厭氧與兼氧微生物薄膜系統開發

Abstract

生物處理技術與薄膜分離技術結合之薄膜生物反應器（Membrane Bio-Reactor, MBR），是近代生化工程的一種突破性創舉，在廢水處理領域之MBR程序，可分成好氧MBR（aerobic MBR）與厭氧MBR（anaerobic MBR）兩種，好氧MBR目前已取得輝煌之實際應用成果，而厭氧MBR之實際應用實績，文獻之記載卻非常稀少。應用好氧MBR最大之限制在於薄膜積垢阻塞問題，薄膜積垢會減損薄膜通量、增加薄膜操作壓力，除增加操作成本外，也會影響薄膜使用壽命；厭氧MBR除薄膜積垢問題之外，還有因厭氧代謝產生之CO2副產物，所衍生碳酸金屬在薄膜表面導致結垢問題，長期以來一直無法克服，是厭氧MBR無法有效推廣應用之主要原因。 厭氧生物處理技術體積效率高，可降低空間需求，且因厭氧微生物生化反應不需曝氣，可節省大量能源，但厭氧微生物產率低，不易顆粒化，在無完善截流設備下容易流失，因此在厭氧生物處理槽中不易累積大量微生物量，使得厭氧生物處理技術無法完全發揮潛在效率，因此，若能將厭氧生物處理技術與薄膜分離技術有效結合，其經濟效益將高於好氧MBR。但薄膜要成功應用於厭氧生物處理系統，除必須降低薄膜積垢問題，尚須有效克服薄膜表面結垢問題。 本研究開發一種薄膜應用之新技術，利用厭氧微生物與兼氧微生物為薄膜系統之主要功能性細菌，來達到淨化污染物之功能，此系統稱為厭氧與兼氧微生物薄膜系統（Membrane-Coupled Methanogenic and Facultative Biosystem, MCMFB），此系統之特性是利用一組薄膜，同時達到厭氧MBR與好氧MBR之功能，同時MCMFB系統中之薄膜，同時具備高的抗積垢與抗結垢特性。在本論文中，包括建構MCMFB處理系統、利用批次試驗探討環境轉換對厭氧微生物與兼氧微生物活性之影響、以及利用MCMFB組裝設備探討其長期操作穩定性，並於基質中添加CaCl2方式，進行MCMFB處理系統之預防結垢功能研究，最後並將此新技術應用來處理偏光版製程實際廢水，探討其實際可利用性。 實驗中以短期環境轉換與長期環境轉換，對厭氧微生物與兼氧微生物活性之影響研究發現，雖然微生物交替處在厭氧與好氧環境中，但對其活性沒有明顯之影響。在以沒有添加CaCl2之葡萄糖與醋酸混合基質，進行180天MCMFB長期操作穩定性探討，發現厭氧槽與好氧槽均能穩定維持其功能，薄膜槽之操作pH值介於8.5∼9之間，MCMFB之薄膜過濾特性以TMP與Flux表示，發現在長達150天之監測中，Flux由11 L/m2-hr提昇至18 L/m2-hr，在此實驗期間薄膜並未進行任何反洗與清洗操作，但其TMP長期維持在2 □ 1 kPa之間，顯示MCMFB之薄膜具有高的抗積垢特性。 在以添加CaCl2之葡萄糖與醋酸混合基質，進行MCMFB之薄膜預防結垢之功能研究中，將MCMFB處理系統之好氧槽分成，曝氣槽與薄膜槽分開之external membrane system，與曝氣槽與薄膜槽結合在一起之internal membrane system，進行對比試驗，Ca離子濃度介於50-350 mg/L之間，薄膜操作之pH值介於8.2∼8.5，經過70小時之操作發現，internal membrane system 薄膜之過濾行為，其TMP由7 kPa緩慢增加至20 kPa；Flux則由14 L/m2-hr緩慢下降11 L/m2-hr；而後薄膜之TMP短時間內陡升至50 kPa，且Flux 則急速縮減至4 L/m2-hr，TMP之擴增如此迅速，主要是因薄膜無機物結垢所造成；相同操作條件下，external membrane system薄膜之TMP隨時間增加，其TMP仍維持穩定，但Flux有微幅降低之趨勢。internal membrane system 薄膜上之結垢物，經X-ray繞射證實為碳酸鈣，MCMFB處理系統之預防結垢功能研究證明，當廢水具有結垢潛能時，MCMFB處理系統採用曝氣槽與薄膜槽分開，可有效防止薄膜表面結垢發生。 最後MCMFB處理系統以偏光版製程實際廢水，進行長期試驗，以驗證其應用可行性，此廢水鈣鎂離子濃度低，無薄膜結垢問題，在140天之長期操作下，MCMFB處理系統證實之厭氧槽具備高度性能穩定性作用，針對偏光版製程實際廢水，厭氧槽之單位體積去除量可穩定達到5.0 kg COD/m3-day，此體積效率為一般傳統喜氣生物處理法之4∼5倍，薄膜之操作pH均維持在8.0∼8.5之間，在130天之監測中，薄膜之Flux則1 L/m2-hr提昇至5.0 L/m2-hr操作，而薄膜之TMP可長期穩定維持在15∼20 kPa之間，再次證明此MCMFB處理系統之薄膜具抗積垢性。

