Transmembrane Pressure Research Articles

Synergy effect in blend Orange G/Rhodamine B ultrafiltration, using natural bentonite-based membrane

Abstract Attempting to reduce issues with dumping and water pollution, bio-based membrane material (MB1000), based on bentonite was elaborated for application in tangential ultrafiltration. For this, morphological properties, textural properties, and chemical structure of the elaborated membrane material were established using Fourier transform infrared spectroscopy, X-ray diffraction, and Brunauer–Emmett–Teller analyses. Water permeability, chemical resistance, as well as point of zero charge of the membrane material were also investigated. The studied membrane material has a mesoporous structure, with a pore size of 7.20 nm and a water permeability of 318.06 L/h.m2.bar. The effect of transmembrane material pressure, pH solution, and concentration on Orange G (OG) and Rhodamine B (RB) dye rejection efficiency was examined and hence optimized. Besides, a mixture of RB and OG dyes was tested for membrane material ultrafiltration in a simultaneous system (RB/OG). Remarkably, an enhancement of the rejection results was noticed for the two dyes (ROG = 94.33%, RRB = 89.38%) resulting from a synergic effect of hydrogen bonding as well as electrostatic interactions generated from functional groups of the molecules dyes.

Cake layer discrepancy triggered by different pore sizes in an anaerobic membrane bioreactor

Cake layer formation is a key contributor to anaerobic membrane bioreactor (AnMBR) fouling. This study identified the discrepancy in the cake layer formation triggered by the pore size of the AnMBR. Five membrane modules with different pore sizes of 0.1, 0.22, 0.45, 1, and 5 μm were operated synchronously in the same AnMBR over a 120-day period. The transmembrane pressure (TMP) was observed and classified into three stages for each membrane. Pore size did not cause an obvious cake layer discrepancy at the initial stage, where the TMP increased. However, the membranes with larger pore sizes had a longer weak rise in the TMP during cake layer formation. The cake layer on the membranes with smaller pore sizes formed rapidly, but the cake layer on the membranes with bigger pore sizes could mitigate the TMP jump. The 0.45 μm membrane had the highest roughness and most severe cake layer formation. Acinetobacter showed obvious growth during cake layer formation, especially with a higher bacterial capacity on the membranes with smaller pore sizes. Pore size did not cause a genus-level discrepancy. However, there was a variation in bacterial percentage during cake layer formation.

Alternating flow direction improves chemical cleaning efficiency in hollow fibre membranes following skim milk microfiltration

With efficient membrane cleaning remaining a challenge, novel approaches have promising potential to enhance cleaning efficiency. This study examined the concept of feed side cyclical and permanent flow reversal during membrane cleaning, to which so far it has not been applied to. Experiments were conducted in a hollow fibre microfiltration membrane with lengths of 0.5 m and 1.0 m using skim milk for deposit formation, NaOH as a cleaning agent, and flux recovery ratio and protein removal for cleaning evaluation. Overall, flow reversal was found to significantly increase cleaning success. Due to the length-dependent pressure drop and flow reversal, the local transmembrane pressure at the initial feed inlet ΔpTM, inlet and thus the ratio of flow velocity to ΔpTM, inlet was increased compared to steady forward flow cleaning. This proved beneficial as it combines high shear stress with low ΔpTM, inlet where fouling was most pronounced after filtration.

Biological Activated Carbon Filtration Controls Membrane Fouling and Reduces By-Products from Chemically Enhanced Backwashing during Ultrafiltration Treatment

Water purification by ultrafiltration (UF) requires regular membrane cleaning via backwashing. In the case of chemically enhanced backwashing (CEB), it can result in the formation of unwanted by-product precursors due to reactions with organic matters present in the backwashing water and accumulating on the membrane. After subsequent disinfection, these precursors are prone to generate trihalomethanes (THMs) and haloacetic acids (HAAs), posing potential risks to the chemical safety of drinking water. However, limited information was available regarding the removal of these disinfection by-products. In this study, biological activated carbon (BAC) pretreatment followed by UF with chemically enhanced backwashing (CEB) (BAC-UF-CEB) was investigated to mitigate membrane fouling and reduce by-product formation. It was tested in parallel with UF with CEB (UF-CEB) and UF with sole physical backwashing. Compared to UF-CEB, BAC pretreatment prior to UF-CEB reduced transmembrane pressure (TMP) by 49.0%. BAC achieved high removals of dissolved organic carbon (59.99%) and UV254 absorbance (80.82%) in the BAC-UF-CEB effluent. Moreover, BAC-UF-CEB substantially decreased trihalomethane and haloacetic acid formation potentials by 83.28% compared to UF-CEB. BAC alleviated irreversible membrane fouling by 78.7%. By removing disinfection by-product precursors, BAC-UF-CEB markedly improved treated water quality and chemical safety. This study demonstrates BAC pretreatment effectively mitigates membrane fouling and controls disinfection by-products during UF water treatment.

