Uniform Transmembrane Pressure Research Articles

Designing Centrifugal Membrane Filters with uniform-pressure for UF/NF/RO separations

A novel Ortho-Centrifugal Membrane Filter (O-CMF) was designed and assessed to tackle common issues in conventional laboratory centrifugal membrane filters, e.g. non-uniform transmembrane pressure and concentration polarization, and to ease membrane replacement. The O-CMF, manufactured by additive 3D printing in acrylonitrile butadiene styrene, with membrane area of 0.95 cm2, was designed to process a maximum liquid sample of 9 mL. It was tested with nanofiltration of aqueous solutions of NaCl, MgSO4, and lactose (concentrations of 1–20 g/L) at transmembrane pressures of 6–24 bar. Complementary Computational Fluid Dynamics (CFD) simulations, employing a custom solver from the open-source OpenFOAM-2306 c++ toolbox, were also run to seek insight of the O-CMF main features.The permeation experiments displayed minimal impact of concentration polarization. CFD simulations showed that concentration polarization is nearly uniform and that concentrate chamber is homogenized by centrifugal convection. The CFD permeate flux predictions, based on the osmotic pressure model, closely matched experimental data, and a correlation for predicting concentration polarization was also developed.The O-CMF device represents a substantial breakthrough in the technology of centrifugal membrane filters, consistently maintaining uniform transmembrane pressure and effectively minimizing concentration polarization. The device was evaluated using nanofiltration, but its pressure range is versatile enough to cover conditions suitable for both ultrafiltration and reverse osmosis operations. This adaptability extends its application across a variety of laboratory experiments, including sample concentration, hydraulic permeability tests, and membrane screening.

Determination of the efficiency of removal of whey protein from sweet whey with ceramic microfiltration membranes

Our research objective was to measure percent removal of whey protein from separated sweet whey using 0.1-µm uniform transmembrane pressure ceramic microfiltration (MF) membranes in a sequential batch 3-stage, 3× process at 50°C. Cheddar cheese whey was centrifugally separated to remove fat at 72°C and pasteurized (72°C for 15 s), cooled to 4°C, and held overnight. Separated whey (375 kg) was heated to 50°C with a plate heat exchanger and microfiltered using a pilot-scale ceramic 0.1-µm uniform transmembrane pressure MF system in bleed-and-feed mode at 50°C in a sequential batch 3-stage (2 diafiltration stages) process to produce a 3× MF retentate and MF permeate. Feed, retentate, and permeate samples were analyzed for total nitrogen, noncasein nitrogen, and nonprotein nitrogen using the Kjeldahl method. Sodium dodecyl sulfate-PAGE analysis was also performed on the whey feeds, retentates, and permeates from each stage. A flux of 54 kg/m2 per hour was achieved with 0.1-µm ceramic uniform transmembrane pressure microfiltration membranes at 50°C. About 85% of the total nitrogen in the whey feed passed though the membrane into the permeate. No passage of lactoferrin from the sweet whey feed of the MF into the MF permeate was detected. There was some passage of IgG, bovine serum albumen, glycomacropeptide, and casein proteolysis products into the permeate. β-Lactoglobulin was in higher concentration in the retentate than the permeate, indicating that it was partially blocked from passage through the ceramic MF membrane.

Investigation on the spatial filtration performance in spiral-wound membranes – Influence and length-dependent adjustment of the transmembrane pressure

During microfiltration, the length-dependent transmembrane pressure (ΔpTM) causes an inhomogeneous filtration performance along the module. Elimination of this length effect was found to increase the overall filtration efficiency of ceramic membranes significantly. Up to the authors’ knowledge, a systematic investigation on the spatial behavior of polymeric spiral-wound membranes (SWM) during microfiltration and the potential of a homogeneous ΔpTM has not been carried out yet. A modified SWM with permeate pockets divided in four hermetically separated sections was used to assess the length-resolved filtration performance during skim milk fractionation. Along the membrane, flux and fouling resistance decreased, whereas protein permeation increased. By adjusting the permeate pressure comparable to the uniform transmembrane pressure mode in ceramic membranes, the length dependency of ΔpTM along the module was reduced. In turn, the filtration performance was found to be more balanced. The overall whey protein mass flow increased as all sections were operating at the same ΔpTM under optimal condition. For the first time, we have proved with experimental data that SWM behave similar to ceramic membranes with regard to the length dependency of the filtration performance. Thus, the concept of a length-independent ΔpTM seems promising to enhance filtration performance of SWM at industrial scale.

