Fe3+对MBR减缓膜污染的研究进展

膜生物反应器(membrane bioreactor, MBR)作为一种高效的污水处理及回用工艺,比传统的活性污泥法具有更多优势。然而,膜污染问题是限制其广泛应用的关键性问题。众多研究者已证实Fe₃₊能有效的改善MBR中混合液的可滤性及减缓膜污染。本文简述了MBR污泥混合液中主要污染物—胞外聚合物(extracellular polymeric substances, EPSs),并总结Fe₃ 在去除混合液中污染物、减缓膜污染方面的效能及其对污泥混合液的影响。最后,对Fe₃ 在减缓MBR膜污染的未来研究方向进行展望。     

不同价态铁离子对膜生物反应器影响研究进展

膜生物反应器(Membrane bioreactor,MBR)作为一种新型的污水处理技术,近些年来备受关注。然而,膜污染问题成为了该工艺广泛应用的最大障碍。现已证明,向MBR中投加铁系混凝剂能够减缓膜污染。本文首先综述了不同价态铁离子对MBR污染物去除的影响,然后对铁离子在污泥混合液中分布及迁移转化进行了分析,接着阐明了铁离子对膜污染的影响,最后对该领域的研究进行了展望。     

抗污染薄层复合聚酰胺膜的结构设计及改性策略

由活性层和支撑层组成的薄层复合(TFC)聚酰胺(PA)膜,是目前广泛应用于纳滤、反渗透、正渗透和压力延迟渗透过程中的高性能脱盐膜,具有水通量大和截盐率高等优异性能。然而,由于TFC-PA膜存在活性层疏水性强、支撑层孔径大等特点,致使TFC-PA膜在实际使用过程中极易受到膜污染,制约了TFC-PA膜的进一步推广和使用。本文讨论分析了TFC-PA膜的结构特点和表面性质,总结归纳了在不同膜过程中TFC-PA膜污染形成的原因及特点,详细论述了国内外抗污染TFC-PA膜的研究进展。本文重点介绍了活性层抗污染改性和支撑层抗污染改性方法,并对其抗污染机理以及存在的问题进行了阐述与分析,最后对抗污染TFC-PA膜的结构设计与表面改性策略进行了总结及展望。     

NaClO原位清洗对膜生物反应器生物膜污染影响研究进展

膜生物反应器(MBR)的膜污染问题严重制约了该工艺进一步快速的商业化推广,全面认识NaClO原位氧化清洗对MBR生物膜污染的影响,对于开发新型膜清洗技术及MBR工程优化具有重要意义。本文从微生物胞外关键组分空间分布角度综述了NaClO原位清洗对生物膜污染及生物絮凝的影响,并探讨了生物絮体重构机制及强化生物絮凝的相关措施。最后,本文从减缓膜污染的角度,对该领域未来的研究方向进行了论述。     

锇-聚乙烯吡啶复合物与辣根过氧化物酶分子多层膜的制备及电化学性质研究

基于分子间静电相互作用力,将锇-聚乙烯吡啶复合物(PVP-Os)与辣根过氧化物酶(HRP)交替沉积于固体基质表面,制得了包含生物成分的分子多层膜.膜层间的聚合物分子起到了粘接与导电的双重作用.用紫外-可见光谱法跟踪了石英基片上的组装过程,研究了多层膜电极对过氧化氢的电催化还原性能,并描述了多层膜电化学行为.     

