Effect of Time in Chemical Cleaning of Ultrafiltration Membranes

Chemical cleaning of ultrafiltration membranes is often considered successful when the flux through a cleaned membrane is much higher than through a pristine one. Here, a novel definition of cleaning intensity is proposed as the product of the concentration of the cleaning agent and the cleaning time (Ct), and it is shown that Ct values between 0.5 and 1.0 g h L^–1 are sufficient for effective cleaning. Experiments with PES‐30 and PVDF‐30 membranes fouled by bovine serum albumin and cleaned with surfactant, oxidant, and formulated cleaning agents demonstrate that a good cleaning should last for 10–20 min and restore the flux through a virgin membrane. More intensive cleaning increases the membrane hydrophilicity and the water flux, but soon causes more severe fouling and even membrane disintegration.     

Phospholipid coatings for the prevention of membrane fouling

The aim of the present work was the development of phosphorylcholine-based treatments for biofiltration membranes and the demonstration that such treatments prevent or inhibit protein fouling. Microfiltration membranes of cellulose triacetate, polyether sulphone and polyvinylidene fluoride were etched with oxygen in a plasma chamber to generate surface hydroxyl groups and were then treated with the monomer 2-methacryloyloxyethyl phosphorylcholine. These membranes were evaluated with water, buffer, bovine serum albumin (BSA), yeast fermentation broth, beer and orange juice. The treatment of cellulose triacetate membranes reduced both the initial flux and the extent of water fouling. In terms of the integrated flux, these factors tended to cancel each other out. For protein, the membranes gave similar or higher fluxes but worse fouling. The cellular feed (yeast) reacted more favourably to the coating than the BSA. The polyether sulphone was scarcely affected by the coating; fouling remaining high with most ‘real’ feeds. There was lower initial flux but less flux decline with water and beer. Washing with water and cleaning with Tergazyme did not restore the initial flux. Polyvinylidene fluoride membranes gave the most positive results. In most cases, the coating both increased initial flux and decreased the rate of fouling. The coating was particularly effective for BSA and for beer and orange juice, where fouling is probably caused by a polysaccharide rather than by a protein. Electron microscopy showed, nonetheless, that fouling by proteins was accompanied by protein adsorption primarily on the upper surface of the membrane and that coated membranes showed less deposition and in different places than did untreated membranes.     

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% sodium dodecyl benzene sulfonate (SDBS, as surfactant) at 0.04 MPa 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.     

陶瓷膜污染的超声波辅助清洗

膜污染的控制和膜的清洗再生是膜应用的关键,研究了采用超声波辅助清洗被乳化液污染的氧化锆陶瓷膜。结果表明：超声波的功率、超声清洗时间及膜污染程度等对清洗效果均有影响,超声功率越高,清洗后水通量的恢复率越高,超声清洗时间在20 min左右比较适宜。超声波对膜表面的污染清洗效果较好,对膜孔内堵塞清洗效果相对较弱,超声辅助化学清洗可有效恢复膜通量。     

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% sodium dodecyl benzene sulfonate (SDBS, as surfactant) at 0.04 MPa 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.     

Membrane fouling and chemical cleaning in water recycling applications

Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca²⁺ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface.     

超滤组合工艺在线加氯化学清洗中试研究

试验采用次氯酸钠对组合工艺之超滤膜组件进行在线化学清洗,旨在研究膜污染状况与特点。试验结果表明,水力清洗可有效恢复膜通量,反洗水加氯可有效延缓膜污染。在水力清洗废水中,相对分子质量大于1 k的有机物占有机物总量的87.3%,表明膜截留的大分子有机物可通过水力清洗使其从膜表明剥离;而在化学清洗废水中,相对分子质量小于1 k的有机物含量是水力清洗废水的2.6倍,故小分子有机物需要进行化学清洗方可恢复膜运行通量。化学清洗废水中的中性亲水和极性亲水组分分别占总溶解性有机物的44.9%和40.8%,水力清洗废水中的强疏水和弱疏水组分分别占总溶解性有机物的50.9%和23.6%,表明亲水性组分是造成膜不可逆污染的主要因素,而膜截留的疏水性物质可通过水力清洗将其从膜表面清除。     

