Effects of ion-exchange on the pervaporation performance and microstructure of NaY zeolite membrane

Pervaporation performance of NaY zeolite membranes is improved by ion-exchange with di-valent nitrate salt.Different nitrate salts,including Co(NO_(3))_(2),Mg(NO_(3))_(2),Zn(NO_(3))_(2),Ca(NO_(3))_(2),Cu(NO_(3))_(2),KNO_(3),and AgNO_(3),have great effects on the channel structure and water affinity of the NaY zeolite membrane.When the concentration of nitrate salt,ion-exchange temperature and time are 0.1 mol·L^(-1),50℃and 2 h,the ion-exchange degree order of NaY zeolites is Ag^(+)>K^(+)>Ca^(2+)>Zn^(2+)>>Co^(2+)>Mg^(2+).Especially,Ag^(+)and K^(+)cation exchange degree of NaY zeolites are achieved to 96.54% and 82.77% in this work.BET surface,total pore capacity,pore size distribution and water contact angle of the ion-exchanged NaY zeolites are all disordered by mono-and di-valent cations.Di-valent nitrate salt is favor for increasing the dehydration performance of NaY zeolite membranes by ion-exchange.When the ion-exchange solution is Zn(NO_(3))_(2),the total flux variation and separation factor variation of the NaY membrane(M-5)are -45% and 230% for separation of 10%(mass)H_(2)O/EtOH mixture by pervaporation,and the ion-exchanged membranes showed good reproducibility.

Effect of the Ultrasound Generated by Flat Plate Transducer Cleaning on Polluted Polyvinylidenefluoride Hollow Fiber Ultrafiltration Membrane

Polyvinylidenefluoride （PVDF） hollow fiber ultrafiltration membrane is frequently employed in water treatment. However, the fouling of ultrafiltration membranes affects the economic effectiveness of such process significantly. The ultrasound generated by flat plate transducer （UFPT） was used to clean the polluted PVDF ultrafiltration membrane with 2 g·L^-1 of citric acid aqueous solution in our study. The effects of UFPT intensity on the membrane surface were studied. The new membrane was easy to be polluted by the saturated CaCl2 solution. A synergistic effect of UFPT and 2 g·L^-1 citric acid aqueous solution could remove the foul of the membrane, and its flux could be recovered about 81%. The flux recovery of old membrane polluted was increased to 73.2% after 7 h soaking in citric acid aqueous solution, but its flux recovery without soaking was only increased to 56.2%.

Fouling and cleaning of membrane——a literature review

Membrane fouling curtails severely the economical and practical implementation of membrane process. The fundamental principles and mechanisms of membrane fouling as well as factors affecting fouling have been summarized in this paper. It also has covered three fouling resistance models and four kinds of approaches to improve membrane performance. Membrane cleaning methods are also discussed including physical, chemical, physico\|chemical and biological methods. In the four groups of basic cleaning methods, biological cleaning has considerable advantages and potentials. Extensive research work should be carried out further to explore and develop new ideas and techniques in the field of membrane cleaning and restoration.

Recent developments on catalytic membrane for gas cleaning

Catalytic membrane, a novel membrane separation technology that combines catalysis and separation, exhibits significant potential in gas purification such as formaldehyde, toluene and nitrogen oxides(NO_x). The catalytic membrane can remove solid particles through membrane separation and degrade gaseous pollutants to clean gas via a catalytic reaction to achieve green emissions. In this review, we discussed the recent developments of catalytic membranes from two aspects: preparation of catalytic membrane and its application in gas cleaning.Catalytic membranes are divided into organic catalytic membranes and inorganic catalytic membranes depending on the substrate materials. The organic catalytic membranes which are used for low temperature operation(less than 300 °C) are prepared by modifying the polymers or doping catalytic components into the polymers through coating, grafting, or in situ growth of catalysts on polymeric membrane. Inorganic catalytic membranes are used at higher temperature(higher than 500 °C). The catalyst and inorganic membrane can be integrated through conventional deposition methods, such as chemical(physical) vapor deposition and wet chemical deposition. The application progress of catalytic membrane is focused on purifying indoor air and industrial exhaust to remove formaldehyde, toluene, NO_x and PM2.5, which are also summarized. Perspectives on the future developments of the catalytic membranes are provided in terms of material manufacturing and process optimization.