锇—聚乙烯吡啶复合物与辣根过氧化物酶分子多层膜的制备及其电化学性质研究

基于分子间静电相互作用力，将锇－聚乙烯吡啶复合物（PVP－OS）与辣根过氧化物酶（HRP）交替沉积于固体基质表面，制得了包含生物成分的分子多层膜，膜层间的聚合物分子起到了粘接与导电的双重作用，用紫外－可见光谱法跟踪了石英基片上的组装过程，研究了多层膜电极对过氧化氢的电催化还原性能，并描述了多层膜电化学行为。     

膜生物反应器中AHL分析技术研究进展

膜生物污染一直是膜生物反应器(membrane bioreactor,MBR)在废水处理工艺中需要解决的一大难题。最近研究表明：基于群体感应的淬灭技术可以作为MBR活性污泥体系中一种有效的膜生物污染防治策略。因而,识别和分析群体感应产生的信号分子是应用群体淬灭技术防治MBR中膜生物污染的关键。本文首先介绍了活性污泥体系中的群体感应机理和N-酰基高丝氨酸内脂(N-acyl homoserine lactone,AHL);其次,归纳近期研究中针对MBR中AHL定性和定量分析方法;最后,对MBR中AHL识别及分析技术应用进行了展望。     

铁系混凝剂的投加对膜生物反应器运行效能的影响

膜生物反应器(MBR)作为一种高效的污水处理及回用工艺,与传统活性污泥法相比具有众多优势。然而,膜污染问题限制了该工艺的进一步大规模应用。众多研究者已证实,投加铁系混凝剂能有效改善MBR中混合液的可滤性,从而减缓膜污染。本文首先介绍了胞外聚合物对膜污染的影响机制,然后总结了铁系混凝剂投加对MBR污染物去除、膜污染速率及Fe3+在污泥混合液中的分布的影响;最后,对铁系混凝剂在MBR中应用进行了展望。     

磷脂膜色谱及其在药物跨膜转运评价中的应用

磷脂膜色谱是固态基质上的有序磷脂分子单层体系采用色谱学方法仿真药物与细胞膜相互作用过程,可用来评价药物的细胞膜渗透性和活性。硅胶表面上的磷脂单分子层模拟了单层细胞膜,因此药物的磷脂膜色谱保留行为可用于预测药物与细胞膜的相互作用。目前考察药物跨膜转运的模型主要有正辛醇/水系统、脂质体/水系统、反相色谱（ODS）以及磷脂膜色谱。与前述3种系统比较,磷脂膜色谱除了具有高效、简便等特点外,同时能模拟药物与生物膜之间疏水作用力以外的其他作用力,因此对磷脂膜色谱的研究也越来越深入。由于药物细胞膜渗透性对其有效性和安全性起着关键作用,因此磷脂膜色谱在新药研发早期阶段的介入可以有效地降低后期候选药物的淘汰率,提高新药的研发效率。该文就磷脂膜色谱的研究及在药物跨膜转运评价中的应用进行了综述。     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（AFM）对有机分子HTDIOO单层和多层LB膜结构进行了观察·实验结果表明，针尖与LB膜表面分子间的相互作用力会对成像的膜结构有影响．当悬臂针尖与LB膜表面分子的相互作用力较大时，针尖会扰动HTDIOO分子在单层LB膜中的有序排列．HTDIOO单层LB膜具有有序结构；而在多层LB膜中，HTDIOO分子则聚集在一起形成了一定的畴结构．     

Visualisation of polysaccharide fouling on microporous membrane using different characterisation techniques

Although many studies assessed fouling behaviour in microporous membrane processes like membrane bioreactors (MBRs), in situ or direct observation of the fouling layer has not yet been possible. The observation of the fouling layer resulting from the filtration of model solutions allowed better understanding of MBR fouling intensity and mechanisms. In this study, alginate has been used as a model for polysaccharide (one of the main foulants in MBRs). Three visualisation techniques, confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM), and direct observation (DO) have been tested to observe the alginate fouling. The work presented in this paper revealed the advantages and limitations of each technique used for this specific application. Although no coating is required for this technique, ESEM allowed distinct non-destructive observation of clean membrane. However, the lack of structure in the alginate fouling layer limited the use of this technique for fouled membranes. While CLSM requires the use of expensive fluorescent markers, DO appeared as the most promising technique for direct and in situ observation of MBR fouling. DO of alginate/bentonite and alginate/bacteria solutions revealed the creation of a well-structured dual fouling system (bentonite-concentrated layer of 50 μm embedded and covered by a concentration polarisation of alginate greater than 240 μm) on the surface of hollow fibre membrane.     

