結合固定化技術與厭氧氨氧化程序於廢水生物除氮之研究

Abstract

傳統之生物除氮程序包括自營好氧硝化及異營無氧脫硝兩個階段，此程序需要較大的土地面積，操作上亦較為複雜，且會有殘留碳源之後續處理問題。當前除氮技術的發展傾向利用自營性除氮程序，於單槽內結合部分硝化及厭氧氨氧化之完全自營性生物除氮程序，其具有省空間、可減少氧氣供應量及不需外加碳源等優點，極適合用來處理含低濃度有機碳之高濃度氨氮廢水。但參與該反應之厭氧氨氧化菌，是一種生長速率極為緩慢，且在有氧的環境下會對其反應造成抑制的作用，是為一種非常不易培養的自營菌株。所以，如何將此菌株保留在反應槽中，並維持系統穩定性且同時兼顧實際應用的可行性，遂成為該系統有待克服的一項關鍵性問題 起初，本研究希望利用固定化技術將硝化菌及厭氧氨氧化菌分別予以固定化後，置於一個反應槽中並同時進行生物除氮作用。但固定化厭氧氨氧化菌不論經過何種成形方式，以及長時間的活化過程，其實驗結果皆未觀察出厭氧氨氧化之反應。隨後，藉著生死染色技術的結果證實，絕大多數的厭氧氨氧化菌會在固定化成形過程中遭受到不可恢復性的傷害，乃至於固定化厭氧氨氧化菌失去活性所致。 為突破厭氧氨氧化菌在固定化程序失去活性的困境，本研究嘗試開發出Cookies生物除氮反應系統，將具有一定厚度框架之左、右兩側利用不含硝化菌的人工薄膜包覆，而形成一個中空四立方體之生物除氮模組，並在此中空部分直接注入富含厭氧氨氧化菌之活性污泥。由連續流的實驗結果證實，Cookies生物除氮系統可以長時間操作在高亞硝酸鹽濃度（600 mg-N/L）的環境下，且不會對厭氧氨氧化菌造成不可恢復的危害，惟Cookies生物除氮系統必需操作在低溶氧的環境下才能順利運作，否則在經過一段時間的操作後，厭氧氨氧化反應仍然還是會受到氧氣的抑制而停止。 為改良Cookies生物除氮反應系統在使用上的限制，本研究進一步在人工薄膜中包埋硝化菌株，因而成功開發出一個名為「AOB-Cookies」的新型生物除氮系統。此系統不僅能在單一反應槽中同時完成部分硝化及厭氧氨氧化作用，還能操作在高溶氧的環境下（2 mg/L），仍可確保完全部分硝化作用的順利進行，且過程中不會產生氧氣對厭氧氨氧化菌的抑制作用。當初始氨氮濃度介於30至720 mg/L，AOB-Cookies生物除氮系統皆能達到良好的氨氮去除率，經計算後得比氨氮去除速率各為0.034、0.053、0.056和0.069 mg-N/mg-MLSS/day。利用螢光原位雜交技術進行菌相分析，得知厭氧氨氧化菌分別在AOB-Cookies生物除氮系統中所占比例約為76.1%、氨氧化菌約占19.7%、亞硝酸鹽氧化菌約為2.3%。此外，也由於部分硝化效率的提高，所產生的大量亞硝酸鹽可供厭氧氨氧化反應使用，卻也大幅縮短除氮過程所需時間，整個反應在25個小時以內即可完成。最後，系統中部分硝化反應產生的酸度與厭氧氨氧化反應產生的鹼度相互中和，還能減少酸劑或鹼劑的添加量，進而降低操作成本，因此AOB-Cookies生物除氮系統極具實際應用的潛力及操作彈性。

The conventional process for biological removal of nitrogen involves two steps: autotrophic nitrification and heterotrophic anaerobic denitrification. This process requires large land areas. The operation is also more complex and creates subsequent processing problems involving residual carbon sources. Current developmental trends in nitrogen removal technology use the autotrophic nitrogen removal processes. The complete autographic biological nitrogen removal process combines partial nitrification and anaerobic ammonium oxidation in single reactors. This process saves space, reduces oxygen supply, and does not require external carbon sources. The process is suitable for processing high concentrations of ammonia nitrogen wastewater with low concentrations of organic carbon. However, the anammox bacteria taking part in this reaction are an autotrophic strain with a slow growth rate and will be inhibited in aerobic environments. It is also extremely difficult to cultivate. Therefore, preserving this strain in the reactor and maintaining system stability while considering the feasibility of practical application has become a key problem of this system to be overcome. First, we anticipated using the immobilization technology to immobilize the nitrifying bacteria and the anammox bacteria, which are then placed in a reactor for biological nitrogen removal. However, the experimental results for immobilized anammox bacteria with various shaping methods and long activation processes indicated that anammox reactions did not occur. The results of life and death dyeing technology empirically establish that the vast majority of anammox bacteria were irreversibly harmed in the immobilization forming process, to the point that the stabilized anammox bacteria lose activity. To overcome this loss of activity of anammox bacteria during the immobilization process, we developed the Cookies biological nitrogen-removal reaction system. This system had left and right sides with frameworks of specific thickness that was coated with an artificial thin-film without nitrifying bacteria. This formed a biological nitrogen-removal module with four hollow cubes. Activated sludge rich in anammox bacteria was poured directly into these hollow areas. Continuous flow experiments indicated that the Cookies biological nitrogen-removal system could operate for long periods in environments with high concentrations of nitrite (600 mg-N/L) with no adverse effects to anammox bacteria. However, the Cookies biological nitrogen-removal system must operate in environments with low amounts of dissolved oxygen to be successful. If not, the anaerobic ammonium oxidation reaction is will be inhibited and stopped by oxygen after a period of operation. To correct these limitation in the Cookies biological nitrogen-removal reaction system, we further entrapped nitrifying strains in the artificial film and developed a new biological nitrogen-removal system called AOB-Cookies. This system can perform both partial nitrification and anaerobic ammonium oxidation in a single reactor. Additionally, it can also operate in environments with significant amounts of dissolved oxygen (2 mg/L), while still ensuring the successful partial nitrification. Oxygen does not inhibit the anammox bacterium during this process. When initial ammonia concentrations were between 30 to 720 mg-N/l, the AOB-Cookies biological nitrogen-removal system could achieve excellent ammonia removal rates. Our calculation indicates the ammonia removal rates of 0.034, 0.053, 0.056, and 0.069 mg-N/mg-MLSS/d. We employed fluorescence in situ hybridization techniques for microbial community analysis. This analysis showed that the ratio of anammox bacteria in the AOB-Cookies biological nitrogen-removal system was approximately 76.1%, the ratio of ammonia oxidation bacteria was approximately 19.7%, and the ratio of nitrite oxidation bacteria was approximately 2.3%. In addition, the large amounts of nitrite produced due to the increase in partial nitrification efficiency can be used for anaerobic ammonium oxidation reactions. This also substantially reduces the time required by the nitrogen removal process. The entire reaction can be completed within 25 h. Finally, the acidity produced by partial nitrification and the alkalinity produced by anaerobic ammonium oxidation in the system neutralize each other. This can also reduce the amount of acid or alkali agents needed, thereby reducing the operating costs. Therefore, the AOB-Cookies biological nitrogen-removal system has potential for practical application and provides operating flexibility.