Fouling process and anti-fouling mechanisms of dynamic membrane assisted by photocatalytic oxidation under sub-critical fluxes

Membrane fouling is often considered as a hindrance for the application of microfiltration/ultrafiltration(MF/UF) for drinking water production. A novel process of photocatalytic membrane reactor/dynamic membrane(PMR/DM), operating in a continuous mode under sub-critical flux, was proposed for the mitigation of membrane fouling caused by humic acids(HAs) in water. The mechanism of membrane fouling alleviation with synergistic photocatalytic oxidation and dynamic layer isolating effect was comprehensively investigated from the characterization of foulant evolution responsible for the reversible and irreversible fouling. The results showed that the PMR/DM utilized photocatalytic oxidation to enhance the porosity and hydrophilicity of the fouling layer by converting the high molecular weight(MW) and hydrophobic HA molecules with carboxylic functional groups and aromatic structures into low-MW hydrophilic or transphilic fractions, including tryptophan-like or fulvic-like substances. The fouling layer formed in the PMR/DM by combination of photocatalytic oxidation and DM running at a sub-critical flux of 100 L·h^-1·m^-2, was more hydrophilic and more porous, resulting in the lowest trans-membrane pressure(TMP) growth rates, as compared to the processes of ceramic membrane(CM), DM and PMR/CM.Meanwhile, the dynamic layer prevented the foulants, particularly the high-MW hydrophobic fractions,from contacting the primary membrane, which enabled the membrane permeability to be restored easily.

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）.

Fatty acid fouling of forward osmosis membrane:Effects of pH,calcium,membrane orientation,initial permeate flux and foulant composition

Octanoic acid（OA） was selected to represent fatty acids in effluent organic matter（EOM）. The effects of feed solution（FS） properties, membrane orientation and initial permeate flux on OA fouling in forward osmosis（FO） were investigated. The undissociated OA formed a cake layer quickly and caused the water flux to decline significantly in the initial 0.5 hr at unadjusted p H 3.56; while the fully dissociated OA behaved as an anionic surfactant and promoted the water permeation at an elevated p H of 9.00. Moreover, except at the initial stage, the sudden decline of water flux（meaning the occurrence of severe membrane fouling） occurred in two conditions： 1.0.5 mmol/L Ca2＋, active layer facing draw solution（AL-DS） and 1.5 mol/L Na Cl（DS）; 2. No Ca2＋,active layer-facing FS（AL-FS） and 4 mol/L Na Cl（DS）. This demonstrated that cake layer compaction or pore blocking occurred only when enough foulants were absorbed into the membrane surface, and the water permeation was high enough to compact the deposit inside the porous substrate. Furthermore, bovine serum albumin（BSA） was selected as a co-foulant.The water flux of both co-foulants was between the fluxes obtained separately for the two foulants at p H 3.56, and larger than the two values at p H 9.00. This manifested that, at p H 3.56,BSA alleviated the effect of the cake layer caused by OA, and OA enhanced BSA fouling simultaneously; while at p H 9.00, the mutual effects of OA and BSA eased the membrane fouling.

Review on structural control and modification of graphene oxide-based membranes in water treatment: From separation performance to robust operation

Membrane separation has become an important technology to deal with the global water crisis. The polymerbased membrane technology is currently in the forefront of water purification and desalination but is plagued with some bottlenecks. Laminated graphene oxide(GO) membranes exhibit excellent advantages in water purification and desalination due to the single atomic layer structure, hydrophilic property, rich oxygen-containing groups for modification, mechanical and chemical robust, anti-fouling properties, facile and large-scale production, etc. Thus the GO-based membrane technology is believed to offer huge opportunities for efficient and practical water treatment. This review systematically summarizes the current progress on the water flux and selectivity intensification, stability improvement, anti-fouling and anti-biofouling ability enhancement by structural control and modification. To improve the performance of the laminated GO membrane, interlayer spacing tunability and surface modification are mainly used to enhance its water flux and selectivity. It is found that the stability and biofouling also block the service life of the GO membrane. The crosslinking method is found to effectively solve the stability of GO membrane in aqueous environment. Introducing nanoparticles is a widely used method to improve the membrane biofouling ability. Overall, we believe that this review could provide benefit to researchers in the area of GO-based membrane technology for water treatment.

