Hollow Fiber Membrane Filtration Research Articles

Navigating the balance between nanofiltration and oxidation to remove organic micropollutants from wastewater treatment plant effluent

The removal of organic micropollutants (OMPs) from wastewater treatment plant effluent is becoming more important due to the adverse effects of these compounds on the environment. To overcome the limitations of currently available technologies, this study proposes a combination of hollow fiber membrane filtration with advanced oxidation to remove OMPs. The possible synergy between these processes was investigated. The nanofiltration membrane ensures the removal of organic matter and thus an improvement of transmittance, after which oxidation with UV/H2O2 of the permeate can remove OMPs more effectively and at a significantly lower energy consumption than without a membrane. Six membranes were evaluated with a pure water permeability between 6.7 and 106 Lm−2 h−1 bar−1 and a MgSO4 retention ranging from 0.93 to 0. The molecular weight cut-off (MWCO) varied from 250 Da to more than 10 kDa. The measured MWCO can depend strongly on the applied flux. The UV-transmittance of NF permeate of treated wastewater was investigated experimentally to be between 97% and 50%. These values were used for an estimation of the specific energy consumption (SEC) for the membrane and the oxidation step, resulting in a combined SEC of 0.17–0.18 kWhm−3 for 70 or 80% removal of OMPs, respectively. Remarkably, this lowest SEC was not found for the combination with the most dense membrane, but for a slightly more open membrane. The reported SEC is comparable to the total energy consumption required for ozonation and adsorption, while producing clean water with a double barrier, high transmittance and 70–80% removal of OMPs.

CoFe2O4-titanium hollow fiber membrane filtration coupling peroxymonosulfate activation for water purification: Preparation, performance and mechanism

Constructing membrane filtration coupled with peroxymonosulfate (PMS) activation system has emerged as a promising strategy for efficient water purification. In this work, a novel CoFe2O4-titanium hollow fiber membrane (CoFe2O4-THFM) filtration system was proposed, aiming to integrate Co/Fe synergism and membrane filtration for enhancing PMS activation (MFPA) toward phenol (PE) removal. The performance of CoFe2O4-THFM MFPA process was rationally regulated via electro-deposition and calcination process, which displayed 100 % PE removal and showed 4.80 and 1.24 times (under 2 min running time) higher than that of FeO-THFM and CoO-THFM MFPA process. Mechanism analysis revealed a non-radical-dominated oxidation mechanism (involving 1O2, Fe(VI)=O and electron transfer), primarily attributed to the crucial role of Fe. On the one hand, the synergistic promotion mechanism of dual metal centers (Co(III)/Fe(II)) in the PMS activation process significantly enhanced the content of Co(II), and together with Fe(II) acted as active sites to generate reactive oxygen species (ROS, especially 1O2) for PE removal. On the other hand, the generated Fe(VI)=O (from Fe(III)) tend to react with PE (electron-donating), while the formed CoFe2O4-THFM-PMS* complex (oxygen vacancy (OV) mediated) plundered electrons from PE (electron transfer), leading to its oxidation. The notable non-radical process (1O2, Fe(VI)=O and electron transfer) mentioned above contributed to the excellent performance in real water matrix.

How to achieve air resistance control in hollow fiber membrane process: Membrane vibration or inner surface modification?

As a factor affecting the efficiency of hollow fiber membrane filtration, air resistance is gradually being discovered. To obtain a better air resistance control strategy, in the study, two representative strategies have been proposed, namely, membrane vibration and inner surface modification, which was achieved by aeration combined with looseness-induced membrane vibration and dopamine (PDA) hydrophilic modification of the inner surface, respectively. The performance of two strategies was based on Fiber Bragg Grating (FBG) sensing technology and ultrasonic phased array (UPA) technology to achieve real-time monitoring. Mathematical model result shows that in hollow fiber membrane modules, the initial appearance of air resistance causes a rapid reduction in filtration efficiency, while this effect diminishes as the air resistance increases. Besides, experimental results show that aeration combined with fiber looseness helps to inhibit air aggregation and accelerate air escape, while inner surface modification enhances the hydrophilicity of inner surface, weakens the air adhesion and increases the drag force of fluid on air bubbles. In the corresponding optimized state, both strategies perform well in optimizing the air resistance control, and the improvement in flux enhancement ability for the two strategies is 26.92 and 34.10%, respectively.

