Mechanistic Model for CaSO4 Fouling on Nanofiltration Membrane

One of the major limitations of nanofiltration (NF) in drinking water treatment is inorganic scaling. In this study, a mechanistic model has been proposed to describe the permeate flux decline process during CaSO4 scaling in NF. It has been observed that the permeate flux decline follows four distinct stages. At first stage, 22–30% flux is reduced due to concentration polarization. At the second stage, flux is not reduced, instead, nucleation of CaSO4 occurs. The major permeate flux decline (60–70%) occurred at the third stage due to CaSO4 cake formation. At the final stage, the system reached the steady state, where rate of CaSO4 deposition on the membrane is balanced by shearing caused by the increase of concentrate flow rate. Beyond this stage, the flux does not decrease significantly. At each stage, the concentration of the salt at the membrane surface was estimated. The maximum salt concentration was found at the initial stage of permeate flux reduction, which gradually decreases as the filtration proceeds.     

Determination of Perchlorate Rejection and Associated Inorganic Fouling (Scaling) for Reverse Osmosis and Nanofiltration Membranes under Various Operating Conditions

This study focused on perchlorate (ClO4?) rejection and flux-decline in bench-scale cross-flow flat-sheet filtration for two reverse osmosis (RO) and two nanofiltration (NF) membranes with a natural water, and addressed estimation of precipitative fouling/scaling with inorganic salts and characterizations of inorganic fouling and antiscalants. Thus the study considered tradeoffs between productivity (increased recovery and flux) versus ClO4? rejection versus membrane fouling/scaling. In this study, the rejection of water quality parameters (cations, anions, dissolved organic carbon, UVA254, total dissolved solids) and flux-decline trends for four different membranes were investigated over a various range of operating conditions (i.e., J0/k ratio and recovery). Inorganic foulants on the membrane surface were analyzed by various methods (i.e., x-ray diffraction and scanning electron microscopy), and demonstrated inhibition effects of antiscalant. With increasing recovery and J0/k ratio, high productivity (flux) was achieved, however, the rejections of perchlorate and other water quality parameters decreased and the precipitative fouling/scaling potential of membranes increased. At the same operating conditions in the presence of an antiscalant, embodying phosphonate functional groups, flux decline trends for the four membranes indicated lower scale formation supported by the results of the fouled membrane characterizations.     

NOM Accumulation at NF Membrane Surface: Impact of Chemistry and Shear

The effects of solution chemistry, surface shear, and composition of natural organic matter (NOM) were investigated for their impact on accumulation of foulant material at the surface of charged polymeric nanofiltration membranes. The source of NOM was the Suwannee River. A bench-scale, batch recycle system was used with 20 hollow fiber, nanofiltration membranes. Membrane flux decline and foulant accumulation increased at low pH and high ionic strength as a result of neutralization of charge, electric double layer compression, and the apparent shift in conformation of charged NOM macromolecules. The rate of NOM accumulation decreased with operating time, suggestive of an eventual steady state between adsorption and desorption. The effect of NOM composition on membrane fouling could not be discerned by a standard technique to isolate hydrophobic and hydrophilic NOM fractions, quite possibly because of the fractionation methodology's failure to recover a small but important fouling fraction or because of NOM interactions that are lost when individual fractions are separately tested. However, a greater percentage of the hydrophilic than hydrophobic fraction permeated the membrane, in agreement with prior observations by others. Increasing the cross flow velocity from 85 to 255 cm∕s reduced the extent of flux decline, presumably due to hydrodynamic disruption of cake layer formation.     

Application of nanofiltration to treat rare earth element （neodymium） containing water

The scope of present work was to study the feasibility of a commercial nanofiltration(NF) membrane to reject Nd(III) ions fromsynthetic aqueous solution.The permeates were analyzed using inductively coupled plasma-atomic emission spectrometry(ICP-AES) to findNd(III) concentration.Experimental results indicated that the Nd(III) rejection increased with increase in applied pressure and feed flow rate;and decreased with increase in feed concentration.Rejection of Nd(III) ions using NF membrane were widely influenced by solution pH dueto the charged nature of the membrane which changed with the variation in pH.The use of a surfactant(sodium dodecyl sulphate) in aqueoussolution resulted in its adsorption on the membrane surface,thereby changing membrane characteristics,and in turn influencing the rejection.The complexation step induced had also increased the rejection to a greater extent by forming [Nd-EDTA]-complex thereby increasing itsmolecular weight and thus increasing rejection.     