Optimization of protein fractionation by skim milk microfiltration: Choice of ceramic membrane pore size and filtration temperature

The objective of this study was to investigate how ceramic membrane pore size and filtration temperature influence the protein fractionation of skim milk by cross flow microfiltration (MF). Microfiltration was performed at a uniform transmembrane pressure with constant permeate flux to a volume concentration factor of 2.5. Three different membrane pore sizes, 0.05, 0.10, and 0.20µm, were used at a filtration temperature of 50°C. Furthermore, at pore size 0.10µm, 2 different filtration temperatures were investigated: 50 and 60°C. The transmission of proteins increased with increasing pore size, giving the permeate from MF with the 0.20-µm membrane a significantly higher concentration of native whey proteins compared with the permeates from the 0.05- and 0.10-µm membranes (0.50, 0.24, and 0.39%, respectively). Significant amounts of caseins permeated the 0.20-µm membrane (1.4%), giving a permeate with a whitish appearance and a casein distribution (αS2-CN: αS1-CN: κ-CN: β-CN) similar to that of skim milk. The 0.05- and 0.10-µm membranes were able to retain all caseins (only negligible amounts were detected). A permeate free from casein is beneficial in the production of native whey protein concentrates and in applications where transparency is an important functional characteristic. Microfiltration of skim milk at 50°C with the 0.10-µm membrane resulted in a permeate containing significantly more native whey proteins than the permeate from MF at 60°C. The more rapid increase in transmembrane pressure and the significantly lower concentration of caseins in the retentate at 60°C indicated that a higher concentration of caseins deposited on the membrane, and consequently reduced the native whey protein transmission. Optimal protein fractionation of skim milk into a casein-rich retentate and a permeate with native whey proteins were obtained by 0.10-µm MF at 50°C.

Effect of ceramic membrane channel geometry and uniform transmembrane pressure on limiting flux and serum protein removal during skim milk microfiltration

Our objectives were to determine the effects of a ceramic microfiltration (MF) membrane’s retentate flow channel geometry (round or diamond-shaped) and uniform transmembrane pressure (UTP) on limiting flux (LF) and serum protein (SP) removal during skim milk MF at a temperature of 50°C, a retentate protein concentration of 8.5%, and an average cross-flow velocity of 7m·s−1. Performance of membranes with round and diamond flow channels was compared in UTP mode. Performance of the membrane with round flow channels was compared with and without UTP. Using UTP with round flow channel MF membranes increased the LF by 5% when compared with not using UTP, but SP removal was not affected by the use of UTP. Using membranes with round channels instead of diamond-shaped channels in UTP mode increased the LF by 24%. This increase was associated with a 25% increase in Reynolds number and can be explained by lower shear at the vertices of the diamond-shaped channel’s surface. The SP removal factor of the diamond channel system was higher than the SP removal factor of the round channel system below the LF. However, the diamond channel system passed more casein into the MF permeate than the round channel system. Because only one batch of each membrane was tested in our study, it was not possible to determine if the differences in protein rejection between channel geometries were due to the membrane design or random manufacturing variation. Despite the lower LF of the diamond channel system, the 47% increase in membrane module surface area of the diamond channel system produced a modular permeate removal rate that was at least 19% higher than the round channel system. Consequently, using diamond channel membranes instead of round channel membranes could reduce some of the costs associated with ceramic MF of skim milk if fewer membrane modules could be used to attain the required membrane area.