Evaluation of Organic and Inorganic Foulant Interaction Using Modified Fouling Models in Constant Flux Dead-End Operation with Microfiltration Membranes.

The goal of this study was to elucidate the interaction of complex feed solutions under modified membrane fouling models for constant flux operation. The polyvinylidene fluoride membrane (PVDF) was tested for three types of solutions containing inorganic foulants (Al, Mn, and Fe), organic foulants, and suspended solids at 0.5 mM Ca2+ ionic strength. The membrane's performance was evaluated by measuring the increase in transmembrane pressure (TMP) during two different filtration scenarios: continuous filtration lasting 1 h and cyclic filtration lasting 12 min, with 3 min backwashing cycles included. Statistical analysis (linear regression results (R2), p-value) was used to verify the fouling model propagation along with the determination of the contributing constant of each fouling model. An increasing TMP percentage of 164-302%, 155-300%, and 208-378% for S1 (HA + Ca2+), S2 (inorganics + kaolin + Ca2+), and S3 (HA + inorganics + kaolin + Ca2+) was recorded for 1 h filtration, respectively. Furthermore, a five percent increase in irreversible resistance was noted for the S3 solution due to the strong adsorption potential of foulants for the PVDF membrane caused by the electrostatic and hydration forces of foulants. In addition to that, the participation equation elucidated the contribution of the fouling model and confirmed that complete blocking and cake layer contribution were dominant for the S1 and S3 solutions, while standard blocking was dominant for the S2 solution with a high significance ratio. Moreover, R2 and cyclic filtration analysis also confirmed the propagation of these fouling models. The statistical confirmation and regression results analysis of the modified model gave comparative results and satisfied the filtration mechanism and can be used for the constant flux dead filtration analysis of water treatment.

Forecasting multicycle hollow fiber ultrafiltration fouling using time series analysis

This study proposes the application of time series analysis and exponential smoothing (ETS) to predict multicycle membrane fouling with high accuracy and great interpretability. First, lab-scale filtration tests were performed with foulant surrogates to assess the potential of ETS models in predicting multicycle membrane fouling. Two models, ETS (A,A,A) and ETS (A,A,M), were found to be most suitable for describing the variation of transmembrane pressure. The ETS (A,A,A) model showed a slight edge over the ETS (A,A,M) model when reversible fouling was dominant. In contrast, the ETS (A,A,M) performed better when irreversible fouling was prevalent. Then, the effectiveness of ETS models in multicycle forecasting during the filtration of natural water resources was evaluated. Residual mean squared errors between 0.02 bar and 0.15 bar were obtained for horizons going from 2 up to 10 filtration cycles. Finally, ETS models were applied to predict the variation in permeability of drinking water treatment plant membrane skid. A three-month dataset was utilized to predict the next 41 days of permeability variation, yielding an average error of 3.2 %. Along with that, a web application designed to assist membrane users in utilizing ETS was developed and presented at the end. The web application can be accessed through the following link: https://fouling-ets.shinyapps.io/shiny-ets-forecasting/.