Membrane Fouling Test: Apparatus Evaluation

Flux decline with time is one of the most serious shortcomings of microfiltration and ultrafiltration membranes. It is highly desirable to have a membrane (fouling) testing procedure that is short in duration, utilizes a minimum amount of test solution, only requires a small membrane area, and is representative of the large-scale process. The objective of this study was to compare the results of the testing of a given membrane using a number of different test units (reverse osmosis, ultrafiltration, dead-end, and cross-flow cells) and testing procedures. It was of particular interest to determine if smaller cells used in the literature perform similarly to the Sepa CF cell, as it is a standard. During six-day runs the flux decline of the polyethersulfone membrane tested was mainly caused by membrane compaction and much less due to fouling. As various membrane materials compact to a different extent, studies into the fouling characteristics of different types of membranes should incorporate precompaction and pure water testing to quantify the contribution of membrane compaction and true fouling to the overall flux decline. The dead-end cell performed very differently from continuous cells, so their use is not recommended. The six-day continuous flow tests showed that the reverse osmosis (RO), ultrafiltration (UF), and cross-flow (CF) cells yielded very similar dissolved organic carbon removals and flux decline, despite UF and RO cells using membrane coupons eight times smaller than CF cells.     

纳滤膜处理除铁后浸出液富集铜的研究

采用纳滤膜处理江西德兴铜矿除铁后生物浸出液,通过试验考察操作压力、温度等对渗透通量、铜离子截留率和渗透液电导率的影响.研究结果表明纳滤膜较佳操作条件为：温度30℃,运行压力15bar,流量14L/min;在此条件下浓缩3.7倍时,Cu2＋截留率R为93.1％,浓缩液中Cu浓度为0.764g· L-1.     

酸盐分离技术在镍电积阳极液中的应用

目前酸盐分离技术主要有树脂吸附法、离子交换法和膜分离技术三大类,但将其应用于镍湿法冶炼中镍电积阳极液的报道较少。总结了三大类酸盐分离技术的原理和应用,并分别采用树脂吸附法、扩散渗析法、特种纳滤膜和电渗析结合的方法对镍电积阳极液进行酸盐分离试验。结果表明,三种方法对镍电积阳极液均有一定的分离效果,其中树脂吸附法易饱和,需反洗再生,造成体积膨胀;扩散渗析法对硫酸的回收率在80%以上,镍的截留率在90%以上,但回收的硫酸浓度较低,同样存在体积膨胀问题;特种纳滤膜和电渗析结合法对镍离子的截留率可达90%以上,氢离子去除率可达70%以上,同时浓缩后的氢离子浓度可提高400%以上,镍离子浓度可提高500%以上,淡化液中各种离子浓度小于50 mg/L,可用作纯水,并且该方法不会造成系统体积膨胀,具有工业化应用价值。     

Removal of Copper Ions from Waters Using Surfactant-Enhanced Hybrid PAC/MF Process

