利用通氣式薄膜生物反應槽與厭氧氨氧化程序進行廢水除氮之研究

Abstract

在低碳氮比廢水之生物除氮技術發展方面，諸多學者投入部分硝化及厭氧氨氧化等自營脫硝程序之研究，前者係將廢水中大約一半之氨氮氧化為亞硝酸鹽氮，後者則以氨氮為電子供給者並以亞硝酸鹽氮為電子接受者，將部分硝化反應槽出流水之殘餘氨氮與亞硝酸鹽氮一併轉變為氮氣。相較於傳統生物除氮程序，其不但節省氧氣需求量、免除有機碳添加，更可縮短生物脫氮流程，故能提升脫硝速率並大幅節省操作成本。 本研究乃基於上述原理，藉由適當之反應槽設計與操作條件之控制，針對低碳氮比廢水或地下水進行本土化自營性生物除氮技術之開發。在反應槽的設計上包括通氣式薄膜硝化反應槽，以及填充床式厭氧氨氧化反應系統，廢水須先行部分硝化至氨氮與亞硝酸鹽氮之濃度大致相等，之後再進行厭氧氨氧化反應，此外並以分子生物技術進行各反應槽菌相之定性與定量分析，以為日後反應槽實際應用之參考。 研究結果顯示此薄膜生物反應器對於低碳氮比廢水之部份硝化極為有利，其操作穩定性高乃一般生物處理所罕見。開放式矽膠管為該反應器之供氣系統，僅通入空氣於矽膠管內即可使反應槽液相維持在低溶氧之狀況，初始鹼度添加量適當可使50%的部份硝化反應在短時間內達成，而產生NO2-/NH4+之比值接近1:1的出流水，由於在反應過程當中無需再添加鹼液來維持適當之pH值，故可省卻一般生物處理程序pH調控之費用；至於系統操作彈性方面則可藉由反應槽氨氮表面負荷(ASL)來加以調控，由廢水氨氮濃度範圍來決定反應槽內矽膠管之長度。綜上所述，此一薄膜生物反應器應可做為Anammox process之理想的前置處理程序。 在厭氧氨氧化微生物之馴養方面，以一般都市污水處理廠之活性污泥於適當條件馴養約四個月，即可獲得具有穩定活性之Anammox biomass，其沉降性良好呈淡褐色且無臭味。研究結果顯示NO2-之消耗速率較NH4+為快，在適當之濃度範圍內且二者初始濃度相近時，NO2-在短時間內有將近100%的去除率，過多的NO2-對於Anammox反應活性有顯著之負面影響， NO2-初始濃度為60~70 mg-N/L之時有最大反應速率，超過80 mg-N/L則除氮效率受限。填充床式厭氧氨氧化反應系統長時間連續進流後，管柱內多孔隙網格擔體或因代謝產物累積而有活性降低之情形，此時若改以循環批次式操作即可獲得改善而逐漸恢復活性。Anammox反應之進行係以NH4+為電子供給者，並優先以NO2-為電子接受者，待NO2-用罄則以NO3-為電子接受者繼續反應，此一現象於本研究中獲得印證。 本研究以PVA-褐藻膠共聚包埋法將馴化之Anammox biomass加以固定化處理，並探討固定化球形顆粒之反應活性，研究顯示此一技術適用於屬性特殊之厭氧氨氧化微生物，其包埋於顆粒中受到良好之保護，外在環境不良亦能存活並保有活性；此外固定化技術有利於固液分離，應用於廢水處理實務應可免除固液分離及污泥流失(biomass washout)之問題。

In the last decade, some new biological nitrogen removal processes have been developed to reduce operational costs related to the oxygen and organic carbon source requirements. Many studies focused on the development of autotrophic nitrogen elimination technology such as combination of partial nitrification and the Anammox process, which is regarded as a promising new method for removing nitrogen from wastewater or groundwater with a low C/N ratio and a fairly large quantity of ammonium. In this study, a combined partial nitrification MABR－Anammox system was developed to achieve a condition wherein only approximately one-half of ammonium is converted to nitrite, followed by the Anammox process to ensure total nitrogen removal. In addition, a molecular biotechnology method was applied to identify the bacterial community of the biofilm and the acclimated biomass. The experimental results showed that the developed membrane aeration bioreactor is an efficient, economical system to achieve 50% partial nitrification for ammonium-rich wastewater. The open-ended silicone tube in this bioreactor provided a large specific surface area for oxygen transfer and biofilm attachment. An appropriate initial alkalinity was also an important factor to achieve stable partial nitrification. Bicarbonate that serves carbon and alkalinity sources was added into the wastewater only once from the beginning. There is no need for pH adjustment by adding a base or an acid throughout the reaction if the initial alkalinity is appropriately controlled. Furthermore, an appropriate ammonium surface loading resulted in approximately 50% partial nitrification within a short period of time by adjusting the tube’s length in accordance with the range of initial ammonium loading. As mentioned above, the MABR system developed in this study is very stable and easy to operate. This system has great flexibility for partial nitrification, making it an ideal pretreatment system for Anammox. Regarding the acclimation of Anammox biomass, the concentrated activated sludge collected from a local municipal WWTP was used as seed sludge. The macroscopic appearance of the enriched biomass remained a light brown color after cultivation under appropriate conditions for about 4 months. Additionally the settling efficiency of the biomass was very remarkable; the consumption of ammonium and nitrite resulted in the production of N2 and a small amount of nitrate. Anammox is denitrification of nitrite with ammonium as the electron donor to yield nitrogen gas, in which reaction nitrite is consumed faster than ammonium. The batch experimental results showed that the maximum anammox reaction rate occurred when the nitrite concentration ranged from 60 to 70 mg-N/L, whereas the activity was inhibited when higher than 80 mg-N/L. With regard to cell-immobilization technique, the PVA-alginate sodium nitrate method was proven appropriate for enriched anammox biomass because the nitrogen removal activity of immobilized anammox beads was quite satisfactory. This approach demonstrated that the established immobilization technique offers a promising way to granulate valuable anammox biomass, to protect these microorganisms against the unfavorable surroundings, and to efficiently retain anammox activity in the reactor. Therefore, the problems encountered in conventional bioprocesses for nitrogen elimination such as solid-liquid separation and biomass washout could be solved simultaneously.