Hybrid modeling of a biorefinery separation process to monitor short-term and long-term membrane fouling

Membrane filtration is commonly used in biorefineries to separate cells from fermentation broths containing the desired products. However, membrane fouling can cause short-term process disruption and long-term membrane degradation. The evolution of membrane resistance over time can be monitored to track fouling, but this calls for adequate sensors in the plant. This requirement might not be fulfilled even in modern biorefineries, especially when multiple, tightly interconnected membrane modules are used. Therefore, characterization of fouling in industrial facilities remains a challenge. In this study, we propose a hybrid modeling strategy to characterize both reversible and irreversible fouling in multi-module biorefinery membrane separation systems. We couple a linear data-driven model, to provide high-frequency estimates of trans-membrane pressures from the available measurements, with a simple nonlinear knowledge-driven model, to compute the resistances of the individual membrane modules. We test the proposed strategy using real data from the world’s first industrial biorefinery manufacturing 1,4-bio-butanediol via fermentation of renewable raw materials. We show how monitoring of individual resistances, even when done by simple visual inspection, offers valuable insight on the reversible and irreversible fouling state of the membranes. We also discuss the advantage of the proposed approach, over monitoring trans-membrane pressures and permeate fluxes, from the standpoints of data variability, effect of process changes, interaction between module in multi-module systems, and fouling dynamics.

Size-dependent water transport in laminar graphene oxide membranes: An interplay between interlayer spacing versus tortuosity of transport pathway

Graphene oxide membranes (GOMs), consisting of graphene oxide (GO) laminar microstructures, offer great potential as nanofiltration membranes due to their unique laminar nanochannelled galleries created between the stacked GO flakes. Recently, GOMs made from smaller GO flakes (S-GOMs) were favored for the reason that the less tortuous transport pathways could render better water permeability. Here, we found that this may not necessarily be true. We designed experiments, which suggested that the interlayer spacing between GO flakes may be a more important factor affecting the water permeability than the tortuosity of the water pathway, especially when the two-dimensional nanochannels were smaller than expected under a pressurized filtration setting. Notably, our results showed that as the GO flakes were fragmented into smaller pieces by high-power probe sonication, they underwent a thermal reduction that decreased the size of the interlayer spacing. Coupled with a less wrinkled microstructure that caused tighter compaction under a 3-bar transmembrane pressure, the overall water transport through the S-GOM was reduced despite a less tortuous pathway that was 2.5 times shorter based on theoretical calculation. This led to S-GOM showing 3.3 times lower water permeability than that of GOM made from large GO flakes. On the whole, our results unveil the interplay between the two most important parameters governing the water permeability of GOMs, which will help researchers with more instructional support when developing better performing GOMs for nanofiltration application.

Monitoring Membrane Fouling Using Fluid Dynamic Gauging: Influence of Feed Characteristics and Operating Conditions.

Recent studies on membrane fouling have made considerable progress in reducing its adverse effects. However, a lack of comprehensive studies focusing on the underlying fouling mechanisms remains. This work aims to address a part of this gap by investigating the influence of feed suspension chemistry and operating conditions on the fouling characteristics of microcrystalline cellulose. Fluid dynamic gauging (FDG) was employed to monitor the properties of fouling layers under varied conditions. FDG results revealed that the cohesive strength of fouling layers increased in the direction towards the membrane, which can be associated with the higher compressive pressures exerted on foulants deposited near the surface. At lower pHs and higher ionic strengths, reduced electrostatic repulsions between particles likely resulted in particle agglomeration, leading to the formation of thicker cakes. In addition, thicker cake layers were also observed at higher feed concentrations, higher operating transmembrane pressures, and longer filtration times. The cross-flow velocity influenced the resilience of fouling layers significantly, resulting in thinner yet stronger cake layers in the transition and turbulent flow regimes. These findings regarding the influence of feed characteristics and operating conditions on the fouling behavior can be beneficial in developing effective antifouling strategies in membrane separation processes.

The long-term removal of dissolved Mn from drinking water via membrane filtration using sodium permanganate as a pre-oxidant

Dissolved Mn, often found in water sources, can cause various problems such as discoloration, and poor taste and odor. In this study, the long-term removal of dissolved Mn via a membrane-filtration process using sodium permanganate (NaMnO4) as a pre-oxidant was evaluated for drinking water treatment. Thereby, 0.67 M NaMnO4 pre-oxidation for 10 min was optimal and removed 91% of the dissolved Mn from raw water. In addition, increasing the pH improved the removal efficiency, as did varying the temperature (83% to 89% for 5.1 to 25 °C). Additionally utilizing poly aluminum chloride as a coagulant helped to remove both dissolved Mn and organic matter from the water. Using NaMnO4 as a pre-oxidant also played a significant role in the membrane filter-based removal of dissolved Mn using both pressurized and submerged membrane filters over the long term. The results show that the average removal rate of dissolved Mn in the range of 0–0.039 mg/L via membrane-filtration processes with and without NaMnO₄ pre-oxidation was 19% and 92%, respectively. The removal rate by both membranes was similar while the increase in trans-membrane pressure was insignificant. Thus, NaMnO4 pre-oxidation coupled with membrane filtration is an enterprising solution for removing dissolved Mn from drinking water.

