浸入式超滤膜污染特征与形成机理研究
文献类型：学位论文
| 作者 | 肖萍 |
| 学位类别 | 博士 |
| 答辩日期 | 2013-11 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 王东升 |
| 关键词 | 天然有机物 “短流程”工艺 超滤 膜污染 污染指数 Fouling index Membrane fouling Natural organic matter Shortened-water-process Ultrafiltration |
| 其他题名 | Characteristic and Mechanism of Fouling in Submerged Low Pressure Ultrafiltration Membrane |
| 学位专业 | 环境工程 |
| 中文摘要 | 膜分离技术在近几十年来发展迅速，且因能够获得优质安全水质，被誉为“21世纪的水处理技术”。目前已在海水淡化、水和废水处理及回用、纯水制备等行业中得到应用。然而，膜污染始终是制约膜技术应用和推广的瓶颈。本文以浸入式中空纤维超滤膜为研究对象，研究了实际工程运行的超滤膜效能、污染过程和累积效应，并在实验室条件下，对膜污染评价指数进行了改良，评价了天然有机物（NOM）超滤膜过程，考察了复合有机体系的膜污染机理和影响因素，得出以下主要结论： （1）“短流程”超滤膜工艺采用低通量、低跨膜压差的运行方式，膜运行效能稳定，能量消耗少。混凝水直接超滤和混凝-沉淀-超滤工艺通量差异不明显，但随着过滤时间的增加，后者膜池内浊度逐渐升高。混凝水直接过膜后，在表面形成松散的絮体，在外力作用下具有二次絮凝功能，在膜表面形成保护层，泥水分离效果好，有利于降低膜深层次污染。 （2）通过实际水厂膜样品的分析，发现随着运行时间的增加，膜表面有机物不断累积，污染层也随之增厚。有机物是造成聚氯乙烯（PVC）超滤膜污染的主要物质，其中以蛋白类和微生物代谢产物（SMP）类更为重要，腐殖酸类的贡献相对较小。蛋白类有机物总量较大，但随着过滤时间的增加而逐渐下降，而SMP类含量则逐渐上升，腐殖酸类含量基本保持不变。SMP类有机物在膜污染的累积过程中有着重要作用，控制其含量可能对降低和预防膜污染起关键的作用。 （3）天然有机物（NOM）的膜滤过程分为快反应和慢反应。前者污染指数FIF大，污染速率较快，而后者膜污染指数FIS较小，污染速率缓慢。快慢反应均对膜污染行为有着重要意义。NOM能在短时间内即造成膜不可逆污染。腐殖酸（HA）和牛血清蛋白（BSA）更容易造成PVC超滤膜的不可逆污染，但碱洗能够有效去除。海藻酸钠（SA）造成的不可逆污染比重最低，但是化学不可逆污染的比例最高，难以被碱洗去除。 （4）膜污染指数（FI）不区分污染机理，且计算方法简明扼要，能够表征污染速率。根据产水量和FI，可以推出压力的损失，有重要的物理意义。通过计算不同阶段的FI（总污染指数、水力不可逆污染指数和化学清洗不可逆污染指数），能够确定各阶段的污染情况。 （5）尽管有机物浓度比例不同，复合有机溶液对超滤膜的污染阻力增加顺序始终为：HA/BSA＞BSA/SA＞HA/SA。由于有机物沉降速率的差异，污染层结构也不相同。HA/BSA在膜表面形成均匀的污染层，且BSA较多的位于污染外层，HA则更靠近膜表面。HA和SA形成的污染层较为密实，两种有机物随机分布。由于竞争吸附作用，使得BSA和SA形成的污染层形貌变化较大，外层主要为BSA，而内层则多为SA。 （6）溶液特性决定了复合有机体系对PVC超滤膜的污染行为。溶液粒径对膜过滤过程几乎没有影响，而分子量小于5kDa和位于15 - 20kDa之间的有机物含量和溶液电位则起着重要的作用。此外，分子量小于5kDa的有机物的含量对膜污染行为的影响更为关键。 |
| 英文摘要 | Membrane processes are highly efficient separation technology developed rapidly in recent decades，and is expected to be the prevalent water treatment technology for the 21 century. Membrane technology has been widely used in water softening, desalination, water and wastewater treatment and resuse. However, membrane fouling is the main limitation of membrane technology encountered in practical engineering application. In present work, a in-line coagulation low pressure ultrafiltration (UF) membrane made of polyvinyl chloride (PVC) was used in a full scale drinking water treatment plant. The membrane performance, organics fouling behavior and their accumulation in the membrane filtration were investigated in details. Furthermore, membrane fouling index was improved and the mechanism and key factors affecting the mixtures of dissolved organic matters fouling in the laboratory were systematically investigated. The results were outlined as follows: (1) The shortened-water-process (in-line coagulation ulfitration membrane) is operated in low flux and low transmembrane pressure in order to reduce membrane fouling and save energy consumption. The difference of flux between coagulation - ultrafiltration and coagulation - sedimentation - ultrafiltration is not significant. However, tubidity increased with filtation time in the second technology. The typical characteristic of shorten-water-process is raw water flowing into membrane directly after coagulation. Therefore, a cake layer with