Microfiltration of skim milk and modified skim milk using a 0.1-µm ceramic uniform transmembrane pressure system at temperatures of 50, 55, 60, and 65°C

Increasing the temperature of microfiltration (MF) to >50°C may allow for operation at higher fluxes and reduce the bacterial growth during MF. However, there is a concern that operating at higher temperatures could cause calcium phosphate precipitation that would lead to membrane fouling. Our objective was to determine the effect of operating a 0.1-µm ceramic uniform transmembrane pressure MF unit at temperatures of 50, 55, 60, and 65°C on membrane fouling and serum protein (SP) removal from skim milk with and without removal of low-molecular-weight soluble milk components by ultrafiltration (UF) before MF at a flux of 54kg/m2 per hour. For each replicate, 1,000kg of pasteurized skim milk was split into 2 batches. One batch was ultrafiltered (with diafiltration) to remove an average of 89±2% of the lactose and a percentage of the soluble calcium and phosphorus. The retentate from UF was diluted back to the protein concentration of skim milk, creating the diluted UF retentate (DUR). On subsequent days, both the DUR and skim milk were run on the MF unit with the flux maintained at 54kg/m2 per hour and a concentration factor of 3× and the system run in recycle mode. The temperature of MF was increased in 5°C steps from 50 to 65°C, with a 1-h stabilization period after each increase. During the run, transmembrane pressure was monitored and permeate and retentate samples were taken and analyzed to determine if any changes in SP, calcium, or phosphorus passage through the membrane occurred. Increasing temperature of MF from 50 to 65°C at a flux of 54kg/m2 per hour did not produce a large increase in membrane fouling when using either skim milk or a DUR as the MF feed type as measured by changes in transmembrane pressure. Increasing the temperature to 65°C only caused a slight reduction in calcium concentration in the permeate (11±3%) that was similar between the 2MF feed types. Increasing processing temperature reduced the percentage of SP removal by the process, but the increased temperature also caused a decrease in casein contamination in the permeate with no evidence of membrane fouling.

Development and shelf-life determination of pasteurized, microfiltered, lactose hydrolyzed skim milk

The segment of the world population showing permanent or temporary lactose intolerance is quite significant. Because milk is a widely consumed food with an high nutritional value, technological alternatives have been sought to overcome this dilemma. Microfiltration combined with pasteurization can not only extend the shelf life of milk but can also maintain the sensory, functional, and nutritional properties of the product. This studied developed a pasteurized, microfiltered, lactose hydrolyzed (delactosed) skim milk (PMLHSM). Hydrolysis was performed using β-galactosidase at a concentration of 0.4mL/L and incubation for approximately 21h at 10±1°C. During these procedures, the degree of hydrolysis obtained (>90%) was accompanied by evaluation of freezing point depression, and the remaining quantity of lactose was confirmed by HPLC. Milk was processed using a microfiltration pilot unit equipped with uniform transmembrane pressure (UTP) ceramic membranes with a mean pore size of 1.4 μm and UTP of 60 kPa. The product was submitted to physicochemical, microbiological, and sensory evaluations, and its shelf life was estimated. Microfiltration reduced the aerobic mesophilic count by more than 4 log cycles. We were able to produce high-quality PMLHSM with a shelf life of 21 to 27d when stored at 5±1°C in terms of sensory analysis and proteolysis index and a shelf life of 50d in regard to total aerobic mesophile count and titratable acidity.

The effect of linear velocity and flux on performance of ceramic graded permeability membranes when processing skim milk at 50°C