Integrated electroflocculation-membrane process for pre-concentration of domestic wastewater: Filtration performance, organics recovery and membrane fouling characteristics

A novel electroflocculation-membrane (EFM) reactor for pre-concentrating domestic wastewater (DWW) is proposed in this study, using a conventional direct membrane filtration (DMF) reactor as a control. The results showed that under the operating conditions of a current density of 5 A/m2, an electrolysis time of 2.5 h and an inter-electrode distance of 25 mm, an obviously higher organics recovery efficiency of 72.92 % can be achieved in EFM, while only 55.14 % was obtained in DMF. Concentrate with chemical oxygen demand (COD) concentration of 4391.50 mg/L and 3322.88 mg/L was finally got by EFM and DMF, respectively. The higher retention effect of the dissolved organics remained key to the enhanced organics recovery capability of the EFM. Membrane fouling was also mitigated with EFM in continuous operation, with transmembrane pressure (TMP) increasing rate of 0.15 kPa/h (1.27 kPa/h for DMF). The loose and porous floc structure and small size distribution of the supernatant in EFM were the main contributors for reducing the resistance of the cake layer to mitigate membrane fouling. This study provides a new perspective on future wastewater resource recovery.

H2 permeance and surface characterization of a thin (2 μm) Pd-Ni composite membrane prepared by electroless plating

The high cost of palladium membranes limits their widespread use in industrial applications. We report a novel strategy for the preparation of economic hydrogen separation membranes. In this study, a Pd88-Ni12 composite membrane was prepared with a considerable nickel content (>10 wt%) for the first time using the organic–inorganic activation method in the ELP approach. The H2 permeance of the Pd88-Ni12 composite membrane was 4.34 × 10-7 mol m−2 s−1 Pa−1 at 500 °C with infinite selectivity (H2/N2). The membrane exhibited suitable performance when exposed to binary mixtures under various operating conditions. At 500 °C and 100 kPa, with the same concentration of impurity gases, the H2 permeance of the Pd88-Ni12 composite membrane was 3.33 × 10 -7 mol m−2 s−1 Pa−1 for the H2-Ar mixture, 3.12 × 10 -7 mol m−2 s−1 Pa−1 for the H2-N2 mixture, 2.56 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO2 mixture, and 2.54 × 10 -7 mol m−2 s−1 Pa−1 for the H2-CO mixture. The effect of operating parameters and the amount of impurity concentration in the gas feed on the stage cut in binary gas mixtures was investigated. Increasing operating temperature and pressure enhanced the stage cut for all mixtures while increasing the impurity concentration in the gas feed led to a decrease in the stage cut, independent of operating conditions. The Pd88-Ni12 composite membrane indicated suitable long-time permeance stability for 150 h at a transmembrane pressure range of 100–300 kPa and 500 °C under an H2/N2 gas atmosphere. Finally, the cost investigation demonstrated that the Pd88-Ni12 composite membrane had a 38 % lower specific cost than the pure palladium composite membrane.

Gaseous Nitric Oxide-Cangrelor Combination to Prevent Clots in Extracorporeal Life Support System

IntroductionThe objective of this study was to investigate the potential synergistic utility of a combination of gaseous nitric oxide (gNO)-intravenous Cangrelor as an effective pharmacological option for the prevention of thrombosis in an animal model of extracorporeal life support (ECLS) circuits. Methods10 newborn lambs were placed on ECLS. 5 of them were administered a combination of gNO and intravenous Cangrelor. The remaining 5 were not administered any anticoagulant. The primary end point was duration of ECLS without clot formation. The secondary outcome measure was the absolute maximum transmembrane pressure gradient. ResultsThe mean duration of ECLS were 168 min (standard deviation 224.98 min) in the control group and 402 min (standard deviation 287.5 min) in the experimental group (P = 0.17). The peak trans-oxygenator pressure difference was 43 mm Hg (standard deviation 23 mm Hg) in the control group and 62 mm Hg (standard deviation 71 mm Hg) in the experimental group(P = 0.64). Two animals in the experimental group were supported up to 12 h without clot formation. Clot formation in the experimental group occurred after placement of the cannulae but prior to initiation of ECLS flows after cannulation. ConclusionsA combination of gNO and Cangrelor is prevents clot formation in an experimental animal model when administered through a clean clot-free circuit. However, the combination s ineffective when there are pre-existing clots in the circuit. A bolus of anticoagulation prior to cannulation is needed prior to testing this combination in future studies with a larger sample size.

