Low-pressure Membrane Research Articles

Application of volume retarded osmosis – Low pressure membrane hybrid process for recovery of heavy metals in acid mine drainage

Recovery of heavy metals in acid mine drainage (AMD) such as Mn, Fe, Cu, Zn, As, Cd and Pb was evaluated using volume retarded osmosis and low-pressure membrane (VRO-LPM) process. In VRO-LPM process, the draw solution (DS) is regenerated by the naturally generated pressure, giving its economic value. Ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) and Poly (sodium-4-styrenesulfonate, PSS-Na) were used and compared to determine more suitable DS in heavy metal recovery from the AMD. Forward osmosis (FO) and nanofiltration (NF) membrane were employed in VRO-LPM process, due to the low EDTA-4Na rejection (about 50%) in ultrafiltration (UF) process. For the FO part in the VRO-LPM process, PSS-Na had flux values of 0.12, 0.11 and 0.05 L m−2 h−1 and at osmotic pressure of 8.9, 12 and 13 bar, respectively. Unlike the flux values, the RSF of PSS remained at 0.01 mmol h−1 at all osmotic pressures. For EDTA-4Na, the flux values were 0.10, 0.06 and 0.04 L m−2 h−1, which are relatively higher than those of PSS-Na; and the RSF values were 0.1, 1.2, 2.2 mmol h−1, which are higher compared to those of PSS-Na. Unlike PSS-Na, RSF for EDTA-4Na increased as the concentration increases. In the NF part of the VRO-LPM process, PSS-Na had higher water flux and rejection than EDTA-4Na, and the flux and rejection both decreased with concentration for both PSS-Na and EDTA-4Na. The overall rejection in VRO-LPM process was over 95% for all heavy metal ions. Therefore, VRO-LPM process has proven its ability to be used in AMD treatment for heavy metal removal.

Flux Optimization in Reverse Osmosis via the Solution-Diffusion Model

This paper suggests a new method of predicting flux values at reverse osmosis (RO) desalination plants. The study is initiated by using the solution-diffusion model that is applied to the groundwater source at Abqaiq plant (500 RO plant) at Saudi Aramco, Dhahran, Saudi Arabia in order to calculate the osmotic pressure of the treated water for Shedgum/Abqaiq groundwater. For modelling purposes, the same technique is used to determine the osmotic pressure drops at the same plant configuration and operating conditions when using seawater sources such that of Arabian Gulf and the Red Sea waters. High rejection brackish water RO (BWRO) element Toray TM720D-400 with 8" is the RO membrane type that is used at Abqaiq plant. The calculated osmotic pressures of the three water sources, assuming that they are all treated at Abqaiq plant, are utilized to determine the appropriate flux values as well as membrane resistances of different BWRO Toray membranes. Values of numerous parameters such as water permeability constant, applied pressure, gas constant, water temperature, water molar volume and membrane thickness, water salinity/TDS are taken into account to develop our calculations through the solution-diffusion model. A comparison between low-pressure, standard and high-pressure BWRO Toray membranes performance have been established to select the ideal membrane type for the treatment of water from various sources at Abqaiq plant. The model results confirm an inverse relationship between the membrane thickness and the water flux rate. Also, a proportional linear relation between the overall water flux and the applied pressure across the membrane is identified. Higher flux rates and lower salinity indicate lower membrane resistance which yields to the higher water production. Modelled data predict that BWRO Toray TM720D-440 with 8" membrane is the optimal BWRO membrane choice for the three water sources at Abqaiq plant.