Advanced reverse osmosis process with automatic sponge ball cleaning for the reclamation of municipal sewage

These experiments were conducted with secondary effluent from the terminal plant at Osaka, Japan, in order to determine the potential of the sponge ball cleaning system as an advanced reverse osmosis membrane cleaning technique. It was confirmed that sandfiltration of the feed as a method for reverse osmosis pretreatment and the use of chemical cleaning reagents to restore flux levels were unnecessary, when sponge ball cleaning was used.As a result, the product water flux was maintained at 0.65 ～ 0.75m³/m² day at 25°C and membrane rejection was more stable. No damage to the membrane, which would mean a decline of rejection ability, was recognized by scrubbing of the membrane surface by sponge rubber balls.It was confirmed that tight membranes were more suitable than loose ones because firstly it was easier to remove membrane fouling, secondly the product flux was nearly equal, and finally the product water was of better quality.     

微生物固定化技术—膜生物反应器膜的清洗研究

对IMO-MBR处理生活污水的膜污染进行了酸洗、碱洗及酸洗加次氯酸钠清洗的试验研究。结果显示:酸洗加次氯酸钠清洗后,膜的通量可以烣复到原通量的94%,达到清洗的目的。     

麦芽糖醇纳滤浓缩过程中膜的污染和清洗再生

采用纳滤方法对麦芽糖醇进行提纯和浓缩,可以节约大量的能耗。文中系统研究了该纳滤过程中操作条件对膜污染的影响,并对膜的清洗和再生效果进行了考察。实验结果表明,膜的污染程度随操作压差和原料液质量分数的增大而加剧,随循环流量和操作温度的升高而减轻。另外,采用常压、循环流量为100—120 L/h,40℃左右的去离子水冲洗30 m in,可达到满意的效果,再将被污染的膜浸泡36 h,基本能使膜纯水通量恢复到使用前的状态。     

Poly(ether imide) membranes modified with charged surface‐modifying macromolecule—Its performance characteristics as ultrafiltration membranes

Modification of poly (ether imide) (PEI) ultrafiltration (UF) membranes was attempted by blending charged surface modifying macromolecule (cSMM). Compared to the pure PEI membrane, blending of PEI with cSMM resulted in blend membranes with enhanced UF characteristics such as lower hydraulic resistance (R_m) and higher pure water flux (PWF) coupled with higher water content (WC). Among the various modified membranes, blend membranes with 5 wt % cSMM concentration exhibited higher PWF (60.38 L m^?2 h^?1), WC (73.6%), protein permeate flux (27.12 L m^?2 h^?1) and lower flux decline rate (R_fd) (55.1%), R_m (5.21 kPa/L m^?2 h^?1), bovine serum albumin (BSA) rejection (87.1%). Meanwhile, the fouling resistant ability was studied by flux recovery ratio (FRR) after water and alkali cleaning, irreversible and reversible fouling rate. Higher FRR after water cleaning (95.07%), FRR after alkali cleaning (97.1%), reversible fouling rate (50.14%) and lower irreversible fouling rate (5%) exhibited by 5 wt % cSMM membranes showed its better antifouling ability compared to pure PEI and other blend membranes because of its higher hydrophilic nature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40320.     