Fouling behavior of poly(vinylidene fluoride)(PVDF)ultrafiltration membrane by polyvinyl alcohol(PVA)and chemical cleaning method

Severe fouling to poly(vinylidene fluoride)(PVDF)membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration(UF)process.In the paper,fouling behavior and mechanism were investigated,and the low-concentration polyvinyl alcohol(PVA)contained in the sedimentation tank wastewater was found as the main foulant.Consequently,the corresponding cleaning approach was proposed.The experiment and modeling results elaborated that the fouling mode developed from pore blockage to cake layer along with filtration time.Chemical cleaning conditions including the composition and concentration of reagents,cleaning duration and trans-membrane pressure were investigated for their effect on cleaning efficiency.Pure water flux was recovered by over 95% after cleaning the PVDF membrane using the optimal conditions 0.5 wt% NaClO(as oxidant)and 0.1 wt% sodiumdodecyl benzene sulfonate(SDBS,as surfactant)at 0.04MPa for 100 min.In the chemical cleaning method,hypochlorite(ClO−)could first chain-scissor PVA macromolecules to small molecules and SDBS could wrap the fragments in micelles,so that the foulants were removed from the pores and surface of membrane.After eight cycling tests,pure water flux recovery maintained above 95% and the reused membrane was found intact without defects.

Characterization of polysulfone hollow-fiber ultrafiltration membrane and its cleaning efficiency by streaming potential and flux method

Polysulfone(PS)hollow-fiber ultrafiltration membrane was characterized combined with flux and streaming potential in single electrolyte solutions.The effects of trans-membrane pressure,electrolyte concentration,ion valence and pH value of electrolyte solution on the streaming potential(SP)of the membrane were investigated.The zeta potential and surface charge density of the membrane were calculated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory.The results indicate that the valence and concentration of cation have a greater influence on the SP and surface charge density of PS membrane than those of anion,and the pH value of electrolyte solution has great effects on the SP and zeta potential of the membrane surface. Both the absolute value of the streaming potential and water flux of the adsorbed membrane decrease,compared with those of the clean membrane.The streaming potential and flux of the cleaned membrane can be completely recovered by cleaning with the mass fraction of 0.8%EDTA at pH=10.

A RAPID METHOD TO DETERMINE DIFFUSION COEFFICIENTS OF COUNTER-IONS IN AN ION-EXCHANGE MEMBRANE

1 INTRODUCTIONRapid and precise methods to obtain the diffusion coefficients of counter-ions are im-portant for the characterization of ion exchange membranes.Many theoreticaldescriptions of ion transport in ion exchange membranes have been developed by usingthe principles of irreversible thermodynamics,or the Nernst-Planck equations.Fick’s law can also be used for the description of the transport of ions with equaldiffusivity.However,for counter-ions of different diffusivities,Nerst-Planck

Pilot study on treatment of low turbidity and low temperature water by coagulation-immersed membrane process

The objective of this paper was to investigate the practicability of coagulation-immersed membrane process during low-temperature period through the study of steady operation,chemical cleaning methods,water quality and agent consumption.Experimental results showed that:membrane performance decreases with the reduction of temperature,but low temperature has little effect on stable operation of immersed membrane when coagulation as pretreatment.EFM with 1200 mg/L sodium hypochlorite after every 48 filtration cycles was made for reducing membrane fouling efficiently,and the method,with 1.5% sodium hydroxide and 3500 mg/L sodium hypochlorite for 10 h and then 2% hydrochloric acid for 4 h,is an appropriate cleaning method under low temperature.Compared with convention treatment process,immersed membrane process not only has same agent consumption,but also permeated water quality is more superior such as fine removal effect on turbidity with average 0.10 NTU.Therefore,coagulation-immersed membrane process is more appropriate for increasing water quality demand and the treatment of low turbidity and low temperature water.

