Mean Transmembrane Pressure Research Articles

Propidium monoazide - polymerase chain reaction reveals viable microbial community shifts in anaerobic membrane bioreactors treating domestic sewage at low temperature

An anaerobic membrane bioreactor (AnMBR) treated domestic sewage at 15 °C under different hydraulic retention time (HRT) conditions (6, 12, 16, and 24 h). Propidium monoazide (PMA)-PCR excluded microorganisms without intact cell membranes, focusing on the viable microbial community in anaerobic digestion. The results showed that the 6-hour HRT had poor treatment performance: low chemical oxygen demand removal efficiency (below 80%) and high mean trans-membrane pressure and flux (15 kPa and 9.4 L/(m2 h)). Comparatively, PMA-PCR combined with next-generation sequencing improved the identification of microbial changes compared to conventional 16S rRNA gene sequencing. HRT influenced microorganisms in the hydrolysis and acid-production stages, including carbohydrate-degrading bacteria such as Bifidobacterium and Prevotella 1. Remarkably, a comparison with an AnMBR at 25 °C showed Proteobacteria to be the main cause of membrane fouling in the low-temperature AnMBR, with most operational taxonomic units negatively correlated with HRT and solids retention time.

Comparison of circuit patency and exchange rates between the original and generic versions of nafamostat mesylate in critically ill adults receiving continuous renal replacement therapy

Background: Nafamostat mesylate is widely used as an anticoagulant in continuous renal replacement therapy (CRRT). The generic versions of nafamostat mesylate have identical main components to the original product. However, it is questionable whether the generic versions have the same efficacy as the original. Therefore, we compared the circuit patency and exchange rates of the original nafamostat mesylate and a generic version to determine which is more efficient as an anticoagulant in CRRT.Methods: This retrospective study enrolled 1,255 patients hospitalized to receive CRRT who received the original version of nafamostat mesylate or a generic version between January 2010 and July 2018. We evaluated the filter lifespan, number of filters used per day, mean blood flow, and transmembrane pressure (TMP).Results: The mean filter lifespan was 36.3±15.1 hours in the original product group and 22.2±16.2 hours in the generic product group, which was not a statistically significant difference (p=0.060). The mean TMP was 62.2±47.3 mmHg in the original product group and 74.5±45.6 mmHg in the generic product group (p=0.045).Conclusions: This retrospective study suggests no meaningful difference in filter lifespan between the original and generic versions of nafamostat mesylate. However, TMP was lower in the original product group than in the generic product group.

Membrane-based therapeutic plasma exchange: Hemodynamics and operational characteristics leading to procedure failure.

Therapeutic plasma exchange (TPE) is a blood purification treatment capable of removing large molecular weight substances from plasma. It is commonly used for the removal of circulating pathogenic immunoglobulins presumed to be the cause of many autoimmune diseases. TPE can be performed with a membrane-based system (mTPE) or a centrifugal-based system (cTPE). When plasma separation is performed with a membrane, filter clotting can lead to longer treatment time, higher cost and can negatively impact patient satisfaction. In this study, we examine the operational characteristics that might influence filter life. We report on 24 patients, with a total of 135 mTPE treatments in a single tertiary care academic center using the NxStage machine. The study focuses on treatment specific parameters that may lead to procedure failure. The main parameters of interest were transmembrane pressure (TMP) and the filtration fraction as displayed on the machine (FFd) compared to the calculated filtration fraction (FFc). Primary outcome was to measure whether TMP, FFc, and FFd influenced filter survival. Secondary outcomes included factors that might have indirectly resulted in filter failure, including hematocrit (Hct), platelet count, heparin use, and intra-treatment calcium administration. In this study, we demonstrated that machine displayed filtration fractions (FFd) were lower than FFc and this difference was significantly larger in TPE sessions that experienced a clotting event (7.58 vs 6.22, P=.031). TPE sessions that clotted had a higher mean TMP (57.48 mmHg vs 44.43 mmHg, P=.001) and clotting events tended to have a lower mean blood flow rate (175.83 mL/min vs 189.55 mL/min, P=.002). In TPE sessions that received prefilter calcium administration, a higher mean dose of calcium gluconate was found in the sessions that experienced clotting (3.27 g vs 2.70 g, P=.013). Patients who experienced at least one clotting event were noted to be heavier than those patients without any clotting events (91.52 kg vs 72.15 kg, P=.040). Prefilter heparin administration was not associated with a lower incidence of filter clotting. We did not find a statistically significant difference in clotting events based upon type of intravenous access, pretreatment hematocrit, or pretreatment platelet counts. Among patients undergoing mTPE, machine FFd on the NxStage system are consistently lower than FFc. Treatments where there was a greater difference between displayed and FFc had a greater likelihood of filter clotting. Treatments with higher TMP were associated with failed treatments. Prefilter calcium administration during treatment was associated with increased filter clotting. Lower blood flow rates and higher patient weight were also associated with increased filter clotting. Prefilter heparin administration did not reduce the incidence of filter clotting.