淹没式加压MBR膜污染机理及治理措施

研究了加压MBR膜通量衰减规律,膜污染阻力的分布;尝试了空曝、水反冲洗、压缩空气反冲洗、物化清洗四种膜清洗方式的膜通量恢复．研究结果表明：加压MBR膜通量衰减迅速,运行17d后膜通量衰减83．5％;膜污染阻力主要由凝胶极化阻力Rp和内部污染阻力Rif构成。     

Optimisation of ultrafiltration of a highly viscous protein solution using spiral-wound modules

The ultrafiltration process of highly viscous protein process water with spiral-wound modules was optimised by analysing the fouling and developing a strategy to reduce it. It was shown that the flux reduction during filtration is mainly caused by the adsorption of proteins on the membrane and not by the high osmotic pressure. In laboratory experiments, the concept of the critical flux was proved to reduce fouling. Additionally, the reduction of the effect of concentration polarisation by spacers at laboratory and pilot scale was evaluated. While at laboratory scale the spacers influenced the mass transfer, the effect in spiral-wound modules was low. However, pilot plant experiments showed that operating at low pressures to reduce the fouling and avoid local fouling required a spacer with a low pressure drop along the module. A cleaning strategy including a hygienic evaluation was tested. An enzymatic cleaning followed by a caustic cleaning step gave sufficient results. This investigation has also shown that the concentrated protein solution as well as the produced water in the permeate are hygienically safe, and, in principle, the latter could be reused somewhere else within the production process.     

Seawater desalination by direct contact membrane distillation

Membrane fouling still posts as one of the major obstacles in membrane distillation (MD). This is why the MD approach still cannot successfully compete with other conventional seawater desalination methods. In this study, both the NaCl solution and real seawater are used as the feed of MD processes to investigate the differences in permeate flux, product water quality and membrane fouling. The results indicate the accumulation rate of membrane scale can be depressed by reducing the degree of polarization if NaCl solution is used as the feeding fluid, however, this kind of depression effect is not so obvious when real seawater is used as the feeding fluid. An ultrasonic cleaning technique is found to be an effective way to restore the flux rate for these MD processes and extend the life span of MD membrane.     

无纺布膜生物反应器膜污染分析及其控制技术

利用自行开发的无纺布膜生物反应器（NWMBR）处理洗浴废水。结果表明,在有机负荷0.64 kgCOD/(m3?d)、污泥浓度5 g/L、水力停留时间6.3 h和膜通量13 L/(m2?h)条件下,出水可始终稳定在COD<20 mg/L,BOD5<3 mg/L,LAS<0.3 mg/L,NH3-N<0.5 mg/L以及浊度<0.5 NTU。在13 L/(m2?h)通量下膜表面形成松散的泥饼层,反应器稳定运行约50天后泥饼层泥量达到9.3 g/m2时导致膜污染的发生;当通量升至18 L/(m2?h)时迅速形成密实的泥饼层导致膜污染。经过分析发现,膜表面污染物主要由亲水有机物、羧酸类、多糖类、蛋白质类等有机物质组成,也存在少量的由Na、Ca、Si、Al等元素形成的无机污染。采用次氯酸钠反冲式清洗,可使无纺布膜的清水通量恢复率达98%,膜平均孔径可从8.25 μm恢复至47.2 μm。     

膜污染机理与化学清洗方式研究

膜污染是膜技术应用中面临的关键问题,其影响膜运行的稳定性,决定膜清洗周期以及膜的更换频率。因此,要使膜获得长期稳定的运行效果,必须研究其膜污染的机理与清洗方法。确定了膜污染机理,对于了解膜通量下降原因、预测膜通量、控制和消除膜污染具有指导意义。膜面形成污染层,会影响通量以及脱盐率,因此需定期进行膜清洗以恢复性能,但也有不可恢复的损失,造成运行成本提高。故文中总结了膜清洗的方式与污染机理以望对膜行业的发展有所促进作用。     

MBR污水处理工艺长期运行中的膜强化清洗方式

基于上海城镇污水处理厂AAO-MBR膜工艺长期运行中膜不可逆污染严重、离线化学清洗难以恢复理想通量的问题,对其清洗方式进行改进。在原清洗方式的基础上增加草酸二次清洗,探究污染膜产水能力恢复情况,并通过中试试验进行验证。结果表明：膜清洗方式改进后,离线清洗对膜污染物的去除更加彻底,清水通量可恢复至新膜的95.1%,较原清洗方式提高了27.2%。在相同通量下中试运行24 d后,膜运行压力比原清洗方式低18.2 kPa,膜污染速率明显减慢。研究通过改进MBR长期运行平板膜的污染物清洗方法,为今后MBR污水厂膜清洗提供参考,具有较好的工程指导意义。     

