Hollow Fiber Microfiltration Membranes Research Articles

Adsorption of trace steroid estrogens to hydrophobic hollow fibre membranes

This paper discusses adsorption of the natural estrogen estrone to microfiltration hollow fibre membrane from aqueous phase. The partitioning of estrone between membrane and aqueous phase at equilibrium, the concept of membrane retention of estrone as a result of adsorption, adsorption kinetics, and the potential application of membrane adsorption have been assessed through batch adsorption and dead-end filtration studies using solutions containing trace estrone. The results show that adsorption could result in significant accumulation of estrone on membrane surfaces. The partitioning of estrone between membranes and aqueous phase can be characterized by the Freundlich equation. The microfiltration membrane could exhibit high retention to estrone due to adsorption but the retention decreases with increase in amount of estrone accumulated on the membrane surface. The results of this study have important implications, especially in drinking water applications. Contaminants such as natural and synthetic hormones may accumulate on membranes during treatment and desorb during backwash or membrane cleaning. Further studies are needed to address risk issues involved.

Fouling control in activated sludge submerged hollow fiber membrane bioreactors

The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid—liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH 4) 2SO 4 as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600–8400 mg/L. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.

Demonstrating the integrity of a large scale microfiltration plant using a Bacillus spore challenge test

For protection against Cryptosporidium and Giardia New Zealand drinking water regulations established a goal of removal of all particles of 1μm and larger. The City of Tauranga, New Zealand, commissioned a 36 ML/d (9.5 mgd) microfiltration (MF) plant, the Joyce Road Water Processing Plant (JRWPP), to meet this stringent reduction goal. The plant consists of ten USF Memcor 90M10C units. This paper details a bacillus spore challenge test conducted on the JRWPP. The objectives were to (1) confirm that the plant could achieve the required 5 log reduction of particles, and (2) evaluate direct and indirect integrity testing methods as means to confirm log-5 particle reduction performance over the life of the plant. The test used Bacillus megaterium spores dosed into the feed water with the plant operated to maximise the challenge on the MF hollow fibre membranes. The results showed (1) the ability of an integral MF plant to reject Bacillus megaterium spores and achieve at least log 5.9 reduction in organisms; (2) Bacillus spores are a good medium for testing as they are robust, easy to handle, cultured in large quantities, and easily identified; (3) the spore challenge test cannot be economically used to monitor full-scale plant performance; (4) particle counting results correlated poorly with bacillus counts in feed or filtrate; and (5) the USF Memcor integrity test methods, which included a pressure hold test and a diffusive airflow test, underestimated spore rejection.

Production and separation of α-agarase from Altermonas agarlyticus strain GJ1B

This paper presents results on the production of α-agarase by a fermentation process and its separation using membrane microfiltration (MF). Optimization of fermentation conditions for α-agarase production using Altermonas agarlyticus grown on medium containing agar as a carbon source was done in batch, fed-batch and continuous fermentations. Continuous culture at a dilution rate of 0.03 h −1 appeared to be best suited for production of α-agarase by this organism. At 0.03 h −1 dilution rate, enzyme activity was 0.9 U/ml. Clarification of broth was done using a hollow-fibre microfiltration membrane. The influence of hydrodynamic parameters on permeate flux and enzyme activity was studied. The best performance was obtained with prefiltered fermentation broth. A stable permeate flux of about 250–270 ml/min·m 2 and an enzyme retention rate between 0% and 25% was obtained at temperatures between 6°C and 22°C, transmembrane pressure of 100 mm Hg and fluid cross-flow velocity of 4×10 −2 m/s. From the experiments on concentration of fermentation broth, the best compromise between enzyme activity transmission and permeate flux was obtained at a concentration factor of 2.