Mitigated membrane fouling in a vertical submerged membrane bioreactor (VSMBR)

In a laboratory-scale study, characteristics of membrane fouling in an A/O (anoxic/oxic) series membrane bioreactor (MBR) and in a vertical submerged membrane bioreactor (VSMBR) treating synthetic wastewater were compared under the same operating conditions. Accordingly, fouling characteristics of a pilot-scale VSMBR treating municipal wastewater were studied under various operating conditions. Various physical, chemical, and biological factors were used to describe membrane resistances. As a result, it was concluded that high concentrations of extracellular polymeric substances (EPS), high viscosity and a high sludge volume index (SVI) corresponded to high membrane resistance indicating severe membrane fouling in both the laboratory-scale MBRs and the pilot-scale VSMBR. In addition, high fouling potential was observed in the pilot-scale VSMBR at 60-day sludge retention time (SRT). In this case, as hydraulic retention time (HRT) decreased from 10 to 4 h, EPS concentrations increased and the average particle size increased, leading to reduced settling of the sludge and increased membrane fouling. To mitigate fouling, two different methods using air bubble jets were adopted in the pilot-scale VSMBR. As a result, it was found that air backwashing was more efficient for fouling mitigation than was air scouring.     

Impact of gel layer formation on colloid retention in membrane filtration processes

Colloidal particles in the feed streams of membrane filtration processes control membrane fouling rate in many instances. In this study, the non-gelling colloidal Na-alginate and the gelling colloidal Ca-alginate are employed to investigate the significance of gel layer formation in membrane filtration processes in terms of contribution to membrane fouling and supplementary impurity removal. The results show that contribution of colloidal particles to membrane fouling depends on the gelling propensity of the colloids and the operational mode (constant pressure or constant flux) implemented. A small dose of either Na-alginate or Ca-alginate was found to greatly increase membrane fouling rate during constant pressure filtration. Both the resistance to removal by application of shear and the lower susceptibility of the concentration polarization layer to shear resulted in more severe fouling during constant flux filtration in the presence of Ca-alginate assemblages than in the presence of Na-alginate. Apparent channel sizes of the Ca-alginate gel layer were calculated from the material properties of the fouling layer. Incomplete catalase retention highlighted the likely heterogeneity in size of liquid transport pathways. Adsorption also contributed to the trapping of colloidal particles according to the retention behaviour of BSA by the Ca-alginate gel layer. Gel layer formation propensity should be seriously considered for the operation of membrane filtration processes. Two simple methods based on (i) a permeability recovery experiment and (ii) comparison of dead-end filtration behaviour with and without shear application are proposed for evaluation of the gelling propensity of colloidal dispersions.     

Fouling in direct contact membrane distillation process

The formation of deposit on the membrane surface (fouling) is one of the major operating problems of membrane distillation process. The influence of fouling on the performance of this process was investigated during the concentration of wastewater with proteins, bilge water, brines, and the production of demineralized water. The experiments were performed with polypropylene capillary membranes. The morphology and composition of the fouling layer were studied using Fourier transform infrared with diffuse reflectance spectroscopy and scanning electron microscopy coupled with the energy dispersing spectrometry. Fouling with various intensity was observed in most of the studied cases. Permeate flux decline was mainly caused by an increase in the heat resistance of the fouling layer. However in the case of non-porous deposit, a magnitude of the permeate flux was also determined by a resistance of water transport through the deposit layer. It was found the deposits were formed not only on the membrane surface, but also inside the pores. Salt crystallization in the membrane pores besides their wetting, also caused the mechanical damage of the membrane structure. The intensity of the fouling can be limited by the pretreatment of feed and a selection of the operating conditions of membrane distillation.     

