【作者】 张劲松；

【导师】 周集体； Anthony Gordon Fane；

【作者基本信息】 大连理工大学 ， 环境工程， 2007， 博士

【摘要】 浸没式膜生物反应器(SMBR)日益广泛的应用于城市污水和工业污水的处理上。MBR的成功运行与经济性和膜污染紧密相关。SMBR中，在给定通量(flux)条件下，膜污染主要表现透膜压力(TMP)的上升。MBR的膜污染十分复杂并受到反应器的设计特点、操作模式和生物学因素的影响。因此，降低膜污染，提高MBR的表现需要综合考虑解决办法。本论文探索了膜污染的机理和各种改善MBR可持续操作的策略。在膜污染机理的研究中，透膜压力的上升被描述为三个阶段：第一阶段发生在初始的几小时内，由于膜孔的缩窄或堵塞造成的膜表面特性的改变，导致透膜压力突然的上升。第二阶段表现为透膜压力的长时间慢速上升过程，主要原因是膜表面的胞外高分子物质(EPS)累积。膜表面EPS主要来源是膜对混合液中的EPS截留。第三阶段是透膜压力的突然跃升并导致膜过滤无法继续操作，形成这一阶段有多种原因，但都符合恒通量过滤中膜污染自我加速的基本特点。为了理解SMBR膜污染的复杂特性，“污染路线图”揭示了膜生物反应器的操作和设计特点与一般污染因素(例如：被过滤液的特性、膜本身的特性、流体力学条件等)的联系。MBR的污染机理图描述了3阶段的污染和相应的多样化的污染机理。在相同的污泥条件下，利用Millipore公司的系列微滤和超滤膜，考察了膜的材质和孔径对于膜的污染特性和截留特性的影响。膜材质、孔径的不同主要影响微滤膜在初始阶段膜污染，表现在初始透膜压力的跃升程度不同。不同操作通量下，不同孔径的膜对有机物的截留能力随污染程度的加重而提高。凝胶渗透色谱(GPC)试验结果表明，微滤膜在污染后对有机高分子聚合物都有一定的截留作用。通过对污染后膜表面特性的考察发现，污染后膜表面的ZETA电位受活性污泥混合液的ZETA电位影响并与活性污泥混合液ZETA电位相似。被污染膜的傅里叶变换红外光谱图显示，污染后膜表面发生了多糖类与蛋白质的附着。共聚焦激光扫描电子显微镜(CLSM)与场发射扫描电镜(FSEM)照片显示，低通量下污泥颗粒的附着并不严重，高通量下会迅速形成EPS与污泥颗粒混合的滤饼层。应用通量阶梯方法，通过对超滤及微滤的平板和中空纤维膜的考察，建立了可持续通量的确定方法，也同时建立了MBR中膜污染的比较方法。在存在一定误差情况下，能够通过短时间的通量阶梯试验来大致预测长周期的膜污染情况。污泥停留时间(SRT)作为MBR的重要操作参数会影响活性污泥的生物特性进而影响膜污染。DGGE图说明了随着污泥停留时间的延长，污泥中占主导地位的菌群发生了变化。污泥停留时间10天和30天时，在相同的进水体积负荷条件下，包含了活性污泥上清液中溶解态和污泥絮体上附着态EPS之和的总EPS浓度相似，然而，EPS的溶解态和附着态分布比例不同。上清液中占主导的多糖类的EPS随污泥停留时间延长而降低。活性污泥混合液的黏度随污泥停留时间延长而升高，然而由曝气引发的液相流速相近。通量阶梯试验结果显示污泥停留时间延长能够降低膜污染速率(dTMP／dt)，提高可持续通量。在恒通量20L／m~2·h(LMH)下长时间运行中发现，延长污泥停留时间，长期膜污染程度降低。采用两个平行运行160天的MBR，在相同平均污泥负荷条件下，分别采用恒定负荷和波动负荷进水，活性污泥在非稳态与稳态条件下微生物代谢特性不同。通量阶梯试验与长时间过滤实验证明，在80天的非稳态时，波动负荷条件下的膜污染高于其在恒定负荷条件下。在达到稳态条件下，波动负荷条件下的膜污染低于其在恒定负荷条件下。微生物代谢比较发现，上清液中的SMP、多糖类的EPS以及污泥颗粒粒径是影响膜污染的主要因素，并导致了稳态与非稳态下膜污染结果的差异。稳态条件下，波动负荷的活性污泥的比耗氧速率远远高于恒定负荷的活性污泥的比耗氧速率，推测可能其活性污泥中处于活跃状态的微生物比例高，从而降低了“F／M”，并导致了两种活性污泥的EPS代谢差异。在MBR平行比较实验中，通过应用增强膜过滤表现的高分子絮凝剂(MPE50)来研究絮凝剂对膜污染的影响。通量阶梯试验结果显示，加入MPE后能使反应器的可持续通量高于空白反应器50％。长周期的实验结果表明，在可持续通量的范围内，加入MPE轻微改善膜污染。高于可持续通量，加入MPE后的MBR的膜污染显著减轻。通过MPE的絮凝作用，提高了污泥的粒径分布，降低了上清液中SMP和EPS浓度(主要是多糖类的EPS物质)。停止加入维持剂量的MPE，应用MPE的膜生物反应器的膜污染比空白反应器严重。停止加入MPE后，污泥粒径虽有下降，但依然大于空白污泥。停止加入MPE会造成上清液中SMP和EPS浓度大幅提高。通过膜污染比较发现，上清液中SMP和EPS浓度比污泥粒径对膜污染影响显著，是造成膜污染主要原因。采用连续出水和间歇出水操作方式的对比实验结果表明，间歇出水操作能有效控制污染速率并防止透膜压力的较快跃升：在低于可持续通量操作时，间歇出水操作能推迟透膜压力跃升出现。在高于可持续通量操作时，间歇出水操作能降低透膜压力快速上升。主要原因是通过间歇出水，控制了滤饼层的厚度和密度。更多还原

【Abstract】 The submerged membrane bioreactor (sMBR) is being increasingly applied for municipal and industrial wastewater treatment. The success and economics of the membrane bioreactor (MBR) is linked to the fouling of the membranes, Which is manifest in a rise in transmembrane pressure (TMP) at a given flux. Fouling in MBRs is complex and influenced by MBR design features, mode of operation and biological factors. Thus, the enhancement of MBR performance, which involves minimizing fouling, will require a range of solutions. This thesis explores membrane fouling mechanisms and various strategies to improve the sustainable operation of membrane bioreactors (MBRs).In membrane fouling study, the rise in TMP is described as a 3-stage process. Stage 1 occurs in a period of a few hours and involves abrupt TMP rise-up due to ’conditioning’, presumably