Model for flux prediction in high-shear microfiltration systems

A semi-empirical model that predicts permeate fluxes in high-shear microfiltration systems is proposed. The model assumes that non-diffusive transport phenomena are the main mechanisms for the back-transport of particles from the membrane surface to the bulk solution during filtration. It also considers the use of reverse filtration (back-flushing) to control and minimize concentration polarization and fouling. This model incorporates an equation for the transient flux based on a particle mass balance at the membrane surface. The model has been validated by laboratory experiments using two different suspensions: flexographic ink (Φ b=0.005) and yeast (Φ b=0.01), where Φ b is the solid volume fraction in the suspension. The membrane system adopted in this research consists of a bundle of hollow-fiber microfiltration membranes submerged in a tank into which the effluent is introduced. Vacuum is used inside the fiber lumen to create transmembrane pressure differential, and aeration to promote high-shear stress at the membrane surface to minimize concentration polarization and fouling. Periodic reverse filtration (back-flushing) is also used. The experimental validation of the model was carried out by substituting the experimentally determined suspension and operating variables into the model. The results showed good agreement between model prediction and experimental observations.

Treatment of domestic wastewater using microfiltration for reuse of wastewater

This study was conducted to evaluate the applicability of microfiltration in treating domestic wastewater for reuse. A hollow fiber microfiltration membrane was used in the pilot test. The pore size of the membrane was 0.1 μm and effective surface area was 20 m 2. The maximum capacity of the pilot plant was 10m 3/d. The microfiltration system could be operated for 120 days without any cleaning procedure. It was found that agitation in the membrane tank had an effect on fouling prevention. In particular, the bi-directional agitation significantly reduced fouling. Chemical cleaning was effective in recovering of permeate flux and resistance, but in spite of chemical cleaning, fouling slowly progressed. According to the particle size distribution, in the membrane tank particles were transformed into smaller size by agitator-induced shear force. Based on mass balance analysis, about 60% of dissolved TOC mass removal in the system was attributed to biodegradation, indicating its important role. But suspended solids and colloidal matter were removed by the sieve mechanism of the membrane. Effluent quality was found to be lower than 30 mg/L of COD, 10 mg/L of BOD, 10 mg/L of TOC, 1 NTU of turbidity and 2 mg/L of SS, respectively. It satisfies the standard for wastewater reuse.

Membrane as Solid/Liquid Separator and Air Diffuser in Bioreactor

A bench-scale pilot plant was operated to evaluate the potential of using microfiltration hollow fiber membrane modules as an air diffuser and solid/liquid separator in an alternate cycle within a bioreactor treating domestic wastewater. Two modules capable of air backwashing were immersed in a bioreactor. Compressed air backwashing and filtration by suction were effected alternatively. The experimental results reveal that application of the air backwashing technique to submerged membrane modules is capable of not only declogging the membranes but also of aerating the mixed liquor. Thus, better filtration flux rate and aeration without a separate aeration device were attained simultaneously. It was also noted that the introduction of an anoxic zone enhanced the removal of nitrogen. In addition, operation at low hydraulic retention time with high sludge concentration and the absence of a sedimentation tank indicate considerable savings on the plant area.

Hollow fiber microfiltration membranes from poly(ether ether ketone) (PEEK)

A procedure for obtaining high performance large internal diameter (ID; >1 mm) hollow fiber microfiltration membranes from poly(ether ether ketone) (PEEK) is presented. A simple mixture of isomers of diphenylphthalate is a good solvent for employing the thermal-phase inversion process to obtain PEEK membranes. Obtaining large ID hollow fibers with substantial transmembrane flux requires sufficient melt strength during spinning to prevent excessive draw of the extruding fiber. The use of a second leachable polymer to the blend satisfies the conditions, and polysulphone (PS) is found to provide superior membranes relative to either poly(etherimide) (PEI) or poly(ether sulphone) (PES) as a second polymer. PEEK membranes obtained by this process yield better chemical resistance to a concentrated warm surfactant/oil solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 175–181, 1999

Microfiltration of activated sludge using submerged membrane with air bubbling (application to wastewater treatment)