Design and development of layer-by-layer based low-pressure antifouling nanofiltration membrane used for water reclamation

Recent studies have confirmed the advantages of low-pressure nanofiltration (NF) membranes in integrated nanofiltration membrane bioreactor system followed by the reverse osmosis (RO) process for high recovery water reclamation. However, fouling of low-pressure NF membranes restricts their application in providing high quality feed to subsequent RO process. In this study, an antifouling low-pressure NF membrane was designed and fabricated via rapid co-deposition of polydopamine (PDA)/polyethylenimine (PEI) on electrostatic layer-by-layer (LBL) assembled polyethersulfone (PES) flat sheet membrane followed by crosslinking with glutaraldehyde. The optimized resultant membrane (LBL-cPP) presented approximately 11 LMH/bar pure water permeability with more than 90% rejection divalent cations under 2 bar pressure. The newly developed selective layer exhibited excellent antifouling performance and chemical stability ascribing to the inherent hydrophilicity of PDA/PEI and dual covalent reaction of PDA with the LBL layer. By feeding real municipal wastewater, the LBL-cPP membrane also achieved superior permeate quality, leading to lower RO fouling rate in subsequent RO unit as compared to commercial NF 270 membrane. Further organic foulant analysis indicated that 96.8% of dissolved organic carbons were effectively removed by the LBL-cPP membrane. Specifically, the novel NF membrane demonstrated high removal rate (>93%) for foulants with low molecular weights which was largely responsible for RO fouling, while maintaining the desired flux recovery rate and reduced cleaning frequency. This study demonstrates the potential of PDA/PEI modified low-pressure NF membranes in designing efficient and sustainable water reclamation technology.

Biofilm compressibility in ultrafiltration: A relation between biofilm morphology, mechanics and hydraulic resistance

Poroelastic fluid-structure interaction models were coupled to experimental data to determine the effects of biofilm spatial distribution of mechanical and hydraulic properties on the biofilm hydraulic resistance and compressibility in membrane filtration processes. Biofilms were cultivated on ultrafiltration membranes for 20 and 30 days under high (0.28 bar) and low (0.06 bar) transmembrane pressure (TMP), in dead-end filtration mode. Subsequently, biofilms were subjected to a compression/relaxation cycles by step-wise TMP changes. Structural deformation of biofilms during compression was observed in-situ using optical coherence tomography.Experimental results show that the observed increase in the biofilm hydraulic resistance during compression is not necessarily accompanied by a detectable biofilm thickness reduction. A dual-layer biofilm model with a dense base and porous top layer could explain these observed results. Because porosity controls indirectly the mechanical response of biofilms under compression, results could be described without assuming a gradient in mechanical properties within the biofilm. The biofilm surface roughness did not significantly influence the water flux in this study. However, the fraction of biofilm base layer directly exposed to bulk liquid could be a good indicator in the determination of water flux. The main implications of this study for the design and operation of low-pressure membrane systems (e.g., MF and UF with fouling layer being the main filtration resistance) lays in the selection of favorable operational TMP and biofilm morphology.

A novel method for measuring cake porosity by ions detection technique in a conventional coagulation-ultrafiltration process

Cake porosity plays an important role for evaluating membrane fouling in low-pressure membrane filtration process. Current method for calculating cake porosity is based on Carman-Kozeny equation. It would have many limitations due to the indirect analysis. CLSM has been applied to directly measure the structure of chemical particle models, but requirement that materials need to be fluorescent is difficult to achieve in conventional coagulation-ultrafiltration processes. Our study investigated a novel method using fluorescence probe to measure cake porosity for making up the defect of non-fluorescent of cake layer in conventional coagulation-ultrafiltration process. Two metal ions probes, quercetin and carbon nanodots (CNDs), were applied to detect the Al3+ ions and Fe3+ ions from Al-based salt and Fe-based salt coagulants respectively. Cake morphology could be directly observed by an established method (CLSM and image analysis technique). Using t-test to compare the obtained porosities with those calculated from specific cake resistance by Carman–Kozeny equation. Result shows that they are not significantly different at the confidence level of 95% and 98%, which proves fluorescence identification has higher accuracy. Furthermore, characters of the complexing formed by different cations and hydroxide ions also affect the cake porosity. Porosities of Al-based cake are smaller and those of Fe-based cake are larger. Effect of both fractal dimension and floc size on porosity were also investigated and concluded that role of the fractal dimension is prior to floc size.