Sludge yield and degradation of suspended solids by a large pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater at 25 °C

Sludge yield and suspended solid are important factors concerned in the anaerobic treatment of municipal wastewater. In this study, a large pilot-scale anaerobic membrane bioreactor (AnMBR) was constructed for effectively treating real municipal wastewater at an ambient temperature of 25 °C. The sludge yield and the degradation of influent suspended solids were evaluated during the long-term operation of the AnMBR. This reactor with 5.0 m3 effective volume is the largest one-stage submerged AnMBR that has ever been used to treat municipal wastewater. During the long-term operation of 217 days, this AnMBR obtained excellent COD and BOD5 removal efficiency over 90%. Stable biogas production was also successfully obtained from treating municipal wastewater. The sludge yield of the AnMBR was approximately 0.19–0.26 g MLSS g−1 COD removed for the treatment of real municipal wastewater. The shortest SRT of the AnMBR was calculated as 29 days for an HRT of 6 h at an empirical MLSS of 10 g L−1. While the influent suspended solid (SS) contained in the municipal wastewater was completely removed by the AnMBR, only 57%–66% of the influent SS was degraded. The rest of influent SS was directly converted to MLSS instead of being degraded. The AnMBR maintained a stable membrane filtration using a hollow-fiber membrane with a total area of 72 m2, realizing a flux of 2.75–17.83 LMH, and the mean transmembrane pressure (TMP) was 0.9–23.5 kPa. An online chemical backwash cleaning system helped to lower the TMP timely using sodium hypochlorite and citric acid when the TMP increased rapidly and reached the rated limit of membrane. This is the first report on demonstrating the successful operation and detailed performance of a large pilot-scale AnMBR applied to the treatment of real municipal wastewater.

High throughput screening of ultrafiltration and diafiltration processing of monoclonal antibodies via the ambr® crossflow system.

As the biopharmaceutical industry moves toward high concentration of monoclonal antibody drug substance, additional development is required early on when material is still limited. A key constraint is the availability of predictive high-throughput low-volume filtration screening systems for bioprocess development. This particularly impacts final stages such as ultrafiltration/diafiltration steps where traditional scale-down systems need hundreds of milliliters of material per run. Recently, the ambr® crossflow system has been commercialized by Sartorius Stedim Biotech (SSB) to meet this need. It enables parallel high throughput experimentation by only using a fraction of typical material requirements. Critical parameters for predictive filtration systems include loading, mean transmembrane pressure (Δ TMP ), and crossflow rate (QF ). While axial pressure drop (ΔPaxial ) across the cartridge is a function of these parameters, it plays a key role and similar values should result across scales. The ambr® crossflow system is first presented describing typical screening experiments. Its performance is then compared to a traditional pilot-scale tangential flow filtration (TFF) at defined conditions. The original ambr® crossflow (CF) cartridge underperformed resulting in ~20x lower ΔPaxial than the pilot-scale TFF flat-sheet cassette. With an objective to improve the scalability of the system, efforts were made to understand this scale difference. The ambr® CF cartridge was successfully modified by restricting the flow of the feed channel, and thus increasing its ΔPaxial . Additional studies across a range of loading (100-823 gm-2 ); Δ TMP (12-18 psi); and QF (4-8 L/min/m2 ) were conducted in both scales. Comparable flux and aggregate levels were achieved.