Removal of Natural Organic Matter by Forward Osmosis Membrane： Flux Behaviour and Foulant Characterization

Fouling of cellulose triacetate（CTA） forward osmosis（FO） membranes by natural organic matter（NOM） was studied by means of a cross-flow fiat-sheet forward osmosis membrane system. The NOM solution was employed as the feed solution（FS）, and a sodium chloride solution（3 tool/L） was used for the draw solution（DS）. The process was conducted at various temperatures and cross-flow velocities. The flux decline was investigated with 3 h forward osmosis operation. The substances absorbed on the membranes were cleaned by ultrasonic oscillation of the fouled membranes and were characterized by methodologies including fluorescence excitation-emission matrices （EEMs） and liquid chromatography with an organic carbon detector（LC-OCD）, and the variations of membrane properties were also investigated by Fourier transform infrared spectrometer（FTIR） and a contact angle meter. It was noted that the rejection efficiency of NOM is remarkable and that ultrasonic oscillation is an effective method to extract the NOM fouled on the CTA membranes after FO process. A higher cross-flow velocity and lower temperature benefit the anti-fouling capacity of the membrane significantly. Although humic substances accounted for the majority of the NOM, aromatic proteins and amino acids were the main fouling components on the membranes, with symbolic FTIR peaks at 2355, 1408 and 873 cm^-1. The present surface foulant made the membranes becoming more hydrophilic, as demonstrated by a significant decrease in contact angle（ranging from 20% to 46%） under all the operation conditions.

Operating Conditions Optimization on Indonesian ＂Batik＂ Dyes Wastewater Treatment by Fenton Oxidation and Separation Using Ultrafiltration Membrane

Broadly speaking, this study aims to develop ＂batik＂ dyes wastewater treatment technologies by hybrid process that combines Fenton oxidation and separation using ultrafiltration membranes. Specifically, the purpose of this study was to determine the effect of membrane characteristics, feed solution pH, operating pressure of ＂Dead-end＂ membrane reactor, and the frequency of membranes which uses on the percentage of COD reduction in ＂batik＂ wastewater. In this study, the filtrate from wastewater pre-treatment with Fenton oxidation, both without and with addition of activated carbon, is passed to the ultrafiltration （UF） separation system. Fenton oxidation process was carried out at optimum conditions, i.e. at pH 3, temperature 50 ℃, and the addition FeSO4·7H2O and H2O2 at 747-830 mg/L and 1,168-1,460 mg/L, respectively. The optimum reduction percentage of COD can be achieved when the membranes used for separation has a pore size of 0.01 to 0.015 lam, feed solution pH 2, operating pressure 1 atm and frequency of membranes uses I x. To determine the fouling potential on ultrafiltration membranes that are used, flux measurements were performed 3 times for each membrane. These stages can see that the flux decline reached 22.5% when the effluent filtered directly to the membrane; 17.3% when performed pre-treatment prior to separation processes using membranes and 10% when combined pre-treatment process, use of activated carbon and the separation using ultrafiltration membranes.

矿井水直接超滤试验研究

为了解决矿井水处理现有工艺流程长、出水水质不稳定等问题,优化矿井水处理工艺,以河北某矿井水为研究对象,采用直接超滤短流程工艺进行试验研究,探究反洗时长、反洗周期、工作压力等工艺参数对超滤的影响,并筛选膜污染清洗药剂。结果表明:最佳工艺参数为反洗时长120 s,反洗周期60 min,跨膜压差0.25 MPa,在此条件下经过300 min试验测试,膜通量为136 L/(m^(2)·h),维持在初始膜通量的91%,出水浊度稳定在0.05 NTU以下;膜污染最佳清洗药剂为0.2%HCl,对污染前后及酸洗碱洗后的膜片进行SEM和EDS测试分析,结果表明造成酸洗碱洗效果差异的主要因素为矿井水中的硬度离子和铝离子。

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。

电化学氧化技术在MBR中的膜污染控制研究与应用进展

膜生物反应器(MBR)已发展成为高效且成熟的市政和工业污水处理技术,基于MBR建成并投产的污水处理厂数量持续增加且规模不断扩大,但膜污染仍是MBR进一步推广和应用的瓶颈,开发高效率、低成本的膜污染控制方法是领域内的研究热点。作为一种典型的高级氧化工艺,电化学氧化(electrochemical oxidation,EO)在水环境中具有突出的净污和杀菌能力,可同步实现膜表面污染物的降解和细菌的灭活,在MBR中展现出巨大的抗膜污染潜力。近年来,基于EO的膜污染控制技术蓬勃发展,促进了MBR抗膜污染方法的创新,并引发了对抗膜污染机制的新思考。为了紧跟MBR快速发展的步伐,迫切需要对EO在MBR中膜污染控制的研究和应用进行全面总结和讨论。介绍了EO的工作原理并分析了电化学氧化MBR(eMBR)中产生活性氧自由基并抑制膜污染的多种途径;根据国内外的最新研究进展,从电极装载方式、电极与滤膜的结合方式、电极的制备材料等角度系统讨论了eMBR的运行模式和抗膜污染效果;总结了EO抑制膜污染的影响因素及其实际应用的现存挑战;对eMBR的未来研究进行了展望,对其进一步优化与创新提出了建议。

