥脫水性變差。若欲得到最佳之降解效果，則本研究建議以20天作為操作時之水力停留時間，然而就經濟上之考量，將水力停留時間縮短為5天所得之降解率尚佳，因此當處理大量之污泥時，可縮短其水力停留時間。高溫下微生物對DEHP降解能力劣於DBP，因此其對環境之危害較甚，固相中DEHP降解模式與一階動力模式較為符合，最大反應常數為0.49 d-1，半生期為1.40天。

Thermophilic aerobic digestion (TAD) was used to degrade phthalic acid esters (PAEs) in sludge in this study. Among PAEs, di-2-thylhexyl phthalate (DEHP) and di-butyl phthalate (DBP) were chosen as target components owing to the widely separation and accumulation in the environment. Laboratory scale experiments were performed with different hydraulic retention times (HRT) in order to realize the effect of different F/M ratios on the degradation of DEHP and DBP by microbial treatment. The results demonstrated that the degradation of PAEs achieved quasi steady state in one week in acclimation stage; the degradation of total DEHP achieved 90% to 94%, and 83% to 94% for DBP degradation. The optimal HRT for PAEs degradation were determined to be 20 days in this stage. Further more, in the end of this stage; the ability of dewatering of sludge became worse, and the concentration of NH3-N increased, but the concentration of total phosphate decreased. After acclimation by 100 mg/L PAEs, the results of SOUR tests showed that the best activity of microorganism was found in the PAEs concentration of 100 mg/L. To assume the ability of PAEs degradation, batch experiments were performed after SOUR tests. In the solid phase, the degradation of DEHP had a better agreement with the first-order reaction, and the reaction factors were between 0.11 d-1 to 0.49 d-1. The degradation of DBP in solid phase occurred within the first 24 hours of operation. The concentration of PAEs in liquid phase was much fewer than solid phase. PAEs will release from solid phase to liquid phase to maintain the balance of concentration in operation before degradation completely. For this reason, the change of concentration can not reveal the behavior of PAEs degradation. Thus, the kinetic of PAEs degradation in liquid phase didn’t analysis in this study. In conclusion, the results suggested that TAD treatment is a more effective way to treat sludge. And the degradation of PAEs in TAD process also faster than the other treatments. The optimal HRT for PAEs degradation were determined to be 20 days.