Performance of simultaneous organic and nutrient removal in a pilot scale anaerobic–anoxic–oxic membrane bioreactor system treating municipal wastewater with a high nutrient mass ratio

A pilot-scale anaerobic–anoxic–oxic membrane bioreactor (A2O-MBR) was applied to treat Shiraz municipal wastewater with high ratio of total phosphorous (TP): total nitrogen (TN): chemical oxygen demand (COD) (3.4: 21.4: 100) and remarkable nitrate concentration. Various operating conditions were tested to investigate nutrient and organic matter removal as well as membrane capacity and biomass development. The pilot system was operated at a constant sludge retention time of 60 d. During different runs, the biomass concentration increased with a reduction of HRT while the F/M ratio was stable around an average of 0.087 gCOD g−1MLSS d−1. Results also showed that the treatment performance of A2O-MBR system was extremely stable and was not affected by aerobic hydraulic retention time (HRT) changes (12, 10, 8, 6 h). COD reduction reached over 95% and nitrification was completed. The maximum efficiency of TN and TP removal was 86.2% and 55.9%, respectively, which occurred with an overall HRT of 12 h, external and internal mixed liquor recycle rate of 200%. Membrane capacity measurements showed an average flux of 5.5 L m−2h−1 with a mean transmembrane pressure of 30 kPa under periodical air backwashing without any chemical cleaning over three months.

Investigation of membrane fouling mechanisms using blocking models in the case of shear-enhanced ultrafiltration

Shear-enhanced ultrafiltration is considered as an important membrane technology that can contribute to pre-treat dairy wastewater and recycle valuable components such as milk proteins. However, to be efficient, it necessitates the establishment of proper methods for the assessment of membrane fouling. Four membrane blocking models proposed by Hermia were used to quantify and assess the membrane fouling of shear-enhanced filtration observed in dairy wastewater treatment. The experiments were performed with various shear rates, mean transmembrane pressure (TMP), temperature and membrane types. Good agreement between complete pore blocking model and experimental data was found, confirming the validity of the Hermia models for assessing the membrane fouling of shear-enhanced filtration system and that only some “sealing” of membrane pores occurs which is due to the high speed shearing effect. Furthermore, the increments of shear rate, TMP, and temperature can decrease the degree of “sealing” of membrane pores and improve filtration performance. In addition, a three-step membrane cleaning mode has achieved very satisfying results in subsequent membrane cleaning. This work confirms that, unlike traditional filtration mode (dead-end and cross flow filtration), high shear dynamic filtration possesses a low degree of membrane fouling and a higher membrane permeability recovery after cleaning.

Evaluation of hydrogen permselective separation from “synthesis gas” components based on single gas permeability measurements on anodic alumina membranes

Anodic alumina membranes were prepared by anodizing aluminum followed by chemical and hydrothermal treatments. Anodization was performed on both tube surfaces. External anodization was restricted to selected spots leaving an aluminum mechanically strong frame. Nitrogen sorption data analysed with the CPSM method (Corrugated Pore Structure Model) detected a mesopore structure (i.e. D mean;15–20) and surface areas of 2–20 m 2/g. SEM microscopy images revealed a regular pore structure of independent pores with densities of N pore ~ 5.6 × 10 14 pores/m 2. Single gas permeances (Π) for X: H 2, CH 4, CO and CO 2 were measured on a Wicke–Kallenbach apparatus at varying mean transmembrane pressure P m by the “dead-end” method. The observed slight dependence of Π on Ρ m is indicative of strong Knudsen diffusion and weak viscous flow contributions. By correlating the experimental data with a linear Π vs Ρ m relationship, Knudsen contribution evaluation was enabled, and found to vary in the range K C ≈ 0.7–1.0. The Knudsen number criterion for flow regime discrimination is critically discussed and a realistic dual Knudsen number approach is proposed. Experimental permselectivities α Η2Χ = Π H2/Π X (X ≠ H 2) approach by 70–100% their Knudsen selectivity counterparts. Anodic alumina membranes exhibit pore structure and gas permeability characteristics useful in designing integrated gas separation and catalytic membrane reactor systems.