Effect of mechanical scouring on fouling control in greywater filtration with fluidized bed submerged membrane reactor for decentralized wastewater treatment process

Synthetic greywater was applied into a novel, fluidized submerged membrane reactor (FSMR) to compare membrane fouling with three different types of scouring agents: granular activated carbon (GAC), tubular polyvinylidene fluoride (PVDF) media, and spherical polyethylene terephthalate (PET) beads. Trans-membrane pressure (TMP) was investigated to estimate the extent to the fouling in the FSMR operated at 13 and 40 L/m2.h of permeate flux. The selection of scouring agents affected transient behavior of TMP value significantly to reduce membrane fouling. Fluidization of spherical PET beads driven by recirculating bulk suspension only through the FSMR was a prominent way to mitigate fouling. However, the cake layer was formed on membrane surface extensively as GAC or tubular PVDF media was fluidized over the course of reactor operation. At 13 L/m2.h, the TMP reached 0.74, 0.7, and 0.04 bar after 7 d operation with FSMR added with GAC particles, tubular PVDF media, and spherical PET beads as scouring agent, respectively. For the non-adsorbing PET beads, organic compound such as humic acids and proteins were a main organic fraction in cake layer. The organic removal efficiency was enhanced by complex formation resulting from the concentrated greywater in the reactor operated during extended filtration time. However, small carbon particles produced by the pulverization of GAC particles in the FSMR system disrupted fouling control and led rapid TMP rise.

Dissolved gas recovery from water using a sidestream hollow-fiber membrane module: First principles model synthesis and steady-state validation

This paper presents a first-principles model for the recovery of dissolved gases from liquids using a sidestream hollow-fiber membrane module. The model avoids the use of new empirical coefficients, thus providing a parametric understanding of the process behavior for future design and optimization of membrane modules. This type of first-principles model could be particularly useful when gas recovery is beneficial to biological or chemical reactions of interest, such as the acetogenesis reactions in two-stage anaerobic digesters. The steady-state behavior of the model was validated against both new experimental data for the recovery of H2, CH4 and H2–CH4 mixtures from pure water, as well as existing published data. The modeled gas recovery predictions agreed with experimental data to an absolute average error of 13%, and an average R2 value of 0.98. Parametric analysis of mixed-gas recovery suggests possible key transition points in the composition of the recovered gases. For example, at 40 °C, increasing trans-membrane pressure while keeping hydraulic residence time (HRT) under 0.5 s will result in an increase in the ratio of H2 to CH4 recovered. Otherwise, increasing trans-membrane pressure will instead decrease the ratio of H2 to CH4 recovered. The model has potential to be extended to transient analysis, but has yet to be validated with transient experimental data. This model was successfully implemented in both Python and MATLAB, and provides valuable insights for future net-energy optimization for anaerobic digestion systems with in-situ gas recovery.

Hydrodynamics and Energy Analysis in Suspended Catalyst Photocatalytic Membrane Reactors

Photocatalysis is a non-selective advanced oxidation process (AOP) that can be effective for degradation of toxic compounds. Its main drawback however has been high processing costs compared to other AOPs. Suspended catalyst photocatalytic membrane reactors (SPMR) are promising design configuration for implementation of the technology. This work involves experimental and theoretically analysis of the hydrodynamics and energy consumption in a SPMR under crossflow and oscillatory shear conditions. An optimization approach is presented for intensification of the reactor performance that considers the coupling effects of the applied shear and the transmembrane pressure on the hydrodynamics and the specific energy consumption (kWh/m3). The results showed that the optimum shear rate decreases with increasing the membrane area due to the relatively high contribution of the permeate pumping power to the energy consumption which makes the advantages of operating at higher shear rate relevant. This trend changes for larger membranes areas where the energy consumption due to higher shear outweighs the advantage of its performance enhancement resulting in increasing the system specific energy consumption. In general, the latter was found to be higher for a crossflow system compared to an oscillatory membrane design, which in addition to its smaller footprints, can make such design an attractive option for confined and/or limited space applications.

