【作者】 瞿芳术；

【导师】 李圭白； 梁恒；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2012， 博士

【摘要】 随着饮用水水质卫生标准日趋严格，具备高效除污染效能的超滤技术在饮用水处理中将拥有广泛的应用前景。但在天然水体富营养化现象尚不能有效控制的背景下，藻类引起的膜污染会严重制约超滤净水工艺的推广。因此超滤膜处理高藻水过程中膜污染特性及其控制研究对超滤技术在饮用水处理领域的推广应用具有重要意义。针对这个问题，本论文以铜绿微囊藻作为天然高藻水的代表藻种，开展了藻源膜污染物的表征及其膜污染特性研究、超滤膜藻源污染的影响因素研究以及超滤膜藻源污染控制研究，并在此基础上结合天然高藻水进行了中试研究。藻细胞及其胞外有机物（Extracellular organic matter, EOM）是高藻水中主要的膜污染物。本论文通过高速冷冻离心法实现了藻细胞和EOM的分离，并利用基于比通量下降、膜污染可逆性分析和有机碳质量平衡的膜污染评价方法以及扫描电镜和傅里叶红外光谱等表征技术对藻细胞和EOM引起膜污染进行了详细的分析。实验结果表明：藻细胞和EOM都能引起严重的膜通量下降和不可逆膜污染。为了进一步阐释EOM引发不可逆膜污染的机理，本论文考察了EOM的荧光特性、分子量分布以及亲疏水特征，发现EOM由蛋白质类、多糖类和腐殖质类有机物组成，以大分子和亲水性为主要特征。在此基础上，本论文通过预过滤、投加钙离子以及XAD树脂预处理等方法改变EOM的特性，并通过超滤对照实验研究了EOM的性质对膜污染的影响。结果表明，EOM中大分子组分（100kDa-0.45μm）对膜污染的贡献最大；在中性条件下EOM呈负电性，静电相斥作用会阻止其吸附在膜表面上；EOM的疏水组分更易于吸附在膜表面形成不可逆膜污染，而亲水组分引起膜通量下降的能力远远大于疏水组分。此外，本论文还详细研究了溶解型EOM（dissolved EOM, dEOM）和附着型EOM（bound EOM, bEOM）的性质和膜污染作用，得出以下结论：bEOM主要由蛋白质类有机物组成，以大分子和疏水性为主要特征；而dEOM含有多糖类、蛋白质类以及腐殖质类有机物，具有较强的亲水性。dEOM在超滤过程中引起的膜通量下降比bEOM严重，但bEOM能引起更为严重的不可逆污染。bEOM和dEOM都能加重藻细胞引起的膜污染。就污染机理而言，滤饼层污染是藻细胞和EOM引发超滤膜污染的主要机理，膜孔堵塞和疏水吸附对藻源膜污染的形成也具有一定的贡献。超滤膜藻源污染的影响因素研究表明：碱性条件对藻细胞和EOM引起的膜污染都没有显著的影响，而酸性条件会导致藻细胞破裂及IOM的释放，加重膜污染。无机颗粒污染物会减轻藻细胞引起的膜通量下降和不可逆膜污染，但它对EOM引起的膜污染没有明显的影响。天然腐殖质类有机物会同时加重藻细胞和EOM引起的膜通量下降以及不可逆膜污染。超滤膜的截留分子量越大，藻细胞和EOM引起的膜通量下降均越严重，但是膜污染的可逆性越好。亲水性超滤膜抗藻源污染的能力强于疏水性超滤膜，疏水作用会促进藻细胞和EOM在膜表面吸附。采用浸没式超滤膜处理高藻水时，缩短反冲洗周期和增大反冲洗流量都有利于膜污染的控制；气水反冲洗会引起藻细胞的重新悬浮以及破裂，加重藻源膜污染控制。基于藻源膜污染的特性研究和影响因素研究的结果，本论文开展了高锰酸盐强化混凝缓解超滤膜藻源污染试验研究。结果表明：混凝预处理能减轻藻细胞和EOM引起的膜通量下降和不可逆膜污染，但过量投加混凝剂亦不利于膜污染的控制。KMnO₄强化混凝预处理均能明显减轻藻细胞和EOM引起的膜通量下降和不可逆膜污染，降低污染物负荷和改善滤饼层结构是主要的膜污染缓解机理。高锰酸盐复合药剂（Potassium permanganate composites，PPC）强化混凝和超滤组合工艺处理引黄水库高藻水的参数优化研究表明：PACl的最佳投量为4mg/L，PPC的最佳投量为0.6mg/L。组合工艺中试试验的结果表明：PPC强化混凝不仅能提高出水的水质，还能有效缓解高藻水超滤过程中的膜污染现象。本论文完成了高藻水超滤过程中膜污染物的表征及其膜污染特性研究，并提出了适于高藻水处理的高锰酸钾强化混凝预处理和超滤组合工艺。本论文的研究成果可以为季节性藻类爆发时超滤工艺水厂的运行提供技术支持。更多还原

