xDLVO理论解析混凝预处理对葡聚糖超滤膜污染的影响机理

发布时间：2018-03-14 12:17

本文选题：超滤膜污染　切入点：葡聚糖　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：膜污染现象是制约超滤技术发展的重要因素。混凝技术作为一种预处理措施,被应用到膜分离技术中来减缓膜污染。本研究运用XDLVO(extended Derjaguin-Landau-Verwey-Overbeek)理论定量解析在不同聚合氯化铝(PACl)或Ca~(2+)浓度条件下葡聚糖超滤膜污染中的界面相互作用,评价不同界面作用力(范德华作用力、双电层作用力以及极性作用力)对膜污染的贡献程度,探究混凝预处理中絮凝剂浓度、Ca~(2+)浓度和pH影响葡聚糖超滤膜污染的主控机制。在对界面作用力进行定量解析的基础上,分别对不同实验条件下葡聚糖膜污染趋势与界面作用能之间的线性关系进行定性分析与定量解析,从而更为全面、系统的对xDLVO理论描述葡聚糖预混凝-超滤膜污染行为的适用性做出评价。结果表明,在所有实验条件下,AB作用是影响膜污染趋势的主要因素。葡聚糖预混凝-超滤膜污染过程中的超滤膜-葡聚糖和葡聚糖-葡聚糖界面相互作用力随着絮凝剂浓度和钙离子浓度呈现一定的变化规律。当絮凝剂浓度逐渐升高时,超滤膜-葡聚糖和葡聚糖-葡聚糖界面相互作用能按照6930mg/l PACl的顺序依次降低;当溶液中有钙离子存在时,界面自由能有所下降,且随着钙离子浓度的升高进一步降低;在pH为7时,界面作用能最大,酸性和碱性环境下有所降低。PACl、Ca~(2+)和pH主要通过降低AB作用的排斥性或增强吸引性来影响膜污染趋势,同时预混凝过程会显著增大污染物粒径,进而使界面自由能的绝对值增大。膜过滤初始和后期阶段的相对膜通量下降量分别与膜和污染物以及污染物之间的界面作用能有较强的线性相关性,证明XDLVO理论对预测混凝预处理-超滤过程中的膜污染趋势有较高的适用性。絮凝剂浓度、Ca~(2+)浓度和pH对葡聚糖预混凝-超滤膜污染行为具有重要的影响。随着絮凝剂PACl浓度的升高,相对通量呈现先递增后递减的趋势,且在PACl浓度为6mg/l时,相对通量达到最大。而随着Ca~(2+)浓度的升高,PES膜葡聚糖超滤过程中的相对通量逐渐降低。在pH为7时,膜污染最轻,酸性和碱性环境下有所加重。不同絮凝剂浓度以及钙离子浓度条件下,PES膜过滤初始阶段和后期阶段中的膜污染趋势分别与超滤膜-葡聚糖和葡聚糖-葡聚糖界面相互作用能具有良好的负线性相关性。因此xDLVO理论适用于描述不同絮凝剂浓度、Ca~(2+)浓度和pH条件下的膜污染趋势。不同絮凝剂浓度、Ca~(2+)浓度和pH对整个超滤过程中膜污染行为的影响主要是通过改变极性作用力来实现的。葡聚糖为亲水性中性物质,表面zeta电位趋于0,因此静电作用能对膜污染趋势的影响很小。而范德华作用能与絮凝剂浓度和钙离子浓度的变化没有一致的规律性,其对膜污染趋势的影响也很小。
[Abstract]:Membrane fouling is an important factor restricting the development of ultrafiltration technology. In this study, XDLVO(extended Derjaguin-Landau-Verwey-Overbeek theory was used to quantitatively analyze the interfacial interaction of dextran ultrafiltration membrane fouling with different concentrations of polyaluminum chloride (PACl) or Ca~(2. To evaluate the contribution of different interface forces (van der Waals force, double layer force and polarity force) to membrane fouling. The main control mechanism of the influence of flocculant concentration and pH on the fouling of dextran ultrafiltration membrane in coagulation pretreatment was investigated. The linear relationship between the fouling trend of dextran membrane and the interfacial interaction energy under different experimental conditions was analyzed qualitatively and quantitatively respectively. The applicability of xDLVO theory to describe the fouling behavior of dextran precoagulation-ultrafiltration membrane was systematically evaluated. Under all experimental conditions, the action of AB is the main factor affecting the trend of membrane fouling. Interaction between UF membrane and dextran and dextran interface with flocculant concentration in the process of Dextran precoagulation-UF membrane fouling. When the concentration of flocculant gradually increased, The interaction energy of ultrafiltration membrane and dextran / dextran interface decreased in the order of 6930 mg / l PACl, and the free energy of interface decreased with the increase of calcium ion concentration in the solution. When pH was 7:00, the interfacial energy was the largest, and the pH value was decreased in acidic and alkaline environment, and pH affected the fouling tendency of the membrane mainly by reducing the repellency or enhancing the attraction of AB, and the particle size of the pollutants was significantly increased during the pre-coagulation process. Then the absolute value of the interface free energy is increased, and the relative membrane flux decreases in the initial and late stages of membrane filtration have a strong linear correlation with the interface energy of the membrane, pollutants and pollutants, respectively. It is proved that XDLVO theory is more suitable for predicting membrane fouling tendency during coagulation pretreatment and ultrafiltration. The concentration of flocculant and pH have important effects on the fouling behavior of dextran precoagulation-ultrafiltration membrane. The increase of PACl concentration, The relative flux increased at first and then decreased, and the relative flux reached the maximum when the concentration of PACl was 6 mg / l. With the increase of Ca~(2 concentration, the relative flux of PES membrane decreased gradually. At pH 7:00, the membrane fouling was the least. The fouling tendency of PES membrane in the initial and late stage of filtration was different with the interface of ultrafiltration membrane dextran and dextran dextran under the condition of different flocculant concentration and calcium concentration. The interaction energy has a good negative linear correlation. Therefore, xDLVO theory can be used to describe the membrane fouling tendency under different flocculant concentration and pH. Different flocculant concentration and pH influence the whole ultrafiltration process. The effect of membrane fouling is mainly achieved by changing polarity force. Dextran is a hydrophilic neutral substance. The surface zeta potential tends to be zero, so the electrostatic action energy has little effect on the membrane fouling trend, while van der Waals interaction energy has no consistent regularity with the change of flocculant concentration and calcium ion concentration, and its influence on the membrane fouling trend is also very small.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703;TU991.2

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