by pore blockage and closure. Stage 2 is a prolonged period of slow TMP rise, which we ascribe to accumulation of extracellular polymeric substances (EPS). Stage 3 is a sudden rise in TMP, which rapidly leadsto inoperability of the membranes. This stage could have several causes, which are all driven by the self-accelerating nature of fouling under constant flux operation. In order to understand the complex nature of fouling in submerged MBRs, the MBR fouling ’Roadmap’ has been developed that shows the relationship between the many operational and design characteristics of the MBR and the generic ’fouling factors’, i.e. the nature of the feed (to the membrane), the membrane properties, and the hydrodynamic environment. MBR ’Fouling mechanism map’ which depicts the 3 stages of fouling and the multiple fouling mechanisms that could occur has been also presented.Under the same activated sludge condition, using Millipore series MF and UF membrane, the effect of membrane material and pore size on membrane fouling and SMP rejection have been studied. The initial fouling in TMP "jump" is mainly affected by different material and pore size of MF membrane. At different flux, the TOC rejection by MF membrane in different pore size is stronger and stronger with membrane fouling intensity increassing. Gel Permeation Chromatography (GPC) results show the fouled MF membranes are able to reject EPS, the rejection ability is linked to membrane pore size and fouling intensity. Through the investigation on surface fouling property of fouled membrane, the surface zeta potential of fouled membrane is affected by the activated sludge property. The zeta potential of fouled membrane surface is similar to the activated sludge. The Fourier Transform Infrared Spectroscopy (FTIR) result shows polysaccharide and protein deposit on the membrane surface. Images of Confocal Laser Scanning Microscope (CLSM) and Field Emission Scanning Electron Microscope (FSEM) show the deposit of activated sludge particles is not serious at low flux, while at high flux, EPS and the activated sludge particles will form combined cake layer.Applying Flux-stepping method, through the investigation of flat sheet and hollow fibre MF and UF membrane, the "sustainable flux" determination method and membrane fouling comparison method in MBR are set up. The short-term flux-stepping experiment results are able to predict long-term membrane fouling in MBR despite some errors.Sludge Retention Time (SRT), an important operating parameter of the MBR as it affects the biological characteristics of the sludge and therefore influences membrane fouling. The DGGE profiles suggest a shift in the dominant bacterial community with the prolonged SRT. The total amount of extracellular polymeric substance (EPS) extracted from the floc and the supernatant is approximately constant at the two SRTs under the same organic loading rate. However, The EPS distribution is different. The polysaccharide EPS is dominant in the supernatant EPS, its concentration is decreasing