Experimental study of ultrafiltration membrane fouling by sodium alginate and flux recovery by backwashing

Membrane fouling is the major limitation for a broader application of membrane technology. One of the main causes of membrane fouling in advanced wastewater reclamation and in membrane bioreactors (MBR) are the extracellular polymeric substances (EPS). Among the main constituents in EPS, polysaccharides are the most ubiquitous. This study aims at a better understanding of the fouling mechanisms of EPS and the efficiency of backwashing technique, which is applied in practice to restore membrane flux. For that purpose, the evolution of fouling by sodium alginate, a microbial polysaccharide, is studied in ultrafiltration. Fouling experiments are carried out in a single fiber apparatus, aiming at identifying the significance of distinct fouling mechanisms and their degree of reversibility by backwashing. An important parameter considered in the study is the concentration of calcium ions, which promote sodium alginate aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. A rapid irreversible fouling takes place due to internal pore constriction, at the beginning of filtration, followed by cake development on the membrane surface. With increased calcium addition, cake development becomes the dominant mechanism throughout the filtration step. Furthermore, fouling reversibility is increased with the increase of calcium concentration. A unique behavior of sodium alginate solution in the absence of calcium is also noted, i.e. the formation of a labile layer on the membrane surface, which is affected by the small cross-flow that exists inside hollow fibers, even in the nominally dead-end mode of operation.     

State-of-the-art of membrane bioreactors: Worldwide research and commercial applications in North America

Membrane bioreactor (MBR) technology is advancing rapidly around the world both in research and commercial applications. Despite the increasing number of studies and full-scale applications of MBR systems, directions and trends in academic research as well as commercial developments require further analysis. This paper aims to critically characterize and review worldwide academic research efforts in the area of MBRs as well as focus attention to commercial MBR applications in North America. A total of 339 research papers published in peer-reviewed international journals from 1991 to 2004 and a total of 258 full-scale MBR installations in North America were used as the database for the analysis provided in this paper. After a surge of MBR publications in 2002, research appears to have reached a plateau in the last 3 years using both submerged and external MBR units. Although much of the pioneering research occurred in Japan, France and the UK, countries such as South Korea, China and Germany have significantly contributed to the research pool in the last 5 years. The primary research focus has been on water filtration MBRs with limited growth in extractive and gas diffusion MBRs which still hold un-tapped potential. Fundamental aspects studied in academic research predominantly involve issues related to fouling, microbial characterization and optimizing operational performance. Research in North America presents a unique picture as a higher ratio of industrial wastewater treatment and side-stream MBR applications have been studied compared to other parts of the world. For MBR commercial application, the North America installations constitute about 11% of worldwide installations. Zenon occupies the majority of the MBR market in North America, whereas Kubota and Mitsubishi-Rayon have a larger number of installations in other parts of the world. Due to more stringent regulations and water reuse strategies, it is expected that a significant increase in MBR plant capacity and widening of application areas will occur in the future. Potential application areas include nitrate removal in drinking water treatment, removal of endocrine disrupting compounds from water and wastewater streams, enhancing bio-fuels production via membrane assisted fermentation and gas extraction and purification MBRs.     

Influence of membrane structure on fouling layer morphology during apple juice clarification

The flux behavior of 0.2 μm nylon, polysulfone (PS), polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes was examined during dead-end microfiltration of commercial apple juice. On nylon membranes, a 0.1 μm thick surface fouling layer rapidly formed that acted as a secondary membrane. The colloidal particles retained by this surface layer aggregated to form a thick loose gel structure, producing an anisotropic fouling structure. In contrast, the 4 μm thick surface fouling layer of PES was slower to form and had a more open structure with a lower flux resistance per unit thickness. The morphology of the PES surface layer also did not differ dramatically from the loose gel structure that subsequently formed on top of this secondary membrane. The PS surface fouling layer was similar in structure to nylon whereas the PVDF layer more closely resembled that found with PES. The density of the surface fouling layer did not directly correlate to membrane surface hydrophobicity or pure water flux. Atomic force microscopy (AFM) indicated that surface roughness strongly influenced surface fouling layer morphology. The membrane surface appears to act as a template for the fouling process; therefore, smooth membranes (nylon and PS) produce a dense surface fouling layer whereas this same layer on rough membranes (PES and PVDF) is much more open. Consequently, the fluxes of PES and PVDF membranes are less affected by fouling formation.     

