- 學位論文
包埋微生物細胞載體脫碳、硝化與脫硝反應動力之研究
Modeling the Bio-Degradation of Carbon and Nitrogen in Biological Carriers of the Entrapped Mixed Microbial Cell
摘要
本研究顯示於單一好氧槽中使用包埋混合微生物細胞（Entrapped Mixed Microbial Cell，EMMC）法，在去除廢水中有機物與含氮化合物方面，具有優秀的潛能及處理效率。 本研究發現不同厚度固定化活性污泥板，在好氧環境下能同時去除廢水中碳氮化合物。也探討廢水通過不同厚度固定化活性污泥板時，對同時去除廢水中有機物和氮的影響。首先將化學需氧量（Chemical Oxygen Demand，COD）濃度300 mg/L、氨氮（Ammonia Nitrogen，NH4+N）濃度27 mg/L的廢水注入包埋混合微生物細胞（EMMC）活性污泥板固定床中，經過8小時的水力停留時間之後，廢水流出液中化學需氧量（COD）的去除率可以達到90%，而氨氮（NH3-N）的去除率則介於30%和50%之間，殘留的硝酸鹽濃度也低於0.75 mg/L。 發現增加活性污泥板厚度將不會提高去除率，及氧氣為活性污泥板去除碳氮化合物之反應速率控制步驟，也就是說，在固定床中，由於氧氣傳輸限制，導致部份好氧反應在一定厚度停止進行，如氨硝化反應。 化學需氧量（COD）的去除，必須藉由微生物的有氧呼吸才得以進行；而去除氮的硝化作用，則是將氨氮（NH3-N）氧化成硝酸鹽；這兩者均發生在包埋混合微生物細胞（EMMC）固定床靠近入口表面的有氧區域中。而去除硝酸鹽的脫硝作用則發生在較深層的固定床厭氧區域，經過處理後的廢水流出液，殘留的硝酸鹽濃度可低於0.75 mg/L。 經本研究計算得到去除COD和氨氮的一級視反應速率常數分別為>0.29（1/hr，基於在8小時得到的90%去除率）和>0.045（1/hr，基於在8小時得到的30%去除率）。 本研究也以量化方式，模擬EMMC去除廢水中COD和氨氮過程中的水力特性和生物化學反應步驟，也提供作為EMMC球狀載體中的質量傳輸限制與氧質量傳輸限制進行檢視與了解。 基於本研究提出概念動力模式和實驗結果，計算得到EMMC載體內之COD降解作用和氨氮硝化反應之水力傳導係數和反應速率常數，進而模擬沿著EMMC載體半徑的溶氧量（Dissolved Oxygen，DO）分佈情形。 本研究實驗與模式模擬結果一致，發現由於COD的去除氧化反應和氨硝化反應引起溶氧量的質量運輸情形，導致在EMMC載體中的溶氧量消耗非常快速。 在EMMC載體中所發展出的缺氧/厭氧區域，為從載體外表與主體液相接觸面算起小於1公分以內。更深入載體內部的缺氧/厭氧範圍，同時將會利用殘餘COD進行硝酸鹽之脫硝反應。 有機物降解和硝化作用的效率，並沒有受到EMMC載體的厚度或是半徑大小的影響。1公分厚的EMMC載體便足以維持藉由生物降解作用去除有機物、以及經由硝化與脫硝作用去除含氮化合物的去除反應能夠順利進行。 EMMC載體能夠在好氧槽中，結合硝化與脫硝作用；這顯示廢水處理技術之加強，已從使用缺氧/好氧（AO）或厭氧/缺氧/好氧（A2O）反應器系統的傳統活性污泥法（Activated Sludge Process，ASP），提升到能在單一好氧槽中，利用EMMC載體進行廢水處理。
並列摘要
This work investigated the concurrent removal of organics and nitrogen from wastewater as it passed through a slab of immobilized activated sludge of different thicknesses. Removals of COD by 90% from feed of 300 mg/L and of NH3-N by 30% to 50% from of 27 mg/L in the same feed were achieved as the wastewater exited the EMMC bed after a hydraulic retention time of 8 h. Increasing the bed thickness resulted in no enhancement, indicating aerobic processes ceased within the bed depth. The removal of COD was by aerobic respiration and the removal of nitrogen by oxidation via nitrification, both occurring in the aerobic zone of the EMMC bed near the entrance surface. Denitrification occurred deeper into the anaerobic zone of the bed that removed nitrate, leaving behind <0.75 mg/L of nitrate in the effluent. Apparent first-order rate constants were >0.29 /hr (based on 90% removal in 8 h) and 0.045/hr for nitrification (based on 30% removal in 8 h) for COD and NH3-N removal, respectively. Entrapped mixed microbial cell (EMMC) process offers good capability to remove organics and nitrogen compounds from wastewater in a single aerobic chamber. This research modeled quantitatively the hydraulic characteristics and biochemical process of immobilized activated sludge process for the removal of COD and NH4+-N, providing insights to mass and oxygen transfer limitation in EMMC spherical carriers. Based on the conceptual kinetic model and previous experimental results, hydraulic and reaction rate constants were determined for both COD degradation and NH4+-N nitrification with the EMMC carrier. The dissolved oxygen (DO) distribution profile along the radius of EMMC carriers was also simulated. The depletion of DO in the EMMC carrier was very rapid resulting from COD removal and ammonia nitrification given the mass transport condition of DO. The anoxic/anaerobic zone developed in the EMMC carrier within 1 cm from its external surface in contact with the bulk water phase. Beyond this anoxic/anaerobic boundary, denitrification of nitrate occurred utilizing the residual COD. The efficiency of organics biodegradation and nitrification were not influenced by the thickness or diameter of the EMMC carriers. EMMC carriers of 1 cm in thickness supported removal of organics by biodegradation and nitrogen compounds via nitrification and denitrification processes. The EMMC carrier enabled combined nitrification and denitrification (CND) in the aerobic chamber, which signified the enhancement of a traditional activated sludge process to an anoxic/oxic (AO) or anaerobic/anoxic/oxic (A2O) reactor system via the EMMC carrier in an aeration tank.