with prolonged SRT. The viscosity of the biomass increases with the prolonged SRT, while the estimated average air induced water velocity is almost same for at the two SRTs. The results of flux stepping tests show that the membrane fouling rate (dTMP/dt) can be decreased and "sustainable flux" can be increased with prolonged SRT. Long-term experimental run at a constant flux of 20 L/m~2.h clearly shows long term fouling is decreased with prolonged SRT.Two parallel lab scale MBRs have been operated for 160 days. Under the same average sludge loading rate, fed with constant concentration synthetic wastewater and regularly variable concentration wastewater to simulate the daily feed fluctuation, the activitated sludge properties are different in stable and unstable state. In 80days unstable state (stage 1), the membrane performance at variable loading is worse than that at constant loading; while in the stable state, the result is reverse. The difference in microbial activities of activitated sludge shows SMP, polysaccharide in supernatant and particle size has been found to impact the fouling and cause the difference on membrane performance in stable state and unstable state.In stable state, the SOUR of sludge at variable loading is higher than that at constant loading, presumably the active bacteria ratio is high in the sludge at variable loading and the "F/M" is decreased, which result in the difference of EPS production by the two kinds of sludge.The polymeric membrane performance enhancer (MPE50) has been applied in two parallel submerged membrane bioreactors to test its effect on membrane fouling. The ’critical flux’ determined by the flux stepping test has been increased by 50% after the addition of MPE. Long-term experiments results show, below the "sustainable flux", the membrane performance of MBR with MPE is slightly improved. Above the "sustainable flux", the addition of MPE is found to apparently.mitigate membrane fouling. The possible explanations for these results are the increased in the particle size distribution of the activated sludge as well as the decreased in SMP and EPS (mainly polysaccharides) concentrations in the supernatant due to MPE flocculation. After the termination of the maintenance MPE addition, the particle size doesn’t drop too much, while the supernatant EPS and SMP concentration increase dramatically. The membrane performance has been found to be worse than the MBR without MPE, which suggests that SMP and is the dominant fouling factor, membrane fouling will be affected stronger by supernatant polysaccharide than the particle size of sludge.The comparison result shows intermittent permeation is able to control fouling rate and prevent TMP jump. Below sustainable flux, intermittent permeation operation is able to postpone TMP jump. Above sustainable flux, intermittent permeation operation is able to decrease the TMP increase rate at high flux. The main possible reason is the cake layer thickness and density is controlled by intermittent permeation.更多还原