Cross-flow Membrane Filters Research Articles

Investigation of membrane fouling in cross flow microfiltration of non-alcoholic beer and modeling of tubular membrane flow

In the present work, numerical simulation of cross flow microfiltration of non-alcoholic beer in a tubular membrane has been studied theoretically and verified experimentally. Finite element method was used as a powerful tool for simulation. The feed stream, which flows mainly tangentially to the porous membrane surface, is modeled by the Navier–Stokes equations whereas the porous wall conditions are described by the Darcy equation that relates the pressure gradient within a flow stream to the flow rate through the permeable wall. A new model that considers transient behavior of the membrane due to fouling was used to estimate the permeate flux reduction. A pilot-scale cross flow membrane filter was developed to verify the model results in which ceramic tubular membranes were used. The cross flow velocity of the feed solution was controlled in the laminar region. It was shown that the model results have good agreement with experimental observations and therefore the model developed in this work can be used for design or optimization of the microfiltration of non-alcoholic beer.

Use of Cross-Flow Membrane Filtration in a Recirculating Hydroponic System to Suppress Root Disease in Pepper Caused by Pythium myriotylum

Zoosporic pathogens in the genera Pythium and Phytophthora cause extensive root disease epiphytotics in recirculating hydroponic vegetable-production greenhouses. Zoospore cysts of Pythium myriotylum Drechsler were used to evaluate the effectiveness of cross-flow membrane filters to control pythiaceous pathogens in recirculating hydroponic systems. Four membrane filter brands (Honeycomb, Polypure, Polymate, and Absolife) were tested alone or in combination to determine which filters would effectively remove infective propagules of P. myriotylum from solutions and reduce disease incidence and severity. Zoospore cysts of P. myriotylum generally measured 8 to 10 microm, and it was hypothesized that filters with pore-sizes<5 microm would be effective at removing 100% of the infective propagules and protect pepper plants from root infection. Single-filter assays with Honeycomb and Polypure brands removed 85 to 95% of zoospore cysts when pore sizes were rated at 1, 5, 10, 20, or 30 microm. Single-filter assays of Polymate and Absolife brands were more effective, exhibiting apparently 100% removal of zoospore cysts from nutrient solutions on filters rated at 1 to 10 microm. However, plant bioassays with Honeycomb and Polymate single filters failed to give long-term protection of pepper plants. Double-filter assays with 1- and 0.5-microm Polymate filters significantly increased the protection of pepper plants grown in nutrient film technique systems but, eventually, root disease and plant wilt could be observed. Insect transmissions by shore flies were not factors in disease development. Scanning electron microscopy images of zoospore cysts entrapped on Polymate filters revealed zoospore cysts that were either fully encysted, partially encysted, or of unusually small size (3 microm in diameter). It was concluded that either the atypically small or pliable pleomorphic zoospore cysts were able to penetrate filter membranes that theoretically should have captured them.

Experimental Study on Revolving Cross-flow Microfiltration of Highly Viscous Liquids

Experimental investigation of the microfiltration (MF) using a revolving cross-flow membrane filter was performed under the condition of constant pressure difference, and different flat membranes made of polyvinylidene fluoride (PVDF, 0.1 μm), cellulose acetate (CA, 0.22 μm), sulfonated polyethersulfone (SPES, 0.22 μm) and polyamide (PA, 0.45 μm), respectively, were used in filtration experiments. The dependence of the filtrate mass of the cross-flow MF on time was measured on-line. The experimental results showed that the effect of the cross-flow on high viscosity medium was more significant than that on the low viscosity one.

Pressure, flow, and concentration profiles in open and spacer-filled membrane channels

A finite element model was developed to study momentum and mass transport in cross flow membrane filtration systems with open and spacer-filled channels. Simulated conditions represented a range of membrane desalination applications and considered both open and spacer-filled straight through channels, as well as a geometry representing lab-scale cross flow membrane filtration cells. The finite element model agreed with classical analytical models for pressure drop, fluid shear, and concentration polarization in straight-through open channels at low flux and high cross flow. In simulations of representative lab-scale cross flow membrane filters, stagnant regions at the entrance and exit regions, as well as developing flow lead to significant deviations between analytic model and finite element model results. In spacer-filled channels, axial pressure drops were substantially higher than in open channels, varying by a factor of 2 for different spacer configurations (cavity < zigzag < submerged), while shear rates were on average enhanced, but appeared to create stagnant zones where the filaments contacted the membrane. On average, feed channel spacers reduced the extent of concentration polarization because of the enhanced wall shear rates. However, the stagnant regions (in front and behind some spacer filaments) led to enhanced concentration polarization, which suggests certain spacer designs could promote local scale and cake formation in spiral wound elements.

