Reduce Membrane Fouling in a Novel Bio-Entrapped Membrane Reactor: Impact of Soluble Microbial Products

薄膜生物系統(MBR)目前已被廣泛應用於處理都市生活污水二級處理程序中，但MBR系統通常會有薄膜積垢、薄膜阻塞及滲流率衰減之現象與問題。此薄膜操作問題，一般被認為可能是經由二級生物處理出流水中懸浮顆粒、胞外聚合物(Extracellular Polymeric Substances, EPS)及溶解性胞外聚合物(Soluble Microbial Products, SMP)等所造成，致使薄膜過濾阻力(Filtration Resistance)上升及滲流率衰減。傳統生物處理程序會產生大量污泥與終沉池污泥沉降效果不佳等缺點，其中EPS和SMP已被確定為造成薄膜積垢主要原因。因此，固定生物處理程序(Bio-Entrapped Process, BER)及固定生物處理程序結合薄膜反應系統(Bio-Entrapped Membrane Reactor, BEMR)已被研究發展，本研究利用此技術具有較長生物污泥停留時間(Sludge Retention Time, SRT)技術、高密度污泥及污泥產率低及可同時去除有機物和氮等優點，進行與傳統薄膜生物系統(Conventional Membrane Bioreactor, CMBR)作比較探討 研究結果顯示，具較長污泥停留時間BER程序相較傳統活性污泥法能夠提高25%~30%薄膜過濾通量，並減少薄膜積垢速率，此外發現固定生物處理技術所產生之溶解性胞外聚合物(Soluble Microbial Products, SMP)相較傳統活性污泥法能夠降低約71%，且能提升薄膜反清洗後恢復速度。固定生物處理技術結合薄膜系統(Bio-Entrapped Membrane Reactor, BEMR) 以食品工業廢水進行薄膜積垢研究，結果顯示BEMR對於有機物和氨氮具有超過90%以上的去除效率，並可提升薄膜過濾時間、不易積垢及降低操作維護成本。以BEMR濾程可長達39天，相較CMBR濾程僅只有5天即需進行化學清洗，BEMR亦產生較少蛋白質和碳水化合物，分別約為34%-48%和16%-29%。長污泥停留時間為影響bio-fouling之重要因子，亦相對影響薄膜操作效能及EPS/SMP特性，而隨污泥停留時間增加SMP有明顯減少趨勢。此外本研究結果顯示，懸浮固體物和EPS並非造成薄膜積垢之主因，薄膜積垢主要積垢原因為SMP所造成，研究發現BEMR與CMBR中SMP之分子量主要介於10-100kDa，而主要化學組成中蛋白質分別佔約59%與64%，其中結果顯示SMP分子量介於10-100 kDa之成份會對薄膜產生嚴重積垢問題，其能輕易進入和黏附在薄膜孔徑進而造成薄膜內孔徑吸附阻塞。另外為了解蛋白質和碳水化合物對薄膜積垢之影響，分別利用了蛋白質(L-tyrosine, Protein)和碳水化合物(Glucose, Carbohydrate)進行薄膜積垢實驗，結果顯示在不同濃度比較下，蛋白質造成薄膜通量下降情形皆比碳水化合物較為嚴重。 固定生物處理技術和固定生物薄膜反應系統確實能有效改善傳統薄膜生物系統問題，如提高處理效率、減緩薄膜積垢、降低SMP濃度，並能增加產水效率及減少化學清洗頻率，降低操作成本。Membrane bioreactors (MBRs) have been widely adopted for secondary treatment of municipal wastewater in the past decade, especially in developed countries. However, a major issue of MBRs is the rapid decline of permeate flux due to a high level of biomass in the reactor that accelerates membrane fouling. High sludge concentration and extracellular polymeric substances (EPS) or soluble microbial products (SMP) have been determined to be the major factors affecting membrane bioreactor operation. Therefore, the development of a novel biological reactor that contains a lower concentration of biomass and SMP is warranted. The bio-entrapped reactor (BER) has been developed for treatment of various wastewaters to achieve high simultaneous removal of carbon and nitrogen, and that reduced suspended biomass and increased SRT in the reactor with the objectives to achieve high organics removal in a more facile operation with a short start-up period. Thus, the BER was coupled with membrane as bio-entrapped membrane reactor (BEMR) was investigated the SMP and their characteristics on membrane fouling in treating food processing wastewater, and also compared with conventional membrane bioreactor (CMBR) with the overall study goal is to reduce membrane fouling commonly encountered in MBRs. The results show that BER with a longer sludge retention time (SRT) has demonstrated that membrane filtration performed well and achieved an approximately 25%-30% higher filtration flux and better flux recovery after backwashing than the activated sludge process (ASP) system. The BEMR could remove the carbon and ammonia nitrogen with more than 90% under different hydraulic retention time (HRT). The novel BEMR sustained operation at constant permeate flux (20 LMH) that required seven times less frequent chemical cleaning than did the conventional membrane bioreactor. Membrane fouling was improved in the new reactor, which led to a longer membrane service period with the new reactor. As in the CMBR, rapid membrane fouling was attributed to increased production of biomass and SMP, this is because the BEMR produced less SMP than did CMBR (34%-48% less protein and 16%-29% less carbohydrate) due to slow-growing microorganisms with longer SRT in the BEMR. Further, results of this thesis also indicated that suspended solids and bound EPS unexpectedly played a negligible role in membrane fouling and the fouling was actually controlled by SMP, which proved the SMP was the major contributor or foulant to the membrane fouling. Both MBRs (BEMR and CMBR) produced SMP of 10-100 kDa primarily of protein (59% in BEMR and 64% in CMBR), which likely caused membrane pores clogging because the 10-100 kDa of SMP could easily penetrate to the membrane pores by adsorption in a 100 kDa membrane used in this work. The impact of protein and carbohydrate to the membrane fouling was also been found because, the findings with L-Tyrosine and glucose as the model foulants for protein and carbohydrate respectively showed that protein (L-Tyrosine) caused more severe permeate flux decline than carbohydrate (glucose). The conclusion stated that the bio-entrapped membrane reactor could really improve the MBR performance by reducing the membrane fouling and producing less concentration of SMP with conventional membrane bioreactor. Therefore, the new BEMR offers effective organics removal while reducing membrane fouling with the potential for improving and encountering the current problems faced by conventional MBR