The assessment of microorganism growth in the membrane distillation system

Growth of microorganism in the membrane distillation (MD) system has been evaluated, and their presence on the membrane surface was studied using scanning electron microscopy (SEM) coupled with energy dispersion spectrometry (EDS). The membrane samples were collected from MD modules used for the following applications: concentration of salts and acids, production of demineralized water from tap water, separation of ethanol from fermentation broth in a membrane bioreactor and treatment of saline wastewater containing Pseudomonas and Streptococcus faecalis bacteria and Penicillium and Aspergillus fungi. The MD experiments were performed with polypropylene capillary membranes. SEM examinations of the membranes used for the treatment of saline wastewater indicated a significant amount of S. faecalis bacteria and Aspergillus fungi. The polypropylene membranes used did not reject S. faecalis bacteria, which were detected on the membrane surface on the distillate side. The presence of fungi in the membrane pores was observed only on the feed side. The contamination of the membrane surface by yeast cells was not observed in the case of the membrane bioreactor operated over one year. The running conditions of the MD process (such as elevated temperature, significant salt concentrations and low pH values) inhibited the growth of microorganism in the MD system.     

Ceramic membranes applied to membrane distillation: A comprehensive review

Membrane distillation (MD) has been increasingly studied in the past decade for its potential as a separation process of nonvolatile components. The present study demonstrates a comprehensive overview of the current progress and challenges in the application of ceramic membranes to MD based on the available state of the art. There are already published review papers about MD, but the present study focuses on ceramic membranes, which are still the few used in MD when compared to polymeric membranes. Significant issues such as membrane material, module, characteristics, and hydrophobic modification are discussed. The main operating conditions and their effects on the separation process are given. Current applications of ceramic membranes in MD are also presented. Likewise, challenges and future perspectives associated with MD performance using ceramic membranes are highlighted. A review focused on ceramic membranes applied specifically to MD will contribute for future research in order that this process achieves successful implementation in industry.     

膜蒸馏过程强化及优化技术研究进展

膜蒸馏作为一种新型的膜分离技术,具有脱盐率高、可处理高浓度原料液等技术优势,近年来引起学术界及工业界的广泛关注.膜蒸馏技术可被应用于海水淡化,工业废水/苦盐水脱盐及糖、盐、果汁、有机/无机酸、碱液等的浓缩过程.但由于当前膜蒸馏能耗及成本较高,一定程度上限制了该技术的工业化.本文重点介绍了可用于强化膜蒸馏过程和优化该过程能量利用的方法及研究进展,主要包括膜材料和膜制备方法/工艺的进展、膜蒸馏过程操作条件的优化、改进膜组件和辅助装置的应用、太阳能和低品位热源的使用、蒸发冷凝潜热的回收以及耦合其他分离过程的复合膜蒸馏系统,同时分析了膜蒸馏技术处理高盐工业废水的应用前景,最后探讨和总结了膜蒸馏过程强化及优化的研究方向,为该技术的进一步发展提供了科学性指导.     

Recent advances in reverse osmosis and electrodialysis membrane desalting technology

The potential impact of recent developments in both reverse osmosis and electrodialysis membrane desalting technology are summarized.Particular emphasis is given to the status of advanced technology reverse osmosis membranes with chlorine resistance having single pass seawater desalination capability. Membranes capable of using low operating pressures for brackish water desalting are also reviewed.Results obtained with large prototype reverse osmosis modules and their potential effect on lowering plant capital costs are presented.Possible elimination of acid and use of ultrafiltration as the predominant pretreatment step in seawater desalination plants are also described.Recent developments in the high temperature electrodialysis program for seawater desalting and in the use of newly developed anion membranes for brackish water desalination are reviewed.Finally, the effect of recent budget cut-backs imposed on the office of Water Research and Technology (OWRT) and potential impacts on future membrane desalination R&D activity are discussed.     