A membrane bioreactor is one of the applications of membrane technology to wastewater treatment. In this study we present the results obtained using hollow fiber microfiltration membranes directly immersed in the bioreactor. Two sizes of equipment were used: laboratory scale with a specially designed set of microfiltration hollow fibers (filtration area 0.016 m 2) and pilot scale with a bundle of hollow fibers (filtration area 0.5 m 2). Filtered liquid was pumped at a constant flow rate by suction through the membranes at a fairly low transmembrane pressure (less than 300 kPa). The bubbles produced by aeration of the biomass were essential for cake removal. The study was performed with short-term and long-erm experiments successively. In the short-term experiments, the critical conditions, which were the limit of steady operation, were identified. In our conditions of operation the value of critical flux was about 30 l/h.m. 2. The influence of air flow rate on critical flux was investigated. It was demonstrated that aeration was a significant factor governing the filtration conditions and decreasing fouling resistance. With application of optimal air flow rate, it was possible to perform in quasi-steady conditions with a permeate flow rate which was about 30% of the initial pure water flux. During long-term trials, the influence of the impact of sludge residence time (10, 20 and 30 days) was compared in three bioreactors operated in parallel, considering sludge production, sludge concentration and the fouling potential of the different fractions of activated sludge (solid fraction and liquid fraction). Neglecting the negative effect of the anti-foaming agent, very high efficiency of COD removal could be obtained (up to 90%) at a volumetric load of 3.2kg COD/m 3/d and a sludge residence time of 20 days.

Filtration characteristics of hollow fiber microfiltration membranes used in membrane bioreactor for domestic wastewater treatment

Cross-flow microfiltration using submerged membrane with air bubbling can provide a continuous solid-liquid separation system by simple equipment, such as a low-rate suction pump, an air blower and a vessel. In this system, the size of the separation module could be reduced by using hollow fiber membranes packed in high density. In order to apply this beneficial process to a wastewater treatment bioreactor, we constructed filtration models to design the membrane system. Higher transmembrane pressure and lower fluidity of feed operations (e.g. transmembrane pressure of over 40 kPa and air-liquid two phase flow velocity, u∗, of under 0.5 m · s −1) caused the rapid crowding of hollow-fiber membrane elements and reduced the effective membrane surface area. Under the conditions that do not cause the rapid crowding, the steady-state filtration flux, J ss, is expressed as J ss = V L = K' · ф · u∗ 1.0 · MLSS −0.5 , where, V L, K′ and ф were lift velocity, filtration constant and the geometric hindrance coefficient of membrane module, respectively. The J ss values of hollow fiber membranes corresponded to that of rigid tubular ceramic membranes packed in low density. In this study, we defined the conditions that the hollow fiber membrane module packed in high density could be applied for solid-liquid separation. The flexibility and movability of hollow fiber membrane elements could not improve the flux.

Study on fouling materials in the membrane treatment process for potable water

Studies were made on a water treatment process which used hollow fiber microfiltration membranes for potable water. The influent, which was from a eutrophic lake named Kasumigaura, was provided directly into the treatment system, and no pre-treatment such as coagulation was done. Dead-end filtration was carried out under constant rate permeation, and membranes were washed by air-scrubbing. The trans-membrane pressure (TMP) had increased to 100 kPa, and the color of the membranes turned brown after 19 days of operation. X-ray microanalyzer (XMA) revealed that the brown material on the membrane surface was manganese. Furthermore, the amount of total organic carbon (TOC) and manganese in the fouling materials were one order of magnitude higher than that of other inorganic elements. TOC and manganese were dominant fouling materials. By correlating the amount of extracted fouling materials and the recovery of membrane permeability, it was concluded that the decline in membrane permeability was mainly caused by organic matter.