Raw milk (about 500kg) was cold (4°C) separated and then the skim milk was pasteurized at 72°C and a holding time of 16s. The milk was cooled to 4°C and stored at ≤4°C until processing. The skim milk was microfiltered using a pilot-scale ceramic graded permeability (GP) microfilter system equipped with 0.1-µm nominal pore diameter ceramic Membralox membranes. First, about 155kg of pasteurized skim milk was flushed through the system to push the water out of the system. Then, additional pasteurized skim milk (about 320kg) was microfiltered (stage 1) in a continuous feed-and-bleed 3× process using the same membranes. The retentate from stage 1 was diluted with pasteurized reverse osmosis water in a 1:2 ratio and microfiltered (stage 2) with a GP system. This was repeated 3 times, with total of 3 stages in the process (stage 1 = microfiltration; stages 2 and 3 = diafiltration). The results from first 3 stages of the experiment were compared with previous data when processing skim milk at 50°C using ceramic uniform transmembrane pressure (UTP) membranes. Microfiltration of skim milk using ceramic UTP and GP membranes resulted in similar final retentate in terms of serum proteins (SP) removed. The SP removal rate (expressed by kilogram of SP removed per meter-squared of membrane area) was higher for GP membranes for each stage compared with UTP membranes. A higher passage of SP and SP removal rate for GP than UTP membranes was achieved by using a higher cross-flow velocity when processing skim milk. Increasing flux in subsequent stages did not affect membrane permeability and fouling. We operated under conditions that produced partial membrane fouling, due to using a flux that was less than limiting flux but higher than critical flux. Because the critical flux is a function of the cross-flow velocity, the difference in critical flux between UTP and GP membranes resulted only from operating under different cross-flow velocities (6.6 vs 7.12 for UTP and GP membranes, respectively). Conditions that allow microfiltration operation at higher flux will reduce the membrane surface area required to process the same amount of milk in the same length of time. Less membrane surface area reduces investment costs and uses less energy, water, and chemicals to clean the microfiltration system.

Serum protein removal from skim milk with a 3-stage, 3× ceramic Isoflux membrane process at 50°C

Small pore microfiltration (MF) can be used to remove serum proteins (SP) from skim milk. The process's SP removal efficiency directly influences the technology's economic feasibility. Our objective was to quantify the capacity of 0.14μm ceramic Isoflux MF membranes (TAMI, Nyons, France) to remove SP from skim milk. A 3-stage, 3×, feed-and-bleed MF study with diafiltration in the latter 2 stages was conducted at 50°C using Isoflux membranes to determine cumulative SP removal percentages and SP removal rates at each processing stage. The experiment was replicated 3 times starting with 3 separate lots of raw milk. In contrast to 3× MF theoretical cumulative SP removal percentages of 68, 90, and 97% after 1, 2, and 3 stages, respectively, the 3× Isoflux MF process removed only 39.5, 58.4, and 70.2% of SP after 1, 2, and 3 stages, respectively. Previous research has been published that provides the skim milk SP removal capacities of 3-stage, 3× 0.1μm ceramic Membralox (Pall Corp., Cortland, NY) uniform transmembrane pressure (UTP), 0.1μm ceramic Membralox graded permeability (GP), and 0.3μm polymeric polyvinylidene fluoride spiral-wound (PVDF-SW) MF systems (Parker-Hannifin, Process Advanced Filtration Division, Tell City, IN) at 50°C. No difference in cumulative SP removal percentage after 3 stages was detected between the Isoflux and previously published PVDF-SW values (70.3%), but SP removal was lower than published GP (96.5%) and UTP (98.3%) values. To remove 95% of SP from 1,000kg of skim milk in 12h it would take 7, 3, 3, and 7 stages with 6.86, 1.91, 2.82, and 17.98m2 of membrane surface area for the Isoflux, GP, UTP, and PVDF-SW systems, respectively. The MF systems requiring more stages would produce additional permeate at lower protein concentrations. The ceramic MF systems requiring more surface area would incur higher capital costs. The authors hypothesize that SP removal with the Isoflux membranes was lower than theoretical for the following reasons: a range of membrane pore sizes existed (i.e., some pores were too small to pass SP), the selective layer modification and reverse flow conditions at the membrane outlet combined to reduce the effective membrane surface area, and the geometric shape of the Isoflux flow channels promoted early fouling of the membrane and rejection of SP by the foulant.