This paper deals with the removal of copper ions from aqueous solutions by using surfactant-enhanced powdered activated carbon (PAC)/microfiltration (MF) hybrid process, including the evaluation of process performance and fouling dynamics at various linear alkyl benzene sulfonate (LABS), PAC, and Cu2+ concentrations of feed solution. Although the use of surfactant as an additive material increased the adsorption efficiency in PAC/MF hybrid process, a considerable amount of the flux was lost for surfactant concentration above critical micelle concentration. The process could be employed with a performance of 74.7%, 97.2% and 87?L/m2?h for LABS rejection, Cu2+ rejection and permeate flux at the conditions of 2?g PAC/L, 5?mM LABS, 0.2?mM Cu2+, and 60-min process time. Cu2+ rejection, which increased with increasing of LABS, and PAC amounts decreased with the increase in Cu2+ concentration. It was understood that the increments in LABS, PAC, and Cu2+ concentrations being an indicator for the feed solution quality led to the occurrence of more fouling on the membrane. The analyses of dynamics concerning the fouling behaviors, which were carried out using single and combined pore blocking models, put forward that the cake formation was the main predominant mechanism in the process. It was also determined that the variation of feed contents deduced the presence of rather complex fouling behaviors as a simultaneous function of secondary membrane layer formation and clogging and narrowing of membrane pores by surfactants.     

P507+N235高酸砷铁反萃溶液处理工艺的优化

介绍了某锌冶炼厂采用P507+N235组成的双溶剂萃取体系从硫酸浸出液中萃取砷铁的生产情况,并对高酸砷铁反萃溶液返回锌冶炼系统存在的问题进行分析。采用膜分离工艺处理反萃溶液,对比分析纳滤膜和扩散渗析膜分离的工艺条件和投资运行成本。结果表明,纳滤膜和扩散渗析膜均可以有效分离溶液中杂质元素：其中采用纳滤膜工艺时,截留浓液中铁、砷、锌、硫酸和油份的截留率分别为91.2%、88.55%、87.5%、47.44%和50%,酸回收利用率为52.56%;采用扩散渗析膜工艺,渗析残液中铁、砷、锌、硫酸和油份的截留率分别92%、87.94%、90%、5.13%和75%,酸回收利用率为94.87%。截留浓液和渗析残液均采用石灰中和法脱除溶液中的砷铁,过滤溶液返回系统实现资源循环利用,扩散渗析膜相比纳滤膜投资少,操作维护简单,生产成本低,更适合用于工业生产。     

Characterization of Ceramic Composite-Membranes Prepared by ORMOSIL Coating Sol

Sol-gel methods offer many advantages over conventional slip-casting, including the ability to produce ceramic membranes. They are purer, more homogeneous, more reactive and contain a wider variety of compositions. We produced ormosil sol using sol-gel process under different molecular weight of polymer species [polyethylene glycol (PEG) ] in total system [Tetraethyl ortho silicate(TEOS)-polyethylene glycol (PEG)]. The properties of as-prepared ormosil sol such as,viscosity, gelation time were characterized. Also, the ceramic membrane was prepared by dip-coating with synthetic sol and its micro-structure was observed by scanning electron microscopy. The permeability and rejection efficiency of membrane for oil/water emulsion were evaluated as cross-flow apparatus. The ormosil sol coated Membrane is easily formed by steric effect of polymer and it improves flux efficiency because infiltration into porous support decreased. Its flux efficiency is elevated about 200(1/m2·h) compared with colloidal sol coated membrane at point of five minutes from starting test.     

Physical–Chemical Treatment of Groundwater Contaminated by Leachate from Surface Disposal of Uranium Tailings

Leaching of trace elements including heavy metals, nonmetals, and radionuclides from surface impoundments of tailings generated during uranium mining and milling often leads to groundwater contamination. This paper reports results from coagulation and membrane filtration experiments designed to evaluate the capabilities of these processes to remove molybdenum, selenium, uranium, radium, thorium, and other mono- and divalent ions from contaminated groundwater in a shallow unconfined aquifer influenced by uranium tailings. A 10 mg Fe3+/L dose at pH 4 and 10 was found to be very effective for removing radium and thorium that were associated with particles in the raw water. Molybdenum and uranium removals by coagulation are consistent with surface complexation and electrostatic interactions between major coagulant and contaminant complexes in solution. Poor selenium removal suggests that selenate [Se(VI)] was the dominant species in the surficial groundwater. Permeation coefficients (intrinsic transport parameters) for dissolved ions and complexes across three new generation thin-film composite nanofiltration and reverse osmosis membranes evaluated obeyed Gaussian distributions with ionic charge having a mean value of zero. Thus, dissolved solute rejection from brackish multicomponent solutions appears to be only a function of the magnitude of ionic charge and not its sign (positive or negative). Solute permeation coefficients decreased in a power-law fashion with increasing product of molecular weight and absolute ion charge suggesting that both properties determine their removal by nanofiltration and reverse osmosis membranes. Because nanofiltration and reverse osmosis were found to be highly effective for removing a variety of ionic solutes they can be employed in pump and treat operations for groundwater purification prior to reinjection.     

