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.     

Impact of Membrane Surface Modification on the Treatment of Surface Water

New polyethersulfone (PES) based membranes for ultrafiltration (UF) were developed by blending a surface-modifying macromolecule (SMM) in the casting solution, in an attempt to minimize the impact of fouling. Fouling was evaluated using concentrated Ottawa River water (CORW), either unfractionated or fractionated via UF. These membranes also included some polyvinylpyrrolidone (PVP), a pore forming additive. A statistical analysis was conducted to evaluate the impact of some variables on the treatment of the surface water. The independent variables included PVP/PES ratio in the casting solution, with and without SMM, and the nature of the feed CORW [low molecular weight (LMW) fraction, unfractionated, high molecular weight (HMW) fraction]. The performance variables studied were total organic carbon (TOC) removal, the foulant accumulation at the membrane surface after filtration, the flux reduction, and the final permeate flux. The most important variable was the feed water. Filtration of LMW had a higher final flux, less fouling, but slightly lower TOC removal. The SMM did not significantly impact the membrane performance. TOC removal was high, compared with results reported in the literature for UF membranes.     

Surface Properties of Biofouled Membranes from a Submerged Anaerobic Membrane Bioreactor after Cleaning

The surface structural properties of biofouled membranes from a laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating kraft pulping evaporator condensate after cleaning were studied. A flat sheet polyvinylidene fluoride (PVDF) membrane was used for the study. Three different cleaning methods, physical cleaning (PC), maintenance chemical cleaning (MCC), and recovery cleaning (RC) were applied to the fouled membrane surface, and the treated membranes were subject to flux recovery and surface structural analysis by using spectroscopic methods, zeta potential measurement, attenuated total reflectance-Fourier transform infra red spectroscopy (ATR-FTIR), and advanced correlative microscopic methods, including confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Neither PC, MCC, nor RC methods restored the membrane permeability to initial conditions. Adhesion of a thin extracellular polymeric substance (EPS) layer, consisting of proteins and polysaccharides with a thicknesses of 4.0?μm, 5.3?μm, and 7.1?μm and roughness of 190?nm, 236?nm, and 273?nm was observed on RC, MCC, and PC treated membrane surfaces, respectively. Partial flux recovery was achieved with the MCC and RC methods. This was correlated to the reduction of the protein associated with the foulant. Polysaccharides were found to be the most stable and predominant EPS constituent in relation to protein on the biofouled layer of RC and MCC membrane surfaces.     

Comparison of ultra- and microfiltration in the presence and absence of secondary flow with polysaccharides, proteins, and yeast suspensions

The purpose of this research was to show that controlled centrifugal instabilities-Dean vortices-produced by solutions and suspensions from typical biotechnology applications flowing through curved tubes can be used to reduce concentration polarization and/or fouling in pressure-driven ultrafiltration (UF) and microfiltration (MF) processes. Experiments were conducted to (i) evaluate the ultrafiltration performance of hollow fiber membranes in linear and helical configurations with dextran (low fouling) and bovine serum albumin (high fouling) solutions and (ii) compare the performance of linear and helical coiled UF hollow fiber modules with that of similar MF modules using baker's and beer yeast (Saccharomyces cerevisiae) suspensions as feed. Both constant transmembrane pressure (TMP) and constant permeation flux (J) experiments were utilized here. The membrane material was polyether sulfone. For the ultrafiltration experiments, the helical module performed consistently better than the linear module with dextran T500 and BSA solutions, resulting in performance improvements (helical versus linear) from 20 to 200% and up to 85%, respectively. For the comparative experiments between UF and MF, the helical module again performed better than the linear module for low concentration baker's yeast suspensions (0.5-1% dry wt). At constant TMP, the flux improvements for UF were 30-120%, while at constant J, the capacity or loading was 4.5 times higher for the UF as compared to the MF membrane. At high beer yeast concentrations (5.1-6.8% dry wt), although flux improvements were not observed between the linear and helical modules for UF, the UF fluxes were 72% higher than that obtained with MF. Also, for MF, with the same high beer yeast concentrations, the helical module exhibited 30-90% higher fluxes than that obtained with the linear module. At constant flux (117-137 L m-2 h-1) and intermediate baker's yeast concentrations (0.65-2.7% dry wt), 10-20 times the capacity was obtained for the helical over the linear module. Yeast cells were the dominant foulant. For constant UF flux (70 L m-2 h-1) experiments at high beer yeast concentrations ((4.3-7.7) x 10(7) cells/mL or 5.1-6.8% dry wt), the capacity (loading) for the helical module was 10 times that of the linear module. Again, the yeast cells were the dominant foulant. A new mass-transfer correlation for ultrafiltration of dextran T500 solutions for laminar flow in a helical hollow fiber module was obtained, viz. Sh = 0.173Re0.55Sc0.33(a/Rc)0.07.     