Characteristics of Membrane Fouling in an Anaerobic-(Anoxic/Oxic)~n-MBR Process

The characteristics of membrane fouling and cleaning, in a hybrid MBR process, was investigated. Under the condition of sub-critical flux operation, a characteristic three-stage trans-membrane pressure （TMP） profile is observed as time passes. The initially extended period of slow pressure rise, followed by a somewhat faster rise, is then sup- planted by a sudden transition to rapid pressure rise. Membrane cleaning experiments and SEM examination make it apparent that the rapid TMP rise is mainly caused by the accumulation of a surface cake layer, which is a reversible fouling that can be removed by tap water washing. Fouling caused by a gel layer, which is an irreversible fouling, can be removed efficiently by chemical cleaning. NaC10 can oxidize the gel layer, which is formed mainly of macromo-lecular organic substances. The HC1 can remove inorganic particles formed by Ca^2＋, Mg^2＋ ions etc. The sequence of chemicals used in membrane cleaning has an influence on the cleaning result. The effect of the NaC1O＋HC1 cleaning procedure is superior to that of the HCI＋NaC1O one. Particle size distribution measurements （PSD） reveal that fine particles are inclined to deposit or attach on the membrane surface, or in the membrane pores, and caused rapid fouling.

STUDY ON THE DIFFUSION OF Cu^(2+)-H^+ COUPLE IN A CATION EXCHANGE MEMBRANE——A RAPID METHOD TO DETERMINE SELF-DIFFUSION COEFFICIENTS OF COUNTER-IONS WITH UNEQUAL VALENCE

1 INTRODUCTIONKnowledge of the basic transport phenomena of ions in an ion exchange membrane isimportant for the application of such a membrane.Various studies on the developmentof mathematical models for predicting and correlating membrane transport rate havebeen published in recent years.More exact estimation of the diffusion coefficientshas been the subject of chief concern in many of these papers.For a bi-ionic systemwith the same valence,Sato et al.gave a method for estimating diffusion coefficients

Fabrication of cost effective iron ore slime ceramic membrane for the recovery of organic solvent used in coke production

Improvement of coking properties of sub-bituminous coal （A） and bituminous coal （B） was done using blended organic solvents, namely, n-methyl-2-pyrrolidinone （NMP） and ethylenediamine （EDA）. Various solvent blends were employed for the coal extraction under the total reflux condition. A low-cost ceramic membrane was fabricated using industrial waste iron ore slime of M/s TATA steel R＆D, Jamshedpur （India） to separate out the dissolved coking fraction from the solvent-coal mixture. Membrane separations were carried out in a batch cell, and around 75 % recovered NMP was reused. The fractionated coal properties were determined using proximate and ultimate analyses. In the case of bituminous coal, the ash and sulfur contents were decreased by 99.3 % and 79.2 %, respectively, whereas, the carbon content was increased by 23.9 % in the separated coal fraction. Three different cleaning agents, namely deionized water, sodium dodecyl sulphate and NMP were used to regain the original membrane permeability for the reusing.

Pilot-plant Study of Anoxic-aerobic Membrane Bioreactor （AO-MBR） on the Changes of Membrane Flux under Constant Pressure

Under a constant pressure, a pilot-plant test was conducted through the use of anoxic-aerobic membrane bioreactor （AO-MBR）, and this test operated steadily for 251 days. During the experiment, there were a total of four membrane cleaning processes, for the 90th day, the 150th day, the 210th day and the 240th day, respectively （The cleaning cycle was 90 days, 60 days, 60 days and 30 days, respectively）. From the initial 33.26 L/m^2.b dropped to 20.03 L/m^2.h after the fourth membrane cleaning, membrane flux reduced to 60.22% of the initial flux. During the 180 thd-210 thd of the experiment, the powdered activated carbon （PAC）, the segment size of which is 80-100, was put into anoxic reactor. Membrane flux decreased from 16.02 L/m^2·h to 15.29 L/m^2·h, and then rose to 15.65L/m^2·h. The dosing of PAC had a significant effect on the maintenance of a high membrane flux and extending running time. Before several membrane cleanings, a wire of membrane was intercepted from membrane module. It was found that the membrane surface sediments seemed to the inorganic colloid formed by Fe^2＋, Ca^2＋ and biofilm formed by some micro-organisms after the membrane surface pollutants were analyzed preliminarily with scanning electron microscopy （SEM）.