纳滤膜对稀土离子的动态吸附行为及截留特性

采用经碳纳米管改性的亲水化纳滤膜浓缩提取稀土浸出液中的稀土离子,探究纳滤膜表面对La3+、Nd3+、Pr3+、Ce3+和Y3+5种稀土离子吸附动力学行为,考察稀土离子半径的大小对纳滤膜吸附性能和截留性能的影响.结果表明,Freundlich吸附方程比Langmuir方程能更好地描述稀土离子在纳滤膜表面上的动态吸附行为,用Freundlich吸附方程拟合后的结果相关度系数R2能达到0.999以上;在初始浓度为5×105 μg/L,温度为25 ℃,运行压力为0.6 MPa的实验条件下,纳滤膜对稀土离子的浓缩提取过程中,初始阶段的截留机理取决于纳滤膜表面的吸附作用和膜孔的机械筛分效应,膜面吸附达到平衡后以膜孔的机械筛分效应为主,此时La3+、Nd3+、Pr3+、Ce3+和Y3+的截留率分别为94.21 %、81.25 %、85.80 %、89.90 %和81.18 %,表明经碳纳米管改性的亲水化纳滤膜能高效浓缩截留稀土浸出液中的稀土离子.      

Continuous biosorption of copper and lead in single and binary systems using Sphaerotilus natans cells confined by a membrane: experimental validation of dynamic models

Biosorption of heavy metals using membrane reactors as confining devise for free cells is an alternative process to remove these metallic pollutants from aqueous solution. In this paper, experimental data and modelling of heavy metal biosorption onto Sphaerotilus natans cells confined by a ultrafiltration/microfiltration (UF/MF) membrane reactor are reported. Biosorption tests using single and binary metallic solutions (Cu, Pb and Cu–Pb) denoted the biomass affinity (Pb>Cu), the competition among metals simultaneously present in the system, the filtrate flux decline and the change of metal retention coefficient on the membrane for pore plugging by cell fragments. Dynamic modelling is developed considering the unsteady mass balances of the metal in the system and the equilibrium parameters obtained by biosorption batch tests using Langmuir models. Experimental validation of the dynamic models denoted the importance of partial degradation of cells, which is specifically considered in modelling by introducing a time-depending profile for the biomass concentration.     

Rotation and Concentration Effects in High-Shear Ultrafiltration

A parametric waste-specific study was conducted to assess the effects of membrane rotational speed and feed oil concentration on the pressure independent “limiting” flux in a high-shear rotary ultrafiltration (HSRUF) system. The limiting flux data were adequately described by the thin-film model. The transition from pressure dependent to pressure independent behavior occurred at lower oil concentrations as membrane rotational speed was decreased and pressure was increased due to an increase in the thickness of the solute boundary layer at the membrane surface. A gel layer oil concentration, OCgel, of 39% was reported, and OCgel was determined to be constant with respect to average transmembrane pressure and membrane rotational speed. The solute mass transfer coefficient increased with membrane rotation and was greater than reported for conventional ultrafiltration systems. The greater mass transfer characteristics determined for the HSRUF system were attributed to the efficient delivery of “cleaning energy” to the membrane surface due to the effective decoupling of feed pressurization from recirculation∕hydraulic turbulence.     