Investigating Role of Growing Adsorbent Bed in a Dead-End PAC/UF Process

A two-stage mathematical model was developed to describe adsorbate removal in a dead-end powdered activated carbon/ultrafiltration (PAC/UF) membrane process. Para-nitrophenol (PNP) was used as the model organic compound. The first stage accounted for adsorbate removal during transport from the initial PAC contact with the PNP solution to the membrane system, and the second stage accounted for additional PNP removal due to the retention of the PAC in a growing bed on the membrane surface. The PAC adsorptive capacity was described using the Langmuir isotherm, whose parameters were estimated from isotherm experiments. Transport of the PNP through the PAC particle was described using the homogeneous surface diffusion model and the surface diffusivity was estimated from batch experiments. The two stage model predicted the effluent concentrations from the PAC/UF process during the early stages of the experiments, but model improvements are required to more accurately predict the latter stages. A batch model can be used to describe the effluent PNP concentration from the PAC/UF process if dispersion is neglected.     

超滤法处理邯钢冷轧乳化液废水

简述了超滤膜技术在邯钢冷轧含油及乳化液废水处理方面的典型应用,并详细论述了超滤法原理、超滤膜材质、影响超滤性能的因素、超滤工艺的典型操作模式、超滤装置、超滤膜的清洗、超滤膜法处理含油废水及乳化液废水的优缺点以及其处理效果等.实践证明:采用超滤法处理冷轧厂含油废水及乳化液废水,能达到污水净化的目标.     

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.     

Recovery of Metal Working Fluids Using Chelation-Ultrafiltration Process

Metal working (MW) fluids are used to control friction and temperature, improve workpiece surface quality, and reduce tool wear. The batch-life of the MW fluid investigated was controlled primarily by the concentration of metallic soaps (complexes between the oil emulsifier and Al∕Mg. Ethylenediaminetetraacetic acid, a strong metal chelator, was added to the MW fluid to break the oil-Al∕Mg complexes. The aqueous-phase ethylenediaminetetraacetic acid-Al∕Mg complexes were then separated from the oil phase by ultrafiltration (UF). Al levels were reduced between 39 and 49%, and Mg levels were reduced between 67 and 77%. Al transfer from the oil phase to the aqueous phase was slow and increased during UF concentration. Rinsing the concentrated MW fluid with deionized water decreased the ash content but had a lesser impact on Al∕Mg removal. Al mass balances produced errors of 2.8% for run 3 and 6.2% for run 4. The UF system (0.11-μm ceramic membrane) effectively separated the oil and aqueous phases. Permeate turbidity was generally <1 nephelometric turbidity unit and permeate flux ranged from 390 to 220 L∕m2-h (230 to 130 gal.∕ft2-day) depending on the degree of concentration.     

Pressure-Dependent Permeate Flux in Ultra- and Microfiltration

The effect of applied pressure on the permeate flux in cross-flow ultrafiltration (UF) and microfiltration (MF) was investigated both theoretically and experimentally. In UF and MF processes, the permeate fluxes are controlled by concentration polarization and cake formation over the membrane surface. As a better understanding of concentration polarization and cake formation becomes available, the permeate flux under any pressure can be theoretically predicted. Experiments were conducted in a ceramic tubular cross-flow filter with silica colloids of a narrow size distribution (model colloids). The pressure-dependent flux of the model colloidal suspension in cross-flow filtration was investigated under various experimental conditions. The experimental measurements were compared with the theoretical predictions, and the results showed that the pressure-dependent permeate flux in cross-flow filtration can be adequately predicted. Furthermore, theory and experiments demonstrated that the performance and operating state of UF and MF could be well characterized by the so-called “characteristic pressure” of the process.     