Evaluating filter functionality and user competence after a hollow fiber membrane filter intervention in Liberia

Abstract In Liberia, access to safe water is not universal, and waterborne diseases like diarrhea run rampant. As part of a larger border-to-border clean water project in Liberia, hollow membrane fiber filters were distributed to households in remote and/or small villages across Liberia. While filter efficacy has been demonstrated in the laboratory, studies of filter efficacy in real-world settings yield more mixed results. Intervention efficacy in Liberia was evaluated by assessing (1) user ability to correctly filter and backwash and (2) filter functioning at follow-up visits approximately 2 and 8 weeks post-intervention. Ultimately, the results supported the efficacy of this intervention. At arrival of both follow-ups, over 95% of filters were functioning properly and the majority of issues were resolved during visits. This supported the short-term durability of the filters and the importance of follow-up visits for repairs. Furthermore, the vast majority of households were able to correctly demonstrate filtering and backwashing: 88.47% at the first follow-up and 91.79% at the second. This slight increase may indicate the value of follow-up visits as educational tools. The widescale distribution of point-of-use filters as a mechanism for clean water should include on-going education and affordable filter repair and replacement opportunities.

Review of Hollow Fiber (HF) Membrane Filtration Technology for the Treatment of Oily Wastewater: Applications and Challenges

Oily wastewater has been recognized as a threat to the environment due to its hazardous nature and it can negatively affect the ecosystem, and threaten wildlife and human health. Physical, chemical, and biological technologies demonstrated a mixed performance in oily wastewater treatment, and, therefore, a proper treatment technology for oily wastewater needs to be addressed. Membrane filtration using a hollow fiber (HF) membrane is a promising alternative to remove emulsified oil from oily wastewater. This review discusses different sources of oily wastewater, various treatment methods, and membrane technology. The assessment has been focused on the parameters affecting HF membrane performance and applications of HF membrane-based technology to treat oily wastewater. This review paper reveals that HF membrane filtration systems have been previously used for the treatment of oily wastewater in bench-scale studies and few pilot-scale applications, which proved to be favorable in the treatment of recalcitrant wastewater containing oil and high salinity. Limitations associated with membrane fouling and the reduction of membrane permeability and membrane lifespan can be tackled and alleviated through modifying membrane chemistry and adjusting operational parameters. The compilation of studies showed that a low food/microorganism (F/M) ratio, long solid retention time (SRT) with high sludge age, long hydraulic retention time (HRT), and moderate aeration were the preferred operational parameters when treating oily wastewater. Based on this review, future studies should focus on optimizing the hydrodynamic conditions of the HF system, the commercialization of modified HF membranes, and the utilization of green technology in HF membrane construction to broaden HF membrane technology applications.

Treatment of a synthetic decanted oily seawater in a pilot-scale hollow fiber membrane filtration process: Experimental investigation

This study investigates the performance of a pilot-scale submerged hollow fiber (HF) ultrafiltration (UF) polytetrafluoroethylene (PTFE) membrane filtration system for the treatment of two different types of oily seawater (i.e., seawater contaminated with light and heavy crude oil). The effects of membrane flux and aeration flow rate on membrane performance and the removal efficiency of different fractions of hydrocarbon, including polycyclic aromatic hydrocarbons (PAHs) were examined. The results for both heavy and light crude oil contaminated wastewater reveal that total petroleum hydrocarbon (TPH) removal efficiency of more than 91% was achieved. This research paper determined the optimal operational parameters for an HF membrane filtration system to obtain a good TPH removal efficiency. This system can easily be upscaled and placed on a barge to treat oily wastewater generated from marine oil spills, which can significantly improve the oil spill response capacity.

Laboratory Efficacy of Locally Available Backwashing Methods at Removing Fouling in Hollow-Fiber Membrane Filters Used for Household Water Treatment.

