【作者】 邢锴；

【导师】 张宏伟；

【作者基本信息】 天津大学 ， 环境工程， 2010， 博士

【摘要】 针对污水深度处理中的MBR-RO组合工艺,以MBR膜污染机理、缓解MBR膜污染、RO膜污染机理、缓解RO膜污染为四个研究方面,系统地分析了MBR-RO组合系统中的膜污染问题。平行实验表明,中空纤维膜MBR的膜面附着物是污泥泥饼层,而板式膜MBR的膜面附着物是一层二次动态膜,它可以缓解作为板式膜主要污染因素的膜孔堵塞污染;由于泥饼层的作用,EPS与中空纤维膜的膜污染相关性良好,而在板式膜中,EPS与其膜污染相关性很差,并且二次动态膜显著降低了SMP与膜污染的相关性;在板式膜运行过程中,二次动态膜起到了初期缓解膜污染,后期加剧膜污染的作用。运行中试规模板式膜MBR,发现在反应器空间内,污泥EPS的分布并不均匀,而是呈现一定的规律。在水平方向上,EPS呈现出两端高中间低的分布形式,在深度方向上,EPS随深度的增加而降低。这与膜组件的曝气形式和进水方式有关;运行小试规模中空纤维膜MBR,发现加入PAC或者运行好氧颗粒污泥都可显著缓解膜污染。颗粒污泥拥有更好的过滤性能,但在膜面的累积过程中,大粒径的污泥发生了破碎,相比混合液,泥饼层中污泥EPS的含量明显增高。以BSA和藻酸钠代表MBR产水中的有机物,运行RO系统,发现藻酸钠对膜污染的影响高于BSA的影响,BSA与藻酸钠共存时会产生交互作用,显著增加了有机物的污染程度。溶液化学成分中,Ca2+以架桥作用络合了有机物的羧基官能团,加速了有机物的聚集,对有机物污染有高度显著的影响;Mg2+的影响次之;离子强度可改变有机物的电性,显著影响有机物污染的程度。上述三者之间不具有交互作用。有机物会在膜面形成厚密的凝胶层,引起严重的膜污染,且其粘性大于膜本身的粘性,加剧了有机物的聚集。MBR-RO组合系统处理市政污水时可以得到非常优良的水质。在系统运行中,以RO的膜污染机理为理论基础,研究盐水定期冲洗和加入CER预处理对缓解RO膜污染的效果。结果表明,NaCl溶液定期冲洗可显著缓解膜污染,这是因为高浓度的Na+不但可以置换出架桥于有机物之间的二价阳离子,而且其产生的渗透压可以迫使污染层发生膨胀,减弱了有机物分子间的结合;CER预处理显著消减了RO进水中二价阳离子的浓度,减轻了有机物与其络合的程度,有效缓解了有机物污染的发生,延长了RO的使用周期。更多还原

【Abstract】 In combined MBR-RO process for advanced wastewater reclamation, the membrane fouling was studied systematically in four aspects: mechanism of membrane fouling in MBR, reduction of membrane fouling in MBR, mechanism of membrane fouling in RO, reduction of membrane fouling in RO.The parallel experiments show that the object on hollow fiber membrane is sludge cake, but the one on flat sheet membrane is secondary dynamic membrane. Sludge cake and pore block are thought to be the dominating fouling factors in hollow fiber membrane and flat sheet membrane, respectively, but secondary dynamic membrane can reduce pore block fouling. Further more, EPS only significantly affects the fouling of hollow fiber membrane because of the sludge cake, besides, secondary dynamic membrane largely reduces the correlation between SMP and fouling of flat sheet membrane. In long term operation, it is believed that secondary dynamic membrane can reduce membrane fouling in the beginning but accelerate membrane fouling at the last.The results of a pilot-scale flat sheet membrane MBR show that EPS is not uniformly distributed in the reactor. In the horizontal plane, the content of EPS is lowest in the center, and in the vertical plane, the content of EPS reduces with depth increasing. The distribution is effected by the located position of perforated pipe and the influent mode. In a bench-scale hollow fiber membrane MBR, dosing PAC and using granular sludge can both reduce membrane fouling. The filterability of granular sludge is better than that of floc sludge, but in operation, granular sludge is easily broken. It is appeared that the content of EPS in sludge cake is larger than that in the mixed liquor, both in floc sludge and granular sludge.Bovine serum albumin （BSA） and sodium alginate were used as models of protein and polysaccharides, which represent the organics in effluent of MBR in MBR-RO system. The experiments show that the impact of alginate on membrane fouling is more significant than that of BSA, and the synergistic influence between them can enhance membrane fouling notably. Fouling is observed to be more severe in the presence of Ca2+ compared to Mg²⁺ due to its ability to bridge organic substances that results in denser fouling layer. Increase in the ionic strength lead to weaker electrostatic repulsion, and hence more rapid fouling. And there are no synergistic influences between the three chemistries mentioned above. Lastly, the images of fouling layer illustrate that the gel of organic matter on membranes is thick and dense, which can induce severe membrane fouling.The effluent quality of MBR-RO system treating municipal wastewater is very good. In operation, the effect of periodical washing by salt water and using cation exchange resin （CER） as a pretreatment to reduce RO membrane fouling were studied. The results show that NaCl solution can effectively reduce membrane fouling in two ways. First, Na⁺ replaces the Ca²⁺ between organic substances. Second, the high osmotic pressure caused by high salt concentration can expand the fouling layer; CER process can remove divalent cation effectively, which alleviates the aggregation of organic matters, and as the result, the organic fouling of RO is reduced.更多还原