MF薄膜搭配淨水操作程序處理水庫水之薄膜過濾效能與積垢研究

Abstract

薄膜處理程序在淨水處理中佔有很大的優勢，但薄膜在操作上最大的問題在於薄膜積垢，自然水體中天然有機物(natural organic matter, NOM)及藻類有機物(algal organic matter, AOM)因其中成分特性差異相當大，其對薄膜過濾通量及積垢特性之影響也不盡相同，先前研究顯示原水中親水性物質(如多醣類或蛋白質等)含量高較容易使薄膜阻塞，此外水體中有機及無機物質在相互作用下也會導致薄膜不可逆之阻塞，然而較少的研究針對相同孔徑及材質之薄膜在不同親疏水性表面下對水庫水及經淨水操作程序後分別過濾效能及對不同薄膜所造成之不可逆積垢探討。 本研究利用掃流式薄膜模組以不同孔徑之親/疏水性microfiltration (MF)薄膜分別過濾寶一水庫表層水(優養化水體)、寶山給水廠原水、沉澱池出流水及快濾池出流水，以了解各薄膜在搭配現有淨水操作程序下處理水庫水之薄膜過濾效能與積垢。 研究結果發現疏水性polytetrafluoroethylene (PTFE)薄膜對於水庫水中大分子具UV254吸收度之NOM之移除能力優於表面改質後親水性PTFE薄膜，但通量衰減較為嚴重。而親水性PTFE薄膜經水洗後之通量回復率優於疏水性PTFE薄膜。以薄膜處理寶一水庫表層水時發現，因水中藻類可能無法承受掃流式模薄模組所施加之剪力，而導致藻類細胞破裂並釋放藻類胞器及有機物質至水體中，造成薄膜處理後之滲濾液溶解性有機碳(dissolved organic carbon, DOC)上升。在寶山給水廠沉澱池出流水方面，因為其顆粒皆為不易沉降且被放大之顆粒物質，其結構較為鬆散，其顆粒也無法承受模組所施加之剪力作用，導致薄膜處理後之滲濾液DOC上升。在比較各薄膜過濾四種進流水後，使用0.1 μm親水性PTFE薄膜置於給水廠快濾池後處理水庫水可獲得最佳之水質及通量回復率。 薄膜過濾搭配淨水操作程序處理水庫水其薄膜表面積垢物以全反射傅立葉轉換紅外光譜儀(Fourier transform infrared spectroscopy, FTIR)分析主要為多醣類及蛋白質類物質，而以螢光激發放射矩陣(excitation-emission matrix, EEM)分析清洗薄膜後之脫附液可得知芳香族蛋白類、溶解性類微生物、類腐植酸及類黃酸等有機物也會造成薄膜積垢。分析清洗薄膜之脫附液發現鹼洗效果最佳，可脫附大量之有機物及無機離子。而以HCl清洗薄膜，對有機物清洗效果有限，僅能有效脫附鐵離子。 在不同水質條件下，會影響薄膜積垢、出流水品質及清洗後之通量回復率，所以不同水質條件下須搭配不同前處理以延長薄膜壽命，以利薄膜操作。

Membrane processes have been widely applied in water treatment. However, membrane fouling is the main issue in practical application. Likewise, the rate of filtration will also be affected by the membrane characteristics, pore distribution, operational condition, as well as the water properties. This study is aimed in investigating those parameters effect on membrane microfiltration efficiency. In this study, the HPO PTFE and HPI PTFE membrane with different pore size were applied in cross-flow filtration module to treat four kinds of water from different sources, i.e.; from Baoshan reservoir surface water and Baoshan water treatment plant (WTP) taken at different sampling point, namely raw water, sediment tank effluent, and filtration tank effluent. Other than examining the effect of membrane fouling on treated water qualities; the flux decline, the composition of foulants and membrane fouling cause were also investigated. UV spectrometer at 254 nm absorbance was applied to determine the NOM concentration. TOC analyzer and ICP-MS were utilized for organic and inorganic content analysis respectively. Membrane surface composition was observed by using FTIR whilst the influent or permeate solution composition was determined by EEM. Comparing both kinds of membrane performance, the results indicate that the HPI membrane had higher recovery after back flush, however HPO membrane have advantage in improved NOM removal. In term of water characteristic effect; treated water from Baoshan reservoir surface water and sediment tank effluent showed higher DOC content. The reservoir surface water originally has larger amount of algae than other water while effluent of sediment tank have loose structure particle content. Hence, when these water underwent cross-flow filtration, the shear forces would induce the cell breakage and particle rupture that cause organic matter release and eventually further increase the DOC concentration in water. Overall, the raw water of Baoshan WTP can achieve higher flux recovery and enhanced water quality than others. After cross-flow filtration operation, chemical cleaning by NaOH and HCl was applied to each membrane. It was found out that HCl can only desorbed limited amount of organic but effectively removed iron ion off the membrane surface. Contrary, NaOH can successfully wash off either inorganic ions or organic matters including humic acid, fulvic acid, protein-like compound and soluble by product like compound. From FTIR analysis result, it was definite that the foulants are mainly composed of some hydrophilic compounds, such as polysacharine and protein like materials. It is conclusive that in membrane treatment; membrane fouling, effluent quality and flux recovery will be affected by the properties of water being treated. The study shows that overall, using 0.1 μm HPI PTFE give better water quality and flux recovery. Moreover, proper pretreatment process can be applied to improve the operational performance.