Studies on treatment of sodium dodecyl benzene sulfonate solution by high shear ultrafiltration system

The dynamic ultrafiltration of anionic surfactant solution, sodium dodecyl benzene sulfonate (SDBS), using a rotating disk system with hydrophilic polyethersulfone (PES) membranes (MWCO 10 kDa) was studied in this paper. The effects of mean transmembrane pressure (TMP) and disk rotating speed on the permeate flux and surfactant retention have been reported. When the rotating speed of the disk with vanes was above 1000 rpm, it was found that the permeate flux kept rising without reaching a plateau up to a TMP of 2100 kPa. The surfactant retention of the 10-kDa membranes was observed to be 81.5% for a micellar SDBS solution of 1 Critical Micelle Concentration (CMC) at the highest TMP of 2100 kPa and a rotating speed of 1000 rpm, and it reached 92.5% at a rotating speed of 2750 rpm. The dynamic filtration system was proved to be very efficient for decreasing concentration polarization, due to high shear rates on the membrane generated by disk rotation. Then, the influence of the feed concentration on the permeate flux and surfactant retention was investigated at different concentrations up to 5CMC. The unexpected result obtained was that the flux increased with increasing feed concentration, which could be explained by the reduction of concentration polarization by enhanced diffusion of surfactant micelles due to high shear rates. The adsorption of surfactant anions on the membrane surface probably increased the hydrophilicity of PES membrane.

Quantitative Analysis of Pulsatile Flow Contribution to Ultrafiltration

We evaluated the quantitative contribution of pulsatile flow to ultrafiltration (UF) in terms of fluid power, membrane stretch, and reduction of membrane layering. An in vitro comparison of the UF rate using pulsatile and roller pumps was performed with distilled water and bovine whole blood. The mean transmembrane pressure (TMPm) and UF rate were higher with the pulsatile pump for the same mean flow rate: 6.6 mm Hg and 21.1 mL/min higher on average for distilled water and 34.2 mm Hg and 31.4 mL/min higher on average for blood. The average UF rate was 8.4 mL/min higher with the pulsatile pump for the same TMPm with bovine blood. However, the relationship between the UF rate and the TMPm was independent of the flow configuration for distilled water. We showed that the higher UF rate in the pulsatile pump is mainly due to greater fluid power and reduction of membrane layering, while the membrane stretch was not an important factor.

Length dependency of flux and protein permeation in crossflow microfiltration of skimmed milk

Crossflow microfiltration of skimmed milk to fractionate casein micelles and whey protein was investigated regarding length dependency of flux and whey protein permeation using a 1.2 m long, 0.1 μm tubular ceramic membrane. A special module consisting of four sections was constructed allowing to assess the effects of membrane length online by measuring flux and permeation of the whey protein β-lactoglobulin as a function of local processing conditions. It was found that under the applied filtration parameters (mean transmembrane pressure Δ p TM,m = 0.5 bar; temperature ϑ = 55 °C; wall shear stress τ w = 115 Pa) main parts of the membrane were controlled by a deposit layer. In consequence, the transmission of the whey protein β-lactoglobulin increases from 38% to 87% from membrane inlet to membrane outlet. Results show that a local optimum for protein fractionation exists regarding membrane resistance and process conditions.

Vertically aligned carbon nanotube membranes on macroporous alumina supports

Vertically aligned multi-walled carbon nanotube (CNT) membranes are grown on the porous α-alumina support by a multi-step method consisting of growth of vertical CNTs by chemical vapor deposition, filling of inter-CNT gaps with polystyrene and removal of the polystyrene over-layer and CNT tips by polishing and acid treatment. The membranes are defect free and exhibit gas permeance independent of mean transmembrane pressure. CNT membranes grown on the porous alumina support have lower areal tube density of 1.87 × 10 9 CNT/cm 2, lower than the CNT membranes on dense silicon and quartz support reported in the literature. The CNT layer consists of fairly straight carbon nanotubes of 6.3 nm in pore diameter running parallel to each other with a tortuosity factor of about 1.3. Gas permeance through the porous alumina-supported CNT membranes is inversely proportional to the squared root of the gas molecules suggesting a Knudsen diffusion mechanism. However, the diffusivity values measured are about four times larger than the values predicted from the pore size, molecular weight and temperature using the Knudsen diffusion model.

