沉浸式生物薄膜系統之阻塞機制與清洗方式探討

Abstract

沉浸式生物薄膜程序為近年廢水生物處理中一嶄新的研究，由於利用薄膜單元取代傳統的沉澱池，使其處理效能大幅提升，其中處理水更具回收再利用的潛能，因此實具發展的潛能。然而在這些優點的背後，依然存在一個必然發生的問題，即薄膜的阻塞。在此系統中薄膜的阻塞可能為無機、有機、生物性共存的混合性阻塞，使得阻塞複雜程度越高，然現今的阻塞研究多停留在非混合性阻塞，因此本研究欲對此進行包括阻塞機制、阻塞階段、阻塞影響因子及薄膜清洗的探討。 研究中利用SMBR實場取得的污泥經馴養成模擬的進流系統，平板膜掃流式快速膜濾裝置為實驗主體設備，透過其易於調整操作變因(如掃流速度等)使用平板膜來模擬SMBR實場的中空纖維等膜體，利用膜濾的數據與模式驗證得到此系統薄膜阻塞係由孔洞阻塞、中間阻塞、濾餅過濾機制所造成，而薄膜阻塞的階段大致上依次為初始的孔洞阻塞機制為主，之後過渡至中間阻塞與濾餅過濾機制為主，此與先前其它阻塞相關研究大體上相符。 由於阻塞的研究需與實場應用相互結合，因而在阻塞影響因子的部分，以操作因子的膜穿透壓(TMP)、掃流速度(CFV)及阻塞物質的粒徑分佈搭配不同孔徑UF膜做探討。結果顯示阻塞物質粒徑分佈與薄膜孔徑間的相關性，將影響主要的阻塞機制;TMP於超臨界通量操作下隨其增大將使阻塞前、後段嚴重程度更大;CFV因決定濾餅生成的穩定及特性使其於阻塞中後段扮演相當重要的角色。 薄膜清洗主要以超音波及化學清洗做探討，超音波由其清洗機制搭配SEM觀察，發現其清洗對象隨時間的轉換將視薄膜阻塞程度而不同，由阻塞濾餅層轉為孔洞間吸附力較弱的阻塞物質，其清洗效率於30分鐘時可達90%左右。化學清洗以中央合成設計法(CCD)進行清洗劑濃度與清洗時間此2影響因子的實驗，藉由較少的實驗組數(13組)即可有效得到清洗效率的反應曲面、等效率曲線及最佳清洗條件。由針對無機阻塞清洗的檸檬酸及生物阻塞的次氯酸納實驗中可發現清洗的限制因子有所不同，但仍無法確認何種阻塞為此混合性阻塞的清洗決定步驟。

At the past years, custom wastewater biological treatment’s operation range is limited by “sludge settling properties”, but recently a new technology called “membrane bioreactor process”, it use the membrane unit to substitute sediment tank, so can largely enhance treatment performance. Otherwise, its effluent have potential achieve high level water reuse requirement. But it also has the disadvantage of membrane fouling. The fouling behavior in this process may include inorganic, organic, biofouling, much complex than the past study of single fouling, so this study focus on the fouling mechanism, fouling stage, fouling effect factor and membrane cleaning four points in this complex couple-fouling process. In our study, we use rapid plate membrane instrument as main equipment, the acclimated sludge get from wastewater plant as feed system. Using filtration data couple with past fouling model, finds it occurs pore blocking, intermediate and cake filtration mechanism. And, fouling stage goes on pore blocking and then transfer to intermediate and cake filtration, this is incorporate with other fouling research. The fouling effect factor discuss in this study include transmembrane pressure (TMP), cross-flow velocity (CFV), fouling matter’s size distribution and membrane characteristic. Results reveal the relationship between fouling matter’s size distribution and membrane pore size determines main fouling mechanism. Upper critical flux operation, fouling becomes more serious when increasing TMP. CFV influence the cake’s form stabilization and properties, so it plays an important role in the mid and former fouling stage. Membrane cleaning is another topic in this study. Ultrasonic cleaning result shows its cleaning target transfer from cake to weak attached foultants in membrane pores differ from different fouling level. Chemical cleaning experiment were carried out in central composite design (CCD), using chemical concentration and cleaning time as two discussion factors, only thirteen operation runs can effectively get the useful cleaning efficiency information include response surface, contour plot and best cleaning condition. In our different cleaning aim target experiment, we use citric acid aim to inorganic fouling and NaOCl aim to organic couple with biofouling. Result shows the cleaning efficiency limitation factor is significant different. But it still not confirms what fouling type is the key limitation to cleaning.