Bench-Scale Testing of Nanofiltration for Seawater Desalination

A dual-staged nanofiltration process is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. Investigation of this system at the bench-scale level focused on membrane surface characterization, ion rejection (including boron, bromide, and iodide rejection), and flux decline. Results from this study showed that two commercially available nanofiltration membranes can effectively desalinate seawater. Although fouling was apparent—and resulted in approximately 20% flux decline over 3 days—a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on the polarization modulus, and hence on membrane performance.     

Use of Iron Oxides to Enhance Metal Removal in Crossflow Microfiltration

This research investigated whether iron oxyhydroxides used in conjunction with microfiltration could improve the removal of metals from a waste while maintaining adequate flux. Filtration of individual metals, a mixture of metals, and the mixture with two iron oxides were investigated. The research indicated that use of a coagulant (an iron-containing salt) might not be as important in microfiltration systems as in conventional gravity separation systems, because of the small pore size of microfilters. In some cases, filtration efficiency was relatively poor at the beginning of a treatment cycle, but in almost all cases it became excellent once a layer had built up on the membrane surface. The greatest benefit provided by iron oxides might be to reduce membrane fouling. A crystalline iron oxide such as goethite is more attractive than ferrihydrite. The flux improvement with goethite is greatest if a thin layer is deposited on the membrane surface before the contaminant metals are injected into the system, so that the goethite can trap the potentially foulant metal hydroxide particles away from the membrane surface.     

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.     

Effects of Operating Parameters in Tubular Ultrafiltration

A parametric waste-specific study was conducted to develop a more mechanistic understanding of the tubular ultrafiltration system using a surrogate metalworking (MW) fluid as a model waste stream. An average gel layer concentration of 31% oil was calculated and the gel layer concentration was determined to be independent of transmembrane pressure and cross-flow velocity. The thin-film model adequately described limiting flux data collected in this study, due to the use of discrete cross-flow velocity∕MW fluid concentration experiments; thus, an improved mechanistic understanding was achieved. Mass transfer and thus the pressure-independent “limiting” permeate flux were generally comparable to values observed in a high-shear rotary UF system, for oil concentrations <26%. However, a decrease in net permeate flux was observed in the tubular ultrafiltration (UF) system at high feed oil concentrations; thus, a hybrid system (conventional tubular followed by high-shear rotary UF) is proposed for treatment applications where high concentrations are desired.     

Three-dimensional fibroblast culture implant for the treatment of diabetic foot ulcers: metabolic activity and therapeutic range

Dialysis techniques are discussed as a means for effective removal of low-molecular-mass components from fermentation broth to reach high cell density. Reactor systems and process strategies, the relevant properties of membranes and examples for high-density fermentation with dialysis, and problems related to scale-up are addressed. The dialysis technique has turned out to be very efficient and reliable for obtaining high cell densities. As in dialysis processes the membranes are not perfused, membrane clogging is not a problem as it is for micro- and ultrafiltration. By applying a "nutrient-split" feeding strategy, the loss of nutrients can be avoided and the medium is used very efficiently. The potential of dialysis cultures is demonstrated on the laboratory scale in a membrane dialysis reactor with an integrated membrane and in reactor systems with an external dialysis loop. In dialysis cultures with different microorganisms (Staphylococci, Escherichia coli, extremophilic microorganisms, Lactobacilli) the cell densities achieved were up to 30 times higher than those of other fermentation methods. The technique enables high cell densities to be attained without time-consuming medium optimization. For animal cell cultures the concept of a fixed bed coupled with dialysis proved to be very effective.     

Process Limits of Municipal Wastewater Treatment with the Submerged Membrane Bioreactor

The submerged membrane bioreactor (SMBR) is a promising technology for wastewater treatment and water reclamation. This paper presents results from two pilot scale SMBR systems operating in parallel on municipal wastewater in San Diego, Calif. The SMBRs were operated to address the limitations and advantages of the SMBR process compared to conventional activated sludge processes. Minimal membrane fouling was observed throughout the year of testing with the exception of the process limitations. Both pilot units provided consistently high quality effluents throughout the study, even when operating at hydraulic retention times as low as 1.5 h. Two sets of experiments were conducted to identify different fouling conditions. The first experiments were conducted to explore operation at high suspended solids concentrations. The SMBR process experienced adverse performance at mixed liquor suspended solids concentrations greater than approximately 20?g/L. The second experiments explored operation at low mean cell residence time (MCRT). At an MCRT of <2 days, membrane fouling was rapid. Chemical cleaning with sodium hypochlorite solution provided full recovery of the membrane permeability.     