Hollow-fiber membrane filters (HFMFs) for household water treatment (HWT) can efficaciously remove disease-causing organisms in laboratory settings. However, lower effectiveness in use in low- and middle-income countries (LMICs) and humanitarian contexts (HCs) has been observed and attributed to membrane fouling and the associated cleaning. In LMICs/HCs, it is not possible to prevent and control fouling using commonly known methods (e.g., testing influent water, maintenance regimes), and the literature on fouling/cleaning of HFMFs distributed in LMICs is scarce. As such, controlled laboratory experiments were conducted to determine the efficacy of locally available (in LMICs/HCs) backwashing solutions at removing fouling using different influent waters and HFMF types. Four commonly distributed HFMFs were selected; fouling layers were developed by filtering three influent water compositions, representing LMIC/HC waters, for 10-days, and bleach, water, or vinegar backwashing solutions were used for daily backwashing. Filter performance indicators included: fiber mechanical properties (strain at break, break force), water quantity performance (flow), water quality performance (turbidity, E. coli), and imaging. The study found fouling developed rapidly and altered mechanical properties and water quantity indicators within 200 h of filtration. Fouling did not decrease water quality indicators. Backwashing improved the filter’s mechanical properties and water quantity performance, but it did not fully recover the initial performance. Additionally, recovery differed between backwashing solutions, and no universal cleaning recommendation appropriate for HFMFs in LMICs/HCs was identified. Overall, fouling development and control depended on HFMF type, influent water quality, and backwashing solution type; thus, caution before distributing HFMFs for long-term use in LMICs/HCs is recommended.

Diarrhea prevalence in a randomized, controlled prospective trial of point-of-use water filters in homes and schools in the Dominican Republic

BackgroundLack of sustainable access to clean drinking water continues to be an issue of paramount global importance, leading to millions of preventable deaths annually. Best practices for providing sustainable access to clean drinking water, however, remain unclear. Widespread installation of low-cost, in-home, point of use water filtration systems is a promising strategy.MethodsWe conducted a prospective, randomized, controlled trial whereby 16 villages were selected and randomly assigned to one of four treatment arms based on the installation location of Sawyer® PointONE™ filters (filter in both home and school; filter in home only; filter in school only; control group). Water samples and self-reported information on diarrhea were collected at multiple times throughout the study.ResultsSelf-reported household prevalence of diarrhea decreased from 25.6 to 9.76% from installation to follow-up (at least 7 days, and up to 200 days post-filter installation). These declines were also observed in diarrhea with economic or educational consequences (diarrhea which led to medical treatment and/or missing school or work) with baseline prevalence of 9.64% declining to 1.57%. Decreases in diarrhea prevalence were observed across age groups. There was no evidence of a loss of efficacy of filters up to 200 days post-filter installation. Installation of filters in schools was not associated with decreases in diarrhea prevalence in school-aged children or family members. Unfiltered water samples both at schools and homes contained potential waterborne bacterial pathogens, dissolved heavy metals and metals associated with particulates. All dissolved metals were detected at levels below World Health Organization action guidelines.ConclusionsThis controlled trial provides strong evidence of the effectiveness of point-of-use, hollow fiber membrane filters at reducing diarrhea from bacterial sources up to 200 days post-installation when installed in homes. No statistically significant reduction in diarrhea was found when filters were installed in schools. Further research is needed in order to explore filter efficacy and utilization after 200 days post-installation.Trial registrationClinicalTrials.gov, NCT03972618. Registered 3 June 2019—retrospectively registered.

Decentralization policies and clean water practitioners: using hollow fiber membrane water filters to reduce the prevalence of GI-related symptoms and diagnoses in rural Honduras

AbstractIllnesses caused by dirty water are still prevalent in developing countries, resulting in significant health problems. This study explores how hollow fiber membrane point-of-use filters can reduce the prevalence of gastrointestinal (GI)-related symptoms and diagnoses. We summarize the current approach and policies regarding clean water in Honduras, which is marked by decentralization, and note the resulting challenges for clean water provision. To highlight how this works in practice, we combine medical brigade diagnosis data with survey data to explore the effect of point-of-use water filters on the prevalence of GI-related symptoms and diagnoses in rural south-central Honduras. Using OLS and penalized logistic regression, we find that hollow fiber membrane filters are effective in reducing GI-related diseases. Specifically, they reduce the number of GI-related symptoms by 0.30, and specifically those patients complaining of stomach aches (39 percent), diarrhea (39 percent), and vomiting (70 percent). We also find that they reduce the likelihood of a patient receiving an infectious disease/parasitic diagnosis (48 percent in all patients and 87 percent in children under the age of 13 years). These results have significant implications on those working with non-profit and non-governmental organizations to bring clean water to those living in developing nations.