电化学-膜生物反应器强化污废水处理的研究进展

电化学耦合膜生物反应器(EMBR)是新兴的污废水处理技术,除了能够高效去除常规污染物,EMBR在去除微污染物和病原微生物、缓解抗生素抗性基因增殖、控制膜污染和回收生物能源与资源等方面也具有显著的优势。综述了EMBR工艺的原理及特点、污废水处理效能、能源与资源回收效果、膜污染控制和技术挑战。为了推动EMBR的工程应用,未来仍需开发具有高导电性、生物相容性的电极材料,优化反应器构型和操作条件,以持续提升对污废水的处理效能。

梯度纳米纤维膜在纯生啤酒中的除菌过滤研究

针对目前商业化纯生啤酒用除菌滤膜存在孔径分布宽、抗污性差、膜孔易堵塞、可重复使用性差等问题,利用熔融挤出相分离法制备了不同直径大小的乙烯-乙烯醇共聚物(EVOH),通过将粗、细纳米纤维在上、下层的先后排列构筑了一种梯度结构纳米纤维膜。通过对梯度纳米纤维膜过滤性能、抗污性及可重复使用性等进行研究,发现梯度纳米纤维膜对10 g/L的酵母浸膏发酵液重复过滤后,稳定后的通量为22660 L m^(-2)h^(-1),远高于Pall®商业膜(4840 L m^(-2)h^(-1))。经高温蒸汽灭菌处理后的梯度纳米纤维膜的稳定通量为6600 L m^(-2)h^(-1),而商业膜仅为1760 L m^(-2)h^(-1),表现出优异的耐高温水蒸气性能。此外,污染后的梯度纳米纤维膜经80℃水清洗后的通量恢复率可达43%,而商业膜的通量恢复率仅为32%,表明梯度纳米纤维膜显示了优异的可重复使用性。为纯生啤酒用除菌滤膜的国产化替代提供了一种新的途径。

MBR膜污染、影响因素及其控制策略研究进展

膜生物反应器(MBR)在废水处理领域应用广泛,然而膜污染是制约其可持续发展的主要瓶颈。探讨了MBR的膜污染问题,介绍了MBR工艺的基本原理和类型,阐述了膜污染的分类。分析了膜表面特性、污泥混合液性质和系统操作条件等因素对膜污染的影响,总结了膜污染的控制措施。旨在为MBR工艺的进一步优化和发展提供理论指导。

Control of membrane fouling during hyperhaline municipal wastewater treatment using a pilot-scale anoxic/aerobic-membrane bioreactor system

Membrane fouling limits the effects of long-term stable operation of membrane bioreactor （MBR）. Control of membrane fouling can extend the membrane life and reduce water treatment cost effectively. A pilot scale anoxic/aerobic-membrane bioreactor （A/O- MBR, 40 L/hr） was used to treat the hyperhaline municipal sewage from a processing zone of Tianjin, China. Impact factors including mixed liquid sludge suspension （MLSS）, sludge viscosity （Ix）, microorganisms, extracellular polymeric substances （EPS）, aeration intensity and suction/suspended time on membrane fouling and pollution control were studied. The relationships among various factors associated with membrane fouling were analyzed. Results showed that there was a positive correlation among MLSS, sludge viscosity and trans-membrane pressure （TMP）. Considering water treatment efficiency and stable operation of the membrane module, MLSS of 5 g/L was suggested for the process. There was a same trend among EPS, sludge viscosity and TMP. Numbers and species of microorganisms affected membrane fouling. Either too high or too low aeration intensity was not conducive to membrane fouling control. Aeration intensity of 1.0 m3/hr （gas/water ratio of 25：1） is suggested for the process. A long suction time caused a rapid increase in membrane resistance. However, long suspended time cannot prevent the increase of membrane resistance effectively even though a suspended time was necessary for scale off particles from the membrane surface. The suction/suspended time of 12 min/3 rain was selected for the process. The interaction of various environmental factors and operation conditions must be considered synthetically.