【Abstract】 Under the situations that the drinking water quality standard becomes more andmore stringent，ultrafiltration （UF） technology which is excellent in the removal ofpollutant will be widely applied in drinking water production. However, theeutrophication of natural water cannot be effectively controlled till now, and themembrane fouling accosicated with algae will significantly hinder the application ofUF technology. Therefore, the study on the mechanisms and control of UF membranefouling caused by algae is essential for the further promotion of UF technology. Toaddress this problem, the study on the membrane fouling characteristics during thetreatment of algae-rich water by UF membrane, the study on the influence factors ofmembrane fouling caused by algae, and the study on the membrane fouling control bythe pretreatment of permanganate enhanced coagulation were carried out.Cyanobacterium was chosen for these experiments. Based on these bench scale studies,a pilot study was also performed with the natural seasonal algae-rich reservoir water inthe lower reaches of yellow river.Since algal cells and extracellular organic matter （EOM） were the most importantfoulants in algae-rich water, they were previously separated by the high-speedrefrigerated centrifugation, and their fouling effects were subsequently evaluated bythe nominalized flux decline, reversibility analysis of membrane fouling and massbalance of organic carbon. Moreover, the scanning electron microscope （SEM） and thetotal reflectance-fourier transform infrared spectroscopy （ATR-FTIR） were also used toanalyze the membranes fouled by the algal cells or EOM. The experimental resultsindicated that both algal cells and EOM could lead to serious flux decline andirreversible membrane fouling. Meanwhile, fluorescence properties, molecular weight（MW） distribution and hydrophobicity/hydrophilicity of EOM were also studied. Theresults revealed that EOM was comprised of protein-like, polysaccharide-like andhumic-like substances and was characterized by the high-MW （>100kDa） and stronghydrophilicity. In addition，prefiltration, calcium addition and XAD fractionation wereemployed to change the characteristics of EOM, and then the effects of thesecharacteristics on the fouling effects of EOM were compared. It was found that thefraction of EOM between100kDa and0.45μm contributed a significant portion of the fouling. As EOM was negatively charged under neutral condition, the electrostaticrepulsive between foulant and membrane surface could prevent the organics fromadhering to the membrane. The hydrophobic organics in EOM tended to adhere tomembrane surface causing irreversible fouling, while the cake layer formed by thehydrophilic organics caused greater resistance to water flow, leading to faster fluxdecline during UF. Furthermore, EOM was classified into the dissolved EOM （dEOM）which was released into water and the bound EOM （bEOM） which surrounded thecells, and their characteristics and fouling effects were compared. It was found thatbEOM was mainly composed of protein-like substance and was characterized byhigh-MW and strong hydrophobicity, while that dEOM contained protein-like,polysaccharide-like and humic-like substances and was much more hydrophilic.Results of UF experiments indicated that dEOM caused more severe flux decline thanbEOM while that bEOM led to the membrane fouling with much worse reversibility.Both flux decline and irreversible membrane fouling caused by the cells wereaggravated when the cells were together with EOM. In term of fouling mechanisms,cake layer formation, hydrophobic adhesion and pore plugging were the mainmechanisms for membrane fouling when treating algae-rich water with UF.Study on the effects of solution chemistry on the fouling caused by algae showedthat the alkaline condition had not influence on the fouling effects of both algal cellsand EOM, while that the acid environment could lead to the cell lysis and exacerbatedthe flux decline and irreversible fouling. Moreover, the adhesion of EOM onmembrane could also be intensified in the acid environment. Inorganic particles couldalleviated the flux decline and irreversible fouling caused by algal cells, but they wereinefficient in reducing the membrane fouling related to EOM. Natural humic-likesubstance could aggravate the fouling caused by both algal cells and EOM. Theproperties of membrane were also found to apparently affect the membrane fouling.When the membranes with higher molecular weight cutoff （MWCO） were used to treatalgal cell solution or EOM solution, more severe flux decline but better reversibility offouling could be found. The hydrophilic membrane was found to be better inanti-fouling ability than hydrophobic membrane, and the hydrophobic interaction couldenhance the adhesion of algal cells and EOM to the membrane surface. It wasfavorable to increase the frequency and intensity of backwashing for the sake offouling control. However, the combined backwashing with air and water could not mitigate but aggravate the fouling, because it might caused the lysis of algal cells andthe resuspension of cell aggregates on the membrane surface during hydraulicbackwashing.Effects of different pretreatments such as coagulation, KMnO₄preoxidationenhanced coagulation and hydrated manganese dioxide （δ-MnO₂） enhancedcoagulation on the membrane fouling caused by algal cells or EOM were compared. Itwas found that coagulation pretreatment could reduce the fouling caused by both algalcells and EOM under the favorable coagulant dosage. However, the fouling woulddeteriorate when the coagulant was over dosed. In addition, KMnO₄preoxidationenhanced coagulation could dramatically reduce the fouling caused by algal cells orEOM. Reducing the foulant load and improving the structure of cake layer were themain mechanisms for fouling control. The pilot study of treating natural algae-richwater with the hybrid process of preoxidation enhanced coagulation and UF wascarried out. The results of optimizing experiment of the operational parametersindicated that the optimum dosages of PACl and PPC were4and0.6mg/L,respectively. The results of pilot experiment suggested that PPC preoxidation could notonly improve the quality of water, but also mitigate the membrane fouling during UFof natural algae-rich water.This thesis focused on the identification of foulants associated with algae and theeffects of their characteristics on UF membrane fouling. Based on these results, thehybrid process of premangnate preoxidation enhanced coagulation and UF wasconstructed for the treatment of algae-rich water. This thesis can provide supports forthe running and manage of the waterworks in which UF technology is used, when theseasonal algae bloom occurs.更多还原