A Review of Downhole Separation Technology

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 94276, “A Review of Downhole Separation Technology,” by O.O. Ogunsina, SPE, and M.L. Wiggins, SPE, U. of Oklahoma, prepared for the 2005 SPE Production and Operations Symposium, Oklahoma City, Oklahoma, 17–19 April. Downhole oil/water separation (DOWS) allows water to be separated in the wellbore and injected into a suitable injection zone downhole while oil, with traces of water, is produced to the surface. After introduction of DOWS in the 1990s, several trial applications were undertaken to test the technology. These trials allowed information to be collected on DOWS feasibility. The full-length paper reviews the status of downhole separation technology and presents an extensive list of references. Introduction Produced water is water produced to the surface from hydrocarbon-bearing formations during oil and gas extraction and can include formation water, injection water, and any chemicals added downhole. Conventional production processes involve producing both oil and water to the surface and then separating them at the surface. Surface separation is accomplished by use of separation and dehydration equipment including skimmer vessels, plate coalescence, hydrocyclones, and, in some cases, crossflow membrane filters to reduce the oil content in the water phase and improve water quality before disposal. As a reservoir matures and oil and gas production peaks, often there is an associated increase in water cut and a corresponding increase in both lifting and water-disposal costs. The increased water cut also necessitates additional maintenance for production equipment and downhole treatment for corrosion, bacteria, and scale. Although producers still have a variety of choices in either disposing of the water or reusing it, there is a growing concern from the public related to the handling of this waste product. Public concern about the environmental impact of produced-water disposal has become a major issue, especially related to surface damage caused by spillage or subsurface contamination of drinking water caused by poor injection practices. Environmental regulations pertaining to produced-water management are expected to become more stringent in the future, requiring new practices and techniques to manage produced water. DOWS technology was introduced to the oil and gas industry in the 1990s, and work to assess its feasibility was sponsored by the U.S. Dept. of Energy in 1999. DOWS, unlike conventional separation processes, separates oil and gas from produced water at the bottom of the well and injects the separated produced water into another formation, usually deeper than the producing formation, while the oil and gas are pumped to the surface. Depending on DOWS type, typical DOWS project costs (procurement and installation) range from U.S. $120,000 to$300,000. Although reports show that some DOWS projects have had payback periods as short as 2 months, the relatively high project costs suggest that the design life or time to failure is a critical factor for the success of a DOWS project. The degree and duration of benefit that can be realized with DOWS technology depend on the characteristics of the producing well, reservoir rock and fluid properties, and the robustness of the separator/pump assembly.

The use of multiobjective optimization to improve wine filtration

Multiobjective optimization method was applied to achieve high quality wines using membrane filtration. Different Hungarian wines were filtered by ceramic cross-flow membrane filters with changed recycle rates. The quality parameters of wines (polyphenol, protein, colloid and tartaric acid concentrations, etc.) and the permeate flux were measured as functions of membrane pore size, recycle flow rate and pretreatment of wine. The quality and operating parameters were expressed by regression functions for each wine. To calculate the multiobjective optimum the minimal loss method was used with weight factors. Case studies are shown for producing bottled wine and champagne taking into account at the same time quality and economic purposes.

Influence of Crossflow Membrane Filter Geometry and Shear Rate on Colloidal Fouling in Reverse Osmosis and Nanofiltration Separations

A laboratory-scale crossflow membrane filtration apparatus was designed to investigate the relative influence of filter geometry and shear rate on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes. An expression that allows clarification of the mechanisms of flux decline due to colloidal fouling in RO and NF separations was derived by combining the solution-diffusion model, film-theory, and a modified cake filtration model. With this new fouling model, the interplay between the salt concentration polarization layer and a growing colloid deposit layer may be quantified. The hydraulic pressure drop across a colloid deposit layer was shown to be negligible compared to cake-enhanced osmotic pressure. The difference in flux decline observed in filters with different channel heights resulted from different cake layer thickness, and thus, different cake-enhanced osmotic pressure. A moderate reduction in the initial concentration polarization and cake-enhanced osmotic pressure was obtain...

Finite element analysis as a tool for crossflow membrane filter simulation

Finite element analysis (FEA) is a very powerful tool in analyzing many engineering problems. In this study, FEA was used to simulate the development of concentration polarization in ultrafiltration of protein solutions. A miniature crossflow membrane filter was developed to verify the FEA models. Polysulfone membrane disks (47 mm) were used in this study. Bovine serum albumin (BSA) solutions of different concentrations were pumped across the membrane flow channel. The crossflow velocity of the feed solution was carefully controlled at the laminar region. With the flow velocities within the flow channel estimated by a perturbation solution, the protein concentration on the membrane surface and the mass transfer coefficient were accurately predicted by FEA. This simulation method may provide a useful tool in engineering analysis and design of a membrane filtration process.