Biofouling Response of Laboratory-Scale Polysulfone Membranes Modified with Bioinspired Polydopamine and Silver Nanoparticles

Abstract Low-pressure membranes provide high-quality water through physical removal of bacteria, cysts, and particles. Bacteria can attach to the membrane surface and form biofilms that reduce ener...

Ferric Oxyhydroxide as Fouling Prevention Reagent for Low-Pressure Membranes

Ferric Oxyhydroxide as Fouling Prevention Reagent for Low-Pressure Membranes

In Situ Modification of Reverse Osmosis Membrane Elements for Enhanced Removal of Multiple Micropollutants

Reverse osmosis (RO) membranes are widely used for desalination and water treatment. However, they insufficiently reject some small uncharged micropollutants, such as certain endocrine-disrupting, pharmaceutically active compounds and boric acid, increasingly present in water sources and wastewater. This study examines the feasibility of improving rejection of multiple micropollutants in commercial low-pressure RO membrane elements using concentration polarization- and surfactant-enhanced surface polymerization. Low-pressure membrane elements modified by grafting poly(glycidyl methacrylate) showed enhanced rejection of all tested solutes (model organic micropollutants, boric acid, and NaCl), with permeability somewhat reduced, but comparable with commercial brackish water RO membranes. The study demonstrates the potential and up-scalability of grafting as an in situ method for improving removal of various classes of organic and inorganic micropollutants and tuning performance in RO and other dense composite membranes for water purification.

Preparation and characterization of low-pressure and high MgSO4 rejection thin-film composite NF membranes via interfacial polymerization process

Low-pressure nanofiltration membrane produced by FILMTEC-DOW is generally considered by membrane industries as the commercial standard; according to its specification, for a 2000 ppm MgSO4(aq) feed, it yields 98.2% MgSO4 rejection and 22 GFD permeate flow at 70 psi applied cross-flow filtration pressure. Here we want to report our nanofiltration membrane development works on improved reactant formulation and fabrication process to produce our nanofiltration membrane having 98.2% MgSO4 rejection and 33 GFD permeate flow for the similar test conditions as FILMTEC-DOW did. Our near 50% improvement on water permeate flux over FILMTEC-DOW low-pressure nanofiltration membrane was due to the fact that an adduct salt named TEACSA was added to the aqueous piperazine aqueous solution during our membrane fabrication process. Besides evaluating the nanofiltration performances of our NF membranes, characterizations of the polyetherimide (PEI) microporous supports fabricated in our laboratory in the areas of pure water permeate fluxes at 40 psi cross-flow filtration pressure, wet–dry studies of hydrophobic porous polyetherimide and polysulfone supports, AFM and SEM were performed.

Turning complexity into clarity: polyuria and hypernatremia

Turning complexity into clarity: polyuria and hypernatremia

Analysis of the Flux Performance of Different RO/NF Membranes in the Treatment of Agroindustrial Wastewater by Means of the Boundary Flux Theory.

Dynamic membrane system behaviour must be adequately addressed to avoid process unfeasibility. The lack of proper analysis will mean relying on erroneous permeate flux values in the system design, which will lead to quick and/or steady high fouling rates. In this paper, the authors present additional data supporting the boundary flux theory as a helpful tool for membrane engineers to carefully avoid process failures. By fitting the dynamic permeate flux data to the boundary flux model, it was possible to calculate the β fouling index for the three selected membranes (one nanofiltration (NF) and two reverse osmosis (RO) ones). The dynamic flux given by the low-pressure RO membrane did not follow sub-boundary operating conditions, since a sharp flux loss was measured throughout the whole operating cycle, pinpointing that supra-boundary flux conditions were governing the system. This was supported by the calculated value of the β fouling parameter, which resulted to be in the order of ten times higher for this membrane. However, the values of β→0 for the SC-RO and DK-NF ones, supported by the very low value of the sub-boundary fouling parameter α (0.002 and 0.007 L·h−1·m−2·bar−2, respectively), ensure nearly boundary operating conditions for these membranes.