自抗扰控制器在同步电机调速系统中的应用

针对同步电机磁场定向控制系统受负载扰动、电机参数变化影响问题,将自抗扰控制器(ADRC)应用于调速系统中.为解决传统磁链观测器存在的直流偏置和依赖电机参数的问题,提出了基于ADRC的磁链观测器.仿真结果表明:ADRC对负载扰动和参数变化具有较强的鲁棒性,并且响应速度快、超调小,具有优良的稳态和动态性能;改进后的磁链观测器能有效抑制直流偏置和参数变化带来的影响,提高磁链的观测精度.      

Evaluation of Membrane Processes for Reducing Total Dissolved Solids Discharged to the Truckee River

Truckee Meadows Water Reclamation Facility (TMWRF) is a 150,000?m3/day (40?mgd) tertiary wastewater treatment facility that serves the cities of Reno and Sparks, Nev. The effluent from TMWRF is discharged into the Truckee River which flows to Pyramid Lake—a very sensitive ecosystem and habitat for endangered species. Reverse osmosis (RO) and nanofiltration (NF), in conjunction with ultrafiltration (UF) pretreatment, were evaluated for total dissolved solids (TDS) and nutrient removal from the effluent of TMWRF at bench and pilot scale. Results from short-term pilot-scale tests showed that RO and NF membrane processes can successfully remove both TDS and nutrients from the effluent when paired with coagulation-enhanced UF pretreatment. NF membranes were able to achieve the necessary removal while maintaining higher fluxes and lower specific power consumption.     

Laminin localization in enterocytic basement membrane of rat small bowel grafts. A light and electron microscopic study

In vitro laminins stimulate numerous biological effects, such as cell migration, proliferation, attachment and differentiation. In vitro laminins influence immunocompetent cells and in vivo possibly play an important role in graft rejection. To establish how laminins could be involved in the regulation of acute rejection of small bowel allografts (with and without immunosuppression), we investigated laminin distribution in rat small bowel allografts four days after transplantation, i.e., before the onset of histological signs of rejection, using antibodies against alpha1, beta1, gamma1 chain of laminin-1. In immunosuppressed allografts, the ultrastructure of the enterocytic basement membrane appeared normal, but no laminin staining was seen in this membrane, although basement membranes of intramural blood vessels and muscle cells were normally stained. In non-operated immunosuppressed rats, laminin staining was clearly reduced in the enterocytic basement membrane, demonstrating that cyclosporin A is able to affect this membrane. Since only rats in which laminin is altered survive, this laminin alteration in the enterocytic basement membrane presumably plays an important role in overcoming the acute rejection.     

基于膜技术处理离子型稀土矿开采废水的研究

探究了更加实用的膜技术应用于处理稀土矿开采的废水,提出采用两级反渗透膜浓缩加硫酸调pH值工艺,使得二级反渗透出水的氨氮浓度低至5.05 mg/L,清液可直接达标排放或回用。浓缩液再经过纳滤膜,可进一步分离稀土离子,稀土离子总回收率达到93.01%。纳滤膜的清液中只有硫酸铵,可作为浸出试剂再利用。此实验过程中稀土离子和氨氮资源都可被回收利用,具有较好的经济价值。      

Existence of Critical Recovery and Impacts of Operational Mode on Potable Water Microfiltration

Results from a potable water microfiltration (MF) pilot study employing untreated surface water are reported. The effects of filtrate flux and recovery on direct flow, outside-inside, hollow fiber MF fouling rates, and backwash effectiveness are presented. Constant flux experiments suggested the existence of a critical recovery below which MF fouling rates were low and effectiveness of backwashes was high and relatively independent of the recovery. However, in the range of experimental conditions investigated, fouling rates increased dramatically and backwash effectiveness decreased steeply when this critical recovery was exceeded regardless of the flux. In general, for a fixed recovery, specific flux profiles analyzed on the basis of volume filtered per unit membrane area were insensitive to filtrate flux. Fouling was accelerated by operating membranes at constant flux rather than at constant pressure, in part, because of membrane compaction and cake compression. Changing the mode of filtration between constant flux and constant pressure is shown to have no effect on MF filtrate water quality. For any given capacity, membrane area requirements are decreased, and power requirements are increased when membranes are operated at constant flux rather than at constant pressure.