Organic waste water treatment by activated sludge process using integrated type membrane separation

In tests on activated sludge wastewater treatment using hollow fiber microfiltration membranes, during continuous filtration 2 stages of filtration pressure were found - a stationary phase where fouling progresses and a non-stationary stage with interfiber clogging.

Recycling of waste water from buildings by application of membrane technology

In urban districts the existing municipal water supply and effluent facilities are almost saturated as the result of the concentrated population and raised level of living. In order to solve such a problem, miscellaneous water utilization systems to treat waste water for reuse have been introduced in newly constructed large-size buildings in large cities such as Tokyo. Among such various systems an actual example of reusing building waste water with tubular UF membranes is shown and the result of the study on applications of a dynamic membrane filtration method using hollow fiber microfiltration (MF) membranes is discussed.

Protein fractionation using fast flow immobilized metal chelate affinity membranes

A new group-specific affinity membrane using metal chelates as ligands and inorganic glass hollow fiber microfiltration membranes as support matrices is developed and tested. The study focused on developing the optimum activation and coupling procedures to bind the chelating agent (iminodiacetic acid, IDA) to the surface of the microporous glass hollow fiber membrane and testing the resultant affinity membrane. Starting with three different glass surfaces, five modification reactions were evaluated. All the modified "active surfaces" were first tested for their protein adsorptive properties in batch mode with suspended microporous glass grains using model proteins with known binding characteristics with Cu-IDA systems. The metal loading capacities of the surfaces exhibiting favorable fractionation were then measured by atomic absorption spectroscopy.The results were compared with the results obtained with a commercial material used in immobilized metal affinity column chromatography. The protein binding characteristics of the hollow fiber affinity membranes were also evaluated under conditions of convective flow. This was performed by flowing single solute protein solutions through the microporous membrane at different flow rates. These results were then used to estimate the optimum loading and elution times for the process. A mathematical model incorporating radial diffusion was solved using a finite difference discretization method. Comparison between model predictions and experimental results was performed for four different proteins at one flow rate. These results suggested that the kinetics of adsorption was concentration dependent. Finally, the hollow fiber affinity membranes were challenged with two component mixtures to test their ability to fractionate mixed protein solutions. Efficient separation and good purity were obtained.The results presented here represent the development of a new fast flow affinity membrane process-immobilized metal affinity membranes (IMAM). (c) 1994 John Wiley & Sons, Inc.

Sorption kinetics of cobalt in chelating porous membrane

Glycidyl methacrylate was grafted onto a microfiltration hollow-fiber membrane. Subsequently, the produced epoxide group was converted into an iminodiacetate (IDA) group. The cobalt solution was permeated across the chelating porous membrane through the submicron-diameter pores. The efficient removal of cobalt ion during permeation was demonstrated by the resulting breathrough curve. Furthermore, the prove of the amount of cobalt sorbed across the membrane was determined as a function of the effluent volume by X-ray microanalysis (XMA)

中空糸精密ろ過膜によるプール水循環利用技術

中空糸精密ろ過膜によるプール水循環利用技術

Membrane separation of protein precipitates: Studies with cross flow in hollow fibers

Hollow fiber ultrafiltration and microfiltration membranes are examined for the processing of isoelectric soya protein precipitate suspensions. A model based on the various resistances to permeate flux is used to describe membrane performance. The main resistance to permeate flux is due to the interaction between the active membrane and the soluble and precipitated protein; that is, as compared with resistances due to the active membrane itself or the membrane support structure, or arising from concentrated soluble or precipitated protein layers over the membrane surface. Soluble protein rejection and precipitate mean particle diameter are correlated with observed values of this main resistance.In contract to the ultrafiltration of soluble proteins, the flux rates observed when processing protein precipitate suspensions under a similar range of operating conditions do not approach a limiting value with increased transmembrane pressure. At high protein concentrations, greater flux rates may be achieved for precipitated as compared with soluble proteins. The use of a microfiltration membrane does not give further improvement in flux rate; this may be attributed to problems of pore fouling with precipitate particles.