Bottlenecks and recent improvement strategies of ceramic membranes in membrane distillation applications: A review

Ceramic membranes have received more attention currently from researchers in membrane distillation (MD) applications due to their outstanding properties. However, despite their superior mechanical, thermochemical stability, and resistance to harsh operating conditions, several bottlenecks still limit their applications in MD. Although there are several published articles on ceramic membranes in MD, the uniqueness of this review lies in the fact that it discusses the critical bottlenecks that significantly affect the performance of ceramic membranes in long-term operation and limit their scale-up to commercial MD applications. Furthermore, recent advances, strategies, and techniques to mitigate these limitations have also been discussed. A discussion on high ceramic membrane fabrication costs and mitigation strategies using alternative low-cost ceramic materials to erstwhile conventional ceramic materials has been presented. In addition, the inherent problems of the brittleness and wetting/fouling of ceramic membranes and recent advances in strengthening ceramic membranes and fouling/wetting control via the development of superhydrophobic and omniphobic ceramic surfaces in MD have been addressed. Consequently, technical bottlenecks that still exist despite recent development in ceramic membranes for MD applications have been highlighted and future research direction in developing robust ceramic membranes in MD applications has been elaborated.     

Recent progress on low-cost ceramic membrane for water and wastewater treatment

Great progress in the development of low-cost ceramic membranes from alternative materials have been achieved recently towards various application especially water and wastewater treatment. However, their significance has not been fully recognized and understood especially in term of their microstructural analysis such as formation of grain growth and microcracks. This review paper summarizes fabrication method, alternative materials, microstructure, wettability, mechanical properties and application of low-cost ceramic membrane. The fabrication method including slip casting, tape casting, extrusion, pressing method and phase inversion technique are described. Alternative materials used in low-cost ceramic membrane fabrication are discussed and categorized into clays, agricultural waste, industrial waste and animal bone waste. The mechanisms of morphology formation, microstructure and wettability properties are analysed. Modification strategies for the surface of low-cost ceramic membrane are discussed, and classified into modification for separation application, modification for photocatalytic application and modification for membrane distillation and membrane contactor system. Modification improves the membrane structure by changing the pore size, porosity and wettability properties of low-cost ceramic membranes. Mechanical properties of low-cost ceramic membranes are also discussed in detail towards several mechanism, like grain growth phenomenon and formation of microcracks which also considered as membrane defects. Grain growth phenomenon can be divided into normal and abnormal grain growth. Meanwhile, formation of microcracks could be occurred in single-phase polycrystalline ceramics that have anisotropic grains or biphasic polycrystalline grains. The application of low-cost ceramic membrane in seawater desalination, oily wastewater treatment, heavy metal adsorption, textile separation and photocatalytic application are reviewed. Finally, some possible opportunities and challenges for further development of low-cost ceramic membrane are pointed out.     

Recent progress in electrospun nanofibers and their applications in heavy metal wastewater treatment

Novel adsorbents with a simple preparation process and large capacity for removing highly toxic and nondegradable heavy metals from water have drawn the attention of researchers. Electrospun nanofiber membranes usually have the advantages of large specific surface areas and high porosity and allowing flexible control and easy functionalization. These membranes show remarkable application potential in the field of heavy metal wastewater treatment. In this paper, the electrospinning technologies, process types, and the structures and types of nanofibers that can be prepared are reviewed, and the relationships among process, structure and properties are discussed. On one hand, based on the different components of electrospun nanofibers, the use of organic, inorganic and organic−inorganic nanofiber membrane adsorbents in heavy metal wastewater treatment are introduced, and their advantages and future development are summarized and prospected. On the other hand, based on the microstructure and overall structure of the nanofiber membrane, the recent progresses of electrospun functional membranes for heavy metal removal are reviewed, and the advantages of different structures for applications are concluded. Overall, this study lays the foundation for future research aiming to provide more novel structured adsorbents.     

Highly hydrophobic oil−water separation membrane: reutilization of waste reverse osmosis membrane

The increasing applications of seawater desalination technology have led to the wide usage of polyamide reverse osmosis membranes, resulting in a large number of wasted reverse osmosis membranes. In this work, the base nonwoven layer of the wasted reverse osmosis membrane was successfully modified into the hydrophobic membrane via surface deposition strategy including TiO₂ and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS), respectively. Various techniques were applied to characterize the obtained membranes, which were then used to separate the oil–water system. The optimally modified membrane displayed good hydrophobicity with a contact angle of 135.2° ± 0.3°, and its oil–water separation performance was as high as 97.8%. After 20 recycle tests, the oil–water separation performance remained more than 96%, which was attributed to the film adhesion of the anchored TiO₂ and PFOTS layer on the surface. This work might provide a new avenue for recycling the wasted reverse osmosis membrane used in oily wastewater purification.     