Spatial distribution of foulants on membranes during ultrafiltration of protein mixtures and the influence of spacers in the feed channel

Using matrix assisted laser desorption ionisation mass spectrum (MALDI-MS), this study reports the observations of the fouling distribution and composition along the membrane channel after the membranes were subjected to ultrafiltration of protein mixture solution in a crossflow module with and without spacer. In the fouling layer on a fully retentive membrane, the protein components with high molecular weight has higher presentation after 2 h of filtration and the presentation reduced to be lower than the smaller components after 6 h of filtration due to protein exchange and displacement phenomena in deposition layer caused by the differences in structure and diffusivity of different components. The protein exchange and replacement in the deposition layer was also observed on partial retentive membrane using a sequential fouling procedure. Fouling distribution along the membrane channel with spacer inserted in the module was more uniform and the flux was higher than that without spacer despite higher protein deposition observed in some cases.     

Membrane fouling in a submerged membrane bioreactor (MBR) under sub-critical flux operation: Membrane foulant and gel layer characterization

Membrane foulants and gel layer formed on membrane surfaces were systematically characterized in a submerged membrane bioreactor (MBR) under sub-critical flux operation. The evaluation of mean oxidation state (MOS) of organic carbons and Fourier transform infrared (FT-IR) spectroscopy demonstrated that membrane foulants in gel layer were comprised of not only extracellular polymeric substances (EPS) (proteins, polysaccharides, etc.) but also other kinds of organic substances. It was also found that fine particles in mixed liquor had a strong deposit tendency on the membrane surfaces, and membrane foulants had much smaller size than mixed liquor in the MBR by particle size distribution (PSD) analysis. Gel filtration chromatography (GFC) analysis showed that membrane foulants and soluble microbial products (SMP) had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M_w) compared with the influent wastewater and the membrane effluent. Scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analysis indicated that membrane surfaces were covered with compact gel layer which was formed by organic substances and inorganic elements such as Mg, Al, Fe, Ca, Si, etc. The organic foulants coupled the inorganic precipitation enhanced the formation of gel layer and thus caused membrane fouling in the MBR.     

Characterization of floc size and structure under different monomer and polymer coagulants on microfiltration membrane fouling

The characteristic of aggregates pre-coagulated by inorganic monomer alum, polymer aluminium chlorohydrate(ACH) and polyaluminium chloride(PACl) coagulants impose major impact on the removal of humic acids (HAs) and the reduction of microfiltration (MF) membrane fouling. The fractal dimension of flocs formed by ACH and PACl is higher than that by monomer alum, indicating Keggin structure produced by polymer coagulants is much more compact compared with hexameric ring structure of alum hydrolysis species. Correspondingly, cake layer specific resistance is far higher and the MF membrane flux deteriorates much more severely when pre-coagulated by ACH and PACl than by alum. Moreover, the higher basicity contains in PACls, the cake layer fouling is more serious for producing more proportion of dense hydrolysis species Al₁₃. Thus, the polymer coagulant ACH and PACl seems not adapt to the pre-coagulation–MF process for cake layer resistance increase two to three times although they save 60–70% dose in comparison with alum for HAs removal. Additionally, for three Al-based coagulants under sweep coagulation condition, insufficient dose result in lower HAs removal and produce more small particles caused higher cake layer specific resistance according to Carman–Kozeny relationship. On the other hand, coagulant hydrolysis species as direct contaminant loading aggravated cake resistance on the MF membrane when overdosed. The optimum dose should keep the minimum to provide better HAs removal efficiency, and produce lower cake layer specific resistance and higher membrane filterability for pre-coagulation–MF hybrid process.