電化生物薄膜反應器中混凝效應對薄膜阻塞及泥污特性之影響

Abstract

薄膜積垢問題是生物薄膜反應器在應用上最大的限制，儘管已有許多研究針對薄膜積垢的機制及預防進行廣泛地探討，薄膜積垢的問題依然存在於生物薄膜反應器中。薄膜上的積垢不僅會導致出水通量的衰減，同時也縮短了薄膜的壽命，增加操作成本。因此本研究結合電混凝程序及生物薄膜反應器，建立一套電化生物薄膜反應系統(electro-MBR)，探討不同電流效率對於薄膜積垢延緩的效能，以污泥特性、微生物活性及出流水水質作為電化生物薄膜系統對薄膜積垢延緩效能的三大指標。本研究設定電流密度範圍介於10–40 A/m2，利用批次試驗來找出最佳的電流密度後應用於長期連續式電化生物薄膜系統，試驗時間為15天。胞外聚合物(extracellular polymeric substances, EPS)的量測包含溶解型及結合型的聚合物；便攜式流式细胞攝像(Portable Series FlowCAM)來分析污泥特性如平均顆粒粒徑、污泥長寬比及污泥絮狀物的表面型態。試驗結果顯示當電流密度為20 A/m2對長期連續式電化生物薄膜系統可有效提高污泥絮狀物的聚集且有最佳延緩薄膜積垢之能力。電化生物薄膜系統具有優良之出流水水質，出流水中的有機物及氨去除率皆可高於98%。連續式及間歇式的電化生物薄膜系統在試驗15天後其積垢率皆遠低於傳統的生物薄膜反應器，分別為5.7及7.8倍，且在試驗期間，間歇式的系統因薄膜的透膜壓力上升緩慢，故不需要任何化學清洗，而連續式的系統則需清洗1次。此外，亦可顯著地觀察到在電化生物薄膜反應系統中沒有絲狀菌膨化問題和污泥絮狀物的結構和型態的改變。綜合上述結果所述，電化生物薄膜系統中的掃沉混凝(sweep-coagulation)及電氧化作用(electro-oxidation)是影響薄膜積垢延緩的重要因素。

Membrane fouling is the main obstacle that hinders the widespread applications of membrane bioreactors (MBRs). Numerous studies have been conducted to deal with membrane fouling. However, this phenomenon is still inevitable in MBRs. The occurrence of fouling not only reduces the permeability, but deteriorates the membrane lifespan, leading to accelerating the operation costs. In order to overcome this drawback, a combination of electro-coagulation process with MBR (electro-MBR) was built to investigate the capacity of electro-coagulation on reducing membrane fouling under different electric currents (ECs) applied modes. The effect of electro-coagulation process on the change of sludge characteristics, microbial activities, and effluent qualities was investigated in this study. The optimal EC was firstly ascertained from the batch-scale experiments within a range of ECs between 10 A/m2 and 40 A/m2. Then, this value was further applied for the long-time operations with electro-MBR. In this study, the contents of extracellular polymeric substances (EPS) was quantified in both soluble and bound types, while sludge characteristics such as particle size mean (PSM), aspect ratio (AR), and sludge floc morphology were monitored through the Portable Series FlowCAM. The results demonstrated that electro-coagulation at EC of 20 A/m2 was suitable for the long-time operation of electro-MBR according to its efficacy in reducing fouling and enhancing floc agglomeration. In long-time electro-MBR study, the excellent performance on the removal of total organic compunds (> 98%) and ammonia (> 98%) were obtained. The fouling rates in both continuous and intermittent modes of electro-MBR were 5.7 and 7.8 times less than that in control-MBR during 15 days of operation, respectively. No chemical cleaning was used in the case of intermittent mode, whereas only one time cleaning was conducted in the continuous mode. The most striking observations in this study were that electro-MBR can be operated without the problem of filamentous bulking, and electro-coagulation significantly alternated the structural and morphological sludge flocs. The results implied that the sweep-coagulation and electro-oxidation might be the key factors for the success in fouling mitigation in electro-MBR.