界面聚合聚酰胺纳滤膜渗透选择性能优化的研究进展

纳滤因其分离效率高、操作压力低、环境友好等优点，在废水处理、海水淡化和工业分离纯化等众多领域有着重要的应用。界面聚合法制备的聚酰胺（PA）纳滤膜是最为常用的纳滤膜种类之一。然而界面聚合反应速度快，如何通过调控界面聚合过程，优化纳滤膜选择分离层的结构从而提高渗透选择性，以满足不同领域对纳滤膜需求仍是亟需解决的问题。本文从影响界面聚合单体扩散因素的角度出发，综述了近年来PA纳滤膜渗透选择性能优化的研究进展，包括新型PA纳滤膜、纳米材料/PA混合基质膜及超薄PA纳滤膜3个方面，探讨了选择分离层结构调控与纳滤膜渗透选择性能优化的关系，最后指出目前界面聚合制备高渗透选择性PA纳滤膜在规模化、稳定性及可控性存在的问题，并对未来界面聚合纳滤膜在微观结构和聚合过程调控方面的研究进行了展望。     

膜技术处理丙烯腈工业废水的研究与应用

膜技术在水处理领域的应用越来越广泛.针对目前丙烯腈工业废水处理技术的不足,介绍了膜技术处理丙烯腈工业废水的研究现状.根据膜分离过程的特点,讨论了膜技术处理丙烯腈工业废水的研究方向和发展前景.     

陶瓷膜在水处理中的发展与应用

介绍了无机陶瓷膜的结构、原理及特性;综述了陶瓷分离膜技术的发展过程及其国内外发展现状;分类介绍了其在给水处理、海水淡化、废水处理等方面的应用研究及进展;最后讨论了陶瓷膜在水处理应用中存在的问题及发展趋势,指出其在水处理中具有良好的应用前景.     

疏水性油水分离膜及其过程研究进展

油水分离是治理含油废水和含水油液的重要工业过程。本文概括了疏水性油水分离膜的类型与制备方法,包括常规分离膜和高度疏水/超亲油分离膜。前者为常规微滤、超滤及纳滤过程用膜;后者由构筑高度疏水（水滴接触角≥120°）表面方法得到,形式有金属网膜、纤维膜、滤纸、复合膜及不对称膜,其为制备耐污染的疏水性油水分离膜提供了新思路。指出了疏水性膜用于油水分离的过程原理及应用现状：含油废水除油中,疏水性膜可实现O/W乳液的破乳、粗粒化油滴、滤除油滴及吸附油分子几方面的功能;含水油液除水中,膜被用来截留水滴,可直接得到净化的油品。最后,指出了其过程规模化应用前尚需解决的重要问题,特别是高度疏水/超亲油分离膜的制备、相关过程研究的深入及其规模化试验等方面需着力加强。     

膜分离技术在油田含油污水处理中的应用研究进展

介绍了膜分离技术及其优点,有机膜、无机膜和复合膜在油田含油污水处理中的应用研究进展;分析了膜处理含油污水过程中的破乳机理、影响含油污水处理效果的各种因素、产生膜污染的原因及其控制措施;探讨了膜分离技术的研究方向和发展前景.最后指出,深入研究分离膜的分离过程和机理,探索合适的清洗周期,研究合适的清洗剂和清洗工艺,明确分离膜的预处理指标要求,合理安排工艺流程,开发新型膜及膜组件是膜分离技术在油田含油污水处理中应重点解决的问题.     

膜蒸馏海水淡化研究进展及发展趋势

海水淡化是解决我国水资源短缺的重要措施之一。膜蒸馏海水淡化技术可以充分利用太阳能等低品位热源，具有成本低、设备简单、操作容易、能耗低等优点，在海水及苦咸水淡化方面应用前景广阔。     

纳米材料在放射性废水处理中的应用进展

放射性污染会引起生态环境问题，安全高效地处理放射性废水是我国应对环境安全的迫切需求，因此，研发高效的放射性处理技术和材料具有重要意义。近年来，纳米材料因其独特的物化性质受到广泛关注，被尝试用于放射性废水处理，并表现出良好的应用潜力。本文综述了国内外研究者利用纳米材料处理放射性废水的研究进展，总结了纳米材料作为吸附剂和膜材料对水体放射性核素的处理性能和应用情况：一方面，高比表面积的纳米材料作为新型吸附剂，经适当化学处理后具有大量活性位点和纳米孔，可高效吸附处理放射性废水；另一方面，种类丰富的纳米材料可作为制膜材料和添加剂，增加膜材料种类和制备调控维度，改善传统膜对水体放射性核素的去除效果。最后，总结了处理放射性废水的纳米材料选择依据，并讨论了纳米材料在放射性废水处理中需要引起重视的几个问题。     

