膜生物反应器生物污染的成因及防治研究
文献类型：学位论文
| 作者 | 罗金学 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 庄国强 ; Yehuda Cohen |
| 关键词 | 膜生物反应器 膜生物污染 生物膜 微生物群落 一氧化氮 membrane bioreactor biofouling biofilm microbialcommunity nitric oxide |
| 其他题名 | Formation mechanisms and control of biofouling in submerged MBRs |
| 学位专业 | 环境科学 |
| 中文摘要 | 膜生物反应器是一项结合了活性污泥介导的生物降解和高分子有机膜介导的水泥分离的污水处理技术。与传统的污水处理工艺相比，膜生物反应器有如下优势，比如较少的反应器空间、较少的污泥排放，以及高质量的出水。但是，膜生物反应器存在一个内在的技术缺陷，即膜表面生物污染的产生。膜表面生物污染层会增加膜的滤水阻滞，导致出水透膜压力的升高或者出水流量的降低。因此，膜表面生物污染的形成机理与防治研究迫在眉睫。 生物污染是由微生物细胞和生物大分子在滤膜上沉积造成的。它会堵塞滤膜，降低膜生物反应器的处理效率。本研究中，我们对4种生物膜的组成成分，即Alpha-多糖、Beta-多糖、蛋白质和微生物细胞，在生物污染发生发展过程中的作用进行了研究。研究发现，这4种生物膜成分的生物量的增加都与膜生物反应器中透膜压力的上升呈正相关的关系。其中，蛋白质在透膜压力快速跃升过程中是含量最丰富且增长速率最快的成分。通过研究生物污染成分的空间分布，我们发现在压力增长过程中至少60%的生物大分子成分与微生物成分的分布是共定位的关系。这说明这些生物大分子很可能是由这些微生物细胞分泌的，并且生物污染的发生是由生物膜在滤膜上的生长造成的。因此，控制生物膜的生长有可能成为减少生物污染现象发生的一个有用手段。 生物膜的形成是膜生物反应器中膜生物污染的关键原因。本实验研究了在透膜压力增长过程中微生物群落在膜生物污染中的组成及变化。定量PCR结果表明在生物污染中细菌所占的微生物比重远高于真菌以及古菌，真菌次之，古菌最低。无论在低透膜压力阶段还是在高透膜压力阶段，生物膜微生物群落与污泥微生物群落是不完全相同的。相对于污泥微生物群落，伯克氏菌目（Burkholderiales）、假单胞菌目（Pseudomonadales）和根瘤菌目（Rhizobiales）在生物膜中得到了富集。而且，生物膜微生物群落在透膜压力增长过程中发生了分化。这种微生物群落的分化早于透膜压力由缓慢增长向快速增长的转变。在生物膜微生物群落的演变过程中，红环菌目（Rhodocyclales）在生物膜中逐渐被稀释，而红螺菌目（Rhodospirillales）、鞘脂单胞菌目（Sphingomonadales）和根瘤菌目（Rhizobiales）越来越占主导地位。这种微生物群落的演变有可能是导致透膜压力快速跃升的原因。通过控制这些目标微生物的生物膜形成有可能减缓透膜压力的增长，并控制生物污染现象的发生。 膜生物污染是膜生物反应器在污水处理中更广泛应用的限制因素。本实验研究了一种利用一氧化氮诱导生物膜分散来控制膜生物污染的方法。在高透膜压力（TMP）状态下，滤膜表面被成熟生物膜所覆盖。此时，向滤膜反冲洗80 μM PROLI NONOate溶液37天后，生物污染出水阻力（Rf）的增长减慢了75%。当从反应器运行的起始阶段开始定期用80 μM PROLI NONOate浸泡滤膜85天后，透膜压力TMP和生物污染出水阻力Rf的增长分别减缓了32.3%和28.2%。焦磷酸测序（pyrosequencing）分析显示PROLI NONOate处理并没有改变生物膜的主要微生物种类。但是， PROLI NONOate处理组生物膜第85天的细菌群落与对照组生物膜第71天的细菌群落的相似度要高于其与对照组生物膜第85天的细菌群落的相似度，这说明生物膜细菌群落的演变因PROLI NONOate处理而减缓。同时，某些生物膜微生物菌群的丰度因PROLI NONOate的处理而降低。这些微生物菌群包括硫发菌目（Thiotrichales）、芽单胞菌目（Gemmatimonadales）、黄色单胞菌目（Xanthomonadales）、肉座菌目（Hypocreales）和球囊霉目（Glomerales）。激光共聚焦显微镜观察显示生物膜中的生物多聚物和微生物细胞组分的生物量都因PROLI NONOate的处理而有所降低。其中，蛋白质减少了37.7%，微生物细胞减少了66.7%。这些结果表明一氧化氮处理是控制膜生物反应器中生物污染的一条可能的途径。 |
| 英文摘要 | Membrane bioreactors （MBRs） are increasingly being applied in modern wastewater treatment plants. Biofouling of the MBRs represents a significant challenge in the application of membrane based technologies for water purification, which is the build-up of organic and biological cake-layers on the membranes that may block the membrane pores. The biofouling layers reduce membrane permeability and increase the hydraulic resistance of the membrane. Thus, membrane fouling results in an increase of the trans-membrane pressure （TMP） when operated at a constant flux or a decreased flux when operated at a constant pressure. Therefore, it is necessary to identify the relative contribution of microbes and macromolecules to the biofouling process in order to develop appropriate strategies to reduce fouling and hence increase operational efficiency. Two identical laboratory-scale MBRs were operated at a low, constant flux （13-15 LMH） to treat artificial synthetic wastewater （TOC of 200 mg/L）. The TMP was maintained at a low pressure （3-15 KPa）, steady state for the first 80-87 days of operation and then was observed to increase exponentially from 15 to 90 KPa over 30 days. The biofouling layers on the hollow fiber membrane surfaces were observed to contain significant amounts of Alpha--polysaccharides, Beta--polysaccharides, proteins and microorganisms that were always present on the hollow fiber membranes, even during the early stages of MBR operation when the TMP was still in the low pressure phase. The quantitative image analysis indicated that each of these components on membrane correlated positively with the TMP increase, Pearson’s correlation coefficients 0.7-0.95. Among the four components, the proteins increased fastest when the TMP was rapidly increasing and comprised the greatest proportion of the individual components when TMP increased. This indicated that the production of proteins was more important than the two types of polysaccharides or the cells during the transition of from the low to high TMP stage. Additionally, co-localization analysis revealed that