An efficient large-scale refolding technique for recovering biologically active recombinant human FGF-21 from inclusion bodies

Fibroblast growth factor 21 (FGF-21) is an important regulator in glycolipid metabolism that is a promising drug candidate for treatment of diabetes and obesity. However, the productivity of recombinant hFGF-21 (rhFGF-21) in Escherichia coli (E. coli) is relatively low, which limits its clinical application. To meet the clinical demand and control the production cost, rhFGF-21 proteins were expressed in inclusion bodies (IBs) form in Rosetta (DE3) by high cell density fermentation in 50-L scale. Hollow fiber membrane filtration technology was used to enrich the bacteria, wash, denature and refold the IBs in the current report. The renatured proteins were purified by two-step affinity chromatography. Authenticity of the purified rhFGF-21 was confirmed by the N-and C-terminal sequence, disulfide bond composition and molecular weight analyses. Results showed that the average target protein and recovery of rhFGF-21 expressed in IBs form of three batches were more than those of the soluble form. Both the rhFGF-21 proteins from the two forms showed equal potency in improving the glucose uptake in HepG2 cells and anti-diabetic effect in db/db mice. In this study, an efficient method for preparation of FGF-21 was established. This novel process provides an important technical basis for the large-scale production of rhFGF-21.

Acceptability, effectiveness, and fouling of PointOne membrane filters distributed in South Sudan

Abstract The Sawyer PointOne™ household hollow fiber membrane filter (PointOne) efficaciously removes microbiological indicators in the laboratory, and is increasingly considered for emergency response. To our knowledge, PointOne effectiveness in emergencies had not been evaluated. In South Sudan, 773 PointOnes were distributed. For 13 months after distribution, household surveys were completed quarterly, water quality testing was conducted monthly, and post-mortem analysis was completed at study midline to assess acceptability, effectiveness, and membrane fouling, respectively. Recipients found PointOnes acceptable, with high rates of demonstrated correct use (97–100%) and correct backflushing (96–100%). PointOnes effectively reduced thermotolerant coliforms for four months. When surface water use increased, effectiveness dropped, with 38% of filtrate samples contaminated. After backflushing filters with 0.2% chlorine solution, effectiveness improved; however, 5–38% of PointOne filtrate samples remained contaminated over subsequent months. Irreversible fouling was documented during post-mortem analysis. These results highlight that while PointOnes can improve household water quality within an emergency, PointOnes can foul within 4–6 months of use, depending on influent water quality. It is recommended that future PointOne distributions include continuous monitoring and an appropriate cleaning regime, based on influent water quality, to ensure continued performance. Further research on source water quality impacts on PointOne performance is recommended.

Transient Simulation of Hollow-Fiber Membrane Filtration with Nonuniform Permeability Distribution

Transient Simulation of Hollow-Fiber Membrane Filtration with Nonuniform Permeability Distribution

CFD simulations of fiber-fiber interaction in a hollow fiber membrane bundle: Fiber distance and position matters

This CFD study aims to simulate the impact of fiber distance and position on fiber-fiber interaction within a bundle. In order to display the filtration performance of fibers at different positions, a hollow fiber membrane filtration setup based on nine fibers arranged in a 3 × 3 square array was constructed. A CFD porous media model approach was employed using the liquid phase as the main phase. The numerical simulation of multiphase flow on the average velocity of each fiber is validated by the experimental results. The presence of “bundle resistance” and “permeate competition” among fibers was confirmed by the axial liquid velocity simulation. When fiber distance was less than the fiber diameter, the interaction between fibers became notable due to “permeate competition”. When fiber distance was equal to fiber diameter, the “permeate competition” effect disappeared, while the “bundle resistance” became dominant within the bundle. When the fiber distance was larger than the fiber diameter, both “permeate competition” and “bundle resistance” could be neglected. The variations of fiber flux at different positions along the fiber height also proved the distribution of axial liquid velocity and sludge density in the bundle. These results highlight the difference between fiber distance and position in the bundle that ensured the fouling deposition.