PREPARATION OF SA-Fe CATION EXCHANGE MEMBRANE AND IT’S APPLICATION IN ELECTRODIALYSIS FOR TREATING WASTEWATER

An insoluble SA-Fe membrane was prepared by being linked soluble sodium alginate with FeCl3. SEM was used to observe its surface structure. 1R spectrum indicated that Fe^3＋ was linked with -COOH and -OH in SA membrane. As a cationic exchanging membrane in electrodialysis the membrane was applied in treating inorganic wastewater with high concentration of inorganic ammonia and azote. The results of experiment showed that it was well-selective to ammonia and azote. The percentage of the removal of ammonia and azote in wastewater was up to 80%.

Advancing ion-exchange membranes to ion-selective membranes:principles,status,and opportunities

Ion-exchange membranes(IEMs)are utilized in numerous established,emergent,and emerging applications for water,energy,and the environment.This article reviews the five different types of IEM selectivity,namely charge,valence,specific ion,ion/solvent,and ion/uncharged solute selectivities.Technological pathways to advance the selectivities through the sorption and migration mechanisms of transport in IEM are critically analyzed.Because of the underlying principles governing transport,efforts to enhance selectivity by tuning the membrane structural and chemical properties are almost always accompanied by a concomitant decline in permeability of the desired ion.Suppressing the undesired crossover of solvent and neutral species is crucial to realize the practical implementation of several technologies,including bioelectrochemical systems,hypersaline electrodialysis desalination,fuel cells,and redox flow batteries,but the ion/solvent and ion/uncharged solute selectivities are relatively understudied,compared to the ion/ion selectivities.Deepening fundamental understanding of the transport phenomena,specifically the factors underpinning structure-property-performance relationships,will be vital to guide the informed development of more selective IEMs.Innovations in material and membrane design offer opportunities to utilize ion discrimination mechanisms that are radically different from conventional IEMs and potentially depart from the putative permeability-selectivity tradeoff.Advancements in IEM selectivity can contribute to meeting the aqueous separation needs of water,energy,and environmental challenges.

Application of heat-activated peroxydisulfate process for the chemical cleaning of fouled ultrafiltration membranes

Na Cl O has been widely used to restore membrane flux in practical membrane cleaning processes,which would induce the formation of toxic halogenated byproducts.In this study,we proposed a novel heatactivated peroxydisulfate(heat/PDS)process to clean the membrane fouling derived from humic acid(HA).The results show that the combination of heat and PDS can achieve almost 100%recovery of permeate flux after soaking the HA-fouled membrane in 1 mmol/L PDS solution at 50℃ for 2 h,which is attributed to the changes of HA structure and enhanced detachment of foulants from membranes.The properties of different treated membranes are characterized by scanning electron microscopy(SEM),atomic force microscope(AFM),attenuated total reflection Fourier transform infrared spectroscopy(ATRFTIR),and X-ray photoelectron spectroscopy(XPS),demonstrating that the reversible and irreversible foulants could be effectively removed by heat/PDS cleaning.The filtration process and fouling mechanism of the cleaned membrane were close to that of the virgin membrane,illustrating the good reusability of the cleaned membrane.Additionally,heat/PDS which can avoid the generation of halogenated byproducts shows comparable performance to Na Cl O on membrane cleaning and high performance for the removal of fouling caused by sodium alginate(SA),HA-bovine serum albumin(BSA)-SA mixture and algae,further suggesting that heat/PDS would be a potential alternative for membrane cleaning in practical application.