Application of solid-phase extraction in the method development for determination of SEPA, an acronym for soft enhancement of percutaneous absorption, in human, rat, and rabbit serum using GC-FID method

A new nonaqueous topical minoxidil formulation containing SEPA (2-n-nonyl-1,3-dioxolane) for enhancement of percutaneous absorption was under evaluation. SEPA does not have chromophore for either ultraviolet or fluorescence detection using liquid chromatography and has no functional groups for derivatization. Therefore, a direct gas-chromatographic method with flame-ionization detection (GC-FID) was developed. Owing to the limited detection response of the FID detection, it needs a selective and concentrated extract for GC-FID analysis to improve the assay sensitivity to meet the requirement for pharmacokinetic evaluation after topical application. In addition, SEPA is a very volatile compound. Any extraction procedures involving evaporation will result in a poor recovery. The application of solid-phase extraction (SPE) makes it possible to achieve a selective and a 10-fold concentrated extract with an absolute extraction recovery of approximately 90%, which greatly improved the assay sensitivity. This method involved the extraction of SEPA and the internal standard (2-n-heptyl-1,3-dioxolane) from serum (0.1-1 ml) with 100 microliter of hexane-chloroform (1:1, v:v) using a 50 mg 1.0 ml-1 phenyl SPE column (Varian, Harbor City, CA, USA), followed by direct GC-FID analysis on a fused-silica column chemically bonded with cross-linked methyl silicone gum phase (Hewlett Packard Ultra-1, 12 m x 0.2 mm x 0.33 micron, Avondale, PA, USA). The assay demonstrated a lower limit of quantitation of 2.5 ng ml-1 and a linear range of 2.5 to 250 ng ml-1 with intra- and inter-assay precision and accuracy of < or = 10%.     

Mucosal and serosal fluxes of alanine in rabbit ileum

The four unidirectional fluxes of alanine across the mucosal and serosal borders of rabbit ileum were evaluated as functions of the alanine concentration on a single piece of tissue using a method previously described (Naftalin, R.J. and Curran, P.F. (1974) J. Membrane Biol. 16, 257-278). The effects of Na+ removal and of ouabain on these fluxes were investigated. Alanine was actively transported across the mucosal membrane under control conditions; Na+ removal or ouabain inhibited this process as a result of a decrease in flux from the mucosal solution to the cell and an increase in the flux in the opposite direction. The results concerning mucosal efflux of alanine are apparently inconsistent with the carrier model for alanine transport at this border. Alanine transfer across the serosal membrane appeared to involve a facilitated transfer mechanism. Alanine movement at the serosal side of the cell was not influenced by Na+.     

Application of stirred mill to upgrading of graphite concentrate by flotation

It is difficult to obtain high-grade concentrates for layered minerals, such as graphite, by mineral processing due to the existence of impurities between interlayers. Conventional grinding mills are inefficient in liberating the mineral layers. Upgrading a graphite concentrate by re-grinding with a designed stirred mill is investigated in this paper. Better liberation of mineral layers was achieved, compared with a ball mill and a rod mill. Through re-grinding with the stirred mill followed by a two-stage cleaning flotation process, a low-grade graphite concentrate containing 84.59% fixed carbon could be refined to a high-quality concentrate containing 98.62% fixed carbon with a graphite recovery of 94.15%. It is demonstrated that the stirred mill is more suitable for selective grinding, mineral flake protection and upgrading of layered minerals.     

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.     

去除烧结和电炉废气中二恶英的方案

20世纪90年代初,由于各国政府和绿色环保组织要求极大降低二恶英和其他有害物质的排放量,使钢铁工业遭受巨大压力,从那时起,奥钢联工程技术公司（VAI）就着手进行新一代烧结废气净化系统和创新型电炉废气净化技术的开发,一个主要目标就是要开发出一种新系统,与传统系统相比,不仅具有更高的除尘效率,而且还能够有效地去除二恶英和其他有害物质,努力的结果是,开发出的系统可使二恶英的去除效率达到80％－99％,即净化后气体中二恶英的浓度可降至0．1－0．4ng I-TEQ。