Scale-Up Testing of a Novel Cleaning Method for Low-Pressure Hollow Fiber Membranes Treating High Algae Surface Waters

Abstract The objective of this study was to determine an optimum flux maintenance protocol for a hollow fiber membrane filtration, treating a surface water with high concentrations of algae and chl...

Laboratory efficacy and field effectiveness of hollow fiber membrane microfilters used for household water treatment in Honduras

The Sawyer PointONE™ hollow fiber membrane filter is increasingly promoted for long-term household water treatment in developing countries. Limited data demonstrate PointONE™ microbiological laboratory efficacy and short-term diarrheal disease reduction among users, but household microbiological data is lacking. To compare laboratory and household PointONE™ filter microbiological performance, we enumerated Escherichia coli (E. coli) and total coliforms in source and filtrate water from: (1) one new filter with E. coli-spiked water (107–109 CFU/100 mL) in the laboratory, (2) one new filter with natural Maine and Honduran surface waters, and (3) 50 filters used in Honduran homes for 1–3 years. In laboratory tests, all filtrate samples had <1 CFU/100 mL E. coli (>99.99999% reduction). In natural surface waters, all filtrate samples had ≤1 MPN/100 mL E. coli (≥99.5% reduction). In households, filtrate samples had geometric mean 5.1 MPN/100 mL E. coli (90% reduction), with only 30% of filtrate samples complying with international standards of undetectable E. coli. Total coliform presence in natural water filtrate varied for both new and household filters. The discrepancy between laboratory and household results and premature filter failure are not well understood. Further research is recommended to understand this performance disparity and determine filter failure mechanisms in households.

Fouling of submerged hollow fiber membrane filtration in turbulence: Statistical dependence and cost-benefit analysis

In the present study, we expanded the scope to a full range of turbulence conditions with a total of 79 experiments, to establish the statistical dependence between the energy consumption due to turbulence dissipation and improved productivity with reduced membrane fouling so that the cost-benefit tradeoff can be evaluated. The turbulence was generated by vibrating perforated plates. Increasing vibration frequency/stroke or solidity of the perforated plate resulted in more intense turbulence inside the reactor, and that the eddy length scale increased with solidity in general. Hollow fiber membrane filtration experiments were then performed within the turbulence ambient in both inorganic Bentonite and organic yeast suspensions. The variance analysis of the results further confirmed the link between the membrane fouling rate and both turbulence kinetic energy and eddy length scale and their cross interactions, as well as that an optimum eddy length scale existed beyond which its influence diminished. Higher TKE induced more fouling reduction, but it also required larger power consumption. A cost-benefit analysis of membrane fouling in turbulence is then presented for evaluation of the tradeoff between membrane filtration performance and power consumption. Finally, the effect of turbulence on membrane filtration performance was also examined in conjunction with the fiber bundle characteristics of the membrane module. An optimized fiber spacing and fiber looseness were identified that consistently performed the best in all experiments, allowing the fluctuating turbulence eddies to penetrate and mobilize the fibers in the most efficient manner against fouling.

Effect of turbulence on fouling control of submerged hollow fibre membrane filtration

In this study, we investigated the effect of turbulence on hollow fibre membrane filtration in terms of membrane fouling performance experimentally. In particular, a special setup with a turbulence generator using a vibrating perforated plate was constructed in the laboratory. The setup enabled the hollow fibre membrane filtration to be carried out within a design ambient with targeted levels of turbulence without mean shears. The non-intrusive laser imaging approach of Particle Image Velocimetry (PIV) was used to quantify the characteristics of the turbulence ambient. Subsequently, by monitoring the rate of trans-membrane pressure (TMP) rise with constant permeate flux experiments using 4 g/L yeast feed suspensions, we obtained unique data sets that revealed the quantitative effects of turbulence on membrane fibre filtration, which are not available in the literature so far. Overall, the results indicated that the presence of turbulence moderated the membrane fouling and reduced the corresponding rate of TMP rise (dTMP/dt). Two key turbulence parameters, namely, turbulence kinetic energy (TKE) and eddy length scale, were found to relate to the membrane fouling reduction, with the rate of TMP rise generally decreasing when TKE or eddy length scale increases. In addition, there exists an optimum eddy length scale beyond which the eddy size (comparable to approximately ten times of the hollow fibre diameter in the present study) has no more influence on the fouling behaviour. A direct comparison between turbulence and membrane vibration for fouling control was also performed. The implications of the present results on the design of membrane bioreactors (MBRs) are discussed.