Influence of casein on flux and passage of serum proteins during microfiltration using polymeric spiral-wound membranes at 50°C

Raw milk (approximately 1,800kg) was separated at 4°C, pasteurized (at 72°C for 16s), and split into 2 batches. One batch (620kg) was microfiltered (MF) using pilot-scale ceramic uniform transmembrane pressure Membralox membranes (model EP1940GL0.1μA, 0.1-μm alumina; Pall Corp., East Hills, NY) to produce retentate and permeate. The permeate from the MF uniform transmembrane pressure was casein-free skim milk (CFSM). The CFSM was MF using polymeric spiral-wound (SW) membranes (model FG7838-OS0x-S, 0.3 μm; Parker-Hannifin Corp., Process Advanced Filtration Division, Tell City, IN) at a concentration factor of 3× and temperature of 50°C. Following the processing of CFSM, the second batch of skim milk (1,105kg) was processed using the same polymeric membranes to determine how casein content in the feed material for MF with polymeric membranes affects the performance of the system. There was little resistance to passage of milk serum proteins (SP) through a 0.3-μm polyvinylidene fluoride (PVDF) SW membrane at 50°C and no detectable increase in hydraulic resistance of the membrane when processing CFSM. Therefore, milk SP contributed little, if any, to fouling of the PVDF membrane. In contrast, when processing skim milk containing a normal concentration of casein, the flux was much lower than when processing CFSM (17.2 vs. 80.2kg/m2 per hour, respectively) and the removal of SP from skim milk with a single-pass 3× bleed-and-feed MF system was also much lower than from CFSM (35.2 vs. 59.5% removal, respectively). Thus, when processing skim milk with a PVDF SW membrane, casein was the major protein foulant that increased hydraulic resistance and reduced passage of SP through the membrane.

Numerical and experimental methodology for the development of a new membrane prototype intended to microfiltration bioprocesses. Application to milk filtration

In tangential flow filtration, the non-uniform TransMembrane Pressure (TMP) on the membrane length produces a non homogeneous filtration cake, initiates process selectivity changes and modifies the permeate quality. The purpose of this study is to create a tubular ceramic membrane prototype with a more uniform TMP, intended to filtration of fouling fluids. The principle of this membrane structure is to waterproof the external membrane surface to limit flow circulation in the porous support of the membrane. The production was controlled by sizing «permeation vents». This development was achieved using a CFD modelling tool interacting with experiments. A preliminary modelling study was made with water. This work was afterwards applied to the industrial process of casein micelle separation from skim milk. The influence of operating conditions on the membrane hydrodynamics was highlighted. The modelling results were experimentally confirmed, with a discrepancy smaller than 3% and a reproducible water permeability of 2.3 L h −1 bar −1 for 1 mm-wide vent (TMP = 1 bar, T = 20 °C). Then, milk filtration experiments showed a production ratio milk/water equal to 1/2. The permeate quality parameters were studied and the fouling phenomena were taken into account. A parametric study led to the sizing of a final prototype. Its efficiency was experimentally evaluated.

Micellar casein concentrate production with a 3X, 3-stage, uniform transmembrane pressure ceramic membrane process at 50°C

The production of serum protein (SP) and micellar casein from skim milk can be accomplished using microfiltration (MF). Potential commercial applications exist for both SP and micellar casein. Our research objective was to determine the total SP removal and SP removal for each stage, and the composition of retentates and permeates, for a 3×, continuous bleed-and-feed, 3-stage, uniform transmembrane pressure (UTP) system with 0.1-μm ceramic membranes, when processing pasteurized skim milk at 50°C with 2 stages of water diafiltration. For each of 4 replicates, about 1,100kg of skim milk was pasteurized (72°C, 16s) and processed at 3× through the UTP MF system. Retentate from stage 1 was cooled to <4°C and stored until the next processing day, when it was diluted with reverse osmosis water back to a 1× concentration and again processed through the MF system (stage 2) to a 3× concentration. The retentate from stage 2 was stored at <4°C, and, on the next processing day, was diluted with reverse osmosis water back to a 1× concentration, before running through the MF system at 3× for a total of 3 stages. The retentate and permeate from each stage were analyzed for total nitrogen, noncasein nitrogen, and nonprotein nitrogen using Kjeldahl methods; sodium dodecyl sulfate-PAGE analysis was also performed on the retentates from each stage. Theoretically, a 3-stage, 3× MF process could remove 97% of the SP from skim milk, with a cumulative SP removal of 68 and 90% after the first and second stages, respectively. The cumulative SP removal using a 3-stage, 3× MF process with a UTP system with 0.01-μm ceramic membranes in this experiment was 64.8±0.8, 87.8±1.6, and 98.3±2.3% for the first, second, and third stages, respectively, when calculated using the mass of SP removed in the permeate of each stage. Various methods of calculation of SP removal were evaluated. Given the analytical limitations in the various methods for measuring SP removal, calculation of SP removal based on the mass of SP in the skim milk (determined by Kjeldahl) and the mass SP present in all of the permeate produced by the process (determined by Kjeldahl) provided the best estimate of SP removal for an MF process.