Membrane bio-reactor (MBR), combining biological treatment with membrane separation, has recently become an innovative biochemical technology for wastewater treatment. MBR can be grouped into anaerobic and aerobic MBR depending upon the type of the bacteria. Many successful applications of aerobic MBR have been documented. Anaerobic MBR, on the other hand, has rarely been mentioned in the literature. The most limiting factor in operating aerobic MBR is the membrane fouling, which reduces the membrane flux and increases the TMP resulting in increased operation cost and shortened membrane life. As for anaerobic MBR, scaling is one additional problem besides fouling due to the formation of CO2 which forms the scales of metal carbonates on the membrane surface. This is the main reason that anaerobic MBR is seldom practiced. Anaerobic biological treatment requires less space because of the high volumetric treatment capacity and low in energy consumption. However, because the production of anaerobic biomass is substantially slow, the granule is difficult to form resulting in biomass loss. The MBR technology can effectively retain the biomass in the reactor and greatly enhance the biological treatment. The only problems left are the fouling and the scaling. In this study, the Membrane-Coupled Methanogenic and Facultative Biosystem (MCMFB) was invented, in which both anaerobic and facultative microorganisms were used. In this system, only one membrane module was utilized to serve both the anaerobic and aerobic bioreactors. The effects of environmental parameters on microbial activities and the stability of long-term operation due to potential fouling and scaling were evaluated. The feasibility of the system was evaluated by applying on the wastewater from a polarizer plant. After 180 days of operation, the system appeared stable and the activities of the microorganisms remained unaffected although they were alternated between anaerobic and aerobic conditions. The flux rose from 11 to 18 L/m2-hr and the TMP remained 2 □ 1 kPa, indicating that the MCMFB was highly resistant to fouling. Calcium chloride was added in the substrate to test the response of MCMFB to scaling. Both external and internal membrane systems were tested. It was discovered that by using the external membrane system the inorganic scaling on membrane surface was reduced substantially. X-ray diffraction (XRD) identified calcium carbonate as the scale on the membrane of the internal membrane system. Therefore, the aeration tank and the membrane tank of the MCMFB system must be separated if the wastewater is of risk of scaling. The wastewater from polarizer process contains low concentrations of calcium and magnesium. After 140 days of operation, the MCMFB system remained stable, of which the volumetric removal capacity of the anaerobic tank was maintained around 5.0 kg COD/m3-day which was four to five times that of aerobic biological treatment. The flux was between 1 to 5.0 L/m2-hr and the TMP was between 15 and 20 kPa. The result proved that the MCMFB could effectively prevent membrane fouling.