Hemolysis in Double-Filtration Plasmapheresis

To evaluate the occurrence of hemolysis during double-filtration plasmapheresis (DFP) treatment and its causes, we prospectively treated 113 myasthenic patients and monitored transmembrane pressure (TMP), arterial line pressure (Pa), and venous line pressure (Pv) at 30-minute intervals (M30, M60, M90, and M120) during treatment. Laboratory and clinical parameters related to the development of hemolysis were also analyzed. The overall frequency of hemolysis was 35.4%. Peripheral venous access was associated with a higher rate of hemolysis (45.3%). The mean TMP increased significantly after M30 for the hemolysis group compared with the no hemolysis group. A similar trend was present for Pa. Pv did not differ between the 2 groups during treatments until M90 and M120. Pa and TMP changed significantly with time (both P < .0001). Vascular access through large veins and stable TMP during the procedure may help avoid hemolysis.

Hemolysis in Double-Filtration Plasmapheresis

To evaluate the occurrence of hemolysis during double-filtration plasmapheresis (DFP) treatment and its causes, we prospectively treated 113 myasthenic patients and monitored transmembrane pressure (TMP), arterial line pressure (Pa), and venous line pressure (Pv) at 30-minute intervals (M30, M60, M90, and M120) during treatment. Laboratory and clinical parameters related to the development of hemolysis were also analyzed. The overall frequency of hemolysis was 35.4%. Peripheral venous access was associated with a higher rate of hemolysis (45.3%) The mean TMP increased significantly after M30 for the hemolysis group compared with the no hemolysis group. A similar trend was present for Pa. Pv did not differ between the 2 groups during treatments until M90 and M120. Pa and TMP changed significantly with time (both P < .0001). Vascular access through large veins and stable TMP during the procedure may help avoid hemolysis.

A statistical method for quantifying the different fouling effects of three combined water sources on an ultrafiltration membrane

A simple statistical model has been developed to explain the fouling of an ultrafiltration (UF) membrane treating three mixed feedwater matrices. A tubular UF membrane operating under dead-end conditions, based at the Millennium Dome Water Recycling Plant, was used for this study. The feedwaters comprised surface water, greywater and groundwater, all having distinct quality differences. The analysis utilises the least-squares fit regression technique. Fouling, as manifested in the diurnal change in trans-membrane pressure (TMP), is related numerically to the volumes of the feedwaters, the mean TMP and the cross product of mean TMP with water volume. It was found that the impact of the recovered greywater on TMP was not statistically significant only due to the low daily volumes of this matrix generated, compared with those of the other sources. The model that best described the data was chosen on the basis of highest R 2 and lowest residual mean square, and demonstrated the surface water to be more fouling than the ground water by a factor, which is a function of the mean TMP.

Performance of a bioreactor with submerged membranes for aerobic treatment of municipal waste water

Aerobic treatment of municipal waste water in a membrane bioreactor was studied for 535 d. Apart from sampling, sludge was retained completely by a submerged hollow fibre membrane with a pore-size of 0.2 μm. The pilot plant comprised an anoxic zone to enable denitrification. The maximum liquid hold-up of the plant was 3.9 m 3. In this study the reactor performance and the stability of the process and the membrane capacity were investigated. A stable flux of 18 l m −2 h −1 could be realised with a mean transmembrane pressure difference of 0.3 bar with air-bubbling and backflushing the membrane and cleaning it in place every two months for one or two hours. For about 140 d, a flux of 27 l m −2 h −1 was achieved, but cleaning became necessary more often. The hydraulic retention time (HRT) varied between 10.4 and 15.6 h. Accordingly the volumetric loading rate was between 1.1 and 1.7 kg COD m −3 d −1. No inoculum was used. The mixed liquor suspended solids (MLSS) concentration gradually increased to 18–20 g MLSS l −1. The feed to microorganism ( F/ M) ratio varied according to the operation conditions but decreased against a value of 0.07 kg COD kg −1 MLSS d −1. Treatment performance was very stable and on a high level. The COD was reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified.