Mammalian cell retention devices for stirred perfusion bioreactors.

Within the spectrum of current applications for cell culture technologies, efficient large-scale mammalian cell production processes are typically carried out in stirred fed-batch or perfusion bioreactors. The specific aspects of each individual process that can be considered when determining the method of choice are presented. A major challenge for perfusion reactor design and operation is the reliability of the cell retention device. Current retention systems include cross-flow membrane filters, spin-filters, inclined settlers, continuous centrifuges and ultrasonic separators. The relative merits and limitations of these technologies for cell retention and their suitability for large-scale perfusion are discussed.

The effect of denaturants on the crossflow membrane filtration of Escherichia coli lysates containing inclusion bodies

Recovery of inclusion bodies from Escherichia coli cell lysates often includes a washing step to remove associated contaminants that may otherwise interfere with refolding of the solubilized protein. The effects of denaturants typically used in the washing step on the cell lysate viscosity and membrane filtration performance were examined. Guanidine HCl alone and in combination with the nonionic detergent, Triton X-100, had the greatest effect on the cell lysate viscosity, the dead-end filtration rate and the performance of the crossflow membrane filters. Triton X-100 reduced the dead-end filtration rate, but had less of an effect than guanidine HCl on permeate flux during crossflow membrane filtration. Urea had minimal effect on either the dead-end filtration rate or the permeate flux and protein transmission during crossflow membrane filtration. The use of low concentrations of urea along with a PVDF membrane allowed for inclusion body washing without detrimental changes in the permeate flux and protein transmission during crossflow membrane filtration.

The design and costing of a continuous ethanol process using wheat and cell recycle fermentation

The preliminary design and costing of a 100 million litres/year wheat-ethanol plant using continuous cell recycle fermentation, where the cells were separated after the fermentation using cross-flow membrane filters, were investigated. As part of the design, two other unconventional steps were required: the separation of suspended solids before saccharification and the hydrolysis of dextrins by immobilized enzymes. The total capital cost was estimated as $Can51.2 million (based on an exchange rate of $Can1.15 = $US1.00) and, based on a wheat price of $Can90/tonne, a total operating expenditure of $Can450 per 1000 litres of ethanol. Assuming an ethanol price of $Can460 per 1000 litres of ethanol, the total income (including by-products) was estimated at $Can630 per 1000 litres of ethanol, giving a net profit after sales, administrative overheads and taxes of $Can7 million/year. It should be noted, however, that the wheat cost makes up over 60% of the total operating expenditure and as such the profit would drop rapidly with increases in this cost.

Macrocolloidal Transport in Membrane Filters in Slow Laminar Flows: Polarization Chromatography

Particle transport in crossflow membrane filters is the result of complex interactions originating from module hydrodynamics, suspension chemistry and external forces. Experimental and theoretical investigations of particle transport in dilute suspensions were conducted in a laboratory model membrane filter to understand fundamental aspects of macrocolloidal transport. Particle residence time distributions (RTDs) were obtained experimentally under varying hydrodynamic conditions in the filter by making pulse inputs. Under conditions of laminar flow, particle transport can be divided into two regimes: convection dominated and diffusion dominated. Convective transport is described quantitatively by theories of particle mechanics as evidenced by correlations presented regarding the first passage time as well as the peak response. Diffusive transport is demonstrated by multiple peaks in the RTDs under existing experimental conditions. Understanding these transport processes can lead to a more rational design, selection and operation of membrane systems and pre-treatment options.

Cross-flow membrane filtration of yeast suspensions

The feasibility of harvesting yeast cells using synthetic membranes was studied. Three cross-flow membrane filters were compared in terms of flux and cell yields: a pleated-sheet microfilter, a tubular microfilter and a hollow fiber ultrafiltration module. Flux declined in an exponential manner with time with all three modules. In general, lower fouling rates were observed at lower cell concentrations, lower transmembrane pressures and higher velocity. Media components played a relatively greater role in the fouling phenomenon at low cell concentrations. The ultrafiltration module had much lower fouling rates than the microfilters. The pleated-sheet microfilter experienced rapid plugging, significant cell loss and considerably greater difficulty in cleaning. In contrast, the other membrane modules showed almost quantitative cell recoveries. The flux of the tubular microfilter was more than 100 L m −2 h −1 (LMH) at yeast cell concentrations of 100 g L −1, while the hollow fibers had a flux of 40 LMH at 250 g L −1.