Production efficiency of micellar casein concentrate using polymeric spiral-wound microfiltration membranes

Most current research has focused on using ceramic microfiltration (MF) membranes for micellar casein concentrate production, but little research has focused on the use of polymeric spiral-wound (SW) MF membranes. A method for the production of a serum protein (SP)–reduced micellar casein concentrate using SW MF was compared with a ceramic MF membrane. Pasteurized (79°C, 18s) skim milk (1,100kg) was microfiltered at 50°C [about 3 × concentration] using a 0.3-μm polyvinylidene fluoride spiral-wound membrane, bleed-and-feed, 3-stage process, using 2 diafiltration stages, where the retentate was diluted 1:2 with reverse osmosis water. Skim milk, permeate, and retentate were analyzed for SP content, and the reduction of SP from skim milk was determined. Theoretically, 68% of the SP content of skim milk can be removed using a single-stage 3× MF. If 2 subsequent water diafiltration stages are used, an additional 22% and 7% of the SP can be removed, respectively, giving a total SP removal of 97%. Removal of SP greater than 95% has been achieved using a 0.1-μm pore size ceramic uniform transmembrane pressure (UTP) MF membrane after a 3-stage MF with diafiltration process. One stage of MF plus 2 stages of diafiltration of 50°C skim milk using a polyvinylidene fluoride polymeric SW 0.3-μm membrane yielded a total SP reduction of only 70.3% (stages 1, 2, and 3: 38.6, 20.8, and 10.9%, respectively). The SP removal rate for the polymeric SW MF membrane was lower in all 3 stages of processing (stages 1, 2, and 3: 0.05, 0.04, and 0.03 kg/m2 per hour, respectively) than that of the comparable ceramic UTP MF membrane (stages 1, 2, and 3: 0.30, 0.11, and 0.06 kg/m2 per hour, respectively), indicating that SW MF is less efficient at removing SP from 50°C skim milk than the ceramic UTP system. To estimate the number of steps required for the SW system to reach 95% SP removal, the third-stage SP removal rate (27.4% of the starting material SP content) was used to extrapolate that an additional 5 water diafiltration stages would be necessary, for a total of 8 stages, to remove 95% of the SP from skim milk. The 8-plus stages necessary to remove >95% SP for the SW MF membrane would create more permeate and a lengthier process than required with ceramic membranes.

A comparison between ceramic and polymeric membrane systems for casein concentrate manufacture

Skim milk microfiltration (MF) is a well established dairy processing operation to remove whey proteins. This is classically completed using ceramic membranes under the uniform transmembrane pressure (UTMP) concept. However, there is a growing interest in the use of spiral wound polymeric membranes for this purpose due to their lower capital cost. In this work we show that polymeric and ceramic membranes provide comparable performance during skim milk MF when operated at comparable levels of transmembrane pressure (TMP), shear stress and temperature. Operation is strongly affected by both TMP and temperature but is less affected by crossflow velocity under the conditions utilised here. However, while polymeric membranes offer similar performance, it will be operationally difficult to retain the necessarily low TMP at the industrial scale, due to the lack of a comparable UTMP configuration.