Novel “loose” GO/MoS2 composites membranes with enhanced permeability for effective salts and dyes rejection at low pressure

Graphene oxide-based nanofiltration membrane, have attracted tremendous interest due to the highly permeability and excellent rejection behavior. Here we show that a novel low-pressure nanofiltration membranes (LPMs) comprising MoS2 nano-supporting spacer among the graphene oxide (GO) layers, which were fabricated by forward pressure-assisted assembly and heat-treatment. The resultant GO/MoS2 LPMs exhibited a pure water permeability about 10.2 ± 1.68 L/(m2·h·bar) at low pressure (2 bar), which was much higher ( about 13.6 times) than that of pristine GO membrane (~0.75 L/(m2 h bar)). Meanwhile, high rejection to different charged dyes ( ≥ 95%) and moderate rejection for salts (43.2%, 65.2%, 26.5% and 24.3% for NaCl, Na2SO4, MgCl2 and MgSO4, respectively) was remained. The satisfied filtration performance was attributed to the loose interlayer-structure of composite membrane and the cooperative effect of Gibbs-Donnan exclusion mechanism and steric hindrance. In addition, the GO/MoS2 LPMs presented satisfied stability and antifouling properties. Experimental results and molecular dynamics simulation results demonstrated that the increase of vertical distance between GO sheets by introducing the MoS2 nanoparticles could accelerate the water transport in the channels. This paper was not only provided a new design idea for adjusting the channel size of GO membrane, but also gave a promise of GO-based membrane for practical wastewater treatment and purification.

Application of a volume retarded osmosis–low pressure membrane hybrid process for treatment of acid whey

This study evaluated the treatment of acid whey through a volume-retarded osmosis–low-pressure membrane (VRO-LPM) hybrid process. The VRO-LPM process uses pressure naturally generated inside the closed draw solution (DS) tank to regenerate the DS, making it an economic process. Poly (sodium-4-styrenesulfonate) (PSS) and carboxymethyl cellulose (CMC) were compared to determine which was a more suitable DS for acid whey treatment. Forward osmosis (FO) and ultrafiltration (UF) membranes were used in the VRO-LPM hybrid process because a single UF process showed high water flux and rejection efficiencies above 85% for both PSS and CMC. In both the FO and UF parts of the VRO-LPM process, PSS had a higher water flux than CMC. However, the increasing rate of the feed solution (FS) for CMC was greater than that of PSS, however the overall rejection efficiencies were similar for both DS. Therefore, the VRO-LPM process can be applied to acid whey treatment, and CMC seems to be a better choice of DS than PSS because of its higher concentrating ratio of FS and high overall rejection.

New prospects for immersed hollow-fiber membranes in fruit juices microfiltration: Case of grapefruit juice

Side-stream tubular membranes are largely used to perform cross-flow microfiltration of fruit juices. However, this configuration presents well-known drawbacks (e.g. energy consumption). Immersed membranes configurations have been developed in many fields to overcome these disadvantages. This paper investigates for the first time the possibility of using immersed configuration for fruit juices microfiltration. Firstly, a lab-scale methodology was adopted to characterize the fouling propensity of the juice, while studying the impact of transmembrane pressure, membrane material and the role of large particles on the juice fouling behavior. Secondly, pilot-scale experiments were performed to identify the optimal operating conditions for both configurations. Both lab-scale and pilot-scale experiments suggested that the operating conditions of immersed configuration (no removal of large particles, low pressure and organic membranes) could be suitable to perform juice microfiltration. The optimal permeate flux of immersed configuration was in accordance with the ones reported in other fields. A productivity similar to the one related to side-stream configuration might be obtained through an increase of the filtration surface, made possible by the great packing density and low membrane cost related to immersed configuration. These findings offer new application for immersed membrane configuration in the microfiltration of delicate fruit juices.