Ceramic membrane fouling mechanisms and control for water treatment

Membrane separation, as an important drinking water treatment technology, has wide applications. The remarkable advantages of ceramic membranes, such as chemical stability, thermal stability, and high mechanical strength, endow them with broader prospects for development. Despite the importance and advantages of membrane separation in water treatment, the technique has a limitation: membrane fouling, which greatly lowers its effectiveness. This is caused by organics, inorganic substances, and microorganisms clogging the pore and polluting the membrane surface. The increase in membrane pollution greatly lowers purification effectiveness. Controlling membrane fouling is critical in ensuring the efficient and stable operation of ceramic membranes for water treatment. This review analyzes four mechanisms of ceramic membrane fouling, namely complete blocking, standard blocking, intermediate blocking, and cake filtration blocking. It evaluates the mechanisms underlying ceramic membrane fouling and summarizes the progress in approaches aimed at controlling it. These include ceramic membrane pretreatment, ceramic membrane surface modification, membrane cleaning, magnetization, ultrasonics, and nanobubbles. This review highlights the importance of optimizing ceramic membrane preparation through further research on membrane fouling and pre-membrane pretreatment mechanisms. In addition, combining process regulations with ceramic membranes as the core is an important research direction for ceramic membrane-based water treatment.

Membrane fouling control by ultrasound in an anaerobic membrane bioreactor

fouling online in an anaerobic membrane bioreac-tor(AMBR).Short-term running experiments were carried out under different operating conditions to explore feasible ultrasonic parameters.The experimental results indicated that when the crossflow velocity was more than 1.0 m/s,mem-brane fouling could be controlled effectively only by hydro-dynamic methods without ultrasound.When ultrasound was applied,an ultrasonic power range of 60-150 W was suitable for the membrane fouling control in the experimental system.The experimental results showed that the membrane fouling was controlled so well that membrane filtration resistance(ΣR)could stay at 5×10^(11)m^(−1) for more than a week with the crossflow velocity of 0.75 m/s,which equaled the effect of crossflow velocity of more than 1.0 m/s without ultrasound.

超滤系统在高难废水处理中的应用及污染控制

某焦化废水处理站处理规模为150 m^(3)/d,废水成分复杂、色度高,含有大量难降解及有毒有害物质,如酚类、苯系物等。针对工艺出水水质不稳定的问题,以超滤系统为核心,对原有废水处理工艺进行了工艺升级。结果表明,超滤膜系统可作为回用工艺中反渗透系统的预处理工艺稳定运行,出水SS稳定低于5 mg/L,出水浊度稳定低于0.5 NTU。在设计水量下,通过周期性的维护性清洗,系统运行稳定。当处理量超过设计水量连续运行时,膜污染加剧,跨膜压差急剧上升至-55 kPa,周期性维护性清洗丧失作用。取膜丝切片在扫描电子显微镜(SEM)下观察,发现中空纤维膜表面形成了连续致密的污染层,过流孔道完全被覆盖,表明膜丝已严重污染。采用预酸洗-碱洗-酸洗的混合清洗方式,跨膜压差恢复至初始运行状态。项目的改造及运行维护为超滤系统在高难废水处理中的应用以及膜污染的控制提供参考。

反渗透膜专用中性清洗剂的研究

以鞍钢厂内中水回用系统污堵的反渗透膜元件为例,利用EDS辅助双膜池膜片测试装置实现反渗透膜专用清洗剂的快速筛选研究,并成功研制出一种绿色高效中性水基清洗剂。通过正交实验优化配方,探讨了其清洗效果,与膜厂家推荐的清洗剂进行比较。结果表明:自制清洗剂最佳组成(质量分数)为1.5%柠檬酸三铵、0.15%HEDP、0.15%FMEE、0.3%OP-10、0.3%FMES、0.01%HPMC,余量为水。受污染膜片30℃下浸泡8 h后,膜通量恢复率高达99%,远高于膜厂家推荐的清洗剂,应用前景广阔。

低碳氨比生活污水处理中多级AO-MBR工艺的启动阶段分析与参数优化研究

研究对改良型多级厌氧/好氧-膜生物反应器工艺进行了参数优化,以提高污水处理效率和膜组件寿命。研究调整了进水流量和流量分配比,并在好氧区添加了挂膜填料以增强硝化反硝化。研究结果显示,添加填料的系统在6 h水力停留时间下化学需氧量去除率提高至90.60%,出水浓度为23.18 mg/L,优于无填料系统的86.20%。在氨氮去除上,填料系统达到98.55%的效率,出水浓度为0.64 mg/L,而无填料系统在8 h和6 h水力停留时间下的效率分别为98.26%和96.46%,出水浓度较高。研究成果可为污水处理技术的发展提供科学依据。