Isoflux ® ceramic membranes — Practical experiences in dairy industry

Three marketed ceramic microfiltration membranes working in so called 'Uniform Transmembrane Pressure' mode with special focus on ISOFLUXR concept have been presented in this paper. Microfiltration of liquids treated in dairy industry has been described in the examples of milk and cheese brine. Industrial results of spore and bacteria removal from consumer milk (ESL milk) and cheese brine along with chosen economical aspects of investment/operation cost of working MF plants have been reported. Advantages of the micelar casein/whey protein separation process and examples of industrial applications of products being results of such a separation process along with a sample description of industrial milk protein separation plants have been reported.

Effects of in-phase oscillation of retentate and filtrate in crossflow filtration at low Reynolds number

The effects of in-phase oscillation of the retentate and filtrate in crossflow filtration at low Reynolds number are investigated experimentally. Two flat membranes with mean pore size of 0.2 μm and a filter plate with pore size of 40 μm were used for the study. The experiments were performed with polymethylmethacrylate (PMMA) suspension and baker's yeast ( Saccharomyces cerevisiae) suspension. The solid volume fraction of the suspensions was φ s = 0.01. Reynolds number in the laminar range of 0 < Re < 300 was studied. The height of the non-oscillating crossflow velocity v is 0.02 m/s. The frequency f of the oscillation is in the range of 10 Hz < f < 50 Hz and the amplitude A = 0.43 mm. This yields oscillating velocity in the range of 0.06 m/s ≤ v o s c ≤ 0.10 m/s . The transmembrane pressure lies between 1.0 and 20 kPa was applied. The resulting flow was visualized using a CCD camera. The transmembrane flux due to the superimposed oscillations is significantly higher than the flux from conventional crossflow filtration. Manipulation of both the retentate and filtrate/permeate yields constant flux with time. Flux enhancement between 125% and 320% was obtained. The particle deposition on the surface of the filter materials is significantly reduced by the imposed oscillation. With the in-phase oscillation of both retentate and permeate, uniform transmembrane pressure is possible. In general, the flow reversal leads to reduction of membrane fouling and concentration polarization resistance. The calculated friction power input due to applied oscillation is comparatively low.

Efficiency of serum protein removal from skim milk with ceramic and polymeric membranes at 50°C

Raw milk (2,710kg) was separated at 4°C, the skim milk was pasteurized (72°C, 16s), split into 3 batches, and microfiltered using pilot-scale ceramic uniform transmembrane pressure (UTP; Membralox model EP1940GL0.1μA, 0.1μm alumina, Pall Corp., East Hills, NY), ceramic graded permeability (GP; Membralox model EP1940GL0.1μAGP1020, 0.1 μm alumina, Pall Corp.), and polymeric spiral-wound (SW; model FG7838-OS0x-S, 0.3 μm polyvinylidene fluoride, Parker-Hannifin, Process Advanced Filtration Division, Tell City, IN) membranes. There were differences in flux among ceramic UTP, ceramic GP, and polymeric SW microfiltration membranes (54.08, 71.79, and 16.21 kg/m2 per hour, respectively) when processing skim milk at 50°C in a continuous bleed-and-feed 3× process. These differences in flux among the membranes would influence the amount of membrane surface area required to process a given volume of milk in a given time. Further work is needed to determine if these differences in flux are maintained over longer processing times. The true protein contents of the microfiltration permeates from UTP and GP membranes were higher than from SW membranes (0.57, 0.56, and 0.38%, respectively). Sodium-dodecyl-sulfate-PAGE gels for permeates revealed a higher casein proportion in GP and SW permeate than in UTP permeate, with the highest passage of casein through the GP membrane under the operational conditions used in this study. The slight cloudiness of the permeates produced using the GP and SW systems may have been due to the presence of a small amount of casein, which may present an obstacle in their use in applications when clarity is an important functional characteristic. More β-lactoglobulin passed through the ceramic membranes than through the polymeric membrane. The efficiency of removal of serum proteins in a continuous bleed-and-feed 3× process at 50°C was 64.40% for UTP, 61.04% for GP, and 38.62% for SW microfiltration membranes. The SW polymeric membranes had a much higher rejection of serum proteins than did the ceramic membranes, consistent with the sodium-dodecyl-sulfate PAGE data. Multiple stages and diafiltration would be required to produce a 60 to 65% serum protein reduced micellar casein concentrate with SW membranes, whereas only one stage would be needed for the ceramic membranes used in this study.