approximately 50% of the EPS co-localized with 80-90% of the cells. The co-localization data indicated that the majority of the EPS components were closely associated with the cells, suggesting that the EPS components may be the byproducts of microorganisms on membrane rather than being randomly distributed on the membrane from the aqueous phase. Therefore, formation of microbial biofilms on the membranes is the key driver of the biofouling process in MBR. Thus, it is vital to develop methods to prohibit or reduce biofilm formation on the membranes in situ or to disperse the mature biofilms. As part of the development of novel strategies to control biofilms on membranes, it is also essential to determine if the biofilm is formed by a selected subset of microorganisms in the sludge community or if biofilm formation is a stochastic process. The qPCR results indicated that the bacteria were the most abundant microbial community in biofilm, which was followed by fungi and archaea. Therefore, the microbial biofilm community was investigated through 16S tagged pyrosequencing at different stages of the biofouling process. At low TMP, the biofilms were most highly similar to the sludge and as the biofilm developed, and as the TMP increased, the biofilm communities diverged from the sludge. Ultimately the biofilm community appeared to be distinct from the sludge and the greatest differences were seen for the bacterial community. This was mostly seen in subtle shifts in the percentage composition, but was still dominated by the same groups. Compared to the community in sludge, the bacteria including Burkholderiales, Pseudomonadales and Rhizobiales were enriched in the biofilm, indicating these microorganisms had stronger ability to form sessile biofilm rather than live in the planktonic sludge. Additionally, during the process of TMP increase, the Alphaproteobacteria, represented by Rhodospirillales, Sphingomonadales and Rhizobiales in this project became more dominant in late biofilms, indicating these organisms may contribute more to the construction of late biofilms rather the early biofilm and may play an important role to the TMP increase in the biofouling process. These results indicated that the change of microbial community that occurred before the TMP jump may be the most important in its effect on biofouling process. It may be possible to target those organisms to ultimately delay their incorporation into the biofilm and hence delay the TMP jump. Finally, strategies based on nitric oxide （NO） induced biofilm dispersal were tested to control biofilm formation and TMP rise in the MBR. The potential for NO to control biofilms in MBR systems was tested using two distinct approaches. The first was to disperse pre-established, mature biofilms that had developed during MBR operation and the second was to prevent biofilm accumulation by applying the NO from the beginning of the MBR operation. The results showed that treatment using the NO donor PROLI-NONOate resulted in a 75% （in pre-established biofilm dispersal experiment） and 28.2% （in the biofilm prevention experiment） reduction of fouling resistance. The CLSM analysis showed that, in the biofilm prevention experiment, the NO treatment also resulted in a reduction of biofilm biomass, for both cells （66.7% reduction） as well as macromolecules （e.g. 37.7% reduction for proteins）. Pyrosequencing analysis of rRNA indicated that the bacterial Orders of Thiotrichales, Gemmatimonadales and Xanthomonadales and fungal Orders of Hypocreales and Glomerales were reduced in abundance by the PROLI NONOate treatment. Furthermore, the succession of the bacterial community was delayed, but not entirely prevented, by the PROLI treatment. These results demonstrated that the NO donor PROLI NONOate had the potential to control biofouling in a MBR. |
| 公开日期 | 2015-06-16 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/13482]  |
| 专题 | 生态环境研究中心_中国科学院环境生物技术重点实验室 |
| 推荐引用方式 GB/T 7714 | 罗金学. 膜生物反应器生物污染的成因及防治研究[D]. 北京. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：生态环境研究中心
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