Ozone Cleaning of Fouled Poly(Vinylidene) Fluoride/Carbon Nanotube Membranes

This research demonstrates for the first time that ozone is an effective cleaning agent for polyvinylidene fluoride (PVDF) membranes fouled by natural organic matter (NOM). Bare PVDF membranes as well as PVDF impregnated with CNTs (pristine (CNTs–P) and oxidized (CNTs–O)) at 0.3% mass membranes were used. Three different methods were investigated for cleaning the fouled membranes including; A: 10-min cleaning by pure water, B: 5-min water followed by 5-min ozonated water, and C: 10-min fully ozonated water. It was found that the application of fully ozonated water for 10 min was very effective to reinstate the flux to almost its original value of unfouled membrane. The CNTs–P/PVDF membrane exhibited the highest fouling with a total fouling ratio of 81%, while for the bare PVDF and the CNTs–O/PVDF membranes, the fouling ratios were 76% and 74%, respectively. The full ozonated water cleaning method gave the highest removal of fouling leaving the lowest irreversible fouling on the membrane as compared to the other cleaning methods. On the other hand, the highest removal of NOM fouling was obtained for CNTs–O/PVDF membranes indicating that fouling on CNTs–O/PVDF membrane was less bound than the other membranes. Contact angle measurements of the fouled membranes showed that all membranes exhibited increased contact angles due to the NOM deposition but after cleaning, particularly with ozonated water, the membrane contact angles returned to almost their original values. FTIR analysis of the membranes corroborated the results obtained.     

天然有机物对国产纳滤膜的污染及清洗效果研究

为考察水体中天然有机物(NOM)对纳滤膜性能产生的影响,以腐殖酸(HA)、牛血清蛋白(BSA)和海藻酸钠(SA)分别模拟水中常见NOM,腐殖质、蛋白质和多糖,对国产NF-1812纳滤膜进行单组分及其混合物定性定量有机污染及清洗实验。结果表明,有机污染造成膜通量下降,膜污染程度为SA>HA>BSA;NOM截留率可稳定在99.2%~99.6%;膜污染阻力主要为浓差极化阻力,其次是凝胶层阻力和内部污染阻力,有机污染液综合黏度和综合含量越大,浓差极化阻力的比例越高;对多组分有机污染膜进行错流速度9 cm/s的物理水力清洗和pH=10.0的质量分数分别为0.1%的NaOH+0.025%Na-SDS化学药剂清洗,膜通量、NOM截留率、苦咸水截留率、SEM成像均恢复至原膜状态,纳滤膜清洗效果良好,适用于中国西北苦咸水地区。     

Cleaning efficiency and impact on production fluxes of oxidising disinfectants on a pes ultrafiltration membrane fouled with proteins

The cleaning step in the ultrafiltration of skim milk is not always complete before the following disinfection start, raising concerns about the effect of disinfectants on any protein remaining. For a Koch polyethersulfone (PES) UF membrane [model HFK131], the fouling in skim milk UF is exclusively due to proteins. Used in right quantity, hypochlorite well finishes the cleaning and can also be used alone as a cleaner [removing 95% of the proteinaceous fouling]. However, if the amount of hypochlorite is not sufficient to end the cleaning, this can lead to large reductions production flux [a 13% decrease on skim milk flux was observed]. Other oxidants such as PVP-iodine, hydrogen peroxide, peracetic acid and sodium perborate do not achieve hydraulic cleanliness [90% of flux recovery]. Oxidants based on hydrogen peroxide and PVP-iodine, when used on a membrane which was still fouled by protein, yielded flux recovery worse than for a single rinsing.