a loose structure and good permeability aggregates on membrane surface. These flocs still have activity, which have flocculation effect, so that tiny particles are retained by adsorption and easy to remove by hydraulic back washing. (2) Organics were the main foulants caused PVC ultrafitration membrane fouling. Protein/protein-like substances and SMP-like substances were the main components of the organic foulants, while the contribution of humic substances to the foulants should be very limited. The organics accumulated on membrane surface as well as the increased roughness with filtration time. SMP-like substances in fouling layer increased with the filtration time, which were highly attributed to the transition from proteins according to the FRI method. Thus, the increase of SMP in the combined fouling layer would make a significant role on the accumulation of irreversible fouling. (3) The fouling caused by NOMs can be considered as two steps, fast fouling stage followed by a slow one. The flux declined more rapidly suggested a faster fouling and a higher fouling index (FI) value. Both of fast response and slow response had important effects on filtration process with different fouling mechanisms. Irreversible fouling caused by humic acid (HA) and bovine serum albumin (BSA) was higher than that of sodium alginate (SA), but it could be easily removed by alkaline soaking, while chemical cleaning had rather limited effect on irreversible fouling caused by SA. (4) FI with a simple expression was shown to be a useful tool to describe membrane performance. The variations of FI values were consistent to the results of mass balances and flux variation, which revealed that this method was validated and reliable. Different fouling indices were determined to describe different operational cycles. (5) The overall order of the resistance caused by the mixtures of dissolved organics matters regardless of the concentration ratio was: HA/BSA＞BSA/SA＞HA/SA. According to the scanning electronic microscopy (SEM) and the attenuated total reflectance-Fourier transform infrared spectroscopy (FTIR) examinations, the fouling layer formed by HA/BSA had a structure that the protein was mainly in the outer layer and HA in the inner layer. Both HA and SA had contributed to the outer of the compacted fouling layer. The resultant thick fouling layer of BSA and SA was attributed to competitive absorption. (6) The properties of feed water decided the fouling behavior of UF membrane by the mixtures. The results demonstrate that particle size had no apparent effect on membrane fouling behavior, while molecules (less than 5 kDa and in the range from 15 kDa to 20 kDa) and solution zeta poteintial (ZP) played important roles according to the statistical analysis. Furthermore, the former is more significant than the latter. |
| 公开日期 | 2015-07-08 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/15702]  |
| 专题 | 生态环境研究中心_环境水质学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 肖萍. 浸入式超滤膜污染特征与形成机理研究[D]. 北京. 中国科学院研究生院. 2013. |
入库方式： OAI收割
来源：生态环境研究中心
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