Low-pressure electroneutral loose nanofiltration membranes with polyphenol-inspired coatings for effective dye/divalent salt separation

Low-pressure electroneutral loose nanofiltration (NF) membranes were facilely fabricated by co-deposition of polyphenol-inspired epigallocatechin gallate (EGCg) and polyethyleneimine (PEI) on polyethersulfone (PES) ultrafiltration substrates. The effects of PEI with different molecular weights on co-deposition behavior, morphologies, surface properties, as well as separation performance of the resultant membranes were investigated in detail. The results showed that with the increase of PEI molecular weight from 600 to 10,000, the co-deposition amount of EGCg/PEI on membrane surface decreased, while the EGCg/PEI selective layer became denser. As a result, the EGCg/PEI 600 co-deposited membrane, which possessed an electroneutral surface with the best hydrophilicity, exhibited the optimal separation performance among the co-deposited membranes in the context of textile wastewater treatment. It had the highest pure water permeability (19.0 L/(m2·h·bar)) and excellent rejections towards dyes with different charges (e.g. 99.0% for Congo Red) as well as the lowest rejections towards divalent salts (e.g. 4.1% for Na2SO4) at an operating pressure of 2 bar. Moreover, the membranes exhibited good organic solvent resistance, structural stability together with favorable performance in dealing with textile effluent, demonstrating their great potential in practical applications.

Membrane Fouling Prevention and Control Strategies in Pulp and Paper Industry Applications: A Review

Membrane separation technologies have recently received much attention, from lab-scale studies to full-scale operations, in the forest industry. However, membrane fouling comprises a signifcant obstacle to their broad application. Thus, to ensure cost-effective operation of membrane separation processes, the improved elucidation of membrane fouling and establishment of effective fouling control strategies are critical. Membrane fouling decreases process performance efciency, thereby increasing operational and maintenance costs. Although much research has been conducted in this feld, a review has not yet been undertaken to address membrane fouling in pulp and paper mill applications. Further, membrane fouling is still not fully understood. In this review, a survey of the present state of fouling management strategies in the pulp and paper industry (PPI) is presented alongside the latest advances and innovative methods in fouling management. This article also discusses the key parameters that affect membrane fouling, fouling characterization techniques, as well as fouling mechanisms and strategies that are employed for fouling control. In addition, future research opportunities related to membrane fouling control strategies in both low-pressure membranes and MBRs are proposed.

Removal of polar organic micropollutants by pilot-scale reverse osmosis drinking water treatment

The robustness of reverse osmosis (RO) against polar organic micropollutants (MPs) was investigated in pilot-scale drinking water treatment. Experiments were carried in hypoxic conditions to treat a raw anaerobic riverbank filtrate spiked with a mixture of thirty model compounds. The chemicals were selected from scientific literature data based on their relevance for the quality of freshwater systems, RO permeate and drinking water. MPs passage and the influence of permeate flux were evaluated with a typical low-pressure RO membrane and quantified by liquid chromatography coupled to high-resolution mass spectrometry. A strong inverse correlation between size and passage of neutral hydrophilic compounds was observed. This correlation was weaker for moderately hydrophobic MPs. Anionic MPs displayed nearly no passage due to electrostatic repulsion with the negatively charged membrane surface, whereas breakthrough of small cationic MPs could be observed. The passage figures observed for the investigated set of MPs ranged from less than 1%–25%. Statistical analysis was performed to evaluate the relationship between physicochemical properties and passage. The effects of permeate flux were more pronounced for small neutral MPs, which displayed a higher passage after a pressure drop.