二沉池出水造成的超滤膜污染在NaClO溶液中化学清洗效能研究

二沉池出水中含有大量微生物代谢产物,这些物质在采用超滤膜对二沉池出水进行深度处理时会产生严重的膜污染,NaClO溶液常用于化学清洗有机物及微生物造成的膜污染。该研究采用NaClO溶液对二沉池出水造成的超滤膜污染进行化学清洗,结合膜通量、膜表面形貌、官能团、主要元素组成在NaClO溶液清洗前后的变化深入分析了NaClO化学清洗膜污染的效能及对膜特性的影响。结果表明NaClO溶液化学清洗可高效去除膜污染并恢复膜通量,但会改变膜表面形貌及元素组成;清洗温度、清洗时间、初始pH及NaClO浓度都会对清洗效能产生影响,在近中性、常温条件下,将污染膜浸泡在100 mg/L NaClO溶液内2 h即可有效去除膜污染,且过度清洗会导致膜损伤。因此,采用NaClO溶液化学清洗二沉池出水造成的膜污染时,需要严格控制清洗条件以实现膜污染高效去除并减少对膜结构特性的影响。

超疏水-高疏油SiC膜的制备及性能

基于SiO_(2)粒子共混喷涂与浸渍方法,研发了一种在SiC膜上制备超疏水-高疏油表面的工艺。通过喷涂不同粒径的SiO_(2)颗粒,在SiC膜表面构造具有双疏性能的微纳双重粗糙结构,然后通过浸渍将十七氟癸基三甲氧基硅烷接枝至SiC膜表面,成功制备了具有超疏水-高疏油特性和优异自清洁性能的SiC膜。通过改变含氟量、粗糙度,分析了各参数对表面润湿性的影响。经改性后所得超疏水-高疏油SiC膜表面上水和正十六烷的静态接触角分别为152.6°和146.3°,滚动角分别为5.2°和10.2°,这归因于SiC膜表面的微纳结构和低表面能物质降低了其与其他物质的黏附力。在强酸和强碱溶液中,超疏水-高疏油SiC膜表现出稳定的双疏性。本研究为在无机膜上构建具有优异耐酸碱性的超疏水-高疏油表面提供了一种简便的工艺。

废水处理中纳滤膜化学清洗技术研究现状、挑战与展望

纳滤技术由于其操作压力较低、对二价离子截留率高等优势,在市政污水、纺织废水、制药废水等废水处理领域有广阔的应用前景。然而膜污染问题的存在限制了纳滤技术的发展,膜污染不仅会导致膜通量衰减、分离性能下降,还会大大缩短膜的使用寿命。化学清洗可有效缓解膜污染,但常用的清洗剂均会对膜结构和分离性能产生影响,还可能引发生物耐药性及膜清洗废水二次污染等问题。本文对不同类型废水处理中纳滤膜的污染特征及化学清洗方法进行综述,并且重点阐释了酸、碱、次氯酸钠等化学清洗剂与聚酰胺纳滤膜的作用机制,以及频繁的化学清洗对膜面微生物的影响和所引发的生物风险,最后对有关问题的解决措施提出展望,以期为膜污染控制方法的优化提供参考。

浸没式超滤膜在大型给水厂的应用与思考

浙江省某地两个大型水厂(J水厂和T水厂)的生产规模分别为2.0×10^(5)m^(3)/d和5.0×10^(5)m^(3)/d,其运行时间分别为2年和7年,均采用浸没式超滤膜为核心净水工艺。文章结合两个水厂的实际运行情况,研究和总结了两个水厂的运行管理经验,得到如下结论:膜运行方面,两水厂膜进水浑浊度日常在0.15~4.25 NTU,台风季偶有短时13.6~35.2 NTU的情况下,膜出水浑浊度一直稳定在0.1 NTU以下,2μm以上的颗粒数偶有检出;膜污染控制方面,物理清洗时两水厂均在产水中间阶段进行一次气冲清洗,可有效缓解膜污染;化学清洗时发现J水厂仅采用柠檬酸清洗效果好,T水厂采用先次氯酸钠、后柠檬酸清洗效果好;水厂设计方面,J水厂泵吸式产水整体能耗高达27 kW·h/km^(3),T水厂虹吸式产水最低能耗仅为13 kW·h/km^(3),有效降低了能耗;运行管理方面,扩大清水池容积可有效解决因清水池调蓄能力不足导致的超滤膜长时间超负荷运行的问题;同时在膜池的进水管上增设膜前加氯点,保证出水余氯质量浓度稳定在0.2 mg/L左右可有效解决藻类滋生问题。