Purification of monoclonal antibodies derived from transgenic goat milk by ultrafiltration

With the goal of recovering heterologous immunoglobulin (IgG), which comprises 10-15% of the total proteins, from transgenic goat milk at 80% yield and 80% purity, we have developed and tested a two-step membrane isolation and purification process. In the first step, reported earlier by Baruah and Belfort, microfiltration was used to fractionate the milk proteins and recover > 90% of the original IgG at a purity of about 15-20% in the permeate stream. Here, we focus on ultrafiltration (UF) to increase the purity of the target protein to 80%, while maintaining a relatively high IgG yield (80%). Tangential flow UF experiments in diafiltration mode were conducted with 100 kDa cellulosic membranes to evaluate the optimal pH, ionic strength, and uniform transmembrane pressure (TMP). The TMP was kept uniform by permeate circulation in co-flow mode. The traditional approach of conducting the UF process close to the pI of the predominant whey proteins (15-40 kDa, pI 5.2), to transmit these proteins while retaining heterologous IgG (155 kDa), could not be applied here because of precipitation of residual casein at pH values lower than 8.5. Instead, the packing characteristics of the cake layer on the membrane wall, as elucidated in the Aggregate Transport Model presented by Baruah et al. was utilized to achieve a selectivity of > 15, which was sufficient to meet the stated goals of purity and yield for this difficult separation. This combined process is expected to reduce the load on subsequent purification and polishing steps for eventual therapeutic use.

Scale-up from laboratory microfiltration to a ceramic pilot plant: Design and performance

A highly instrumented pilot microfiltration (MF) plant featuring a ceramic microfiltration membrane, back-pulsing device, permeate re-circulation in co-flow to achieve uniform transmembrane pressure (UTMP) and a cooling/temperature control system was designed, built and tested successfully with transgenic whole goat milk (TGM). In a previous study, it was shown that >90% of heterologous IgG could be recovered from TGM in the permeate by adopting close process control with low UTMP and operation at the iso-electric point (p I) of the target IgG. Here, these concepts were successfully employed to recover >90% of another IgG (p I = 7.1–7.5) from TGM by MF at the pilot-scale. The pilot plant MF system gave 90% yield for the same target protein with a 50% higher permeation flux rate (47 lmh instead of 32 lmh) and increased protein transmission (70% instead of 46%) as compared with the laboratory-scale MF unit. Thus, this study demonstrated the efficacy of the pilot MF plant and reinforced the generality at larger scale of the optimization methodology reported earlier by us.

Effect of temperature and pore size on the fractionation of fresh and reconstituted buttermilk by microfiltration.

The objective of this research was to evaluate the effect of temperature (7, 25, and 50 degrees C) and pore size (0.1, 0.8, and 1.4 micro m) on the separation of proteins and lipids (neutral lipids and phospholipids) during microfiltration (MF) of fresh or reconstituted buttermilk. Buttermilk was subjected to MF using a pilot-scale unit mounted with ceramic membranes. The MF runs were carried out in a uniform transmembrane pressure (UTP) mode. Changes in processing temperature had no significant impact on protein transmission, whereas increasing temperature reduced both lipid and phospholipid transmission. A maximum concentration factor (CF) for lipids was reached at 25 degrees C, as protein CF remained essentially unaffected by temperature. The use of the smaller pore size (0.1 microm) resulted in low lipid (10%) and protein (approximately 20%) transmission. Larger pore sizes (0.8 and 1.4 microm) resulted in higher levels of protein, lipid, and phospholipid transmission (>50%), but gave high permeation fluxes. Transmission of both proteins and lipids was markedly different when using fresh buttermilk as opposed to reconstituted buttermilk. This study showed that MF temperature, pore size, and buttermilk type influence fractionation but that MF alone cannot achieve optimal separation of lipids and proteins for the production of novel ingredients from buttermilk.