Bench and pilot scale performance assessment of recycled membrane converted from old nanofiltration membranes

ABSTRACTRecycling of end-of-life polyamide-based thin film composite (TFC) membranes is gaining interest in academic and industrial contexts. The effects of chlorine exposure on the performance of polyamide membranes result in an increase in membrane permeability, whereas the solute rejection decreases. Therefore, the controlled chemical conversion of old reverse osmosis (RO) membranes has been reported by some previous papers. The objectives of this study were to assess recycling of old nanofiltration (NF) membrane, to assess the performance of the recycled membranes for a river water treatment application, and to conduct preliminary cost evaluations. Recycling technique consisted of exposing the membrane to a sodium hypochlorite solution in order to remove its polyamide layer and conversion to a low-pressure membrane. The work conducted bench scale and long-time pilot tests, and the recycled membranes showed a low fouling tendency. The difference between some results in bench- and pilot scale underscores the importance of evaluating design parameters using pilot scale units. Based on the cost analysis, the total cost of chemical recycling end-of-line NF membranes for a river water treatment is approximately 1.1% of the cost of using a new UF membrane. There is a great potential in using recycled membranes for rivers water treatments.

Graphene oxide incorporated thin film nanocomposite membrane at low concentration monomers

A high flux thin film nanocomposite (TFN) nanofiltration (NF) membrane under low pressure (4 bars) was prepared through a facilitated interfacial polymerization (IP) reaction between low concentrations of piperazine (PIP) and organic trimesoyl chloride (TMC) in the presence of graphene oxide (GO) nanosheets. The prepared GO-TFN membranes exhibited an improved water flux and chlorine-resistance performance without compromising the salt rejection. At the optimized GO dosage of 0.01 wt%, the synthesized GO-TFN membrane achieved a water permeance of 15.63 L/m2 h bar with the Na2SO4 rejection of 96.56% and MgSO4 rejection of 90.5%. The characterization of the TFN membranes by SEM, AFM, zeta potential and FTIR revealed that GO nanosheets improved the surface roughness, hydrophilicity and surface charges at low PIP and TMC concentrations, leading to both high water flux and salt rejection. The GO-TFN membrane also exhibited enhanced anti-chlorine ability. The study provides new insights into the development of low-pressure NF membranes with superior performance.

Insights into the roles of recently developed coagulants as pretreatment to remove effluent organic matter for membrane fouling mitigation

Membrane fouling by dissolved organic matter (EfOM) in secondary treated effluent is a problematic and inevitable issue during wastewater reclamation using low pressure membrane filtration. This study evaluates the performance of coagulation/flocculation (C/F) using two recently developed coagulants (namely TiCl4 and ZrCl4) in comparison to conventional alum (i.e. Al2(SO4)3) as pretreatment to remove EfOM for subsequent ultrafiltration (UF) membrane fouling mitigation. At the optimal dosage, TiCl4-based C/F pretreatment showed the greatest performance in membrane fouling mitigation, followed by ZrCl4 and then alum. The underlying mechanisms were well explained by classical fouling models and the extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory, highlighting a dominant role of standard blocking in the fouling potential of the C/F treated EfOM. The interfacial free energy of cohesion and adhesion showed that C/F pretreatment using TiCl4 and ZrCl4 as coagulant can lower the binding affinity between EfOM molecules and between EfOM molecules and membrane surface, ultimately reduce membrane fouling. The results of size exclusion chromatography (SEC) and fluorescence excitation emission matrix- parallel factor analysis (EEM-PARAFAC) also supported the classical fouling mechanisms, providing additional insights into the potential roles of chemical interactions in the preferential removal of certain organic substances by C/F pretreatment and the chemical composition of subsequent membrane foulants. Protein-like components were highly associated with reversible fouling after the C/F, while the reversibility of humic-like substances was enhanced upon C/F pretreatment. After C/F pretreatment, small sized EfOM molecules became the dominant fraction responsible for UF membrane fouling.