Performance Modeling and Analysis of a Hollow Fiber Membrane System

A mathematical model was developed for performance of hollow fiber membrane filtration system by considering both frictional and kinetic pressure losses along the fiber. The model was solved numerically as a whole and analytically with the kinetic term omitted with constant driving pressure as the primary control parameter. Numerical simulations first deuctivity (exit velocity) of a hollow fiber was greatly affected by the radius of the fiber. The axial velocity reached a plateau value rapidly along a fiber of a small diameter while increased linearly along a fiber of sufficiently large radius. For given membrane materials (resistance) and fiber length, an optimal diameter of the fiber can be determined to maximize exit velocity.monstrated that the kinetic pressure loss in the hollow fiber was negligible compared to the frictional pressure loss for the current hollow fiber membranes. It was further demonstrated that the prod

Enhanced performance of submerged hollow fibre microfiltration by fluidized granular activated carbon

The effect of fluidized granular activated carbon (GAC) on membrane filtration performance was investigated using a bench-scale upflow hollow fibre membrane filtration setup under constant flux operation. The membrane fouling tendencies were compared among five different experimental parameters, namely, GAC size, GAC packing amount, hollow fibre spacing, filtration/idle duration, and fluidization/idle duration. The results indicate that larger-sized GAC particles, higher packing amounts and a ratio of hollow fibre spacing to fluidized particle size of approximately 3–5 are most beneficial for fouling control. Unexpectedly, the intermittent filtration (under continuous fluidization) could not further alleviate membrane fouling compared to continuous filtration, possibly due to inefficient interaction of fluidized GAC particles with membrane surface in absence of permeate driving force. To lower energy consumption, the optimization of intermittent fluidization (under continuous filtration) was performed. Results indicate that the nature of the cake layer formed during non-fluidization period determined the membrane fouling development rather than the fluidization time span. Finally, by comparing the membrane permeability, sodium alginate rejection rate, and membrane properties before and after GAC abrasion, the GAC scouring on membrane integrity was negligible.

Nanofiltration to remove microparticles and decrease the thrombogenicity of plasma: in vitro feasibility assessment

As plasma contains procoagulant microparticles (MPs), removing MPs by 75-nm nanofiltration may decrease plasma in vitro thrombogenicity while maintaining the hemostatic activity from coagulation factors. We defined conditions to nanofilter leukoreduced plasma on a 75-nm hollow-fiber membrane filter. Plasma quality was assessed by coagulation, immunochemical, and electrophoretic assays. MP removal was evaluated by biophysical (flow cytometry, dynamic light scattering, nanoparticle tracking analysis, and tunable resistive pulse sensing) and functional (thrombin generation assay [TGA; Technothrombin], prothrombinase [Zymuphen MP-activity], tissue factor [Zymuphen MP-TF], and procoagulant phospholipid-dependent clotting time [STA-Procoag-PPL] assays) methods. Spiking experiments using platelet MPs were performed to determine extent of removal by nanofiltration. Freshly collected leukoreduced, but not previously frozen, plasma could be readily nanofiltered on a 0.01-m2 75-nm nanofilter under conditions preserving protein and lipoprotein profile, coagulation factor content, and global coagulation activity (prothrombin time, activated partial thromboplastin time). Biophysical methods confirmed an extensive removal of MPs during nanofiltration. All functional assays indicated a marked reduction of plasma in vitro thrombogenicity. There was no thrombin generation in nanofiltered plasma tested by TGA assay with "RC-low phospholipid concentration" reagent, while it was similar to that of starting and leukoreduced plasma samples when using "RC-high phospholipid concentration" reagent. More than 9 log of MPs were removed by nanofiltration. Nanofiltration of 75 nm efficiently removes MPs and decreases in vitro thrombogenicity of plasma without affecting the protein content or the hemostatic activity of coagulation factors. Studies are needed to evaluate the impact of MP removal on in vivo thrombogenic risks and hemostatic efficacy.