High-porosity thin membrane for high-efficiency capture of rare cells

High efficiency capture of rare cells such as circulating tumor cells (CTCs) in the blood of cancer-patient is challenging for size-based separation methods, because of the heterogeneity of the cells, the presence of a huge number of background cells (red and white blood cells), and the overlap in size of the rare cells and some of the background cells. In this work, we developed a systematic study to evaluate the parametric dependence of rare cell capture efficiency by using model cells. High-porosity and thin membranes with supporting honeycomb microframe are fabricated by using a two-level lithography technique. They are then integrated into a microfluidic device for real-time monitoring of flow-induced transmembrane pressure with a solution with or without cells. Our results show both experimentally and theoretically a great importance of the pore number of the membrane and the flow rate. When more than 80% of pores are clogged by large background cells, the rare cell capture efficiency decreases significantly. Otherwise, a lossless capture is theoretically achievable with a high-porosity and large-area membrane under optimal flow conditions.

Optimal control of backwash scheduling for pumping energy saving: Application to the treatment of urban wastewater

An optimal control strategy for municipal wastewater MBR treatment was applied to investigate its efficiency in minimizing the pumping energy of the system. Based on a simple mathematical model to capture the dynamic evolution of the TransMembrane Pressure (TMP), an optimal switching instant between filtration/backwash was determined to reduce the supplementary pumping energy caused by fouling for a predefined net permeate volume. A MBR pilot treating municipal wastewater was used to generate dynamic data of TMP. The pilot was operated with two different strategies: a classical strategy with known operating conditions (10 min filtration and 45 s backwash) and an optimal strategy where the frequency was determined based on adjustment of model parameters. Results demonstrated that a satisfactory agreement was achieved between experimental data and model prediction. The optimal strategy was then applied experimentally on the MBR pilot. The two strategies were compared in terms of energy consumption and fouling degree. The results showed the feasibility of the optimal solution and its reliability to reduce the pumping energy of the system by 7 % and decrease residual fouling by 14 % compared with a classical strategy.

Recycling of homogenous catalyst using organic solvent filtration and electrochemical separation

Homogenous catalyst has great selectivity and kinetic advantages. However, it is quite difficult to recover because it has same phase as the reaction mixture, so their utilization is being limited. A popular method to recover the catalyst is organic solvent nanofiltration, which use the transmembrane pressure and the different composition of the solvents to achieve the catalyst recovery. In recent research, a new method-separation using electrochemistry had been discovered which seems to increase the recovery percentage. In this paper, both strategies with recent developments are summarized, and focused on how the accompanied components such as solvents, electrolytes and electrode usage will influence the catalyst recovery.

Green management of wet olive pomace by means of ultrafiltration of an aqueous extract of phenolic compounds

Wet olive pomace is a major by-product generated by olive mills. To contribute to the circular economy of the olive industry, the recovery of interesting compounds from wet olive pomace was assessed. To that end, a previously optimized solid-liquid extraction, only employing water as the extractant, was first applied to the wet olive pomace. Afterwards, an ultrafiltration process to treat the obtained extract was developed. Several membranes (UP005, UH030, UH050, and UP150, from Microdyn Nadir) were studied, in a wide range of cross-flow velocities (1.5–3.5 m/s) and transmembrane pressures (0.75–5.5 bar). By a thorough characterization of the ultrafiltration streams by LC-ESI-QToF-MS, it was possible to describe the evolution of the rejection of 29 phenolic compounds. Some adsorption processes were also observed in the ultrafiltration process. The UP005 and UH030 membranes displayed satisfactory values of permeate flux and rejection. Both membranes efficiently retained a high fraction of the total solids, chemical oxygen demand, and color. On the contrary, the phenolic compounds were obtained in the ultrafiltration permeate, which constitutes a source of antioxidant molecules with applications in cosmetics, pharmacy, and nutraceutics.