基于二维纳米材料的水处理功能膜研究进展

二维纳米材料是制备膜材料中一类重要的掺杂材料或膜构筑单元,也是新型水处理功能膜的研究热点。已有许多研究报道了二维纳米材料通过有序的堆叠和自组装在膜内构建出规整的水通道,可以赋予膜可调控的分离性能,进而实现trade-off效应的突破,被认为是“下一代膜材料”（next-generation membranes）。同时,二维纳米材料的独特片层结构、催化性能及可修饰性可使膜材料获得新的功能,如导电性能、光/电催化性能等。本文综述了近年来基于二维纳米材料的水处理功能膜研究进展,重点介绍了共混法、自组装等制备方法,并总结了此类功能膜在抗污染、膜通量恢复、强化污染物去除、调控盐截留及污染物监测领域的应用。最后对基于二维纳米材料的水处理功能膜发展方向,如限域催化、调控盐分离、监测传感等新兴领域进行了分析和展望。     

Development of hierarchical surface roughness on porous poly (vinylidene fluoride) membrane for membrane distillation process

The surface hydrophobicity of a poly (vinylidene fluoride) membrane was increased through the phase separation of polycarbonate (PC) solution on the membrane surface. A variety of characterization techniques including surface contact angle measurement, scanning electron microscopy, liquid entry pressure measurement, atomic force microscopy, porosity measurement, pore size measurement, and attenuated total reflectance-Fourier transform infrared spectroscopy were performed to investigate the membrane surface modification. According to the results, the formation of PC deposits on the membrane surface provided hierarchical structures consisting of micro and nanoscale roughness which enhanced the surface hydrophobicity. Direct contact membrane distillation (DCMD) experiments, in which an aqueous solution of sodium chloride (3.5 wt%) resembling the seawater was used as feed, were carried out to assess the performance of membranes. This surface modification technique led to the improved pore wetting resistance of the coated membrane in DCMD application. This novel method is believed to have a great potential to apply on a wide variety of membranes for MD application.     

Development of polyethersulfone phase‐inversion membranes for membrane distillation using oleophobic coatings

Highly porous macrovoid‐free polyethersulfone membranes have been prepared using the phase‐inversion process with water as the non‐solvent. These membranes are of great interest for membrane distillation (MD) after application of a hydrophobic/oleophobic coating. The membrane structure was controlled by optimizing the process conditions and dope composition. Counter intuitively, increasing the polymer concentration favors the formation of larger surface pores under similar process conditions. A symmetric membrane is obtained when a sufficient amount of high‐molecular‐weight polyvinylpyrrolidone was added to the dope solution, which appears to play an important role in the structure formation process. The final membrane shows similar performance compared to commercial MD membranes. However, the membranes developed in this study show an oleophobic character, broadening the applications of MD. Moreover, the compressibility of these membranes is severely reduced compared to stretched membranes, which is expected to result in an improved MD performance at full scale. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45516.     

膜生物反应器中污泥特性对膜污染的影响研究

膜生物反应器(MBR)是膜技术与污水生物技术的组合工艺，与传统污水处理工艺相比具有许多优点，但膜污染目前仍是限制MBR广泛应用的突出问题。有效的膜污染防治技术，可以增加膜通量，增强系统稳定性，减少系统维护和运行费用。在膜过滤过程中，污泥混合液的特性对于膜污染具有重要作用。近年来围绕污泥特性对膜污染的防治问题取得了许多研究成果，膜污染的数学模型研究也得到了很大发展。     

Fouling and cleaning of polymer-entwined graphene oxide nanocomposite membrane for forward osmosis process

In this study, we have characterized membrane fouling of polymer-entwined graphene oxide membranes with a simulated feed solution containing organic foulants for wastewater treatment applications, as well as with a simulated inorganic wastewater with high iron and silicon concentrations relevant to steel industry wastewater reclamation. Membrane cleaning processes by cross-flow surface flushing with water were then applied to demonstrate water flux recovery for long-term application. Salt rejection property was retained constant during fouling process, whereas water flux was found to be reduced continuously due to fouling but was readily recoverable following surface flushing.