以不同次臨界通量操作之生物薄膜反應槽 之薄膜積垢的研究

Abstract

近年來，薄膜過濾系統已被廣泛應用於水回收及廢水處理系統。其中，薄膜生物反應器(membrane bioreactor, MBR)於廢水處理之技術結合了薄膜之物理性過濾及活性汙泥之生物性降解；然而，操作生物薄膜反應器之過程中，薄膜積垢問題常導致操作及物料成本之提高；因此，如何將生物薄膜反應器之薄膜積垢完全去除便成了各國專家學者主要的研究課題。 臨界通量(critical flux)理論發展於1990年代中期，其主要之定義為當薄膜生物反應系統中通量控制於臨界通量以下，其清水通量(permeate flux)將不會下降，此值亦稱為次臨界通量(sub-critical flux)。換言之，當操作於次臨界通量之條件下薄膜積垢現象理論上將不會發生；但實際上，薄膜生物反應器中於次臨界通量之條件下操作仍會有積垢之現象產生。 本研究中，臨界通量與逐步通量增加法(flux-step method)之訂定皆須列入考量。其中，親水性膜(HPI membrane)操作於7,000 – 7,500 mg/l活性汙泥下之臨界通量為18 lm-2h-1，於6,000 – 6,500 mg/l活性汙泥下使用親水膜及疏水性膜(HPO membrane)之臨界通量分別為33及30 lm-2h-1。此外，疏水膜於短時間試驗中顯示其較親水膜易形成積垢，薄膜生物反應器中較高之活性汙泥濃度亦較容易造成薄膜積垢現象。於薄膜生物處理系中，胞外聚合物(Extracellular polymeric substance)於薄膜積垢現象中常扮演重要角色，而蛋白質與多醣體為其主要之成分，因此於本研究中蛋白質及多醣體為判別薄膜積垢的重要指標，其薄膜積垢物(foulants)之分析為以FTIR進行表面分析，並同時以EEM與CLSM進行薄膜積垢之特性分析。結果顯示，於垂直分布之分析中，其薄膜表面各物質的濃度皆低於膜上結垢物(cake)表面之濃度，且諸類物質大多分布於積垢物40-80%之深度位置

In recent years, membrane filter has become popular not only in water reuse but also in wastewater treatment. Among them, membrane bioreactor (MBR) is one of the remarkable methods combining membrane filtration and biodegradation of activated sludge for wastewater treatment. Membrane fouling, however, occurred during the operation of MBR process, is considered a major problem causing increased operational cost as well as material cost. Therefore, how to remove membrane fouling has become a big challenge for most researchers interested in MBR in the world. Critical flux concept has been established in the middle 1990s. The common definition of critical flux is that the permeate flux will not decline if the MBR system is controlled at a flux below critical flux – that is so-called sub-critical flux. In other words, theoretically, fouling will not be observed during sub-critical flux operation. But in practice, membrane fouling still occurs during MBR operation even under sub-critical flux operation. In this study, to determine critical flux, flux-step method was considered. By which, critical flux for HPI membrane operated with activated sludge of 7,000 – 7,500 mg/l, HPI and HPO membranes under 6,000 – 6,500 mg/l were found at 18, 33 and 30 lm-2h-1, respectively. In addition, HPO membrane was fouled much easier than HPI membrane in short-term experiments. A higher propensity of membrane fouling occurred at a reactor with higher sludge concentration. Extracellular polymeric substance plays an important role in causing membrane fouling in MBR. In general, protein and polysaccharide are considered the major compositions of EPS. Therefore, protein and polysaccharide were identified in this study to indicate membrane fouling. The presence of proteins and polysaccharides in membrane foulants were determined by FTIR analysis. In addition, EEM and CLSM were also used to characterize membrane fouling. Vertical distribution analysis shows that the concentration of fouling substances on the membrane surface is lower than that on cake layer surface. They are distributed from 40% to 80% of the depth of cake layer