Ultrafiltration/Reverse Osmosis Concentration of Lobster Extract

ABSTRACTA membrane concentration system consisting of tubular polysulphone ultrafiltration (UF) and polyamide reverse osmosis (RO) was evaluated for concentrating key water soluble flavor compounds from lobster extracts. Major flavor‐giving compounds in the extract were glutamic acid, glycine, arginine, uridine 5′‐monophosphate (UMP), succninic acid and glucose. Factors affecting performance of the UF/RO systems, such as flow rate, feed solid level, temperature and pressure, on permeate flux and solids rejection were measured. The optimum UF conditions were 1.5% feed solid level, 15 L/min feed flow rate, 50°C feed temperature and 1 MPa log mean transmembrane pressure. The RO system retained all dissolved flavor components and its ideal operating conditions were 40°C, 2.8 MPa log mean transmembrane pressure and a flow rate of 15 L/min.

Hemolysis During Membrane Plasma Separation With Pulsed Flow Filtration Enhancement

The use of pulsed blood flow in membrane plasmapheresis permits enhancement of plasma filtration yet may result in high levels of hemolysis due to large increases in instantaneous transmembrane pressure (TMP). This work investigates the occurrence of hemolysis as a function of TMP and wall shear rates (gamma w) for both steady and pulsed blood flow conditions. Two types of hollow fiber filters with identical polypropylene membranes but different lengths and membrane areas (0.1 and 0.25 m2) were tested. Fresh citrated bovine blood was circulated through the fibers at various blood flowrates and TMP in a single pass circuit using a pulsation generator, made of a single roller peristaltic pump. The free hemoglobin concentration of the plasma, Hbm, was measured from permeate samples collected at each set of TMP and gamma w conditions. It was found that the net hemolysis generated by the filtration was proportional to the membrane area. This justified the introduction of an hemolysis index, IH, equal to the plasma hemoglobin per unit membrane area. The boundary for the occurrence of hemolysis was thus defined by setting IH = 30 mg/dl.m2. For both steady and pulsed flow conditions the hemolysis boundaries were found to be straight lines in the TMP-gamma w plane. They were identical for the two filters under steady flow but different for pulsed flow. At the same time mean wall shear rates hemolysis occurred at a lower time mean TMP under pulsed flow conditions than under steady flow conditions.

Flux enhancement in crossflow microfiltration using a collapsible-tube pulsation generator

A dilute suspension of silica particles in water was microfiltered in an unbaffled tubular ceramic membrane. The crossflow was varied periodically at frequencies inducing fluid-dynamic unsteadiness using a novel device for this application, namely a flexible tube compressed to non-circular cross-section by external pressure. This arrangement is unstable and leads to self-sustained oscillations which can be used to add a pulsatile component to a steady flow. With this arrangement, and a time-averaged crossflow sufficient for turbulence in the membrane filter, filtrate flux increases due to pulsation of up to 60% were demonstrated, without systematic optimisation of the pulse parameters. The gain persisted over the entire range of mean transmembrane pressure and crossflow velocity investigated.

Scaling up pulsatile filtration flow methods to a pilot apparatus equipped with mineral membranes

This paper addresses the problem of extrapolating the technique used for filtration enhancement by superimposing pressure and flow pulsations to a pilot model of an actual production unit equipped with 14 Carbosep mineral membranes. The experimental results obtained with raw apple juice show that the maximum permeate flux enhancement is obtained at a frequency of 1 Hz and a pulsed volume of 200 ml which is significantly less than the internal volume of the membranes. The flux enhancement is a linear function of the ratio of pulsatile to steady flow and can reach up to 140% when the circuit settings are unchanged. However, when the time-averaged mean transmembrane pressure is conserved the flux enhancement is much smaller and barely exceeds 25%.